HK1083953A

HK1083953A - Mean square estimation of channel quality measure

Info

Publication number: HK1083953A
Application number: HK06103802.6A
Authority: HK
Inventors: J．M．霍兹曼
Original assignee: 高通股份有限公司
Priority date: 2002-09-23
Filing date: 2003-09-23
Publication date: 2006-07-14

Description

Mean square estimation of channel quality measurements

Background

FIELD

The present invention relates generally to communications, and more particularly to analyzing feedback of channel information, which may be used to improve traffic scheduling and rate control over a wireless communication system.

Background

In a wireless communication system, a receiver, such as a mobile station, may observe channel conditions, such as carrier-to-interference (C/I) ratio, of a received transmission and report this information to a transmitter, such as a serving base station. The base station then uses this knowledge to selectively schedule transmissions to the remote stations.

In a communication system that uses a feedback mechanism to determine the quality of the transmission medium, the channel conditions are continuously transmitted over the reverse link. Errors caused by such transmissions interfere with efficient allocation of resources, the quality of future transmissions and affect the performance of the system. Complex algorithms and calculations are typically used at the transmitter (i.e., the element receiving the quality feedback information) to determine the accuracy of the received quality feedback information. The accuracy and reliability of the quality feedback information needs to be confirmed. There is a further need to reduce the complexity of such validation.

Brief description of the drawings

Fig. 1 is a diagram illustrating forward and reverse links in a communication system.

Fig. 2 is a diagram of a wireless communication network.

Fig. 3A, 3B, and 3C are timelines depicting interactions between a resynchronization channel and a difference (differential) feedback subchannel.

Fig. 4 is a block diagram of a remote station in communication with a base station.

Fig. 5 is a mapping of codewords to link quality measurements.

Fig. 6 is a diagram of full link quality codewords and differential indicator transmission timing associated with link quality measurements.

Fig. 7 is a flow chart of a method for assessing link quality.

FIG. 8 is a flow chart of a method for evaluating a difference indicator.

Detailed Description

The field of wireless communications has many applications including, for example, cordless telephones, paging, wireless local loops, Personal Digital Assistants (PDAs), internet telephony, and satellite communication systems. A particularly important application is cellular telephone systems for mobile subscriber stations. As used herein, the term "cellular" system includes both cellular and Personal Communication Services (PCS) frequencies. Various air interfaces have been developed for such cellular telephone systems including, for example, Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). In connection with this, various national and international standards such as enhanced mobile phone service (AMPS), Global System for Mobile (GSM), and interim standard 95(IS-95) have been established. IS-95 and its derivatives IS-95A, IS-95B, ANSI J-STD-008 (often collectively referred to as IS-95), and proposed high data rate systems are promulgated by the Telecommunications Industry Association (TIA) and other well-known standards organizations.

Cellular telephone systems configured in accordance with the use of the IS-95 standard use CDMA signal processing techniques to provide efficient and robust cellular telephone service. Exemplary cellular telephone systems configured primarily for use in accordance with the IS-95 standard are described in U.S. patent nos. 5103459 and 4901307, assigned to the assignee of the present invention. An exemplary system using CDMA techniques is the CDMA2000 ITU-R Radio Transmission Technology (RTT) candidate submission (referred to herein as CDMA2000) issued by the TIA. The standard for Cdma2000 IS given in the draft version of IS-2000 and agreed to by TIA and 3GPP 2. Another CDMA standard is the W-CDMA standard, as embodied in the third Generation partnership project "3 GPP", with document numbers 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214.

The telecommunications standards described herein are but a few of the various communication systems that can be implemented. Some of these various communication systems are configured to enable a remote station to transmit information relating to the quality of the transmission medium to a serving base station. This channel information can then be used by the serving base station to optimize the power level, transmission format, and timing of forward link transmissions, and further to control the power level of reverse link transmissions.

As used herein, the "forward link" refers to transmissions from a base station to a remote station, and the "reverse link" refers to the link from the remote station to the base station. Fast fading on the forward and reverse links is uncorrelated, meaning that one does not necessarily provide information about the other.

Channel conditions such as carrier-to-interference ratio (C/I) of the received forward link transmission may be observed by the remote station, which reports this information to the serving base station. The base station then uses this knowledge to selectively schedule transmissions to the remote stations. For example, if the remote station reports a deep fade, the base station may abandon the scheduled transmission until the fade condition has passed. Alternatively, the base station may decide to schedule transmissions, but use a high transmission power level to compensate for fading conditions. Alternatively, the base station may decide to change the data rate of the transmission by sending data in a format that can carry more information bits. For example, if the channel conditions are poor, data may be transmitted in a transmission format with redundancy such that corrupted symbols are more likely to be recovered. Thus, the data throughput is lower than if a transport format without redundancy is used.

The base station may also use the channel information to balance the power levels of all remote stations within operating range so that reverse link transmissions are at the same power level. In a CDMA based system, channelization between remote stations is generated using a pseudorandom code, which allows the system to overlay multiple signals on the same frequency. Reverse link power control is therefore based on the basic operation of a CDMA system, since excessive transmission power sent from one remote station may "drown" its neighbors' transmissions.

