HK1091080B - Congestion control in a wireless data network - Google Patents

Description

Congestion control in a wireless data network

Claim priority under U.S. 35 clause 119

This application is a non-provisional application claiming priority from U.S. provisional application No. 60/448,269 entitled "reverse link data communication" filed on 18/2/2003, U.S. provisional application No. 60/452,790 entitled "method and apparatus for reverse link communication in a communication system" filed on 6/3/2003, and U.S. provisional application No. 60/470,770 entitled "outer loop power control for rel.d" filed on 14/5/2003.

Technical Field

The present invention relates generally to wireless communications, and more particularly, to a novel and improved method and apparatus for congestion control in a wireless data network.

Background

Wireless communication systems are widely deployed to provide various types of communication such as voice and data. These systems may be based on Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), or some other multiple access technique. CDMA systems provide certain advantages over other types of systems, including increased system capacity.

A CDMA system may be designed to support one or more CDMA standards such as (1) "TIA/EIA/IS-95-B mobile station-base station compatibility standard for dual-mode wideband spread-spectrum cellular systems" (IS-95 standard), (2) the standard provided by the consortium named "third generation partnership project" (3GPP) and embodied in a set of documents including document numbers 3G TS 25.211, 3GTS 25.212, 3G TS 25.213, and 3G TS 25.214(W-CDMA standard), (3) the standard provided by the consortium named "third generation partnership project 2" (3GPP2) and embodied in "TR-45.5 physical layer standard for CDMA2000 spread-spectrum systems" (IS-2000 standard), and (4) some other standard.

In the above-mentioned standards, the available spectrum is shared simultaneously among many users, and techniques such as power control and soft handoff are employed to maintain sufficient quality to support delay-sensitive services such as voice. Data services are also available. Recently, systems have been proposed that increase the capacity for data services by using more advanced modulation, very fast feedback of the carrier-to-interference ratio (C/I) of the mobile station, very fast scheduling, and scheduling for services with more relaxed delay requests. An example of such a data-only communication system using these techniques IS a high rate data (HDR) system that conforms to the TIA/EIA/IS-856 standard (IS-856 standard).

In contrast to other above-mentioned standards, the IS-856 system uses the entire spectrum available in each cell to transmit data to a single user that IS selected based on link quality over a period of time. In this case, the system spends a greater percentage of time sending data at higher rates when the channel is good, thereby reducing the allocable resources to support inefficient rate transmissions. The net result is higher data capacity, higher peak data rates, and higher average system throughput.

The system may include support for delay sensitive data, such as voice channels or data channels supported in the IS-2000 standard, and support for packet data services, such as the services described in the IS-856 standard. Of IS-2000 standard (including C.S0001.C to C.S0006.C)Revision C is such a system and is referred to as 1xEV-DV system below. In the rest of the document, we willVersions 0, A and B of the standard are referred to as cdma2000, while revision C and above will be referred to as the 1xEV-DV system.

An exemplary 1xEV-DV system includes a reverse link control mechanism for allocating shared reverse link resources for transmission by multiple mobile stations. The mobile station may request a transmission permission having a maximum rate supportable by the mobile station from the serving base station. Alternatively, the mobile station is allowed to autonomously transmit at the highest achievable determined autonomous maximum rate without making a request. The serving base station predicts the expected amount of autonomous transmissions on the reverse link, checks for any requests made by the mobile station, and allocates shared resources accordingly. The base station may choose to make one or more dedicated grants to the requesting mobile station and include the maximum rates for those grants. The remaining requesting mobile stations may be issued licenses to transmit at the associated maximum transmission rate according to the common license. Thus, in the case of autonomous transmissions by other mobile stations, the serving base station attempts to maximize the utilization of the shared resources in conjunction with the dedicated and common grants. Various techniques may be used to allow the mobile station to transmit continuously with a minimum amount of request signaling based on the determined allocation and associated grant.

The amount of load on the reverse link may at times exceed the amount predicted by the serving base station. Various factors can lead to over-utilization of this system, one example of which is the uncertainty in the actual number of autonomous transmissions that can occur. When the system becomes congested, the overall throughput and the effective capacity of the system may decrease. For example, the eventual increase in error rate may result in a failure of a successful data transfer, and subsequent retransmissions will use the extra capacity of the shared resource. While the allocation and grant process just described may be used to alleviate overload of the system, there may be a time delay associated with the request message. Capacity and throughput may be adversely affected during this period. It is desirable to reduce system load very quickly to minimize these negative effects.

In addition, the extra messages also use system capacity. In some cases, system overload is a temporary situation, after which previous allocations and associated permissions will be appropriate for the expected system load. It is desirable for various mobile stations to return the assigned assignments while minimizing message overhead. There is therefore a need in the art for congestion control to effectively reduce system load.

Disclosure of Invention

Embodiments disclosed herein address the need for congestion control. In one embodiment, the base station allocates the shared resource by using a combination of zero or more dedicated grants and zero or more common grants, and generates a busy signal in response to a load condition exceeding a predetermined level. In another embodiment, a subset of transmitting mobile stations reduce their transmission rate in response to a busy signal. In one embodiment, an autonomously transmitting mobile station adjusts the transmission rate in response to a busy signal. In another embodiment, the commonly admitted mobile stations adjust the transmission rate in response to a busy signal. In yet another embodiment, the exclusively licensed mobile station adjusts the transmission rate in response to a busy signal. In various embodiments, the rate adjustment may be random or deterministic. In one embodiment, a table of rates is used and the mobile station reduces or increases the transmission rate from one rate in the table to a lower or higher rate in the table, respectively, in response to a busy signal. Various other aspects are also provided. These aspects have the ability to provide efficient utilization of reverse link capacity, to satisfy benefits such as low time delay, high throughput, or varying quality of service requests, and to reduce forward and reverse link overhead that provides these benefits, thereby avoiding excessive interference and increasing capacity.

As described in further detail below, the present invention provides methods and system components that implement various aspects, embodiments, and features of the present invention.

Drawings

The features, nature, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings. In the drawings, like reference numerals are correspondingly identified throughout and wherein:

FIG. 1 is a general block diagram of a wireless communication system capable of supporting multiple users;

fig. 2 depicts an exemplary mobile station and base station configured in a system suitable for data communication;

FIG. 3 is a block diagram of a wireless communication device, such as a mobile station or base station;

fig. 4 depicts an exemplary embodiment of data and control signals for reverse link data communication;

FIG. 5 compares R-ESCH power levels with and without fast control;

fig. 6 depicts a method of congestion control that may be performed in a base station;

fig. 7 depicts a general method of congestion control performed on a mobile station;

FIG. 8 depicts a method of congestion control with prescribed rate limits;

figure 9 depicts a method of congestion control using a three value busy signal; and

fig. 10 depicts an embodiment of a rate table that may be used in conjunction with any congestion control method.

Detailed Description

Fig. 1 IS a diagram of a wireless communication system 100 that may be designed to support one or more CDMA standards and/or designs (e.g., W-CDMA standard, IS-95 standard, CDMA2000 standard, HDR specification, 1xEV-DV system). In an alternative embodiment, system 100 may additionally support any wireless standard or design other than a CDMA system. In the exemplary embodiment, system 100 is a 1xEV-DV system.

For simplicity, system 100 is shown to include three base stations 104 in communication with two mobile stations 106. The base stations and their coverage areas are often collectively referred to as a "cell". For example, in IS-95, cdma2000, or 1xEV-DV systems, a cell may include one or more sectors. In the W-CDMA standard, each sector of a base station and the sector's coverage area are referred to as a cell. As used herein, the term base station can be used interchangeably with the terms access point or node B. The term mobile station can be used interchangeably with the terms User Equipment (UE), subscriber unit, subscriber station, access terminal, remote terminal or other corresponding terms in the art. The term mobile station includes fixed wireless applications.

Depending on the CDMA system being implemented, each mobile station 106 may communicate with one (or possibly more) base stations 104 on the forward link at any given moment, and may communicate with one or more base stations on the reverse link depending on whether the mobile station is in soft handoff. The forward link (i.e., downlink) refers to transmission from the base station to the mobile station, and the reverse link (i.e., uplink) refers to transmission from the mobile station to the base station.

While the various embodiments described herein are directed to providing reverse link or forward link signals for supporting reverse link transmissions, and some may well suit the nature of reverse link transmissions, those skilled in the art will appreciate that mobile stations as well as base stations can be equipped to transmit data as described herein and that aspects of the present invention apply in those situations. The word "exemplary" is used exclusively herein to mean "serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" is not necessarily preferred or advantageous over other embodiments.

1xEV-DV forward link data transmission and reverse link power control

A system 100, such as that described in the 1xEV-DV scheme, typically includes four types of forward link channels: overhead channels, dynamically varying IS-95 and IS-2000 channels, forward packet data channel (F-PDCH), and some backup channels. Overhead channel allocation changes slowly: for example, they may not change for months. Typically, they are changed when there is a change in the primary network configuration. The dynamically changing IS-95 and IS-2000 channels are allocated or used on a per call basis for IS-95, or IS-2000 release 0 to B, packet services. Typically, the remaining available base station power after the overhead channels and dynamically varying channels have been allocated is allocated to the F-PDCH for the remaining data services. The F-PDCH may be used for data services that are less sensitive to delay while the IS-2000 channel IS used for services that are more sensitive to delay.

Like the F-PDCH of the traffic channel in the IS-856 standard, IS used to transmit data to one user in each cell at the highest supportable data rate at a time. In IS-856, the total power of the base station and the entire space of walsh functions are available when transmitting data to the mobile station. However, in the proposed 1xEV-DV system, some base station power and some walsh functions are allocated to overhead channels with existing IS-95 and cdma2000 services. The supportable data rate depends primarily on the power used for the overhead channels, the IS-95 channels, and the IS-2000 channels and the available power and walsh codes after the walsh codes have been assigned. Data transmitted on the F-PDCH is spread using one or more walsh codes.

In a 1xEV-DV system, a base station typically transmits to one mobile station at a time on the F-PDCH, although many users in a cell may be using data services. The mobile station is selected for forward link transmission based on some scheduling algorithm (it is possible to transmit to both users by scheduling transmissions for both users and allocating power and walsh channels appropriately to each user).

In IS-856 or 1 xEV-DV-like systems, scheduling IS based in part on channel quality feedback from the mobile stations being served. For example, in IS-856, the mobile station estimates the quality of the forward link and calculates the transmission rate that IS expected to support the current conditions. The desired rate from each mobile station is communicated to the base station. For example, to more efficiently utilize the shared communication channel, the scheduling algorithm may select for transmission mobile stations that support relatively high transmission rates. As another example, in a 1xEV-DV system, each mobile station transmits a carrier-to-interference (C/I) estimate as a channel quality estimate on a reverse channel quality indication channel (R-CQICH). A scheduling algorithm is used to determine the mobile stations selected for transmission, as well as the appropriate rates and transmission formats, based on the channel quality.

