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Owing to the ever increasing of information privacy requirement, covert communication has gained more and more attention, whose effective range is limited by the trade-off between the covertness and the transmit power. Benefiting from the high mobility and easy deployment, unmanned aerial vehicles (UAVs) can be utilized to expand the range of covert networks. Thus, we propose a UAV-relayed covert communication scheme with finite blocklength to maximize the effective transmission bits from the transmitter to the legitimate receiver against a flying warden. The transmitter adopts the maximum ratio transmission and the relay performs Gaussian signalling transmission to cause uncertainty at the warden. First, the optimal detection thresholds are derived at the warden towards the transmitter and the relay, respectively. Then, the hovering location of the warden is optimized to maximize the summation of relative entropies from the transmitter and the relay, which can greatly threaten the covertness. With this worst covert situation, the blocklength and transmit power at the transmitter and the relay are jointly optimized under the constraint of the end-to-end error detection probability to maximize the effective transmission rate from the transmitter to the legitimate receiver. Numerical results are provided to demonstrate the effectiveness of the proposed UAV-relayed covert communication scheme. [ABSTRACT FROM AUTHOR]

This work investigates the secrecy capability of energy harvesting based overlay cognitive networks (EHOCNs). To this end, we assume that a message by a licensed transmitter is relayed by an unlicensed sender. Critically, the unlicensed sender uses energy harvested from licensed signals, enhancing the overall energy efficiency and maintaining the integrity of licensed communications. To secure messages broadcast by the unlicensed sender against the wire-tapper, full-duplex destinations – unlicensed recipient and licensed receiver – jam the eavesdropper at the same time they receive signals from the unlicensed sender. To this effect, we derive closed-form formulas for the secrecy outage probability, which then quantify the security performance of both unlicensed and licensed communications for EHOCNs with jamming-assisted full-duplex destinations, namely EHOCNwFD. In addition, optimum operating parameters are established, which can serve as essential design guidelines of such systems. [ABSTRACT FROM AUTHOR]

We investigate the model of a single primary-transceiver pair with multiple secondary-transceiver pairs. The secondary pairs can act as relays for the primary transmitter enabling access to its channel resources. Each secondary user (SU) is assumed to be a radio-frequency energy-harvester node. We formulate a framework that aims at specifying the optimal SU set that operates as relay nodes for the primary user (PU) data message. The set of the SUs is selected such that the SUs total throughput is maximized under a certain quality-of-service (QoS) requirement constraint on the PU target data rate. We propose both centralized and distributed approaches for solving the formulated optimization problems. The centralized approach is based on solving a convex optimization problem at the PU. On the other hand, the distributed approach leverages a Sackelberg game where all users interact to achieve the best relay-selection scheme and PU’s transmit power. We prove the uniqueness and Nash equilibrium of the considered Stackelberg game, and develop a game-theoretic relay and PU’s transmit power selection algorithm. We also introduce a fairness optimization-based scheme (FOBS) that aims at enhancing the fairness among the SUs under our proposed centralized approach. Our simulation results show the efficiency of our proposed schemes in terms of SUs total throughput. [ABSTRACT FROM AUTHOR]

The capacity of the semi-deterministic relay channel (SD-RC) with non-causal channel state information (CSI) only at the encoder and decoder is characterized. The capacity is achieved by a scheme based on cooperative-bin-forward. This scheme allows cooperation between the transmitter and the relay without the need of the later to decode a part of the message. The transmission is divided into blocks, and each deterministic output of the channel (observed by the relay) is mapped to a bin. The bin index is used by the encoder and the relay to choose the cooperation codeword in the next transmission block. In causal settings, the cooperation is independent of the state. In non-causal settings, dependence between the relay’s transmission and the state can increase the transmission rates. The encoder implicitly conveys partial state information to the relay. In particular, it uses the states of the next block and selects a cooperation codeword accordingly, and the relay transmission depends on the cooperation codeword and, therefore, also on the states. We also consider the multiple access channel with partial cribbing as a semi-deterministic channel. The capacity region of this channel with non-causal CSI is achieved by the new scheme. Examining the result in several cases, we introduce a new problem of a point-to-point (PTP) channel where the state is provided to the transmitter by a state encoder. Interestingly, even though the CSI is also available at the receiver, we provide an example showing that the capacity with non-causal CSI at the state encoder is strictly larger than the capacity with causal CSI. [ABSTRACT FROM AUTHOR]