In a communication system that uses a feedback mechanism to determine the quality of the transmission medium, the channel conditions are continuously transmitted on the reverse link. This results in a large burden on the system, consuming system resources that could otherwise be allocated to other functions.

As illustrated in fig. 1, transmission links within the wireless communication network 100 are defined in terms of the direction of propagation between a Base Station (BS)104 and a Mobile Station (MS) 102. Communication from the BS 104 to the MS 102 is transmitted over the Forward Link (FL). The forward link is controlled by the BS 104, which determines the transmit power and data rate for the data transmission. Communication from the MS 102 to the BS 104 is sent over a Reverse Link (RL). MS 102 measures the FL quality and sends an indication of the measured quality to BS 104 via the RL. MS 102 may measure the C/I or other signal-to-noise ratio (SNR) of the received signal. MS 102 may quantize the measurements and send the quantized values. The BS 104 then uses the quality information to effect control of the FL.

Network or system 100 may include multiple MSs (also referred to as remote stations, subscriber units, or user equipment), multiple BSs (also referred to as Base Transceiver Stations (BTSs) or node BS in a High Data Rate (HDR) system such as that described by 3GPP2, Base Station Controllers (BSCs) (also referred to as radio network controllers or packet control functions), Mobile Switching Centers (MSCs), Packet Data Serving Nodes (PDSNs) or inter-network interworking functions (IWFs), Public Switched Telephone Networks (PSTNs) (typically telephone companies), and/or Internet Protocol (IP) networks (typically the internet). fig. 2 illustrates a system including various components The number of base stations 14, BSCs 16, and PDSNs 20 may be more or less.

In one embodiment, the wireless communication network 10 is a packet data service network. The mobile stations 12a-12d may be any of a number of different types of wireless communication devices such as a mobile telephone, a cellular telephone linked to a laptop computer running an IP-based Web browser application, a cellular telephone with associated hands-free car kits, a Personal Data Assistant (PDA) running an IP-based Web browser application, a wireless communication module included in a laptop computer, or a fixed location communication module such as might be found in a wireless local loop or meter reading system. In most general embodiments, the mobile station may be any type of communication unit.

The mobile stations 12a-12d may advantageously be used to implement one or more wireless packet data protocols as described in, for example, the EIA/TIA/IS-707 standard. In particular embodiments, mobile stations 12a-12d generate IP packets destined for IP network 24 and encapsulate the IP packets using a point-to-point protocol (PPP).

In one embodiment, the IP network 24 is coupled to a PDSN20, the PDSN20 is coupled to a MSC 18, the MSC is coupled to the BSC16 and to the PSTN22, and the BSC16 is coupled to the base stations 14a-14c by wires for transmission of voice and/or data packets according to any of several known protocols, such as El, T1, Asynchronous Transfer Mode (ATM), IP, PPP, frame Relay, HDSL, ADSL, or xDSL. In other embodiments, the BSC16 may be directly coupled to the PDSN 20.

In general operation of the wireless communication network 10, the base stations 14a-14c receive and demodulate sets of reverse signals from respective mobile stations 12a-12d engaged in telephone calls, Web browsing, or other data communications. Each reverse signal received by a given base station 14a-14c is processed within the base station 14a-14 c. Each base station 14a-14c may communicate with a plurality of mobile stations 12a-12d by modulating and transmitting sets of forward signals to the mobile stations 12a-12 d. For example, as shown in fig. 2, the base station 14a communicates with first and second mobile stations 12a, 12b simultaneously, and the base station 14c communicates with third and fourth mobile stations 12c, 12d simultaneously. The resulting packets are forwarded to the BSC16, which provides call resource allocation and mobility management functions, including coordinating soft handoff of a call for a particular mobile station 12a-12d from one base station 14a-14c to another base station 14a-14 c. For example, the mobile station 12c communicates with two base stations 14b, 14c simultaneously. Eventually, when the mobile station 12c is far enough away from one base station 14c, the call will be handed off to the other base station 14 b.

If the transmission is a conventional telephone call, the BSC16 will route the received data to the MSC 18, which provides additional routing services for interfacing with the PSTN 22. If the transmission is a packet-based transmission, such as a data call destined for the IP network 24, the MSC 18 will route the data packet to the PDSN20, which will send the packet to the IP network 24. Alternatively, the BSC16 may route the packets directly to the PDSN20, which sends the packets to the IP network 24.

In some communication systems, packets carrying data traffic are divided into subpackets, which occupy slots of a transmission channel. For simplicity of explanation, the terminology of the cdma2000 system is used hereinafter. This use is not intended to limit the implementation of the embodiments herein to cdma2000 systems. Implementations in other systems, such as WCDMA, may be implemented without affecting the scope of the embodiments described herein.

