MXPA06014940A - Robust erasure detection and erasure-rate-based closed loop power control - Google Patents

Abstract

Techniques for performing erasure detection and power control for a transmission without error detection coding are described. For erasure detection, a transmitter transmits code words via a wireless channel. A receiver computes a metric for each received codeword, compares the computed metric against an erasure threshold, and declares the received codeword to be"erased"or"non-erased". The receiver dynamically adjusts the erasure threshold based on received known codeword to achieve a target level of performance. For power control, an inner loop adjusts the transmit power to maintain a received signal quality (SNR) at a target SNR. An outer loop adjusts the target SNR based on the status of received codewords(erased or non-erased) to achieve a target erasure rate. A third loop adjusts the erasure threshold based on the status of received known codewords ("good","bad", or erased) to achieve a target conditional error rate.

Description

DETECTION OF ROBUST DELETION AND LOOP POWER CONTROL CLOSED BASED ON DELETE SPEED FIELD OF THE INVENTION The present invention generally relates to data communication, and more specifically to techniques for executing erasure detection and power control in a wireless communication system.

BACKGROUND OF THE INVENTION A multiple access wireless communication system can simultaneously support communication for multiple wireless terminals. Each terminal establishes communication with one or more base stations through transmissions in forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. Multiple terminals can, simultaneously, transmit on the reverse link multiplexing their transmissions to be orthogonal to each other. Multiplexing attempts to achieve orthogonality among the multiple reverse link transmissions in time, frequency and / or code domain. The complete orthogonality, if achieved, results in the transmission from each terminal that does not interfere with the transmissions of other terminals in a receiving base station. However, the complete orthogonality between transmissions from different terminals is often not made due to channel conditions, receiver imperfections, and so on. The loss in orthogonality results in each terminal producing certain amounts of interference for other terminals. The performance of each terminal is then degraded due to the interference of all other terminals. In the reverse link, a power control mechanism can be used to control the transmit power of each terminal in order to ensure good performance for all terminals. This power control mechanism is usually executed with two power control loops, which are often referred to as an "internal" loop and an "external" loop. The internal loop adjusts the transmit power of a terminal, so that its received signal quality (SNR), as measured in a receiving base station, is maintained in a target SNR. The external loop adjusts the target SNR to maintain a block error rate (BLER) or desired packet error rate (PER). The conventional power control mechanism adjusts the transmit power of each terminal, so that the desired packet / block error rate is achieved for the transmission of the reverse link from the terminal. An error detection code, such as a cyclic redundancy check (CRC) code, is typically used to determine whether each received block / data packet is decoded correctly or in error. The target SNR is then adjusted accordingly, based on the result of the error detection decoding. However, an error detection code may not be used for some transmissions, for example, if the overload for the error detection code is considered excessive. A conventional power control mechanism that is based on an error detection code can not be used directly for these transmissions. Therefore, there is a need for techniques to appropriately adjust the transmission power for a transmission when the error detection coding is not used.

SUMMARY OF THE INVENTION Here, techniques for erasing erasure detection and power control for a transmission in a "physical" channel (e.g., a control channel or a data channel) that does not employ error detection coding are described. The data is transmitted as "key words" in the physical channel, where each keyword can be a block of encoded or uncoded data. For erasure detection, a transmission entity (e.g., a wireless terminal) transmits keywords in the physical channel and through a wireless channel to a receiving entity (e.g., a base station). The base station calculates a metric for each received keyword, as described below, and compares the calculated metric against the clear threshold. The base station declares each received keyword to be a "deleted" keyword, or a "not deleted" keyword based on the comparison result. The base station dynamically adjusts the erase threshold to achieve a target performance level, which can be quantified by means of a target conditional error rate that indicates the probability that a received keyword will be decoded in error when declared as a keyword not deleted The erasure threshold can be adjusted based on the known received keywords, which are received key words for known key words transmitted by the terminals in communication with the base station, as described below. The adjustable erasure threshold can provide robust erasure detection performance in various channel conditions. A power control mechanism with three loops (an internal loop, an external loop, and a third loop) can be used to control the transmit power for the physical channel. The internal loop adjusts the transmit power so that the physical channel maintains the received SNR at or near a target SNR. The external loop adjusts the target SNR based on the state of the received keywords (erased or not erased) to achieve an objective erasure speed, which is the probability of declaring a received keyword as an erased keyword. The third loop adjusts the erase threshold based on the state of the known known keywords ("good", "bad", or erased) to achieve the target conditional error rate. The target erase rate and the target conditional error rate are two performance measures for the physical channel. In the following, various aspects and embodiments of the invention are described in greater detail.

BRIEF DESCRIPTION OF THE FIGURES The characteristics and nature of the present invention will be more apparent from the detailed description that is mentioned below, when considered in conjunction with the figures, wherein similar reference characters are identified correspondingly in the text and where: Figure 1 shows a multiple access wireless communication system; Figure 2 shows a power control mechanism with three loops; Figures 3A and 3B show a process for updating the second and third loops for the power control mechanism shown in Figure 2; Figure 4 shows data and control channels for a data transmission scheme; and Figure 5 shows a block diagram of a base station and a terminal.

