Research on Channel State Information Feedback in Underwater Acoustic Adaptive OFDM Communication Based on Sequenced Codebook
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摘要: 水声(UWA)信道时延扩展大等特点导致信道频响(CFR)快衰落,水声通信(UWAC)技术发展受到挑战。发射端获取有效可靠的信道状态信息(CSI)是自适应通信的前提,针对水声自适应正交频分复用(OFDM)通信的需求,该文提出基于排序码本的信道状态信息分组排序拟合反馈算法(CSI-GSFF),包括分组、排序、数据拟合3个步骤。该算法首先将相邻导频子载波分组,以组为反馈单元;然后对各组内的导频子载波按照信道增益值进行排序,以减轻水声信道频响快衰落造成的反馈开销大等不利影响;最后进行多项式拟合,排序操作有效地降低了拟合阶数。通过实测海试时变信道数据仿真,结果表明,该文提出的信道状态信息反馈算法能够基本达到完美信道状态信息情形下的水声自适应OFDM通信系统误码率性能,同时可以有效地减少反馈开销。Abstract: As a result of the characteristics of UnderWater Acoustic (UWA) channel, such as rapid fading of Channel Frequency Response (CFR) due to large delay spreading, the development of UnderWater Acoustic Communication (UWAC) technology is challenged. The acquisition of effective and reliable Channel State Information (CSI) at the transmitter is a prerequisite for adaptive communication. To meet the needs of UWA adaptive OFDM communication, a CSI-Grouping-Sequencing-Fitting-Feedback (CSI-GSFF) based on sequenced codebook algorithm is proposed, which consists of three steps, including grouping, sequencing, and data fitting. Firstly, adjacent pilot subcarriers are divided into several groups and each group is seen as a feedback cell. Then, the pilot subcarriers within each group are sorted according to the channel gains to mitigate adverse effects such as high feedback overhead caused by the rapid fading of CFR. Finally, polynomial fitting is performed, and the sorting operation effectively reduces the fitting order. Through the simulation of time-varying channel data in sea trials, the results show that the CSI-GSFF algorithm can achieve the Bit Error Rate (BER) performance of the UWA adaptive OFDM communication system under the perfect CSI, while effectively reduce the feedback overhead.
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表 1 仿真参数设置表
参数名称 参数值 调制方式 BPSK/QPSK/8PSK/16QAM 采样频率(kHz) 48 中心频率(kHz) 9 信号带宽(kHz) 6 总子载波数目 1024 数据子载波数目 704 导频子载波数目 256 OFDM符号周期(ms) 171 循环前缀(ms) 50 表 2 不同反馈算法间归一化均方误差对比
反馈算法 归一化均方误差(×10–5) 多项式拟合(20阶) 21.4 多项式拟合(10阶) 23.9 压缩感知(压缩比为0.1) 8.2 压缩感知(压缩比为0.05) 26.8 分组排序拟合(32组2阶) 1.1 分组排序拟合(32组1阶) 2.5 表 3 反馈量对比
反馈算法 反馈量(Byte) 多项式拟合(20阶) 42 多项式拟合(10阶) 22 压缩感知(压缩比为0.1) 408 压缩感知(压缩比为0.05) 204 分组排序拟合(32组2阶) 256 分组排序拟合(32组1阶) 19 -
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