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This paper investigates the capacity gain of full duplex (FD) self-backhauling over the half duplex (HD) counterpart in downlink cellular systems, and then proposes an opportunistic FD scheme. The first step is to derive the capacity gain of FD self-backhauling over the HD counterpart as a function of the system parameters in a computationally tractable form. Unlike previous studies on the capacity of FD self-backhauling, a practical constraint is imposed so that the end-to-end link achieves a target signal-to-interference-plus-noise ratio (SINR) for a successful link connection. Also, a condition under which FD is more beneficial than HD is derived. Specifically, the minimum allowable self interference cancellation factor and the maximum allowable cell radius for the benefit of FD are derived as an explicit function of system parameters. Their dependencies on the system parameters are investigated and compared with counterparts derived for single-hop point-to-point links. Lastly, to overcome the weak points of FD and HD, this paper proposes a user-wise opportunistic FD (OFD) self-backhauled scheme. To this end, an instantaneous channel gain-based FD/HD switching rule is derived from a condition under which FD cannot instantaneously satisfy the target SINR. We confirm the substantial capacity gain of the proposed user-wise instantaneous OFD over a cell-wise static duplex switching scheme, as well as the fixed duplex (HD or FD) schemes. When compared to the static duplex switching scheme, the proposed OFD is most beneficial at the boundary of HD-preferred and FD-preferred regions. Based on this, a system-level guideline is proposed for selecting the most practical scheme among OFD, FD, and HD by trading off capacity gain and switching overhead. Extensive simulation results are provided to confirm the correctness of the derivations and the related investigations. [ABSTRACT FROM AUTHOR]

This paper investigates the outage and throughput performance of full-duplex (FD) cooperative relaying (CR) based non-orthogonal multiple access system (NOMA) with energy harvesting (EH) i.e., FD-CR-EH-NOMA system. We consider a network scenario, where the base station (BS) serves two downlink users, with the near user configured as a FD relay to deliver messages to the far user. We derive analytical expressions for the outage probabilities experienced by the users and the system outage probability of FD-CR-EH-NOMA network under time switching relaying (TSR) protocol in the presence/absence of direct link from BS to the far user. Assuming imperfect successive interference cancellation (i-SIC), we derive analytical expressions for (i) optimal power allocation (OPA) factor at the BS and (ii) optimal time switching (OTS) factor at the relay that independently minimizes the system outage probability. Further, we use the alternating optimization technique to determine the jointly optimal power allocation and time switching factors that minimize the system outage probability. Furthermore, we determine the OTS factor that maximizes the asymptotic throughput of the system in the delay-limited transmission mode. With the help of numerical and simulation investigations, we show that the system outage and throughput of the considered network improve significantly under the proposed schemes. [ABSTRACT FROM AUTHOR]

In this paper, we propose a full-duplex (FD) relaying system with multi-input multi-output (MIMO) with simultaneous wireless information and power transfer (SWIPT), where the communication from source to destination is assisted by a full-duplex decode-and-forward (DF) relay. The time switching (TS) protocol is used at the relay to harvest the energy of radio-frequency (RF) signals transmitted from the source. To improve both system performance and the amount of harvested energy, multiple antennas are used at source and destination. Transmit antenna selection (TAS) is employed at the source with an assumption that the feedback of channel state information (CSI) is outdated. Meanwhile, both selection combining (SC) and maximal ratio combining (MRC) techniques are applied at the destination. The closed-form expressions of the outage probability (OP), optimal throughput, and symbol error probability (SEP) are derived subject to the outdated CSI over Rayleigh fading channels. We also make a comparison between the performance of the proposed MIMO-FD relaying system with SWIPT and that of MIMO half-duplex (HD) relaying systems with and without SWIPT. The validity of derived mathematical expressions is verified by Monte-Carlo simulations. Numerical results show that the TAS/MRC scheme gives better system performance than the TAS/SC scheme. Moreover, higher energy harvesting time is needed to maximize the throughput than to minimize the OP. [ABSTRACT FROM AUTHOR]

