NSF Award
0098324
To meet rapidly increasing demand for satellite communications and broadcast services, there is a need for more bandwidth efficient techniques, and the use of higher level modulations is a natural choice. However, higher level modulations suffer relatively more performance degradation from satellite amplifier nonlinearity. This research focuses on the design and analysis of digital transmission for the nonlinear satellite channel, especially as regards the combination of highly efficient coded modulation, signal processing and decoding algorithms. <br/><br/>The research involves a comprehensive plan to develop and compare coded modulation, predistortion, equalization, and decoding algorithms for high-rate bandwidth-efficient nonlinear satellite channels (3 bits/symbol information rate and higher). Previous results of the investigator showed that with effective predistortion, the nonlinear channel is well-approximated by a peak power constrained but otherwise linear channel, and suitably optimized (12,4) PSK is superior to 16 QAM trellis coded modulation (TCM). The present work is focused on the following topics: (1) Higher rate TCM and multidimensional TCM for the predistorted channel; (2) Combined equalization and decoding of TCM in the nonlinear channel; (3) Turbo trellis coded modulation (TTCM) in the nonlinear channel, which may be powerful enough to not require predistortion or equalization; and (4) Hierarchical coded modulation in the nonlinear channel, which is suitable for variable error rate protection and/or backward compatibility. Although the focus is on ground-based transmitter or receiver techniques with a high power travelling wave tube amplifier (TWTA) transponder, the work is also applicable to on-board linearization of low power satellite amplifier or even in-hand linearization of a cell phone provided that a digitally generated signal is amplified (versus analog combining), because there is still the fundamental problem of bandwidth and power-efficient coded <br/>modulation design subject to a peak power constraint.