In this paper, secure primary transmission is proposed by using a multi-antenna secondary full-duplex non-orthogonal multiple access (NOMA) relay in cognitive radio (CR) networks. First, the primary signal is transmitted from the primary transmitter to the relay. Artificial noise is generated by using part of the antennas at the relay to disrupt eavesdropping, without affecting the primary transmission. Then, superimposed signals are transmitted from the relay to the primary receiver and secondary receivers via NOMA. The primary security is guaranteed by the modified decoding order and beamforming optimization, which is converted to convex and solved by an iterative algorithm. Simulation results are presented to show the effectiveness of the proposed scheme in guaranteeing the primary security in CR networks. [ABSTRACT FROM AUTHOR]

A visible light communication broadcast channel is considered, in which a transmitter luminaire communicates with two legitimate receivers in the presence of an external eavesdropper. A number of trusted cooperative half-duplex relay luminaires are deployed to aid with securing the transmitted data. Transmitters are equipped with single light fixtures, containing multiple light emitting diodes, and receiving nodes are equipped with single photo-detectors, rendering the considered setting as a single-input single-output system. Transmission is amplitude-constrained to maintain operation within the light emitting diodes’ dynamic range. Achievable secrecy rate regions are derived under such amplitude constraints for this multi-receiver wiretap channel, first for direct transmission without the relays, and then for multiple relaying schemes: cooperative jamming, decode-and-forward, and amplify-and-forward. Superposition coding with uniform signaling is used at the transmitter and the relays. Further, for each relaying scheme, secure beamforming vectors are carefully designed at the relay nodes in order to hurt the eavesdropper and/or benefit the legitimate receivers. Superiority of the proposed relaying schemes, with secure beamforming, is shown over direct transmission. It is also shown that the best relaying scheme depends on how far the eavesdropper is located from the transmitter and the relays, the number of relays, and their geometric layout. [ABSTRACT FROM AUTHOR]

Winding turn-to-turn fault (TTF) is one of the most reported reasons for transformer unplanned outage. If its occurrence is not detected at an early stage, it can develop into a costly phase-to-ground fault. In this paper, a novel algorithm based on the fault-related incremental currents is proposed to detect a low-level transformer TTF. This paper shows that the performance of the proposed method is independent of the transformer operating condition. Therefore, it is reliable even under the presence of power system transients such as the external faults. In addition, the proposed algorithm can be configured uniquely and easily. This feature prevents the algorithm from unnecessary trips. These trips can be considered as the general problem that most of the past presented methods face. The experimental tests used for verification of the algorithm show that, regardless of the transformer winding configuration and its pre-fault operating conditions, the proposed algorithm can accurately detect the TTF, which involves only 1% of the winding turns, in less than one cycle of power frequency. The reliable and secure performance of the proposed algorithm shows that it can be widely used in the advanced numerical relays. [ABSTRACT FROM AUTHOR]

Prior works on performance analysis for cognitive radio networks often assume perfect channel state information (CSI), which may not be readily available. This paper investigates the effects of the outdated CSI on the performance of a dual-hop multi-antenna multi-relay spectrum sharing system. To exploit the benefits of available multiple antennas, collaborative zero-forcing beamforming is considered at the secondary user (SU) source node with the outdated CSI and maximum ratio combining diversity reception at the destination node. The $N$ th best relay selection strategy is adopted at the relays. Analytical outage probability and bit-error rate expressions are derived for the SU. Moreover, we examine the high signal-to-noise ratio regime and present closed-form expressions for the asymptotic outage probability and asymptotic bit-error rate with and without feedback delay. In addition, we derive the closed-form ergodic capacity expression for the special case of our considered system, and analyze the effects of delay on the capacity. Furthermore, the closed-form outage probability expression for the primary user is obtained and the impact of delay on the interference on the primary user is investigated. Monte Carlo simulations are carried out to verify our analysis. [ABSTRACT FROM AUTHOR]

