Abstract
Multichannel receivers are usually employed in high-rate underwater acoustic communication to achieve spatial diversity. In the context of multichannel underwater acoustic communications, passive time reversal (TR) combined with a single-channel adaptive decision feedback equalizer (TR-DFE) is a low-complexity solution to achieve both spatial and temporal focusing. In this paper, we present a novel receiver structure to combine passive time reversal with a low-order multichannel adaptive decision feedback equalizer (TR-MC-DFE) to improve the performance of the conventional TR-DFE. First, the proposed method divides the whole received array into several subarrays. Second, we conduct passive time reversal processing in each subarray. Third, the multiple subarray outputs are equalized with a low-order multichannel DFE. We also investigated different channel estimation methods, including least squares (LS), orthogonal matching pursuit (OMP), and improved proportionate normalized least mean squares (IPNLMS). The bit error rate (BER) and output signal-to-noise ratio (SNR) performances of the receiver algorithms are evaluated using simulation and real data collected in a lake experiment. The source-receiver range is 7.4 km, and the data rate with quadrature phase shift keying (QPSK) signal is 8 kbits/s. The uncoded BER of the single input multiple output (SIMO) systems varies between and for the conventional TR-DFE, and between and for the proposed TR-MC-DFE when eight hydrophones are utilized. Compared to conventional TR-DFE, the average output SNR of the experimental data is enhanced by 3 dB.
Highlights
Because of the unique characteristics of underwater acoustic (UWA) channels, achieving reliable high-speed wireless communications over underwater acoustic channels is still a challenging task.Typical UWA channel characteristics include very limited bandwidths, time-varying multipath propagation, double-selective channel fading, and strong background noise; large-delay spread of the multipath leads to severe inter-symbol interference (ISI) in the received signal
To mitigate ISI and signal fading caused by multipath propagation, spatial diversity and equalizers are widely used in high-rate underwater acoustic communications [1–3]
Compared with the conventional time reversal (TR)-DFE, the average bit error rate (BER) of TR-Multichannel decision feedback equalization (MC-DFE) was reduced by an order of magnitude
Summary
Because of the unique characteristics of underwater acoustic (UWA) channels, achieving reliable high-speed wireless communications over underwater acoustic channels is still a challenging task. Empirical results have shown that partitioning an array with large numbers of elements into subarrays, independently processing the signals received on each subarray, and combining the soft outputs of the processors for each subarray can lead to improved performance and reduced computational complexity [7]. We proposes a new receiver structure which combines passive TR processing of subarrays and a low-order adaptive multichannel DFE (TR-MC-DFE) to improve the performance of conventional passive TR. The contributions of this paper include the following aspects: (1) A TR-MC-DFE method is proposed to improve the performance of conventional passive TR communication; (2) The performances of TR-DFE and TR-MC-DFE are compared and analyzed using the data collected from one lake experiment; (3) The influence of three channel estimation algorithms on the performance of the TR-MC-DFE method is analyzed and compared.
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