DETAILED DESCRIPTION OF THE INVENTION The word "exemplary" here is used to say "what serves as an example, case or illustration". Any modality or design herein described as "exemplary" will not necessarily be construed as preferred or advantageous over other modalities or designs. Figure 1 shows a multiple access wireless communication system 100. The 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 establish communication with the terminals and it can also be referred to as an access point, a Node B, or some other terminology. The terminals 120 are typically dispersed in the system, and each terminal can be fixed or mobile. A terminal may also be referred to as a mobile station, a user equipment (UE), a wireless communication device, or some other terminology. Each terminal can establish communication with one or more base stations in the forward and reverse links at any given moment. This depends on whether the terminal is active, whether a soft transfer is supported, and whether the terminal is in soft transfer. For simplicity, Figure 1 only shows transmissions on the reverse link. A system controller 130 is coupled to the base stations 110, provides coordination and control for these base stations, and further controls the data routing for the terminals that receive service from these base stations. The erasure detection and power control techniques described here can be used for several wireless communication systems. For example, these techniques can be used for a Code Division Multiple Access (CDMA) system, a Time Division Multiple Access (TDMA) system, a Frequency Division Multiple Access (FDMA) system, a system of Multiple Access by Division of Orthogonal Frequency (OFDMA), and so on. A CDMA system uses code division multiplexing, and transmissions for different terminals are orthogonalized by using different orthogonal codes (for example, Walsh) for the forward link. The terminals use different sequences of pseudo-random numbers (PN) for the reverse link in CDMA and are not completely orthogonal to each other. A TDMA system uses time division multiplexing, and transmissions for different terminals are orthogonalized by transmission in different time intervals. An FDMA system uses multiplexing by frequency division, and transmissions for different terminals are orthogonalized by transmission in different frequency sub-bands. An OFDMA system uses orthogonal frequency division multiplexing (OFDM), which effectively divides the bandwidth of the global system into a number of orthogonal frequency sub-bands. These sub-bands are also commonly referred to as tones, sub-carriers, deposits and frequency channels. An OFDMA system can use several orthogonal multiplexing schemes and can employ any combination of time division multiplexing, frequency and / or code. The techniques described herein can be used for several types of "physical" channels that do not employ error detection coding. Physical channels can also be referred to as code channels, transport channels, or some other terminology. Physical channels typically include "data" channels used to send traffic / packet data and "control" channels used to send control / overload data. A system can use different control channels to send different types of control information. For example, a system may use (1) a CQI channel to send channel quality indicators (CQI) indicating the quality of a wireless channel, (2) an ACK channel to send acknowledgments (ACK) for an automatic retransmission scheme hybrid (H-ARQ), (3) a REQ channel to send data transmission requests and so on. Physical channels may or may not use other types of encoding, even if error detection encoding is not used. For example, a physical channel may not use any coding, and the data is sent "free" in the physical channel. A physical channel can also use block coding, so that each block of data is coded to obtain a corresponding block of encoded data, which is then sent in the physical channel. The techniques described here can be used for any and all of these different physical channels (data and control). For clarity, the erasure detection and power control techniques are specifically described below for an exemplary control channel used for the reverse link. The transmissions from different terminals in this control channel can be multiplexed orthogonally in space of frequency, time, and / or code. With full orthogonality, no interference is observed for each terminal in the control channel. However, in the presence of selective frequency fading (or variation in frequency response across the system bandwidth) and Doppler (due to motion), transmissions from different terminals may not be orthogonal to each other at a base station of reception. The data is sent in blocks in the exemplary control channel, where each block contains a predetermined number of (L) data bits. Each data block is encoded with a block code to obtain a corresponding keyword or block of coded data. Because each data block contains L bits, there are 2 different possible data blocks that are mapped to 2L possible keywords in an encryption and decryption code, one keyword for each different data block. The terminals transmit keywords for the data blocks in the control channel. A base station receives the keywords transmitted in the control channel by different terminals. The base station executes the complementary block decoding in each received keyword to obtain a decoded data block, which is a block of data that is considered most likely to have been transmitted for the received keyword. The block decoding can be done in several ways. For example, the base station can calculate a Euclidean distance between the received keyword and each of the 2L possible valid keywords in the encryption and decryption code. In general, the Euclidean distance between the received keyword and a given valid keyword is shorter the closer the keyword received to the valid keyword is, and the longer it is the further away the keyword received from the keyword is valid The data block corresponding to the valid keyword with the shortest Euclidean distance to the received keyword is provided as the decoded data block for the received keyword. As an example, the L data bits for a data block, can be mapped to a keyword containing K modulation symbols for a particular modulation scheme (for example, BPSK, QPSK, M-PSK, M-QAM, and so on ). Each valid keyword is associated with a different set of K modulation symbols, and the 2L sets of modulation symbols for the 2L possible valid keywords can be selected to be as separate (in Euclidean distance) from each other as possible. possible. A received keyword would then contain K received symbols, wherein each received symbol is a noisy version of a transmitted modulation symbol. The Euclidean distance between the received keyword and a given valid keyword can be calculated as: Equation 1 where §k (j) is the jth symbol received for the received keyword k; If (j) is the j-th modulation symbol for the valid keyword i; and say. { k) is the Euclidean distance between the received keyword A: and the valid keyword i. Equation (1) calculates the Euclidean distance as the mean square error between the K symbols received for the received keyword and the K modulation symbols for the valid keyword. The data block corresponding to the valid keyword with the smallest d (J) is provided as the decoded data block for the received keyword. Without an error detection code, there is no direct way to determine if the block decoding of a given received keyword is correct or in error, and if the block of. Decoded data is, in fact, the data block transmitted. A metric can be defined and used to provide an indication of the confidence in the decoding result. In one modality, a metric can be defined as follows m (k) = dn2 (k) Equation 2 where dni (k) is the Euclidean distance between the received keyword J and the nearest valid keyword; dnz. { ) is the Euclidean distance between the received keyword Je and the next nearest valid keyword; Y (k) is the metric for the received keyword k.

