Distributed MIMO long training field method and system

1. A method for processing distributed multiple-input and multiple-output (DMIMO) orthogonal frequency-division multiplexing (OFDM) signals received by a receiver from a plurality of transmitters which transmits the DMIMO OFDM signals over a channel, the method comprising:

performing an initial carrier frequency offset (CFO) correction;

receiving a plurality of OFDM symbols;

estimating a residual CFO for each of the transmitters based upon a long training field (LTF);

re-constructing the channel every N symbols based upon a channel estimate for each transmitter and the estimate of the residual CFO for each of the transmitters, wherein N is an integer; and

equalizing the received OFDM symbols using the re-constructed channel.

2. The method of claim 1 , wherein the LTF includes a plurality of LTFs wherein each LTF is associated with a transmitter of each of the plurality of transmitters and wherein estimating the residual CFO for each transmitter is based upon its associated set of LTF.

3. The method of claim 1 , further including a plurality of LTFs wherein each LTF is associated with a subset of transmitters the plurality of transmitters,

wherein each of the plurality of LTFs associated with the subset of transmitters includes a plurality of subsets of interleaved frequency tones,

wherein each of the plurality of subsets of interleaved frequency tones is associated with one transmitter in the subset of transmitters, and

wherein the residual CFO estimate for each of the transmitters is based upon the subset frequency tones and LTF associated with the transmitter.

4. The method of claim 1 , wherein

the LTF includes a plurality of subsets of interleaved frequency tones,

each of the plurality of subsets is associated with one of the plurality of transmitter, and

the residual CFO estimate for each of the transmitters is based upon the subset associated with the transmitter.

5. The method of claim 4 , wherein the channel estimate for each of the transmitters includes interpolating the channel estimate for frequency tones outside the subset of frequency tones for each transmitter.

6. The method of claim 4 , wherein estimating a residual CFO includes estimating the residual CFO for each of a plurality of subsets of received pilot tones and averaging the plurality of estimated residual CFOs for each of the plurality of subsets.

7. The method of claim 4 , wherein estimating a residual CFO includes assigning a pilot tone to each of the plurality of transmitters from a set of orthogonal transmit pilot tones and estimating the residual CFO for each of the plurality transmitters based upon the assigned pilot tone.

8. The method of claim 1 , further comprising receiving a mid-amble every M symbols, wherein the mid-amble is used to re-estimate the channel and M is an integer.

9. The method of claim 1 , wherein performing the initial CFO correction is part of a receiver initiated synchronization request.

10. The method of claim 1 , wherein performing the initial CFO correction is part of a master transmitter initiated synchronization request and wherein the receiver responds to the synchronization request.

11. The method of claim 1 , further comprising periodically receiving an STF sequence and adjusting a gain of the receiver based upon the received STF.

12. A device for processing received distributed multiple-input and multiple-output (DMIMO) orthogonal frequency-division multiplexing (OFDM) signals from a plurality of transmitters, comprising:

a receiver configured to:

perform an initial carrier frequency offset (CFO) correction;

receive a plurality of OFDM symbols;

a residual CFO estimator configured to estimate a residual CFO for each of the transmitters based upon a long training field (LTF);

a channel re-constructor configured to re-construct the channel every N symbols based upon a channel estimate for each transmitter and the estimate of the residual CFO for each of the transmitters, wherein N is an integer; and

an equalizer configured to equalize the received OFDM symbols using the re-constructed channel.

13. The device of claim 12 , wherein the LTF includes a plurality of LTFs wherein each LTF is associated with a transmitter of each of the plurality of transmitters and wherein estimating the residual CFO for each transmitter is based upon its associated set of LTF.

14. The device of claim 12 , wherein the LTF includes a plurality of LTFs wherein each LTF is associated with a subset of transmitters the plurality of transmitters,

wherein each of the plurality of LTFs associated with the subset of transmitters includes a plurality of subsets of interleaved frequency tones,

wherein each of the plurality of subsets of interleaved frequency tones is associated with one transmitter in the subset of transmitters, and

wherein the residual CFO estimate for each of the transmitters is based upon the subset frequency tones and LTF associated with the transmitter.

15. The device of claim 12 , wherein

the LTF includes a plurality of subsets of interleaved frequency tones,

each of the plurality of subsets is associated with one of the plurality of transmitter, and

the residual CFO estimate for each of the transmitters is based upon the subset associated with the transmitter.

16. The device of claim 15 , wherein the channel estimate for each of the transmitters includes interpolating the channel estimate for frequency tones outside the subset of frequency tones for each transmitter.

17. The device of claim 15 , wherein estimating a residual CFO includes estimating the residual CFO for each of a plurality of subsets of received pilot tones and averaging the plurality of estimated residual CFOs for each of the plurality of subsets.

18. The device of claim 15 , wherein estimating a residual CFO includes assigning a pilot tone to each of the plurality of transmitters from a set of orthogonal transmit pilot tones and estimating the residual CFO for each of the plurality transmitters based upon the assigned pilot tone.

19. The device of claim 12 , wherein the receiver is further configured to receive a mid-amble every M symbols, wherein the mid-amble is used to re-estimate the channel and M is an integer.

20. The device of claim 12 , wherein performing the initial CFO correction is part of a receiver initiated synchronization request.

21. The device of claim 12 , wherein performing the initial CFO correction is part of a master transmitter initiated synchronization request and wherein the receiver responds to the synchronization request.

22. The device of claim 12 , wherein the receiver is further configured to periodically receive an STF sequence and adjust the gain of the receiver based upon the received STF.