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On optimal policies for network-coded cooperation:theory and implementation

Khamfroush, H. ; Lucani, D. E. ; Pahlevani, Phd ; Barros, J.

IEEE Journal on Selected Areas in Communications Vol. PP, Nº 99, pp. 1 - 15, January, 2015.

ISSN (print): 0733-8716
ISSN (online): 1558-0008

Scimago Journal Ranking: 2,09 (in 2015)

Digital Object Identifier: 10.1109/JSAC.2014.2384291

Abstract
Network coded cooperative communication (NC- CC) has been proposed and evaluated as a powerful technol- ogy that can provide a better quality of service in the next generation wireless systems, e.g., D2D communications. Previous contributions have focused on performance evaluation of NC- CC scenarios rather than searching for optimal policies that can minimize the total cost of reliable packet transmission. We break from this trend by initially analyzing the optimal design of NC-CC for a wireless network with one source, two receivers and half duplex erasure channels. The problem is modelled as a special case of Markov decision process (MDP), called stochastic shortest path (SSP), and is solved for any field size, arbitrary number of packets, and arbitrary erasure probabilities of the channels. The proposed MDP solution results in an optimal transmission policy per time slot and we use it to design near- optimal heuristics for packet transmission in a network of one source and N ≥ 2 receivers. We also present numerical results that illustrate the performance of the proposed heuristics under a variety of scenarios. To complete our analysis, our heuristics are implemented in Aalborg University’s Raspberry Pi test-bed and compared with random linear network coding (RLNC) broadcast in terms of completion time, total number of required transmissions, and percentage of delivered generations. Our measurements show that enabling cooperation only amongst pairs of devices can decrease the completion time by up to 4.75 times while delivering 100% of the 10000 generations transmitted, compared to RLNC broadcast delivering only 88% of them in our tests.