As described above, the wireless communication system 100 may support multiple users sharing communication resources simultaneously, such as an IS-95 system, may allocate an entire communication resource to one user at a time, such as an IS-856 system, or may allocate communication resources to allow both types of access. A 1xEV-DV system is an example of a system that divides communication resources between two types of access and dynamically allocates according to user requirements. This is followed by a brief background on how communication resources can be allocated to accommodate different users in two types of access systems. Power control for simultaneous access by multiple users IS described, such as IS-95 type channels. Rate determination and scheduling for time-shared access by multiple users IS discussed, such as the data-only portion (i.e., F-PDCH) of an IS-856 system or a 1xEV-DV type system.

Capacity in a system, such as an IS-95CDMA system, IS determined in part by interference generated in transmitted signaling to and from different users in the system. A typical CDMA system features coded and modulated signals for transmission to and from mobile stations, such signals being viewed as interference to other mobile stations. For example, on the forward link, the channel quality between a base station and a mobile station is determined in part by other user interference. In order to maintain a desired level of performance in communication with a mobile station, the transmit power to that mobile station must be sufficient to exceed the power delivered to other mobile stations served by the base station, as well as other interference and attenuation experienced in that channel. Therefore, to increase capacity, it is desirable to transmit the minimum power required to each served mobile station.

In a typical CDMA system, when multiple mobile stations are transmitting to a base station, it is desirable to receive multiple mobile station signals at the base station at a normalized power level. Thus, for example, the reverse link power control system may adjust the transmit power from each mobile station so that signals from nearby mobile stations do not overwhelm signals from more distant mobile stations. For the forward link, maintaining the transmit power of each mobile station at the minimum power level required to maintain a desired level of performance may allow capacity to be optimized, and also have other power saving advantages, such as increased talk and standby time, reduced battery requirements, and so forth.

Capacity in a typical CDMA system, such as IS-95, IS limited by some other occurrence, other user interference. Other user interference may be mitigated through the use of power control. The overall performance of the system, including capacity, voice quality, data transmission rate, and throughput, depends on the mobile station transmitting at the lowest power level possible to maintain the desired level of performance. To accomplish this, different power control techniques are known in the art.

One type of technique is closed loop power control. For example, closed loop power control may be applied on the forward link. Such a system may employ an inner power control loop and an outer power control loop in the mobile station. The outer loop determines a target received power level in accordance with the desired received error rate. For example, a target frame error rate of 1% may be predetermined as the desired error rate. The outer loop may update the target received power level at a relatively low rate, such as once per frame or per block of data (block). In response, the inner loop then sends an increase or decrease power control message to the base station until the received power reaches the target. These inner loop power control commands are generated relatively frequently in order to quickly bring the transmit power to the level necessary for the desired received signal to noise interference ratio required for effective communication. As described above, keeping the forward link transmit power for each mobile station at a minimum reduces other user interference seen at each mobile station and allows the remaining available transmit power to be reserved for other purposes. In systems such as IS-95, the remaining available transmit power can be used to support communication with other users. In systems such as 1xEV-DV, the remaining available transmit power can be used to support other users, or to increase the throughput of the data-only portion of the system.

In a "data-only" system such as IS-856, or in the "data-only" portion of a system such as 1xEV-DV, a control loop may be utilized to manage the transmission from the base station to the mobile station in a time-shared manner. For clarity, in the following discussion, a transmission to a mobile station at a time may be described. This IS to be distinguished from simultaneous access systems, an example of which IS-95, or different channels in cdma200 or 1xEV-DV systems. Two points are noted at this time.

First, the terms "data-only" or "data channel" may be used to distinguish the channel from an IS-95 type voice or data channel (i.e., a simultaneous access channel using power control, as described above), merely for clarity of discussion. It will be apparent to those skilled in the art that the data-only or data channel described herein may be used to transmit any type of data, including voice (e.g., voice over internet protocol, or VOIP). The use of any particular embodiment for a particular type of data may be determined in part by throughput requirements, latency requirements, and the like. Those skilled in the art will readily adapt the various embodiments to combine any one of the access types with the selected parameters to provide the desired level of latency, throughput, quality of service, etc.

Second, the data-only portion of the system, such as that described for 1xEV-DV, which is described as a time-shared communication resource, can be modified to provide access to more than one user simultaneously over the forward link. In the examples herein, where communication resources are described as being time-shared to provide communication with one mobile station or user for a period of time, those skilled in the art will readily adapt those examples to allow time-sharing of transmissions to or from more than one mobile station during that period of time.

A typical data communication system may include one or more different types of channels. More specifically, one or more data channels are typically utilized. It is also common for one or more control channels to be utilized, although in-band control signaling may be included on the data channel. For example, in a 1xEV-DV system, the forward packet data control channel (F-PDCCH) and the forward packet data channel (F-PDCH) are defined as the transmission of control and data, respectively, on the forward link.

Fig. 2 illustrates an exemplary mobile station 106 and base station 104 configured for data communication in system 100. Base stations 104 and mobile stations 106 are shown communicating over forward and reverse links. The mobile station 106 receives the forward link signal in the receive subsystem 220. As described in detail below, the base station 104 that communicates forward data and control channels may be referred to herein as a serving station for the mobile station 106. An exemplary receiving subsystem is described in further detail below in connection with fig. 3. A carrier/interference (C/I) estimate is made in the mobile station 106 for the received forward link signal from the serving base station. C/I measurements are examples of channel quality measures used as channel estimates, and alternative channel quality measures may be utilized in alternative embodiments. The C/I measurements are communicated to a transmit subsystem 210 in the base station 104, an example of which is described in further detail below in connection with fig. 3.

The transmit subsystem 210 communicates the C/I estimate over the reverse link, which is communicated to the serving base station. It is noted that in the case of soft handoff, the reverse link signal transmitted from the mobile station may be received by one or more base stations that are not serving base stations (referred to herein as non-serving base stations), as is known in the art. In the base station 104, the receive subsystem 230 receives C/I information from the mobile station 106.

In the base station 104, a scheduler 240 is used to determine whether and how data should be transmitted to one or more mobile stations within the coverage area of the serving cell. Any type of scheduling algorithm may be utilized within the scope of the present invention. An example is disclosed in U.S. patent application No. 08/798,951 entitled "method and apparatus for forward link rate scheduling", filed on 11/2/1997, which is assigned to the assignee of the present invention and is incorporated herein by reference.

In an exemplary 1xEV-DV embodiment, when a C/I measurement received from a mobile station indicates that data can be transmitted at a certain rate, that mobile station is selected for forward link transmission. In terms of system capacity, it is beneficial to select a target mobile station because it allows the shared communication resources to always be utilized at their maximum supported rate. Thus, a typical selected target mobile station may be the mobile station with the largest reported C/I. Other factors may also be introduced into the schedule determination. For example, minimum quality of service guarantees may have been made for different users. It is likely that mobile stations with relatively low reported C/I are selected to transmit to maintain a minimum data transmission rate to that user.

In the exemplary 1xEV-DV system, the scheduler 240 determines which mobile station to transmit to, and also determines the data rate, modulation format, and power level for that transmission. In an alternative embodiment, such as an IS-856 system, for example, the supportable rate/modulation format may be determined at the mobile station based on the channel quality measured at the mobile station, and the transmission format may be transmitted to the serving mobile station as a substitute for the C/I measurement. Those skilled in the art will recognize that many known combinations of rate, modulation format, power level, and the like can be utilized within the scope of the present invention. Furthermore, although the scheduling tasks are performed at the base station in the different embodiments described herein, in alternative embodiments some or all of the scheduling process may be performed at the mobile station.

The scheduler 240 directs the transmit subsystem 250 to transmit to the selected mobile station over the forward link using the selected rate, modulation format, power level, etc.

In an exemplary embodiment, messages on the control channel or F-PDCCH are sent along with data on the data channel or F-PDCH. The control channel can be used to identify the mobile station receiving data on the F-PDCH and to identify other useful communication parameters during the communication session. When the F-PDCCH indicates that the mobile station is a transmission target, the mobile station should receive and demodulate data from the F-PDCH. After receiving such data, the mobile station responds over the reverse link with a message indicating the success and failure of the transmission. As is well known in the art, retransmission techniques are commonly used in data communication systems.

In one state known as soft handoff, a mobile station may communicate with more than one base station. Soft handoff may include multiple sectors from one base station (or one Base Transceiver Subsystem (BTS)), known as softer handoff, and sectors from multiple BTSs. The base station sectors in soft handoff are typically stored in the mobile station's Active Set. In a simultaneously shared communication resource system, such as IS-95, IS-2000, or a corresponding portion of a 1xEV-DV system, a mobile station may combine forward link signals transmitted from all sectors in an active set. In a data-only system, such as IS-856, or a corresponding portion of a 1xEV-DV system, a mobile station receives a forward link signal from one of the base stations in the active set, the serving base station (as determined by a mobile station selection algorithm such as those described in the c.s0002.c standard). Other forward link signals, examples of which are described in more detail below, may also be received from non-serving base stations.

Reverse link signals from the mobile station may be received at multiple base stations and the quality of the reverse link is typically maintained for the base stations in the active set. It is possible for reverse link signals received at multiple base stations to be combined. In general, soft combining (soft combining) of reverse link signals received from non-collocated base stations will require a very small delay and a very large amount of network communication bandwidth, so the above-mentioned example does not support it. In softer handoff, the reverse link signals received at multiple sectors in a single BTS can be combined without network signaling. Although any type of reverse link signal combination can be utilized within the scope of the present invention, in the exemplary system described above, reverse link power control maintains communication quality, which allows reverse link frames to be successfully decoded in one BTS (switch diversity).

In a corresponding portion of a simultaneously shared communication resource system, such as an IS-95, IS-2000, or 1xEV-DV system, a base station in soft handoff (i.e., in the mobile's active set) for each mobile station measures the reverse link pilot quality for that mobile station and sends out a stream of power control commands. In IS-95 or IS-2000rev.b, each stream IS sent on either a forward fundamental channel (F-FCH) or a forward dedicated control channel (F-DCCH), if both channels are allocated. The command stream for a mobile station is referred to as the forward power control subchannel (F-PCSCH) for that mobile station. For each base station, the mobile station receives parallel command streams from all its active set members (sectors from one BTS, the same command being sent to that mobile station if all in the mobile station's active set) and determines whether to issue an "up" or "down" command. The mobile station modifies the reverse link transmit power level accordingly using the "Or-of-downs" principle (i.e., decreasing the transmit power level if any "down" command is received, and increasing the transmit power level otherwise).

Typically, the transmit power level of the F-PCSCH is tied to the primary F-FCH or F-DCCH carrying the sub-channels. The primary F-FCH or F-DCCH transmit power level at that base station is determined by feedback transmitted by the mobile station over the reverse power control subchannel (R-PCSCH), which occupies the last quarter of the reverse pilot channel (R-PICH). Since the F-FCH or F-DCCH from each base station forms the traffic channel frame of a single stream, the R-PCSCH reports the combined decoding results of the legs (legs). Erasure (erasures) of the F-FCH or F-DCCH determines the Eb/Nt set point for the outer-loop requirement, which in turn drives the inner-loop commands on the R-PCSCH and thus determines the base station transmission levels of the F-FCH, F-DCCH, and the F-PCSCH on them.

Some base stations in the active set cannot reliably receive the R-PCSCH and properly control the forward link power of the F-FCH, F-DCCH, and F-PCSCH due to potential differences in reverse path loss from a single mobile station in soft handoff to each base station. The base stations may need to redistribute the transmission levels among them so that the mobile station can maintain the spatial diversity gain of soft handoff. Otherwise, a portion of the forward link leg may carry little or no traffic signal energy due to errors in the feedback from the mobile station.

