KR100887299B1 - Robust erasure detection and erasure-rate-based closed loop power control - Google Patents

Abstract

The present invention relates to a technique for performing erase detection and power control for transmission without error detection coding. For erasure detection, the transmitter transmits a codeword over a wireless channel. The receiver calculates a metric for each received codeword, compares the calculated metric with an erase threshold, and declares the received codeword as "erased" or "non-erased". The receiver dynamically adjusts the erase threshold based on the known codeword received to achieve the target level of performance. For power control, the inner loop adjusts the transmit power to maintain the received signal quality (SNR) at the target SNR. The outer loop adjusts the target SNR based on the state of the received codeword (erased or unerased) to achieve the target erase rate. The third loop adjusts the erase threshold based on the state ("good", "bad" or "clear") of the known codeword received to achieve the target condition error rate.

Description

Robust Erase Detection and Erasure Rate-Based Closed Loop Power Control {ROBUST ERASURE DETECTION AND ERASURE-RATE-BASED CLOSED LOOP POWER CONTROL}

This application claims priority to US provisional application No. 60 / 580,819, filed June 18, 2004, entitled "Reverse Link Power Control Algorithm."

TECHNICAL FIELD The present invention generally relates to data communications, and more particularly to techniques for performing erasure detection and power control in wireless communication systems.

A wireless multiple access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base station to the terminal, and the reverse link (uplink) refers to the communication link from the terminal to the base station.

Multiple terminals may transmit simultaneously on the reverse link by multiplexing their transmissions to be orthogonal to each other. Multiplexing attempts to achieve orthogonality between multiple reverse link transmissions in the time, frequency and / or code domains. If achieved, complete orthogonality results in transmissions from each terminal that do not interfere with transmissions from other terminals at the receiving station. However, complete orthogonality between transmissions from different terminals is often not realized due to channel conditions, receiver imperfections, and the like. Loss in orthogonality causes each terminal to cause a certain amount of interference with other terminals. Thus, the performance of each terminal is degraded by interference from all other terminals.

On the reverse link, a power control mechanism may be used to control the transmit power of each terminal to ensure good performance for all terminals. This power control mechanism is implemented in two power control loops, which are often referred to as "inner" loops and "outer" loops. The inner loop adjusts the transmit power of the terminal so that the received signal quality (SNR) measured at the receiving base station remains at the target SNR. The outer loop adjusts the target SNR to maintain the desired block error rate (BLER) or packet error rate (PER).

Conventional power control mechanisms adjust the transmit power of each terminal such that the desired block / packet error rate is achieved for the reverse link transmission from the terminal. An erase detection code, such as a cyclic redundancy check (CRC) code, is typically used to determine whether each received data block / packet was correctly or error coded. Thus, the target SNR is adjusted based on the result of the error detection coding. However, the error detection code is not used for a given transmission, for example, if the overhead of the error detection code is considered excessive. Conventional power control mechanisms that rely on error detection codes cannot be used directly for such transmissions.

Therefore, what is needed in the technical field is a technique for properly adjusting the transmission power for transmission when error detection coding is not used.

Techniques for performing error detection and power control for transmission on a "physical" channel (eg, a control channel or a data channel) that do not use error detection coding are described. Data is transmitted as "codewords" on a physical channel, where each codeword may be a block of coded or uncoded data.

For erasure detection, a transmitting entity (e.g., wireless terminal) transmits a code word on a physical channel and over a wireless channel to a receiving entity (e.g., base station). The base station calculates a metric for each received codeword, as described below, and compares the calculated metric with an erase threshold. The base station declares whether each received codeword is an "erased" codeword or a "non-erased" codeword based on the comparison result. The base station dynamically adjusts the erase threshold to achieve a target level of performance that can be quantified by a target condition error rate that indicates the probability that the received codeword is decoded including an error when declared as a non-erase codeword. do. The erase threshold may be adjusted based on the received known codeword, which is the codeword received for the known codeword transmitted by the terminal in communication with the base station as described below. The adjustable erase threshold can provide robust erasure detection performance under various channel conditions.

A power control mechanism with three loops (inner loop, outer loop, and third loop) may be used to control the transmit power for the physical channel. The inner loop adjusts the transmit power for the physical channel to maintain the received SNR at or near the target. The outer loop adjusts the target SNR based on the state of the received codeword (erased or unerased) to achieve the target erase rate, which is the probability of declaring the received codeword as an erased codeword. The third loop adjusts the erase threshold based on the state ("good", "bad", or erased) of the known codeword received to achieve the target condition error rate. The target erase rate and target condition error rate are two measures of performance for a physical channel.

Various features and embodiments of the invention are further described below.

The features and characteristics of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

1 is a wireless multiple access communication system.

2 is a power control mechanism with three loops.

3A and 3B are processes for updating the second and third loops for the power control mechanism shown in FIG.

4 shows a data and control channel for a data transmission scheme.

5 is a block diagram of a base station and a terminal.

The term "example" is used to mean an illustration, example or illustration. Examples or designs described by way of example do not necessarily mean preferred or advantageous over other embodiments.

1 illustrates a wireless multiple access communication system 100. System 100 includes a number of base stations 110 that support communication for a number of wireless terminals 120. A base station is a fixed station used to communicate with a terminal and may also be called an access point, a Node B, or some other technical term. Terminals 120 are typically distributed throughout the system, and each terminal may be fixed or mobile. A terminal may be called a mobile station, user equipment (UE), wireless communication device, or some other terminology. Each terminal may communicate with one or more base stations on the forward and reverse links at any given moment. This depends on whether the terminal is active, whether soft handoff is supported, and whether the terminal is in soft handoff. For simplicity, Figure 1 only shows transmissions on the reverse link. System controller 130 is coupled to base station 110, provides coordination and control for such base stations, and controls the routing of data to terminals served by such base stations.

