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Simple metrics derivation for a discrete time continuous phase modulation receiver

Monteiro, F. A. ; Rodrigues, A. J.

Simple metrics derivation for a discrete time continuous phase modulation receiver, Proc Wireless Personal Multimedia Communications Symp. - WPMC, Aalborg, Denmark, Vol. -, pp. 395 - 400, September, 2001.

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Abstract
This paper presents a practical quasi-optimum full digital receiver for a particular class of continuous phase modulation (CPM). The first step is the sampling of the received signal. Afterwards, only digital signal processing (DSP) is made. The detection process is composed of two software tasks: Viterbi maximum likelihood sequences detection (MLSD) preceded by phase transition metrics calculation. It is presented a low complexity procedure for metric calculations suitable for schemes having a number of CPM states S=0 mod 4 (S≥4). Those schemes exhibit certain symmetries on the plan of complex phase transitions that allow metric derivations from the metrics of transitions initiating in first quadrant states. ¾ of the metrics are derived by a copy and paste formula, substituting discrete time integrations. As well, metrics of the Q branch can be derived from the I ones. Therefore, a reduction factor of 4×2 can be accomplished for the number of stored transitions and the number of metrics computations.