Long training sequence for MIMO WLAN systems

• US 20050232370A1
• Filed: 08/30/2004
• Published: 10/20/2005
• Est. Priority Date: 04/14/2004
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Moorti, R. Tushar, Hansen, Christopher J., Trachewsky, Jason A.
• Granted Patent: US 7,555,053 B2
• Time in Patent Office: Days
• US Class Current: 375/267
• CPC Class Codes: H04B 7/0613 using simultaneous transmission H04B7/0686 takes precedence

Abstract

A method for configuring a multiple input multiple output (MIMO) wireless communication begins by generating a plurality of preambles for a plurality of transmit antennas. Each of the plurality of preambles includes a carrier detection sequence at a legacy transmit rate, a first channel sounding at the legacy transmit rate, a signal field at the legacy transmit rate, and Z−1 channel soundings at a MIMO transmit rate, where L corresponds to a number of channel soundings. The method continues by simultaneously transmitting the plurality of preambles via the plurality of transmit antennas.

Claims

1. A method for configuring a multiple input multiple output (MIMO) wireless communication, the method comprises:

generating a plurality of preambles for a plurality of transmit antennas, wherein each of the plurality of preambles includes;

a carrier detection sequence at a legacy transmit rate;

a first channel sounding at the legacy transmit rate;

a signal field at the legacy transmit rate; and

a plurality of channel soundings at a MIMO transmit rate; and

simultaneously transmitting the plurality of preambles via the plurality of transmit antennas.

2. The method of claim 1, wherein the MIMO transmit rate includes the legacy transmit rate.

3. The method of claim 1 further comprises generating the signal field by:

indicating frame length of the MIMO wireless communication such that legacy wireless communication devices can set collision avoidance for a duration of the MIMO wireless communication; and

setting a reserve bit to indicate the MIMO wireless communication.

4. The method of claim 3 further comprises generating the signal field, with the reserve bit set, by:

utilizing rate bits of the signal field to indicate transmit antenna configuration and preamble configuration.

5. The method of claim 4 further comprises generating the signal field, with the reserve bit set, by:

specifying a dummy rate within the rate bits and within length bits of the signal field, wherein the dummy rate indicates a frame length of the MIMO wireless communication, the transmit antenna configuration and the preamble configuration.

6. The method of claim 3 further comprises, with the reserve bit set:

utilizing a default rate to specify a frame length of the MIMO wireless communication, a transmit antenna configuration, and a preamble configuration.

7. The method of claim 1, wherein the legacy transmit rate comprises:

applying a weighting factor to each of the first channel sounding and the signal field.

8. The method of claim 7, wherein the generating the plurality of channel soundings comprises:

selecting a symbol to transmit at the first time instant on a second to Mth antennas of the plurality of antennas to be a first symbol transmitted at the first time instance on a first antenna of the plurality of antennas multiplied by a real scalar value multiplied by a first column of an N×

M unitary matrix; and

selecting another symbol to transmit at second to Mth time instants on the first to Mth antennas of the plurality of antennas to be a symbol transmitted at the first time instance on the first antenna multiplied by second to Mth columns of the N by M unitary matrix.

9. The method of claim 1, wherein the transmitting the plurality of preambles comprises:

transmitting tones of each of the L−

1 channel soundings at substantially equal energy levels.

10. The method of claim 1, wherein the generating the plurality of preambles comprises:

applying a weighting factor matrix to tones of at least one of the plurality of preambles for beam forming.

11. The method of claim 10 comprises at least one of:

utilizing known beam forming coefficients for the weighting factor matrix; and

transmitting, within the at least one preamble, beam forming coefficients to establish the weighting factor matrix.

12. A method for generating a training symbol sequence for a multiple-output OFDM RFIC, the method comprising:

generating M+1 OFDM symbols, where M is the number of RF outputs;

selecting the symbol transmitted at the first time instant on the second to Mth antennas to be the first symbol transmitted at the first time instance on the first antenna multiplied by a real scalar value multiplied by the first column of an M×

M unitary matrix;

selecting the symbol transmitted at the third to (M+1)th time instants on the first to Mth antennas to be the first symbol transmitted at the first time instance on the first antenna multiplied by the second to Mth columns of the same unitary matrix; and

selecting the symbol transmitted at the second time instant on the first to Mth antennas to be the first symbol transmitted at the first time instant on the first to Mth antennas.

