HK1154453B - Long-term interference mitigation in an asynchronous wireless network - Google Patents

Description

Long term interference mitigation in asynchronous wireless networks

This application claims priority to the following U.S. provisional patent applications, including: U.S. provisional patent application serial No. 61/040,347, entitled "asynchronous-terminterferefeacevadience", filed on 28/3/2008; U.S. provisional patent application serial No. 61/040,481, entitled "asynchronusshort-terminterferorencevoidence", filed on 28/3/2008; U.S. provisional patent application serial No. 61/076,366, entitled "flex multimedia communication system," filed on 27.6.2008, assigned to the assignee of the present application and incorporated herein by reference.

Technical Field

The present disclosure relates generally to communication, and more specifically to techniques for mitigating interference in a wireless communication network.

Background

Wireless communication networks are widely deployed to provide various types of communication content (e.g., voice, video, packet data, messaging, broadcast, etc.). These wireless networks may be multiple-access networks capable of supporting communication with multiple users by sharing the available network resources. Examples of such multiple-access networks include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, orthogonal FDMA (ofdma) networks, and single carrier FDMA (SC-FDMA) networks.

A wireless communication network may include multiple base stations capable of supporting communication for multiple terminals. A terminal may communicate with a base station via the downlink and uplink. The downlink (or forward link) refers to the communication link from the base stations to the terminals, and the uplink (or reverse link) refers to the communication link from the terminals to the base stations.

A base station may transmit data to a terminal on the downlink and/or receive data from the terminal on the uplink. On the downlink, transmissions from a base station may experience interference caused by transmissions from neighboring base stations. On the uplink, transmissions from a terminal may experience interference caused by transmissions from other terminals communicating with neighboring base stations. For the downlink and uplink, the interference caused by interfering base stations and interfering terminals may degrade performance.

Thus, there is a need in the art for techniques for mitigating interference in a wireless network.

Disclosure of Invention

Techniques for mitigating interference in a wireless communication network are described. A terminal may desire to communicate with a weak serving base station and may experience strong interference on the downlink from a strong interfering base station. In addition, the serving base station may also experience strong interference on the uplink from interfering terminals. The serving base station and the interfering base station may be asynchronous and have different frame timings.

In an aspect, strong interference on the downlink and/or on the uplink can be mitigated by having the interfering base station reserve some resources (e.g., frequency resources and/or time resources). The reserved resources include reserved downlink resources and/or reserved uplink resources. The interfering base station transmits at a low power level or does not transmit at all on the reserved downlink resources to reduce interference to the terminal on the downlink. A plurality of interfering terminals served by the interfering base station transmit at a low power level or not at all on the reserved uplink resources to reduce interference to the serving base station on the uplink resources. The terminal can then communicate with the serving base station in the presence of the interfering base station and its terminal. Frequency resource reservation is particularly applicable to asynchronous networks. The time resource reservation can avoid receiver desensitization at the terminal due to severe interference from interfering base stations, as will be described below.

Various aspects and features of the disclosure are described in further detail below.

Drawings

Fig. 1 illustrates a wireless communication network.

Fig. 2 illustrates asynchronous operations performed by multiple base stations.

Fig. 3 shows the division of frequency resources.

Fig. 4 shows an example of frequency reservation.

Fig. 5 illustrates reserving frequency resources in a predetermined order.

Fig. 6 shows an example of time reservation.

Fig. 7 shows a processing procedure performed by the terminal.

Fig. 8 shows an apparatus for a terminal.

Fig. 9 shows a process performed by the interfering base station.

Fig. 10 shows an apparatus for an interfering base station.

Fig. 11 shows a process performed by the serving base station.

Fig. 12 illustrates an apparatus for a serving base station.

Fig. 13 shows another processing procedure performed by the serving base station.

Fig. 14 shows another apparatus for serving a base station.

Fig. 15 shows another processing procedure performed by the terminal.

Fig. 16 shows another apparatus for a terminal.

Fig. 17 shows a block diagram of a terminal and two base stations.

Detailed Description

The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms "network" and "system" are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), CDMA2000, etc. UTRA includes wideband CDMA (W-CDMA) and other CDMA variations. cdma2000 covers IS-2000, IS-95 and IS-856 standards. TDMA networks may implement wireless technologies such as global system for mobile communications (GSM). OFDMA networks may implement methods such as evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE802.11(Wi-Fi), IEEE802.16(WiMAX), IEEE802.20, Flash-Etc. wireless technologies. UTRA, E-UTRA and GSM are part of the Universal Mobile Telecommunications System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-advanced (LTE-A) are new versions of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE-A, and GSM are described in documents from an organization named "third Generation partnership project (3 GPP)". In addition, cdma2000 and UMB are described in documents from an organization named "third generation partnership project 2(3GPP 2)". The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies.

Fig. 1 shows a wireless communication network 100, which includes a plurality of base stations and other network entities. For simplicity, fig. 1 shows only two base stations 120 and 122 and one network controller 130. A base station is a station that communicates with multiple terminals and may also be referred to as an access point, a node B, an evolved node B (enb), etc. A base station provides communication coverage for a particular geographic area. The term "cell" can refer to a base station coverage area and/or a base station subsystem serving the base station coverage area, depending on the context in which the term is used.

