Legacy compatible spatial multiplexing systems and methods

1. A method comprising:

generating a first packet comprising two copies of a long training symbol;

generating a second packet comprising a cyclically-shifted long training symbol and an inverted version of the cyclically-shifted long training symbol;

transmitting the first packet from a first antenna; and

transmitting the second packet from a second antenna.

2. The method of claim 1 , wherein the cyclically-shifted long training symbol of the second packet corresponds to a cyclically advanced or delayed copy of the long training symbol of the first packet.

3. The method of claim 1 , wherein one copy of the long training symbol of the first packet and the inverted version of the cyclically-shifted long training symbol of the second packet correspond to a spatial multiplexing transmission protocol.

4. The method of claim 1 , wherein the first and second packets further comprise OFDM data symbols.

5. The method of claim 1 , wherein the first packet further comprises OFDM data symbols, and wherein the second packet further comprises cyclically-shifted OFDM data symbols.

6. A method, comprising:

receiving a first packet on a first channel at an antenna, wherein the first packet comprises two copies of a long training symbol;

receiving a second packet on a second channel at the antenna, wherein the second packet comprises a cyclically-shifted long training symbol and an inverted version of the cyclically-shifted long training symbol; and

determining a channel estimate for the first and second transmission channels based on the two copies of the long training symbol, the cyclically-shifted long training symbol, and the inverted version of the cyclically-shifted long training symbol.

7. The method of claim 6 , wherein determining a channel estimate comprises performing a Walsh transform in the time domain.

8. The method of claim 6 , wherein determining a channel estimate comprises performing a Walsh transform in the frequency domain.

9. The method of claim 6 , wherein determining a channel estimate for the first and second channels is based on the equations:

H 1=( RLTS 1+ RLTS 2)/(2* LTS )

H 2=( RLTS 1− RLTS 2)/(2* LTSCS )

wherein H 1 corresponds to the channel estimate for the first channel;

wherein H 2 corresponds to the channel estimate for the second channel;

wherein RLTS 1 corresponds to the combination of the received first copy of the long training symbol of the first packet and the received cyclically-shifted long training symbol of the second packet;

wherein RLTS 2 corresponds to the combination of the received second copy of the long training symbol of the first packet and the received inverted version of the cyclically-shifted long training symbol of the second packet;

wherein LTS corresponds to the long training symbol; and

wherein LTSCS corresponds to the cyclic-shifted long training symbol.

10. The method of claim 6 , wherein determining a channel estimate comprises determining a channel estimate for the first channel and determining a cyclically-shifted channel estimate for the second channel based on the equations:

H 1=( RLTS 1+ RLTS 2)/(2* LTS )

H 2 CS =( RLTS 1 − RLTS 2)/(2* LTS )

wherein H 1 corresponds to the channel estimate for the first channel;

wherein H 2 CS corresponds to the cyclically-shifted channel estimate for the second channel;

wherein RLTS 1 corresponds to the combination of the received first copy of the long training symbol of the first packet and the received cyclically-shifted long training symbol of the second packet;

wherein RLTS 2 corresponds to the combination of the received second copy of the long training symbol of the first packet and the received inverted version of the cyclically-shifted long training symbol of the second packet; and

wherein LTS corresponds to the long training symbol.

11. The method of claim 6 , wherein the first and second packets further comprise OFDM data symbols.

12. The method of claim 6 , wherein the first packet further comprises OFDM data symbols, and wherein the second packet further comprises cyclically-shifted OFDM data symbols.

13. A system, comprising:

a first transmit processor configured to generate a first packet comprising two copies of a long training symbol; and

a second transmit processor configured to generate a second packet comprising a cyclically-shifted long training symbol and an inverted version of the cyclically-shifted long training symbol.

14. The system of claim 13 , wherein the first transmit processor is communicatively coupled to a first antenna configured to transmit the first packet, and wherein the second transmit processor is communicatively coupled to a second antenna configured to transmit the second packet.

15. The system of claim 13 , wherein the cyclically-shifted version of the long training symbol associated with the second packet corresponds to a cyclically advanced or delayed copy of the long training symbol associated with the first packet.

16. The system of claim 13 , wherein one copy of the long training symbol of the first packet and the inverted version of the cyclically-shifted long training symbol of the second packet correspond to a spatial multiplexing transmission protocol.

17. The system of claim 13 , wherein the first and second transmit processors comprise one of hardware or a combination of hardware and software.

18. The system of claim 13 , wherein the first and second packets further comprise OFDM data symbols.

19. The system of claim 13 , wherein the first packet further comprises OFDM data symbols, and wherein the second packet further comprises cyclically-shifted OFDM data symbols.

20. A system, comprising:

a receive processor configured to determine a channel estimate for a first and second channel based on a first packet received on the first channel from a first antenna and a second packet received on the second channel from a second antenna, wherein the first packet comprises two copies of a long training symbol, and wherein the second packet comprises a cyclically-shifted long training symbol and an inverted version of the cyclically-shifted long training symbol.

21. The system of claim 20 , wherein the first and second receive processors are further configured to compute a Walsh transform in the time domain.

22. The system of claim 20 , wherein the first and second receive processors are further configured to compute a Walsh transform in the frequency domain.

23. The system of claim 20 , wherein the first and second receive processors comprise one of hardware or a combination of hardware and software.

