Abstract: Underwater acoustic sensor networks
(UWASN) have been attracting growing
research interests in recent decades due
to various promising applications.
Underwater acoustic communications
(UAC), which adopts acoustic waves as
the information carrier, is the key
communication technique to realize
UWASN. However, UAC is very
challenging due to low carrier frequency,
distance-dependent bandwidth, large
delay spread, long and variable
propagation delay, and doubly-selective
fading. In this research, we will consider
cooperative communications to improve
the reliability and energy efficiency of
dual-hop UAC. OFDM is adopted as the
physical-layer transmission technique.
First, we will examine the power
allocation of dual-hop relay
communications. Two transmission
scenarios are considered: for the short-
range transmission scenario, an adaptive
system is developed based on the the
instantaneous channel state information
(CSI); for the medium-long range
transmission scenario, an selective
relaying protocol is designed based on
the statistical CSI. Secondly, we will
focus on the fountain codes design for
dual-hop relay communications to
enable reliable communications with
higher energy efficiency. In addition, to
improve the packet transmission
reliability, data repetition within one or
two consecutive OFDM symbols is
implemented according to the mirror-
mapping rules. Theoretical analyses and
simulation results demonstrate that the
reliability and energy efficiency can be
substantially improved using the
aforementioned techniques.

Adviser: Dr. Liuqing Yang
Co-Adviser: N/A
Non-ECE Member: Dr. Haonan Wang, Statistics
Member 3: Dr. Mahmood Azimi-Sadjadi, Electrical and Computer Engineering
Addional Members: Dr. Jie Luo, Electrical and Computer Engineering

Publications:
[J1] X. Cheng, R. Cao, and L. Yang ``Stochastic Polynomial Decomposition Based Energy-Efficient Hybrid DLT Codes,'' IEEE Transactions on Communications (to be submitted).
[J2] R. Zhang, X. Cheng, L. Yang, and X. Cheng ``Interference-Graph-Based TDMA Protocol for Underwater Acoustic Sensor Networks,'' IEEE Transactions on Wireless Communications (to be submitted).
[J3] X. Cheng, L. Yang, and X. Cheng ``Adaptive Relay-Aided OFDM Underwater Acoustic Communications,'' (to be submitted).
[J4] M. Wen, X. Cheng, L. Yang, Y. Li, X. Cheng, F. Ji ``Index Modulated OFDM for Underwater Acoustic Communications,'' IEEE Communications Magazine (submitted).
[J5] X. Cheng, M. Wen, X. Cheng, and L. Yang, ``Effective Mirror-Mapping-Based Intercarrier Interference Cancellation for OFDM Underwater Acoustic Communications,'' Elsevier Ad Hoc Networks Journal, 2014.
[J6] X. Cheng, R. Cao and L. Yang, ``Relay-Aided Powerline Communications with Amplify-and-Forward,'' IEEE Transactions on Smart Grid, vol. 4, no. 1, pp. 265 - 272, March 2013.
[C1] X. Cheng, R. Zhang, L. Yang, and X. Cheng ``Heuristic IG-TDMA Protocol for Underwater Acoustic Sensor Networks,'' in Proceedings of
2015 IEEE Global Conference on Signal and Information Processing, Orlando, Florida, Dec. 14-16, 2015.
[C2] X. Cheng, L. Yang, and X. Cheng ``Adaptive Relay-Aided OFDM Underwater Acoustic Communications,'' in Proceedings of 2015 IEEE International Conference on Communications, London, UK, June 8-12, 2015.
[C3] Miaowen Wen, Xiang Cheng, Liuqing Yang and X. Cheng, ``Information-Guided Pilot Insertion for Capacity Improvement in OFDM Underwater Acoustic Communications,'' in Proceedings of the 48th Asilomar Conference on Signals, Systems and Computers, Pacific Grove, CA, November 2-5, 2014.
[C4] X. Cheng, B. Yu, X. Cheng and L. Yang, ``Two-Way Full-Duplex Amplify-and-Forward Relaying,'' in Proceedings of MILCOM Conference, San Diego, CA, Nov 18-20, 2013.
[C5] X. Cheng, M. Wen, X. Cheng and L. Yang, ``Effective Self-Cancellation of Intercarrier Interference for OFDM Underwater Acoustic Communications,'' in Proceedings of the International Conference on UnderWater Networks and Systems (WUWNet), Kaohsiung, Taiwan, November 11-13, 2013.
[C6] M. Wen, X. Cheng, X. Cheng, L. Yang and B. Jiao, ``Effective Intercarrier Interference Reduction Techniques for OFDM Underwater Acoustic Communications,'' in Proceedings of the 47th Asilomar Conference on Signals, Systems and Computers, Pacific Grove, CA, November 3-6, 2013 (invited).
[C7] X. Cheng, R. Cao and L. Yang, ``Practical Implementation of Hybrid DLT Codes for Cooperative Relay Communications,'' in Proceedings of MILCOM Conference, Orlando, FL, October 29- November 1, 2012.
[C8] X. Cheng, R. Cao, F. Qu and L. Yang, ``Relay-Aided Cooperative Underwater Acoustic Communications: Selective Relaying,'' in Proc. of MTS/IEEE Oceans Conference (OCEANS), Yeosu, Korea, May 21-24, 2012.
[C9] X. Cheng, R. Griffin, F. Qu and L. Yang, ``A Comparison of Multiband and Single-Band OFDM for Underwater Acoustic Communications,'' in Proc. of THE ACOUSTICS 2012 HONG KONG conference and exhibition, Hong Kong, May 13-18, 2012.
[C10] X. Cheng, F. Qu and L. Yang, ``Single Carrier FDMA over Underwater Acoustic Channels,'' in Proc. of 6th International ICST Conference on Communications and Networking in China, Harbin, China, August 17-19, 2011.
[C11] X. Cheng, R. Cao and L. Yang, ``On the System Capacity of Relay-Aided Powerline Communications,'' in Proceedings of IEEE International Symposium on Power Line Communications and Its Applications, Udine, Italy, April 3-6, 2011.

Program of Study:
ECE 520
ECE 568
ECE 799
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