Adaptive signaling schemes with imperfect channel-quality estimates in wireless CDMA communications

Adaptive signaling techniques can be used to more-efficiently utilize system resources in wireless communication systems. We have previously shown that adaptive signaling with non-uniform M-ary phase-shift-keying can improve the throughput in a CDMA wireless communication system. This additional throughput can be used to include a second multimedia message, called an additional message, along with the standard message that would be transmitted without the use of adaptive signaling. The schemes that we have investigated adapt the spacing of points in the signal constellation and the code rate and signaling rate for the additional message. Techniques that employ only adaptation of the code rates for both messages have also been suggested to achieve this same goal. In this paper we analyze the effects of imperfect channel estimates on the performance of adaptive signaling schemes that use nonuniform signaling and schemes that adapt only the code rate. The results show that, in a variety of situations, the nonuniform signaling schemes provide a higher throughput than the schemes that use uniform constellations. We also analyze the effect of using code-combining automatic repeat request (ARQ) with these adaptive techniques.