HK1113031B - A method for selecting downlink modulation and coding settings and a method for providing channel quality measurements for allocation of downlink resources - Google Patents

Description

Method for selecting a downlink modulation code set and method for providing channel quality measurements for downlink resource allocation

The patent application of the invention is a divisional application of an invention patent application with the international application number of PCT/US02/15242, the international application date of 5-month-14-year 2002, the application number of 02809799.8 entering the Chinese national stage and the name of 'channel quality measurement of downlink resource allocation'.

Technical Field

The present invention relates to wireless digital communication systems, and more particularly, to communication stations that use Code Division Multiple Access (CDMA) measurement techniques to efficiently determine downlink resource allocations.

Background

In modern communication systems, the capacity requirements of such systems have increased as the composition of communication traffic has switched from predominantly voice traffic to the sharing of ever increasing data traffic, such as internet applications. Therefore, it is highly desirable to provide a technique for maximizing Downlink (DL) transmission capacity.

The propagation loss between the transmitter and the receiver is not fixed or constant. In addition to propagation loss over distance, the obstruction of paths and interactions between paths between the transmitter and receiver causes variations. These changes are called fading. Furthermore, the attenuation varies with time.

In some communication systems, it is customary to transmit to a particular user, or several of a plurality of users, at each moment in time, which enjoys the best transmission situation at that time. In such systems, it is necessary to define a channel quality that can be assessed from time to time by the users for transmission to each user at the most appropriate time. Although the selection of the most appropriate moment is not mandatory from a fading point of view, the instantaneous path loss will be one of the factors considered in the selection.

One measure of channel quality is instantaneous path loss. The channel quality improves as the instantaneous path loss decreases, and is best when the instantaneous path loss is minimal.

Another measure of channel quality is the interference seen by the user, since higher interference typically requires higher transmission power. When transmission power is limited, it produces a reduction in system capacity. Channel Quality (CQ) can thus be defined as the ratio of the received power of a fixed level base station transmission to the received interference. This ratio is inversely proportional to the transmission power required by the base station for the user data. Maximizing this ratio, by continuously selecting the users with the highest CQ (and thus the lowest path loss and/or interference), at any time, tends to increase the system capacity as a whole over time.

The particular signal used to determine the path loss and calculate this ratio is not important. For example, this signal may be any pilot signal (pilot signal), beacon (beacon), or even a data-bearing signal transmitted at a fixed or known power. In some systems, the received power is the final Received Signal Code Power (RSCP) and the received interference power is the final Interference Signal Code Power (ISCP). For example, in the Universal Mobile Telecommunications System (UMTS) Frequency Division Duplex (FDD) standard, the common pilot channel (CPiCH) is measured and CQ is defined as CPiCH _ RSCP/ISCP. In the UMTS Time Division Duplex (TDD) standard, a beacon channel (PCCPCH) is measured and CQ is defined as PCCPCH _ RSCP/ISCP. Because the channel conditions change rapidly, it is preferable to use a short time allocation, (i.e., a small time slot) for each transmission. The measurement information for allocation must therefore be in real time.

In some communication systems it is customary to time separate transmissions to a user, or to time separate one type of user-selected transmission from another type of transmission, such as normal voice service or data service. Such temporal differentiation can be obtained in different ways. For example, an iterative frame (frame) may be partitioned into multiple slots. Each time slot may be allocated to one or more users at one time. In addition, several time slots, adjacent or not, may be allocated to one or more users. If a collection of one or more time slots are allocated together, it may be considered a subchannel.

In time division transmission, it is likely that the interference within all time slots or sub-slots is not equal. A signal value for all timeslots often results in improper allocation and information in some timeslots may be lost, so it is desirable to report individual measurements for each timeslot.

Disclosure of Invention

The present invention provides real-time CQ measurement and appropriate signaling of information to the base station. The present invention provides several embodiments to measure and send out CQ signals for each slot or subchannel, from the UE to the base station. Measurements may be made at a high rate for all relevant timeslots or subchannels, or may be made at a lower rate by selectively reducing the rate at which such measurements are made.