If the received keyword is much closer to the nearest keyword than the next closest keyword, then the metric m (k) is a small value and there is a high degree of confidence that the decoded data block is correct . Conversely, if the received keyword has approximately a distance equal to the closest keyword and the next closest keyword, then the metric m. { k) approaches one, or m (k)? l, and there is less confidence that the decoded data block is correct. Equation (2) shows an exemplary metric that is based on the relationship of Euclidean distances and that can be used to determine whether the block decoding of a given received keyword is correct or in error. Other metrics for erasure detection may also be used, and this is within the scope of the invention. In general, a metric can be defined based on any convenient reliability function f (r, C), where r is a received keyword and C is an encryption and decryption code or collection of all possible keywords. The function f. { r, C) should be indicative of the quality / reliability of a received keyword and should have the appropriate characteristic (eg, monotonic with detection reliability). Erase detection can be performed to determine if the decoding result for each received keyword meets a predetermined confidence level. The metric m. { k) for a received keyword can be compared against an erase threshold, THB, to obtain a decoding decision for the received keyword, in the following way: m (k) < THborrar, declares a non-barred keyword, m (k) > THboc declares a barred keyword. Equation 3 As shown in equation (3), the received keyword is declared as (1) a "deleted" keyword if the metric m (k) is equal to, or greater than, the erasure threshold and (2) a word key "not erased" if the metric (k) is less than the erasure threshold. The base station can process the decoded data blocks for deleted and not erased keywords differently. For example, the base station may use decoded data blocks for non-erased keywords for further processing and may discard the decoded data blocks for erased keywords. The probability of declaring a received keyword as an erased keyword is called an erase speed and is denoted as Prororate. The erase rate depends on the erase threshold used for erasure detection and the received signal quality (SNR) for the received keyword. The signal quality can be quantified by a signal-to-noise ratio, a signal-to-noise-e-interference ratio, and so on. For a given received SNR, a low erasure threshold increases the probability that a received keyword will be declared as an erased keyword, and vice versa. For a given erase threshold, a low SNR received also increases the probability that a received keyword will be declared as an erased keyword, and vice versa. For an erase threshold, the received SNR can be configured (by controlling the transmit power for the control channel, as described below) to achieve the desired erase rate. The erase threshold can be configured to achieve the desired performance for the control channel. For example, a conditional error probability in non-erased keywords, which is called a conditional error rate, can be used for the control channel. This conditional error rate is denoted as Prerror and means the following: Because a received keyword is declared as a non-deleted keyword, the probability that the decoded data block for the received keyword is incorrect is Prerror >; A low Prerror (for example 1% or 0.1%) corresponds to a high degree of confidence in the decoding result when a non-deleted keyword is declared. A low Prerror may be desirable for many types of transmission where reliable decoding is important. The erase threshold can be set at the appropriate level to achieve the desired Prerror. We can expect the existence of a well-defined relationship between the erase speed Prorbar / conditional error rate Prerror, the erase threshold THborrar, and the received SNR. In particular, for a given clearing threshold and a given received SNR, there is a specific clearing speed and a specified conditional error rate. When changing the erase threshold, a trade-off between the erase speed and the conditional error rate may occur. A computer simulation can be performed and / or empirical measurements can be taken to determine or predict the relationship between the erase speed and the conditional error rate for different erasure threshold values and different received SNRs. However, in a practical system, the relationship between these four parameters may not be known in advance and may depend on deployment scenarios. For example, the specific erase threshold that can achieve the desired erase speed and the conditional error rate may not be known a priori and may even change over time, but probably slowly. Furthermore, it is not known if the "predicted" relationship between the speed of erasure and the conditional error rate, obtained through simulation or some other means, will remain true in a real deployment. A power control mechanism can be used to dynamically adjust the erasure threshold and the received SNR to achieve the desired performance for the control channel. The performance of the control channel can be quantified by a clear erase target speed (for example, 10% clear speed, or Prb0rrar = 0.1) and a target error rate conditional Prerror (for example, 1% error rate conditional, or Prerror = 0.01), that is, a Prerror pair) · Figure 2 shows a power control mechanism 200 that can be used to dynamically adjust the erase threshold and to control the transmission power for a transmission sent in the control channel from a terminal to a base station. The power control mechanism 200 includes an internal loop 210, an external loop 220, and a third loop 230. The internal loop 210 attempts to maintain the received SNR for transmission, as measured at the base station, as close as possible of a target SNR. For the internal loop 210, a SNR estimator 242 in the base station calculates the SNR received for the transmission and provides the received SNR to a transmission power control (TPC) generator 244. The TPC generator 244 also receives the target SNR for the control channel, it compares the received SNR against the target SNR, and generates TPC commands based on the comparison results.