13. The method of claim 12, wherein each vector of M symbols transmitted at the first through (M+1)th time instant is also multiplied by a diagonal matrix each of whose nonzeros entries is a different root of unity.

14. The method of claim 13, wherein the upper left entry of the diagonal matrix is 1.

15. The method of claim 12, wherein the real-valued scalar multiplied by the unitary matrix equals the discrete Fourier transform matrix.

16. The method of claim 12, wherein M=2 and the real-valued scalar multiplied by the unitary matrix has a first row equal to 1, −

1 and a second row equal to 1 1.

17. A method for generating a training symbol sequence for a multiple-output OFDM RF transceiver, the method comprising:

generating p*M OFDM symbols, where M is the number of RF outputs and p is an integer greater than 1;

selecting the symbol transmitted at the first time instant on the second to Mth antennas to be the first symbol transmitted at the first time instance on the first antenna multiplied by a real scalar value multiplied by the first column of an M×

M unitary matrix;

selecting the symbol transmitted at the second to Mth time instants on the first to Mth antennas to be the first symbol transmitted at the first time instance on the first antenna multiplied by the second to Mth columns of the same unitary matrix; and

selecting the symbols transmitted on each of the M antennas at the (M+1)th to the (p*M)th time instants to be (p-1) duplicate copies of the first M symbols transmitted on each of the M antennas.

18. A method for computing an estimate of an N×

M channel matrix for each of J subcarriers of a received OFDM transmission, N being the number of expected transmit antennas and M being the number of receive antennas, the method comprising;

removing the first K samples of each block of I+K, I>

=J samples;

applying a discrete Fourier transform to the remaining I samples of each block;

selecting from each output block of I samples the J subcarriers known to be excited at the transmitter with nonzero symbols;

forming an N×

L matrix of such outputs from each of the J subcarriers, each column of the matrix corresponding to the outputs on the jth subcarrier over L consecutive time instants from one receiver antenna and each row of the matrix corresponding to the outputs on the jth subcarrier over one time instant from all N receiver antennas;

post-multiplying this matrix by the Hermitian transpose of the M×

M unitary matrix used to multiply the known first symbol sent on the first transmit antenna; and

multiplying the resulting N×

M matrix by the complex conjugate of the known first symbol sent on the first transmit antenna.

19. A radio frequency integrated circuit (RFIC) transmitter comprises:

baseband processing module operably coupled to generate a plurality of preambles; and

a radio frequency (RF) transmitter section operably coupled to transmit the plurality of preambles at a radio frequency via a plurality of antennas, wherein the baseband processing module generates the plurality of preambles to include;

a carrier detection sequence at a legacy transmit rate;

a first channel sounding at the legacy transmit rate;

a signal field at the legacy transmit rate; and

L−

1 channel soundings at a MIMO transmit rate, where L corresponds to a number of channel soundings.

20. The RFIC transmitter of claim 19, wherein the MIMO transmit rate includes the legacy transmit rate.

21. The RFIC transmitter of claim 19, wherein the baseband processing module further functions to generate the signal field by:

indicating frame length of the MIMO wireless communication such that legacy wireless communication devices can set collision avoidance for a duration of the MIMO wireless communication; and

setting a reserve bit to indicate the MIMO wireless communication.

22. The RFIC transmitter of claim 21, wherein the baseband processing module further functions to generate the signal field, with the reserve bit set, by:

utilizing rate bits of the signal field to indicate transmit antenna configuration and preamble configuration.

23. The RFIC transmitter of claim 22, wherein the baseband processing module further functions to generate the signal field, with the reserve bit set, by:

specifying a dummy rate within the rate bits and within length bits of the signal field, wherein the dummy rate indicates a frame length of the MIMO wireless communication, the transmit antenna configuration and the preamble configuration.

