Abstract
Problem statement: Multiple Access Interference (MAI) signals and poor estimation of the unknown channel parameters in the presence of limited training sequences are two of the major problems that degrade the systems’ performance. Two synchronous multiuser receivers with Rake reception of Interleave Division Multiple Access (IDMA) and Code Division Multiple Access (CDMA) systems, in conjunction with channel estimation, are considered for communication over different short range shallow water acoustic channels. Approach: The proposed hard/soft chip channel estimation and carrier phase tracking are jointly optimized based on the Mean Square Error (MSE) criterion and adapted iteratively by the reconstructed MAI signal. This is generated from exchanged soft information in terms of Log-Likelihood Ratio (LLR) estimates from the single-users’ channel decoders. The channel parameters and error estimation are used to enable the chip cancellation process to retrieve an accurate measurement of the detrimental effects of Intersymbol Interference (ISI) and MAI. Results: The performance of the proposed receiver structures with small processing gain are investigated and compare with 2 and 4 synchronous users using memoryless Quadrature Phase-Shift Keying (QPSK) at an effective rate of 439.5 bps per user. Conclusion: The results demonstrate that the performance is limited by MAI and ISI signals and the IDMA performance outperforms long code CDMA and short code CDMA.
Highlights
Underwater acoustic communication networks are a technology for the development of ocean communication systems
Since underwater communication uses acoustic waves instead of electromagnetic waves, it is only capable of low data rates compared with terrestrial communication
In short code Code Division Multiple Access (CDMA) packets, the signatures assigned to users during simulation are listed in Table 1 and they are periodic or remain the same for all symbols
Summary
Underwater acoustic communication networks are a technology for the development of ocean communication systems. Since underwater communication uses acoustic waves instead of electromagnetic waves, it is only capable of low data rates compared with terrestrial communication In such propagation mediums a low speed of sound propagation, time varying multipath channels and limited bandwidth are the main characteristics that result in a poor communication link and high latency posing challenges very different from terrestrial wireless networking. In order to maximize the power and bandwidth efficiency, IDMA with user specific interleaves has been proposed to meet these requirements by devoting the entire bandwidth expansion to low rate channel coding It mitigates the MAI and Intersymbol Interference (ISI) jointly by using a low complexity chip strategy (Ping et al, 2006; Zhou et al, 2007), which is far less complex than optimal (Moher, 1998) and suboptimal detectors (Wang and Poor, 1999) used in CDMA systems. The receivers with symbol rate adaptation may not perform satisfactorily in dynamic underwater channels, where the channel variations over symbol duration are not Corresponding Author: Aliesawi, S., School of Electrical, Electronics and Computer Engineering, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK 556
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