A base station may provide communication coverage for a macrocell, picocell, femtocell, and/or other types of cells, etc. A macro cell covers a relatively large geographic area (e.g., covering a radius of several kilometers) which allows unrestricted access by terminals subscribed to the service. A pico cell covers a relatively small geographic area that allows unrestricted access by terminals subscribed to the service. A femto cell covers a relatively small geographic area (e.g., a home) that allows restricted access by terminals associated with the femto cell (e.g., terminals belonging to a Closed Subscriber Group (CSG)). The CSG includes a home user terminal, a user terminal subscribed to a specific service plan, and the like. The base station used for the macro cell may be referred to as a macro base station. The base station for the pico cell may be referred to as a pico base station. A base station for a femto cell may be referred to as a femto base station or a home base station.

Wireless network 100 may also include relay stations. A relay station is a base station that receives transmissions of data and/or other information from an upstream station and transmits the transmissions of data and/or other information to a downstream station. The upstream station may be a base station, another relay station, or a terminal. The downstream station may be a terminal, another relay station, or a base station. A relay station may also be a terminal for relaying transmissions of other terminals.

Network controller 130 may couple to and coordinate and control a set of base stations. Network controller 130 may be a single network entity or a collection of network entities. The network controller 130 may communicate with the base stations 120 and 122 via a backbone (backhaul). Base stations 120 and 122 may also communicate with each other (e.g., directly or indirectly via wireless or wired trunks).

Wireless network 100 may be a homogeneous network including only macro base stations. Wireless network 100 may also be a heterogeneous network that includes different types of base stations (e.g., macro base stations, pico base stations, home base stations, relay stations, etc.). The techniques described herein may be used for homogeneous networks as well as heterogeneous networks.

Terminals 110 and 112 are two terminals of a plurality of terminals supported by wireless network 100. A terminal may be fixed or mobile and may also be referred to as an Access Terminal (AT), a Mobile Station (MS), a User Equipment (UE), a subscriber unit, a station, etc. A terminal may be a cellular telephone, Personal Digital Assistant (PDA), wireless modem, wireless communication device, handheld device, laptop computer, cordless telephone, Wireless Local Loop (WLL) station, or the like. A terminal may be capable of communicating with macro, pico, femto, and/or other base stations.

A terminal communicates with a serving base station and may interfere with one or more interfering base stations and may also be interfered by one or more interfering base stations. A serving base station is a base station designated to serve a terminal on the downlink and/or uplink. An interfering base station is a base station that causes interference to a terminal on the downlink and/or is interfered by a terminal on the uplink. In fig. 1, base station 120 is a serving base station for terminal 110, and base station 122 is an interfering base station for terminal 110. Terminal 112 is in communication with base station 122 and is an interfering terminal with base station 120.

Wireless network 100 supports synchronous or asynchronous operation. For synchronous operation, multiple base stations have the same frame timing, and transmissions from different base stations are aligned in time. For asynchronous operation, multiple base stations have different frame timing, and transmissions from different base stations are not aligned in time.

An example of asynchronous operation performed by a plurality of base stations 1 to L is shown in fig. 2, where L > 1. For each base station, the horizontal axis represents time and the vertical axis represents frequency or transmit power. The transmission timeline for each base station may be partitioned into units of subframes. Each subframe has a predetermined duration, such as 1 millisecond (ms), and so on. A subframe may also be referred to as a slot, frame, etc.

For asynchronous operation, each base station independently maintains its frame timing and autonomously assigns indices to subframes. For example, base station 1 has a start at time T₁Sub-frame f₁Base station 2 has a start at time T₂Sub-frame f₂By analogy, base station L has a start at time T_LSub-frame f_L. As shown in fig. 2, the start time T₁、T₂、…T_LIs not aligned in time. In addition, the subframe index f₁、f₂、…f_LMay be different.

Wireless network 100 may use frequency division multiplexing (FDD). For FDD, one frequency channel is allocated for the downlink and another frequency channel is allocated for the uplink. The frequency channel of each link may be considered a frequency resource that may be used for transmissions on that link. The frequency resource of each link may be divided in various ways.

Fig. 3 shows a design of partitioning frequency resources for one link (e.g., downlink or uplink). The system bandwidth of the link may be fixed or configurable. For example, LTE and UMB support system bandwidths of 1.25 megahertz, 2.5 megahertz, 5 megahertz, 10 megahertz, or 20 megahertz (MHz). The system bandwidth may be partitioned into M subbands, indexed 1 through M, where M may be any value. Each sub-band occupies a predetermined frequency range, say 1.08MHz of LTE. The number of subbands depends on the system bandwidth and subband size. For example, 1, 2, 4, 8, or 16 subbands are available for a system bandwidth of 1.25MHz, 2.5MHz, 5MHz, 10MHz, or 20MHz, respectively.

With Orthogonal Frequency Division Multiplexing (OFDM) or single-carrier frequency division multiplexing (SC-FDM), the system bandwidth may be divided into multiple (K) subcarriers. These subcarriers may also be referred to as tones (tones), bins (bins), and so on. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) depends on the system bandwidth. For example, K may be 128, 256, 512, 1024 or 2048, corresponding to a system bandwidth of 1.25MHz, 2.5MHz, 5MHz, 10MHz or 20MHz, respectively. Each subband may include S subcarriers, where S may be any value. For example, in LTE, each subband occupies 1.08MHz, including 72 subcarriers.

