A comparative study is presented showing the relative merits of four modulation techniques for use in line-of-sight digital radio systems operating at 45 Mbith in a bandwidth of 10 MHz. Candidate modulations are: conventional WQAM, reduced-bandwidth lSQAM, reduced-bandwidth 44QPRS, conventional 81 -QPRS.Comparisons are made from three points of bit-error-rate performance with unfaded robustness to multipath fading, sensitivity to timing and phase errors.Extensive numerical calculations show that none of the above signaling techniques is uniformly better than the others. Conventional 64-QAM seems the best solution to combat selective fading. On the other hand, reduced bandwidth 16-QAM and 44QPRS as well as conventional 81-QPRS all have the advantage of lower bit-errorrates and less sensitivity to synchronization errors. view: channels,
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