Network-coded Cooperative Communications Research Articles

Multi-source network-coded D2D cooperative content distribution systems

In this paper, we investigate the information transmission in a typical 5G device-to-device (D2D) communication application scenario, i.e., a content distribution system with a number of information sources intending to broadcast their messages to multiple destinations in the vicinity. Due to the dynamic nature of wireless signal propagation links, it is hard to guarantee a satisfactory performance by direct source-destination transmissions, especially when the system is operating in a reuse-mode. Relays can be introduced to the system to solve this problem. However, adopting the conventional repetition coding at relays inefficiently utilizes the available resources, for the considered multi-source scenario. Therefore, we investigate applying a class of finite-field network codes at the relays, when potentially three types of relays are deployed to assist the information distribution process. We proposed the algorithms to derive the system outage probability and analyze the trade-off between energy efficiency and spectral efficiency. Our analytical and numerical results clearly demonstrate the potential of exploiting network-coded cooperative communications in future 5G D2D systems.

Network-coded cooperative communications with multiple relay nodes: Achievable rate and network optimization

Network-coded cooperative communications (NC-CC) refers to the use of network coding (NC) in cooperative communications (CC). Prior studies have shown that NC has the potential to improve the performance of CC when there are multiple sessions in the wireless network. These studies were done for the case when multiple sessions are sharing a single relay node. However, how NC-CC behaves when multiple relay nodes are employed remains an open problem. In this paper, we explore this problem by analyzing the achievable rate of each session in this setting. We develop closed form formulas for the mutual information and the achievable data rate for each session. We show that prior results for a single relay is a special case of our result. Based on these findings, we then study a network optimization problem that requires joint optimization of session grouping, relay node grouping, and matching of session/relay groups. We show that this problem is NP-hard, and present a polynomial time heuristic algorithm to solve this problem. Using simulation results, we show this algorithm is highly competitive and can produce results that are near to optimality.

Joint Optimization of Session Grouping and Relay Node Selection for Network-Coded Cooperative Communications

Network-coded cooperative communications (NC-CC) is a new paradigm for communications in wireless networks that employs network coding (NC) to improve the performance of CC. A key problem to harness the potential of NC-CC is how to put sessions into different groups, and assign a relay node for each group. In this paper, we study this joint grouping and relay node selection problem for NC-CC. We provide a formal proof of NP-hardness for this problem. Due to NP-hardness, we propose a distributed and online algorithm and show that it offers near-optimal solution to this problem. The key idea in this algorithm is to have each neighboring relay node of a new session calculate the best local group that it can offer and advertise this information; and then to have the source node of the new session select the best local group to join among all offers. We show that our distributed algorithm has polynomial time complexity. Using extensive numerical results, we show that our distributed algorithm adapts well to online network dynamics.

Energy Efficiency of Network Coded Cooperative Communications in Nakagami-$m$ Fading

In this letter, we evaluate the energy efficiency of a wireless network-coded cooperative system where multiple nodes cooperatively transmit their information to a common destination. The energy consumption of the transmission and reception circuits is taken into account. It is shown that network coding can provide significant energy savings compared to direct transmission and traditional cooperation techniques. We consider a Nakagami- m fading model, so that the influence of a line-of-sight is also investigated. The optimal number of users that minimizes the energy consumption is obtained analytically, and confirmed by numerical results. Using this number to organize the nodes in clusters can provide considerable energy savings and decrease the network encoding/decoding complexity.

Network Coding in Cooperative Communications: Friend or Foe?

A major benefit of employing network coding (NC) in cooperative communications (CCs) is its ability to reduce time-slot overhead. Such approach is called network-coded CC (or NC-CC). Most of the existing works have mainly focused on exploiting this benefit without considering its potential adverse effect. In this paper, we show that NC may not always benefit CC. We substantiate this important finding with two important scenarios: employing analog network coding (ANC) in amplify-and-forward (AF) CC, and digital network coding (DNC) in decode-and-forward (DF) CC. For both scenarios, we introduce the important concept of network coding noise (NC noise). We analyze the origin of this noise via a careful study of signal aggregation at a relay node and signal extraction at a destination node. We derive a closed-form expression for NC noise at each destination node and show that the existence of NC noise could diminish the advantage of NC in CC. Our results shed new light on how to use NC in CC most effectively.