We study an improved receiver with iterative channel estimation and decoding. A soft modulator processes the soft output of the Turbo decoder after a decoding iteration. If some symbols are deemed reliable at the output of the soft modulator, then these symbols act as extra pilot symbols for the channel estimator to refine the channel estimates that aid the demodulator, whose output is given to the decoder for another decoding iteration. The conventional Turbo decoder needs to be modified to yield soft information for both the systematic as well as the parity bits and two methods are presented to accomplish this. To keep the complexity in terms of memory and processing low, the iterative channel estimation is done on the equivalent channel at the output of the RAKE combiner instead of per-finger iterative channel estimation before the RAKE combining. Numerical results are presented that show that good improvement is possible over the current receiver.
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