ON THE ACHIEVABLE INFORMATION RATES OF DPSK

The achievable information rates of differential phase shift keying (DPSK) with differential detection are investigated. DPSK detection creates a dependency between two consecutive receiver outputs, thus introducing memory in the corresponding channel model. It is commonly assumed that this memory is eliminated by the use of interleaving-deinterleaving. However, with interleaving the performance of DPSK over the additive white Gaussian noise (AWGN) channel is substantially degraded compared to that of coherent PSK. We use the suboptimal phase-difference receiver to show that in this case noninterleaved DPSK achieves the performance of coherent detection (employing independent increment phase keying) when the channel phase is assumed constant throughout the coded block. Both capacity and cutoff rate are examined, and the results are compared to the (known) respective expressions evaluated for the interleaved case. The generalised cutoff rate for a scheme employing multiple-symbol detection over (short) subsequences is also examined.