We consider systems in which the transmitter conveys messages to the receiver through a capacity-limited relay station. The channel between the transmitter and the relay station is assumed to be a frequency-selective additive Gaussian noise channel. It is assumed that the transmitter can shape the spectrum and adapt the coding technique so as to optimize performance. The relay operation is oblivious (nomadic transmitters), that is, the specific codebooks used are unknown. We find the reliable information rate that can be achieved with Gaussian signaling in this setting, and to that end, employ Gaussian bottleneck results combined with Shannon’s incremental frequency approach. We also prove that, unlike classical water pouring, the allocated spectrum (power and bit rate) of the optimal solution could frequently be discontinuous. These results can be applied also to a MIMO transmission scheme. We also investigate the case of an entropy-limited relay. We show that the optimal relay function is always deterministic, present lower and upper bounds on the optimal performance (in terms of mutual information), and derive an analytical approximation. [ABSTRACT FROM AUTHOR]

In this paper, we consider a network reconstruction problem using unmanned aerial vehicles (UAVs) where stationary ad hoc networks are severely damaged in a post-disaster scenario. The main objective of this paper is to repair the network by supplementing aerial wireless links into the isolated ground network using UAVs. Our scheme performs network probing from the air and finds out crucial spots where both local and global routing performance can significantly be recovered if deployed. First, we propose a novel distributed coverage path planning algorithms with independent and computationally lightweight navigation based on adaptivezigzagpatterns. Second, we present route topology discovery schemes that capture both local andnon-local network connectivity by extracting inherent route skeletons via stitching partial local paths obtained from the simple packet probing by UAVs. Finally, we find the optimal UAV relay deployment positions that can improve network-wide data delivery most effectively based on three novel approaches of an optimization technique, an iterative heuristic algorithm, and a topology partitioning ofstrongly connected component. Simulation results demonstrate that our distributed traversing algorithms reduce the complete coverage time, the travel distance, and the duplicate coverage compared to other counterpart algorithms. Our deployment algorithms recover severely impaired routes, incurring reasonable computational overhead. [ABSTRACT FROM AUTHOR]

In conventional cooperative non-orthogonal multiple access (NOMA) networks, spectral efficiency loss occurs due to a half-duplex constraint. To address this issue, we propose an incremental cooperative NOMA (ICN) protocol for a two-user downlink network. In particular, this protocol allows the source to adaptively switch between a direct NOMA transmission mode and a cooperative NOMA transmission mode according to a 1-bit feedback from the far user. We analytically prove that the proposed ICN protocol outperforms the conventional cooperative NOMA protocol. In addition, an optimal power allocation strategy at the source is studied to minimize the asymptotic system outage probability. Finally, numerical results validate our theoretical analysis, present insights, and quantify the enhancement achieved over the benchmark scheme. [ABSTRACT FROM AUTHOR]

This correspondence paper studies joint beamforming optimization and time allocation for a wireless powered two-way hybrid-relay network. As a general relaying architecture accommodating the existing relaying architectures in the literature as two special cases, we consider the two-way communication system where both energy-harvesting (EH) relays and non-EH relays exist. We aim to maximize the minimum rate by jointly optimizing the distributed beamforming vector at the relays, the energy beamforming matrix at the non-EH relays, and the EH time allocation with the energy constraints at the relays. The formulated problem is intractable to solve because the objective function and the energy constraints are highly nonconvex. We solve the optimization problem using the successive convex approximation. Simulations demonstrate that the proposed iterative algorithm considerably outperforms any existing approaches. [ABSTRACT FROM AUTHOR]

This paper studies the degrees of freedom (DoF) of two-way $2\times 2\times 2$ MIMO interference networks, a class of two-way four-unicast networks. We first provide upper and lower bounds on the sum DoF of general two-way $2\times 2\times 2$ MIMO interference networks with any number of antennas in each node. We then investigate the special case where all user nodes have $M$ antennas and relay nodes have $N$ antennas, and provide the simplified bounds on the sum DoF. We show that our proposed achievable rate for this special case is higher than the achievable rates recently proposed in. Moreover, for this special case, we obtain the exact DoF $=4M$ when $N \geq 2M$ , and DoF $=4N$ when $M \leq 2N$. [ABSTRACT FROM AUTHOR]