Since different base stations may require different mobile station transmit powers for the same reverse link set point or reception quality, the power control commands from different base stations may be different and cannot be soft combined at the MS. When a new member is added to the active set (i.e., soft handoff from non-soft handoff to one-way (1-way) or from one-way to two-way (2-way), etc.), the FPCSCH transmit power is increased relative to its primary F-FCH or F-DCCH. This may be because the latter has more spatial diversity (requires less total Eb/Nt) and load sharing (less energy per branch), while the former does not.

In a 1xEV-DV system, a forward common power control channel (F-CPCCH) conveys reverse link power control commands for a mobile station when neither a fundamental channel (F-FCH) nor a forward dedicated control channel (F-DCCH) is currently allocated. The serving base station may use information on a reverse channel quality indication channel (R-CQICH) to determine a transmit power level of the F-CPCCH. The R-CQICH is mainly used in scheduling to determine an appropriate forward link transmission format.

However, when the mobile station is in soft handoff, the R-CQICH only reports the forward link pilot quality of the serving base station sector and thus cannot be used directly for power control of the F-CPCCH from the non-serving base station. Such a technique is disclosed in U.S. patent application No. 60/356,929, entitled method and apparatus for forward link power control during soft handoff in a communication system, filed on 12/2/2002, which is assigned to the assignee of the present patent and is incorporated herein by reference.

Exemplary base station and Mobile station embodiments

Fig. 3 is a block diagram of a wireless communication device, such as a mobile station 106 or a base station 104. The functional blocks shown in this exemplary embodiment are typically a subset of the components that are included in either the base station 104 or the mobile station 106. Those skilled in the art will readily adapt the embodiment shown in fig. 3 for use with any number of base station or mobile station configurations.

The signal is received at antenna 310 and transmitted to receiver 320. Receiver 320 performs processing in accordance with one or more wireless system standards, such as those listed above. Receiver 320 performs various processing such as Radio Frequency (RF) to baseband conversion, amplification, analog to digital conversion, filtering, and so forth. Different reception techniques are known in the art. When the device is a mobile station or a base station, respectively, although a separate channel quality estimator 335 is shown for simplicity of illustration, the receiver 320 may be used to measure the channel quality of the forward or reverse link, as will be described in more detail below.

The signal from receiver 320 is demodulated in demodulator 325 in accordance with one or more communication standards. In an exemplary embodiment, a demodulator capable of demodulating 1xEV-DV signals is utilized. In alternative embodiments, alternative standards may be supported, and embodiments may support multiple communication formats. Demodulator 330 may perform RAKE reception, quantization, combining, deinterleaving, decoding, and other various functions required by the format of the received signal. Different demodulation techniques are known in the art. In base station 104, demodulator 325 will demodulate according to the reverse link. In mobile station 106, demodulator 325 will demodulate according to the forward link. The data and control channels described herein are examples of channels that can be received and demodulated in receiver 320 and demodulator 325. As described above, demodulation of the forward data channel will be in accordance with signaling on the control channel. Message decoder 330 receives the demodulated data and extracts the signals or messages on the forward link or reverse link that are intended for mobile station 106 or base station 104, respectively. Message decoder 330 decodes various messages used in setting up, maintaining and tearing down a call (including voice or data sessions) of the system. The messages may include channel quality indications such as C/I measurements, power control messages, or control channel messages used to demodulate the forward data channel. Various types of control messages transmitted on the reverse or forward links may be decoded in the base station 104 or the mobile station 106, respectively. For example, described below are request and grant messages generated in a mobile station or base station, respectively, for scheduling reverse link data transmissions. Other different message types are known in the art and may be specified in the different communication standards being supported. The message is passed to processor 350 for subsequent processing. Although a separate functional block is shown for clarity of discussion, some or all of the functions of message decoder 330 may be performed in processor 350. Alternatively, demodulator 325 may decode and send certain information directly to processor 350 (a single bit message such as an ACK/NAK or a power control increase/decrease command is an example). For example, a forward link command signal, referred to as a common congestion control subchannel (F-OLCH), may be transmitted as a subchannel on a forward common power control channel (F-CPCCH) and can be used to indicate the load on the reverse link. Various embodiments described below detail the means for generating this signal for transmission on the forward link and the corresponding mobile station is responsible for transmitting on the reverse link.

Channel quality estimator 335 is coupled to receiver 320 and is used to make the different power level estimates used in the steps described herein and also used in different other processes used in the communication, such as demodulation. In the mobile station 106, C/I measurements may be made. Also, measurements of any signal or channel used in the present system may be made in channel quality estimator 335 of the present embodiment. As will be described more fully below, a power control channel is another example. In either the base station 104 or the mobile station 106, signal strength estimates, such as received pilot power, may be made. Channel quality estimator 335 is shown as a separate functional block for clarity of discussion only. Typically for such functional blocks to be combined within a functional block such as receiver 320 or demodulator 325. Different types of signal strength estimates may be made depending on which signal or which system type is being estimated. In general, any type of channel quality measure estimation function may be utilized in place of channel quality estimator 335 within the scope of the present invention. In base station 104, the channel quality estimates are passed to a processor 350 for scheduling, or determining, the reverse link quality, as described further below. The channel quality estimate may be used to determine whether an increase or decrease power control command is needed to drive the forward or reverse link power toward a desired set point. The desired set point may be determined using an outer-loop power control mechanism, as described above.

The signal is transmitted via antenna 310. The transmitted signals are formatted in transmitter 370 in accordance with one or more wireless system standards, such as those listed above. Examples of components that may be included in transmitter 370 are amplifiers, filters, digital-to-analog (D/a) converters, Radio Frequency (RF) converters, and so forth. Data for transmission is provided to transmitter 370 by modulator 365. The data and control channels can be formatted for transmission in different formats. Data for transmission on the forward link data channel may be formatted in modulator 365 according to a rate and format indicated by a scheduling algorithm according to a C/I or other channel quality measurement. A scheduler, such as scheduler 240 described above, may reside in processor 350. Similarly, transmitter 370 may be directed to transmit at a power level in accordance with a scheduling algorithm. Examples of components that may be combined into modulator 365 include encoders, interleavers, spreaders, and different types of modulators. Reverse link designs suitable for use in 1xEV-DV systems, including exemplary modulation formats and access controls, are also described below.

Message generator 360 may be used to prepare different types of messages as described herein. For example, the C/I message may be generated in the mobile station for transmission on the reverse link. Different types of control messages may be generated in the base station 104 or the mobile station 106, respectively, to be transmitted on the forward or reverse link. For example, described below are request messages and grant messages that are used to schedule reverse link data transmissions generated in a mobile station or base station, respectively.

Data received and demodulated in demodulator 325 may be passed to a processor 350 for use in voice or data communications, as well as to various other components. Data similarly intended to be transmitted may be sent from processor 350 to modulator 365 and transmitter 370. For example, different data applications may be present in the processor 350, or in another processor (not shown) included in the wireless communication device 104 or 106. The base station 104 may be connected to one or more external networks, such as the internet (not shown), via other means not shown. The mobile station 106 may include a link to an external device such as a laptop computer.

Processor 350 may be a general purpose microprocessor, a Digital Signal Processor (DSP), or a special purpose processor. Processor 350 may perform some or all of the functions of receiver 320, demodulator 325, message decoder 330, channel quality estimator 335, message generator 360, modulator 365, or transmitter 370, as well as any other processing required by the wireless communication device. Processor 350 may be connected with dedicated hardware to assist in these tasks (details not shown). The data or voice applications may be external, such as an externally connected laptop or connection to a network, may run on an additional processor (not shown) within the wireless communication device 104 or 106, or may run on the processor 350 itself. Processor 350 is coupled to memory 355, which is used to store data and instructions for performing the various steps and methods described herein. Those skilled in the art will recognize that memory 355 may include one or more memory components of various types, which may be embedded in whole or in part within processor 350.

1xEV-DV reverse link design considerations

In this section, various factors are described to be considered in designing an exemplary embodiment of a reverse link for a wireless communication system. In many of these embodiments, as described in further detail in the following sections, the signals, parameters, and steps associated with the 1xEV-DV standard are used. These standards are described for illustrative purposes only and may be applied to any number of communication systems within the scope of the present invention. Although this section is not exhaustive, it serves to partly summarize the different aspects of the invention. Example embodiments are described in further detail in subsequent sections below, in which additional aspects are described.

In many cases, the reverse link capacity is interference limited. To be efficiently utilized to maximize throughput in accordance with the quality of service (QoS) requirements of the various mobile stations, the base station allocates available reverse link communication resources to the mobile stations.

Maximizing the use of reverse link communication resources includes several factors. One factor to consider is the mix of reverse link transmissions from different mobile stations that are scheduled, each of which may experience varying channel quality at any given moment. To increase the overall throughput (the aggregate data sent by all mobile stations in a cell), it is desirable that the entire reverse link be fully utilized whenever there is reverse link data to send. To fill the available capacity, mobile stations may be granted access at the highest rate they can support, and other mobile stations may be granted access until capacity is reached. One factor that the base station may consider in determining which mobile stations to schedule is the maximum rate that each mobile station can support and the amount of data that each mobile station has transmitted. A mobile station capable of supporting higher throughput may be selected instead of another mobile station whose channel does not support higher throughput.

Another factor to consider is the quality of service required by each mobile station. Although access to one mobile station may be allowed to be delayed in hopes that the channel will improve, instead of selecting a more suitable mobile station, a mobile station that may be less than optimal may need to be granted access to meet minimum quality of service guarantees. Thus, the scheduled data throughput may not be the absolute maximum, but certainly maximizes the considered channel conditions, available mobile transmit power, and traffic demand. Any configuration is desirable to reduce the signal to noise ratio of the selected mix.

Various scheduling mechanisms are described below that enable a mobile station to transmit data over the reverse link. One type of reverse link transmission includes a mobile station requesting transmission over the reverse link. The base station determines whether the resources can accommodate the request. Permission may be made to allow the transmission. This handshaking between the mobile station and the base station introduces a delay before reverse link data can be transmitted. This delay may be acceptable for certain classes of reverse link data. Other types of data may be more sensitive to latency, and alternative techniques for reverse link transmission are described in detail below to eliminate latency.

In addition, reverse link resources are consumed at request transmissions, while forward link resources are consumed at responses to the requests, i.e., transmit grants. When the channel quality of the mobile station is low, i.e., low geometry or deep fading, the power required on the forward link to reach the mobile station may be relatively high. Various techniques are described in detail below to reduce the number of requests and grants required for reverse link data transmission or the required transmit power.

Autonomous reverse link transmission modes are supported in order to avoid the delay introduced by the request/grant handshake and to conserve the forward and reverse link resources needed to support them. The mobile station can transmit data on the reverse link at a defined rate without making a request or waiting for permission.

