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This paper first analyzes the symbol error rate (SER) performance of the space-time network coding (STNC) over independent but not necessarily identically distributed (i.n.i.d) Nakagami- $m$ fading channels, where multiple sources transmit information symbols to a destination through multiple helping amplify-and-forward (AF) relays. The exact expressions of the overall end-to-end received signal-to-noise ratio (SNR) via multiple STNC-AF relays and its moment generating function (MGF) are derived. Based on these results, the closed-form expression of STNC-AF for the SER with $M$ -ary phase-shift keying and $M$ -ary quadrature-amplitude modulation (QAM) modulations are then presented by adopting the unified MGF method. Furthermore, an approximate SER expression with low computational complexity is also given. In order to observe the performance limit, the diversity order and the nonorthogonality of STNC codes are discussed. Simulation results demonstrate our analytical results and it is illustrated that the diversity order of the STNC with multiple AF relay nodes is a sum function of the fading index of the direct link and the minimal fading indices of the multiple two-hop links. [ABSTRACT FROM PUBLISHER]

We investigate the multicast throughput of a butterfly network, which may be a promising topology for network coding application in next-generation wireless communication systems. The butterfly network consists of two sources, two destinations and a relay, where each destination requires decoding of data from two independent sources. It is assumed that all the nodes are operated in half-duplex mode. Each end-to-end packet transmission should be completed in a two-phase period. In order to reduce processing complexity and multiple interference, other nodes should keep silent when the relay transmits a signal. By using Avestimehr, Diggavi and Tse's deterministic model, we first introduce a deterministic butterfly network and demonstrate that its maximal multicast rate region can be achieved by employing a network coding policy. According to the results obtained in deterministic case, we then put forward a near-optimal design on the transmitted signal and decoding scheme for Gaussian scenarios based on a nested lattice code. It is proved that the gap between the achievable rate region and an outer bound is less than 3bits/s/Hz, which is not related to the signal-to-noise ratio. That is, the proposed scheme can approach the maximal multicast throughput. Finally, numerical results demonstrate that the gap is robust to both channel gains and time division of the two phases. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This letter investigates the outage performance of overhearing amplify-and-forward (AF) cooperative relaying system, where multiple sources transmit information symbols to a destination through multiple helping overhearing AF relays with space-time network coding (STNC) employed. First, by introducing the overhearing among the relays of STNC, a new transmission protocol, i.e., the STNC-based cooperative relaying with overhearing AF relays (STNC-OHAF), is presented. Then, the instantaneous end-to-end SNR expression of STNC-OHAF is analyzed. Based on this, an explicit expression of the outage probability for STNC-OHAF over independent but not necessarily identically distributed (i.n.i.d) Rayleigh fading channels is theoretically derived and the ability of STNC-OHAF to achieve full diversity order is proved. Numerical results validate our theoretical analysis and show that by introducing overhearing among relays, the outage performance of the STNC-based AF relaying system can be greatly improved. Besides, it is also shown that there is a trade-off between the normalized sum efficient system transmission rate and the number of sources. [ABSTRACT FROM PUBLISHER]

