Multiantenna communications apparatus, methods, and system

1. A method comprising:

estimating a multipath environment for each of a plurality of orthogonal frequency division multiplexing (OFDM) subchannels between a transmitter and a receiver;

when the multipath environment includes multiple uncorrelated paths for each of the plurality of OFDM subchannels, preparing the transmitter to transmit using an OFDM multiple-input-multiple-output (MIMO) format by pre-filtering using separate channel estimation data for each of the OFDM subchannels;

when the multipath environment includes multiple uncorrelated paths for less than all of the plurality of OFDM subchannels, preparing the transmitter to transmit using an OFDM-MIMO format by pre-filtering all OFDM subchannel data using channel estimation data from only one of the plurality of OFDM subchannels;

when the multipath environment includes multiple correlated paths for each of the plurality of OFDM subchannels, preparing the transmitter to transmit using an OFDM spatial division multiple access (SDMA) format; and

transmitting data from the transmitter.

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 corresponding to a plurality of orthogonal frequency division multiplexing (OFDM) subchannels;

transmitting using an OFDM multiple input multiple output (MIMO) format wherein each OFDM subchannel is pre-filtered using channel state information corresponding to that OFDM subchannel if the channel state information indicates the existence of a rich multipath scattering environment for all OFDM subchannels;

transmitting using an OFDM-MIMO format wherein all OFDM subchannels are pre-filtered using channel state information corresponding to a single OFDM subchannel if the channel state information indicates the existence of a rich multipath scattering environment for less than all OFDM subchannels; and

otherwise transmitting using an OFDM spatial division multiple access (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 5 wherein transmitting using a OFDM-MIMO format wherein each OFDM subchannel is pre-filtered using channel state information corresponding to that OFDM subchannel 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.

9. The method of claim 5 wherein transmitting using a OFDM-MIMO format wherein all OFDM subchannels are pre-filtered using channel state information corresponding to a single OFDM subchannel if the channel state information indicates the existence of a rich multipath scattering environment for less than all OFDM subchannels 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.

10. 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.

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

12. The method of claim 11 wherein transmitting a training sequence comprises transmitting a plurality of OFDM symbols with N antennas simultaneously.

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

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

configuring a transmitter to transmit using an orthogonal frequency division multiplexing multiple input multiple output (OFDM-MIMO) format by pre-filtering using separate channel estimation data for each of a plurality of OFDM subchannels when channel state information indicates the existence of a rich multipath scattering environment in each of the plurality of OFDM subchannels;

configuring the transmitter to transmit using an OFDM-MIMO format by pre-filtering all of the plurality of OFDM subchannels using channel estimation data from only one of the plurality of OFDM subchannels when channel state information indicates the existence of a rich multipath scattering environment in less than all of the plurality of OFDM subchannels;

configuring the transmitter to transmit using an OFDM spatial division multiple access (SDMA) format when channel state information indicates the existence a strong line of sight component; and

transmitting from the transmitter.

15. The apparatus of claim 14 wherein configuring the transmitter to transmit using a OFDM-MIMO format comprises:

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

16. The apparatus of claim 14 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.