The base station allocates a portion of the reverse link capacity to one or more mobile stations. The mobile stations granted access are given the maximum power level. In the exemplary embodiment described herein, the reverse link resources are allocated by using a traffic/pilot (T/P) ratio. Since the pilot signal of each mobile station is adaptively controlled through power control, the specified T/P ratio indicates the power available when transmitting data on the reverse link. The base station may make a dedicated grant to one or more mobile stations indicating a dedicated T/P value for each mobile station. The base station may also make a common grant to the remaining mobile stations that have requested access indicating the maximum T/P values that those remaining mobile stations are allowed to transmit. Autonomous and scheduled transmissions, as well as dedicated and common grants, are described in further detail below.

Different scheduling algorithms are known in the art and still in development for more algorithms that can be used to determine different private and public T/P values for grants based on the number of registered mobile stations, the probability of mobile stations transmitting autonomously, the number and size of unacknowledged requests, the expected average response to grants, and any number of other factors. In one example, the selection is made based on QoS priority, efficiency, and achievable throughput from the set of requesting mobile stations. An exemplary scheduling technique is disclosed in co-pending provisional U.S. patent application No. 60/439,989, entitled "system and method for time-scalable priority-based scheduler," filed on 13/1/2003, assigned to the assignee of the present invention and incorporated herein by reference. Additional references include U.S. patent 5,914,950 entitled "method and apparatus for reverse link rate scheduling" and U.S. patent 5,923,650 entitled "method and apparatus for reverse link rate scheduling," both of which are assigned to the assignee of the present invention.

The mobile station may transmit the data of a packet using one or more subpackets, each of which contains the entire packet information (each subpacket need not be coded exactly the same, as different subpackets may utilize different coding or redundancy). Retransmission techniques may be utilized to ensure reliable transmissions, such as ARQ. Thus, if the first subpacket is received error-free (e.g., by using a CRC), a positive Acknowledgement (ACK) is sent to the mobile station and no further subpackets will be sent (recall that each subpacket includes the entire packet message, in one form or another). If the first subpacket is not received correctly, a negative acknowledgement signal (NAK) is transmitted to the mobile station, and a second subpacket is transmitted. The base station can combine the energy of the two subpackets and try to decode. Although a maximum number of subpackets is typically specified, the process may be repeated indefinitely. In the exemplary embodiment described herein, a maximum of four subpackets may be transmitted. Thus, the probability of correct reception increases when other subpackets are received. (Note that the third response from the base station, ACK-and-Continue, is useful for reducing request/grant overhead

As described, the mobile station may trade off throughput for latency to decide whether to send data with low latency using autonomous transmissions or to request higher rate data transmissions and wait for a common or dedicated grant. In addition, for a given T/P, the mobile station may select a data rate to accommodate latency or throughput. For example, a mobile station with a relatively few bits for transmission may decide that a low latency is desired. For the available T/P (which in this example may be the maximum value for autonomous transmission, but could also be a dedicated or common grant T/P), the mobile station may select the rate and modulation format so that the base station has a higher probability of correctly receiving the first subpacket. It is likely that this mobile station will send its data bits in one packet, although retransmission may be utilized if necessary. In the exemplary embodiment described herein, each subpacket is transmitted within 5 ms. Thus, in this example, the mobile station may make an immediate autonomous transmission that is likely to be received at the base station within the immediately following 5ms interval. Note that the mobile station may optionally use the availability of other subpackets to increase the amount of data transmitted for a given T/P. Thus, the mobile station may choose to autonomously transmit to reduce the latency associated with the request and grant, and may additionally balance the throughput for a particular T/P to minimize the number of subpackets required (and hence the latency). Even if the full number of subpackets is selected, autonomous transmission will be less delayed than request and grant for relatively small data transmissions. Those skilled in the art will recognize that as the amount of data to be transmitted increases, requiring multiple packets to be transmitted, by switching to the request and grant format, the overall latency can be reduced because the disadvantages of the request and grant are offset by the increased throughput at higher data rates across multiple packets. This process is described in further detail below, with an exemplary set of transmission rates and formats that may be associated with different T/P allocations.

A mobile station that is in a changing location within a cell and moving at a changing rate will experience changing channel conditions. Power control is used to maintain the reverse link signal. The pilot energy received at the base station may be power controlled to be approximately equal to that received from different mobile stations. Thus, as described above, the T/P ratio is an indicator of the amount of communication resources used during reverse link transmission. It is desirable to maintain an appropriate balance between pilot and traffic for a given mobile station transmit power, transmission rate, and modulation format.

The mobile station may have a limited amount of available transmit power. Thus, for example, the communication rate may be limited by the maximum power of the mobile station power amplifier. The mobile station transmit power may also be managed by the base station through the use of power control and various data transfer scheduling techniques to avoid causing excessive interference to other mobile stations. The mobile station transmit power availability amount will be allocated to convey one or more pilot channels, one or more data channels, and any other associated control channels. To increase data throughput, the transmission rate may be increased by reducing the coding rate, increasing the symbol rate, or using a more advanced modulation scheme. To be effective, the associated pilot channel must be reliably received to provide a phase reference for demodulation. Therefore, a portion of the available transmit power is allocated to the pilot, and increasing that portion increases the reliability of pilot reception. However, increasing the portion of available transmit power allocated to pilot also reduces the amount of power available for data transmission, and increasing the portion of available transmit power allocated to data also increases modulation reliability. For a given T/P, the appropriate modulation format and transmission rate can be determined.

Due to the change in the data transfer commands, and the discontinuous allocation of the reverse link to the mobile station, the transfer rate for the mobile station may change rapidly. Thus, as just described, the desired pilot power level for the transmission rate and format may vary instantaneously. Without a priori knowledge of the rate variations (which can be expected when there is a lack of costly signaling or when there is reduced flexibility in scheduling), the power control loop can attempt to counteract sudden changes in the base station received power, which may interfere with decoding of the beginning of the packet. Similarly, due to the increased step size typically used in power control, it takes a relatively long time to reduce the pilot once the transmission rate and format have been reduced. One technique and other phenomenon (described in further detail below) that overcomes these problems is to use secondary pilots in addition to the primary pilots. The primary pilot can be used for power control and demodulation of all channels, including the control channel and the low rate data channel. Additional pilot power can be transmitted over the secondary pilot when needed for higher level modulation or increased data rates. The power of the secondary pilot can be determined relative to the primary pilot and the pilot power increment required for the selected transmission. The base station may receive both pilots, combine them, and use them to determine phase and amplitude information for traffic demodulation. The momentary increase or decrease in the secondary pilot does not interfere with power control.

As just described, the exemplary embodiments, which are described in further detail below, achieve the benefits of the secondary pilot by using already deployed communication channels. Thus, capacity is generally improved since, in part, the desired operating range, little or no additional capacity is required for information communicated over the communication channel as compared to the capacity required to perform the pilot function. As is well known in the art, because the pilot signal is a known sequence, it is useful for demodulation, and thus the phase and amplitude of the signal can be derived from the pilot sequence for demodulation. However, transmitting pilots that do not carry data consumes reverse link capacity. Therefore, the unknown data is modulated "on the secondary pilot" and therefore the unknown sequence must be determined in order to extract information useful for demodulation of the traffic signal. In an example embodiment, a reverse rate indication channel (R-RICH) is used to provide a Reverse Rate Indicator (RRI), the rate associated with the transmission of a reverse enhanced supplemental channel (R-ESCH). In addition, the R-RICH power is adjusted based on the pilot power request, which can be used at the base station to provide the secondary pilot. The RRI is one of a set of known values that are useful in determining the unknown component of the R-RICH channel. In alternative embodiments, any channel may be modified to act as a secondary pilot. This technique is described in further detail below.

Reverse link data transfer

One goal of reverse link design is to maintain a relatively stable rise-over-thermal (RoT) at the base station when there is reverse link data to transmit. Transmissions on the reverse link data channel are handled in two different modes:

and (3) autonomous transmission: this situation is for services that require low latency. The mobile station is allowed to immediately transmit at a transmission rate determined by the serving base station, i.e., the base station to which the mobile station transmits its Channel Quality Indicator (CQI). The serving base station may also be referred to as a scheduling base station or a licensed base station. The maximum allowed transmission rate for autonomous transmission may be dynamically signaled by the serving base station based on system load, congestion, etc.

Scheduling and sending: the mobile station sends an estimate of its buffer size, available power, and other parameters. The base station determines when the mobile station is allowed to transmit. The purpose of the scheduler is to limit the number of simultaneous transmissions, thereby reducing interference between mobile stations. The scheduler may try to have the mobile stations in the inter-cell region transmit at a lower rate to reduce interference of neighboring cells and tightly control RoT to protect voice quality on R-FCH, DV feedback and acknowledgement (R-ACKCH) on R-CQICH, and stability of the system.

Various embodiments described in detail herein include one or more features designed to improve the throughput, capacity, and overall system performance of the reverse link of a wireless communication system. For illustrative purposes only, the following are described: the data portion of a 1xEV-DV system, in particular, optimizes transmission by different mobile stations over an enhanced reverse supplemental channel (R-ESCH). The different forward and reverse link channels used in one or more exemplary embodiments are detailed in this section. These channels are typically a subset of the channels used in the communication system.

Fig. 4 illustrates an exemplary embodiment of data and control signals for reverse link data communication. The mobile station 106 is shown communicating over different channels, each of which is connected to one or more base stations 104A-104C. Base station 104A is labeled as a scheduling base station. The other base stations 104B and 104C are part of the active set of the mobile station 106. Four types of reverse link signals and two types of forward link signals are shown. Which will be described below.

R-REQCH

A reverse request channel (R-REQCH) is used by the mobile station to request reverse link transmission of data from the scheduling base station. In an exemplary embodiment, the request is for transmission on the R-ESCH (as will be described in further detail below). In an exemplary embodiment, the request on the R-REQCH includes a T/P ratio that varies according to changing channel conditions, and a buffer size (i.e., the amount of data waiting to be transmitted) that the mobile station can support. The request may also specify a quality of service (QoS) for data waiting to be transmitted. It is noted that a mobile station may have a single QoS level assigned to the mobile station or, alternatively, different QoS levels for different types of data. Higher layer protocols may indicate the QoS, or other desired parameters for different data services (such as latency or throughput requirements). In an alternative embodiment, a reverse dedicated control channel (R-DCCH) used with other reverse link signals, such as a reverse fundamental channel (R-FCH) (e.g., for voice traffic), may be used to carry the access request. In general, an access request may be described as comprising a logical channel, i.e., a reverse scheduling request channel (R-SRCH), which may be mapped onto any existing physical channel, such as an R-DCCH. The exemplary embodiment is backward compatible with existing CDMA systems, such as CDMA2000, release C, and R-REQCH is a physical channel that can be utilized without R-FCH or R-DCCH. For clarity, the term R-REQCH is used to describe the access request channel in the description of embodiments herein, although those skilled in the art will readily extend this principle to any type of access request system, regardless of whether the access request channel is logical or physical. The R-REQCH may be disabled (gate off) until a request is needed, thus reducing interference and conserving system capacity.

In an exemplary embodiment, the R-REQCH has 12 input bits, which include the following: 4 bits specifying the maximum R-ESCH T/P ratio that the mobile station can support, 4 bits specifying the amount of data in the mobile station buffer, and 4 bits specifying QoS. Those skilled in the art will recognize that any number of bits and various other fields may be included in alternative embodiments.

