Weak signal detection in wireless communication systems

Abstract

A mechanism for weak signal packet detection in a wireless receiver. Cross-correlation and self-correlation operations are performed on a plurality of short training field symbols associated with a plurality of RF signals received at a plurality of receiver chains of the wireless receiver. A plurality of self-correlation outputs generated in the plurality of receiver chains are summed and the sum of the self-correlation outputs is accumulated over a predetermined number of STF symbol periods. A moving sum operation is performed on the accumulation output when the accumulation output is greater than a first predetermined threshold. A signal indicating a data packet has been detected is generated when the moving sum output is greater than a second predetermined threshold.

1 . A method for implementing weak signal packet detection comprising:
 performing cross-correlation and self-correlation operations on a plurality of short training field (STF) symbols associated with a plurality of RF signals received at a plurality of receiver chains of a wireless receiver;   summing a plurality of self-correlation outputs generated in the plurality of receiver chains;   accumulating the sum of the self-correlation outputs over a predetermined number of STF symbol periods;   performing a moving sum operation on the accumulation output when the accumulation output is greater than a first predetermined threshold; and   generating a signal indicating a data packet has been detected when the moving sum output is greater than a second predetermined threshold.   
     
     
         2 . The method of  claim 1 , wherein said performing cross-correlation operations comprises cross-correlating the STF symbols received at each receiver chain with a known STF symbol sequence. 
     
     
         3 . The method of  claim 2 , wherein said performing self-correlation operations comprises self-correlating the cross-correlation output at each receiver chain with a delayed version of the cross-correlation output. 
     
     
         4 . The method of  claim 1 , further comprising weighting the sum of the self-correlation outputs, wherein said accumulating the sum of the self-correlation outputs over a predetermined number of STF symbol periods comprises accumulating the weighted sum of the self-correlation outputs over the predetermined number of STF symbol periods. 
     
     
         5 . The method of  claim 4 , wherein said weighting the sum of the self-correlation outputs comprises:
 calculating a power of the plurality of STF symbols associated with the plurality of RF signals received at the plurality of receiver chains;   summing the calculated power outputs generated in the plurality of receiver chains; and   dividing the sum of the self-correlation outputs by the sum of the calculated power outputs.   
     
     
         6 . The method of  claim 4 , further comprising:
 identifying peak locations in the accumulation output by detecting when the accumulation output is greater than the first predetermined threshold;   determining a coarse timing estimate and a fine timing estimate based, at least in part, on the peak locations in the accumulation output and the weighted sum of the self-correlation outputs.   
     
     
         7 . The method of  claim 1 , further comprising:
 determining locations of peaks in the accumulation output, wherein the peak locations are determined by detecting when the accumulation output is greater than the first predetermined threshold;   determining an energy associated with each symbol of a plurality of symbols from the sum of the self-correlation outputs, wherein the energy associated with a symbol is determined by summing the energies at each of the peak locations associated with the symbol;   comparing the energy associated with each symbol to a third predetermined threshold; and   determining a course timing estimate based, at least in part, on one of the plurality of symbols from the sum of the self-correlation outputs having an energy greater than the third predetermined threshold.   
     
     
         8 . The method of  claim 7 , further comprising summing sample values across the plurality of symbols from the sum of the self-correlation outputs up to the coarse timing estimate, and determining a fine timing estimate based, at least in part, on a sample instant where an energy of the summed sample values has a maximum value. 
     
     
         9 . The method of  claim 8 , further comprising determining a timing offset estimate by summing the fine timing estimate and a product of the coarse timing estimate and a number of samples per short training symbol. 
     
     
         10 . The method of  claim 8 , further comprising determining a frequency offset estimate by calculating an angle of the summed sample values at the sample instant corresponding to the fine timing estimate. 
     
     
         11 . A wireless receiver comprising:
 a plurality of receiver chains operable to receive a plurality of RF signals, wherein each of the receiver chains comprises a cross-correlation unit coupled to a self-correlation unit, wherein the cross-correlation units and the self-correlation units are operable to perform cross-correlation and self-correlation operations, respectively, on a plurality of short training field (STF) symbols associated with the plurality of received RF signals;   a first summing unit operable to sum outputs of the self-correlation units in the plurality of receiver chains;   an accumulation unit operable to accumulate an output of the first summing unit over a predetermined number of STF symbol periods;   a moving sum unit operable to perform a moving sum operation on an output of the accumulation unit when the output of the accumulation unit is greater than a first predetermined threshold; and   a detection unit operable to generate a signal indicating a data packet has been detected when an output of the moving sum unit is greater than a second predetermined threshold.   
     
