Designs for pilot-symbol-assisted burst-mode communications with fading and frequency uncertainty

Abstract

High performance and reasonable complexity have made pilot-symbol-assisted modulation (PSAM) of great practical interest in mobile communications. However, no previous work has investigated PSAM in burst-mode operation which is commonly encountered in multiple-access schemes (time-division or slow-frequency-hopped system). This paper examines the burst structure design problem in a frequency-flat fading environment. The explicit relationship between error performance and the design parameters, including pilot allocation, frequency offset, Doppler spread, and modulation scheme, is explored. Periodic pilot insertion commonly used for continuous transmission produces degraded performance in burst-mode operation. A new, unequal-pilot-spacing burst architecture is proposed in this paper to achieve better error performance. This work also focuses on the potential performance improvement of a frequency offset estimator and a Doppler spread estimator. The results show that an improvement up to 2.5 dB in SNR/bit can be attained by a Doppler spread estimator. A significant frequency offset can produce an irreducible error floor or a severe reduction in the throughput rate if no compensation is implemented. The performance degradation investigated in this paper can be used to determine the specification of the frequency offset estimator and the Doppler spread estimator used in conjunction with PSAM.