On the performance of DQPSK communication systems impaired bytiming error, mixer imbalance, and frequency nonselective slow Rayleighfading

摘要

In this paper, the error performance of the differential detectionnscheme is assessed for differentially encodednquaternary-phase-shift-keying (DQPSK) and Π/4-shifted-DQPSK signals,nIt is assumed that the receiver suffers from mixer imbalance and timingnerror impairments. Expressions for the system bit-error rate (BER) arenobtained when the channel is free of fading and when the channel suffersnfrom frequency nonselective (flat) slow Rayleigh fading in the face ofnadditive white Gaussian noise. To arrive at the desired expressions, thenprobability density function (pdf) of the phase angle between a pair ofnGaussian random vectors is used to obtain the probability of bit errornconditioned on the channel fading and timing error. The resultingnexpressions are then averaged over the nonnegligible timing error andnthe channel fading to arrive at the desired expressions for the systemnBER. Finally, with the aid of numerical analysis and in the presence ofnthe aforementioned impairments, a number of conclusions are drawn andnthe performance of differential receivers for DQPSK andnΠ/4-shifted-DQPSK modulation schemes are compared. It is shown herenthat the performance of a DQPSK receiver in the absence of fading andntiming error is substantially impaired by mixer imbalance for BERs lessnthan 10-4. In the presence of fading, the performance isnnoticeably degraded due to mixer imbalance when a nonzero timing errornis present