In this paper, to perform an energy-efficient and high-throughput time-switching (TS)-based energy-harvesting (EH) relaying in a practical block-by-block manner, an adaptive discrete TS-based EH relaying scheme is proposed. Specifically, focusing on both dual-hop amplify-and-forward (AF) and decode-and-forward (DF) systems, we make full use of the channel state information (CSI) at the relay to determine an adaptive relaying power as well as an adaptive TS factor based on the relay's current accumulated energy. For such, an effective analytical framework is proposed to characterize the throughput performance of the proposed scheme, which shows the superiority of the proposed scheme over the conventional one. In particular, the limiting throughput efficiency of the proposed scheme is shown to achieve the limiting/best throughput efficiency of 50% for half-duplex relaying regardless of channel fading types, while the limiting throughput efficiency of the conventional scheme is always less than 50%. Furthermore, simulation results are given to validate our theoretical analysis, showing that for AF mode, the proposed scheme can provide up to 7.4 dB threshold signal-to-noise ratio (SNR) gain over the conventional solution. In addition, a comprehensive comparison between the proposed scheme and other state-of-the-art protocols is also made via representative numerical examples. [ABSTRACT FROM AUTHOR]

In this paper, we compare the performance of time-switching relaying (TSR) and power-splitting relaying (PSR) protocols in two-hop networks with a battery-assisted energy-harvesting (EH) amplify-and-forward relay. In this battery-assisted relay framework, the EH relay augments the harvested energy with energy drawn from a battery. Using expressions derived for throughput and average battery energy consumption, we investigate maximization of throughput for given battery energy availability per time slot and minimization of battery energy consumption for target throughput requirement. When only statistical channel knowledge is available, PSR results in better throughput performance at practical signal-to-noise ratios. However, in the typical low battery energy and low target throughput regime, it is TSR that is more battery energy efficient. When second-hop instantaneous channel knowledge is available, we observe dramatical energy savings that increases lifetime of nodes. Simulation results are presented to demonstrate accuracy of the derived expressions. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the optimal throughput performance for simultaneous wireless information and power transfer relaying network in the presence of direct link between the source and the destination. By considering the direct link, system performance can be improved when the channel condition is good from source to destination. The cooperative network consists of a source, an amplify-and-forward relay, and a destination, where the relay harvests energy from the source and then uses the harvested energy to forward information to the destination. At the destination node, the signals from the direct link and relay are combined by the maximum ratio combining (MRC) method. The time switching (TS) relaying protocol is applied to enable energy harvesting and information processing simultaneously. At the same time, we made progress on analyzing the throughput of information transmission on the basis of the MRC method with power switching (PS) relaying protocol. Additionally, adaptive-MRC protocol is proposed based on the TS and PS relaying protocols, which can choose better mode to achieve the communication. The numerical analyses provide practical insights into the effect of various system parameters, such as energy harvesting time splitting ratio, source transmission rate, distance between nodes, and noise power at the destination and the relay. [ABSTRACT FROM AUTHOR]