The forward link from a base station to a remote station operating within range of the base station includes multiple channels. Some channels of the forward link may include, but are not limited to, a pilot channel, a synchronization channel, a paging channel, a quick paging channel, a broadcast channel, a power control channel, an assignment channel, a control channel, a dedicated control channel, a Medium Access Control (MAC) channel, a fundamental channel, a supplemental code channel, and a packet data channel. The reverse link from the remote station to the base station also includes multiple channels. Each channel carries different types of information to the target destination. Typically, voice traffic is carried on the fundamental channel and data traffic is carried on the supplemental channel or packet data channel. The supplemental channels are typically dedicated channels, while the packet data channels typically carry signals to different parties in a time and/or code multiplexed manner. Alternatively, the packet data channel may also be described as a shared supplemental channel. For purposes of the description of the embodiments herein, the supplemental channel and the packet data channel are referred to generally as data traffic channels.

Voice traffic and data traffic are typically coded, modulated, and spread before being transmitted on the forward or reverse links. The coding, modulation, and spreading may be implemented in a variety of formats. In a CDMA system, the transmission format ultimately depends on the type of channel over which the voice traffic and data traffic are transmitted and the channel conditions, which may be described in terms of fading and interference.

The predetermined transmission format may be used to simplify the selection of the transmission format corresponding to each transmission parameter combination. In one embodiment, the transmission format corresponds to a combination of any or all of the following transmission parameters: the modulation scheme used by the system, the number of orthogonal or quasi-orthogonal codes, the identity of the orthogonal or quasi-orthogonal codes, the size of the data payload in bits, the message frame duration, and/or details relating to the coding scheme. Some examples of modulation schemes used within communication systems are Quadrature Phase Shift Keying (QPSK), 8-ary phase shift keying (8-PSK), and 16-ary quadrature amplitude modulation (16-QAM). Some of the various encoding schemes that can be selectively implemented are convolutional encoding schemes, which can be implemented at various rates, and turbo encoding, which includes multiple encoding steps separated by interleaving steps.

Orthogonal and nearly orthogonal codes, such as Walsh code sequences, are used to channelize the information transmitted to each remote station. In other words, Walsh code sequences are used on the forward link to allow the system to overlay multiple users, each assigned one or several different orthogonal or nearly quasi-codes, on the same frequency and for the same time duration.

A scheduling element within the base station is configured to control the transmission format of each packet, the rate of each packet, and the time slot in which each packet is to be transmitted to the remote station. The term "packet" is used to describe system traffic. The packets may be divided into subpackets, which occupy slots of a transmission channel. "time slot" is used to describe the duration of a message frame. The use of such terms is common within cdma2000 systems, but the use of such terms is not meant to limit the implementation of the embodiments herein to cdma2000 systems. Implementations in other systems such as wideband CDMA (W-CDMA) may be accomplished without affecting the scope of the embodiments described herein.

Scheduling is an important factor in achieving high data throughput in packet-based systems. In a cdma2000 system, a scheduling element (also referred to herein as a "scheduler") controls the grouping of the payload into redundant and duplicate subpackets, which may be soft combined at the receiver so that in the event a received subpacket is corrupted, it may be combined with another corrupted subpacket to determine the data load within an acceptable Frame Error Rate (FER). For example, if a remote station requests a data transmission at 76.8kbps, but the base station knows that the transmission rate is not possible at the requested time due to channel conditions, a scheduler within the base station may control the division of the data payload into a plurality of subpackets. The remote station may receive multiple corrupted subpackets but may recover the data payload by soft combining its uncorrupted subpackets. Thus, the actual transmission rate of the bits may be different from the data throughput rate.

A scheduling element within the base station uses an open-loop algorithm to adjust the data rate and scheduling of forward link transmissions. Open loop algorithms adapt transmissions according to changing channel conditions in a typical wireless environment. Typically, the remote station measures the forward link channel quality and sends this information to the base station. The base station uses the received channel conditions to predict the most efficient transmission format, rate, power level, and timing of the next packet transmission. In a cdma 20001 xEV-DV system, a remote station may use a channel quality indicator feedback channel (CQICH) to communicate channel quality measurements for the best serving sector to a base station. Channel quality may be measured in terms of carrier-to-interference (C/I) ratio and based on the received forward link signal. The C/I value is mapped to a five-bit Channel Quality Indicator (CQI) symbol, wherein the fifth bit is reserved. Thus, the C/I value can have one of sixteen quantized values.

Since the remote station is not foreseen, the remote station continuously transmits the C/I value so that the base station knows the channel conditions if any packets need to be transmitted to the remote station on the forward link. Continuously transmitting the 4-bit C/I value consumes remote station battery life by occupying hardware and software resources within the remote station.

In addition to battery life and reverse link load issues, there are latency issues. Due to propagation and processing delays, the base station uses outdated information to schedule transmissions. If the typical propagation delay is 2.5 milliseconds, which corresponds to a2 slot delay in a system with a 1.25 millisecond slot, the base station may reflect a station that is no longer present or may not react to the new situation in a timely manner.

For the foregoing reasons, there is a need for a mechanism for communicating information to a base station so that the base station can quickly reschedule transmissions in the event of a sudden change in the channel environment. In addition, the foregoing mechanism should reduce battery life consumption for the remote station and load on the reverse link.

