In this letter, we propose an efficient relay antenna selection algorithm for the amplify and forward (AF) two-way multiple-input multiple-output (MIMO) relay systems with analogue network coding (ANC). The proposed algorithm greedily selects the additional receive-transmit antenna pair that provides the maximum sum-rate. An iterative computation method is also designed to evaluate the sum-rate efficiently.

Traditional authentication protocols are based on cryptographic techniques to achieve identity verification. Distance bounding protocols are an enhanced type of authentication protocol built upon both signal traversal time measurement and cryptographic techniques to accomplish distance verification as well as identity verification. A distance bounding protocol is usually designed to defend against the relay attack and the distance fraud attack. As there are applications to which the distance fraud attack is not a serious threat, we propose a streamlined distance bounding protocol that focuses on the relay attack. The proposed protocol is more efficient than previous protocols and has a low false acceptance rate under the relay attack.

In this letter, we use the the protograph low-density parity check (LDPC) codes to create bit-interleaved coded modulation (BICM) for the half-duplex decode-and-forward (DF) relay network. The DF relay BICM design problem can be transformed into a problem of rate-compatible BICM design, where the different segments of modulated symbols experience different signal-to-noise ratios (SNRs). To optimize the BICM based on the protograph structure, we use the protograph extrinsic information transfer (EXIT) to evaluate the thresholds of different mapping patterns between the variable nodes and the modulated bits. With this tool, we search for the most efficient mapping pattern of BICM for the half-duplex DF relay network. Our work can achieve significant gains over the existing work.

This paper considers the power allocation (PA) problem for three-node decode-and-forward (DF) relay communication systems, where the aggregate transmit power constraint is imposed on the source and the relay and the optimization target is to maximize the system's instantaneous information rate. Since the relay is equipped with multiple antennas, the receiver and transmitter beamforming strategies are generally adopted. In this paper, we start by proposing a closed-form solution for the frequency-flat (FF) fading environment, then give a bisection algorithm with low complexity to obtain an optimal solution for the frequency-selective (FS) fading scenario. Finally, simulations validate the proposed methods.

In this paper, cell searching and direction-of-arrival (DoA) estimation methods are proposed for mobile relay stations with a uniform linear arrays in OFDM-based cellular systems. The proposed methods can improve the performance of cell searching and DoA estimation, even when there exist symbol timing offsets among the signals received from adjacent base stations and Doppler frequency shifts caused by the movement of the mobile relay station. The performances and computational complexities of the proposed cell searching and DoA estimation methods are evaluated by computer simulation under a mobile WiMAX environment.

In this letter, we consider a cognitive radio based multihop network under the spectrum sharing underlay paradigm. By taking into account the interference constraints, we present an exact closed-form expression for outage probability, which is valid for the whole signal-to-noise ratio regime. In addition, some numerical examples of interest that study the effect of the number of hops and/or the interferer threshold on primary users are illustrated and discussed. Numerical results show that multihop systems still offer a considerable gain as compared to direct transmission under the same limit of interference.

In this paper, we analyze the best relay selection scheme for the soft-decision-and-forward (SDF) cooperative networks with multiple relays. The term `best relay selection' implies that the relay having the largest end-to-end signal-to-noise ratio is selected to transmit in the second phase transmission. The approximate performances in terms of pairwise error probability (PEP) and bit error rate (BER) are analyzed and compared with the conventional multiple-relay transmission scheme where all the relays participate in the second phase transmission. Using the asymptotics of the Fox's H-function, the diversity orders of the best relay selection and conventional relay scheme for the SDF cooperative networks are derived. It is shown that both have the same full diversity order. The numerical results show that the best relay selection scheme outperforms the conventional one in terms of bit error rate.