The erase detection and power control techniques described may be used in various wireless communication systems. For example, such techniques may be used for code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. CDMA systems use code division multiplexing, where transmissions for different terminals are orthogonal using different orthogonal (eg, Walsh) codes for the forward link. The terminals use different pseudo random number (PN) sequences for the reverse link in CDMA and are not completely orthogonal to each other. TDMA systems use time division multiplexing, where transmissions for different terminals are orthogonalized by transmissions at different time intervals. FDMA systems use frequency division multiplexing, and transmissions for different terminals are orthogonal by transmitting in different frequency bands. OFDMA systems use Orthogonal Frequency Division Multiplexing (OFDM), which effectively partitions the overall system bandwidth into multiple orthogonal frequency subbands. Such subbands may typically also be referred to as tones, subcarriers, bins and frequency channels. OFDMA systems use various orthogonal multiplexing schemes and may use any combination of time, frequency, and / or code division multiplexing.

The described technique may be used for various types of "physical" channels that do not utilize error detection coding. Physical channels may also be called code channels, transport channels, or some other terminology. Physical channels typically include a "data" channel used for traffic / packet data and a "control" channel used for transmitting overhead / control data. The system may use different control channels to transmit different types of control information. For example, the system may include (1) a CQI channel that transmits a channel quality indicator (CQI) indicating the quality of the wireless channel, and (2) an ACK that transmits an acknowledgment (ACK) for the hybrid automatic retransmission (H-ARQ) scheme. Channel, (3) a REQ channel that transmits a request for data transmission, and the like. The physical channel may or may not use other types of coding, even if error detection coding is not used. For example, a physical channel may not use some coding, and data is transmitted "in clear" on the physical channel. The physical channel may use block coding such that each block of data is coded to obtain a corresponding block of coded data to be transmitted on the physical channel. The described technique may be used for certain and all such different physical (data and control) channels.

For clarity, erase detection and power control techniques are described below for examples of the control channels used, in particular for the reverse link. Transmissions from different terminals on such control channels may be orthogonally multiplexed in frequency, time and / or code space. Due to full orthogonality, no interference is observed by each terminal on the control channel. However, with the presence of frequency selective fading (or change in frequency response over system bandwidth) and Doppler (due to movement), transmissions from different terminals may not be orthogonal to each other at the receiving station.

Data is transmitted in blocks on the example control channel, each block comprising a predetermined number (L) of data bits. Each data block is coded with a block code to obtain a corresponding codeword or coded data block. Since each data block obtains L bits, there are 2 ^L capable different data blocks in which one codeword is mapped to 2 ^L capable codewords in the code block for each different data block. The terminal transmits a codeword for a block of data on the control channel.

The base station receives the codewords transmitted on the control channel by different terminals. The base station performs complementary block decoding on each received codeword to obtain a decoded data block, which is the data block considered to be most likely transmitted for the received codeword. Block decoding may be performed in various ways. For example, the base station can receive ^2L of the received codeword and codebook. Euclidean distance may be calculated between each of the possible valid codewords. Typically, the Euclidean distance between a received codeword and a given valid codeword is shorter as the received codeword is closer to the valid codeword, and longer as the received codeword is farther from the valid codeword. A data block corresponding to a valid codeword with a shorter Euclidean distance for the received codeword is provided to the decoded data block for the received codeword.

여기서,

는 수신된 코드워드 k에 대해 j번째 수신된 심볼이며,

는 유효 코드워드 i에 대해 j번째 변조 심볼이며, 및

는 수신된 코드워드 k와 유효 코드워드 i 사이의 유클리드 거리이다. By way of example, the L data bits for a data block may be mapped to a codeword that includes a K modulation scheme for a particular modulation scheme (eg, BPSK, QPSK, M-PSK, M-QAM, etc.). Each valid codeword is associated with a different set of K modulation symbols, and the 2 ^L sets of modulation symbols for the 2 ^L possible valid codewords may each be chosen to be as far apart from each other (at Euclidean distance) as possible. The received codeword then comprises K received symbols, where each received symbol is a noise version of the transmitted modulation symbol. The Euclidean distance between the received codeword and the given valid codeword can be calculated as follows:

here,

Is the jth received symbol for the received codeword k,

Is the j th modulation symbol for the valid codeword i, and

Is the Euclidean distance between the received codeword k and the valid codeword i.

유효 코드워드 데이터 블록에 대응하는 데이터 블록이 수신된 코드워드에 대한 디코딩된 데이터 블록으로서 제공된다. Equation (1) calculates the Euclidean distance as the mean squared error between the K received symbol for the received codeword and the K modulation symbol for the valid codeword. Minimal

The data block corresponding to the valid codeword data block is provided as a decoded data block for the received codeword.

여기서,

는 수신된 코드워드 k와 가장 가까운 유효 코드워드 사이의 유클리드 거리이며,

는 수신된 코드워드 k와 다음으로 가장 가까운 유효 코드워드 사이의 유클리드 거리이며, 및

는 수신된 코드워드 k에 대한 메트릭이다. Without an error detection code, there is no direct way to determine whether a given given codeword is correct or error, and whether the decoded data block is a truly transmitted data block. Metrics can be defined and used to provide an indication of confidence in the decoding result. In an embodiment, the metric is given as

here,

Is the Euclidean distance between the received codeword k and the closest valid codeword,

Is the Euclidean distance between the received codeword k and the next closest valid codeword, and

Is a metric for the received codeword k.

는 작은 값이며, 디코딩된 데이터 블록이 정확하다는 높은 확실성이 존재한다. 결론적으로, 만일 수신된 코드워드가 가장 가까운 코드워드 및 다음으로 가장 가까운 코드워드와 거의 같은 거리를 가지면, 메트릭

은 1로 접근 또는 m(k)→1이며, 디코딩된 데이터 블록이 정확하다는 낮은 확실성이 존재한다. If the received codeword is closer to the nearest codeword than the next nearest codeword, the metric

Is a small value and there is a high certainty that the decoded data block is correct. In conclusion, if the received codeword has a distance approximately equal to the nearest codeword and the next nearest codeword, then the metric

Is approaching 1 or m (k) → 1, and there is a low certainty that the decoded data block is correct.

Equation (2) represents an example of a metric based on the ratio of Euclidean distance, which may be used to determine whether the block decoding of a given received codeword is correct or there is an error. Other metrics may be used for erasure detection, which is within the spirit of the present invention. Typically, the metric may be limited to being based on any suitable reliability function f (r, C), where r is a received codeword and C is a codebook or a collection of all possible codewords. The function f (r, C) represents the quality / reliability of the received codeword and has an appropriate characteristic (eg monotonic with detection certainty).

