一种改进LS信道估计算法在稀疏多径水声信道中的应用

Application of an improved LS channel estimation algorithm to sparse multipath underwater acoustic channel

为了消除水声正交频分复用调制(Orthogonal Frequency Division Multiplexing,OFDM)系统中噪声对稀疏多径信道估计的影响,提出了一种改进的最小二乘(Least-Square,LS)信道估计算法。该方法在传统基于离散傅里叶变换(Discrete Fourier Transform,DFT)插值的信道估计结构上进行了改进,得到了基于阈值探测的DFT插值信道估计方法,该方法将小于阈值的时域信道响应置零,探测最有效信道抽头,有效消除噪声干扰的影响。仿真结果验证了DFT插值在稀疏多径水声信道估计中的实用性;得到了当循环前缀长度与信道长度越接近时信道估计性能(Bit Error Rate,BER)越好的结论;确定了在两种调制方式下算法的阈值系数范围;且该新算法与已有算法所需的信噪比可低约2 d B,解决了用循环前缀长度来近似信道真实长度的实际问题。

In order to eliminate the effect brought from the noise in underwater orthogonal frequency division multip- lexing （OFDM） system, an improved least-square （LS） channel estimation method is proposed for sparse multi-path channel estimation. The conventional discrete Fourier transform （DFT）-based interpolation channel estimation method is improved by using threshold detecting channel estimation, which can decide significant channel taps and erase the effect of noise by comparing the time domain channel estimation value with the predetermined threshold. The pro- posed method increases estimation precision effectively. Simulation results demonstrate that the DFT-based interpola- tion is practical in sparse multipath underwater acoustic channel, and the bit error rate （BER） becomes better when the circular prefix approximate actual channel length gradually. Moreover, the threshold coefficient regions of this method for two modulation modes are ascertained. The results show that BER of the proposed LS channel estimation is better than that of the conventional DFT-based channel estimations by about 2 dB, therefore the problem of using circular prefix to substitute actual channel length, which exists in the conventional DFT-based channel estimation method, is solved.