Differential Group Space-Time Block Coded CPM

Abstract

Motivated by the desirable attributes of unitary space-time (ST) codes and constant envelope modulations, we introduce an ST continuous phase modulation (CPM) methodology and its companion noncoherent receiver. We consider M-ary full-response CPMs, with a modulation index of 1/M and multiple transmit antennas. Through careful selection of an underlying differential group code, the defining characteristics of the CPM transmissions (constant envelope and spectral bandwidth) are effectively maintained. Using a set of interference suppressed statistics and taking advantage of the underlying ST differential encoding, the receiver performs conventional differential detection (CDD). Results for M = 2 with four transmit antennas show that the proposed CDD performs within 4 dB of the coherent detection lower bound, at a symbol-error-rate of 10-. Furthermore, due to the underlying unitary structure of the ST-CPM, the CDD achieves a diversity order comparable to that of coherent detection at high SNR.