DIET, Università "La Sapienza" di Roma, via Eudossiana 18, 00184 Roma, Italy.
Sensors (Basel). 2019 Oct 23;19(21):4604. doi: 10.3390/s19214604.
Underwater acoustic digital communications suffer from inter-symbol interference deriving from signal distortions caused by the channel propagation. Facing such kind of impairment becomes particularly challenging when dealing with shallow water scenarios characterized by short channel coherence time and large delay spread caused by time-varying multipath effects. Channel equalization operated on the received signal represents a crucial issue in order to mitigate the effect of inter-symbol interference and improve the link reliability. In this direction, this contribution presents a preliminary performance analysis of acoustic digital links adopting pulse position modulation in severe multipath scenarios. First, we show how the spectral redundancy offered by pulse position modulated signals can be fruitfully exploited when using fractional sampling at the receiver side, which is an interesting approach rarely addressed by the current literature. In this context, a novel blind equalization scheme is devised. Specifically, the equalizer is blindly designed according to a suitably modified Bussgang scheme in which the zero-memory nonlinearity is replaced by a -memory nonlinearity, being the pulse position modulation order. Numerical results not only confirm the feasibility of the technique described here, but also assess the quality of its performance. An extension to a very interesting complex case is also provided.
水下声数字通信会受到符号间干扰的影响，这种干扰是由信道传播引起的信号失真产生的。在处理短信道相干时间和由时变多径效应引起的大延迟扩展的浅水环境时，这种干扰尤其具有挑战性。为了减轻符号间干扰的影响并提高链路可靠性，对接收信号进行信道均衡是一个至关重要的问题。在这方面，本文针对严重多径环境下采用脉冲位置调制的水声数字链路进行了初步的性能分析。首先，我们展示了当在接收端采用分数采样时，脉冲位置调制信号提供的频谱冗余如何得到有效利用，这是当前文献中很少涉及的一种有趣方法。在这种情况下，设计了一种新的盲均衡方案。具体来说，均衡器是根据适当修改的 Bussgang 方案进行盲设计的，其中零记忆非线性被替换为记忆非线性， 为脉冲位置调制阶数。数值结果不仅证实了这里描述的技术的可行性，还评估了其性能的质量。还提供了一个非常有趣的复杂情况的扩展。