The system bandwidth may also be divided into multiple (C) carriers. Each carrier has a particular center frequency and a particular bandwidth. The number of carriers depends on the system bandwidth and the carrier bandwidth size.

Generally, the available frequency resources for each link may be partitioned in different manners, with subbands, subcarriers, and carriers being three examples. The available frequency resources are allocated and used for transmission.

Wireless network 100 may include different types of base stations, e.g., macro base stations, pico base stations, femto base stations, etc. These different types of base stations may have different transmit power levels, different coverage areas, and different effects on interference in wireless network 100. For example, macro base stations transmit at high power levels (e.g., 20 watts), while pico and femto base stations transmit at low power levels (e.g., 1 watt).

Referring back to fig. 1, terminal 110 is within the coverage of multiple base stations. One of these base stations is selected to serve terminal 110. The serving base station may be selected according to various criteria such as geometry (geometry), path loss, and the like. Geometry may be quantified by signal-to-noise ratio (SNR), signal-to-noise-and-interference ratio (SINR), carrier-to-interference ratio (C/I), and so on.

Terminal 110 may operate in a dominant interference scenario where the terminal is subject to and/or causes strong interference to one or more base stations. Strong interference may be quantified by the interference being experienced exceeding a threshold or according to some other criteria.

A scenario of significant interference may result from an extension of the range, in which case the base station to which the terminal 110 is connected has a lower path loss and a lower geometry among the plurality of base stations detected by the terminal 110. For example, terminal 110 detects base stations 120 and 122, and the received power of terminal 110 to base station 120 is less than its received power to base station 122. However, if the path loss of base station 120 is lower than the path loss of base station 122, terminal 110 desires to connect to base station 120. This may occur if base station 120 (which may be a pico base station) has a much lower transmit power than base station 122 (which may be a macro base station). The terminal 110 is connected to the base station 120 with a lower path loss so that the interference to the wireless network 100 to achieve a given data rate is reduced and the network capacity is increased.

Scenarios of significant interference may also arise from restricted associations. Terminal 110 may be close to base station 122 and thus the received power to base station 122 is high. However, terminal 110 does not belong to the CSG of base station 122, and thus is not allowed to access base station 122. The terminal 110 then connects to the unrestricted base station 120 with lower received power. Terminal 110 then experiences strong interference from base station 122 and also causes strong interference to base station 122.

In an aspect, resource reservation may be used to support communication for terminals 110 operating in scenarios of significant interference. Resource reservation refers to a base station reserving certain resources for one or more other base stations. Resource reservation may also be referred to as resource allocation, "blanking", and the like. Interfering base station 122 reserves some downlink resources (e.g., one or more subbands for the downlink) on which base station 122 transmits at a low power level or does not transmit at all to reduce interference on the reserved downlink resources. Interfering base station 122 may also reserve some uplink resources (e.g., one or more subbands for uplink) on which terminals served by base station 122 transmit at a low power level or do not transmit at all to reduce interference on the reserved uplink resources. Thus, the terminal 110 experiences weaker interference on the reserved downlink resources and the serving base station 120 experiences weaker interference on the reserved uplink resources. Subsequently, terminal 110 is able to communicate with serving base station 120 even in the presence of interfering base station 122 and its terminal. Typically, the reserved resources include frequency resources and/or time resources. For simplicity, much of the description below is related to the reservation of frequency resources, or frequency reservation.

Frequency reservation may be used for both synchronous and asynchronous operation. Since there is no common notion of time between base stations, frequency reservation is particularly suitable for asynchronous operation. Asynchronous operation will be more common as more pico and femto base stations are deployed indoors, but these base stations cannot access synchronous sources such as the Global Positioning System (GPS).

Fig. 4 shows a design of frequency reservation to support communication for terminal 110 operating in a dominant interference scenario. In one operational scenario, for example, the terminal 110 detects the presence of the weak base station 120 and the strong base station 122 from low reuse rate pilots or preambles (LRPs) sent by both base stations. The LRP is a pilot transmitted with a low reuse rate so that it can be received by the distant terminal. A terminal 110 may desire to connect to a weak base station 120 due to range extension or limited association. The terminal 110 informs the strong base station 122 that it desires to connect to the weak base station 120.

In another operational scenario, terminal 110 initially communicates with strong base station 122. The terminal 110 then detects the presence of the weak base station 120 and may desire to connect to the weak base station based on some criteria such as geometry, path loss, trunk quality, etc. The terminal 110 informs the strong base station 122 that it desires to connect to the weak base station 120. In another operational scenario, the terminal 110 initially communicates with the strong base station 122, then detects the presence of the weak base station 120, and then reports the weak base station to the strong base station. The strong base station 122 selects the weak base station 120 to serve the terminal 110 according to some criteria and directs the terminal to perform a handover to the weak base station.

For all of the above operating scenarios, weak base station 120 is the serving base station for terminal 110 and strong base station 122 is the interfering base station. Interfering base station 122 reserves some frequency resources on the downlink or on the uplink or on both the downlink and uplink for terminal 110 to communicate with serving base station 120. The amount of frequency resources per link is negotiated between base station 120 and base station 122 (e.g., via a trunk or messages exchanged through terminal 110). The reserved frequency resources are given in the form of subband units, subcarrier units, carrier units, etc. The reserved frequency resources are valid for a predetermined amount of time (e.g., 100 milliseconds); or the reserved frequency resources may remain active for an unlimited time before some change is made. The interfering base station 122 informs the serving base station 120 of the reserved frequency resources via the backbone or by the terminal 110.