In this correspondence paper, a decode-forward relay system with a source, a relay, and a destination is considered. A new switching superposition-coded (NSSC) relay scheme is proposed to improve error performance by increasing the equivalent squared minimum distance. On the receiver side, a low-complexity linear-combining successive-interference-cancellation decoder is proposed for the NSSC scheme. The theoretical and simulation results show that the NSSC scheme achieves better performance compared to the existing superposition-coded relay schemes. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel physical layer strategy to improve the secrecy performance of multiuser multiple-input single-output networks. In this strategy, orthogonal space-time block code (OSTBC) is employed at an A\text{A}-antenna base station and artificial noise (AN) is employed at an A\text{J} -antenna cooperative relay to enhance the security level of the network. Moreover, two opportunistic scheduling schemes, namely selection combining (SC) and scan-and-wait combining (SWC), are leveraged to select one legitimate user for data transmission. To evaluate the secrecy performance of the proposed OSTBC-SC-AN and OSTBC-SWC-AN schemes, we derive new exact closed-form expressions for the secrecy outage probability and the effective secrecy throughput. Using numerical results, we show that the OSTBC-SWC-AN scheme outperforms the OSTBC-SC-AN scheme when the switching threshold is carefully chosen, while the OSTBC-SC-AN scheme is independent of the switching threshold. We also show that increasing A\text{A} at a low switching threshold or decreasing A\rm{A} at a high switching threshold achieves secrecy enhancement for the OSTBC-SWC-AN scheme, while increasing A\rm{A} brings better secrecy performance for the OSTBC-SC-AN scheme. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate the outage performance of a decode-and-forward (DF) relay system with two low-complexity relay selection schemes and interference at the relays and the destination. The schemes are mainly based on the switch-and-examine diversity combining (SEC) and SEC postexamine selection (SECps) techniques in which a relay out of multiple relays is selected to forward the source message to the destination. The selection process is performed such that the signal-to-noise ratio (SNR) of the second hop of the selected relay satisfies a predetermined switching threshold. In this paper, we first derive the probability density function (pdf) of the SNR of the relay selection scheme and the conditional cumulative distribution function (cdf) of the end-to-end (e2e) signal-to-interference-plus-noise ratio (SINR), assuming Rayleigh fading channels. The derived statistics, along with the statistics of first-hop channels of the relays and the direct link, are then used to derive a closed-form expression of the e2e outage probability. Maximal-ratio combining (MRC) is used at the destination to combine the signals from the relay and the direct link. Furthermore, the outage performance is studied at the high-SNR regime where approximate expressions for the outage probability, diversity order, and coding gain are derived and analyzed. Monte Carlo simulations and some numerical examples are provided to illustrate the validity of the derived results and to show the effect of interference and other parameters on the system performance. Main results illustrate that when the interference power is fixed, the system can still achieve some performance gain when more relays are added, particularly at SNR values that are comparable with the switching threshold. Asymptotic results show that at a high SNR, the system with the SEC and SECps relaying schemes achieves a diversity order of 2 and approximately the same coding gain. Finally, findings illustrate that the interference at the destination is more severe on the system performance compared with that at the relays. [ABSTRACT FROM PUBLISHER]

Efficient utilization of wireless communication resources and increases in the capacity of the communication networks have become very crucial claims for next-generation cellular networks. Full-duplex (FD) is a very promising technique that allows for the efficient use of wireless communication resources, given that the self-interference level can be suppressed to an acceptable level. In this paper, we consider a simple FD communication system, consisting of one FD access point (AP) and two half-duplex (HD) mobile users, and investigate when it is more advantageous for the communication network to operate in FD or HD multiuser multiple-input multiple-output (MIMO) mode. Since FD transmission is degraded by self-interference while HD suffers from spatial correlation between MIMO antennas, which causes rate loss, we study the effect of both the self-interference cancelation parameter at the FD AP and the mutual distance between the HD users on FD performances and the effect of the spatial correlation coefficient on HD MIMO. Afterward, a switching criterion is proposed, which chooses the operation mode that maximizes the downlink channel capacity while maintaining the uplink channel capacity at a certain level. Subsequently, based on our study of the system's parameters that affect the performance of both FD and HD, theoretical thresholds for these parameters are derived. Finally, numerical analysis is presented, verifying the validity of the optimization problem solution and the derived thresholds. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel demodulation-and-forward (DMF) scheme for the two-path succussive relay system. While the two-path relaying avoids the data rate loss that occurs in many one-relay cooperative systems, its performance is severely limited by interrelay interference. In this paper, we propose a hybrid DMF scheme for the two-path relay system so that the relays can switch between direct and differential demodulation modes according to channel conditions. The hybrid DMF scheme not only performs better than existing two-path approaches but is easy to achieve synchronization at the relays as well, which is particularly important as a relay receives signals from both the source and the other relay. The proposed hybrid DMF scheme provides an innovative way to implement the two-path relaying scheme. [ABSTRACT FROM PUBLISHER]