Each TPC command is (1) an UP command to direct an increase in transmit power for the control channel or (2) a DESCENDENT command to direct a reduction in transmit power. The base station transmits the TPC commands in the forward link (cloud 260) to the terminal. The terminal receives and processes the forward link transmission from the base station and provides "received" TPC commands to a TPC processor 262. Each received TPC command is a noisy version of a TPC command sent by the base station. The TPC processor 262 detects each received TPC command and obtains a TPC decision, which may be (1) a UP decision if the received TPC command is considered to be a UPCOMING command or (2) a DESCENDING decision if the received TPC command is considers that it is a DESCENDING command. A transmission power adjustment unit (TX) 264 adjusts the transmission power for the transmission in the control channel based on the TPC decisions of the TPC processor 262. The unit 264 can adjust the transmission power in the following way: + J > a ascending for an UP decision, descending for a DESCENDING decision, Equation 4 where PCCh (^) is the transmission power for the internal loop update interval n; APascent is a step-up size for the transmission power; and AP descending is a down-pass size for the transmission power. The PCCh transmission power (-n) and the APaScendente and APdescendente pass sizes are in units of decibels (dB). As shown in equation (4), the transmit power is incremented by the ascending AP for each UP decision and decreased by the AP descending for each DESCENDING decision. Although not previously described for simplicity, a TCP decision can also be a "non-OP" decision if a received TPC command is considered very unreliable, in which case, the transmission power can be kept at the same level, or CCP ( -n + l) = Pcch (^). The AP and Back-up AP sizes are typically the same, and both can be set to 1.0 dB, 0.5 dB, or some other value. Due to path loss, fading and multipath effects in the reverse link (cloud 240), which typically vary over time and especially for a mobile terminal, the SNR received for transmission in the channel control fluctuates continuously. The internal loop 210 attempts to keep the SNR received at or near the target SNR in the presence of changes in the channel condition of the reverse link. The external loop 220 continuously adjusts the target SNR so that the target clearing speed is achieved for the control channel. A metric calculation unit 252 calculates the metric m. { k) for each received received keyword from the control channel, as described above. An erase detector 254 performs deletion detection for each received keyword based on the calculated metric (m) for the keyword and the erase threshold and provides the status of the received keyword (either deleted or not deleted) to a target SNR adjustment unit 256. The target SNR adjustment unit 256 obtains the status of each received keyword and adjusts the target SNR for the control channel, as follows: [SNR O, target (K) + ASNR, for a deleted keyword SNR ', target (* +!) = SNR', target (K) - &SNRdown, e, for a keyword not deleted Equation 5 where . { k) is the target SNR for the external loop update interval k; ASNRascendant is a step-up size for the target SNR; and AS R descending is a step-down size for the target SNR. The SNR target SNRDlbjet vo (k) and the step sizes ASNRasCendente V ASNRdeScendente are in units of dB. As shown in equation (5), the unit 25 6 reduces the target SNR by ASNR ofScendent if a received keyword is considered as a non-deleted keyword, which may indicate that the received SNR for the control channel is higher than necessary. Conversely, unit 25 6 increases the target SNR per ASNR ascending if a received keyword is considered as an erased keyword, which may indicate that the received SNR for the control channel is below what is necessary. The ASNRasCendente and the ASNRdeScendente pads sizes to adjust the target SNR can be established based on the following relationship: Equation 6 For example, if the target erase speed for the control channel is 10% (or Prbrate = 0. 1), then the step size is 9 times the size of the downward step (or ASNRascendant = 9 · ASNRdown) · Yes the rising step size is selected to be equal to 0.5 decibels (dB), then the downslope size is approximately 0.056 dB. Larger values for rising ASNR and rising ASNR accelerate the convergence rate for external loop 220. A large value for ascending ASNR also causes more fluctuation or variation of the target SNR in a constant state. The third loop 230 dynamically adjusts the clear threshold so that the target conditional error rate is achieved for the control channel. The terminal can transmit a known key word in the control channel periodically or whenever it is activated. The base station receives the known transmitted keyword. The metric calculation unit 252 and the deletion detector 254 perform erasure detection for each known keyword received based on the erasure threshold and in the same manner as for the received keywords. For each received known keyword that is considered not deleted, a decoder 262 decodes the known known keyword and determines whether the decoded data block is correct or in error, which can be done because the keyword is known. The decoder 262 provides a deletion threshold adjustment unit 264 the status of each known received keyword, which may be: (1) an erased keyword, (2) a "good" keyword if the known keyword received is a keyword not deleted and is decoded correctly, or (3) a "bad" keyword if the known keyword received is a keyword not deleted but is decoded in error. The erasure threshold adjustment unit 264 obtains the status of the known known keywords and adjusts the erasure threshold, as follows: TH delete a) + A TH 'ascending Pa ™ A word cldVe bwna, THhorrar (e + i) = \ TH delete á) ~ TH' descending '? ° ™ Unü Pal bra key ala, and [THhorrar (£), for an erased keyword, Equation 7 where THborrar (i) is the erase threshold for the update interval of the third bond £; ATHascendente is an ascending step size for the erase threshold; and ATH descending is a step-down size for the erase threshold. As shown in equation (7), the erase threshold is reduced by ATHdesCendente for each known keyword received which is a bad keyword. The lower erasure threshold corresponds to a stricter erasure detection criterion and results in a received keyword with a higher likelihood of being considered erased, which in turn results in the received keyword being more likely to be decoded correctly when it is considered not deleted. Conversely, the erase threshold is incremented by ascending ATH for each known keyword received which is a good keyword. The upper erasure threshold corresponds to a less strict erasure detection criterion and results in a received keyword with a lower probability of being considered erased, which in turn results in the received keyword having a higher probability of being decoded in error when considered not deleted. The erase threshold is kept at the same level for the known received received keywords that are deleted. The step sizes ATHaScendente and ATHdesCendente for the adjustment of the erase threshold can be established based on the following relationship: ATH, descending = ATH a, scendente Equation 8 For example, if the conditional or etive error rate for the control channel is 1%, then the down-pass size is 99 times the step-up size. The magnitude of ATHaScendente and ATHdescendente can be considered based on the expected