The amount of frequency resources reserved for each of the downlink and uplink may be determined in a variety of ways based on a variety of factors. In one design, the amount of reserved frequency resources may be determined based on a number of factors, such as a load of serving base station 120, a load of interfering base stations 122, an amount of data transmitted to terminal 110, a degree of improvement in network capacity, and/or the like. In one design, a fixed number of frequency resources may be reserved. In another design, a configurable number of frequency resources may be reserved that may vary from time to time and/or from base station to base station. In the example shown in fig. 4, interfering base station 122 reserves subband x for serving base station 120. The specific frequency resources to be reserved are determined according to the following description.

Fig. 5 shows a design for reserving frequency resources in a predetermined order. In the example shown in fig. 5, three base stations A, B and C reserve frequency resources in the form of subband units. For each base station, the horizontal axis represents frequency and the vertical axis represents transmit power. Terminal 110 is subject to strong interference from base stations A, B and C. If the interfering base stations reserve different subbands, then terminal 110 may then be interfered on all of the reserved subbands. For example, if only base station a retains subband 1, terminal 110 may then be strongly interfered with by base station B and/or base station C on subband 1 and may not be able to communicate on subband 1.

In one design, the interfering base station may reserve frequency resources in a predetermined order. In the example shown in fig. 5, a first sub-band 1 is reserved or nulled, then a second sub-band 2 is reserved or nulled, then a third sub-band 3 is reserved or nulled, and so on. Base station a decides to reserve three subbands and then reserves subbands 1, 2, and 3. Base station B decides to reserve one subband and then subband 1. Base station C decides to reserve two subbands and then reserves subbands 1 and 2. Terminal 110 may be weakly interfered by all three base stations A, B and C on subband 1, base stations a and C on subband 2, and base station a only on subband 3. Terminal 110 may be able to achieve a higher SINR on subband 1, a medium SINR on subband 2, and a lower SINR on subband 3.

In one design, different base stations (e.g., all macro base stations) with the same power level may reserve frequency resources in a predetermined order. For example, base stations A, B and C in fig. 5 are macro base stations. Terminal 110 may desire to connect to pico base stations located within the coverage of all three macro base stations A, B and C and be able to achieve a higher SINR on subband 1 reserved by all three macro base stations. The predetermined order of reserving frequency resources is known in advance by the base stations, or the predetermined order of reserving frequency resources may be transmitted to the base stations.

Referring back to the examples shown in fig. 1 and 4, interfering base station 122 reduces its interference on the reserved downlink frequency resources in a number of ways. In one design, interfering base station 122 refrains from transmitting on the reserved frequency resources and thus does not cause interference on these frequency resources. In another design, interfering base station 122 may transmit at a low power level to reduce interference on the reserved frequency resources. In one design, the transmit power level of interfering base station 122 may be selected to achieve a target interference level for terminal 110. Terminal 110 sends a request to interfering base station 122 to reserve frequency resources including a target interference level and possibly its transmit power level. Interfering base station 122 determines the path loss from terminal 110 to interfering base station 122 based on the known or reported transmit power level of the terminal, the requested received power measured at the interfering terminal. Interfering base station 122 then determines its transmit power level based on the path loss and the target interference level. Similarly, interference on the reserved uplink frequency resources may also be reduced by causing terminals served by interfering base station 122 to refrain from transmitting on the reserved uplink frequency resources or to transmit at a lower power level.

The serving base station 120 uses the reserved frequency resources in a variety of ways. In one design, serving base station 120 may transmit one or more downlink control channels (e.g., only) on the reserved downlink frequency resources and/or may receive one or more uplink control channels (e.g., only) on the reserved uplink frequency resources. This design enables serving base station 120 to reliably transmit control information to terminal 110 and/or reliably receive control information from terminal 110 on the frequency resources that are subject to weaker interference. The serving base station 120 transmits data on the reserved downlink frequency resources (if available) or on other downlink resources that are otherwise reserved. Serving base station 120 may also receive data from terminal 110 on reserved uplink frequency resources (if available) or on other uplink resources that are otherwise reserved. For example, the serving base station 120 may send a reduce interference request requesting that interfering terminals reduce interference on certain uplink resources so that the terminal 110 may send data to the serving base station 120 on those uplink resources. Accordingly, terminal 110 may send a reduce interference request requesting interfering base station 120 to reduce interference on certain downlink resources so that serving base station 120 may send data to terminal 110 on these downlink resources. This design allows interfering base station 122 to reserve a small amount of frequency resources for a long period of time. The reduced interference request, also referred to as a Resource Usage Message (RUM), can be used to dynamically reserve uplink resources and/or downlink resources for transmitting data as needed.

In another design, serving base station 120 may transmit downlink control channels and downlink data channels on the reserved downlink frequency resources and/or may receive uplink control channels and uplink data channels on the reserved uplink frequency resources. Interfering base station 122 reserves a sufficient amount of frequency resources on each link for the control and data channels on that link.

In one design, interfering base station 122 broadcasts information to convey the frequency resources reserved for serving base station 120. In another design, serving base station 120 broadcasts information to convey the reserved frequency resources for the control channel. The base station broadcasts information related to the reserved frequency resources in the LRP or some other signal sent by the base station.

