O2-GIDNC: Beyond instantly decodable network coding

Recently, it has been proven that retransmission based on Network Coding (NC) can greatly improve the performance of wireless networks with broadcast erasure channels. However, network coding also introduces additional delay at the both sending and receiving sides, resulting in the decline of the Quality of user Experience (QoE). In this paper, we consider the users' waiting time and the decoding delay as the performance metrics and then propose MixCode, a NC-based loss recovery method, to improve the delay performance in heterogeneous wireless networks. MixCode incorporates Opportunistic Network Coding (ONC) with Random Linear Network Coding (RLNC), where a NC packet can be decoded by simply XORing operation at some destinations, but by Gaussian elimination at other destinations. Simulation results show that our proposed algorithm can efficiently reduce both the waiting time and the decoding delay in comparison with the existing NC-based schemes.

In this paper, we investigate the use of instantly decodable network coding (IDNC) for improving two fundamental performance metrics, namely, the completion time (as a measure of throughput) and mean decoding delay, in multicast cooperative data exchange (CDE) systems, where a group of geographically close clients cooperate with each other to obtain their missing packets. Here, an IDNC scheme is used for the transmissions across these clients. We utilize the stochastic shortest path (SSP) technique to study the minimum mean completion time problem. However, since finding the optimum solution is intractable, we use the obtained formulation to draw some theoretical guidelines to heuristically find solutions that can efficiently reduce the completion time. Second, we formulate the minimum mean decoding delay problem as selecting the appropriate maximal clique over well-structured graphs at the clients, and in order to reduce its complexity, we propose a simple heuristic algorithm for it. The effectiveness of our proposed algorithms is verified through extensive simulations and comparisons with existing techniques.

A recent approach--COPE, presented by Katti et al. (Proc. ACM SIGCOMM 2006, pp. 243-254)--for improving the throughput of unicast traffic in wireless multihop networks exploits the broadcast nature of the wireless medium through opportunistic network coding. In this paper, we analyze throughput improvements obtained by COPE-type network coding in wireless networks from a theoretical perspective. We make two key contributions. First, we obtain a theoretical formulation for computing the throughput of network coding on any wireless network topology and any pattern of concurrent unicast traffic sessions. Second, we advocate that routing be made aware of network coding opportunities rather than, as in COPE, being oblivious to it. More importantly, our model considers the tradeoff between routing flows close to each other for utilizing coding opportunities and away from each other for avoiding wireless interference. Our theoretical formulation provides a method for computing source-destination routes and utilizing the best coding opportunities from available ones so as to maximize the throughput. We handle scheduling of broadcast transmissions subject to wireless transmit/receive diversity and link interference in our optimization framework. Using our formulations, we compare the performance of traditional unicast routing and network coding with coding-oblivious and coding-aware routing on a variety of mesh network topologies, including some derived from contemporary mesh network testbeds. Our evaluations show that a route selection strategy that is aware of network coding opportunities leads to higher end-to-end throughput when compared to coding-oblivious routing strategies.

In recent years, network coding has emerged as an innovative method that helps wireless network approaches its maximum capacity, by combining multiple unicasts in one broadcast. However, the majority of research conducted in this area is yet to fully utilize the broadcasting nature of wireless networks, and still assumes fixed route between the source and destination that every packet should travel through. This assumption not only limits coding opportunities, but can also cause buffer overflow in some specific intermediate nodes. Although some studies considered scattering of the flows dynamically in the network, they still face some limitations. This paper explains pros and cons of some prominent research in network coding and proposes FlexONC (Flexible and Opportunistic Network Coding) as a solution to such issues. The performance results show that FlexONC outperforms previous methods especially in worse quality networks, by better utilizing redundant packets spread in the network.

In this article, we consider a buffer-aided two-way relay network in which a wireless-powered relay acts as an intermediate node for exchanging the data between two sources. The relay applies a time-switching (TS) policy to switch between data decoding (DD) and energy harvesting (EH) modes. Due to the presence of data queues at the relay, the relay is capable of employing opportunistic network coding (ONC) for transmission of the packets. Based on some realistic assumptions, we derive the stability region of such a network through designing TS and ONC policies. It is proved that the stability region is characterized by the TS policy and zero-wait ONC policy. Moreover, we derive the throughput-optimal and power-optimal policies and show that these policies provide the maximum coding opportunities. Also, we derive the average delay of an applied TS-ONC policy at the relay through modeling the data queues and energy buffer of the relay by two inter-related quasi-birth-death processes. We show that although waiting in ONC does not contribute to throughput-optimal and power-optimal policies, it can reduce the average delay. Finally, through simulation, we confirm our analytical results.