은 이하와 같이 수신된 코드워드에 대한 디코딩 결정을 획득하기 위해 소거 임계치(TH_erasure)와 비교될 수도 있다.

Erasure detection may be performed to determine if the decoding result for each received codeword meets a predetermined level of confidence. Metrics for Received Codewords

May be compared with an erase threshold TH _erasure to obtain a decoding decision for the received codeword as follows.

As shown in equation (3), the received codeword is declared as an "erasing" codeword if the metric m (k) is greater than or equal to the erase threshold, and if the metric m (k) is less than the erase threshold. It is declared as a "non-erasing" codeword. The base station may handle data blocks that are decoded differently for unerased and erased codewords. For example, the base station may use the decoded data block for the non-erasing codeword for later processing, and may discard the decoded data block for the erase codeword.

The possibility of declaring a codeword received as an erasure codeword is called the erasure rate and denoted by Pr _erasure . The cancellation rate depends on the cancellation threshold used for erase detection and the received signal quality (SNR) for the received codeword. Signal quality may be limited by signal to noise ratio, signal to noise and interference ratio, and the like. For a given received SNR, a low erase threshold increases the likelihood that a received codeword is declared an erase codeword, and vice versa. For certain erase thresholds, the low SNR received increases the likelihood that the received codeword is declared an erase codeword, and vice versa. For certain erase thresholds, the received SNR may be set (by controlling the transmit power for the control channel to be described later) to achieve the desired erase rate.

The erase threshold may be set to achieve the desired performance for the control channel. For example, the probability of an error defined for a non-erasing codeword, also called a condition error rate, may be used for the control channel. These conditions are shown in the error rate Pr _error, if the received codeword is declared to be a non-erased codeword, the probability of the decoded data block for the received codeword correct that means that the Pr _error. Low Pr _errors (e.g., 1% or 0.1%) correspond to a high degree of certainty in the decoding result when an unerased codeword is declared. Low Pr _error may be desirable for many types of transmissions where reliable decoding is important. The erase threshold may be set to an appropriate level to obtain the desired Pr _error .

A well defined relationship may be expected to exist between the erase rate Pr _erasure , the condition error rate Pr _error , the erase threshold TH _erasure , and the received SNR. In particular, for a given erase threshold and a given received SNR, there is a specific erase rate and a specific condition error rate. By changing the erase threshold, a choice may be made between the erase rate and the condition error rate. Computer simulations may be performed and / or empirical measurements may be made to determine or predict the relationship between the cancellation rate and the condition error rate for different cancellation thresholds and different received SNRs.

However, in a practical system, the relationship between these four parameters may not be known earlier and may depend on the deployment scenario. For example, the specific erase thresholds and condition error rates that can achieve the desired erase rate are not known a priori and may change slowly over time. Moreover, the “predicted” relationship between the erase rate and the condition error rate, obtained through simulation or through some other means, will remain intact in the actual deployment.

The power control mechanism may be used to dynamically adjust the received SNR and erase threshold to achieve the desired performance for the control channel. The control channel performance is based on the target erasure rate Pr _erasure (e.g., 10% erasure rate, or Pr _erasure = 0.1) and target condition error rate Pr _error (e.g., 1% condition error rate, or Pr _error = 0.01) It may be limited by (Pr _erasure , Pr _error ) pairs.

2 illustrates a power control mechanism 200 that may be used to dynamically adjust the erase threshold and control the transmit power for the transmitted transmission for the control channel from the terminal to the base station. The power control mechanism 200 includes an inner loop 210, an outer loop 220, and a third loop 230.

Inner loop 210 attempts to maintain the received SNR for transmission, as measured at the base station, as close as possible to the target SNR. For inner loop 210, SNR evaluator 242 at the base station estimates the received SNR for transmission and provides the received SNR to transmit power control (TPC) generator 244. The TPC generator 242 also receives a target SNR for the control channel, compares the received SNR with the target SNR, and generates a TPC command based on the comparison result. Each TPC command is either (1) an up command that commands an increase in transmit power for the control channel or (2) a down command that commands a decrease in transmit power. The base station sends a TPC command on the forward link (cloud 260) to the terminal.

The terminal receives and processes the forward link transmission from the base station and provides a "received" TPC command to the TPC processor 262. Each received TPC command is a noise version of the TPC command sent by the base station. The TPC processor 262 detects each received TPC command and obtains a TPC decision, which is either (1) if the received TPC command is considered an up command, or (2) if the received TPC command is a down command. If considered, it may be a down decision.

여기서,

는 내부 루프 업데이트 간격(n)에 대한 송신 전력이며,

은 송신 전력에 대한 업 스텝 크기이며,

는 송신 전력에 대한 다운 스텝 크기이다. The transmit (TX) power adjustment unit 264 adjusts the transmit power for transmission on the control channel based on the TPC decision from the TPC processor 262. Unit 264 adjusts the transmit power as follows.

here,

Is the transmit power for the inner loop update interval n,

Is the upstep size for transmit power,

Is the down step size for the transmit power.

및 스텝 크기(

)는 데시벨(dB) 단위이다. 식(4)에 도시된 바와 같이, 송신 전력은 각각의 업 결정에 대해

만큼 증가하며, 각각의 다운 결정에 대해

만큼 감소된다. 비록 간략화를 위해 전술되지는 않았지만, TPC 결정은 만일 수신된 TPC 명령이 너무 의존적인 것으로 간주되면 "no-OP"로 될 수도 있는데, 이 경우, 송신 전력은 동일한 레벨, 또는 P_cch(n+1)=P_cch(n)으로 유지될 수도 있다.

및

스텝 크기는 통상적으로 동일하며, 1.0 dB, 0.5dB 또는 소정의 다른 값으로 설정될 수도 있다. Transmit power

And step size (

) Is in decibels (dB). As shown in equation (4), the transmit power is calculated for each up decision.

For each down decision

Is reduced by. Although not described above for the sake of simplicity, the TPC decision may be “no-OP” if the received TPC command is considered too dependent, in which case the transmit power is at the same level, or P _cch (n + 1). ) = P _cch (n).

