Weak signal detection in wireless communication systems

• US 8,335,283 B1
• Filed: 11/11/2008
• Issued: 12/18/2012
• Est. Priority Date: 11/11/2008
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm Atheros Incorporated (Qualcomm, Inc.)
• Inventors: Sun, Qinfang
• Primary Examiner(s): Liu, Shuwang
• Assistant Examiner(s): TAYONG, HELENE E
• Application Number:
  US12/268,550
• Time in Patent Office: 1,498 Days
• Field of Search: 375/347, 375/365, 375/343, 370/208
• US Class Current: 375/343
• CPC Class Codes: H04B 1/7073 Synchronisation aspects
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/2663 Coarse synchronisation, e.g. by correlation
• CPC Class Codes: H04L 27/2671 Time domain
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2688 Resistance to perturbation, e.g. noise, interference or fading
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15

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.

Claims

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;

weighting the sum of the self-correlation outputs, 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;

accumulating the weighted 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:

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.

5. 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 weighted 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.

6. The method of claim 5, further comprising summing sample values across the plurality of symbols from the weighted 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.

7. The method of claim 6, 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.

8. The method of claim 6, 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.

9. 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;

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 weighting unit operable to weight the sum of the self-correlation outputs comprises,

a power unit of each of the plurality of receiver chains operable to calculate a power of each of the STF symbols received at the receiver chain;

a second summing unit operable to sum outputs of the power units in the plurality of receiver chains; and

the weighting unit 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;

an accumulation unit operable to accumulate the weighted sum of the outputs of the self-correlation units at the output of the weighting 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.

10. The wireless receiver of claim 9, 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.

11. The wireless receiver of claim 10, 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.

12. The wireless receiver of claim 9, 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.

13. The wireless receiver of claim 9, wherein each of the plurality of receiver chains further comprise an antenna operable to acquire RF signals.

14. One or more non-transitory machine-readable storage media having instructions stored therein, which when executed by one or more processors causes the one or more processors 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;

weighting the sum of the self-correlation outputs, 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;

accumulating the weighted 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.

15. The non-transitory machine-readable storage media of claim 14, wherein the operations further 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.

16. 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 first summing unit operable to sum outputs of the self-correlation units in the plurality of receiver chains;

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 weighting unit operable to weight the sum of the self-correlation outputs comprises,

a power unit of each of the plurality of receiver chains operable to calculate a power of each of the STF symbols received at the receiver chain;

a second summing unit operable to sum outputs of the power units in the plurality of receiver chains; and

the weighting unit 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;

an accumulation unit operable to accumulate the weighted sum of the outputs of the self-correlation units at output of the weighting 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.

17. The WLAN device of claim 16, 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.