F-GCH

A forward grant channel (F-GCH) is transmitted from the scheduling base station to the mobile station. The F-GCH may include multiple channels. In an exemplary embodiment, a common F-GCH channel is used to make common grants and one or more dedicated F-GCH channels are used to make dedicated grants. The grant is made by a scheduling base station responsive to a signal from one or more mobile stationsOne or more requests sent over their respective R-REQCHs. The grant channel may be labeled GCH_xWhere the subscript x identifies the channel number. The channel number 0 may be used to indicate a common grant channel. The index x may vary from 1 to N if N dedicated channels are utilized.

The dedicated grant may be made to one or more mobile stations, each of which allows the identified mobile station to transmit at a specified T/P ratio or lower on the R-ESCH. Making a grant on the forward link would naturally introduce overhead that consumes some forward link capacity. Various options for eliminating the overhead associated with licensing are detailed below, and other options will be apparent to those skilled in the art in light of the principles described herein.

One consideration is that the mobile stations will be located such that each mobile station experiences varying channel quality. Thus, for example, a high geometry mobile station with good forward and reverse link channels may require relatively low power for the grant signal and is likely to be able to take advantage of the high data rates, and thus is expected to take advantage of the dedicated grant. A low geometry mobile station, or a mobile station experiencing more fading, may require significantly more power to reliably receive the dedicated grant. Such mobile stations may not be the best candidates for dedicated permission. Less forward link overhead may be consumed for common grants for such mobile stations, as described in detail below.

In an exemplary embodiment, multiple dedicated F-GCH channels are utilized to provide a corresponding number of dedicated grants at a particular time. The F-GCH channels are code division multiplexed. This facilitates the ability to send each grant at the power level just needed to reach a particular target mobile station. In an alternative embodiment, a single dedicated grant channel may be utilized, with the number of dedicated grants being time multiplexed. To change the power per grant on a time multiplexed dedicated F-GCH, additional complexity may be introduced. Any signaling technique for communicating a common or dedicated grant may be utilized within the scope of the present invention.

In some embodiments, a relatively large number of dedicated grant channels (i.e., F-GCH) are utilized, which may be utilized to simultaneously allow a relatively large number of dedicated grants. In this case, it may be desirable to limit the number of dedicated licensed channels that each mobile station must monitor. In one exemplary embodiment, different subsets of the total number of dedicated licensed channels are defined. Each mobile station is assigned a subset of dedicated grant channels to monitor. This allows the mobile station to reduce the complexity of the processing and correspondingly reduce power consumption. Scheduling complexity is traded off because the scheduling base station may not be able to arbitrarily assign a subset of the dedicated grants (e.g., all dedicated grants cannot be made to members of a single group because those members are not designed to monitor one or more of these dedicated grant channels). It is noted that the loss of complexity does not necessarily result in a loss of capacity. For purposes of illustration, consider an example that includes four dedicated grant channels. Even mobile stations may be assigned to monitor the first two licensed channels and odd mobile stations may be assigned to monitor the last two licensed channels. In another example, the subsets may overlap, such as even mobile stations monitoring the first three licensed channels and odd mobile stations monitoring the last three licensed channels. It is clear that the scheduling base station cannot arbitrarily allocate four mobile stations from any one group (even or odd). These examples are for illustration only. Any number of channels having any subset configuration may be utilized within the scope of the present invention.

The remaining mobile stations that have made requests but have not received the dedicated grant may be permitted to transmit on the R-ESCH with a common grant that specifies the maximum T/P ratio that each of the remaining mobile stations must adhere to. The common F-GCH may also be referred to as a forward common grant channel (F-CGCH). The mobile station monitors one or more dedicated grant channels (or a subset thereof) as well as the common F-GCH. Unless given a private license, the mobile station may transmit if a public license is issued. The common grant indicates the maximum T/P ratio that the remaining mobile stations (common grant mobile stations) may utilize to send certain types of QoS data.

In an exemplary embodiment, each common grant is valid for a plurality of subpacket transmission intervals. Upon receiving the common grant, a mobile station that has sent a request but not received a dedicated grant may begin transmitting one or more code packets in a subsequent transmission interval. The license information may be repeated multiple times. This allows the common grant to be transmitted at a reduced power level relative to the dedicated grant. Each mobile station can combine energy from multiple transmissions to reliably decode the common grant. Thus, a common grant may be selected for a mobile station with low geometry, for example, when a dedicated grant is considered too wasteful in terms of forward link capacity. However, common channels still require overhead, and different techniques for reducing this overhead are detailed below.

The F-GCH is sent by the base station to each mobile station that the base station schedules for transmission of a new R-ESCH packet. In the event congestion control becomes necessary, during transmission or retransmission of the code packet, the F-GCH may also be sent to force the mobile station to modify its T/P ratio for sub-packet transmission of subsequent code packets.

Detailed below are examples of timing, including various embodiments of requests that are presented for either type (private or public) of access request and grant correlation. Further, techniques for reducing the number of grants and thus the associated overhead, and techniques for congestion control are detailed below.

In an example embodiment, the common grant consists of 12 bits, including a 3-bit type field to specify the format of the next nine bits. The remaining bits indicate the maximum allowed T/P ratio for three classes of mobile stations, as specified in the type field, with 3 bits representing the maximum allowed T/P ratio for each class of mobile stations. The mobile station may be categorized based on QoS requests or other criteria. Various other common license formats are envisioned and will be apparent to those of ordinary skill in the art.

In an example embodiment, the dedicated grant comprises 12 bits, including: the 11 bits specify the mobile ID and the maximum allowed T/P ratio for the mobile station that is being granted permission to transmit or explicitly signaling the mobile station to change its maximum allowed T/P ratio, including setting the maximum allowed T/P ratio to 0 (i.e., telling the mobile station not to transmit R-ESCH). These bits specify the mobile station ID (one of 192 values) and the maximum allowed T/P (one of 10 values) for a given mobile station. In an alternative embodiment, 1 long grant bit may be set for a particular mobile station. When the long grant bit is set to 1, the mobile station is allowed to transmit a relatively large fixed, predetermined number of packets (which may be updated with signaling) on the ARQ channel. If the long grant bit is set to 0, the mobile station is allowed to transmit a packet. If the long grant bit is reset or the long grant bit is in a set longer time, the mobile station may be notified to stop its R-ESCH transmission with a zero T/P ratio specification and this may be used to signal the mobile station to stop its transmission of a single subpacket transmission for a single packet on the R-ESCH.

R-PICH

A reverse pilot channel (R-PICH) is transmitted from the mobile station to the base stations in the active set. Power in the R-PICH may be measured at one or more base stations for reverse link power control. As is known in the art, for use in coherent demodulation, pilot signals may be used to provide amplitude and phase measurements. As described above, the amount of transmit power available to the mobile station (whether limited by the scheduling base station or inherent limitations of the mobile station's power amplifier) is divided among the pilot channel, the traffic channel or channels, and the control channel. Additional pilot energy may be required for higher data rates and demodulation formats. To simplify the use of the R-PICH for power control and to avoid some problems associated with instantaneous changes in required pilot power, additional channels may be allocated for supplemental or secondary pilots. Although the pilot signal is typically transmitted using a known data sequence as disclosed herein, the information-bearing signal may also be utilized for use in generating the reference information for demodulation. In an exemplary embodiment, an R-RICH (described in more detail below) is used to carry the required additional pilot power.

R-RICH

The reverse rate indicator channel (R-RICH) is used by the mobile station to indicate the transmission format on the reverse traffic channel, R-ESCH. The R-RICH includes a 5-bit message. The orthogonal encoder block maps each 5-bit input sequence to an orthogonal sequence of 32 symbols. For example, every 5-bit input sequence can be mapped to a different walsh code of length 32. The sequence repeat function repeats a sequence of 32-bit input symbols three times. The bit repetition block provides at its output the input bits which are repeated 96 times. The sequence selector module selects between these two inputs and passes that input to the output. For zero rate, the output of the bit repetition block passes. For all other rates, the output of the sequence repetition module passes. The signaling point mapping module maps input bit 0 to +1 and input 1 to-1. The next signaling point mapping module is a walsh spreading module. The walsh spreading module spreads each input symbol into 64 chips. Each input symbol is multiplied by a walsh code W (48, 64). The walsh code W (48, 64) is a walsh code of length 64 chips with an index of 48. TIA/EIA IS-2000 provides a table describing Walsh codes of different lengths.

Those skilled in the art will recognize that this channel structure is for example only. In alternative embodiments, various other coding, repetition, interleaving, point mapping, or walsh coding parameters can be utilized. Additional encoding or formatting techniques well known in the art may also be utilized. Such modifications are intended to fall within the scope of the present invention.

R-ESCH

In the exemplary embodiment described herein, an enhanced reverse supplemental channel (R-ESCH) is used as the reverse link traffic data channel. Any number of transmission rates and modulation formats may be utilized for the R-ESCH. In an exemplary embodiment, the R-ESCH has the following characteristics: physical layer retransmissions are supported. For retransmission, when the first code is a Rate 1/4 code (Rate 1/4 code), the retransmission uses a Rate 1/4 code and Chase combining is used. For retransmissions when the first code is a rate greater than 1/4 code, incremental redundancy (incremental redundancy) is used. The base code is a rate 1/5 code. Alternatively, incremental redundancy may be used for all cases as well.

Both autonomous and scheduled users support hybrid automatic repeat request (HARQ), both of which may access the R-ESCH.

For the case where the first code is a rate 1/2 code, the frame is encoded as a rate 1/4 code and the encoded symbols are equally divided into two parts. The first part of the symbol is sent in a first transmission and the second part in a second transmission, then the first part in a third transmission, and so on.

Due to the fixed timing between retransmissions, the synchronous operation of multiple ARQ channels may be supported: a fixed number of subpackets may be allowed between consecutive subpackets of the same packet. Interleaved transmission is also allowed. As an example, for a 5ms frame, a 4-channel ARQ can be supported with a 3 subpacket delay between subpackets.

Table 1 lists exemplary data rates for the enhanced reverse supplemental channel. A sub-packet size of 5ms is described and the supplemental channel has been designed to be suitable for this option. Other subpacket sizes may also be selected, as will be apparent to those skilled in the art. The pilot reference level is not adjusted for these channels, i.e., the base station has the flexibility to select T/P to reach a given operating point. The maximum T/P value may be signaled on the forward grant channel. The mobile station may use a lower T/P if it runs out of transmitted power to let HARQ meet the required QoS. Layer 3 signaling messages may also be sent over the R-ESCH, allowing the system to operate without the FCH/DCCH.