In this letter, we propose a distributed switch-and-stay combining network with partial relay selection and show that the system spectral efficiency can be improved via adaptive modulation. Analytical expressions for the achievable spectral efficiency and average bit error rate of the proposed system over Rayleigh fading channels are derived for an arbitrary switching threshold. Numerical results are gathered to substantiate the analytical derivation showing that in terms of spectral efficiency, the system with single relay outperforms that with more than one relay at high signal-to-noise ratios (SNRs) and the optimal switching threshold can significantly improve the system performance at medium SNRs.

The explosive growth of Internet usage has caused problems for the current Internet in terms of traffic congestion within networks and performance degradation of end-to-end flows. Therefore, a reconsideration of the current Internet has begun and is being actively discussed worldwide with the goals of enabling efficient share of limited network resources (i.e., the link bandwidth) and improved performance. To directly address the inefficiency of TCP's congestion mitigation solely on the end-to-end basis, in this paper we propose an adaptive split connection scheme on advanced relay nodes; this scheme dynamically splits end-to-end TCP connections on the basis of congestion status in output links. Through simulation evaluations, we examine the effectiveness and potential of the proposed scheme.

This paper proposes single antenna relay system using De-noise and forward (DNF) scheme for MIMO transmission. In this scheme, the relay node eliminates the noise by identifying constellation, and retransmits after amplification. DNF does not amplify the noise, and the channel information is unnecessary in the transmitting side. In this paper, we propose the de-noising scheme for MIMO application. Particularly, DNF can be used for the multi-stream transmission even though each relay nodes have single antenna. The simulation demonstrates the proposed scheme can improve the data transmission quality than the conventional scheme.

In this letter, signal to interference plus noise ratio (SINR) performance is analyzed for orthogonal frequency division multiplexing (OFDM) based amplify-and-forward (AF) relay systems in the presence of carrier frequency offset (CFO) for fading channels. The SINR expression is derived under the one-relay-node scenario, and is further extended to the multiple-relay-node scenario. Analytical results show that the SINR is quite sensitive to CFO and the sensitivity of the SINR to CFO is mainly determined by the gain factor and the different power of the direct link channel and relay link channel.

In this letter, the diversity-multiplexing tradeoff (DMT) function for a special half-duplex dynamic decode and forward (DDF) relay protocol using two source-antennas, two destination-antennas, and more than two relay-antennas is derived. It is shown that the performance of the DDF relay protocol can be substantially improved by increasing the relay-antenna number, but only for low multiplexing gains.

This letter introduces a joint design method for uplink-downlink multiple-input multiple-output (MIMO) relay communication systems in which the source nodes transmit information to the destination nodes with the help of a relay. We propose a signal forwarding schceme based on the minimum mean-square error (MMSE) approach in uplink relay systems. Exploiting the duality of relay systems, we also propose a relaying scheme for downlink relay systems. Simulation results confirm that the proposed joint design method improves the performance of the relay systems compared with that of conventional relaying schemes in uplink and downlink MIMO relay systems.

In Long-Term Evolution (LTE)-Advanced, an important goal in addition to achieving high-speed, high-capacity communications is throughput enhancement for cell-edge users. One solution is to relay radio transmissions between an eNode B and user equipment (UE). Relays are expected to extend the coverage to the cell boundary and coverage hole areas, and are expected to reduce network costs. It was agreed that in Release 10 LTE, a Layer-3 (L3) relay, which achieves self-backhauling of radio signals between an eNode B and a UE in Layer 3 should be standardized. Meanwhile, a Layer-1 (L1) relay, which amplifies and forwards received radio frequency signals, has already found widespread use in second-generation and third-generation mobile communication systems. This paper investigates the downlink system level performance for L3 and L1 relays with orthogonal frequency division multiple access (OFDMA) in LTE-Advanced. Various practical factors are taken into account in the evaluations such as the processing delay and upper bound of the amplifier gain of the L1 relay, capacity limitation of the backhaul channels, and empty buffer status at the L3 relay. We also propose and investigate a downlink backhaul link (radio link between the eNode B and L3 relay node) scheduling method for the in-band half-duplex L3 relay. In the proposed scheduling method, radio resources from an eNode B to an L3 relay node and macro UE are multiplexed in the same backhaul subframe considering the number of relay UEs and macro UEs, and the channel quality of the backhaul link to the L3 relay and the access link to the macro UE. Based on system-level simulations, we clarify the system impact of several conditions for the relay such as the number of relay nodes and the number of backhaul (radio link between eNode B and L3 relay) subframes, the distance between the eNode B and relay, and show the throughput performance gain of the L3 relay compared to the L1 relay. We also clarify that the cell-edge UE throughput performance is increased by approximately 10% by applying the proposed scheduling method due to more efficient and fair resource allocation to the L3 relay and macro UEs.

