Opportunistic file transfer over a fading channel: A POMDP search theory formulation with optimal threshold policies

• Published in: IEEE transactions on wireless communications Vol. 5; no. 2; pp. 394 - 405
• Main Authors: Johnston, L.A., Krishnamurthy, V.
• Format: Journal Article
• Language: English
• Published: Piscataway, NJ IEEE 01.02.2006; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Applied sciences; Automatic repeat request; Batteries; Channels; Delay; Energy transmission; Exact sciences and technology; Fading; Mathematical models; Optimal control; Optimization; Policies; Search problems; Searching; State feedback; Studies; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Thresholds; Transmission and modulation (techniques and equipments); Transmitters; Wireless application protocol; Wireless sensor networks; Fading channels; Performance evaluation; Markov process; Markov decision; File transfer; Partially observed Markov decision process; Transmission channel; ARQ protocol; Gilbert Elliott channel; Algorithm; Implementation; threshold policy; optimal search theory; Algorithm performance; Optimal control; Heuristic method; Notices; Numerical simulation; Automatic repeat request; Transmission error
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/TWC.2006.1611063

We present a computationally efficient algorithm that minimizes the transmission energy and latency associated with transmitting a file across a Gilbert Elliott fading channel. We formulate the optimal tradeoff between transmission energy and latency as a partially observed Markov decision process problem (POMDP). The channel state is not directly observed and hence transmission decisions must be based on ACK/NAK information provided over a feedback channel. The key idea is to reformulate the resulting POMDP as a Markovian search problem, with optimal transmission control policies that are threshold in nature. Threshold policies are computationally inexpensive to implement. Our analysis shows that for different parameter values of the Gilbert Elliott fading channel, the optimal transmission policy, while threshold in structure, exhibits vastly different behaviour - from persistent retransmission to back-off and wait. Numerical examples demonstrate the performance improvements that can be obtained using the optimal threshold policies as compared to existing heuristic algorithms.