COPE, presented by Katti et al. (Proc. ACM SIGCOMM 2006, pp.243-254), exploits the broadcast nature of the wireless medium through opportunistic network coding. In this paper, we introduce the basic knowledge and characteristic of COPE, and propose a multi-channel multi-interface wireless network coding algorithm based on guesswork (GUESS-MCMI-COPE). By reducing the space of reception reports and implementing multi-channel multi-interface, GUESS-MCMI-COPE can increase network throughput. We evaluate our design on NS2, and discuss the results. The results show that the performance of GUESS-MCMI-COPE is superior to that of COPE.

This paper investigates the delay minimization problem for instantly decodable network coding (IDNC) based device-to-device (D2D) communications. In D2D enabled systems, users cooperate to recover all their missing packets. The paper proposes a game theoretic framework as a tool for improving the distributed solution by overcoming the need for a central controller or additional signaling in the system. The session is modeled by self-interested players in a non-cooperative potential game. The utility functions are designed so as increasing individual payoff results in a collective behavior which achieves both a desirable system performance in a shared network environment and the Nash equilibrium. Three games are developed whose first reduces the completion time, the second the maximum decoding delay and the third the sum decoding delay. The paper, further, improves the formulations by including a punishment policy upon collision occurrence so as to achieve the Nash bargaining solution. Learning algorithms are proposed for systems with complete and incomplete information, and for the imperfect feedback scenario. Numerical results suggest that the proposed game-theoretical formulation provides appreciable performance gain against the conventional point-to-multipoint (PMP), especially for reliable user-to-user channels.

This paper investigates network coding with full diversity and a high rate for improving the reliability of wireless communications against the co-channel interference. We consider a cellular network composed of two user terminals that are intended to communicate with a common base station (BS), where a two-way relay node is used to assist the bidirectional communications between the users and BS. We propose an opportunistic network coding (ONC) scheme with the two-way relay, called two-way ONC, which operates depending on whether or not the relay node successfully decodes data packets of the user terminals and BS. Closed-form outage probability expressions of the uplink transmission (from users to BS) and downlink transmission (from BS to users) are derived for the proposed two-way ONC scheme in the presence of co-channel interference over Rayleigh fading channels. We also develop the diversity-multiplexing tradeoff (DMT) of the two-way ONC scheme and show that it obtains the full diversity and an increased multiplexing gain , as compared with conventional one-way relay methods. Additionally, numerical outage probability results demonstrate that the proposed two-way ONC scheme outperforms the conventional one-way relay approaches in terms of improving the communication’s reliability against co-channel interference.

Opportunistic network coding (ONC) has shown high potential in enhancing the quality-of-experience for the clients of cellular networks using their previously downloaded files. In this paper, we study the problem of offloading clients from the macrocell base station (MBS) with the help of femtocaches (FCs) and ONC. We formulate this MBS offloading problem as an optimization problem over an ONC graph, and prove that it is nondeterministic polynomial-time (NP)-hard. Thus, we propose an ONC-broadcast offloading scheme, which utilizes separate ONC graphs at the MBS and FCs in addition to uncoded broadcasting, to offload the clients from the MBS. We analyze the performance of the ONC-broadcast offloading scheme and show that it is asymptotically optimal using random graph theory. Since even this ONC-broadcast offloading scheme is still NP-hard to implement, we devise an efficient heuristic to simplify the implementation. We show that the proposed heuristic reduces the worst case complexity of implementing the ONC-broadcast offloading scheme from an exponential to a quadratic function of the total number of vertices in the FC ONC graph. Simulation results show that, despite its low complexity, the proposed heuristic achieves similar MBS offloading performance to the ONC-broadcast offloading scheme.

Opportunistic routing is a recent routing paradigm that achieves high throughput in the face of universally lossy wireless links in mobile ad hoc networks, likewise, network coding popularly investigated by many institutes is another approach for improving the throughput in wireless networks. How to combine both the techniques is an interesting research. To our knowledge, this is still an open issue to implement the multicast routing in mobile ad hoc networks simultaneously employing both the mechanisms. Due to feedback explosion, most existing wireless network multicast protocols do not guarantee the reliable delivery. In this paper, we propose a novel reliable multicast protocol based on the opportunistic routing and network coding. Additionally, we also provide an expected number of transmission-based cost metric formula of the multicast sub-group. Extensive simulation reveals that the performance of the novel presented multicast routing protocol outperforms the conventional multicast routing protocol in ad hoc wireless networks.

