Multiantenna communications apparatus, methods, and system

• US 20050141624A1
• Filed: 12/24/2003
• Published: 06/30/2005
• Est. Priority Date: 12/24/2003
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Guchhait, Atanu, Lakshmipathi, Sondur, Biswas, Ashim
• Granted Patent: US 7,352,819 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04B 17/24 with feedback of measurements to the transmitter
• CPC Class Codes: H04B 7/0408 using two or more beams, i.e. beam diversity
• CPC Class Codes: H04L 27/2602 Signal structure

Abstract

A transmitter may transmit using OFDM-MIMO or OFDM-SDMA depending on channel characteristics.

Claims

1. A method comprising:

estimating a multipath environment between a transmitter and a receiver;

when the multipath environment includes multiple uncorrelated paths, preparing the transmitter to transmit using an orthogonal frequency division multiplexing (OFDM) multiple-input-multiple-output (MIMO) format; and

when the multipath environment includes multiple correlated paths, preparing the transmitter to transmit using an OFDM spatial division multiple access (SDMA) format.

2. The method of claim 1 wherein estimating a multipath environment between a transmitter and a receiver comprises:

receiving at the receiver at least one OFDM symbol from each of N antennas at the transmitter.

3. The method of claim 2 wherein estimating the multipath environment further comprises calculating L subchannel matrices.

4. The method of claim 3 wherein estimating the multipath environment further comprises transmitting information regarding the L subchannel matrices from the receiver to the transmitter.

5. A method comprising:

receiving channel state information;

transmitting using an OFDM-MIMO format if the channel state information indicates the existence of a rich multipath scattering environment; and

otherwise transmitting using an OFDM-SDMA format.

6. The method of claim 5 wherein receiving channel state information comprises receiving pre-filtering matrices from a receiver.

7. The method of claim 6 wherein transmitting using a OFDM-MIMO format comprises pre-filtering data using the pre-filtering matrices.

8. The method of claim 6 wherein transmitting using a OFDM-MIMO format comprises pre-filtering data using one of the pre-filtering matrices.

9. The method of claim 5 wherein transmitting using a OFDM-MIMO format if the channel state information indicates the existence of a rich multipath scattering environment comprises:

determining if a plurality of subchannel matrices are strong full-rank matrices; and

pre-filtering data with a plurality of matrices corresponding to the plurality of subchannel matrices.

10. The method of claim 5 wherein transmitting using a OFDM-MIMO format if the channel state information indicates the existence of a rich multipath scattering environment comprises:

determining if less than all of a plurality of subchannel matrices are strong full-rank matrices; and

pre-filtering data with one singular matrix corresponding to one of the plurality of subchannel matrices.

11. The method of claim 5 wherein otherwise transmitting using an OFDM-SDMA format comprises:

determining if a plurality of subchannel matrices are rank-one matrices; and

weighting signals prior to transmission by N antennas.

12. The method of claim 5 further comprising transmitting a training sequence to the receiver.

13. The method of claim 12 wherein transmitting a training sequence comprises transmitting a plurality of OFDM symbols with N antennas simultaneously.

14. The method of claim 13 wherein transmitting a training sequence further comprises transmitting a second plurality of OFDM symbols with the N antennas non-simultaneously.

15. A method comprising:

receiving a training sequence;

calculating a number of antennas at a transmitter;

estimating a plurality of subchannels; and

transmitting information regarding the plurality of subchannels to the transmitter.

16. The method of claim 15 wherein receiving a training sequence comprises receiving a plurality of OFDM symbols from N antennas at the transmitter.

17. The method of claim 16 wherein receiving a plurality of OFDM symbols comprises receiving ten short training sequences transmitted simultaneously by the N antennas.

18. The method of claim 16 wherein receiving a plurality of OFDM symbols comprises receiving two long training sequences transmitted separately by each of the N antennas.

19. The method of claim 15 wherein estimating a plurality of subchannels comprises calculating a subchannel matrix for each subchannel.

20. The method of claim 19 wherein estimating a plurality of subchannels further comprises calculating a singular value decomposition for each of the subchannel matrices.

21. The method of claim 19 wherein transmitting information regarding the plurality of subchannels comprises transmitting information derived from the singular value decomposition.

22. An apparatus comprising:

a first number of transform mechanisms to apply transform matrices to symbols, wherein the first number is denoted by L;

a second number of OFDM modulators to modulate L symbols each, wherein the second number is denoted by N; and

N antennas.

23. The apparatus of claim 22 further comprising a weighting mechanism coupled between each OFDM modulator and antenna, the weighting mechanism to weight signals for SDMA transmission.

24. The apparatus of claim 22 wherein the apparatus is adapted to:

transmit OFDM-MIMO signals by applying transform matrices corresponding the subchannels; and

transmit OFDM-SDMA signals by applying unity transform matrices and applying beamforming weights.

25. An apparatus having a machine-readable medium with instructions stored thereon that when accessed, result in a machine performing:

configuring a transmitter to transmit using a OFDM-MIMO format when channel state information indicates the existence of a rich multipath scattering environment; and

configuring the transmitter to transmit using an OFDM-SDMA format when channel state information indicates the existence a strong line of sight component.

26. The apparatus of claim 25 wherein configuring the transmitter to transmit using a OFDM-MIMO format comprises:

pre-filtering data using pre-filtering matrices corresponding to subchannels; and

applying substantially uniform weights to signals transmitted by a plurality of antennas.

27. The apparatus of claim 25 wherein configuring the transmitter to transmit using a OFDM-SDMA format comprises:

pre-filtering data using unity matrices; and

applying beamforming weights to signals transmitted by a plurality of antennas.

28. An electronic system comprising:

a first number of transform mechanisms to apply transform matrices to symbols, wherein the first number is denoted by L;

a second number of OFDM modulators to modulate L symbols each, wherein the second number is denoted by N;

N antennas; and

an Ethernet interface.

29. The electronic system of claim 28 further comprising a weighting mechanism coupled between each OFDM modulator and antenna, the weighting mechanism to weight signals for SDMA transmission.

30. The electronic system of claim 28 wherein the system is adapted to:

transmit OFDM-MIMO signals by applying transform matrices corresponding the subchannels; and

transmit OFDM-SDMA signals by applying unity transform matrices and applying beamforming weights.