In an embodiment, the full C/I value is sent on the resynchronization subchannel while the incremental 1 bit value is sent on the difference feedback subchannel. Incremental 1-bit values of 1 and 0 are mapped to +0.5dB and-0.5 dB, but may also be mapped to other values of ± K, where K is a system defined step size.

The values sent on the resynchronization and difference feedback subchannels are determined based on forward link C/I measurements. The value sent on the resync subchannel is obtained by quantizing the most recent C/I measurements. A one bit value is sent on the difference feedback subchannel and is obtained by comparing the most recent C/I measurement with the contents of the internal registers. The internal registers are updated based on the most recent values sent in the past on the resynchronization and difference feedback sub-channels and represent the best estimate of the C/I value for the remote station that the base station will decode.

In a first mode, a channel element may be located within the remote station to generate a re-synchronization sub-channel and a difference feedback sub-channel on a CQI channel (CQICH), wherein the re-synchronization sub-channel occupies one time slot of a CQICH frame of N time slots and the difference feedback sub-channel occupies all time slots of the CQICH frame of N time slots such that an incremented 1 bit value is transmitted within each time slot.

In one embodiment, the resynchronization subchannel and the difference feedback subchannel are not transmitted in parallel. Instead, the re-synchronization subchannel is transmitted over one time slot and the system foregoes transmitting the differential feedback subchannel within that particular time slot. In another embodiment, the full C/I value and the incremented 1 bit value are transmitted to the base station in at least one slot of the CQICH frame of N slots. The burst transmission is possible by using orthogonal or quasi-orthogonal spreading codes, or in another embodiment, by time interleaving two sub-channels in some predetermined manner. Fig. 3A is a timeline illustrating the transmission timing of the re-synchronization channel and the difference feedback sub-channel operating in parallel in a later embodiment.

The channel element may be configured to re-synchronize subchannel generation such that both subchannels operate at a reduced rate. The re-synchronization channel operates at a reduced rate when the full C/I value extends over at least two slots of the N-slot CQICH frame. For example, the full C/I value may be transmitted at a reduced rate within 2, 4, 8, or 16 slots of a 16 slot CQICH frame. The differential feedback subchannel occupies all the slots of the N-slot CQICH frame. Thus, an incremented 1 bit value is sent in parallel with the resynchronization subchannel within each time slot. When the reverse link is affected by adverse channel conditions, the remote station should transmit the full C/I value at a reduced rate. In an embodiment, the base station determines the reverse link channel condition and sends a control signal to the remote station, wherein the control signal informs the remote station whether the re-synchronization sub-channel should operate at a reduced rate. Alternatively, the remote station may be programmed to determine independently.

In one implementation, the two sub-channels operate in parallel at a reduced rate, with the full C/I value spread across all slots of the N-slot CQICH frame, and each slot also carrying an incremented 1-bit value. In another embodiment, the difference feedback subchannel occupies all but the first slot of the N-slot frame. In another embodiment, the difference feedback subchannel and the resynchronization subchannel are not transmitted in parallel at all; the re-synchronization subchannel operates first on the M slots and the difference feedback subchannel operates on the next N-M slots of the N slot frame. Fig. 3B and 3C are diagrams illustrating transmission timings of a resynchronization subchannel and a difference feedback subchannel. The internal registers of the remote station may be updated in the first, second or mth time slot depending on which mode of operation is used.

In another embodiment, the full C/I value may also be transmitted in an unscheduled time slot whenever the remote station determines that the C/I estimate reserved at the base station is out of synchronization. The base station continuously monitors the CQICH to determine whether there are non-scheduled full C/I value symbols.

In another embodiment, the full C/I value is only sent when the remote station determines that the C/I estimate remaining at the base station is out of synchronization. In this embodiment, the full C/I values are not transmitted at regular scheduling intervals.

A scheduling element within the base station may be used to monitor the channel information received on the re-synchronization sub-channel and the difference feedback sub-channel, wherein the channel information from each sub-channel is used to make transmission decisions that take into account the channel conditions. The scheduling element may include a processing element coupled to a memory element and communicatively coupled with a receiving subsystem and a transmitting subsystem of the base station.

Fig. 4 is a block diagram of some functional components of a base station with a scheduling element. Remote station 300 transmits on the reverse link to base station 310. At the receiving subsystem 312, the received transmission is despread, demodulated, and decoded. Scheduler 314 receives the decoded C/I values and coordinates the appropriate transmission format, power level, and data rate for transmissions from transmit subsystem 316 on the forward link. The base station 310 also includes a memory storage device 318 for storing link quality indicator information.

At remote station 300, a receive subsystem 302 receives the forward link transmission and determines the forward link channel characteristics. The transmit subsystem 306 transmits the forward link channel characteristics to the base station 310.

In the embodiments described herein, scheduling element 314 may be programmed to interpret the channel information received on the re-synchronization sub-channel and the channel information received on the difference feedback sub-channel together, or separately. The scheduling element may also be configured to implement a method to change which sub-channel will be used to update the channel information.

