Network Coding for Delay Constrained Wireless Systems with Feedback
Rui Filipe Mendes Alves da Costa · Open Repository of the University of Porto (University of Porto) · 2012
The advent of network coding brought a disruptive view to protocol design for communication networks. By combining different source packets in a single coded packet, network coding brings higher robustness and throughput for wireless networks. However, delay is not a primary concern in the design of standard network coding solutions. The topic of this thesis is how to use feedback information to design network coding solutions that can cope with traffic with delay constraints. We start by analyzing the delay that standard network coding solutions induce, when the time necessary to decode individual packets is of crucial importance. We then propose network coding schemes that allow receivers to immediately recover a new source packet from each coded packet. From a different angle, we propose delay control mechanisms for throughput optimal network codes. The proposed schemes offer a fine trade-off between the delay experienced by the receivers and the amount of throughput sacrificed to achieve such delay performance. We then focus our attention in scenarios where packets have to be delivered before strict deadlines. We propose a network coding protocol that makes use of periodic feedback transmissions to adapt its coding decisions in order to minimize the number of packets that miss the corresponding deadline. We further show that our proposal is suited for current wireless standards, by implementing the proposed scheme in a IEEE 802.11 wireless testbed. Finally, we provide a characterization of optimal network codes for maximizing the mean number of delivered packets over a half-duplex channel, when the receiver requires that a subset of the source packets is delivered with high probability. By jointly optimizing the scheduling of the feedback transmissions and the code design, we show that a judicious use of the feedback channel has a significant impact both in the mean number of delivered packets to the receiver and in the reliability level achieved.