Separable Implementation of L2-Orthogonal STC CPM with Fast Decoding

TL;DR

This paper introduces a separable implementation of L2-orthogonal STC CPM that simplifies decoding, generalizes to multiple antennas, and maintains full diversity with minimal bandwidth increase.

Contribution

It presents a novel separable structure for L2-orthogonal STC CPM, enabling easier generalization, full diversity proof, and simplified receiver design.

Findings

Decoding effort grows linearly with transmit antennas.

Full diversity achieved with general correction functions.

Simplified receiver with single CPM demodulator.

Abstract

In this paper we present an alternative separable implementation of L2-orthogonal space-time codes (STC) for continuous phase modulation (CPM). In this approach, we split the STC CPM transmitter into a single conventional CPM modulator and a correction filter bank. While the CPM modulator is common to all transmit antennas, the correction filter bank applies different correction units to each antenna. Thereby desirable code properties as orthogonality and full diversity are achievable with just a slightly larger bandwidth demand. This new representation has three main advantages. First, it allows to easily generalize the orthogonality condition to any arbitrary number of transmit antennas. Second, for a quite general set of correction functions that we detail, it can be proved that full diversity is achieved. Third, by separating the modulation and correction steps inside the receiver, a simpler receiver can be designed as a bank of data independent inverse correction filters followed by a single CPM demodulator. Therefore, in this implementation, only one correlation filter bank for the detection of all transmitted signals is necessary. The decoding effort grows only linearly with the number of transmit antennas.