magnitude of the symbols received, the desired convergence speed for the third loop, and possibly other factors. In general, the setting of the erase threshold depends on how the metric used for the erase detection is defined. Equations (7) and (8) are based on the metric defined as shown in equation (2). The metric can also be defined in other ways (for example, m { K) = dn2 (k) / dní (k) instead of m (k) = dnl (k) / dn2 (k)), in which In this case, the erasure threshold setting can be modified accordingly. The adjustable erasure threshold can also be used in combination with any erasure detection technique to achieve robust erasure detection performance for various channel conditions. The erase threshold, THb0rrar (i) can be adjusted dynamically in several ways. In one embodiment, a third separated loop is maintained by the base station for each terminal in communication with the base station. This mode allows the erase threshold to be adjusted individually for each terminal, which then allows the performance of the control channel to be adjusted specifically for the terminal. For example, different terminals may have different target conditional error rates, which can be achieved by operating separate third-party links for these terminals. In another embodiment, a single third link is maintained by the base station for all terminals in communication with the base station. The common erasure threshold is then used for erasure detection for all these terminals and is also updated based on known keywords received by the base station from these terminals. This mode provides good performance for all terminals, if the control channel performance is robust for these terminals for various channel conditions. This mode allows a faster convergence speed for the third loop and also reduces the overhead because each terminal can transmit the known keyword at a lower speed (for example, once every few hundred milliseconds). In still another embodiment, a single third loop is maintained by the base station for each group of terminals that has the same control channel performance, and the clearing threshold is updated based on the keywords received by the base station from all terminals in the group. The internal loop 210, external loop 220, and third loop 230 are typically updated at different speeds. The internal loop 210 is the fastest loop of the three loops, and the transmission power for the control channel can be updated at a particular speed (for example, 150 times per second). External loop 220 is the next fastest loop, and the target SNR can be updated whenever a keyword is received in the control channel. The third loop 230 is the slowest loop, and the clearing threshold can be updated whenever a known keyword is received in the control channel. The refresh rates for the three loops can be selected to achieve the desired performance for erasure detection and power control. For the modality described above, the target conditional error rate Prerror is used as one of the performance measurements for the control channel, and the third loop is designed to achieve this Prerror- Other performance measurements can also be used for the channel of control, and the third loop can be designed accordingly. For example, an objective probability that a received keyword will be decoded in error when it is considered deleted, can be used for the third link. Figures 3A and 3B show a flow chart of a process 300 for updating the second and third loops of the power control mechanism 300. A received key word k is initially obtained from the control channel (block 312). The metric m. { k) is calculated for the received keyword, for example, as described above, (block 314) and compared against the erase threshold (block 316). If the calculated metric m (k) is greater than, or equal to, the erase threshold, as determined in block 320, and if the received keyword is not a known keyword, as determined in block 322, then the received keyword is declared as an erased keyword (block 324). The target SNR is increased by the step size ASNR ascending if the calculated metric. { k) is greater than, or equal to, the erasure threshold, without considering whether the keyword is known or unknown (block 326). After block 326, the process returns to block 312 to process the next received keyword. If the calculated metric m. { k) is less than the erasure threshold, as determined in block 320, and if the received keyword is not a known keyword, as determined in block 332, then the received keyword is declared as a keyword not deleted (block 334), and the target SNR is reduced by the step size ASNR descending (block 336). The process returns to block 312 to process the next received keyword. If the calculated metric. { k) is less than the erasure threshold, as determined in block 320, and if the received keyword is a known key word, as determined in block 332, then (referring to figure 3B), the word received key is decoded (block 340). If the decoding was successful, as determined in block 342, then the known known received keyword is declared as a good keyword (block 344), and the clearing threshold is increased by the ascending ATH step size (block 346). Otherwise, if there was a decoding error, as determined in block 342, then the known known received keyword is declared as a bad keyword (block 354), and the clearing threshold is reduced by the step size ATHde Scendente (block 356). From blocks 346 and 356, the process returns to block 312 in FIG. 3A to process the next received keyword. As noted above, the techniques described herein can be used for several types of physical channels that do not employ error detection coding. The use of these techniques for an exemplary data transmission scheme is described below. For this transmission scheme, a terminal, which wants a forward link transmission, calculates the quality of the signal received from the forward link for its service base station (for example, based on a pilot transmitted by the base station) . The quality estimate of the received signal can be translated to a value of L-bits, which is called a channel quality indicator (CQI). The CQI can indicate the received SNR for the forward link, the data rate supported for the forward link, and so on. In any case, the block coding is done in the CQI to obtain a CQI keyword. As a specific example, L can be equal to 4, and the CQI keyword can contain 16 QPSK modulation symbols, or [Si (l) s (2) ... s¿ (16)]. The terminal transmits the CQI keyword in the CQI channel (which is one of the control channels) to the service base station. The service base station receives the keyword from the CQI sent in the CQI channel and executes erasure detection in the received CQI keyword. If the received CQI keyword is not deleted, then the serving base station decodes the received CQI keyword and uses the decoded CQI to schedule a data transmission for the terminal. Figure 4 shows a set of data and control channels that are used for the exemplary data transmission scheme. The terminal measures the signal quality received from the forward link and transmits a CQI keyword in the CQI channel. The terminal continuously takes measurements of the quality of the forward link and sends CQI keywords updated in the CQI channel. Therefore, the fact of discarding received CQI keywords, considered as deleted, is not detrimental to the performance of the system. However, the received CQI keywords, considered as not deleted, should be of high quality because a forward link transmission can be programmed