Linear equalization for use in low latency high speed communication systems

1. A communication system comprising:

a transmitter for transmitting frames, at least two consecutive frames containing different training sequences, the transmitter comprising:

a time variable linear equalizer for applying equalization to at least a first training sequence to produce an equalized first training sequence; and

a fixed linear equalizer for applying equalization to a second training sequence to produce an equalized second training sequence; and

a receiver for receiving data communicated from the transmitter over a channel, the receiver combining and jointly processing the at least two consecutive frames transmitted by the transmitter to estimate a channel state of the channel, the receiver comprising:

a receiver linear equalizer for receiving the equalized first training sequence, for applying equalization thereto, and for estimating equalization coefficients to be used by the receiver linear equalizer in future equalization; and

a channel estimator for receiving the equalized second training sequence, and for estimating the channel state of the channel,

wherein the channel state is fed back to the transmitter which estimates from the channel state equalization coefficients to be used for generating the coefficients of the time variable linear equalizer.

2. A communication system according to claim 1 wherein the time variable linear equalizer of the transmitter further applies equalization to a data payload to produce an equalized data payload and, upon receipt of the equalized data payload by the receiver, the receiver linear equalizer further applies equalization to the equalized data payload.

3. A communication system according to claim 1 wherein:

the time variable linear equalizer and the receiver linear equalizer further perform I/Q mismatch compensation;

the receiver linear equalizer further estimates parameters to be used for the I/Q mismatch compensation in the receiver linear equalizer from the equalized first training sequence; and

the transmitter further estimates parameters to be used for the I/Q mismatch compensation in the time variable linear equalizer from the channel state fed back from the receiver.

4. A communication system according to claim 3 wherein the I/Q mismatch compensation is performed using linear filters.

5. A communication system according to claim 1 wherein the equalization applied to the second training sequence by the fixed linear equalizer has a constant impulse response in the frequency domain.

6. A communication system according to claim 1 wherein the first and second training sequences are orthogonal in the frequency domain.

7. A communication system according to claim 1 wherein the channel state is fed back to the transmitter over a return channel.

8. A method for performing equalization in a communication system, the method comprising the steps of:

applying equalization to at least a first training sequence by a time variable linear equalizer of a transmitter to produce an equalized first training sequence;

transmitting by the transmitter the equalized first training sequence to a receiver over a channel;

applying equalization to the equalized first training sequence by a receiver linear equalizer to produce first data;

estimating equalization coefficients to be used by the receiver linear equalizer in future equalization from the first data;

applying equalization to a second training sequence by a fixed linear equalizer of the transmitter to produce an equalized second training sequence;

transmitting by the transmitter the equalized second training sequence to the receiver over the channel;

estimating a channel state of the channel in the receiver from the equalized second training sequence;

feeding back the channel state to the transmitter from the receiver; and

estimating from the channel state equalization coefficients to be used for generating the coefficients of the time variable linear equalizer in future equalization.

9. A method according to claim 8 further comprising the steps of:

applying, by the time variable linear equalizer of the transmitter, equalization to a data payload to produce an equalized data payload;

transmitting the equalized data payload by the transmitter to the receiver over the channel; and

applying, by the receiver linear equalizer, equalization to the equalized data payload.

10. A method according to claim 8 wherein the time variable linear equalizer and the receiver linear equalizer further perform I/Q mismatch compensation, and the method further comprises the steps of:

estimating by the receiver linear equalizer parameters to be used for the I/Q mismatch compensation in the receiver linear equalizer from the equalized first training sequence; and

estimating by the transmitter further parameters to be used for the I/Q mismatch compensation in the time variable linear equalizer from the channel state fed back from the receiver.

11. A method according to claim 8 wherein the channel state is fed back to the transmitter from the receiver over a return channel.

12. A transmitter comprising:

a time variable linear equalizer for applying equalization to a first training sequence and a data payload; and

a fixed linear equalizer for applying equalization to a second training sequence.

13. A transmitter according to claim 12 wherein each of the time variable linear equalizer and the fixed linear equalizer further comprises a pulse shaping filter.

14. A transmitter according to claim 12 wherein each of the time variable linear equalizer and the fixed linear equalizer further comprises a sampling rate convertor for converting symbols from a symbol rate to a chip rate.

15. A transmitter according to claim 12 wherein the time variable linear equalizer further performs I/Q mismatch compensation.