In one design, terminal 110 may periodically send channel information to serving base station 120. The channel information includes Channel Quality Indicator (CQI) information, interference information, channel response information, and the like. In one design, the CQI information may include an SINR estimate for each frequency unit to be reported, e.g., for each subband reserved for serving base station 120, for each subband available for transmission of data to terminal 110, for each subband having a sufficiently high SINR, for each subband having sufficiently low interference, for all frequency resources reserved for serving base station 120, for the entire system bandwidth, and so on. In another design, the CQI information may include at least one Modulation and Coding Scheme (MCS) determined based on the at least one SINR estimate. The interference information includes an interference estimate for each frequency cell to be reported. The frequency unit for reporting CQI may be the same as or different from the frequency unit for reporting interference. The terminal 110 sends the CQI information at a first rate and sends the interference information at a second rate, where the second rate may be the same as or slower than the first rate. Alternatively or additionally, terminal 110 may send CQI information and/or interference information when requested by serving base station 120, when channel conditions change, or based on other triggering events. The serving base station 120 uses the CQI information and/or interference information reported by the terminal 110 to: selecting a terminal for data transmission, selecting a frequency resource for transmitting data to a terminal, selecting a modulation and coding scheme for transmitting data to a terminal, and so on.

Terminal 110 may be severely interfered by interfering base station 122 and, thus, the interfering base station desensitizes (or is referred to as desensitizing) terminal 110 on the downlink. Desensitization occurs when the interference is so strong that the terminal 110 cannot detect the desired signal from the serving base station 120 in the presence of strong interference. For example, terminal 110 performs Automatic Gain Control (AGC) and adjusts the receiver gain so that the input signal provided to an analog-to-digital converter (ADC) has a target signal level, thereby avoiding ADC clipping problems. The ADC input signal includes the desired signal from the serving base station 120 and strong interference from the interfering base station 122. The ADC input signal is dominated by strong interference. The desired signal level may be below the quantization noise level of the ADC and thus undetectable.

The desensitization problem described above cannot be solved by having interfering base station 122 reserve some frequency resources for serving base station 120. If interfering base station 122 reserves some frequency resources but transmits on unreserved frequency resources, strong interference from these frequency resources may still cause the AGC at terminal 110 to adjust the receiver gain, and thus the desired signal is below the quantization noise at the input of the ADC.

In another aspect, the problem of reduced sensitivity of the terminal 110 is addressed by using time reservation. Time reservation refers to one base station reserving certain time resources (e.g., time intervals) for one or more other base stations. Interfering base station 122 reserves certain time intervals (e.g., a set of subframes) for serving base station 120 and transmits at a low power level or not at all during the reserved time intervals. Terminal 110 is then weakly interfered or not interfered by interfering base station 122 during the reserved time intervals and is able to detect the desired signal from serving base station 120 during these time intervals.

Fig. 6 shows an example of reserving time to cope with the problem of desensitization of the terminal 110 in the case where the serving base station 120 and the interfering base station 122 operate asynchronously. For each base station, the horizontal axis represents time and the vertical axis represents frequency or transmit power. The serving base station 120 expects in subframe f_sServes the terminal 110. Subframe f of serving base station 120 due to asynchronous operation_sSubframe f with interfering base station 122_i、f_i+1 overlap. In this way,interfering BS 122 serving BS 120 in subframe f_iAnd f_i+1 reserves all frequency resources.

Fig. 6 shows that the interfering base station 122 reserves two subframes such that the serving base station 120 is not interfered by the interfering base station 122 or only weakly interfered by the interfering base station 122 in one subframe. In general, any amount of time (e.g., any number of subframes) may be reserved for serving base station 120. The reserved time may be contiguous (e.g., a certain number of consecutive subframes), thereby enabling a reduction in the percentage of unused time due to frame timing misalignment of base stations 120 and 122. The time remaining may also be divided. For example, Q interlaces may be defined, each comprising subframes separated by Q subframes, where Q may be equal to 4, 6, 8, and so on. Interfering base station 122 reserves one or more interlaces for serving base station 120. For example, base stations 120 and 122 negotiate an amount of time to reserve and/or a particular time interval to reserve by exchanging information via trunk or terminal 110.

Interfering base station 122 may desensitize terminal 110 on the downlink and likewise terminal 110 may desensitize interfering base station 122 on the uplink. This may occur, for example, if interfering base station 122 is a neighboring femto base station that terminal 110 cannot access due to restricted association. In such a symmetric desensitization scenario, interfering base station 122 remains on the downlink for some time for transmissions from serving base station 120 to terminal 110 (e.g., as shown in fig. 6); interfering base station 122 also reserves some time on the uplink for transmissions from terminal 110 to serving base station 120. Interfering base station 122 avoids scheduling its terminals for uplink transmissions during the time reserved for uplink to avoid strong interference from terminal 110.

In the examples shown in fig. 4 and 6, only interfering base station 122 reserves frequency resources and time for serving base station 120. In general, any base station may reserve frequency resources and/or time for other base stations. Multiple base stations may be subject to strong interference with each other. In terms of frequency reservation, different base stations may use different frequency resources (e.g., different subbands). In terms of time reservation, different base stations may use different time intervals (e.g., different 100 millisecond intervals) or non-overlapping interlaces.

For simplicity, much of the description above relates to interference mitigation on the downlink. The techniques may also be used for interference mitigation on the uplink.