based on the information contained in these non-deleted CQI keywords. If the terminal is programmed for forward link transmission, then the serving base station processes data packets to obtain coded packets and transmits the encoded packets on a forward link data channel to the terminal. For a hybrid automatic retransmission scheme (H-ARQ), each coded packet is divided into multiple sub-blocks, and one sub-block is transmitted at a time for the coded packet. As each sub-block for a given coded packet is received on the forward link data channel, the terminal tries to decode and recover the packet based on all the sub-blocks received up to that moment for the packet. The terminal can recover the packet based on a partial transmission, because the sub-blocks contain redundant information that is useful for decoding when the received signal quality is poor but may not be necessary when the received signal quality is good. The terminal then transmits an acknowledgment (ACK) on an ACK channel if the packet is decoded correctly, or else a negative acknowledgment (NAK). The transmission of the forward link continues in this manner until all the encoded packets are transmitted to the terminal. The techniques described herein can be used conveniently for the CQI channel. Erase detection can be performed on each CQI keyword received as described above. The transmit power for the CQI channel can be adjusted using the power control mechanism 300 to achieve the desired performance for the CQI channel (e.g., the desired erase rate and the desired conditional error rate). The transmission power for other control channels (eg, the ACK channel) and reverse link data channels can also be established based on the controlled power transmission power for the CQI channel. For clarity, the erasure detection and power control techniques have been described specifically for the reverse link. These techniques can also be used for erasure detection and power control for a transmission sent on the forward link. Figure 5 shows a block diagram of a mode of a base station HOx and a terminal 120x. In the reverse link, at the 120x terminal, a transmission data processor (TX) 510 receives and processes (eg, formats, encodes, interleaves and modulates) the reverse channel (RL) traffic data and provides modulation symbols. for traffic data. The data processor TX 510 also processes control data (eg, CQI) from a controller 520 and provides modulation symbols for the control data. A modulator (MOD) 512 processes the modulation symbols for traffic and control data and pilot symbols and provides a sequence of chips with complex values. The processing by the data processor TX 510 and the modulator 512 depends on the system. For example, modulator 512 can execute OFDM modulation if the system uses OFDM. A transmitter unit (TMTR) 514 conditions (for example, converts to analog, amplifies, filters and over-converts to frequency) the chip sequence and generates a reverse link signal, which is guided through a duplexer (D) 516 and transmitted through an antenna 518. In the base station HOx, the reverse link signal of the terminal 120x is received by an antenna 552, guided through a duplexer 554, and provided to a receiver unit (RCVR) 556 The receiving unit 556 conditions (for example, filters, amplifies and sub-converts into frequency) the received signal and also digitizes the conditioned signal to obtain a stream of data samples. A demodulator (DEMOD) 558 processes the data samples to obtain symbol estimates. A reception data processor (RX) 560 then processes (e.g., deinterleaves and decodes) the symbol estimates to obtain decoded data for the 120x terminal. The RX 560 data processor also performs deletion detection and provides a 570 controller with the status of each received keyword that was used for power control. The processing by the demodulator 558 and the data processor RX 560 is complementary to the processing performed by the modulator 512 and the data processor TX 510, respectively. The processing for a forward link transmission can be executed in a manner similar to that described above for the reverse link. The processing for reverse link and forward link transmissions is typically specified by the system. For power control of the reverse link, an SNR estimator 574 estimates the received SNR for the 120x terminal and provides the received SNR to a TPC 576 generator. The TPC 576 generator also receives the target SNR and generates TPC commands for the 120x terminal. The TPC commands are processed by a data processor TX 582, further processed by a modulator 584, conditioned by a transmitter unit 586, guided through a duplexer 554 and transmitted through an antenna 552 to the terminal 120x. At the terminal 120x, the forward link signal from the base station HOx is received by the antenna 518, guided through the duplexer 516, conditioned and digitized by a receiver unit 540, processed by a demodulator 542, and further processed by a RX 544 data processor to get received TPC commands. A TPC processor 524 then detects the received TPC commands to obtain TPC decisions, which are used to generate a transmission power adjustment control. The modulator 512 receives control of the TPC 524 processor and adjusts the transmission power for the transmission of the reverse link. The power control of the forward link can be achieved in a similar way. The controllers 520 and 570 direct the operations of several processing units within the terminal 120x and the base station HOx, respectively. The 520 and 570 controllers can also perform various functions for erasure detection and power control for the forward link and the reverse link. For example, each controller can run the SNR estimator, the TPC generator, and the target SNR adjustment unit for its link. The controller 570 and the data processor RX 560 can also execute the process 300 in FIGS. 3A and 3B. The memory units 522 and 572 store program and data codes for the controllers 520 and 570, respectively. The erasure detection and power control techniques described herein can be executed through various means. For example, these techniques can be executed in hardware, software, or a combination thereof. For a hardware execution, the processing units used to execute the erasure detection and / or power control may be performed within one or more specific application integrated circuits (ASIC), digital signal processors (DSP), digital signal processing (DSPD), programmable logic devices (PLD), field-programmable gate arrays (FPGA), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described here, or a combination thereof. For a software execution, the techniques described herein can be executed with modules (for example, procedures, functions, and so on) that perform the functions described herein. The software codes can be stored in a memory unit (e.g., memory unit 572 in Figure 5) and executed through a processor (e.g., controller 570). The memory unit can be executed inside the processor or outside the processor, in which case it can be communicatively coupled to the processor through various means, as is known in the art. The prior description of the described embodiments is provided to enable those skilled in the art to make or use the present invention. Various modifications to these modalities will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not intended to be limited to the modalities shown herein but will be accorded the broadest scope consistent with the principles and novel features described herein.