To further illustrate the above objects, structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

Drawings

Figure l is a simplified block diagram of the UMTS architecture.

Fig. 2 is a simplified block diagram of a UE and a base station implementing channel quality measurements for downlink resource allocation in accordance with the present invention.

Fig. 3 is a flow chart of a preferred method of performing channel quality measurements for downlink resource allocation in the present invention at a UE and reporting these measurements to a base station.

Detailed Description

Referring to fig. 1, the UMTS network architecture includes a Core Network (CN), a UMTS Terrestrial Radio Access Network (UTRAN), and a User Equipment (UE). The two common interfaces are the Iu interface between the UTRAN and the core network, and the radio interface Uu between the UTRAN and the UE. The UTRAN includes a plurality of Radio Network Subsystems (RNSs) which are interconnected by an Iur interface. This interconnection allows independent procedures between different RNSs. Thus, the radio access technology designation functionality may be maintained outside the core network. The RNS is further divided into a Radio Network Controller (RNC) and a number of base stations (node bs). The node bs are connected to the RNC by an Iub interface. A node B may serve one or more cells (cells) and typically serves multiple UEs. The UTRAN supports both FDD and TDD modes on the radio interface. Both modes use the same network architecture and the same protocol.

Referring to fig. 2, a block diagram of a preferred communication system 10 for performing a CQ measurement procedure for obtaining downlink resource assignments in accordance with the principles of the present invention is shown. The communication system 10 includes a UE12 and a base station/node B30, (hereinafter referred to as base station 30) coupled together via a wireless radio interface 14.

The UE12 includes an antenna 16, a power measurement device 22, a slot interference measurement device 24, a CQ transmitter 26, and a CQ determination device 28. The antenna 16 is coupled via an isolator/switch 18 to a matched filter 20 which receives the downlink signal and provides an output to a power measurement device 22. The reference channel code generator 21 generates a reference channel code, which is input to the matched filter 20. The power measurement means 22 analyzes the output of the matched filter 20 to determine the power level of the downlink signal and outputs the power level to the CQ determination means 28.

The isolator/switch 18 is further coupled to a time slot interference measurement device 24 which measures the downlink channel and provides an output to a second input of the CQ decision device 28. The CQ determination device 28 analyzes the power level output from the power measurement device 22 and the slot interference from the slot interference measurement device 24 and provides a CQ measurement to the transmitter 26. The transmitter 26 is coupled via isolator/switch 18 to the antenna 16 for wireless RF transmission via the wireless radio frequency interface 14 to the base station 30.

Base station 30 includes a reference channel transmitter 36, an isolator or switch 34, a CQ receiver 38, and a CQ storage device 40. The antenna 32 receives wireless RF transmissions from the UE, including CQ measurements over the wireless radio interface 14, and is coupled via the isolator/switch 34 to a received signal and channel quality receiver 38. The received CQ measurements are then stored in CQ storage 40. The reference channel transmitter 36 provides a reference signal that is transmitted in the downlink through the isolator/switch 34 and the antenna 32 to the UE 12. The reference downlink signal from the transmitter 36 is used by the UE12 to generate downlink CQ measurements.

It should be noted that the aforementioned preferred method 50 shown in fig. 3 according to the present invention can be performed by communication systems other than those shown in fig. 1 and 2, and the present invention is not limited thereto.

Referring to fig. 3, the method 50 may be implemented by the digital communication system 10 as explained with reference to fig. l and 2, including a UE12 in communication with the base station 30.

Fast quality estimation per slot or subchannel is the preferred CQ measurement technique used by the present invention to provide the best performance for Downlink (DL) allocation since the base station 30 will have all the information needed to select the modulation and coding, select the best user or users, and assign the best slot or subchannel to them. Although the present invention is applicable to both frequency division duplex and time division duplex standards, only one is used herein as an example. In the FDD standard, for example, the common pilot channel (CPICH) may be measured and divided by each slot or subchannel interference signal code power measurement (ISCP), which is performed in all relevant slots. In the TDD standard, a physical common pilot channel (PCCPCH) is exemplified by a channel that can be measured.

