MXPA06014944A - Power control using erasure techniques - 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 transmitpower based on whether the codewords met the erasure threshold or not.

Description

POWER CONTROL USING DELETION TECHNIQUES FIELD OF THE INVENTION The present invention generally relates to data communication, and more specifically to techniques for adjusting power control using erasure detection 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 between multiple reverse link transmissions in time domain, frequency and / or code. 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 (PER) speed. 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 block / data packet received 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 Accordingly, a method for executing power control in a communication system is provided, wherein the method comprises receiving a keyword through a first wireless link, generating a message to increase power if it is determined that the keyword does not met an erase threshold, generate a message to reduce power if it is determined that the keyword did not meet an erase threshold and transmit the message on the second wireless link. 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 control mechanism of power 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 a flow chart of a process 400 for the power control mechanism; Figure 5 shows data and control channels for a data transmission scheme; and Figure 6 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 herein 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 it uses multiplexing by code division, 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 multiplexing by time division, 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, frequency and / or code division multiplexing. The techniques described here can be used for several types of "physical" channels that do not use 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 movement), 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 (eg, 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: d, (k) =? (§k (j) - s, (j)) 2, 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 di (k) is the Euclidean distance between the received keyword Je 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 block of data corresponding to the valid keyword with the di. { k) smaller is provided as the decoded data block for the received keyword. Without an error detection code, there is no direct way to determine whether the block decoding of a given received keyword is correct or in error, and whether the decoded data block is, in fact, the transmitted data block. A metric can be defined and used to provide an indication of the confidence in the decoding result. In a modality, a metric can be defined in the following way: Equation 2 where dni (k) is the Euclidean distance between the received keyword k and the nearest valid keyword; dn2Ík) is the Euclidean distance between the received keyword Je and the next nearest valid keyword; and m. { k) is the metric for the received keyword k. If the received keyword is much closer to the nearest keyword than the next word closest key, 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 ra (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) < THb0rrar, declares a non-barred keyword, m (k) > Hb0rrar / declares a barred keyword. Equation 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 "not erased" keyword if the m (k) metric 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 keyword received as an erased keyword is called a erase speed and is denoted as Prborrar. 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 P ^ error and means the following: because a received keyword is declared as a non-keyword deleted, the probability that the data block decoded for the received keyword is incorrect is Prerror- A Prerror ba or (for example 1% or 0.1%) corresponds to a high degree of confidence in the decoding result when a keyword not deleted 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. One can expect the existence of a well-defined relationship between the erase speed P DO the conditional error rate Prerror / the erase threshold THBrite, 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 by anticipated 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 target erase speed Prb0rrar (for example, 10% speed of erasure, or Prborrar = 0.1) and a target conditional error rate Prerror (e.g., 1% error rate conditional, or Prerror = 0.01), that is, a pair (Proroar / Prerror) · Figure 2 shows a power control mechanism 200 that can be used to dynamically adjust the erasure threshold and to control the transmission power for a transmission sent on the control channel from a terminal to a base station. He power control mechanism 200 includes an internal loop 210, an external loop 220, and a third loop 230. Internal loop 210 attempts to maintain the received SNR for transmission, as measured at the base station, as close as possible to an objective 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 can be (1) a UP decision if the TPC command received is considered to be a UP command or (2) a DESCENDING decision if the received TPC command is considered to be a DESCENDENT 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: pcch («) + ^ aseadme For UYXa ASCENDING decision, Pcch (n +) = Pcch (n) - U > dmdenie for a DESCENDING decision, Equation 4 where PCch (-n) 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 descendant for each DESCENDING decision. Although it was not described previously for simplicity, a TC P decision can also be a "non-OP" decision if a received T PC command is considered to be very unreliable, in which case, the transmission power can be kept at the same level, or Pcch (n + 1) Pcch ( they 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 executes delete detection for each received keyword based on the calculated metric m. { k) for the keyword and the erase threshold and provides the status of the keyword received (either erased or not erased) to a target SNR adjustment unit 2 5 6. The target SNR adjustment unit 2 5 6 obtains the status of each received keyword and adjusts the target SNR for the control channel, as follows: deleted keyword keyword not deleted Equation 5 where SNR0jb-jetivo (k) is the target SNR for the update interval of external loop k; A SNR Ascending is a step-up size for the target SNR; and ASNR descending is a step-down size for the target SNR. The target SNR SNR0i, jet vo (k) and the step sizes ASNRasCendente and ASNRdescendente are in units of dB. As shown in equation (5), unit 2 5 6 reduces the target SNR per ASNR descending if a received keyword is considered as a non-deleted keyword, which may indicate that the received SNR for the control channel is higher to the necessary. Conversely, unit 25 6 increases the target SNR by ASNR ascent if a word The received key is considered as an erased keyword, which may indicate that the received SNR for the control channel is below what is necessary. ASNRascendant and ASNRdeScendent payroll sizes to adjust the target SNR can be established based on the following relationship: f 1 - Pr delete descending V delete J 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 'ASNR ofScendent). the ascending step size is selected to be equal to 0. 5 decibels (dB), then the downslope size is approximately 0. 056 dB. Larger values for ASNRaScendente and ASNRdescendente accelerate the speed of convergence 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 keyword in the channel of control periodically or whenever 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: THhormr (l) + ascending MHi, for a good keyword, THhorrar. { t + \) = \ THbnrrar (e) - ATH descending, for a bad keyword, and THhorrar (i), for a deleted keyword, Equation 7 where THb0rrar (í) is the erase threshold for the interval of update of the third loop i; ATHascendente is an ascending step size for the erase threshold; Y ATHdown is a downstream step size for the erase threshold.