When the remote station transmits channel information, the serving base station receives the full C/I value (or other link quality indicator) on one slot and the incremental value on all slots of the frame. In one embodiment, the scheduler may be programmed to reset an internal register that stores the current state of the channel, where the register is reset with the full C/I value received on one slot of the re-synchronization sub-channel. The incremented values received on the different feedback sub-channels are then added upon receiving the full C/I value stored in the register. In an aspect, the incremental values sent concurrently with the full C/I value over the slot are intentionally discarded because the full C/I value has already considered the incremental values.

The serving base station may receive the full C/I value over multiple slots and the incremental value over all slots of the frame. In one embodiment, the serving base station estimates the channel condition at the time scheduled for packet transmission by accumulating the incremental values received on the difference feedback subchannel from the second time slot to the mth time slot, where M is the number of time slots over which the full C/I is spread. The accumulated value is then added to the C/I value, which is received on the re-synchronization subchannel for M slots. In another embodiment, this "accumulate and add" method may be implemented concurrently with the independent action of the "up-down" bit, which is directed by the increment value to update the C/I value stored in the register. Thus, the register storing the current channel condition information is updated each time an increment value is received, and the register is then updated with the accumulated value added to the full C/I value.

Fig. 5 illustrates the mapping of the coded values, i.e. the quantized C/I values to the C/I measurement values. The first memory storage 120 stores either quantized values or encoded values. The second memory storage device 130 stores the range of measurements associated with each code. According to one embodiment, the mapping illustrated in FIG. 5 is implemented in software or hardware that performs a calculation to convert the measured value to an encoded value.

Fig. 6 is a transmission timing diagram of quality measurements, both full measurement indications and difference values. As illustrated, a full measurement indication is also identified. Full measurement indications are sent between times t1 and t2 and between times t3 and t 4. The difference is sent for each time slot between the full measurement indications. The full quality measurement indicator or C/I value of one embodiment is 4 bits encoded. The full quality measurement indicator is followed by 15 up/down commands, i.e. difference values. The total slot cycle is 16 slots. The full C/I is updated at least once per slot cycle.

One embodiment provides a method of evaluating link quality feedback information that may be applied to the margin applied by the scheduler. According to this embodiment, a full link quality indicator is received at the BS. The BS then calculates the received codeword probability of receiving the C/I measurements corresponding to the measurements made at the MS. The BS determines the estimate with the minimum mean square error using a conditional mean calculation. The minimum mean square error identifies the codeword for the "best" estimate, and thus estimates the link quality measure for the best estimate. The root mean square error (RMS) is calculated by determining a minimum Mean Square Error (MSE) estimate of the link quality measure. The estimate is then sent to the scheduler, which may include the error estimate within the operating margin. The use of a minimum MSE allows the labeling of unexpected C/I values. For this purpose, the method uses the past full C/I difference to mark new full C/I values that are highly unpredictable. The minimum MSE method may also be applied to the difference (i.e. up/down) indicator.

To determine the quality feedback indicator for the full measurement indicator, which in this embodiment is a C/I measurement, let

{C_iSet of codewords (1) associated with allowable full C/I values

And order

R-the received full C/I codeword. (2)

The method determines an estimate of the received C/I using a minimum Mean Square Error (MSE) calculation. The included MSE estimator is a conditional mean computation. The estimator may be described as:

it is noted that in equation (3), Ci represents the C/I measurement associated with codeword Ci. There are n C/I codewords. In other words, the C/I measurements are quantized and mapped onto a total number n of codewords. The estimator of equation (3) may be considered as an expected value operator E (), determining the measured C/I expected value given the received codeword value.

The estimator described by equation (3) evaluates p (ci) from the past C/I measurement full value. The estimator maintains a running mean and standard deviation of the difference between the full C/I measurements and estimates the probability distribution of possible values, i.e., p (ci). For each received full link quality indicator, a conditional probability is calculated for each possible codeword given the received value. The codeword with the minimum mean square error thus calculated is considered the "best estimate". One method of determining the minimum mean square error is given in equation (3), however, other embodiments may use other calculation methods.

In the presently described embodiment, the link quality indicator is a full link quality indicator, however other embodiments (including those described below) may include other link quality indicators, such as a differential indicator. Other methods of determining the probability that the received link quality indicator corresponds to the originally transmitted indicator may also be used. Moreover, given historical and/or current operating conditions, link quality indicators, and other system parameters, it is possible to compare the probabilities over a subset of available codewords. For example, during operation, only if a subset of available codewords is received over a predetermined period of time, one embodiment may compare only those codewords within the subset.

In evaluating p (ci), a method of increasing an outlier impedance (outlier resistance) may be used. Outlier impedance refers to system robustness with respect to data that is abnormally different from the actual data. Outlier data may corrupt parameter estimation. An example of what is considered to be an outlier data impedance is given below:

the next step is to estimate the RMS error, which is given by the square root of:

fig. 7 illustrates an embodiment previously described when a full link quality indicator is received at a Base Station (BS). The method 200 of fig. 7 includes two modes of operation: 1) a first mode in which the analysis of the full link quality indicator does not take into account any participating differential indicators, and 2) a second mode which takes into account participating differential indicators. While the BS is used in the present discussion, the present embodiments are applicable to any wireless communication device that receives a link quality indicator and makes a transmission decision based thereon.

