Exploiting the Fast Spectral Roll-Off of CPM Sidelobes to Improve Bandwidth Efficiency in Satellite Communications

Abstract

Simple and efficient carrier-overlapping and interference-reduction techniques are addressed for frequency-division multiplexing–continuous phase modulation (FDM–CPM) schemes. CPM carriers are densely multiplexed (packed) in the frequency-domain, without leaving any guard bands, thus allowing frequency content in adjacent bands to overlap, so as to enhance the bandwidth efficiency. The intentional adjacent channel interference, introduced by carrier-overlapping during transmission, is combated at the receiver front-end using simple interference-reduction filters that are designed to exploit the fast roll-off of CPM spectral sidelobes. The receiver back-end is governed by a serially concatenated CPM iterative demodulation/decoding detector. Numerically optimal carrier-packing ratios are determined with respect to information-theoretic bounds. The presented method does not require cooperation among users, and is extended to QAM and PSK schemes as well. Bit error rate analyses show that the proposed non-cooperative receiver design facilitates bandwidth and energy-efficient communication for both the nonlinear and linear satellite channels, without resorting to multiuser detectors, and becomes an attractive solution when cooperation may not be feasible among users that are geographically spread-out.