24. The system of claim 20 , wherein the first receiver processor is configured to determine a channel estimate for the first channel and the second channel based on the equations:

H 1=( RLTS 1+ RLTS 2)/(2* LTS )

H 2=( RLTS 1− RLTS 2)/(2* LTSCS )

wherein H 1 corresponds to the channel estimate for the first channel;

wherein H 2 corresponds to the channel estimate for the second channel;

wherein RLTS 1 corresponds to the combination of the received first copy of the long training symbol of the first packet and the received cyclically-shifted long training symbol of the second packet;

wherein RLTS 2 corresponds to the combination of the received second copy of the long training symbol of the first packet and the received inverted version of the cyclically-shifted long training symbol of the second packet;

wherein LTS corresponds to the long training symbol; and

wherein LTSCS corresponds to the cyclic-shifted long training symbol.

25. The system of claim 20 , wherein the first receiver processor is configured to determine a channel estimate for the first channel and a cyclically-shifted channel estimate for the second channel based on the equations:

H 1=( RLTS 1+ RLTS 2)/(2* LTS )

H 2CS=( RLTS 1− RLTS 2)/(2* LTS )

wherein H 1 corresponds to the channel estimate for the first channel;

wherein H 2 CS corresponds to the cyclically-shifted channel estimate for the second channel;

wherein RLTS 1 corresponds to the combination of the received first copy of the long training symbol of the first packet and the received cyclically-shifted long training symbol of the second packet;

wherein RLTS 2 corresponds to the combination of the received second copy of the long training symbol of the first packet and the received inverted version of the cyclically-shifted long training symbol of the second packet; and

wherein LTS corresponds to the long training symbol.

26. The system of claim 20 , wherein the first and second packets further comprise OFDM data symbols.

27. The system of claim 20 , wherein the first packet further comprises OFDM data symbols, and wherein the second packet further comprises cyclically-shifted OFDM data symbols.

28. A communication system comprising:

A first antenna and a second antenna;

A first transmit processor means for generating a first packet comprising two copies of a long training symbol wherein the first transmit processor means for generating a first packet is communicatively coupled to said first antenna to transmit the first packet; and a second transmit processor means for generating a second packet comprising a cyclically-shifted long training symbol and an inverted version of the cyclically-shifted long training symbol, wherein the second transmit processor means for generating a second packet is communicatively coupled to said second antenna configured to transmit the second packet.

29. The system of claim 28 , wherein the cyclically-shifted version of the long training symbol associated with the second packet corresponds to a cyclically advanced or delayed copy of the long training symbol associated with the first packet.

30. The system of claim 28 , wherein one copy of the long training symbol of the first packet and the inverted version of the cyclically-shifted long training symbol of the second packet correspond to a spatial multiplexing transmission protocol.

31. The system of claim 28 , wherein the first and second packets further comprise OFDM data symbols.

32. The system of claim 28 , wherein the first packet further comprises OFDM data symbols, and wherein the second packet further comprises cyclically-shifted OFDM data symbols.

33. The system of claim 28 , further comprising:

means for receiving the first packet on a first channel from the first antenna and for receiving the second packet on a second channel from the second antenna; and

means for determining a channel estimate for the first and second channels based on the first packet's long training symbols, the second packet's cyclically-shifted long training symbol, and the second packet's inverted cyclically-shifted long training symbol.

34. The system of claim 33 , wherein the means for determining the channel estimate is configured to determine a channel estimate for the first channel and the second channel based on the equations:

H 1=( RLTS 1+ RLTS 2)/(2* LTS )

H 2=( RLTS 1− RLTS 2)/(2* LTSCS )

wherein H 1 corresponds to the channel estimate for the first channel;

wherein H 2 corresponds to the channel estimate for the second channel;

wherein RLTS 1 corresponds to the combination of the received first copy of the long training symbol of the first packet and the received cyclically-shifted long training symbol of the second packet;

wherein RLTS 2 corresponds to the combination of the received second copy of the long training symbol of the first packet and the received inverted version of the cyclically-shifted long training symbol of the second packet;

wherein LTS corresponds to the long training symbol; and

wherein LTSCS corresponds to the cyclic-shifted long training symbol.

35. The system of claim 33 , wherein the means for determining the channel estimate is configured to determine a channel estimate for the first channel and a cyclically-shifted channel estimate for the second channel based on the equations:

H 1=( RLTS 1+ RLTS 2)/(2* LTS )

H 2CS=( RLTS 1− RLTS 2)/(2* LTS )

wherein H 1 corresponds to the channel estimate for the first channel;

wherein H 2 CS corresponds to the cyclically-shifted channel estimate for the second channel;

wherein RLTS 1 corresponds to the combination of the received first copy of the long training symbol of the first packet and the received cyclically-shifted long training symbol of the second packet;

wherein RLTS 2 corresponds to the combination of the received second copy of the long training symbol of the first packet and the received inverted version of the cyclically-shifted long training symbol of the second packet; and

wherein LTS corresponds to the long training symbol.

36. The system of claim 28 , wherein the first and second packets further comprise OFDM data symbols.

37. The system of claim 28 , wherein the first packet further comprises OFDM data symbols, and wherein the second packet further comprises cyclically-shifted OFDM data symbols.