According to the method 200, the BS receives a full link quality indicator at step 202. Processing continues to step 206 to update the deviation and mean of the currently received data. The deviation and mean information is stored in a memory at the BS. The result of step 204 updates the most recent mean and deviation information. One embodiment retains historical information and provides this information to the scheduler. At step 206, the process evaluates the probability p (cj) evaluated as j ═ 1, 2 …, where n is the total number of codewords associated with the link quality measurement, i.e., the set of available codewords. The probability p (cj) is the probability that codeword j is received.

The BS then determines at decision diamond 208 whether to consider the differential indicator in analyzing the received full link quality indicator, e.g., the first mode or the second mode as described above. In other words, whether the current estimate is based solely on the currently received link quality indicator or whether the estimate considers the differential indicator received prior to receiving the full link quality indicator at step 202. Another embodiment may evaluate p (cj) over a subset of the set of available codewords. At step 210, the process determines its mean square error for each codeword evaluated in step 208 and determines the codeword with the smallest mean square error. Step 208 applies equation (3) above. The process then estimates the mean square error at step 212. The BS then provides the link quality information to the scheduler at step 214. Such information, and in particular information relating to estimated reliability and confidentiality of the received signal, is provided for scheduling data transmissions within a system supporting data transmissions.

Continuing with fig. 7, when the estimate and calculation includes a previously received difference indicator, processing continues to step 216 to calculate a weighting function for application to determine the mean square error of the difference indicator. Since the difference indicator is a binary indicator, there are two possibilities: positive or negative. The difference indicator is identified as b. The received difference indicator is given as x, where x is assumed to comprise the received energy E associated with the difference indicator and to comprise the noise N. The energy (i.e., positive or negative) of each likelihood is evaluated to determine the minimum mean square error for each estimate. For example, at a given time instant, the case where the received signal x is a positive difference indicator and the case of a negative difference indicator are evaluated.

The BS may combine the newly received link quality indicator with the most recently previously received full link quality estimate, which is updated by the participating differential indicators. Consider the embodiment where the full indicator is sent on one slot and the system gives up sending the differential indicator in that particular slot, although the information is out of date by one slot, the BS may minimize the error using two (independent) estimatesGiven below:

wherein the weighting factor is given by:

wherein e_iIs the mean square error of the estimate i. This yields a minimum mean square error of:

it is noted that the above description may also apply to embodiments wherein the system transmits the differential indicator when transmitting the full indicator. In this case, the information is not outdated.

It is worth noting thatMay represent a first link quality estimate using only the most recently received full link quality indicator, butA second link quality estimate may be represented that is not calculated with the most recently received full link quality indicator, but rather uses the previous full link quality indicator and applies any received successive participation difference indicators. Each of the first and second estimates may have a corresponding mean squared error and equations (6) and (7) may each be weighted accordingly.

Returning to fig. 7 and the second mode of operation, where the received full link quality indicator analysis takes into account the participating differential indicators, the weighting factor α of equation (7) is calculated as given above at step 216. Another embodiment may use other pairs to include in receiving the samplesTo a method of estimating weights of terms. It is worth noting that if one estimate has a much smaller mean square error than the other, then the estimate with the smaller mean square error is considered to be the better estimate. If e₁Is the smaller mean square error, then e in the denominator₁The term will increase by α, thus highlighting e in equation (6)₁An item. If e₂Is the smaller mean square error, the denominator and the numerator of e₂The term will decrease by α, highlighting e in equation (6)₂An item. Thus, the terms of equation (6) are weighted to facilitate an estimate with minimum mean square error, which is considered to be the "best" or better estimate. It is also worth noting that if 1 (i.e., e) is estimated₁) Approximately equal to estimate 2 (i.e., e)₂) Mean square error ofAnd each term in the right hand of equation (6) is equally weighted.

Returning to fig. 7, the weighting factor of equation (7) is applied to the calculation of equation (6) as described above, and an estimate of the received signal is generated at step 218. Processing then continues to step 220 to minimize the estimated mean square error calculated in step 218. Step 220 uses equation (8) given above. Processing then continues to step 214 to send the link quality information to the scheduler.

As depicted, the processing in the second mode prepares the received samples using two estimates, as illustrated by steps 216 through 220 in FIG. 7The two estimates are: first estimationLink quality indicator estimation, which means that only the most recently received full link quality indicator is used; and the second estimateIndicating a previously received link having a difference indicator applied theretoQuality indicator estimation. Each estimate has a corresponding mean square error. Equations (6) and (7) apply a weighting to each estimate based on the relationship of the mean square error. It is noted that in another embodiment, when a new C/I is received, the transceiver may decide to ignore past up/down decisions and return to the most recently received full link quality measurement.

The process for estimating the difference indicator, i.e., the up/down signal, is described in the following equation. Let x denote the received samples, E denote the received signal energy of the samples, b denote the transmitted difference, and N denote the noise added during transmission. Equation (9) identifies the received signal as containing signal energy and noise associated with the transmitted link quality indicator (difference indicator).

b＝±1， (10)

To minimize the mean square error, b is estimated using the following equation:

the tanh is used to help when the received difference indicator energy is low. The transmitted differential indicator estimate is relatively deterministic when the received differential indicator energy is high. However, if the received difference indicator energy is low, it is uncertain.