And

The step size is typically the same and may be set to 1.0 dB, 0.5 dB or some other value.

The path loss, fading and time typically vary and, in particular for mobile terminals, due to the multipath effect on the reverse link (cloud shape 240), the received SNR fluctuates continuously for transmission on the control channel. Inner loop 210 attempts to maintain the received SNR at or near the target SNR in the presence of a change in reverse link channel conditions.

Outer loop 220 continuously adjusts the target SNR such that a target cancellation rate is achieved for the control channel. The metric calculation unit 252 calculates a metric m (k) for each received codeword obtained from the control channel as described above. The erase detector 254 performs erase detection for each received codeword based on the calculated metric m (k) for the codeword and the erase threshold and determines the state of the received codeword (erased or unerased). To the adjustment unit 256.

여기서,

는 외부 루프 업데이트 간격 k에 대한 목표 SNR이며,

는 목표 SNR에 대한 업 스텝 크기이며,

는 목표 SNR에 대한 다운 스텝 크기이다. The target SNR adjustment unit 256 obtains the state of each received codeword and adjusts the target SNR for the control channel as follows.

here,

Is the target SNR for the outer loop update interval k,

Is the upstep size for the target SNR,

Is the down step size for the target SNR.

) 및 스텝 크기(

및

)은 dB단위이다. 식(5)에 도시된 바와 같이, 만일 수신된 코드워드가 제어 채널에 대해 수신된 SNR이 필요 이상으로 큰 것을 나타내는, 비소거 코드워드로 간주되면, 유닛(256)은 목표 SNR을

만큼 감소시킨다. 반대로, 만일 수신된 코드워드가 제어 채널에 대해 수신된 SNR보다 작은 것을 나타내는, 소거 코드워드로 간주되면, 유닛(256)은 목표 SNR을

만큼 증가시킨다.Goal SNR (

) And step size (

And

) Is in dB. As shown in equation (5), if the received codeword is considered to be an unerased codeword, indicating that the received SNR for the control channel is larger than necessary, unit 256 determines the target SNR.

Decrease by. Conversely, if it is regarded as an erase codeword, indicating that the received codeword is less than the received SNR for the control channel, unit 256 determines the target SNR.

Increase by.

및

스텝 크기는 이하의 관계에 기초하여 설정될 수도 있다.

To adjust the target SNR

And

The step size may be set based on the following relationship.

)이면, 업 스텝 크기는 다운 스텝 크기의 9배(또는

)이다. 만일 업 스텝 크기가 0.5데시벨(dB)로 선택되면, 다운 스텝 크기는 대략 0.056dB이다.

및

에 대한 더 큰 값들은 외부 루프(220)에 대한 수렴율의 속도를 증가시킨다.

에 대한 큰 값은 또한 안정 상태에서 목표 SNR에 대한 더 많은 변동 또는 변화를 초래한다. For example, if the target cancellation rate for the control channel is 10% (or

), The up step size is nine times the down step size (or

)to be. If the up step size is chosen to be 0.5 decibel (dB), the down step size is approximately 0.056 dB.

And

Larger values for increase the rate of convergence for the outer loop 220.

Large values for also result in more variation or change to the target SNR in steady state.

The third loop 230 dynamically adjusts the erase threshold such that a target condition error rate is achieved for the control channel. The terminal may transmit a known codeword on the control channel periodically or whenever triggered. The base station receives the known codeword transmitted. The metric calculation unit 252 and the erase detector 254 perform erase detection for each received known codeword based on the erase threshold and in the same manner as for the received codeword. For each received known codeword considered deasserted, detector 262 decodes the received known codeword and determines whether the decoded data block is correct or an error, which can be done because the codeword is known. . The detector 262 provides the state of the received known codeword to the erasing threshold adjustment unit 264, respectively, which means that (1) the erased codeword, and (2) the known codeword only if it is a non-erasing codeword and If decoded it is a "good" codeword or (3) if the received known codeword is an unerased codeword but it is decoded in error.

The erase threshold adjustment unit 264 obtains the state of the received known codeword and adjusts the erase threshold as follows.

는 제3 루프 업데이트 간격

에 대한 소거 임계치이며,

는 소거 임계치에 대한 업 스텝 크기이며,

은 소거 임계치에 대한 다운 스텝 크기이다. here,

Is the third loop update interval

An erase threshold for,

Is the upstep size for the erase threshold,

Is the down step size for the erase threshold.

만큼 감소된다. 낮은 소거 임계치는 더욱 엄격한 소거 검출 표준에 대응하며, 소거된 것으로 간주되기 쉬운 수신된 코드워드를 초래하며, 이는 차례로 비소거된 것으로 간주될 때 올바르게 코딩되기 더욱 쉬운 수신된 코드워드를 초래한다. 반대로, 양호한 코드워드인 각각의 수신된 알려진 코드 워드의 경우,

만큼 증가된다. 더 높은 소거 임계치는 덜 엄격한 소거 검출 표준에 대응하며, 소거된 것으로 간주되기 쉽지 않은 수신된 코드워드를 초래하며, 이는 차례로 비소거된 것으로 간주될 때 에러로 디코딩되기 더욱 쉬운 수신된 코드워드를 초래한다. 소거 임계치는 소거된 수신된 알려진 코드워드에 대한 동일한 레벨로 유지된다. As shown in equation (7), the erase threshold is for each received known codeword that is a bad codeword.

Is reduced by. Low erase thresholds correspond to more stringent erase detection standards and result in received codewords that are likely to be erased, which in turn results in received codewords that are easier to code correctly when deemed non-erased. Conversely, for each received known code word that is a good code word,

Is increased by. Higher erase thresholds correspond to less stringent erase detection standards and result in received codewords that are less likely to be considered erased, which in turn results in received codewords that are more likely to be decoded into errors when considered to be unerased. do. The erase threshold is maintained at the same level as the received received known codeword.

및

스텝 크기는 이하의 관계에 기초하여 설정될 수도 있다.

To adjust the erase threshold

And

The step size may be set based on the following relationship.