24. The RFIC transmitter of claim 21, wherein the baseband processing module further functions to, with the reserve bit set:

utilizing a default rate to specify a frame length of the MIMO wireless communication, a transmit antenna configuration, and a preamble configuration.

25. The RFIC transmitter of claim 19, wherein the legacy transmit rate comprises:

applying a weighting factor to each of the first channel sounding and the signal field.

26. The RFIC transmitter of claim 25, wherein the baseband processing module further functions to generate the L−

1 channel soundings comprises;

selecting a symbol to transmit at the first time instant on a second to Mth antennas of the plurality of antennas to be a first symbol transmitted at the first time instance on a first antenna of the plurality of antennas multiplied by a real scalar value multiplied by a first column of an N×

M unitary matrix; and

selecting another symbol to transmit at second to Mth time instants on the first to Mth antennas of the plurality of antennas to be a symbol transmitted at the first time instance on the first antenna multiplied by second to Mth columns of the N by M unitary matrix.

27. The RFIC of claim 19, wherein the RF transmitter section functions to transmit the plurality of preambles by:

transmitting tones of each of the L−

1 channel soundings at substantially equal energy levels.

28. The RFIC transmitter of claim 19, wherein the baseband processing module further functions to generate the plurality of preambles comprises:

applying a weighting factor matrix to tones of at least one of the plurality of preambles for beam forming.

29. The RFIC transmitter of claim 28, wherein applying the weighting factor comprises at least one of:

utilizing known beam forming coefficients for the weighting factor matrix; and

transmitting, within the at least one preamble, beam forming coefficients to establish the weighting factor matrix.

30. A method for generating a signal field within a preamble of a wireless communication, the method comprises:

indicating frame length of a multiple input multiple output (MIMO) wireless communication within the signal field such that legacy wireless communication devices can set collision avoidance for a duration of the MIMO wireless communication; and

setting a reserve bit within the signal field to indicate the MIMO wireless communication.

31. The method of claim 30 further comprises generating the signal field, with the reserve bit set, by:

utilizing rate bits of the signal field to indicate transmit antenna configuration and preamble configuration.

32. The method of claim 31 further comprises generating the signal field, with the reserve bit set, by:

specifying a dummy rate within the rate bits and within length bits of the signal field, wherein the dummy rate indicates a frame length of the MIMO wireless communication, the transmit antenna configuration and the preamble configuration.

33. The method of claim 30 further comprises, with the reserve bit set:

utilizing a default rate to specify the frame length of the MIMO wireless communication, a transmit antenna configuration, and a preamble configuration.

34. A radio frequency integrated circuit (RFIC) transmitter comprises:

baseband processing module operably coupled to generate a plurality of preambles; and

a radio frequency (RF) transmitter section operably coupled to transmit the plurality of preambles at a radio frequency via a plurality of antennas, wherein the baseband processing module generates a signal field within each the plurality of preambles;

indicating frame length of a multiple input multiple output (MIMO) wireless communication within the signal field such that legacy wireless communication devices can set collision avoidance for a duration of the MIMO wireless communication; and

setting a reserve bit within the signal field to indicate the MIMO wireless communication.

35. The RFIC transmitter of claim 34, wherein the baseband processing module further functions to generate the signal field, with the reserve bit set, by:

utilizing rate bits of the signal field to indicate transmit antenna configuration and preamble configuration.

36. The RFIC transmitter of claim 35, wherein the baseband processing module further functions to generate the signal field, with the reserve bit set, by:

specifying a dummy rate within the rate bits and within length bits of the signal field, wherein the dummy rate indicates a frame length of the MIMO wireless communication, the transmit antenna configuration and the preamble configuration.

37. The RFIC transmitter of claim 34, wherein the baseband processing module further functions to, with the reserve bit set:

utilize a default rate to specify the frame length of the MIMO wireless communication, a transmit antenna configuration, and a preamble configuration.