As shown in equation (7), the threshold of deleted is reduced by ATHdesCendente for each known keyword received which is a bad keyword. The lower erasure threshold corresponds to a detection criterion of stricter erasure and produces as a result a word key that is most likely to be considered deleted, which in turn results in the received keyword being more likely to be decoded correctly when considered not deleted. On the contrary, the erase threshold is increased by ATHasCendente for each known keyword received which is a good keyword. The upper erase threshold corresponds to a less clear erase detection criteria strict and results in a received keyword with a lower probability of being considered deleted, 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 adjusting the erase threshold can be established based on the following relationship: Pr ATM = A Tf-f erro, ascending descending error Equation 8 For example, if the target conditional error rate for the control channel is 1%, then the downstream step size is 99 times the step-up size. The magnitude of ATHascendente and ATHdesCendente can be considered based on the expected magnitude of the received symbols, the desired convergence rate for the third link, 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) / dni (k) instead of m (k) = dni (A-) / dn2 (A :)), in which case , the adjustment of the erase threshold 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, THborrar (í) 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 erase 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 clear 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 key word, as determined in block 322, then the received keyword is declared as a deleted keyword (block 324). The target SNR is increased by the step size ASNRaScendent if the calculated metric m (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 clear 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 it is declared as a non-deleted keyword (block 334), and the target SNR is reduced by the step size ASNRdown (block 336). 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 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 correct, as determined in block 342, then the received known keyword is declared as a good keyword (block 344), and the erasure threshold is increments by step size ATH ascending (block 346). Otherwise, if there was a decoding error, as determined in block 342, then the known received keyword is declared as a bad keyword (block 354), and the clearing threshold is reduced by the step size ATH descending (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 may contain 16 QPSK modulation symbols, or [Yes (l) Yes (2) ... Yes (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. Here, techniques for executing erasure detection and power control for a transmission on 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 decoded data. For erasure detection, a transmission entity (e.g., a wireless terminal) transmits keywords on 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 describe below, and compare the calculated metric against a clear threshold. The base station declares each received keyword to be either an "erased" keyword or a "not erased" keyword, based on the comparison result. The base station dynamically adjusts the erasure threshold to achieve a target level of performance, which can be quantified by an objective conditional error rate that indicates the probability that a received keyword will be decoded in error, when it is declared to be a keyword not deleted The erase threshold can be adjusted based on the known received keywords, which are received keywords for known key words transmitted by terminals in communication with the base station, as described below. The adjustable clear threshold can provide robust erase detection performance in various channel conditions. A power control mechanism for controlling the transmission power of each terminal can be performed using a "combined" loop which attempts to maintain a target clearing speed in the received signal. The combined algorithm will be converging faster because the refresh rate of the external loop will be higher compared to the separate loop algorithm. This is particularly useful when the channel is changing fast. Another advantage is that the ascending and descending power commands can be used to assess the physical channel quality from one terminal to different base stations. This information is useful when a terminal is communicating with more than one base station. For example, during a "transfer", that is, when a terminal is changing its service base station, this information can be used to adjust the power of different physical channels from the terminal to different base stations. If the combined algorithm is not used, the base stations have to transmit other channels that will be used in the terminals, when determining the quality of the physical channels from the terminals to different base stations, and this will reduce the capacity of the system. In this method, the base station sends up and down power commands to each terminal, depending on whether the keyword received from the terminal has been erased or not. Depending on the target erase speed, the base station also transmits the amount of power that each terminal, "Increase Size" has to increase when a keyword sent from the terminal is deleted, and the amount of power that each terminal, " Reduce the Size "you have to decrease when a keyword sent from the terminal is not deleted. Figure 4 shows a flow chart of a process 400 for the power control mechanism. The base station 11Ox is configured to execute the steps of the process 500 using at least one of the components of the base station 11Ox, for example, the controller 570, the memory 572, the data processor TX 582, the data processor RX 560, etc. The process begins when base station llOx receives a keyword k, described above, in the reverse link. In step 404, the base station llOx, using the techniques described above, determines whether the received keyword is deleted by not meeting the erasure threshold requirements. If the keyword k was deleted (for example, outside the erase