Robust channel estimation in communication systems

1. An apparatus for achieving robust channel estimation in a communication system, comprising:

(A) a training sequence generator to generate a training sequence, wherein the training sequence generator further comprises

(I) a training symbol generator to generate a plurality of training symbols satisfying a predetermined constraint such that the training symbols are insensitive to synchronization error, wherein the training symbol generator further comprises a cyclic left shifter to perform cyclic left shift on a current training symbol in time domain to generate a next training symbol with the amount of the shifting determined by the number of segments in a cyclic prefix to be added to each training symbol; and

(II) a training sequence forming unit configured to form the training sequence from the training symbols generated by the training symbol generator;

(B) a formatter to insert the training sequence into a frame; and

(C) a transmitting module to transmit the frame.

2. The apparatus according to claim 1 , wherein the training sequence forming unit is configured to add a cyclic prefix to each training symbol, and concatenate the plurality of training symbols added with the cyclic prefixes.

3. The apparatus according to claim 1 , wherein the formatter is configured to insert the training sequence into a preamble field of the frame.

4. The apparatus according to claim 1 , wherein the formatter is configured to insert the training sequence into a payload field of the frame.

5. The apparatus according to claim 1 , wherein the communication system is a Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) system, and the transmitting module comprises multiple antennas; and wherein

the training symbol generator is further configured to generate multiple groups of the plurality of training symbols for each antenna;

the training sequence forming unit is further configured to form multiple training sequences that are orthogonal to each other, each training sequence corresponding to a respective antenna and containing the multiple groups of the plurality of training symbols for the respective antenna;

the frame forming unit is further configured to insert each training sequence into a frame to be transmitted from the respective antenna; and

the transmitting module is configured to transmit each frame from the respective antenna.

6. A communication method for archiving robust channel estimation in a communication system, comprising:

generating a plurality of training symbols satisfying a predetermined constraint such that the training symbols are insensitive to synchronization error, wherein generating a plurality of training symbols further comprises performing cyclic left shift on a current training symbol in time domain to generate a next training symbol with the amount of the shifting is determined by the number of segments in a cyclic prefix to be added to each training symbol;

forming a training sequence from the plurality of training symbols;

inserting the training sequence into a frame; and

transmitting the frame.

7. The method according to claim 6 , wherein forming a training sequence further comprises adding a cyclic prefix to each training symbol, and concatenating the plurality of training symbols added with the cyclic prefixes.

8. The communication method according to claim 6 , wherein the training sequence is inserted into a preamble field of the frame.

9. The communication method according to claim 6 , wherein the training sequence is inserted into a payload field of the frame.

10. The communication method according to claim 7 , further comprising:

receiving the frame;

extracting the training sequence from the received frame;

extracting the training symbols from the training sequence by taking a cyclic suffix of a training symbol as a cyclic prefix of a next training symbol in the training sequence; and

performing channel estimation based on the training symbols.