Claims (33)

NOVELTY OF THE INVENTION Having described the present invention, consider as a novelty and, therefore, priority is claimed as contained in the following: CLAIMS

1. - A method for executing erasure detection in a communication system, comprising: obtaining received keywords for keywords transmitted through a wireless channel, each transmitted keyword is a block of encoded or decoded data, and each received keyword it is a noisy version of a transmitted keyword; calculate a metric for each of the received keywords; compare the calculated metric for each received keyword against a clear threshold; declare each received keyword as an erased keyword or a non-erased keyword based on a comparison result for the received keyword; and dynamically adjust the erase threshold to achieve a target level of performance for erasure detection.

2. The method according to claim 1, further comprising: obtaining known key words received for known key words transmitted through the wireless channel, each known key word is a block of known data, and each received known key word is a noisy version of a known key word transmitted; determine a state of each of the known keywords received as a good keyword, a bad keyword or an erased keyword, a good keyword is a known known received keyword that is declared as a non-erased keyword and is decoded correctly, and a bad keyword is a known keyword received that is declared as a keyword not deleted but that is decoded in error; and adjust the erase threshold based on the state of each known keyword received.

3. The method according to claim 2, characterized in that the known keywords are transmitted at known times by one or more transmission entities.

4. - The method according to claim 2, characterized in that the known keywords are transmitted by a transmission entity when they are directed.

5. - The method according to claim 1, characterized in that a non-erased keyword is associated with a particular confidence level of having been received correctly, and an erased keyword is associated with a particular level of confidence of having been received in error

6. - The method according to claim 1, characterized in that the target level of performance, for the detection of erase, is an objective conditional error rate indicative of a predetermined probability that a received keyword is decoded in error if it is declared as a non-deleted keyword.

7. - The method according to claim 1, characterized in that each transmitted keyword is one of a plurality of possible valid keywords, and wherein the metric is based on a function indicative of the reliability of a received keyword.

8. - The method according to claim 7, characterized in that the metric for each received keyword is a ratio of a Euclidean distance to a valid keyword closest to a Euclidean distance to a next nearest valid keyword, the distance Euclidean to the nearest valid keyword is the Euclidean distance between the received keyword and a valid keyword closest to the received keyword, and the Euclidean distance to the next nearest valid keyword is the Euclidean distance between the keyword received and a valid keyword next closest to the received keyword.

9. - The method according to claim 1, characterized in that each transmitted keyword is a block of encoded data obtained by executing block coding in a block of decoded data.

10. - The method according to claim 1, characterized in that each transmitted keyword does not include an error detection code.

11. - An operable apparatus for executing erasure detection in a wireless communication system, comprising: a metric calculation unit operative to obtain received key words for keywords transmitted through a wireless channel and to calculate a metric for each one of the received keywords, wherein each transmitted keyword is a block of encoded or decoded data, and wherein each received keyword is a noisy version of a transmitted keyword; an operational erasure detector for comparing the calculated metric for each received keyword against an erasure threshold and for declaring each received keyword as an erased keyword or an erased keyword based on a comparison result for the received keyword; and an operating adjustment unit for dynamically adjusting the erasure threshold in order to achieve a target level of performance for erasure detection.

12. The apparatus according to claim 11, further comprising: a decoder operable to: obtain known key words received for known key words transmitted through the wireless channel, each known key word is a block of known data, and each known received keyword is a noisy version of a known keyword transmitted; decoding each received known keyword that is considered to be a non-deleted keyword, and determining a state of each of the known keywords received as a good keyword, a bad keyword or an erased keyword, a good keyword is a received known keyword that is declared as a non-deleted keyword and is correctly decoded, and a bad keyword is a received known keyword that is declared as a keyword not deleted but that is decoded in error; and wherein the adjustment unit is operative to adjust the erase threshold based on the state of each known received keyword.

13. An apparatus that operates to execute erase detection in a wireless communication system, comprising: means for obtaining received key words for keywords transmitted through a wireless channel, each transmitted keyword is a block of encoded data or decoded, and each received keyword is a noisy version of a transmitted keyword; means to calculate a metric for each of the received keywords; means for comparing the calculated metric for each received keyword against a clear threshold; means for declaring each received keyword as an erased keyword or a non-erased keyword based on a comparison result for the received keyword; and means for dynamically adjusting the erasure threshold to achieve a target level of performance for erasure detection.

14. - The apparatus according to claim 13, further comprising: means for obtaining known key words received for known key words transmitted through the wireless channel, each known key word is a block of known data, and each known key word received is a noisy version of a known transmitted keyword; means for determining a state of each of the known keywords received as a good keyword, a bad keyword or an erased keyword, a good keyword is a received known keyword that is declared as a non-erased keyword and it is decoded correctly, and a bad keyword is a known keyword received that is declared as a keyword not deleted but that is decoded in error; and means for adjusting the erase threshold based on the state of each known received keyword.

