Rate Aware Instantly Decodable Network Codes

This paper addresses the problem of reducing the delivery time of data messages to cellular users using instantly decodable network coding (IDNC) with physical-layer rate awareness. While most of the existing literature on IDNC does not consider any physical layer complications and abstract the model as equally slotted time for all users, this paper proposes a cross-layer scheme that incorporates the different channel rates of the various users in the decision process of both the transmitted message combinations and the rates with which they are transmitted. The consideration of asymmetric rates for receivers reflects more practical application scenarios and introduces a new trade-off between the choice of coding combinations for various receivers and the broadcasting rate for achieving shorter completion time. The completion time minimization problem in such scenario is first shown to be intractable. The problem is, thus, approximated by reducing, at each transmission, the increase of an anticipated version of the completion time. The paper solves the problem by formulating it as a maximum weight clique problem over a newly designed rate aware IDNC (RA-IDNC) graph. The highest weight clique in the created graph being potentially not unique, the paper further suggests a multi-layer version of the proposed solution to improve the obtained results from the employed completion time approximation. Simulation results indicate that the cross-layer design largely outperforms the uncoded transmissions strategies and the classical IDNC scheme

Instantly Decodable Network Coding for Real-Time Scalable Video Broadcast over Wireless Networks

In this paper, we study a real-time scalable video broadcast over wireless networks in instantly decodable network coded (IDNC) systems. Such real-time scalable video has a hard deadline and imposes a decoding order on the video layers.We first derive the upper bound on the probability that the individual completion times of all receivers meet the deadline. Using this probability, we design two prioritized IDNC algorithms, namely the expanding window IDNC (EW-IDNC) algorithm and the non-overlapping window IDNC (NOW-IDNC) algorithm. These algorithms provide a high level of protection to the most important video layer before considering additional video layers in coding decisions. Moreover, in these algorithms, we select an appropriate packet combination over a given number of video layers so that these video layers are decoded by the maximum number of receivers before the deadline. We formulate this packet selection problem as a two-stage maximal clique selection problem over an IDNC graph. Simulation results over a real scalable video stream show that our proposed EW-IDNC and NOW-IDNC algorithms improve the received video quality compared to the existing IDNC algorithms

Delay Minimization for Relay-Based Cooperative Data Exchange with Network Coding

We study the Relay-based Cooperative Data Exchange (RCDE) problem, where initially each client has access to a subset of a set of n original packets, referred to as their side information, and wants to retrieve all other original packets via cooperation. Unlike traditional Cooperative Data Exchange (CDE), in our proposed relay-based model, clients can only cooperate via a relay. The data exchange is completed over two phases, namely Uploading Phase and Downloading Phase. In the Uploading Phase, the clients will encode the original packets and transmit the coded packets to the relay. In the Downloading Phase, the relay will reencode the received packets and multicast the reencoded packets, each to a subgroup of clients. The coded packets in the two phases are carefully selected so that each client can retrieve all n original packets with minimum total transmission delay, based on its initial side information and on the coded packets it receives from the relay. In addition, we assume that the bandwidths between the relay and different clients are different, and that the upload/download bandwidths between the relay and the same client are also different. We establish a coding scheme that has the minimum total delay and show that it can be found in polynomial time, for sufficiently large underlying fields. We also design a heuristic algorithm that has a low complexity with binary field size. Our simulations show that the performance of the binary solution is very close to that of the optimal solution. All coding schemes considered in this work are scalar