A Weighted Turbo Equalized Multi-Band Underwater Wireless Acoustic Communications

Abstract

The multi-band UWAS (Underwater Wireless Acoustic Sensor) communication techniques are effective in terms of performance and throughput efficiency because they can overcome selective frequency fading by allocating the same data to different frequency bands, in an environment of rapidly changing channel transfer characteristic. However, the multi-band configuration may have a performance worse than the single-band one because performance degradation in one particular band affects the output from all the other bands. This problem can be solved by using a receiving end that analyzes the error rates of each band, sets threshold values and allocates the lower weights to the inferior bands. There are many methods of setting threshold values. In this paper, we proposed an algorithm to set the threshold value by using the preamble error rates, which are known data that have to be transmitted and received. In addition, we have analyzed the efficiency of multi-band transmission scheme in the UWAS communication by applying 1~4 number of multi-bands, using turbo pi codes, with a coding rate of 1/3. We evaluated the performance of the proposed multi-bands transmission model in real underwater environments. Experimental results showed that the performance increased as the number of multiple bands increased. Furthermore, the performance of multi-band was improved when the proposed threshold algorithm was applied.overcomes the frequency-selective fading that occurs due to the underwater multi-path and the Doppler spread [9][10][11]. In other words, the multi-band communication technology overcomes various problems of underwater channel environments and extends the propagation distances, thereby, improving both the performance and the propagation efficiency. However, as long-distance communications use a narrow frequency band, the multi-band communication is based on a limited range of available frequencies. For military submarine applications, UWAS systems are required to remain undetected, be highly reliable, and require long-range communication. The goal of the multi-band underwater communication is to successfully transmit data in various underwater channel environments and extended propagation distances.The research project of EUROPA "UUV Covert Acoustic Communications" tested, at a sea trial, using eight sub-bands with turbo coding techniques, at a data rate of 75 bps, had a range of up to 50 km [12]. In the multi-band transmission and reception structure of the reference [12], the turbo coded 5670 bits of each band and the preamble 2880 bits were divided into 45 and then the divided preamble bits and coded bits were sequentially arranged to form a single packet, which was iteratively propagated to each band. However, the multi-band configuration may have worse performance than the single-band one. It is because the performance degradation in a particular band affects the output from the entire bands, which is input into an encoder, thereby decreasing the overall performance. This problem can be solved through a receiving e...

Multi-Media and Multi-Band Based Adaptation Layer Techniques for Underwater Sensor Networks

“…An algorithm is used to set the threshold for preamble error rates. In this experiment, the performance level was increased as the number of multi bands increased [52]. The dynamic bandwidth schedule algorithm was proposed to attain a multi-condition bandwidth in optical networks using OFDM-PON [53].…”