The optimized link state routing (OLSR) protocol is widely used in wireless ad hoc networks. With OLSR, only one routing path from source to destination is established at a time. However, links of wireless networks are very unreliable, and network topologies might vary rapidly. These features may cause frequent data retransmissions or the route rebuilding. Hence, improving the network throughput becomes a big challenge. This paper designs a new high-throughput routing protocol (HTRP) for wireless sensor networks, which combines the OLSR protocol with opportunistic routing and network coding. Opportunistic routing is able to leverage the wireless channel's characteristic of broadcasting and opportunistically deliver data through multiple routing paths. And OLSR can provide the information about network topologies and other parameters that opportunistic routing needs but cannot gain by itself. We evaluate the performance through both simulation and empirical experiments. The throughput of the HTRP is more than 10× and 2× of the OLSR protocol respectively in simulation and experiments.

A fundamental understanding of the relationship between delay performance and complexity in network coding is instrumental towards its application in practical systems. The main argument against delay-optimal random linear network coding (RLNC) is its decoding complexity, which is O(n 3 ) for n original packets. Fountain codes, such as LT and Raptor codes, reduce the decoding load on the receiver but at the cost of introducing additional, non-negligible delay. The source of this increased delay is the inherent sparsity of the code, which significantly reduces the impact of a new coded packet, i.e., the probability of a packet to be linearly independent from the knowledge at the receiver, as we approach the end of the transmission (when few degrees of freedom are missing). Thus, the additional overhead is mainly due to the transmission of the last data packets. Our key observation is that switching gears to denser codes as the transmission process progresses could considerably reduce the delay overhead while maintaining the complexity advantages of a sparse code. We propose tunable sparse network coding as a dynamic coding mechanism with a code structure with two regions: a sparse region, with various levels of sparsity, and a dense region, where packets are generated as per RLNC. We characterize the problem in multicast sessions on general networks and illustrate trade-offs in especial cases of interest. We also present a novel mechanism to perform efficient Gaussian elimination for sparse matrices that guarantees linear decoding complexity with high probability.

Multi-hop device-to-device (D2D) communications play an important role in expanding D2D coverage. In this paper, we study a relay-based and network-coding-assisted (in particular, XOR coding) multi-hop D2D communication system. In the system, toward jointly considering the impact of interference and network traffic conditions on the quality of D2D communications, various channel fading models and traffic models are investigated, and the packet loss probability of D2D links is meticulously computed using these models. With the packet loss probability of D2D links, the general closed-form expressions of end-to-end packet loss probability (E2EPLP) of the system with the presence (or absence) of XOR coding are subsequently derived. Our experiments reveal that both the number of relays and the mechanism of XOR coding can affect the system performance. Specifically, the increase in the number of relays will lower the overall system performance (e.g., an increase in the E2EPLP and end-to-end completion time, and a decrease of the end-to-end rate may follow as a result). On the other hand, although the presence of XOR coding unfortunately raises the system E2EPLP, it can effectively improve the end-to-end completion time and end-to-end rate. It is our belief that the analytical approach proposed in this paper and the results found in our work can be useful to peer studies in the context of applying network coding in multi-hop D2D networks.

Network coding is proved to improve the throughput, decrease network latency and balance the network overhead. Combined with wireless overhearing, some proposed representative schemes on network coding, such as linear network coding and Completely opportunity encoding (COPE). The former scheme is based on complicated linear operation, while the latter is implemented by the way of pairwise XOR-ing which is simple and low efficiency. In order to resolve these problems, we put forward a group-based XOR-ing network coding scheme, which has the characteristics of high efficiency and low complexity. Experimental results and theoretical analysis demonstrate that our scheme has higher throughput gains and lower delay than traditional schemes. In addition, our proposed scheme has the best characteristic of fairness among the state-of-the-art approaches.

Network Coding has attracted significant attention in recent years, and it has been widely applied in broadcast, multicast and unicast. Nevertheless, the study on network coding in convergecast is still in the theoretical analysis and the simulation stage. In order to investigate the network coding gain of convergecast in realistic wireless sensor networks, a network coding-based convergecast scheme is realized in this paper. The experiment is conducted in the basic size of convergecast whose size is limited below four, which is for the purpose of eliminating as much interference from the large size of convergecast network as possible. Performed in traditional convergecast scheme and network coding convergecast scheme, the experiment on collection rate and energy consumption are evaluated under different link delivery ratios and scales of convergecast network. The experiment results show that network coding is certain to introduce benefit in the case of poor link equality. However, it is inferior to the traditional scheme when the wireless link delivery ratio is high enough due to the conscious overhearing and the prerequisite of successful decoding.