SQUARE-QAM ADAPTIVE MODULATION TDMA/TDD SYSTEMS USING MODULATION LEVEL ESTIMATION WITH WALSH-FUNCTION/

The authors propose a square-QAM adaptive modulation/time division mul tiple access/time division duplex (TDMA/TDD) system for land mobile co mmunications to achieve high quality and high bit rate transmission in both flat and frequency selective fading environments. To further imp rove performance, a new modulation level estimation scheme using the W alsh function and maximum likelihood (MS) estimation is also proposed. Computer simulation confirms that the proposed system gives 8dB bette r performance and four times larger delay spread immunity than that of conventional QPSK systems at BER = 10(-3).