Blind Fractionally Spaced Channel Equalization for Shallow Water PPM Digital Communications Links

Abstract

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 M-memory nonlinearity, M 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.

Performance Analysis of Turbo Codes, LDPC Codes, and Polar Codes over an AWGN Channel in the Presence of Inter Symbol Interference

“…The signal transmitted through the channel suffers various distortions (such as inter symbol interference). To resolve this issue, an equalizer is employed, for instance, a filter positioned at the output of the transmission channel, to fix/recover the transmitted signal [ 39 ].…”

Hybrid Space-Frequency Access for Underwater Acoustic Networks

“…In fact, SNR is essentially considered to be function of the attenuation on the first signal component arrival [33]. Second, a single-tap impulse response is typically the result of channel equalization performed at the receiver [34], [35], [36]. In this direction, communication performance can be reliably evaluated as a function of the SNR rather than the channel impulse response [37], [38].…”

On the Effect of Channel Knowledge in Underwater Acoustic Communications: Estimation, Prediction and Protocol

“…The mitigation of channel impairments is fundamental to provide a reliable communication link. Typical countermeasures consider the use of equalization [12,13] in order to restore the quality of the received signal. Alternatively, adaptive modulation and coding schemes are developed in order to match the transmission parameters with the channel behavior [14][15][16].…”