Table 1 enhanced reverse supplemental channel parameters

Number of bits per encoder packet	Number of 5ms slots	Data Rate (kbps)	Data Rate/9.6 kbps	Encoding rate	Symbol repetition factor before interleaving	Modulation	Walsh channel	Number of binary coded symbols in all sub-packets	The effective code rate includes repetition
										192	4	9.6	1.000	1/4	2	BPSK on I	++--	6,144	1/32
192	3	12.8	1.333	1/4	2	BPSK on I	++--	4,608	1/24
										192	2	19.2	2.000	1/4	2	BPSK on I	++--	3,072	1/16
192	1	38.4	4.000	1/4	2	BPSK on I	++--	1,536	1/8
										384	4	19.2	2.000	1/4	1	BPSK on I	++--	6,144	1/16
384	3	25.6	2.667	1/4	1	BPSK on I	++--	4,608	1/12
										384	2	38.4	4.000	1/4	1	BPSK on I	++--	3,072	1/8
384	1	76.8	8.000	1/4	1	QPSK	++--	1,536	1/4
										768	4	76.8	4.000	1/4	1	QPSK	++--	12,288	1/16
768	3	102.4	5.333	1/4	1	QPSK	++--	9,216	1/12
										768	2	153.6	8.000	1/4	1	QPSK	++--	6,144	1/8
768	1	307.2	16.000	1/4	1	QPSK	++--	3,072	1/4
										1,536	4	76.8	8.000	1/4	1	QPSK	+-	24,576	1/16
1,536	3	102.4	10.667	1/4	1	QPSK	+-	18,432	1/12
										1,536	2	153.6	16.000	1/4	1	QPSK	+-	12,288	1/8
1,536	1	307.2	32.000	1/4	1	QPSK	+-	6,144	1/4
										2,304	4	115.2	12.000	1/4	1	QPSK	++--/+-	36,864	1/16
2,304	3	153.6	16.000	1/4	1	QPSK	++--/+-	27,648	1/12
										2,304	2	230.4	24.000	1/4	1	QPSK	++--/+-	18,432	1/8
2,304	1	460.8	48.000	1/4	1	QPSK	++--/+-	9,216	1/4
										3,072	4	153.6	16.000	1/5	1	QPSK	++--/+-	36,864	1/12
3,072	3	304.8	21.333	1/5	1	QPSK	++--/+-	27,648	1/9
										3,072	2	307.2	32.000	1/5	1	QPSK	++--/+-	18,432	1/6

Number of bits per encoder packet	Number of 5ms slots	Data Rate (kbps)	Data Rate/9.6 kbps	Encoding rate	Symbol repetition factor before interleaving	Modulation	Walsh channel	Number of binary coded symbols in all sub-packets	The effective code rate includes repetition
										3,072	1	614.4	64.000	1/5	1	QPSK	++--/+-	9,216	1/3
4,608	4	230.4	24.000	1/5	1	QPSK	++--/+-	36,864	1/8
										4,608	3	307.2	32.000	1/5	1	QPSK	++--/+-	27,648	1/6
4,608	2	460.8	48.000	1/5	1	QPSK	++--/+-	18,432	1/4
										4,608	1	921.6	96.000	1/5	1	QPSK	++--/+-	9,216	1/2
6,144	4	307.2	32.000	1/5	1	QPSK	++--/+-	36,864	1/6
										6,144	3	409.6	42.667	1/5	1	QPSK	++--/+-	27,648	2/9
6,144	2	614.4	64.000	1/5	1	QPSK	++--/+-	18,432	1/3
										6,144	1	1228.8	128.000	1/5	1	QPSK	++--/+-	9,216	2/3

In an exemplary embodiment, turbo coding is used for all rates. For the R1/4 code, a similar interleaver to the current cdma2000 reverse link is used, and if the second subpacket is sent, its format is the same as the first subpacket. For the R1/5 code, an interleaver similar to the cdma2000 forward packet data channel is used.

The number of bits per encoder packet includes CRC bits and 6 tail bits (tailbits). For an encoder packet size of 192 bits, a 12-bit CRC is used; otherwise, a 16-bit CRC is used. The 5ms slots are assumed to be separated by 15ms to allow time for ACK/NAK responses. If an ACK is received, the remaining slots of the packet are no longer transmitted.

The 5ms subpacket duration and related parameters just described are for example purposes only. Combinations of any number of rates, formats, subpacket repetition selections, subpacket durations, etc., will be apparent to those skilled in the art from the description herein. An alternative 10ms embodiment using 3 ARQ channels can be employed. In one embodiment, a single sub-packet duration or a single frame size is selected. For example, a 5ms or 10ms structure would be selected. In an alternative embodiment, which will be described in further detail below, the system may support multiple frame durations.

F-CACKCH

The forward common acknowledgement channel, or F-CACKCH, is used by the base station to confirm correct reception of the R-ESCH and to extend the existing grant. An Acknowledgement (ACK) on the F-CACKCH indicates that the sub-packet was correctly received. It is no longer necessary for the mobile station to additionally transmit the subpacket. Negative Acknowledgements (NAKs) on the F-CACKCH cause the mobile station to transmit the next subpacket up to the maximum number of subpackets allowed per packet. The third command, ACK-and-Continue, enables the base station to acknowledge the successful receipt of the packet and at the same time allow the mobile station to transmit by using the grant that resulted in the successfully received packet. One embodiment of the F-CAKCH uses a +1 value to represent the ACK symbol, a NULL symbol to represent the NAK symbol, and a-1 value to represent the ACK-and-Continue symbol. In various exemplary embodiments, up to 96 mobile station IDs may be supported on one F-CACKCH, as described in further detail below. Additional F-CACKCH may be employed to support additional mobile station IDs. When the cost (requested power) of doing so is too high, on-off (set-reset) robust control (that is, not sending NAKs) on the F-CACKCH allows the base station (especially a non-scheduling base station) to choose not to send ACKs. This provides a compromise for the base station between forward link and reverse link capacity, since a correctly received packet that is not acknowledged will likely trigger a retransmission at a later point in time.

A Hadamard encoder is an example of an encoder for mapping onto a set of orthogonal functions. Various other techniques may also be employed. For example, any walsh code or other similar error correcting code can be used to encode the information bits. Different users may be transmitted at different power levels if each channel has independent channel gain independently. The F-CACKCH transmits a dedicated three-value flag for each user. Each user monitors the F-ACKCHs from all base stations in its active set (or alternatively, the signaling may define a reduced active set to reduce complexity).

In various embodiments, detailed below, the two channels are each masked by a 128-chip walsh mask sequence. One channel is transmitted on the I channel and the other on the Q channel. Another embodiment of the F-CACKCH uses a single 128-chip walsh mask sequence to support up to 192 mobile stations simultaneously. This method uses a duration of 10ms for each of the three value flags.

There are several ways to operate the ACK channel. In one embodiment, this may be done so that a "1" is sent for the ACK. Not sent means a NAK, or "off" state. And the transmission of "-1" refers to ACK-and-Continue, i.e. the same grant is repeated to the MS. This saves the overhead of a new grant channel.

Recall that when the MS has a packet to transmit that requires the use of the R-ESCH, the MS transmits a request on the R-REQCH. The base station may respond with permission using the F-CGCH, or F-GCH. However, this operation overhead is somewhat large. To reduce the forward link overhead, the F-CAKCH may send an "ACK-and-Continue" flag that extends the existing grants by the scheduling base station at a low cost. This approach can be used for both private and public licenses. ACK-and-Continue is used according to the granted base station and extends the current grant for one more encoder packet on the same ARQ channel.

Note that as shown in fig. 4, not every base station in the active set needs to send back the F-CACKCH. The set of base stations transmitting the F-CACKCH in the soft handover may be a subset of the active set. An exemplary technique for transmitting the F-CACKCH is disclosed in co-pending U.S. patent application No. 10/611,333 entitled "code division multiplexing commands over code division multiplexed channels" filed on 30/6/2003 and assigned to the assignee of the present invention (hereinafter "AAA" application).

F-CPCCH

The forward common power control channel (F-CPCCH) is used to power control the various reverse link channels, including the R-ESCH when the F-FCH and F-DCCH are not provided. The mobile station is assigned a reverse link power control channel by channel assignment. The F-CPCCH may contain many power control subchannels.

The F-CPCCH carries a power control subchannel called the common congestion control subchannel (F-OLCH). The rate of the congestion control subchannel is typically 100bps, although other rates can be used. A single bit (which may be repeated for reliability), referred to herein as a busy bit, indicates whether mobile stations in autonomous transmission mode or common grant mode, or both, should increase or decrease their rate. In an alternative embodiment, the dedicated license mode may also be sensitive to this bit. Various embodiments employing any combination of transmission types of the response F-OLCH may be used (described in further detail below). This can be done randomly or deterministically.

In one embodiment, setting the busy bit to "0" indicates that the mobile stations responding to the busy bit should reduce their transmission rate. Setting the busy bit to "1" indicates a corresponding increase in the transmission rate. Myriad other signaling mechanisms may be used, as will be apparent to those skilled in the art, and various alternative examples are detailed below.

During channel allocation, the mobile station is allocated these particular power control channels. The power control channel may control all mobile stations in the system, or alternatively, a varying subset of the mobile stations may be controlled by one or more power control channels. Note that the use of this specific channel for congestion control is only an example. As will be described in further detail below, the techniques described herein may be used with any device that transmits a signal.

Exemplary congestion control embodiments

To summarize the various features described above, the mobile station is approved to make autonomous transmissions, which may limit throughput but allow low latency. In this case, the mobile station may transmit at the maximum R-ESCH T/P ratio, T/P Max _ auto, without request, and these parameters may be set and adjusted by the base station via signaling.

Scheduling is determined at one or more scheduling base stations and an allocation of reverse link capacity is made by transmitting grants at a relatively high rate over the F-GCH. Scheduling may therefore be used to closely control reverse link load, thereby protecting voice quality (R-FCH), DV feedback (R-CQICH), and DV acknowledgement (R-ACKCH).

Dedicated grants allow detailed control of the mobile station transmissions. The mobile station may be selected based on geometry and QoS to maximize throughput while maintaining a desired level of service. The common grant allows for efficient notification, particularly for low geometry mobile stations.

The F-CACKCH channel can send an "ACK-and-Continue" command, which extends the existing grant with low cost. This works for both private and public licenses. Various embodiments and techniques for scheduling, granting, and transmitting shared resources, such as 1xEV-DV reverse links, are disclosed in co-pending U.S. patent application No. XX/XXX, XXX (attorney docket No. 030239), entitled "scheduling and autonomous transmission and acknowledgement", filed on 21/8/2003, assigned to the assignee of the present invention and incorporated herein by reference.

Fig. 5 compares the R-ESCH power level with and without fast control. During transmissions on the R-ESCH, each mobile station transmits at the maximum rate permitted on the R-GCH (i.e., dedicated grant) or the R-CGCH (i.e., common grant), or autonomously, up to the maximum rate permitted. If the R-ESCH being used by the mobile station has been assigned a congestion control subchannel (F-OLCH), the mobile station adjusts the transmission rate based on the bits received on the congestion control subchannel.

There are different ways to do this. If all mobile stations are classified into three categories: autonomous, commonly licensed, or exclusively licensed, then this channel may be available to all users, only one type of user, or to any two types of users, depending on the level of control desired.

If the mobile station controlled by the F-CGCH changes rate randomly, there is no need to add additional bits on the F-CPCCH. This information (i.e., the busy bit) may be sent on the F-CGCH. The lack of a busy bit may be considered by the mobile station as a grant to increase to the maximum allowed rate. Alternatively, the mobile station may be allowed to randomly increase the rate. Various examples are detailed below.