및

의 크기는 수신된 심볼의 예상된 크기, 제3 루프에 대한 원하는 수렴율, 및 가능한 다른 팩터에 기초하여 결정될 수도 있다. For example, if the target condition error rate for the control channel is 1%, the down step size is 99 times the up step size.

And

The size of may be determined based on the expected size of the received symbol, the desired rate of convergence for the third loop, and possibly other factors.

대신

)으로 한정될 수도 있으며, 이 경우 소거 임계치의 조절은 그에 따라 변경될 수도 있다. 조절가능한 소거 임계치는 다양한 채널 조건에 대한 강건한 소거 검출 성능을 달성하기 위해 소정의 소거 검출 기술과 조합하여 사용될 수도 있다. Typically, adjusting the erase threshold depends on how the metric used for erase detection is defined. Equations (7) and (8) are based on a defined metric as shown in equation (2). Metrics can be accessed in different ways (for example,

instead

), In which case the adjustment of the erase threshold may be changed accordingly. The adjustable erase threshold may be used in combination with certain erase detection techniques to achieve robust erase detection performance for various channel conditions.

는 다양한 방식으로 동적으로 조절될 수도 있다. 일 실시예에서, 개별 제3 루프는 기지국과 통신하는 각각의 터미널에 대해 기지국에 의해 유지된다. 이러한 실시예는 제어 채널 성능이 터미널에 대해 특히 적응되게 한다. 예를 들어, 상이한 터미널은 상이한 타겟 조건 에러율을 가질 수도 있으며, 이는 이러한 터미널에 대한 개별 제3 루프를 동작함으로써 달성될 수도 있다. 다른 실시예에서, 제3의 루프는 기지국과 통신하는 모든 터미널에 대해 기지국에 의해 유지된다. 이어 통상의 소거 임계치는 이러한 모든 터미널에 대한 소거 검출을 위해 사용되며, 이러한 터미널로부터의 기지국에 의해 수신된 알려진 코드워드에 기초하여 또한 업데이트된다. 이러한 실시예는 만일 제어 채널 성능이 다양한 채널 조건에 대한 이러한 터미널에 대해 강건하면, 모든 터미널에 대해 양호한 성능을 제공한다. 이러한 실시예는 각각의 터미널이 더 낮은 레이트(예를 들어, 매 수백 밀리초 마다)로 알려진 코드워드를 송신할 수도 있기 때문에, 제3 루프에 대해 더 신속한 수렴율을 가능하게 하며 또한 오버헤드를 감소시킨다. 또 다른 실시예에서, 단일의 제3 루프는 동일한 제어 채널 성능을 갖는 각각의 터미널 그룹에 대한 기지국에 의해 유지되며, 소거 임계치는 그룹의 모든 터미널로부터 기지국에 의해 수신된 알려진 코드워드에 기초하여 업데이트된다. Erase threshold

May be dynamically adjusted in various ways. In one embodiment, a separate third loop is maintained by the base station for each terminal in communication with the base station. This embodiment allows the control channel performance to be particularly adapted to the terminal. For example, different terminals may have different target condition error rates, which may be achieved by operating separate third loops for these terminals. In another embodiment, the third loop is maintained by the base station for all terminals communicating with the base station. The normal erase threshold is then used for erase detection for all these terminals and is also updated based on known codewords received by the base station from these terminals. This embodiment provides good performance for all terminals if the control channel performance is robust for these terminals for various channel conditions. This embodiment allows for faster convergence rate for the third loop and also reduces overhead since each terminal may transmit a known codeword at a lower rate (eg every hundreds of milliseconds). Decrease. In another embodiment, a single third loop is maintained by the base station for each terminal group having the same control channel performance, and the erase threshold is updated based on known codewords received by the base station from all terminals in the group. do.

Inner loop 210, outer loop 220, and third loop 230 are typically updated at different rates. Inner loop 210 is the fastest of the three loops, and the transmit power for the control channel may be updated at a specific rate (eg, 150 times per second). Outer loop 220 is the next fast loop, and the target SNR may be updated each time the codeword is received on the control channel. The third loop is the latest loop, and the erase threshold may be updated each time a known codeword is received on the control channel. The update rate for the three loops may be selected to achieve the desired performance for erase detection and power control.

은 제어 채널에 대한 성능의 측정치들 중 하나로서 사용되며, 제3의 루프는 이러한

을 달성하기 위해 설계된다. 성능의 다른 측정치는 또한 제어 채널에 사용될 수도 있으며, 제3의 루프는 그에 따라 설계될 수도 있다. 예를 들어, 소거된 것으로 간주된 때 에러로 디코딩될 수신된 코드워드의 목표 가능성이 제3의 루프에 대해 사용될 수도 있다. In the case of the above-described embodiment, the target condition error rate

Is used as one of the measures of performance for the control channel, and the third loop

Is designed to achieve this. Other measures of performance may also be used for the control channel, and a third loop may be designed accordingly. For example, the target likelihood of the received codeword to be decoded in error when considered to be erased may be used for the third loop.

만큼 증가된다. 블록(326) 이후, 프로세 스는 다음으로 수신된 코드워드를 프로세싱하기 위해 블록(312)으로 복귀한다. 3A and 3B are a flow diagram of a process 300 for updating the second and third loops of the power control mechanism 300. The received codeword k is initially obtained from the control channel (block 312). The metric m (k) is calculated for the received codeword, for example as described above (block 314) and for the erase threshold (block 316). If the calculated metric m (k) is greater than or equal to the erase threshold, as determined at block 320, and if the received codeword is not a known codeword as determined at block 332, then the received codeword Is declared as an erase codeword (block 324). The target SNR is equal to or greater than the erase threshold, regardless of whether the received codeword is known or unknown.

Is increased by. After block 326, the process returns to block 312 to process the next received codeword.

스텝 크기만큼 감소된다(블록 336). 프로세스는 다음으로 수신된 코드워드를 프로세싱하기 위해 블록(312)으로 복귀한다. If the calculated metric m (k) is less than the erase threshold, as determined at block 320, and if the received codeword is not a known codeword as determined at block 332, then the received codeword is Declared as a non-erase codeword (block 334), and the target SNR is

Reduced by step size (block 336). The process then returns to block 312 to process the received codeword.

