The paper proposes a pilot symbol-aided technique to reduce the effects of multipath fading on digital signals in mobile radio environments. A pilot symbol from a known sequence is multiplexed into the data symbols at regular intervals to form frames of symbols for transmission. Using the pilot symbols in two consecutive frames, the receiver is able to estimate and correct the fading distortion. The proposed technique uses a linear extrapolation approach that requires no storage of previous data symbols and introduces virtually zero delay to the received message. A series of computer-simulation tests has been carried out to assess the performance of the proposed technique on different signal constellations, including the 8PSK, 16PSK, 16QAM and star-16QAM signals, in the Rayleigh fading channels. The results have shown that significant improvements in bit-error rate performances of the systems can be achieved by the proposed technique. 0-7803-1825-0/94 $4.00 0 1994 IEEE

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The paper studies techniques for transmitting a 16-ary quadrature-amplitude modulated (16QAM) signal in different mobile radio environments. Conventional multipath fading compensation techniques using only the pilot symbols, incorporated with zeroth-order and firstorder prediction methods, are studied. Novel techniques making use both the pilot symbols and the data symbols, together with the improved zeroth-order and first-order prediction methods, are proposed. A series of intensive Monte Carlo simulations has been carried out on these techniques and the results have shown that, at high signal-tonoise ratios (SNRs), the bit-error rate (BER) performance can be reduced by a factor of about 46 and 2 using the improved zeroth-order and first-order prediction respectively, relative to those obtained using the pilot symbols only.

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