Fig. 6 depicts a congestion control method 600 that may be performed in a base station. The process begins at step 610, where a serving base station, such as base station 104, allocates resources and grants to one or more mobile stations when available. As described above, the allocated resources may be part of the shared communication resources. The allocation may be calculated using any received request for transmission and an expected amount of autonomous transmissions, which may be based on statistical models, the number of mobile stations registered in the coverage area of the base station, past autonomous transmissions, and the like. As described above, a private and/or public license may be assigned to one or more mobile stations, and a final message may be transmitted to those mobile stations.

In step 620, the base station measures the system load. The load on the system may result from previous resource allocations, such as described with respect to step 610, as well as autonomous transmissions. The system load may be greater or less than expected when the previous resource allocation was made. For example, the number of desired autonomous transmissions may be greater or less than the actual amount of autonomous transmissions. Other factors such as changes in channel conditions, missed mobile station requests (and subsequent transmissions by that mobile station in response to a common grant), and other factors that may cause the measured system load to be higher or lower than the base station's expected load at a given time. Another source of variation is interference from other cells that vary unpredictably. Mobile stations often use tolerances to address such unexpected situations.

In decision block 630, if the base station determines that the system is exceeding the load on the expected shared resource (R-ESCH in this embodiment) based on the currently measured conditions, then step 640 is entered. Otherwise, return to step 610 to reallocate resources for the next time period. If the previously asserted busy bit is asserted, it may not be asserted. In step 640, when the system is determined to be busy, the busy signal is asserted to indicate that the load needs to be reduced. The busy condition may be signaled to the mobile station in any of a variety of ways. In one embodiment, the busy bit is set on the F-OLCH as described above. This channel is multiplexed onto the F-CPCCH. In another embodiment, the F-OLCH can be multiplexed onto another channel with CDM-based CDM as described in the aforementioned "AAA" application, or can be a separate physical channel. The mobile stations in the system may respond to the asserted busy signal in various ways. Exemplary embodiments are described in further detail below.

Fig. 7 depicts a generalized method 700 of congestion control performed in a mobile station. Processing begins at decision block 710, if the system is identified as busy using any of the signaling techniques described above, such as a busy bit or busy signal, the mobile station proceeds to step 720 and decreases its rate (e.g., as to when or how to decrease the rate, examples of which are detailed below). For example, mobile stations receiving busy signals may reduce their rate at once with a fixed reduction rate, use a random method to determine whether to reduce, use a random method to determine how much to reduce the rate, and so on. The rate reduction value may be predetermined or updated by a transmitted signal during the communication phase. Different base stations may use different mechanisms to determine how to reduce their rates. For example, a mobile station with a higher QoS may be reduced less likely, or by a lesser amount, than a mobile station with a relatively low QoS. Note that mobile stations transmitting under a dedicated or common grant as well as autonomously transmitting mobile stations may change their transmission rate in response to a busy signal. Any subset of mobile stations may be programmed to respond to the busy signal in a different manner than any other subset. For example, a private license may not be designated for reduction, while a public license may be designated for reduction. Or both types may be designated for different levels of reduction. The QoS designation may determine a subset of changes. Alternatively, each mobile station may be signaled with its own unique parameters to respond to the busy signal with congestion control countermeasures. There are various combinations, some of which are described in the following example embodiments, which will be apparent to those skilled in the art and which fall within the scope of the invention.

If the busy signal is not asserted in decision block 710, step 730 is entered and transmitted at the determined rate. This rate can be determined in various ways. The rate may be signaled using a common or dedicated grant, or may be a rate that is an indication of the maximum rate for autonomous transmission. As just described, in the previous loop of the method 700, the rate of any of these examples may be reduced, and thus the determined rate reflects this reduction. Once the busy signal is no longer asserted, the previously decreased rate may be increased with a deterministic or random rate, examples of which are detailed below.

Note that, in general, the mechanism for providing common or private grants may also be used for congestion control. For example, the common license may be reissued at a lower rate. Alternatively, an ACK (but not continue) command may be sent followed by a lower dedicated grant sent to the respective mobile station. Similarly, the autonomous transmission maximum rate may be adjusted by signaling. These techniques require a relatively higher amount of overhead than setting the busy bit, with potentially longer latency on the response. Thus, setting the busy bit allows the serving base station to operate without re-admission through a temporary increase in system load. Nevertheless, as described above, selective re-admission (or removal of a previous admission, i.e., sending an ACK instead of an ACK-and-Continue), may be used in conjunction with the busy bit, as will be apparent to those skilled in the art.

Fig. 8 depicts a congestion control method 800 with a set rate limit. Processing begins with decision block 810, where if the busy signal is asserted, decision block 820 is entered. If the busy signal is not asserted, decision block 840 is entered. At decision block 840, if the mobile station is transmitting at the maximum allowed rate, step 860 is entered to continue transmitting at the current rate. The maximum allowed rate may depend on the type of transfer being performed. The rate may be set as identified in a dedicated grant to the mobile station, a common grant upon which the mobile station may rely, or may be a maximum allowed rate for autonomous transmissions. If the current rate is less than the maximum allowed rate (e.g., due to a previous response busy condition), step 850 is entered to increase the rate. Step 860 is then entered to transmit at the determined rate. Example techniques for increasing and decreasing the rate according to the rate limit are described in further detail below with reference to fig. 10.

In decision block 810, if the busy signal is asserted, then decision block 820 is entered. If the mobile station is transmitting at the minimum specified rate, step 860 is entered to continue transmitting at that rate. If not, step 830 is entered, the rate is reduced, then step 860 is entered and the transfer at the adjusted rate is resumed. Note that the decrease or increase in rate in steps 830 or 850, respectively, may be deterministic or random.

In an alternative embodiment, details are not shown, and the mobile station may begin transmitting at a rate other than the specified maximum rate. For example, a common grant may allow a specified maximum rate. As depicted in fig. 8, the mobile station may begin transmitting at a lower rate and then randomly or deterministically increase its rate until a specified maximum rate is reached.

Figure 9 depicts a congestion control method 900 using a three value busy signal. For example, the busy signal may contain one of three values, a first value indicating that the shared resources are underutilized, or that those rates may increase, a second value indicating that the resources are over-utilized, or that those rates should decrease, and a third value indicating that neither an increase nor a decrease is desired. A three-valued signal similar to F-CACKCH may be used in one embodiment. An increase is signaled by transmitting a positive value and a decrease is signaled by transmitting a negative value, and no transmission means that neither an increase nor a decrease is performed. Any other multi-valued signal may also be used, as will be apparent to those skilled in the art.

Processing begins with decision block 910. If the mobile station receives an increased value on the busy signal, step 920 is entered and the rate is increased. As described above with respect to fig. 8, the rate increase may be random or deterministic and may include a maximum rate limit. Then, in step 950, the mobile station transmits at the determined rate. In one example scenario, the rate increase may be signaled after a rate decrease was previously signaled on a busy signal to reduce congestion. It is useful to eliminate the effect of rate reduction when congestion is mitigated.

If the mobile station does not receive an incremented value on the busy signal in decision block 910, decision block 930 is entered. If a decrease is received on the busy signal, step 940 is entered and the rate is decreased. As described above with respect to fig. 8, the rate reduction may be random or deterministic and may include a minimum rate limit. Then, in step 950, the mobile station transmits at the determined rate. A rate reduction signal may be used to reduce congestion on the shared resource.

If the mobile station receives neither an increase nor a decrease, then in step 950, the current rate is used and the mobile station transmits at the determined rate. After transmitting, processing returns to decision block 910 for the next cycle, where the new value may be transmitted on the busy signal.

In an alternative embodiment not shown, a multi-valued busy signal using more than three values may be used. The additional value may represent an increasing or decreasing degree of variation, and the mobile station may increase or decrease with a varying rate difference based on the respective received signals. For example, one value may represent an increase to the maximum allowed rate, while another value represents an intermediate incremental increase (which may ultimately be limited by the maximum rate). Similarly, a third value may indicate a decreasing increment, while a fourth value indicates that the rate should be adjusted immediately to the minimum rate for the mobile station. The fifth value may indicate that no adjustment is necessary. Multiple combinations of rate adjustment values on the busy signal will be readily used by those skilled in the art based on the learning herein.

Fig. 10 depicts an embodiment of a rate table 1000 that may be used by any congestion control method. In one embodiment, the rate table 1000 may be used in the memory 355 described above. In this example, the rate table 1000 includes N supported rates, where rate 1 is the highest supported rate and rate N is the lowest supported rate. Various parameters associated with the rate may also be stored. The rate and related parameters may be adjusted by the transmitted signal, if necessary, or may be predetermined and fixed. The rate tables may be the same in various mobile stations, but need not be.

In the example of fig. 10, the rate has corresponding alpha and beta parameters for random rate increases and decreases, respectively. The transition from each rate (except the minimum rate) to a lower rate with an associated alpha value is displayed. Similarly, transitions from each rate (except the maximum rate) to a higher rate with an associated β value are displayed. When the busy signal indicates an increase or decrease, the mobile station may transition to a higher or lower rate with a probability α or β, respectively. For example, when a mobile station transmitting at rate 3 receives a decrease signal, it will decrease its rate and use the probability α₃At rate 4. Although receiving the reduced signal, it will use the probability 1-alpha₃Transmission continues at rate 3. Similarly, the mobile station transmits at rate 3 and, after receiving the increased signal, uses the probability β₃Increasing its delivery rate to rate 2. Although receiving the increasing signal, it will use the probability 1-beta₃Transmission continues at rate 3. A reduction parameter a is stored for each rate except for the minimum rate (rate N). An increase parameter β is stored for each rate except for the maximum rate (rate 1). Thus each parameter need not have a unique value and can be modified by sending a signal. In one example, a single probability parameter may be used for all increases and decreases from any rate to a higher or lower rate, respectively. Alternatively, a single increase parameter may be used for all rates, and a different decrease parameter may be used for all rates. Any combination of increasing and decreasing parameters may be used. Those skilled in the art will appreciate that the storage requirements of the rate table 1000 may be adjusted according to the number of unique parameters. As described above, the rate conversion parameter may be used in conjunction with the busy signal to provide congestion control for the base station and any number of mobile stations.

Also depicted in fig. 10 are various pointers representing rate limiting for use in embodiments such as the examples described above. The maximum rate is specified. This rate may correspond to a given rate in the grant from the base station, which may be a dedicated grant or a common grant. Thus, as described above, the maximum rate can be adjusted by request and grant.

The maximum autonomous rate is also shown. This rate can be adjusted by signaling. This rate may be the same for all mobile stations, or different classes of mobile stations may have different maximum autonomous rates based on QoS level. The mobile station will know whether it is transmitting in response to a grant (either a private grant or a public grant) or whether it is transmitting autonomously. Thus, the maximum rate for any given mobile station depends on the type of transmission being performed.

A minimum rate may also be determined. This may be the minimum supported rate in the rate table 1000, or a higher rate may be specified. In one embodiment, the minimum supported rate may be used for autonomous transmissions, while a higher minimum rate is used for transmissions in response to the grant. Thus, the mobile station may limit its rate reduction to different levels based on the type of transmission being performed in response to the busy signal. As described above, the mobile station may be used to respond to the busy signal for any transmission (autonomous or grant), or a subset of the possible transmission types. For example, dedicated grants may be removed from congestion control, and the mobile station may perform rate adjustment for common grant delivery or autonomous delivery in response to a busy signal. For example, the common grant transfer rate may thus be limited to those rates between the maximum rate and the minimum rate. The autonomous transmission rate may be limited to those between the minimum supported rate (rate N) and the maximum autonomous rate (rate M in this example). Rate adjustment may be performed using any congestion control method, examples of which are detailed above with reference to fig. 6-9.

