Robust erasure detection and erasure-rate-based closed loop power control

Abstract

Techniques for performing erasure detection and power control for a transmission without error detection coding are described. For erasure detection, a transmitter transmits codewords 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 codewords 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.

1 . An apparatus operable to perform erasure detection in a wireless communication system, comprising: 
 a metric computation unit operative to obtain received codewords for codewords transmitted via a wireless channel and to compute a metric for each of the received codewords, wherein each transmitted codeword is a block of coded or uncoded data, and wherein each received codeword is a noisy version of a transmitted codeword;    an erasure detector operative to compare the computed metric for each received codeword against an erasure threshold and to declare each received codeword to be an erased codeword or a non-erased codeword based on a comparison result for the received codeword; and    an adjustment unit operative to dynamically adjust the erasure threshold to achieve a target level of performance for erasure detection.    
   
   
       2 . The apparatus of  claim 1 , further comprising: 
 a decoder operative to 
 obtain received known codewords for known codewords transmitted via the wireless channel, each known codeword being a block of a known data, and each received known codeword being a noisy version of a transmitted known codeword,  
 decode each received known codeword deemed to be a non-erased codeword, and  
 determine a status of each received known codeword as being a good codeword, a bad codeword, or an erased codeword, a good codeword being a received known codeword declared to be a non-erased codeword and decoded correctly, and a bad codeword being a received known codeword declared to be a non-erased codeword but decoded in error, and  
   wherein the adjustment unit is operative to adjust the erasure threshold based on the status of each received known codeword.    
   
   
       3 . An apparatus operable to perform erasure detection in a wireless communication system, comprising: 
 means for obtaining received codewords for codewords transmitted via a wireless channel, each transmitted codeword being a block of coded or uncoded data, and each received codeword being a noisy version of a transmitted codeword;    means for computing a metric for each of the received codewords;    means for comparing the computed metric for each received codeword against an erasure threshold;    means for declaring each received codeword to be an erased codeword or a non-erased codeword based on a comparison result for the received codeword; and    means for dynamically adjusting the erasure threshold to achieve a target level of performance for erasure detection.    
   
   
       4 . The apparatus of  claim 3 , further comprising: 
 means for obtaining received known codewords for known codewords transmitted via the wireless channel, each known codeword being a block of a known data, and each received known codeword being a noisy version of a transmitted known codeword;    means for determining a status of each of the received known codewords as being a good codeword, a bad codeword, or an erased codeword, a good codeword being a received known codeword declared to be a non-erased codeword and decoded correctly, and a bad codeword being a received known codeword declared to be a non-erased codeword but decoded in error; and    means for adjusting the erasure threshold based on the status of each received known codeword.    
   
   
       5 . An apparatus operable to perform power control for a transmission sent via a wireless channel in a wireless communication system, comprising: 
 a data processor operative to 
 obtain received codewords for codewords transmitted in the transmission, each transmitted codeword being a block of coded or uncoded data, and each received codeword being a noisy version of a transmitted codeword,  
 determine a status of each received codeword as being an erased codeword or a non-erased codeword based on a metric computed for the received codeword and an erasure threshold,  
 obtain received known codewords for known codewords transmitted via the wireless channel, each known codeword being a block of a known data, and each received known codeword being a noisy version of a transmitted known codeword, and  
 determine a status of each received known codeword as being a good codeword, a bad codeword, or an erased codeword, a good codeword being a received known codeword deemed to be a non-erased codeword and decoded correctly, and a bad codeword being a received known codeword deemed to be a non-erased codeword but decoded in error; and  
   a controller operative to 
 adjust a target signal quality (SNR) based on the status of each received codeword, wherein transmit power for the transmission is adjusted based on the target SNR, and  
 adjust the erasure threshold based on the status of each received known codeword.  
   
   
   
       6 . The apparatus of  claim 5 , further comprising: 
 an SNR estimator operative to estimate a received SNR for the transmission; and    a generator operative to compare the received SNR against the target SNR and generate commands used to adjust the transmit power for the transmission.    
   
   
       7 . The apparatus of  claim 5 , wherein the controller is operative to adjust the erasure threshold to achieve a target conditional error rate indicative of a predetermined probability of a received codeword being decoded in error if declared to be a non-erased codeword.  
   
   
       8 . The apparatus of  claim 5 , wherein the controller is operative to adjust the target SNR to achieve a target erasure rate indicative of a predetermined probability of declaring a received codeword as an erased codeword.  
   
   
       9 . The apparatus of  claim 5 , wherein the transmission is for a control channel.  
   
   
       10 . The apparatus of  claim 9 , wherein the control channel is used to send channel quality information, and wherein each transmitted codeword is for a channel quality indicator.  
   
   
       11 . The apparatus of  claim 5 , wherein the received known codewords are obtained from a plurality of different transmitting entities.  
   
   
       12 . The apparatus of  claim 5  and utilized in a base station.  
   
   
       13 . The apparatus of  claim 5  and utilized in a wireless terminal.  
   
   
       14 . An apparatus operable to perform power control for a transmission sent via a wireless channel in a wireless communication system, comprising: 
 means for obtaining received codewords for codewords transmitted in the transmission, each transmitted codeword being a block of coded or uncoded data, and each received codeword being a noisy version of a transmitted codeword;    means for determining a status of each received codeword as being an erased codeword or a non-erased codeword based on a metric computed for the received codeword and an erasure threshold;    means for adjusting a target signal quality (SNR) based on the status of each received codeword, wherein transmit power for the transmission is adjusted based on the target SNR;    means for obtaining received known codewords for known codewords transmitted via the wireless channel, each known codeword being a block of a known data, and each received known codeword being a noisy version of a transmitted known codeword;    means for determining a status of each received known codeword as being a good codeword, a bad codeword, or an erased codeword, a good codeword being a received known codeword deemed to be a non-erased codeword and decoded correctly, and a bad codeword being a received known codeword deemed to be a non-erased codeword but decoded in error; and    means for adjusting the erasure threshold based on the status of each received known codeword.    
   
   
       15 . The apparatus of  claim 14 , further comprising: 
 means for estimating a received SNR for the transmission;    means for comparing the received SNR against the target SNR; and    means for generating commands based on results of the comparing, wherein the commands are used to adjust the transmit power for the transmission.