The base station 30 transmits a fixed level transmission (step 52), such as a pilot beacon or a data-carrying signal, on the PCCPCH, hereinafter referred to as the reference channel. It should be appreciated that the reference channel can be any type of fixed level (or known) transmission by the base station, whether a control channel or a data channel. The reference channel power need only be made known to the UE12 at the time of the measurement. The UE12 measures the Received Signal Code Power (RSCP) (step 54). The UE12 then measures the ISCP (step 56). The RSCP and/or ISCP may be measured continuously, (i.e., for each frame and slot), or on a less frequent basis as discussed below.

There are many different embodiments in which steps 56 and 54 may be implemented. In a first embodiment, the UE12 measures ISCP and/or RSCP within a particular identified time slot in a particular identified order. In a second embodiment, the UE12 measures ISCP and/or RSCP in all slots in a predetermined order or a random order. In a third embodiment, the UE12 measures ISCP and/or RSCP in the random identification order within the random identification time slot. In the fourth embodiment the UE12 alternates the measurement of time slots. For example, ISCP and/or RSCP in time slots 1-4 of the first frame is measured, followed by time slots 5-8 of a subsequent frame, followed by time slots 9-12 of a subsequent frame, and so on. By using this inherent flexibility, the method 50 according to the present invention can be adapted to the specific needs of the system operator and the specific application.

As discussed above, it is desirable to have the path loss and interference measured at the same rate using the same time pattern. Therefore, the measurement frequency of the ISCP may be less than the RSCP. For example, ISCP may be measured according to the fourth way of table one, and RSCP may be measured according to the second way of table one.

Table one illustrates in general different embodiments of UE measurements. It should be noted that the predetermined and dynamic selection of time slots and/or time slot orders may be used without departing from the spirit and scope of the present invention.

TABLE 1

Detailed description of the preferred embodiments	UE measurements
		First one	Measuring in a particular order within a particular time slot
Second kind	Measured in a predetermined or random order in all time slots
		Second kind	Measured in random order at randomly identified time slots
Fourth type	In different time slots

Returning to fig. 3, regardless of the time slot or the order of the time slots selected and measured, the UE12 determines the downlink CQ from the measurement and reports the downlink CQ to the base station 30 at step 58. This CQ measurement may include transmitting ISCP (from step 56) and RSCP (from step 54) independently, transmitting the ISCP/RSCP ratio calculated by the UE12, or may include one or more other embodiments as will be explained in detail below.

The downlink CQ measurements generated and transmitted by UE12 at step 58 are received by base station 30 at step 60 and analyzed at step 62 to determine the action requirements for subsequent transmissions to UE12, taking into account the downlink CQ measurements.

The manner in which the UE12 collects and transmits this measurement data is typically a trade-off between the amount of data provided and the cost of transmitting the measured data back to the base station 30. For example, the measurement of all data transmissions for both ISCP and RSCP for each selected slot provides the most information. However, the disadvantages are the large amount of data that needs to be transmitted and the expense required to transmit the data.

The present invention aims to recover real-time and correct CQ information and to provide appropriate modulation and coding for the downlink channel. As such, there are many different embodiments for the UE12 to measure and transmit this information to the base station 30. Table two shows different ways of transmitting RSCP and ISCP to the base station 30.

Watch two

These 9 embodiments typically transmit the downlink CQ information from the UE12 to the base station 30 in order of the maximum number of required bits to the minimum number of required bits. It should be understood that this table is not all inclusive and that the invention should not be limited to the particular embodiments listed in the table.

In scheme i, the UE12 transmits the RSCP and ISCP for each slot to the base station 30.

In mode 2, the UE12 transmits the RSCP once per frame and transmits the ISCP for each particular time slot to the base station 30.

In mode 3, the UE12 transmits the RSCP/ISCP ratio for each designated time slot to the base station 30.

In mode 4, the UE12 encodes and transmits the RSCP/ISCP ratio for each designated slot to the base station 30. Proportional coding reduces the number of bits required to transmit information.