Fig. 7 shows a design of a process 700 performed by a terminal for communication with reservation of resources in a wireless network. The terminal detects an interfering base station causing strong interference to it (block 712). The terminal sends a request to reserve resources (e.g., frequency resources and/or time resources) to the interfering base station (block 714). The terminal communicates with the serving base station on resources reserved by the interfering base station (block 716). The serving base station and the interfering base station are asynchronous and have different frame timings. Of course, the serving and interfering base stations may also be synchronized, with similar frame timing.

In one scenario, the terminal detects two base stations, selects one of the base stations as a serving base station, and identifies the other base station as an interfering base station. In another scenario, a terminal initially communicates with a first base station (e.g., a macro base station) and then detects a second base station (e.g., a pico base station). The terminal desires to handover to the second base station and reports the second base station to the first base station. The first base station decides to handover the terminal to the second base station and reserves resources for the terminal to communicate with the second base station. Thus, the first base station is initially the serving base station and subsequently becomes the interfering base station. The serving and interfering base stations may also be determined in other manners.

The reserved resources include downlink resources and/or uplink resources. In terms of frequency reservation, the resources reserved for each link (if any) include: at least one subband, at least one carrier, a set of subcarriers, and so on. In terms of time reservation, the resources reserved for each link (if any) include: a set of subframes in the reserved time interval. In terms of frequency reservation and time reservation, the reserved resources are less interfered by the interfering base stations, for example, due to the following reasons: (i) the interfering base station transmits at a lower power level or does not transmit at all on the reserved resources; and/or (ii) the terminal served by the interfering base station transmits at a lower power level or not at all on the reserved resources.

In one design of block 716, the terminal receives a control channel and/or a data channel that the serving base station transmits only on the reserved resources. The control channel and/or the data channel are mainly located in reserved resources that are subject to weak interference, which can improve performance. In another design, the reserved resources include: reserved downlink resources and reserved uplink resources. The terminal receives a downlink control channel and/or a downlink data channel from the serving base station on the reserved downlink resources. The terminal transmits an uplink control channel and/or an uplink data channel to the serving base station on the reserved uplink resources. The reserved resources may also be used for communication in other ways.

In terms of time reservation, the terminal receives a control channel and/or a data channel from the serving base station during N subframes of the serving base station, where N is equal to 1 or greater than 1. The reserved resources include at least N subframes of the interfering base station that cover N subframes of the serving base station (e.g., as shown in fig. 6). The reserved resources may also include one or more interlaces.

In one design, the terminal may determine channel information for the reserved resources and may send the channel information to the serving base station. The terminal obtains at least one SINR estimate for the reserved resources and determines CQI information based on the at least one SINR estimate. The terminal also obtains at least one interference estimate for the reserved resources. The channel information includes: CQI information, at least one interference estimate, and/or other information.

In one design, the received power of the serving base station may be lower than the received power of the interfering base station at the terminal due to range extension. The path loss from the serving base station to the terminal is also smaller than the path loss from the interfering base station to the terminal. The interfering base station is a macro base station with a high transmit power level (e.g., 20 watts). The serving base station is a pico base station or a femto base station having a low transmit power level (e.g., 1 watt). In another design, the interfering base station may be a femto base station with access restrictions due to restricted association, and the terminal may not be able to access the femto base station. The serving base station is a pico base station or a macro base station without access restriction, so the terminal can access.

Fig. 8 shows a design of an apparatus 800 for a terminal. The apparatus 800 comprises: a module 812, configured to detect an interfering base station causing strong interference to the terminal; a module 814, configured to send a request for reserving resources to an interfering base station; a module 816 is configured to communicate with the serving base station on resources reserved by the interfering base station, where the reserved resources are less interfered by the interfering base station.

Fig. 9 shows a design of a process 900 performed by an interfering base station in a wireless network. The interfering base station obtains an indication that a terminal communicating with the serving base station is strongly interfered by it (block 912). The interfering base station is asynchronous with the serving base station and has different frame timing. In one design, the interfering base station may receive a request to reserve resources (e.g., frequency resources and/or time resources) from the terminal. In another design, the interfering base station may receive pilot reports from the terminal. The interfering base station determines from the request, pilot report, or some other information that the terminal is being strongly interfered with.

The interfering base station reserves resources to facilitate communication between the serving base station and the terminal (block 914). In one design, the interfering base station (e.g., as shown in fig. 5) may reserve resources (e.g., frequency resources) according to a predetermined order. In addition, the interfering base station may reserve resources for a predetermined period of time or for a sustained period of time until the reserved resources are cancelled.

The interfering base station reduces interference on the reserved resources (block 916). In one design, the interfering base station may refrain from transmitting on the reserved resources. In another design, the interfering base station may reduce its transmit power on the reserved resources, e.g., to achieve a target interference level for the terminal. The amount of transmit power reduction may be determined based on the estimated path loss from the interfering base station to the terminal and the target interference level.

Fig. 10 shows a design of an apparatus 1000 for an interfering base station. The apparatus 1000 comprises: a module 1012 for obtaining an indication that a terminal in communication with a serving base station is strongly interfered by an interfering base station; a module 1014 for reserving resources for facilitating communication between a serving base station and a terminal; a module 1016 configured to cause an interfering base station to reduce interference on the reserved resources.

