Researchers use two-way soft decision feedback equalizer for OFDM communication system

[ Instrument network instrument research and development ] OFDM (orthogonal frequency-division multiplexing) technology can effectively combat the multipath effect of the channel, but it is susceptible to the Doppler effect. In a channel with large Doppler spread, the orthogonality between sub-carriers of the OFDM system will be destroyed, resulting in inter-sub-carrier interference. This will affect symbol detection and subsequent channel decoding, and increase the system's bit error rate.

In order to solve the above problems, the team of Yan Shefeng, a researcher at the Key Laboratory of Underwater Vehicle Information Technology of the Institute of Acoustics of the Chinese Academy of Sciences, proposed a bidirectional soft-decision feedback equalizer suitable for OFDM systems based on the bidirectional equalization algorithm in single carrier communication. decision feedback equalizer, BiSDFE). Related research results are published online on IEEE Wireless Communications Letters.

Researchers use a traditional one-way soft-decision feedback equalizer (Soft-decision feedback equalizer, SDFE) to equalize the received signal, perform frequency inversion on the OFDM demodulation symbol and estimated channel matrix, and derive the frequency inversion SDFE. The soft symbols output by the two are weighted and summed to obtain the final equalized output. Since the noise and error position in the output of the two equalizers are relatively low, and the estimated symbol is relatively high, the two-way diversity gain can be obtained through the weighted combination operation and the error propagation problem in the one-way SDFE is reduced, thereby improving the system Bit error rate performance.

The researchers compared the bit error rate performance of BiSDFE with the existing OFDM equalizers. The simulation results show that the new equalizer can achieve better bit error performance than traditional equalizers at all signal-to-noise ratios, and it is more popular. The advantage in the channel with larger Le spread (such as the underwater acoustic channel) is more obvious. In addition, it is in the same order of magnitude as the calculation of one-way SDFE. BiSDFE reveals the potential of OFDM technology and provides a possible solution for its application in Doppler extended channels such as mobile underwater acoustic communications.

The research work was funded by the National Natural Science Foundation of China.