This paper proposes COPE, a new architecture for wireless mesh networks. In addition to forwarding packets, routers mix (i.e., code) packets from different sources to increase the information content of each transmission. We show that intelligently mixing packets increases network throughput. Our design is rooted in the theory of network coding. Prior work on network coding is mainly theoretical and focuses on multicast traffic. This paper aims to bridge theory with practice; it addresses the common case of unicast traffic, dynamic and potentially bursty flows, and practical issues facing the integration of network coding in the current network stack. We evaluate our design on a 20-node wireless network, and discuss the results of the first testbed deployment of wireless network coding. The results show that COPE largely increases network throughput. The gains vary from a few percent to several folds depending on the traffic pattern, congestion level, and transport protocol.

Abstract — We propose to use joint network-channel coding based on turbo codes for the multiple-access relay channel. Such a system can be used for the cooperative uplink for two mobile stations to a base station with the help of a relay. We compare the proposed system with a distributed turbo code for the relay channel and with a system which uses separate network-channel coding for the multiple-access relay channel. Simulation results confirm that the systems with network coding for the multipleaccess relay channel gain cooperative diversity compared to the system with the distributed turbo code for the relay channel. Moreover, the results show that joint network-channel coding outperforms separate network-channel coding. The reason for this is that the redundancy which is contained in the transmission of the relay can be exploited more efficiently with joint networkchannel coding. I.

Abstract — In recent years, network coding has been investigated as a method to obtain improvements in wireless networks. A typical assumption of previous work is that relay nodes performing network coding can decode the messages from sources perfectly. On a simple relay network, we design a scheme to obtain network coding gain even when the relay node cannot perfectly decode its received messages. In our scheme, the operation at the relay node resembles message passing in belief propagation, sending the logarithm likelihood ratio (LLR) of the network coded message to the destination. Simulation results demonstrate the gain obtained over different channel conditions. The goal of this paper is not to give a theoretical result, but to point to possible interaction of network coding with user cooperation in noisy scenario. The extrinsic information transfer (EXIT) chart is shown to be a useful engineering tool to analyze the performance of joint channel coding and network coding in the network. I.

Evaluating the performance of a cooperative relaying protocol requires an implementation for simulators and/or software-defined radios (SDRs) with an appropriate model for error detection, combining, and Medium Access Control (MAC) automaton. Such implementations are essential for meaningful evaluation of practical systems since any protocol introduces overhead that constrains the theoretical performance in non-obvious ways. Unfortunately, protocols for cooperative relaying often yield complex implementations which are tedious to implement and debug. Therefore, we identify basic operations that are inherent to all cooperative relaying protocols, and we propose a new language for their specification. Then, we show how to construct a compiler for the proposed language that generates most of the required implementation (model and MAC automaton) automatically. This approach prevents subtle mistakes during implementation of the protocol, and can significantly increase development time. In addition, this paper discusses code generation exemplarily for OMNeT++/Mobility Framework, but the approach is not restricted to a specific simulator or SDR.

Abstract — We conduct an information theoretic analysis for the adaptive-network-coded-cooperation (ANCC) protocol over large wireless relay networks. The ANCC protocol adaptively encodes the data from different terminals using a single network code by matching the instantaneous network topology with the code graph of a low-density-parity-check (LDPC) code. The ergodic capacity and the outage probability of this protocol are analyzed for both finite and infinite network sizes, and closedform expressions are derived for the infinite case. Comparison with the existing protocols including repetition and space-timecoded-cooperation confirm that ANCC is both low-complexity and high-performance. I.

Abstract—A network with two sources, one relay, and one destination is considered. Under the assumption of noisy sourcerelay links causing the relay to be unable to decode without error, we propose a quantizer design framework where the quantizer jointly compresses the soft information available for both sources at the relay. The quantizer design is based on the information bottleneck method using the notion of relevant information as an optimization criterion. I.

Abstract—Network coding has been leveraged with cooperative diversity to improve performance in single channel wireless networks. However, it is not clear how network coding based cooperative diversity can be exploited effectively in multi-channel networks where overhearing is not readily available. Moreover, the question of how to practically realize the promising gains available, including multi-user diversity, cooperative diversity and network coding in multi-channel networks, also remains unexplored. This work represents the first attempt to unravel these two questions. In this paper, we propose XOR-CD, a novel XOR-assisted cooperative diversity scheme in OFDMA wireless networks. It can greatly improve the relay efficiency by over 100 % mostly, thus uplifting the throughput performance by over 30 % compared to conventional cooperative diversity scheme. In addition, we formulate a unifying optimization framework that jointly considers relay assignment, relay strategy selection, channel assignment and power allocation to reap different forms of gains. We design efficient polynomial time algorithms to solve the NP-hard problem with provably the best approximation factor, and verify their effectiveness using realistic simulations. I.

In wireless networks, cooperative transmission is used as a means to combat channel fading. In this system, a source and a relay transmit each others ’ messages to a common destination using either amplify-and-forward or decode-andforward strategies; the protocols in cooperative transmission can also broadly be categorized as static and adaptive. The idea in a network-coding-based cooperative transmission protocol is to allow the source and relay to combine messages by a network coding operation; a modulo-2 sum operation implements this network coding. In this work, the performance of various decode-and-forward-based cooperative transmission protocols without and with additional network coding is investigated. Outage probability is used as a measure of performance, and results for symmetrical source-relay and source/relay-destination channels are presented; also a source-relay-channels-based comparison is made. Based on these outage results, network-codingbased protocols are found to be suitable when the sourcerelay channels are unreliable; when the source-relay channels are good, protocols without network coding perform better. Moreover, to improve the performance of static protocols, we have introduced a sequence of decoding at the destination, and the corresponding outage results show that these protocols can achieve full diversity. Categories and Subject Descriptors E.4 [Coding and Information Theory]: Formal models

In this paper, we propose a practical scheme, called Non-Binary Joint Network-Channel Decoding (NB-JNCD) for reliable communication in wireless networks. It seamlessly couples channel coding and network coding, and can effectively combat the detrimental effect of fading of wireless channels, especially in large networks. On a high order Galois field, NB-JNCD combines nonbinary LDPC channel coding and random linear network coding through iterative joint decoding, which helps fully exploit the spatial diversity and redundancy residing in both codes. Furthermore, the scheme can unify non-binary source coding and high order modulation without the need of any bit-to-symbol conversion and its inverse. Through analysis and simulation, we demonstrate the significant performance improvement of NB-JNCD against other schemes.

Abstract—Multi-source relay-based cooperative communications can achieve spatial diversity gains, enhance coverage and potentially increase capacity when multiuser detection is used to effect maximum likelihood demodulation. If considered for large networks, traditional relaying entails loss in spectral efficiency that can be mitigated through network coding at the physical layer. These considerations motivate the complex field network coding (CFNC) approach introduced in this paper. Different from network coding over the Galois field, where wireless throughput is limited as the number of sources increases, CFNC always achieves throughput as high as 1/2 symbol per source per channel use. In addition to improved throughput, CFNCbased relaying achieves full diversity gain regardless of the underlying signal-to-noise-ratio (SNR) and the constellation used. Furthermore, the CFNC approach is general enough to allow for transmissions from sources to a common destination as well as simultaneous information exchanges among sources. Index Terms—Cooperative communications, multiuser detection, complex field coding, network coding, diversity gain, linkadaptive regeneration. I.