Coded unicast downstream traffic in a wireless network: analysis and WiFi implementation

Abstract

In this article, we design, analyze and implement a network coding based scheme for the problem of transmitting multiple unicast streams from a single access point to multiple receivers. In particular, we consider the scenario in which an access point has access to infinite streams of data to be distributed to their intended receivers. After each time slot, the access point receives acknowledgments on previous transmissions. Based on the acknowledgements, it decides on the structure of a coded or uncoded packet to be broadcast to all receivers in the next slot. The goal of the access point is to maximize the cumulative throughput or discounted cumulative throughput in the system. We first rigorously model the relevant coding problem and the information available to the access point and the receivers. We then formulate the problem using a Markov decision process with an infinite horizon, analyze the value function under the uncoded and coded policies and, despite the exponential number of states, devise greedy and semi-greedy policies with a running time which is polynomial with high probability. We then analyze the two users case in more detail and show the optimality of the semi-greedy policy in that case. Finally, we describe a simple implementation of the suggested concepts within a WiFi open-source driver. The implementation performs the network coding such that the enhanced WiFi architecture is transparent above the MAC layer.

Coded retransmission in wireless networks via abstract MDPs: Theory and algorithms

“…Denote the size of the maximal clique in s by L(s). Note that while finding a maximal clique is hard in general, graphs resulting from the state matrix in our setting are random and have cliques of logarithmic size [10]. Hence, searching for the max clique is at most polynomial and L(s) can be efficiently found.…”

“…Reference [10] attempted to provide heuristic algorithms for a small number of users, without considering the channel conditions. The algorithms therein show inferior performance compared to the learning-based solutions suggested in this work which account for the packet loss uncertainty.…”

Instantly Decodable Network Coding Schemes for In-Order Progressive Retransmission

“…The packet's weight for the IPE is set as w i = M + 1 − i and the weight vector for the IPE-U is set as w = [10, 9,8,7,6,5,4,3,2,1]. We consider the performance in scenario that no retransmission loss and give the lower bound as in Fig.…”

“…Typically a broadcast session consists of the initial broadcast stage and the retransmission stage. The design of online NC-based retransmission schemes has received significant recent interest [1], [2], [3], [4], [5], [6], [7]. It is known that the random linear network coding (RLNC) scheme [1], [2] minimizes the total transmission delay of the entire set of the desired packets, at the cost that no packet can be decoded until a sufficient number of coded packets are received.…”

“…It is known that for broadcasting data without decoding dependency, the optimal coding is to search for maximal cliques [4], [5], [7]. In this work, the decoding dependency between source packets is addressed via weighting in the coded packets in the construction process to maximize a utility function.…”