스텝 크기만큼 증가된다(블록 346). 그렇지 않고, 만일 블록(342)에서 결정된 바와 같이, 디코딩 에러가 존재하면, 수신된 알려진 코드워드는 불량 코드워드(블록 354)로 선언되며, 소거 임계치는

스텝 크기(블록 356)만큼 감소된다. 블록(346 및 356)으로부터, 프로세스는 다음으로 수신된 코드워드를 프로세싱하기 위해 도3a의 블록(312)으로 복귀한다. If the calculated metric m (k) is less than the erase threshold, as determined at block 320, and if the received codeword is a known codeword as determined at block 332, (see Figure 3). The received codeword is decoded (block 340). If the decoding is correct, as determined at block 342, then the received known codeword is declared a good codeword (block 344), and the erase threshold is

Incremented by the step size (block 346). Otherwise, if there is a decoding error, as determined at block 342, then the received known codeword is declared a bad codeword (block 354), and the erase threshold is

Reduced by step size (block 356). From blocks 346 and 356, the process then returns to block 312 of FIG. 3A to process the received codeword.

을 획득할 수도 있다. 터미널은 CQI 채널(제어 채널 중 하나임)에 대한 CQI 코드워드를 서비스 기지국으로 전송한다. 서비스 기지국은 CQI 채널상에서 전송된 CQI 코드워드를 수신하고 수신된 CQI 코드워드 상에서 소거 검출을 실행한다. 만일 수신된 CQI 코드워드가 소거되지 않으면, 서비스 기지국은 수신된 CQI 코드워드를 디코딩하고 터미널에 대해 데이터 송신을 스케줄링하기 위해 디코딩된 CQI를 이용한다. As noted above, the techniques described herein may be used for various types of physical channels that do not use error decision coding. The use of this technique for an example of a data transmission scheme is described below. For this transmission scheme, the terminal wishing to forward link transmission estimates the received signal quality of the forward link to its serving base station (eg, based on the pilot transmitted by the base station). The received signal quality estimate may be converted to an L bit value, which is called a channel quality indicator (CQI). The CQI may indicate the received SNR for the forward link, the supported data rate for the forward link, and the like. In some cases, block coding is performed on the CQI to obtain a CQI codeword. As a specific example, L equals 4, and the CQI codeword is a 16QPSK modulation symbol or

May be obtained. The terminal sends the CQI codeword for the CQI channel (which is one of the control channels) to the serving base station. The serving base station receives the CQI codeword transmitted on the CQI channel and performs erasure detection on the received CQI codeword. If the received CQI codeword is not erased, the serving base station decodes the received CQI codeword and uses the decoded CQI to schedule data transmission for the terminal.

4 shows a data set and control channel used for an example of a data transmission scheme. The terminal measures the received signal quality of the forward link and transmits a CQI codeword on the CQI channel. The terminal continuously measures forward link quality and transmits the updated CQI codeword on the CQI channel. Thus, ignoring received CQI codewords that are considered to be erased is not beneficial for system performance. However, the received CQI codeword will be of high quality since forward link transmission may be scheduled based on the information contained in this non-erased CQI codeword.

If the terminal is scheduled for forward link transmission, the serving base station processes the data packet to obtain a coded packet and transmits the coded packet on the forward link data channel to the terminal. In the hybrid automatic retransmission (H-ARQ) scheme, each coded packet is divided into a plurality of subblocks, and one subblock is transmitted at a time for the coded packet. As each subblock for a given coded packet is received on the forward link data, the terminal eventually attempts to decode and recover the packet based on all subblocks received remotely for the packet. The terminal may recover the packet based on the partial transmission because it contains redundant information useful for decoding when the received signal quality is poor, but may not be required when the received signal quality is good. The terminal then sends an acknowledgment (ACK) on the ACK channel if the packet is coded correctly, otherwise it sends a negative acknowledgment (NAK). Forward link transmission continues in this manner until all coded packets are sent to the terminal.

The described technique may be useful for CQI channels. Erasure detection may be performed on each received CQI codeword as described above. The transmit power for the CQI channel may be adjusted using the power control mechanism 300 to achieve the desired performance for the CQI channel (eg, desired erase rate and desired condition error rate). The transmit power for the other control channel (eg, the ACK channel) and the reverse link data channel may be established based on the power controlled transmit power for the CQI channel.

For clarity, erase decision and power control techniques are described in particular for the reverse link. This technique may be used for erase detection and power control for transmissions sent on the forward link.

5 shows a block diagram of an embodiment of base station 110x and terminal 120x. For the reverse link, at terminal 120x, the transmit (TX) data processor 510 receives and processes (eg, formats, codes, interleaves, and modulates) the reverse link (RL) traffic data and writes to the traffic data. Provides the modulation symbol for. TX data processor 510 also processes control data (eg, CQI) from controller 520 and provides modulation symbols for the control data. Modulator (MOD) 512 processes the modulation and control data and pilot symbols for the traffic and provides a sequence of complex valued chips. Processing by the TX data processor 510 and modulator 512 is system dependent. For example, modulator 512 performs OFDM modulation if the system uses OFDM. Transmitter unit (TMTR) 514 adjusts (eg, converts to analog, amplifies, filters, and frequency upconverts) a sequence of chips and generates a reverse link signal, which is via duplexer (D) 516. Routed and transmitted via antenna 518.

At base station 110x, the reverse link signal of terminal 120x is received 552 by an antenna, routed through duplexer 554, and provided to a receiver unit (RCVR) 556. Receiver unit 556 adjusts (eg, filters, amplifies, and frequency downconverts) the received signal and further digitizes the adjusted signal to obtain a stream of data samples. Demodulator (DEMOD) 558 processes the data samples to obtain symbol estimates. Receive (RX) data processor 560 then processes (eg, deinterleaves and decodes) the symbol estimates to obtain decoded data for terminal 120x. The RX data processor 560 also performs erase detection and provides the controller 570 with the status of each received codeword used for power control. The processing by demodulator 558 and RX data processor 560 is complementary to the processing performed by modulator 512 and TX data processor 510, respectively.

Processing for the forward link transmission may be performed similar to that described above for the reverse link. Processing for the reverse link and the forward link is typically specified by the system.