Fig. 11 shows a design of a process 1100 performed by a serving base station in a wireless network. The serving base station determines resources (e.g., frequency resources and/or time resources) reserved by the interfering base station (block 1112). The interfering base station is asynchronous with the serving base station and has different frame timing. The reserved resources are less interfered by the interfering base stations. The serving base station broadcasts information indicating the reserved resources, for example, via system information or LRP.

The serving base station communicates with the terminal on the reserved resources (block 1114). In one design, the serving base station may send control channels and/or data channels to the terminal on the reserved resources (e.g., only). In another design, the serving base station may send control channels and/or data channels to the terminal on the reserved resources as well as on other resources. In another design, the reserved resources include: reserved downlink resources and reserved uplink resources. The serving base station transmits a downlink control channel and/or a downlink data channel to the terminal on the reserved downlink resources. The serving base station receives an uplink control channel and/or an uplink data channel from the terminal on the reserved uplink resources.

In one design, the serving base station may receive channel information (e.g., CQI information, interference information, etc.) for the reserved resources from the terminal. The serving base station uses the channel information to: selecting a terminal for data transmission, selecting resources for data transmission, selecting a modulation and coding scheme for data transmission, and so on.

Fig. 12 shows a design of an apparatus 1200 for a serving base station. The apparatus 1200 includes: a module 1212, configured to determine resources reserved by an interfering base station, where the reserved resources are less interfered by the interfering base station; a module 1212 is configured to communicate with the terminal on the reserved resources.

Fig. 13 shows a design of a process 1300 performed by a serving base station for communication with reservation of resources in a wireless network. The serving base station detects strong interference (block 1312). The serving base station determines reserved resources (e.g., frequency resources and/or time resources) that are subject to weaker interference by at least one interfering terminal (block 1314). In one design, a serving base station may send a reserve resource request to a neighboring base station. The neighboring base station then directs at least one interfering terminal to reduce interference on the reserved resources. In another design, the serving base station may send a reduce interference request to the at least one interfering terminal on the reserved resources. Each interfering terminal then reduces interference on the reserved resources. In any case, the serving base station broadcasts information indicating the reserved resources to its terminals.

The serving base station communicates with the terminal on the reserved resources (block 1316). In one design, the serving base station may receive control channels and/or data channels that the terminal transmits on (e.g., only) the reserved resources.

Fig. 14 shows a design of an apparatus 1400 for a serving base station with resource reservation. The apparatus 1400 comprises: a module 1412 for detecting strong interference at a serving base station; a module 1414 for determining reserved resources that are weakly interfered by at least one interfering terminal; a module 1416 for communicating with the terminal on the reserved resources.

Fig. 15 shows a design of a process 1500 performed by a terminal for communication with reservation of resources in a wireless network. The terminal determines resources (e.g., frequency resources and/or time resources) reserved for the serving base station that are less interfered by the at least one interfering terminal (block 1512). In one design, the terminal may receive broadcast information from the serving base station indicating the reserved resources. The terminal communicates with the serving base station on the reserved resources (block 1514). In one design, the terminal may send a control channel and/or a data channel to the serving base station on the reserved resources (e.g., only).

The terminal also receives a reduce interference request that requests the terminal to reduce interference to neighboring base stations that are strongly interfered with by the terminal (block 1516). The terminal receives the request from the neighboring base station or the serving base station. The terminal then reduces interference on a second resource reserved for the neighboring base station (block 1518).

Fig. 16 shows a design of an apparatus 1600 for a terminal in a resource reservation situation. The apparatus 1600 includes: module 1612 for determining reserved resources that are weakly interfered by the at least one interfering terminal at the serving base station; a module 1614 for communicating with a serving base station on the reserved resources; a module 1616, configured to receive a request to reduce interference, the request requesting that interference to a neighboring base station that is strongly interfered by the terminal be reduced; means 1618 for causing the terminal to reduce interference on a second resource reserved for a neighboring base station.

The modules in fig. 8, 10, 12, 14 and 16 may include: a processor, an electronic device, a hardware device, an electronic component, a logic circuit, a memory, software code, firmware code, etc., or any combination thereof.

Fig. 17 shows a block diagram of a design of terminal 110, serving base station 120, and interfering base station 122. At serving base station 120, a transmit processor 1714a receives data from a data source 1712a and control information from a controller/processor 1730a and a scheduler 1734 a. Controller/processor 1730a provides messages for the reserved resources. Scheduler 1734a provides scheduling grants for terminal 120. Processor 1714a processes (e.g., encodes and modulates) the data and control information to provide data symbols and control symbols, respectively. Processor 1714a also generates pilot symbols (e.g., of the LRP). A processor 1714a processes the data symbols (e.g., for OFDM, CDMA, etc.), control symbols, and pilot symbols to provide output samples. A transmitter (TMTR)1716a conditions (e.g., converts to analog, amplifies, filters, and frequency upconverts) the output samples to generate a downlink signal, which is transmitted via an antenna 1720 a.

Similarly, interfering base station 122 processes data and control information for terminals it serves. The data, control information, and pilot are processed by a transmit processor 1714b, conditioned by a transmitter 1716b, and transmitted via the antenna 1720 b.

At terminal 110, an antenna 1752 receives the downlink signals from base stations 120 and 122. A receiver (RCVR)1754 conditions (e.g., filters, amplifies, frequency downconverts, and digitizes) a received signal from antenna 1752 to provide input samples. Receive processor 1756 processes the input samples (e.g., for OFDM, CDMA, etc.) to provide detected symbols. A processor 1756 may further process (e.g., demodulate and decode) the detected symbols, provide decoded data to a data sink 1758, and provide decoded control information to a controller/processor 1770.