The differential indicator sequence is provided as a full link quality indicator sequence. At step n of the sequence of difference indicators, where each difference indicator represents Δ dB, the dB value is given by:

this can be written as:

equations (12) and (13) mathematically describe the operation of accumulating the difference indicators (i.e., up/down indication). Equation (12) provides such a calculation in dB, while equation (13) provides such a calculation in linear variables. The product is a conditional log random variable for the most recent full C/I (r.v.). For a logarithmic distribution, the associated normal r.v. is given by:

(C/I)(n)_linearthe mean and variance of (c) can be derived using the variance, which can be calculated as follows:

other embodiments use a last full link quality indicator that includes a last full link quality indicator from a previous differential indicator. This estimate replaces equations (10) and (11).

FIG. 8 illustrates a method of evaluating received difference indicators, where previously received values are used to determine the accuracy of each received difference indicator. The process 400 begins with the definition of equations (7) and (8). The mean square error is minimized at step 404 as in equation (9). Step 406 performs the calculation as in equation (11). At step 408, the process calculates (C/I) (n)_IinearMean and variance of. Step 410 uses previously received valuesAnd (C/I) (n)_IinearThe received difference indicator is evaluated for mean and variance.

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, circuits, 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 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 logical blocks, modules, and circuits disclosed in the illustrative embodiments herein may be implemented or performed in the manner of: a general purpose processor, a Digital Signal Processor (DSP) or other processor, 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, to implement the functions described herein. A general purpose processor is preferably a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may 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 processor is preferably 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 application specific integrated circuit, 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 preferred 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 the use of the inventive faculty. 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

1. A method in a wireless communication system, comprising:

receiving a link quality indicator having one of a plurality of link quality indicator values;

determining a conditional probability for each of a plurality of link quality indicator values;

one of the plurality of link quality indicators is selected based on the conditional probability.

2. The method of claim 1, further comprising:

estimating a minimum mean square error of the conditional probability;

wherein selecting one of the plurality of link quality indicator values takes into account a minimum mean square error.

3. The method of claim 2, wherein the link quality indicator is a full link quality indicator.

4. The method of claim 3, wherein the link quality indicator is a measure of carrier-to-interference ratio (C/I).

5. The method of claim 4, further comprising:

evaluation of

Where n is the total number of link quality values, C_iRepresenting each link quality indicator, R represents the received link indicator, P (|) is a conditional probability operator, and i and j are indices.

6. The method of claim 4, further comprising:

estimating a root mean square error of the mean square error according to:

whereinIs an estimate of the link quality indicator.

7. The method of claim 6, further comprising:

link transmissions are scheduled using least mean square estimation and root mean square error.

8. The method of claim 5, further comprising:

the link transmissions are scheduled using an estimate of least mean square estimation.

9. The method of claim 1, wherein each of the plurality of link quality indicator values corresponds to a quantized link quality measurement.

10. The method of claim 1, further comprising:

estimating a probability distribution of possible link indicator values; and

the probability distribution estimates are stored in a memory storage device.

11. The method of claim 10, wherein estimating the probability distribution further comprises:

the mean square and standard deviation corresponding to the received link quality indicator is maintained.

12. The method of claim 10, wherein estimating the probability distribution further comprises:

computing

13. The method of claim 1, further comprising:

determining that a first estimate of a link quality indicator is received;

determining a second estimate of the received link quality indicator using the previously received link quality indicator; and

a third estimate of the received link quality indicator is determined, the third estimate being a function of the first and second estimates.

14. The method of claim 13, further comprising:

determining a weighting factor as a function of the first and second estimates; and

a weighting factor is applied in the determination of the third estimate.

15. The method of claim 14, wherein said determining a weighting factor comprises:

computingWherein e₁Is the mean square error of the first estimate and e₂Is the mean square error of the second estimate.

16. The method of claim 15, wherein said determining a third estimate comprises:

calculating (a)₁+(1-α)®₂Therein, wherein₁Is a first estimate, and₂is the second estimate.

17. The method of claim 16, further comprising:

the minimum mean square error of the third estimate is calculated as follows:

18. the method of claim 17, further comprising:

and scheduling link transmission based on the third estimate and the minimum mean square error.

19. The method of claim 16, further comprising:

the link transmission is scheduled based on the third estimate.

20. The method of claim 13, wherein the link quality indicator corresponds to a full link quality measurement.

21. A wireless device, comprising:

means for receiving a link quality indicator having one of a plurality of link quality indicator values;

means for determining a conditional probability for each of a plurality of link quality indicator values;

means for selecting one of the plurality of link quality indicators based on the conditional probability.

22. The apparatus of claim 21, further comprising:

means for estimating a minimum mean square error of the conditional probability;

wherein the selection of one of the plurality of link quality indicator values takes into account a minimum mean square error.