15. - A method for executing power control for a transmission sent through a wireless channel in a wireless communication system, comprising: obtaining received keywords for key words transmitted in the transmission, each transmitted keyword is a block of encoded or decoded data, and each received keyword is a noisy version of a transmitted keyword; determine a status of each keyword received as an erased keyword or a non-erased keyword based on a metric calculated for the received keyword and a clear threshold; adjust an objective signal quality (SNR) based on the status of each received keyword, where the transmission power for the transmission is adjusted based on the target SNR; obtain known known keywords for known keywords transmitted through the wireless channel, each known keyword is a block of known data, and each known known received keyword is a noisy version of a known transmitted keyword; determine a state of each of the known keywords received such as a good keyword, a bad keyword or an erased keyword, a good keyword is a known keyword received that is considered a keyword not erased and is decoded correctly, and a bad keyword is a known keyword received that is considered as a keyword not deleted but that is decoded in error; and adjust the erase threshold based on the state of each known keyword received.

16. - The method according to claim 15, characterized in that the adjustment of the target SNR includes: reducing the target SNR by a descending step for each received keyword that is considered as a non-deleted keyword; and increase the target SNR by one step up for each received keyword that is considered as an erased keyword.

17. - The method according to claim 16, characterized in that the descending step and the ascending step to adjust the target SNR are determined by means of a target erase rate indicative of a predetermined probability of declaring a received keyword as a word deleted key.

18. - The method according to claim 15, characterized in that a lower erasure threshold corresponds to a higher probability that a received keyword is considered an erased key word, and wherein the adjustment of the erasure threshold includes: reducing the erasing threshold by a downward step for each known keyword received that is considered a bad keyword; and increasing the clearing threshold by one ascending step for each known keyword received which is considered as a good keyword.

19. - The method according to claim 18, characterized in that the adjustment of the erasure threshold further includes: maintaining the erasure threshold at the same level for each received known key word that is considered as an erased keyword.

20. The method according to claim 18, characterized in that the descending step and the ascending step to adjust the erase threshold are determined by an objective conditional error rate indicative of a predetermined probability that a received keyword is decoded in error if it is declared as a non-deleted keyword.

21. - The method according to claim 15, characterized in that the known key words received are obtained from a plurality of different transmission entities.

22. - The method according to claim 15, further comprising: estimating a SNR received for the transmission; compare the received SNR against the target SNR; and generate commands based on the results of the comparison, where the commands are used to adjust the transmission potential for the transmission.

23. An apparatus that operates to execute power control for a transmission sent through a wireless channel in a wireless communication system, comprising: a data processor that operates to: obtain received key words for keywords transmitted in the transmission, each transmitted keyword is a block of encoded or decoded data, and each received keyword is a noisy version of a transmitted keyword; determine a status of each keyword received as an erased keyword or a non-erased keyword based on a metric calculated for the received keyword and a clear threshold; obtain known known keywords for known keywords transmitted through the wireless channel, each known keyword is a block of known data, and each known known received keyword is a noisy version of a known transmitted keyword; and determining a state of each known keyword received as a good keyword, a bad keyword or an erased keyword, a good keyword is a known keyword received that is considered as a keyword not erased and is decoded correctly, and a bad keyword is a known keyword received that is considered as a keyword not deleted but that is decoded in error; and a controller that operates to: adjust a target signal quality (SNR) based on the status of each received keyword, where the transmission potential, for transmission, is adjusted based on the target SNR, and adjust the erasure threshold based on the state of each known keyword received.

24. The apparatus according to claim 22, further comprising: an SNR estimator that operates to estimate a SNR received for transmission; and a generator that operates to compare the received SNR against the target SNR and generate commands that are used to adjust the transmission potential for the transmission.

25. - The apparatus according to claim 23, characterized in that the controller operates to adjust the erasure threshold in order to achieve an objective conditional error rate indicative of a predetermined probability of a received keyword that is decoded in error if it is declared as a keyword not barred.

26. - The apparatus according to claim 23, characterized in that the controller operates to adjust the target SNR in order to achieve a target erase rate indicative of a predetermined probability of declaring a received keyword as an erased keyword.

27. - The apparatus according to claim 23, characterized in that the transmission is for a control channel.

28. - The apparatus according to claim 27, characterized in that the control channel is used to send channel quality information, and where each transmitted keyword is for a channel quality indicator.

29. - The apparatus according to claim 23, characterized in that the known key words received are obtained from a plurality of different transmission entities.

30. - The apparatus according to claim 23, and is used in a base station.

31. - The apparatus according to claim 23, and is used in a wireless terminal.

32. - An apparatus that operates to execute power control for a transmission sent through a wireless channel in a wireless communication system, comprising: means for obtaining received keywords for keywords transmitted in the transmission, each transmitted keyword it is a block of encoded or decoded data, and each received keyword is a noisy version of a transmitted keyword; means for determining a state of each received keyword as an erased keyword or a non-erased keyword based on a calculated metric for the received keyword and a clear threshold; means to adjust an objective signal quality (SNR) based on the status of each received keyword, where the transmission power for the transmission is adjusted based on the objective SNR - means to obtain known keywords received for keywords known transmitted via the wireless channel, each known keyword is a block of known data, and each known received keyword is a noisy version of a known transmitted keyword; and means for determining a state of each known keyword received as a good keyword, a bad keyword or an erased keyword, a good keyword is a known known received keyword that is considered a non-erased keyword and is decoded correctly, and a bad keyword is a known keyword received that is considered as a keyword not deleted but that is decoded in error; and means for adjusting the erase threshold based on the state of each known received keyword. The apparatus according to claim 32, further comprising: means for estimating a SNR received for transmission; means for comparing the received SNR against the target SNR; and means for generating commands based on the results of the comparison, where the commands are used to adjust the transmission potential for the transmission.