threshold), then in step 406, the base station llOx generates a power control message to "Increase the Size" (increase by a value, Ascendant) of the transmission power of the terminal. The base station llOx determines the SaScendent and SdesCendente value to be transmitted to the terminal, which varies depending on the target erase or depending on the value of the keyword k and the threshold. The closer the keyword k is to the threshold, the smaller the value of the Sascendant and S-descendant used is. Otherwise, if the keyword was not deleted (for example, within the erase threshold), then in step 408, the base station HOx generates a power control message to "Reduce the Size" (reduction by one value, S) of the power of terminal transmission. In step 410, the base station HOx updates a database used to monitor the number of key words that were "erased" and "not erased". The base station HOx can adjust the erase threshold based on the number of "Increase Size" or "Reduce Size" requested (for example, number of same type of requests). In step 412, the HOx base station can use information from the database to determine the Sascendent value and the S-value, for example a search box associated with an objective erase rate. According to another example, as discussed above, the power control mechanism can be used to dynamically adjust the erase threshold and the received SNR to achieve the desired performance for the control channel. In such a case, SaSt and Descending are calculated in the following way: SasCendente = S descending, * (1-P ^ erase) Prororado- In step 414, the power control message containing the SaScendente and SdeScendente values is transmitted to the mobile station. At the moment of receiving the transmitted message, based on the factors previously analyzed, the terminal will adjust the power and provide another keyword using the requested power level. Figure 5 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 a sub-frame block is transmitted at a time for the encoded packet. As each sub-block for a given coded packet is received on the forward link data channel, the terminal attempts to decode and retrieve the packet based on all sub-blocks received up to that time 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 transmission 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 6 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) 610 receives and processes (eg, formats, encodes, interleaves and modulates) the traffic data of the reverse channel (RL) and provides modulation symbols. for traffic data. The TX data processor 610 also processes control data (eg, CQI) from a controller 620 and provides modulation symbols for the control data. A modulator (OD) 612 processes the modulation symbols for traffic and control data and pilot symbols and provides a chip sequence with complex values. The processing by the data processor TX 610 and the modulator 612 depends on the system. For example, modulator 612 can execute OFD modulation if the system uses OFDM. A transmitter unit (TMTR) 614 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) 616 and transmitted through an antenna 618. In the base station HOx, the reverse link signal of the terminal 120x is received by an antenna 652, guided through a duplexer 654, and provided to a receiving unit (RCVR) 656 The receiving unit 656 conditions (for example, filters, amplifies and subverts the frequency) the received signal and also digitizes the conditioned signal to obtain a stream of data samples. A demodulator (DEMOD) 658 processes the data samples to obtain symbol estimates. A reception data processor (RX) 660 then processes (e.g., deinterleaves and decodes) the symbol estimates to obtain decoded data for the 120x terminal. The RX 660 data processor also performs deletion detection and provides a 670 controller with the status of each received keyword that was used for power control. Depending on the value of the received keyword compared to the erase threshold, the HOx base station adjusts the power level, as discussed above, to comply with the erase rate objective. The processing by the demodulator 658 and the data processor RX 660 is complementary to the processing performed by the modulator 612 and the data processor TX 610, 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 674 estimates the received SNR for the 120x terminal and provides the received SNR to a TPC generator 676. The TPC generator 676 also receives the target SNR and generates TPC commands for the 120x terminal. The TPC commands are processed by a data processor TX 682, further processed by a modulator 684, conditioned by a transmitter unit 686, guided through a duplexer 654 and transmitted through an antenna 652 to the terminal 120x. At the terminal 120x, the forward link signal from the base station HOx is received by the antenna 618, guided through the duplexer 616, conditioned and digitized by a receiver unit 640, processed by a demodulator 642, and further processed by a RX 644 data processor to get received TPC commands. A TPC processor 624 then detects the received TPC commands to obtain TPC decisions, which are used to generate a transmission power adjustment control. As discussed above, the power adjustment occurs for the base station HOx, depending on the ratio of the value of the previously transmitted key word and the value of the clear threshold used by the base station lOOx. The modulator 612 receives control of the TPC 624 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 620 and 670 direct the operations of several processing units within the terminal 120x and the base station HOx, respectively. The controllers 620 and 670 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 670 and the data processor RX 660 can also execute the process 300 in figures 3A and 3B. The memory units 622 and 672 store program and data codes for the controllers 620 and 670, 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 672 in Figure 6) and executed through a processor (e.g., controller 670). The memory unit can be run inside the processor or outside the processor, in which case it can be Communicatively coupling 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 (9)

NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as a priority: CLAIMS

1. - A method for executing power control in a communication system comprising the acts of: receiving a keyword through a first wireless link; generating a message to adjust the power based on whether said keyword was within said erasure threshold; and transmitting said message on the second wireless link.

2. - The method according to claim 1, further comprising the act of generating a message to reduce the power if it is determined that said keyword is within said erase threshold.

3. - The method according to claim 1, further comprising the act of generating a message to increase the power if it is determined that said keyword is not within said threshold of erased . . - The method according to claim 2, characterized in that said act of generating a message to reduce the power comprises an act of determining a reduction value using an objective erase rate. 5. - The method according to claim 3, characterized in that said act of generating a message to increase the power comprises the act of determining an increment value using an objective erase rate. 6. - The method according to claim 3, wherein said act of generating a message to increase the power comprises the act of generating a message for a first physical channel. 7. - The method according to claim 1, further comprising the act of adjusting said erasure threshold based on the number of requested power level adjustments of the same type. 8. - The method according to claim 1, characterized in that said transmission further comprises the act of transmitting in accordance with a scheme of Code Division Expedite Access (CDMA). 9. - The method of compliance with the claim 1, characterized in that said transmission further comprises the act of transmitting according to a scheme of Orthogonal Frequency Division Multiplexing (OFDM). 10. - The method according to claim 1, characterized in that said transmission further comprises the act of transmitting according to a scheme of Multiple Access by Orthogonal Frequency Division (OFDM). 11. - An apparatus for executing power control in a communication system, comprising the acts of: means for receiving a keyword through a first wireless link; means for generating a message for adjusting the power based on whether the means for said keyword were within said erasure threshold; and means for transmitting said message on the second wireless link. 12. - The apparatus according to claim 11, further comprising means for generating a message in order to reduce the power if it is determined that said keyword is within said erasure threshold. 13. - The apparatus according to claim 11, further comprising means for generating a message in order to increase the power if determined that said keyword is not within said erase threshold. 1

4. - The apparatus according to claim 12, characterized in that said means for generating a message in order to reduce the power comprises means for determining a reduction value using a target erase rate. 1

5. - The apparatus according to claim 13, characterized in that said means for generating a message to increase the power comprises means for determining an increment value using an objective erase rate. 1

6. - The apparatus according to claim 13, characterized in that said means for generating a message for increasing the power comprises means for generating a message for a first physical channel. 1

7. - The apparatus according to claim 11, which further comprises means for adjusting said erasure threshold based on the number of requested power level adjustments of the same type. 1

8. - In a wireless communication system, an apparatus comprising: an electronic device, said electronic device configured to receive a keyword through a first wireless link, generate a message in order to adjust the power based on whether said keyword was within said erasure threshold, and transmit said message on the second wireless link. 1

9. - The apparatus according to claim 18, characterized in that said electronic device is further configured to generate a message in order to reduce the power if it is determined that said keyword is within said erasure threshold. 20. - The apparatus according to claim 18, characterized in that said electronic device is further configured to generate a message in order to increase the power if it is determined that said keyword is not within said erasure threshold. 21. - The apparatus according to claim 19, characterized in that said electronic device is further configured to determine a reduction value using an objective erase speed. 22. - The apparatus according to claim 20, characterized in that said electronic device is further configured to determine an increment value using an objective erase speed. 23. - The apparatus according to claim 20, characterized in that said device Electronic is also configured to generate a message for a first physical channel. 24. - A machine-readable medium comprising instructions that, when executed by a machine, cause the machine to perform operations including: receiving a keyword through a first wireless link; generating a message to adjust the power based on whether said keyword was within said erasure threshold; and transmitting said message on the second wireless link. 25. - The machine-readable medium according to claim 24, further comprising that the machine-readable instruction causes the machine to generate a message to reduce power if it is determined that said keyword is within said erasure threshold. 26. - The machine-readable medium according to claim 24, further comprising that the machine-readable instruction causes the machine to generate a message to increase the power if it is determined that said keyword is not within said erasure threshold. .