Conventional OFDM systems employ a guard interval to combat delay spread distortion of the transmitted data. This reduces the efficiency of the OFDM transmission. A combined OFDM-equalization reception strategy is presented in this paper. This strategy employs an adaptive equalizer to combat delay spread distortion instead of a guard interval. This facilitates the use of very short guard intervals and thus the transmission efficiency of the OFDM modulation scheme is improved. This paper presents the combined OFDM-equalization receiver and the pre-FFT equalizer designs. The efficiency of both the conventional OFDM and combined OFDM-equalization strategies is considered and it is demonstrated that combined OFDM-equalization offers a significant improvement in transmission efficiency. The transmission of OFDM signals in single frequency networks is considered and it is shown that the combined OFDM-equalization technique is particularly effective for such applications, offering an improvement in bandwidth efficiency of 14% under severe delay spread conditions. The limitations of the combined OFDM-equalization strategy to operate effectively under both additive noise and time variant conditions are considered. The performance is simulated and the sensitivity to this impairment analyzed.
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Publisher: Institute of Electrical and Electronics Engineers (IEEE)
- OFDM modulation
- digital video broadcasting
- adaptive equalisers