Applying network coding (NC) in the downlink of two-way relay networks can significantly increase the throughput. However, the fading nature of wireless channels usually causes great asymmetry between two downlink channels, which can degrade the performance of NC. Therefore, it is very necessary to perform an opportunistic scheme that selects between broadcast and unicast at the relay node based on channel side information. This paper focuses on the fundamental limit of the sum rate in the downlink. To solve the maximization problem of the sum rate in the downlink, we first introduce an auxiliary variable, known as marginal capacity income of transmit power, and then derive the corresponding power allocation in closed-form expression and present an opportunistic switching selection strategy between broadcast/unicast. Numerical results also show that our proposed scheme achieves a larger downlink sum throughput compared with other existing known schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate a multisource multicast network with the aid of an arbitrary number of relays, where it is assumed that no direct link is available at each S-D pair. The aim is to find the fundamental limit on the maximal common multicast throughput of all source nodes if resource allocations are available. A transmission protocol employing the relaying strategy, i.e., compute-and-forward (CPF), is proposed. We also adjust the methods in the literature to obtain the integer network-constructed coefficient matrix (i.e., a naive method, a local optimal method, and a global optimal method) to fit the general topology with an arbitrary number of relays. Three transmission scenarios are addressed. The first scenario is delay-stringent transmission, where each message must be delivered within one slot. The second scenario is delay-tolerant transmission where no delay constraint is imposed. The associated optimization problems to maximize the short- and long-term common multicast throughputs are formulated and solved, and the optimal allocation of power and time slots are presented. The third case (a general $N$-slot-delay-tolerant scenario) is also discussed, and a suboptimal algorithm is presented. Performance comparisons show that the CPF strategy outperforms conventional decode-and-forward (DF) strategy. It is also shown in the simulation that with more relays, the CPF strategy performs even better due to the increased diversity. Finally, by simulation, it is observed that, with CPF, the $N$-slot-delay-constraint case can perform close to that of the delay-tolerant case in terms of throughput, given that $N$ is relatively large. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate a three-node two-way relaying network over fading channels. The stability of this system is first discussed. Three protocols are then investigated in this work in terms of throughput, including the opportunistic digital network coding (ODNC) scheduling protocol, the physical network coding (PNC) protocol, and the cooperation protocol of DNC with direct link (CDNC-DL). For the first two protocols, we assume that the direct link is not available. For the third protocol, the direct link is available and can support data rates. The problems of maximizing the long-term totally fair optimal throughput with the three protocols, with respect to the stability constraints, are formulated and solved by allocating power resources with respect to channel fluctuations. To complement this work, optimal time resource allocation for each phase of the three protocols as well as the associated end-to-end throughput are investigated. In the end, it is shown in simulation that ODNC performs better than the conventional DNC and that CDNC-DL outperforms the other two proposed protocols as long as the direct link is in relatively good condition. [ABSTRACT FROM PUBLISHER]

Space time network coding (STNC) is a recently proposed time-division multiple-access (TDMA)-based cooperative relaying scheme for multi-relay wireless systems, which can achieve full diversity order with low transmission delay by taking advantage of the concepts of network coding and distributed space time coding. However, STNC does not fully exploit the benefit of the broadcast nature of wireless channels, since it only allows relays to receive signals from the sources. To explore the potential capacity of STNC-based systems, in this paper, we propose a new cooperative relaying scheme, termed space-time network coding with overhearing relays (STNC-OR), by allowing each relay to collect the signals transmitted from not only the sources but also its previous relays. Then, we derive some explicit expressions for the outage probability and symbol error rate (SER) for STNC-OR with decode-and-forward relaying over independent non-identically distributed (i.n.i.d) Rayleigh fading channels. For comparison, we also derive the explicit expression of the outage probability for STNC. To further improve the performance of STNC-OR, we investigate the effect of relay ordering on the performance of STNC-OR and then present the optimal relay ordering algorithm. Further, a suboptimal relay ordering is also designed to reduce the complexity. Extensive simulation and numerical results are presented finally to validate our theoretical analysis. It is shown that the proposed STNC-OR achieves much lower outage probability and SER than STNC and traditional pure TDMA relaying schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we analyze the outage probability of space–time network coding (STNC) in a distributed cooperative relaying system, where multiple sources transmit their information to a common destination with the help of multiple decode-and-forward (DF) relays in timedivision multiple-access (TDMA) mode. We first derive an exact closed-form expression of the outage probability for STNC with an arbitrary number of relays for independent but not necessarily identically distributed (i.n.i.d.) Rayleigh fading channels. With the developed result, we discuss the impact of the transmit SNR, the outage threshold, the number of relays, the nonorthogonal codes, and the relay position on the system performance. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, we propose a subnetwork decomposition/combination approach to investigate the single rate 2-pair problem. It is shown that the solvability of a single rate 2-pair problem is completely determined by four specific link subsets, namely, , , and of its underlying network. As a result, an efficient cut-based algorithm to determine the solvability of a single rate 2-pair problem is presented. [Copyright &y& Elsevier]

In the paper, we investigate the information spread problem in a joint vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communication system. A scene is considered where more information centers (or base stations) are allocated along the road so that the information centers are able to broadcast timely messages to vehicles within the range of the broadcast signal of each base station, which we shall refer to as broadcast zone . The seamless information spread is used to guarantee that messages are correctly received by each vehicle, regardless of whether it pulls into broadcast zones or not. We first derive the maximum throughput of the V2I downlink system for both additive white Gaussian noise (AWGN) channels and Rayleigh fading channels with Doppler effects. A measurement-based algorithm to estimate the throughput is also proposed. We then discuss the maximum achievable amount of information that can be relayed forward along a vehicular stream. A network coding technique will then be proposed to cancel the interference caused by relay signals to vehicles that are receiving messages from the corresponding information center. These theoretical results will give more insight into the vehicular communication system design. [ABSTRACT FROM PUBLISHER]