Bandwidth-Efficient Digital Modulation with Application to Deep-Space Communications

Chapter 6

Summary

This monograph has introduced and discussed a number of different bandwidth-efficient modulation schemes, in each case emphasizing the trade-off between their amount of envelope (or instantaneous amplitude) fluctuation and their bandwidth efficiency. While not specifically focused upon, the trade-off between power and bandwidth efficiency is also of importance. One means of illustrating this trade-off is via a plot of throughput efficiency (or its reciprocal) versus E_b/N₀ required to achieve a given error probability. In the next section, we offer such plots, obtained from a combination of simulation and analysis for many of the modulations (with and without error correction coding) discussed earlier. The measure of spectral containment used to arrive at the throughput is the 99 percent in-band power, which is equivalent to the −20-dB crossing on a fractional out-of-band power chart. Both unfiltered and filtered cases will be considered, the latter being of interest when the need arises to further restrict the transmitted RF bandwidth beyond that inherently achieved by the generic modulation technique.

6.1 Throughput Performance Comparisons

A 3-phase study [1–3] conducted by the CCSDS in response to an action item from the SFCG identified 10 modulations commonly used or planned by space agencies for bandwidth-efficient applications. The 10 modulations so identified were: PCM/PM/NRZ, PCM/PM/Biphase, QPSK, MSK, 8-PSK, BPSK/NRZ, BPSK/Biphase, OQPSK, GMSK, and FQPSK-B. ...