For reverse link power control, SNR evaluator 574 estimates the received SNR for terminal 120x and provides the received SNR to TPC generator 576. The TPC generator also receives the target SNR and generates a TPC command for terminal 120x. TPC commands are processed by TX data processor 582, further processed by modulator 584, regulated by transmitter unit 586, routed through duplexer 554, and through antenna 552. Is sent to terminal 120x.

At terminal 120x, the forward link signal from base station 110x is received by antenna 518, routed through duplexer 516, regulated and digitized by receiver unit 540, and demodulator 542 And is further processed by the RX data processor 544 to obtain the received TPC command. The TPC processor 524 then detects the received TPC command to obtain a TPC decision used to generate the transmit power adjustment control. The modulator 512 receives control from the TPC processor 524 and adjusts the transmit power for reverse link transmission. Forward link power control may be achieved in a similar manner.

Controllers 520 and 570 coordinate the operation of various processing units within terminal 120x and base station 110x, respectively. Controllers 520 and 570 may also perform various functions for erase detection and power control for the forward and reverse links. For example, each controller may implement a target SNR adjustment unit for the SNR evaluator, the TPC generator, and the link. Controller 570 and RX data processor 560 may also implement process 300 in FIGS. 3A and 3B. Memory units 522 and 572 store data and program code for controllers 520 and 570, respectively.

The erase detection and power control techniques described may be implemented by various means. For example, such techniques may be implemented in hardware, software, or a combination thereof. In a hardware implementation, the processing unit used to perform erase detection and / or power control may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs). ), A field programmable gate array (FPGA), a processor, a controller, a microcontroller, a microprocessor, another electronic unit designed to carry out the described functions, or a combination thereof.

In the case of a software implementation, the described techniques may be implemented in modules (eg, procedures, functions, etc.) that implement the described functionality. The software code may be sorted in a memory unit (eg, memory unit 572 of FIG. 5) and may be executed by a processor (eg, controller 570). The memory unit may be executed within the processor or outside the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the described general principles may be used in other embodiments without departing from the spirit of the invention. Thus, the present invention is not limited to the embodiments, but is consistent with the broad concept of the principles and features described.

Claims (33)

