Abstract: The errors of the basis function in the receiver, caused by the difference of the spectrum environment between the transmitter and receiver of Transform Domain Communication System (TDCS), will degrade the system performance significantly. A design method of the basis function, which has suboptimal solution of the Signal-to-Noise Ratio (SNR), is proposed to solve this problem. Based on a detailed study of the data sending and receiving process, the optimized Bitter Error Rate (BER) of the system and its relationship with the basis function of the receiver is discussed. In the case that the system with spectral mismatches can not obtain the optimal basis function, a design method of the basis function similar to equal-gain combing is proposed, and then this basis function is used for modulation. Simulation results show that, in the conditions of both multi-user and single-user with high spectral mismatch ratio, the receiver is suboptimal when the basis function is designed similar to equal-gain combing. In the single-user condition, the BER performance improvement of suboptimal reception is approximately 4 dB compared with the reception method when the mismatch ratio is 40%, and the SNR loss is below 1.5 dB at the spectral efficiency of 80% compared with the optimal reception.

Key words: communication, transform domain communication system, basis function, spectral mismatches, equal gain combing, signal-to-noise ratio suboptimal solution