Interleaver and deinterleaver for use in a diversity transmission communication system

DETAILED DESCRIPTION The current invention enhances the performance of a system utilizing interleaving and transmit diversity by reordering the sequence of symbols transmitted along the different transmission channels.
For example, in the case of a system using two transmission channels, the symbols being transmitted on one channel are shuffled with respect to the symbols transmitted through the other channel.
This shuffling makes it less likely that successive symbols output by the interleaver are lost to correlated fading in the two transmission channels.
Suppose a source frame F is composed of N coded symbols Si (1<i<N).
Suppose also that these symbols Si are distributed over M transmitters (different carriers or antennas or both).
The current invention splits the symbols into M groups Gj (1<j<M), one for each transmitter.
Then each of the groups, Gj, is interleaved independently.
A problem which can occur if the interleavers and splitter are not chosen correctly, or even worse if they are all identical, is that the performance will be severely degraded when the signals from the different transmitters go through channels that are correlated.
Consider the case where there are 2 transmitters that lead to 2 antennas to provide space diversity in a transmitted signal.
If the symbols are allocated for transmission such that odd symbols are provided for transmission through the first antenna and the even symbols are provided for transmission through the second antenna and wherein the symbols are interleaved subsequent to their provision to the respective antennas.
If traditional interleaving strategies are used, correlated fading will severely deteriorate performance.
The goal of the shuffle is to make sure that even if the different transmission paths from the different transmitters become correlated, the performance degradation is minor.
One particularly efficient implementation of the shuffle that each shuffle cyclically rotates the symbols it receives.
Here is an example: Shuffler j: cyclically rotate the symbols to be transmitted by transmitter j by (j-1)*N/M symbols