Selection combining (SC) with full channel state information (CSI) achieves full diversity order in a decode-and-forward (DF) relaying system. However, the estimation of CSI of all the links is a cumbersome process. As an alternative, switched-diversity techniques have been proposed in the literature, in which CSI of all the links are not simultaneously required. In this paper, we compare the variants of the switched-diversity and full-CSI SC schemes through a paired error approach for a multi-DF-relaying-based cooperative diversity system. We derive the exact symbol error probability (SEP) expressions for the full-CSI SC, switch-and-examine combining (SEC), and SEC with post-selection (SECps) schemes, considering $M$-ary phase-shift keying (MPSK) signaling over slow, flat, independent, and nonidentical Nakagami- $m$ fading channels. It is to be noted that the derived SEP expressions are valid for integer values of fading severity parameter $m$. In addition, we also present the closed-form asymptotic SEP expressions for MPSK signaling to evaluate the diversity order. Concisely, from the numerical results, it is observed that the SECps scheme is able to offer the same performance as that of the full-CSI SC scheme. Furthermore, the SECps scheme outperforms the SEC scheme with more CSI. [ABSTRACT FROM AUTHOR]

Recently, the mobile relay technique has been discussed to support communication services for Long-Term Evolution Advanced (LTE-A) high-speed rail networks. In the network, there are several mobile relays in a train. User equipment (UE) devices connect to in-car mobile relays instead of outside evolved NodeBs (eNBs). Mobile relays establish backhaul links with the serving donor eNBs (DeNBs) and coordinate control and data flows for UE devices. Since the train travels in high speed, mobile relays suffer from frequent handovers between DeNBs. We observe that the defined handover procedures in LTE-A specifications may incur message overhead and lengthen handover time. In this paper, we propose an enhanced handover scheme, which contains two procedures. The first procedure is an enhanced measurement procedure, which can accelerate the measurement procedure when the mobile relay knows that the train is moving toward some neighbor DeNBs. The second procedure is a group in-network handover procedure, which can aggregate similar in network handover procedures in the core network. Performance evaluations indicate that our design can conserve both time and messages when handover. [ABSTRACT FROM PUBLISHER]

This paper proposes a generalized interrelay interference cancelation (gIRIC) scheme for a two-path relay model in multisource systems. Both the sources and the relay adopt complex field network coding (CFNC) to remove the interrelay interference (IRI) caused by the two-path relay. Furthermore, we introduce two detecting modes (gIRIC-noSD and gIRIC-SD) for destination in our scheme. Two switching rules are given to select a suitable detecting mode between treating the signal of a direct link as noise (gIRIC-noSD) and utilizing the direct link to assist signal detection (gIRIC-SD). The bounds of average symbol error probability (SEP) and throughput of our scheme are derived. [ABSTRACT FROM PUBLISHER]

In this paper, we propose an analytical framework for determining the outage probability of random and best relay selection schemes given a Poisson field of relay nodes and the presence of path loss and fading. For relay selection, relays geographically close to the source and destination are preferred to others. This selection guideline ensures a target quality of service (QoS) and reduces the signaling overhead and the relay selection delay. A spatial region called the QoS region is obtained for the random relay selection and is shown to shrink as the distance between the source and the destination increases and the interfering node density increases. When the QoS region for random relay selection is not large enough and cannot probabilistically ensure a reliable relay therein, the best relay selection is employed since the required relay node density and selection range for a desired QoS can be reduced for the best relay selection. The gain of the best relay selection with respect to the random relay selection is quantified in terms of relay node density reduction and coverage extension due to selection diversity. [ABSTRACT FROM PUBLISHER]