A method of performing erasure detection on codewords received in a communication system, the method comprising: Obtaining received codewords for codewords transmitted over a wireless channel, where each transmitted codeword is a block of coded or uncoded data, and each received codeword is a noise of the transmitted codeword (noisy) version-; Calculating a metric for each of the received codewords; Comparing the calculated metric for each received codeword with an erase threshold; Declaring each received codeword as an erased codeword or a non-erased codeword based on a comparison result of each received codeword and the erase threshold; And Dynamically adjusting the erase threshold to achieve a target level of performance for erase detection, How to perform erasure detection. The method of claim 1, Obtaining received known codewords for known codewords transmitted over a wireless channel, where each known codeword is a block of known data and each received known codeword is a noise version of the known codeword transmitted Im-; Determining the status of each of the received known codewords as a good codeword, a bad codeword, or an erase codeword, wherein the good codeword is a received known codeword that is declared as a non-erasing codeword and correctly decoded, The bad codeword is a non-erased codeword but is a received known codeword decoded including an error; And Adjusting the erase threshold based on the state of each received known codeword. The method of claim 2, And said known codewords are transmitted a known number by one or more transmitting entities. The method of claim 2, And said known codewords are transmitted by a transmitting entity if indicated. The method of claim 1, A non-erasing codeword is associated with a certain level of certainty that is correctly received, and an erasing codeword is associated with a certain level of certainty that is received including an error. The method of claim 1, And wherein the target level of performance for the erase detection is a target condition error rate indicating a predetermined probability that the received codeword, including an error, is to be decoded when declared as a non-erase codeword. The method of claim 1, Each transmitted codeword is one of a number of possible valid codewords, and the metric is based on a function indicative of the reliability of the received codeword. The method of claim 7, wherein The metric for each received codeword is the ratio of the Euclidean distance for the nearest valid codeword and the Euclidean distance for the next nearest valid codeword, and the Euclidean distance for the nearest valid codeword is the received code. A Euclidean distance between a word and a valid codeword closest to the received codeword, and the Euclidean distance for the next nearest valid codeword is the next valid codeword closest to the received codeword and the received codeword. And Euclidean distance between. The method of claim 1, Wherein each transmitted codeword is a block of coded data obtained by performing block coding on a block of uncoded data. The method of claim 1, Wherein each transmitted codeword does not comprise an error detection code. An apparatus operative to perform erasure detection on codewords received in a wireless communication system, comprising: A metric calculation unit operative to obtain received codewords for codewords transmitted over a wireless channel and calculate a metric for each of the received codewords, wherein each transmitted codeword is coded or uncoded data; Each block is a noise version of the transmitted codeword; Compare the calculated metric for each received codeword with an erase threshold, and compare each received codeword with an erase codeword or non-erasing code based on each received codeword and the comparison result for the erase threshold. An erase detector operative to declare a word; And An adjustment unit operative to dynamically adjust the erase threshold to achieve a target level of performance for erase detection, Erasure detection device. The method of claim 11, Further comprising a decoder, wherein the decoder, Obtain received known codewords for known codewords transmitted over the wireless channel, where each known codeword is a block of known data, and each received known codeword is a noise version of the known codeword transmitted Im-; Decode each received known codeword considered to be an unerased codeword; And Determine the status of each received known codeword as a good codeword, a bad codeword, or an erase codeword—the good codeword is a received known codeword that has been declared as a non-erasing codeword and correctly decoded, Codeword is a known codeword that is declared as a non-erase codeword but decoded with an error-it operates, And said adjusting unit is operative to adjust said erase threshold based on said state of each received known codeword. An apparatus operable to perform erasure detection on codewords received in a wireless communication system, comprising: Means for obtaining received codewords for codewords transmitted over a wireless channel, where each transmitted codeword is a block of coded or uncoded data, and each received codeword is a noise of the transmitted codeword Version; Means for calculating a metric for each of the received codewords; Means for comparing the calculated metric for each received codeword with an erase threshold; Means for declaring each received codeword as an erase codeword or a non-erasing codeword based on a result of the comparison with each received codeword and the erase threshold; And Means for dynamically adjusting the erase threshold to achieve a target level of performance for erase detection, Erasure detection device. The method of claim 13, Means for obtaining received known codewords for known codewords transmitted over a wireless channel, where each known codeword is a block of known data and each received known codeword is a noise version of the known codeword transmitted Im-; Means for determining the status of each of the received known codewords as a good codeword, a bad codeword, or an erase codeword, wherein the good codeword is a received known codeword that is declared as a non-erasing codeword and correctly decoded, The bad codeword is a non-erased codeword but is a received known codeword decoded including an error; And And means for adjusting the erase threshold based on the state of each received known codeword. A method of performing power control for transmission transmitted through a wireless channel in a wireless communication system, Obtaining received codewords for codewords transmitted in the transmission, where each transmitted codeword is a block of coded or uncoded data, and each received codeword is a noise version of the transmitted codeword Im-; Determining a state of each received codeword as an erase codeword or a non-erase codeword based on the metric calculated for the received codeword and an erase threshold; Adjusting a target signal quality (SNR) based on the state of each received codeword, wherein the transmit power for the transmission is adjusted based on the target SNR; Obtaining received known codewords for known codewords transmitted over the wireless channel, where each known codeword is a block of known data and each received known codeword is a noise of a known codeword transmitted Version-; Determining the status of each received known codeword as a good codeword, a bad codeword, or an erase codeword, wherein the good codeword is a received known codeword that is considered a non-erasing codeword and is correctly decoded, and A bad codeword is considered a non-erase codeword but is a received known codeword decoded including an error; And Adjusting the erase threshold based on the state of each received known codeword, Power control method. The method of claim 15, Adjusting the target SNR, Reducing the target SNR by a down step for each received codeword considered to be an unerased codeword; And Increasing the target SNR by an up step for each received codeword considered an erase codeword. The method of claim 16, The down step and the up step for adjusting the target SNR are determined by a target erase ratio indicating a predetermined probability of declaring a received codeword as an erase codeword. The method of claim 15, A low erase threshold corresponds to a higher likelihood that a received codeword will be considered an erase codeword, and adjusting the erase threshold includes: Reducing the erase threshold by a down step for each received known codeword considered to be a bad codeword; And Increasing the erase threshold by an up step for each received known codeword considered a good codeword. The method of claim 18, Adjusting the erase threshold, And maintaining said erase threshold at the same level for each received known codeword that is considered an erase codeword. The method of claim 18, The down step and the up step for adjusting the erase threshold are determined by a target condition error rate indicating a predetermined probability that the received codeword will be decoded including an error if declared as a non-erase codeword. Power control method. The method of claim 15, The received known codewords are obtained from a number of different transmitting entities. The method of claim 15, Estimating the received SNR for the transmission; Comparing the received SNR with the target SNR; And Generating instructions based on the results of the comparison, wherein the instructions are used to adjust the transmit power for the transmission. An apparatus operable to perform power control for transmission transmitted over a wireless channel in a wireless communication system, comprising: Data processor; And A controller, The data processor, Obtain received codewords for codewords transmitted in the transmission—each transmitted codeword is a block of coded or uncoded data, and each received codeword is a noise version of the transmitted codeword -; Determine a state of each received codeword as an erase codeword or a non-erase codeword based on the metric calculated for the received codeword and an erase threshold; Obtain received known codewords for known codewords transmitted over the wireless channel, where each known codeword is a block of known data, and each received known codeword is a noise version of the known codeword transmitted Im-; And To determine the status of each received known codeword as a good codeword, a bad codeword, or an erase codeword-the good codeword is a received known codeword that is regarded as an unerased codeword and correctly decoded, and the bad The codeword is considered a non-erasing codeword but is a received known codeword decoded with an error. The controller, Adjust a target signal quality (SNR) based on the state of each received codeword, wherein the transmit power for the transmission is adjusted based on the target SNR; And Operate to adjust the erase threshold based on the state of each received known codeword, Power control unit. The method of claim 23, wherein An SNR estimator operative to estimate an SNR received for the transmission; And And a generator operable to compare the received SNR with the target SNR and generate instructions used to adjust the transmit power for the transmission. The method of claim 23, wherein The controller is operative to adjust the erase threshold to achieve a target condition error rate indicating a predetermined probability that the received codeword is to be decoded including an error when declared as a non-erase codeword. . The method of claim 23, wherein And the controller is operative to adjust the target SNR to achieve a target erase rate indicative of a predetermined probability of declaring a received codeword as an erase codeword. The method of claim 23, wherein And said transmission is for a control channel. The method of claim 27, Wherein said control channel is used for transmitting channel quality information, wherein each transmitted codeword is for a channel quality indicator. The method of claim 23, wherein And the received known codewords are obtained from a number of different transmitting entities. The apparatus of claim 23, which is used in a base station. The apparatus of claim 23, which is used in a wireless terminal. An apparatus operable to perform power control for a transmission sent over a wireless channel in a wireless communication system, comprising: Means for obtaining received codewords for codewords transmitted in the transmission, where each transmitted codeword is a block of coded or uncoded data, and each received codeword is a noise version of the transmitted codeword Im-; Means for determining a state of each received codeword as an erase codeword or a non-erase codeword based on the calculated metric and an erase threshold for the received codeword; Means for adjusting a target signal quality (SNR) based on the state of each received codeword, wherein the transmit power for the transmission is adjusted based on the target SNR; Means for obtaining received known codewords for known codewords transmitted over the wireless channel, where each known codeword is a block of known data and each received known codeword is a noise of a known codeword transmitted. Version-; Means for determining the status of each received known codeword as a good codeword, a bad codeword, or an erase codeword, wherein the good codeword is a received known codeword that is considered an unerased codeword and is correctly decoded, and A bad codeword is considered a non-erase codeword but is a received known codeword decoded including an error; And Means for adjusting the erase threshold based on the state of each received known codeword; Power control unit. 33. The method of claim 32, Means for estimating a received SNR for the transmission; Means for comparing the received SNR with the target SNR; And Means for generating instructions based on the results of the comparison, wherein the instructions are used to adjust the transmit power for the transmission.

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