Thesis
A BCJR algorithm-based turbo equalizer for multicarrier shallow underwater acoustic channels
Washington State University
Master of Science (MS), Washington State University
2016
Handle:
https://hdl.handle.net/2376/100585
Abstract
We consider a cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) communication system which transmits information over a shallow underwater acoustic channel. In this kind of channel, multipath causes inter-symbol interference (ISI). By using CP-OFDM we can effectively eliminate ISI, at the cost of somewhat reduced data throughput. However, because of the channel's large Doppler spread, the frequency orthogonality assumption of OFDM is not valid. Hence, inter-carrier interference (ICI) is introduced, which leads to higher bit error rates (BER). We first replicate the results in [1] by performing Monte Carlo simulations in Matlab of an approximate iterative maximum likelihood equalizer (IMLE) for mitigating ICI. We then simulate the system over the same conditions for our BCJR equalizer (BCJRE), and compare the performance of both under a range of channel and system parameters. Our simulation results show that the BCJRE consistently outperforms the IMLE. For slow-varying channels, the gain is about 0.5 dB, while for fast-varying channels, it is 8 dB, revealing that the BCJRE is much more robust in high-ICI scenarios. In addition, ISI performance is explored by reducing the cyclic prefix guard time. Since the equalizers are not designed to deal with it, a performance loss of about 2 dB at low BER occurs. We also show how the presence of Doppler diversity allows both equalizers to overcome deep fades in the channel and that, by using turbo iterations, the performance of the equalizers can be further improved between 0.5 and 2 dB.
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Details
- Title
- A BCJR algorithm-based turbo equalizer for multicarrier shallow underwater acoustic channels
- Creators
- Jorge Andres Pires
- Contributors
- Thomas R. Fischer (Co-Chair)Benjamin Joseph Belzer (Co-Chair) - Washington State University, Electrical Engineering and Computer Science, School ofKrishnamoorthy Sivakumar (Committee Member) - Washington State University, Voiland College of Engineering and Architecture
- Awarding Institution
- Washington State University
- Academic Unit
- Electrical Engineering and Computer Science, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525108001842
- Language
- English
- Resource Type
- Thesis