     
         12 . The wireless receiver of  claim 11 , wherein, for each receiver chain, the cross-correlation unit of the receiver chain is operable to cross-correlate the STF symbols received at the receiver chain with a known STF symbol sequence. 
     
     
         13 . The wireless receiver of  claim 12 , wherein, for each receiver chain, the self-correlation unit of the receiver chain is operable to self-correlate an output of the cross-correlation unit of the receiver chain with a delayed version of the output of the cross-correlation unit. 
     
     
         14 . The wireless receiver of  claim 11 , further comprising a weighting unit operable to weight the output of the first summing unit to generate a weighted sum of the outputs of the self-correlation units, wherein the accumulation unit is operable to accumulate the weighted sum of the outputs of the self-correlation units over a predetermined number of STF symbol periods. 
     
     
         15 . The wireless receiver of  claim 14 , wherein each of the plurality of receiver chains further comprises a power unit, wherein, for each receiver chain, the power unit of the receiver chain is operable to calculate a power of each of the STF symbols received at the receiver chain. 
     
     
         16 . The wireless receiver of  claim 15 , further comprising a second summing unit operable to sum outputs of the power units in the plurality of receiver chains, wherein the weighting unit is operable to divide the sum of the outputs of the self-correlation units by the sum of the outputs of the power units to generate the weighted sum of the outputs of the self-correlation units. 
     
     
         17 . The wireless receiver of  claim 11 , further comprising a first peak detection unit operable to identify peak locations in the output of the accumulation unit by detecting when the accumulation unit output is greater than the first predetermined threshold. 
     
     
         18 . The wireless receiver of  claim 11 , wherein each of the plurality of receiver chains further comprise an antenna operable to acquire RF signals. 
     
     
         19 . One or more machine-readable media having stored therein a program product, which when executed a set of one or more processor units causes the set of one or more processor units to perform operations that comprise:
 performing cross-correlation and self-correlation operations on a plurality of short training field (STF) symbols associated with a plurality of RF signals received at a plurality of receiver chains of a wireless receiver;   summing a plurality of self-correlation outputs generated in the plurality of receiver chains;   accumulating the sum of the self-correlation outputs over a predetermined number of STF symbol periods;   performing a moving sum operation on the accumulation output when the accumulation output is greater than a first predetermined threshold; and   generating a signal indicating a data packet has been detected when the moving sum output is greater than a second predetermined threshold.   
     
     
         20 . The machine-readable media of  claim 19 , wherein the program product when executed causes the set of one or more processor units to perform operations that comprise cross-correlating the STF symbols received at each receiver chain with a known STF symbol sequence, and self-correlating the cross-correlation output at each receiver chain with a delayed version of the cross-correlation output. 
     
     
         21 . A wireless local area (WLAN) device comprising:
 a transmitter operable to transmit RF signals via a network; and   a receiver coupled to the transmitter and operable to receive RF signals via the network, wherein the receiver comprises:   a plurality of receiver chains operable to receive a plurality of RF signals, wherein each of the receiver chains comprises a cross-correlation unit coupled to a self-correlation unit, wherein the cross-correlation units and the self-correlation units are operable to perform cross-correlation and self-correlation operations, respectively, on a plurality of short training field (STF) symbols associated with the plurality of received RF signals;   a summing unit operable to sum outputs of the self-correlation units in the plurality of receiver chains;   an accumulation unit operable to accumulate an output of the summing unit over a predetermined number of STF symbol periods;   a moving sum unit operable to perform a moving sum operation on an output of the accumulation unit when the output of the accumulation unit is greater than a first predetermined threshold;   a detection unit operable to generate a signal indicating a data packet has been detected when an output of the moving sum unit is greater than a second predetermined threshold.   
     
     
         22 . The WLAN device of  claim 21 , wherein, for each receiver chain, the cross-correlation unit of the receiver chain is operable to cross-correlate the STF symbols received at the receiver chain with a known STF symbol sequence, and wherein, for each receiver chain, the self-correlation unit of the receiver chain is operable to self-correlate an output of the cross-correlation unit of the receiver chain with a delayed version of the output of the cross-correlation unit. 
     
     
         23 . The WLAN device of  claim 21 , further comprising a weighting unit operable to weight the output of the summing unit to generate a weighted sum of the outputs of the self-correlation units, wherein the accumulation unit is operable to accumulate the weighted sum of the outputs of the self-correlation units over a predetermined number of STF symbol periods.