In mode 5, the UE12 transmits a number of soft symbol errors, which are detected by the UE12, to the base station 30. Soft symbol errors are an indication known to those skilled in the art as downlink CQ.

In mode 6, the UE12 selects an available Modulation and Coding Set (MCS) based on RSCP and ISCP measurements and transmits the selection to the base station, which the base station 30 uses for transmission. There are typically a predetermined number of MCSs available to the UE, e.g., 8 such sets.

In mode 7, the UE12 combines the encoding of the CQ information for all slots. Encoding the common and differential qualities of all slots and subchannels separately yields savings in transmission bits.

In mode 8, the UE12 measures and transmits the average of the CQ for all slots, which is encoded using a large number of bits, and then transmits the difference from the average for each remaining slot using an encoding value with a smaller number of bits. For example, 4 or 5 bits may be used to identify the average value of the slot, and only one or 2 bits are required for each slot or subchannel to differ from the average value.

In mode 9, one of the slots or subchannels is designated as a reference point. The CQ measurement for this slot is transmitted and then only the difference information when referring to the reference point needs to be transmitted for the remaining slots. In a similar manner to the 8 th mode, the reference slot may be 4 or 5 bits, and the difference between the remaining slot and the reference point may be 1 or 2 bits.

In order to reduce the power requirements and the complexity of the implementation required for the measurements and processing, it is desirable to minimize the number of measurements and the amount of processing. Measurements must be performed at the UE12 at all times of undetermined information needs from the base station 30, which may increase the measurement burden on the UE12 if the number of slots or subchannels is large. In the case where the rate of change of interference is different from the attenuation, the time slot measurements may be alternated in such a way that the most recent interference measurement is available for some time slots, while other time slots use older information.

By reducing the number of timeslots being measured, the complexity may be substantially reduced. The large number of timeslots to be measured results in frequent measurement reporting and high complexity. A smaller number of time slots results in less frequent measurement reporting of lower complexity but leading to some degradation in performance. Tradeoffs may be made depending on the needs and/or preferences of a particular application.

While the present invention has been described in detail with reference to the preferred embodiments, such detail is for explanation and not limitation. It will be appreciated by those skilled in the art that variations may be made in the construction and mode of operation without departing from the spirit and scope of the invention as taught herein.

Claims (7)

1. A method for selecting a downlink modulation coding set, comprising:

receiving a signal at a User Equipment (UE);

performing measurements to determine channel quality information for each of a plurality of downlink resources;

for each downlink resource, selecting a supportable Modulation Coding Set (MCS) based on the channel quality information determined for that each downlink resource, wherein the MCS is selected from a predetermined number of potential MCSs; and

transmitting a report to a base station, wherein the report includes an indication of the selected MCS for each of the plurality of downlink resources, and the UE receives at least one subsequent transmission from the base station, the base station using a set of transmissions derived based on information included in the report.

2. The method of claim 1, wherein the signal comprises a downlink reference signal transmitted at a known power level and used to evaluate channel quality of the plurality of downlink resources measured by the UE.

3. The method of claim 2, wherein each downlink resource comprises a time slot or a subchannel.

4. A method for providing channel quality, CQ, measurements for downlink resource allocation, comprising:

transmitting a downlink reference signal to a User Equipment (UE) at a known power level to enable measurement of a plurality of downlink resources;

receiving a report comprising an indication of a plurality of supportable Modulation Coding Sets (MCSs) associated with the plurality of downlink resources, wherein the report comprises an indication of a selected MCS for each of the plurality of downlink resources; and

a modulation coding set is selected in response to the received report.

5. The method of claim 4, wherein each downlink resource comprises a time slot or a subchannel.

6. The method of claim 5, wherein the MCS indicated in the report is determined based on Received Signal Code Power (RSCP) and Interference Signal Code Power (ISCP) measurements.

7. The method of claim 4, wherein each MCS of the plurality of MCSs indicated in the report is selected from a predetermined number of potential MCSs.