23. The method of claim 22, wherein the link quality indicator is a full link quality indicator corresponding to a carrier-to-interference ratio (C/I), wherein the apparatus further comprises:

evaluation ofThe apparatus of (1) is provided with a plurality of the devices,

24. The method of claim 23, further comprising:

means for estimating a root mean square error of the mean square error according to:

whereinIs an estimate of the link quality indicator.

25. The apparatus of claim 23, further comprising:

means for scheduling link transmissions using an estimate of least mean square estimation.

26. The apparatus of claim 21, wherein each of the plurality of link quality indicator values corresponds to a quantized link quality measurement.

27. The apparatus of claim 21, further comprising:

means for estimating a probability distribution of possible link indicator values; and

means for storing the probability distribution estimates in a memory storage device.

28. The apparatus of claim 27, wherein said means for estimating a probability distribution further comprises:

means for maintaining a mean square and a standard deviation corresponding to the received link quality indicator.

29. The apparatus of claim 10, wherein said means for estimating a probability distribution further comprises:

computing

30. The apparatus of claim 21, further comprising:

means for determining a first estimate of the received link quality indicator;

means for determining a second estimate of the received link quality indicator using the previously received link quality indicator; and

means for determining a third estimate of the received link quality indicator, the third estimate being a function of the first and second estimates.

31. The apparatus of claim 30, further comprising:

means for determining a weighting factor as a function of the first and second estimates; and

means for applying a weighting factor in the determination of the third estimate.

32. The apparatus as claimed in claim 31 wherein said means for determining weighting factors comprises:

computingIn which e₁Is the mean square error of the first estimate and e₂Is the mean square error of the second estimate.

33. The apparatus as claimed in claim 32 wherein said means for determining a third estimate comprises:

calculating (a)₁+(1-α)®₂Wherein₁Is a first estimate, and₂is the second estimate.

34. The apparatus of claim 33, further comprising:

means for calculating a minimum mean square error of the third estimate as follows:

35. the apparatus of claim 34, further comprising:

and means for scheduling the link transmission based on the third estimate and the minimum mean square error.

36. The apparatus of claim 34, further comprising:

means for scheduling link transmissions based on the third estimate.

37. A method in a wireless communication system, comprising:

receiving a plurality of differential link quality indicators; and

estimating an originally transmitted differential indicator for each of a plurality of differential link quality indicators, wherein the originally transmitted differential indicator is one of two binary values, the estimating being accomplished by:

determining a minimum mean square error for each of the two binary values; and

the originally transmitted estimate is taken as the binary value corresponding to the minimum mean square error.

38. The method of claim 37, wherein said determining a mean square error comprises:

for each binary value, evaluating

39. An apparatus in a wireless communication system, comprising:

means for receiving a plurality of differential link quality indicators; and

means for estimating an originally transmitted differential indicator for each of a plurality of differential link quality indicators, wherein the originally transmitted differential indicator is one of two binary values, the estimating being performed by:

determining a minimum mean square error for each of the two binary values;

40. The method of claim 39, wherein said determining a mean square error comprises: for each binary value, evaluating

41. A wireless infrastructure element, comprising:

a processor for processing computer readable instructions; and

a memory storage device to store computer-readable instructions to:

42. The wireless infrastructure element of claim 41, wherein the computer-readable instructions are further for:

estimating a minimum mean square error of the conditional probability;

43. The wireless infrastructure element of claim 42, wherein the link quality indicator is a full link quality indicator corresponding to a carrier-to-interference ratio (C/I) metric, wherein the computer-readable instructions are further for:

evaluation of

44. The wireless infrastructure element of claim 43, wherein the computer-readable instructions are further for:

estimating a root mean square error of the mean square error according to:

whereinIs an estimate of the link quality indicator.

45. The wireless infrastructure element of claim 44, wherein the computer-readable instructions are further for:

the link transmission is scheduled using an estimate of the least mean square estimate and a root mean square error.

46. The wireless infrastructure element of claim 44, wherein the computer-readable instructions are further for:

47. The wireless infrastructure element of claim 41, wherein the computer-readable instructions are further for:

estimating a probability distribution of possible link quality indicator values; and

the probability distribution estimates are stored in a memory storage device.

48. The wireless infrastructure element of claim 47, wherein the computer-readable instructions are further for:

a mean and standard deviation corresponding to the received link quality indicators are maintained.

49. The wireless infrastructure element of claim 41, wherein the computer-readable instructions are further for:

determining that a first estimate of a link quality indicator is received;

50. The wireless infrastructure element of claim 49, wherein the computer-readable instructions are further for:

51. The wireless infrastructure element of claim 50, wherein the computer-readable instructions are further for:

52. The wireless infrastructure element of claim 51, wherein the computer-readable instructions are further for:

53. The wireless infrastructure element of claim 52, wherein the computer-readable instructions are further for:

the minimum mean square error of the third estimate is calculated as follows:

54. the wireless infrastructure element of claim 53, wherein the computer-readable instructions are further for:

55. The wireless infrastructure element of claim 53, wherein the computer-readable instructions are further for:

means for scheduling link transmissions based on the third estimate.