A low-complexity orthogonal time frequency space modulation method for underwater acoustic communication

一种低复杂度正交时频空间调制水声通信方法

¹ Research & Development Institute of Northwestern Polytechnical University in Shenzhen, Northwestern Polytechnical University, Shenzhen 518057, China
² School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China

Received: 29 December 2020

Abstract

Compared with the orthogonal frequency division multiplexing (OFDM) modulation, the orthogonal time frequency space(OTFS) modulation has a lower peak-to-average power ratio. It can effectively resist the time selective fading caused by the Doppler effect and has significant performance advantages over doubly dispersive channels. However, the conventional OTFS linear minimum mean square error (LMMSE) method has a high complexity and is not easy to process in real time. In order to solve this problem, we propose a low-complexity equalization algorithm with infinite norm constraints based on the optimal coordinate reduction. The equalization algorithm not only obtains the optimal solution through a certain number of iterations and avoids direct matrix inversion but also equalizes infinite norm constraints to improve the symbol detection performance gains. At the same time, the OTFS delay-Doppler channel matrix we utilize is sparse and the two-norm squares of each column vector equally reduces the complexity of optimal coordinate descent. Finally, the simulation in the underwater acoustic communication scenario we designed verify the effectiveness of the proposed equalization algorithm. The simulation results show that the performance of the proposed equalization algorithm is close to that of the LMMSE method, while its low complexity is ensured.

摘要

相比较正交频分复用，正交时频空间（orthogonal time frequency space，OTFS）调制具有较低峰均功率比，能有效抵抗多普勒产生的时间选择性衰落，在双扩展信道中具有良好的性能优势。然而，常规的OTFS线性最小均方误差（linear minimum mean square error，LMMSE）方法复杂度高，不易实时处理，为解决这一问题，提出了基于最优坐标下降的无穷范数约束均衡算法。该算法通过一定的迭代次数得到最优解，避免了直接矩阵求逆，采用无穷范数约束均衡提升了符号检测的性能增益。同时利用OTFS在时延-多普勒域信道矩阵每列向量二范数平方相等和稀疏性的特点，进一步降低坐标下降的复杂度。在设计的水声通信场景下，对所提均衡算法的有效性进行了仿真验证，结果表明所提均衡算法在保证低复杂度情况下误码性能接近最小均方误差性能。