| Wireless Mobile Communications rely on a host of techniques, all related to one goal, sending the most possible information across a link or a network. In recent years, both spatial and multiuser diversity have proven to be key techniques to achieve this goal. These two diversity dimensions can be exploited by the use of multiple antennas and/or the use of multiple terminals sending at the same time/frequency/code, these terminals can be seen as a multiple antenna emitter. This transmission diversity can be achieved with cooperative space-time encoded transmissions. One of the practical problems with this sort of array of transmitters is that the emitters will be asynchronous to some extent, hence the need for systems that can deal with asynchronicity, both from a signal design point of view and from a signal processing point of view. Having tackled the signal design previously, we take a look at the signal processing aspect and present a channel and delay estimation algorithm for asynchronous cooperative diversity in Block-Flat-Fading channel. The signal design is based on a precoding frame-based scheme with packet-wise encoding. This precoding is based on the addition of a cyclic prefix, implemented as a training sequence. The signal processing takes advantage of the known symbols offered by this cyclic prefix/training sequence and we show that it enables best synchronization and channel estimation which reaches the Cramer-Rao Bound. The BER performances are the same as synchronous MRC case, with full diversity order. |
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