We propose a two-phase diversity scheme to achieve the end-to-end spatial diversity gain for physical-layer network coding (PNC) based two-way relay with a multiple-antenna relay node. A novel binary PNC-specific maximal-ratio-combining like (MRC-L) scheme is proposed to obtain receive diversity in the multiple-access (MA) phase with linear complexity; the Max-Min criterion based transmit antenna selection (TAS) is adopted to obtain transmit diversity in the broadcast (BC) phase. Both the brief diversity analysis and the Monte Carlo (MC) simulation results demonstrate that the proposed scheme achieves full diversity and outperforms other comparable schemes in terms of end-to-end diversity or power advantage.

This paper presents an overview of radio interface technologies for cooperative transmission in 3GPP LTE-Advanced, i.e., coordinated multi-point (CoMP) transmission, enhanced inter-cell interference coordination (eICIC) for heterogeneous deployments, and relay transmission techniques. This paper covers not only the technical components in the 3GPP specifications that have already been released, but also those that were discussed in the Study Item phase of LTE-Advanced, and those that are currently being discussed in 3GPP for potential specification in future LTE releases.

In order to improve the cell boundary throughput performance and to extend the coverage area, relaying transmission with relay stations (RSs) is becoming a promising architecture for the next generation cellular systems. However, if RSs are operated in every cell, the interference between cells increases and the throughput improvement effect with RSs is prone to be restricted. In this paper, we propose a scheme reducing the interference from other cells by using packet transmission control. This packet transmitting control technique is realized by the compound scheduling technique with the Proportional fair (PF) scheduling and the Maximum Carrier-to-Interference power Ratio (Max CIR) scheduling. The proposed scheme can improve the throughput around the cell boundary by controlling the timing of transmission of each cell with appropriate power and user assignment. The simulation results show that the proposed method can also improve the fairness of user throughput and system throughput considering the users of whole cell.

In this letter, we study cooperative transmission in wireless multicast networks. An opportunistic cooperative multicast scheme based on coded cooperation (OCM-CC) is proposed and its closed-form expression of outage performance is obtained. Through numeric evaluation, we analyze its outage probability with different numbers of relays and different cooperative ratios.

A combination of single-carrier frequency-division mult-iple-access (SC-FDMA) and relay transmission is effective for performance improvement in uplink transmission. In SC-FDMA, a mapping strategy of user's spectrum has an enormous impact on system performance. In the relay communication, the optimum mapping strategy may differentiate from that in direct communication because of the independently distributed channels among nodes. In this letter, how each link should be considered in subcarrier mapping is studied and the impact of mapping strategies on the average bit error rate (BER) performance of single-user SC-FDMA relay communications will be given.

This letter reveals that whole link reciprocity does not exist in general amplify-and-forward (AF) time division duplex (TDD) relay systems due to the gain matrix. To resolve this problem, a novel gain matrix design method is proposed. Any existing gain matrix design criterion can be adopted in the downlink (uplink) to ensure optimal performance, and the proposed scheme is used in the uplink (downlink), with small adjustment, to keep whole link reciprocity. Simulation results show that, the proposed method can maintain whole link reciprocity without performance loss.