Joint Transmission Rate Control and OpportunisticNetwork Coding OverWireless Networks
Abstract Existing opportunistic network coding architectures (e.g., COPE) rely on pseudobroadcast
to deliver a coded packet to multiple receivers in a single transmission. Only the
primary receiver acknowledges the reception by MAC-layer acknowledgements (synchronousACKs)
and the other receivers receive the coded packet by overhearing and acknowledge
the reception by asynchronous ACKs, which are usually piggybacked in outgoing data packets.
In realistic wireless networks, this mechanism may cause unnecessary retransmissions if
asynchronous ACKs are dropped due to packet losses or arrive late and thus compromise the
throughput gain brought by network coding. In this paper, we propose a framework of joint
rate control and code selection (ORC) to address this issue, aiming at improving the performance
gain of opportunistic network coding in wireless networks. The framework of ORC
consists of two mechanisms: (1) Rate control: the optimal transmission rate for coded packets
is selected by formulating the rate control process as a Finite Horizon Markov Decision
Process. (2) Code selection: based on the results of rate selection, the packet combination for
forming the coded packet is determined. Numerical results show that ORC can substantially
improve the performance gain of opportunistic network coding compared with COPE.
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