On the uplink, transmit processor 1782 receives and processes data from a data source 1780, and control information (e.g., a request to reserve resources) from controller/processor 1770 to provide output samples. A transmitter 1784 conditions the output samples and generates an uplink signal, which is transmitted via antenna 1752. At each base station, the uplink signals from terminal 110 and other terminals are received by antennas 1720, conditioned by receivers 1742, and processed by a receive processor 1744. Processor 1744 provides decoded data to a data sink 1746 and decoded control information to controller/processor 1730.

Controllers/processors 1730a, 1730b, and 1770 direct the operation at base station 120, base station 122, and terminal 110, respectively. Processor 1770 and/or other modules at terminal 110 may perform or direct process 700 in fig. 7, process 1500 in fig. 15, and/or other processes for the techniques described herein. Processor 1730b and/or other modules at interfering base station 122 may perform or direct process 900 in fig. 9 and/or other processes for the techniques described herein. Processor 1730a and/or other modules at serving base station 120 may perform or direct process 1100 in fig. 11, process 1300 in fig. 13, and/or other processes for the techniques described herein. Memories 1732a, 1732b, and 1772 may store data and program codes for base stations 120, 122 and terminal 110, respectively. Schedulers 1734a and 1734b schedule terminals communicating with base stations 120 and 122, respectively, and allocate resources to the scheduled terminals.

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 disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative 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 disclosure 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 disclosure 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. Of course, the storage medium may also be integral to the processor. The processor and the storage medium may reside in an ASIC. Additionally, the ASIC may reside in a user terminal. Of course, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more exemplary implementations, the functions described herein may be implemented in hardware, software, firmware, or combinations thereof. When implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes Compact Disc (CD), laser video disc, optical disc, Digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks (disks) usually reproduce data magnetically, while discs (discs) reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

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

Claims (18)

1. A method for wireless communications at a serving base station, comprising:

sending, by the serving base station, a message to an interfering base station over a backbone, the message comprising information associated with identifying resources reserved by the interfering base station;

receiving a response message from the interfering base station over the backbone, the response message including information informing the serving base station of resources reserved by the interfering base station, wherein the interfering base station limits transmissions on the reserved resources to reduce interference; and

communicating with the terminal on the reserved resources.

2. The method of claim 1, wherein the communicating with a terminal comprises:

transmitting at least one of a control channel and a data channel to the terminal only on the reserved resources.

3. The method of claim 1, wherein the reserved resources comprise reserved downlink resources and reserved uplink resources; wherein the communicating with the terminal comprises:

transmitting at least one of a downlink control channel and a downlink data channel to the terminal on the reserved downlink resources;

receiving at least one of an uplink control channel and an uplink data channel from the terminal on the reserved uplink resources.

4. The method of claim 1, further comprising:

receiving channel information of the reserved resources from the terminal;

utilizing the channel information to perform the following or a combination of the following:

selecting a terminal for data transmission;

selecting a resource for the data transmission;

a modulation and coding scheme is selected for the data transmission.

5. The method of claim 1, further comprising:

information indicating the reserved resources is broadcast.

6. The method of claim 1, wherein the reserved resources comprise frequency resources reserved by the interfering base station.

7. The method of claim 1, wherein the reserved resources comprise at least one subband, at least one carrier, at least one group of subcarriers, or a combination thereof.

8. The method of claim 1, wherein the reserved resources comprise time resources reserved by the interfering base station.

9. The method of claim 1, wherein the interfering base station and the serving base station are asynchronous and have different frame timings.

10. The method of claim 1, wherein the reserved resources comprise at least N subframes of the interfering base station, wherein N is equal to 1 or greater than 1.

11. An apparatus for wireless communication at a serving base station, comprising:

means for transmitting, by the serving base station, a message to an interfering base station over a backbone, the message comprising information associated with identifying resources reserved by the interfering base station;

means for receiving a response message from the interfering base station over the backbone, the response message including information informing the serving base station of resources reserved by the interfering base station, wherein the interfering base station limits transmissions on the reserved resources to reduce interference; and

means for communicating with the terminal on the reserved resources.

12. The apparatus of claim 11, wherein the means for communicating with the terminal comprises:

means for transmitting at least one of a control channel and a data channel to the terminal only on the reserved resources.

13. The apparatus of claim 11, further comprising:

means for receiving channel information of the reserved resources from the terminal;

means for utilizing the channel information to perform the following or a combination of the following:

selecting the terminal for data transmission;

selecting a resource for the data transmission;

a modulation and coding scheme is selected for the data transmission.

14. The apparatus of claim 11, wherein the reserved resources comprise frequency resources reserved by the interfering base station.

15. The apparatus of claim 11, wherein the reserved resources comprise at least one subband, at least one carrier, at least one group of subcarriers, or a combination thereof.

16. The apparatus of claim 11, wherein the reserved resources comprise time resources reserved by the interfering base station.

17. The apparatus of claim 11, wherein the interfering base station and the serving base station are asynchronous and have different frame timings.

18. The apparatus of claim 11, in which the reserved resources comprise at least N subframes of the interfering base station, where N is equal to 1 or greater than 1.