Bit error rate performance of π / 4 DQPSK for Nakagami-lognormal channels

Introduction: In a recent Letter [1], Tjhung and Chai have derived an infinite series for the bit error rate (BER) of π/4 DQPSK for Nakagami-lognormal (NLN) channels provided the Nakagami fading figure is constrained to be an integer. This modulation scheme, differential quadrature phase shift keying, has been adopted for several practical mobile systems. Therefore, evaluation of its performance under general fading and shadowing conditions is useful. The purpose of this Letter is to suggest some improvements to the infinite-series solution.