It should be noted that in all embodiments described above, method steps can be interchanged without departing from the scope of the invention. The description disclosed herein refers in many cases to signals, parameters and processes associated with the 1xEV-DV standard, but the scope of the present invention is not limited to these. Those skilled in the art will readily apply the principles herein to various other communication systems. These and other modifications will be apparent to those skilled in the art.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (43)

1. An apparatus operable with a plurality of remote stations capable of transmitting on a shared resource, comprising:

a receiver for receiving a plurality of access requests for transmission on the shared resource and for measuring utilization of the shared resource from a respective plurality of remote stations;

a scheduler for allocating a portion of the shared resource to zero or more requesting remote stations in response to the plurality of access requests, and for generating a busy command in response to the measured utilization, wherein the allocating comprises allocating zero or one common access grant to a subset of the requesting remote stations; and

a transmitter for transmitting the common access grant on one or more common grant channels to remaining remote stations not allocated a portion of the shared resources and for transmitting a busy signal comprising one or more busy commands;

a decoder for decoding one or more received packets and determining whether the one or more received packets are decoded without errors; and

wherein:

the receiver further receives one or more packets from one or more remote stations, respectively;

the transmitter further transmits acknowledgement and grant extension ACK-and-Continue commands to the one or more remote stations, respectively, when the received packet is decoded without error and access grants for the one or more remote stations are to be extended; and

the scheduler determines the allocation of the shared resources of the portion based on the private and public grants extended with one or more ACK-and-Continue commands.

2. The apparatus of claim 1, wherein:

the scheduler further comprises an assignment of zero or more dedicated access grants for zero or more requesting remote stations for further assignment; and

the transmitter further transmits the dedicated access grant to the respective plurality of remote stations on one or more dedicated grant channels.

3. The apparatus of claim 1, further operable with the respective plurality of remote stations equipped to autonomously transmit on the shared resource using a limited portion of the shared resource without an access request or an access grant, and wherein:

the scheduler calculates an expected amount of the shared resource consumed by the autonomous transmissions and in response allocates the portion of the shared resource for dedicated and common access grants.

4. The apparatus of claim 1, wherein each busy command includes one of a first value representing a decrease or a second value representing an increase.

5. The apparatus of claim 4, wherein each busy command further includes a third value indicating neither an increase nor a decrease.

6. The apparatus of claim 1, wherein each busy command includes one or more values representing respective one or more decreases representing different amounts of decrease or includes one or more values representing respective one or more increases representing different amounts of increase.

7. The apparatus of claim 6, wherein each busy command further comprises a value indicating neither an increase nor a decrease.

8. A remote station, comprising:

a data buffer for receiving data for transmission;

a message generator for generating an access request message when the data buffer contains data for transmission;

a receiver for receiving one or more common grant channels from a base station and for receiving a busy signal from the base station;

a message decoder for decoding an access grant addressed to the remote station, the access grant including a common grant on one of the one or more common grant channels; and

a transmitter for transmitting the access request message and for transmitting a portion of data from the data buffer in response to the decoded access grant in accordance with the received busy signal;

wherein the receiver further receives an ACK-and-Continue command; and

the transmitter transmits an additional portion of data from the data buffer in response to a previously decoded access grant in accordance with the received busy signal.

9. The remote station of claim 8, wherein:

the receiver further receives one or more dedicated grant channels from the base station; and

the message decoder further decodes an access grant, the access grant including a dedicated grant sent on one of the one or more dedicated grant channels.

10. The remote station of claim 8, wherein the transmitter further autonomously transmits a limited portion of data in the data buffer in response to the received busy signal regardless of whether an access request has been received.

11. The remote station of claim 8, wherein the transmitter further autonomously transmits a limited portion of the data in the data buffer after receiving an ACK based on the received busy signal.

12. The remote station of claim 8, wherein:

the receiver further receives a NAK command; and

the transmitter retransmits the portion of data previously sent in response to the previously decoded access grant from the data buffer in accordance with the received busy signal.

13. The remote station of claim 8, wherein a transmission rate is decreased in response to an assertion on the received busy signal.

14. The remote station of claim 13, wherein the decrease is deterministic.

15. The remote station of claim 13, wherein the reduction is random.

16. The remote station of claim 8, wherein a transmission rate is increased in response to an assertion on the received busy signal.

17. The remote station of claim 16, wherein the increase is deterministic.

18. The remote station of claim 16, wherein the increase is random.

19. The remote station of claim 8, wherein a transmission rate is increased or decreased in response to the received busy signal, the amount of the increase or decrease depending on a quality of service (QoS) service level.

20. A wireless communication system, comprising:

a plurality of remote stations, each of a subset of which transmits an access request message to form a plurality of access request messages;

a base station, comprising:

a receiver for receiving the plurality of access request messages and for measuring utilization of a shared resource;

a scheduler for allocating shared system resources among a plurality of remote stations;

a transmitter for transmitting zero or more dedicated access grants to a subset of the requesting remote stations and zero or more common access grants to the remaining requesting remote stations; and

wherein:

transmitting, by the transmitter, a busy signal when the measured utilization exceeds a predetermined threshold;

the receiver further receives one or more packets from one or more remote stations, respectively;

the transmitter further transmits acknowledgement and grant extension ACK-and-Continue commands to one or more remote stations, respectively, when the respective received packet is decoded without error and the access grant for the respective remote station is to be extended; and

the scheduler determines the allocation of the portion of the shared resource based on the private and public grants extended with one or more ACK-and-Continue commands.

21. The wireless communication system of claim 20, wherein said requesting remote station receives said transmitted one of a private access grant or a public access grant and a busy signal and transmits data to said base station in accordance therewith, respectively, in accordance with said received busy signal.

22. The wireless communication system of claim 20, wherein a subset of the plurality of remote stations autonomously transmit data in accordance with the transmitted busy signal.

23. A method of access control of a shared resource, comprising:

receiving a plurality of access requests for transmission on the shared resource from a respective plurality of remote stations;

allocating a portion of said shared resource to zero or more of said requesting remote stations in response to said plurality of access requests, said allocating comprising allocating zero or more common access grants to a subset of said requesting remote stations;

transmitting the common access grant on one or more common grant channels to remaining remote stations not allocated a portion of the shared resources;

measuring utilization of the shared resource; and

transmitting a busy signal when the measured utilization exceeds a predetermined threshold;

decoding one or more received packets;

determining whether the one or more received packets are decoded error-free;

transmitting acknowledgement and grant extension ACK-and-Continue commands to one or more remote stations, respectively, when the received packet is decoded error-free and the access request for the one or more remote stations is to be extended; and

wherein the allocation of the portion of the shared resource is performed according to the private and public grants extended by the one or more ACK-and-Continue commands.

24. The method of claim 23, wherein:

the allocating further comprises allocating zero or more dedicated access permissions to zero or more requesting remote stations; and

further comprising transmitting the dedicated access grant to the respective plurality of remote stations on one or more dedicated grant channels.

25. The method of claim 23, operable with the respective plurality of remote stations equipped to autonomously transmit on the shared resource using a limited portion of the shared resource without an access request or an access grant, the method further comprising:

calculating an expected amount of the shared resource consumed by the autonomous transmissions and in response allocating the portion of the shared resource for dedicated and common access grants.

26. The method of claim 23, wherein the busy signal comprises a series of commands, each command including one of a first value representing a decrease or a second value representing an increase.

27. The method of claim 26, wherein the series of commands further includes a third value representing neither an increase nor a decrease.

28. The method of claim 23, wherein the busy signal comprises a series of commands, each command comprising one or more values representing a respective one or more decreases, the respective decreases representing different amounts of decrease, or comprising one or more values representing respective one or more increases, the respective increases representing different amounts of increase.

29. The method of claim 28, wherein the series of commands further comprises a value representing neither an increase nor a decrease.

30. A method of transmitting, comprising:

receiving data for transmission;

storing the data in a data buffer;

generating an access request message;

transmitting the access request message;

receiving one or more common grant channels from a base station;

decoding an access grant, the access grant including a common grant on one of the one or more common grant channels;

receiving a busy signal from the base station;

transmitting a portion of data from the data buffer in response to the received busy signal in response to employing the decoded access grant;

receiving an ACK-and-Continue command; and

transmitting an additional portion of data from the data buffer in response to employing a previously decoded access grant in accordance with the received busy signal.

31. The method of claim 30, further comprising:

receiving one or more dedicated grant channels; and

wherein the access grant comprises a dedicated grant sent on one of the one or more dedicated grant channels.

32. The method of claim 30, further comprising autonomously transmitting a limited portion of data in the data buffer in accordance with the received busy signal regardless of whether an access request has been received.

33. The method of claim 30, further comprising autonomously transmitting a limited portion of data in the data buffer after receiving an ACK in accordance with the received busy signal.

34. The method of claim 30, further comprising:

receiving a NAK command; and

retransmitting the portion of data previously sent in response to the previously decoded access grant from the data buffer in accordance with the received busy signal.

35. The method of claim 30, wherein a transmission rate is decreased in response to an assertion on the received busy signal.

36. The method of claim 35, wherein the decrease is deterministic.

37. The method of claim 35, wherein the reducing is random.

38. The method of claim 30, wherein a transmission rate is increased in response to an assertion on the received busy signal.

39. The method of claim 38, wherein the increase is determined.

40. The method of claim 38, wherein the increase is random.

41. The method of claim 30, wherein a transmission rate is increased or decreased in response to the received busy signal, the amount of the increase or decrease depending on a quality of service, QoS, service level.

42. A system for access control of shared resources, comprising:

means for receiving a plurality of access requests from a respective plurality of remote stations for transmission on a shared resource;

means for allocating a portion of the shared resource to zero or more requesting remote stations in response to the plurality of access requests, wherein the allocating comprises allocating zero or one common access grant to a subset of the requesting remote stations;

means for transmitting the common access grant on one or more common grant channels to remaining remote stations not allocated a portion of the shared resources;

means for measuring utilization of the shared resource;

means for transmitting a busy signal when the measured utilization exceeds a predetermined threshold;

means for decoding one or more received packets;

means for determining whether the one or more received packets are decoded error-free;

means for transmitting acknowledgement and grant extension ACK-and-Continue commands to one or more remote stations, respectively, when the received packet is decoded error-free and the access request for the one or more remote stations is to be extended; and

means for performing the allocation of the portion of shared resources according to the private and public grants extended by the one or more ACK-and-Continue commands.

43. A system for transmitting, comprising:

means for receiving data for transmission;

means for storing the data in a data buffer;

means for generating an access request message;

means for transmitting the access request message;

means for receiving one or more common grant channels from a base station;

means for decoding an access grant, the access grant comprising a common grant on one of the one or more common grant channels;

means for receiving a busy signal from the base station;

means for transmitting a portion of data from the data buffer in response to the received busy signal being taken in response to the decoded access grant;

means for receiving an ACK-and-Continue command; and

means for transmitting an additional portion of data from the data buffer in response to employing a previously decoded access grant in accordance with the received busy signal.