In this paper, we study a diamond-relay channel where the source is connected to $M$ relays through orthogonal links and the relays transmit to the destination over a wireless multiple-access channel in the presence of an eavesdropper. The eavesdropper not only observes the relay transmissions through another multiple-access channel but also observes a certain number of source-relay links. The legitimate terminals know neither the eavesdropper’s channel state information nor the location of source-relay links revealed to the eavesdropper except the total number of such links. For this wiretapped diamond-relay channel, we establish the optimal secure d.o.f. In the achievability part, our proposed scheme uses the source-relay links to transmit a judiciously constructed combination of message symbols, artificial noise symbols, and fictitious message symbols associated with secure network coding. The relays use a combination of beamforming and interference alignment in their transmission scheme. For the converse part, we take a genie-aided approach assuming that the location of wiretapped links is known. [ABSTRACT FROM AUTHOR]

In this paper, we propose a full-duplex orthogonal frequency-division multiplexing (OFDM) device-to-device (D2D) system in two-hop networks, where multiple full-duplex decode-and-forward relays assist the transmission from D2D user equipment (DUE) transmitter to DUE receiver. By such a transmission mechanism, the signal transmitted by the DUE transmitter does not need to go through a base station. Meanwhile, due to the adoption of underlay D2D communication protocol, power control mechanisms are thereby necessary to be applied to mitigate the interference to conventional cellular communications. Based on these considerations, we analyze the outage performance of the proposed system, and derive the exact expressions of outage probabilities when bulk and per-subcarrier relay selection criteria are applied. Furthermore, closed-form expressions of outage probabilities are also obtained for special cases when the instantaneous channel state information between BS and cellular user equipments is not accessible, so that a static power control mechanism is applied. Subsequently, we also investigate the outage performance optimization problem by coordinating transmit power among DUE transmitter and relays, and provide a suboptimal solution, which is capable of improving the outage performance. All analyses are substantiated by numerical results provided by Monte Carlo simulations. The analytical and numerical results demonstrated in this paper can provide an insight into the full-duplex relay-assisted OFDM D2D systems, and serve as a guideline for its implementation in next generation networks. [ABSTRACT FROM AUTHOR]

This correspondence paper investigates relay selection (RS) schemes for cooperative downlink nonorthogonal multiple access (NOMA) networks with multiple relays. Two optimal RS schemes, termed as the two-stage weighted-max-min (WMM) and max-weighted-harmonic-mean (MWHM) schemes, are proposed for cooperative NOMA with fixed and adaptive power allocations (PAs) at the relays, respectively. Then, the outage probabilities of the two proposed RS schemes are analyzed, and their diversity gains are also determined. The provided simulation results show that the proposed optimal two-stage WMM and MWHM schemes outperform the existing suboptimal RS schemes for cooperative NOMA networks with fixed and adaptive PAs at the relays, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a bidirectional cognitive cross network using spatial modulation (SM) along with physical-layer network coding (PLNC) is proposed. In our model, a primary user pair located far from each other, exchanges information in the lack of a direct link so that a relay is required for a reliable communication. A secondary user pair shares their relay with the primary user in return for access to the licensed spectrum. Both users exploit SM while the relay also applies PLNC. It is assumed that each user pair can eavesdrop the signal of the other user pair to use these signals as side information and cancel them from the PLNC mapped signal broadcasted by the relay. Optimum power allocation, in which two scenarios are considered, is proposed for sources and the relay. In Scenario 1, the optimization is performed by minimizing the bit error probability (BEP) of the primary user due to its priority in the licensed band. Scenario 2, which minimizes BEP of both users, provides the optimum results for the whole system. A theoretical BEP analysis is performed and the results are supported via computer simulation results, which are in perfect match with theoretical findings. [ABSTRACT FROM AUTHOR]

Robust artificial noise (AN) aided secure precoding for an amplify-and-forward multiple-input multiple-output untrusted relay system is studied, where the relay is untrusted and willing to help forwarding multiple data streams from the source to destination. We consider that the available channel state information is imperfect and modeled by the worst case model. Our objective is to maximize the worst case secrecy rate under the robust transmit power constraints at the source and relay, by jointly designing the signal and AN precoding matrices at the source and the precoding matrix at the relay. The robust secure precoding problem is nonconvex and hard to solve. To overcome this difficulty, we propose the weighted minimum mean square error based method, where the sign-definiteness lemma is used to eliminate the channel uncertainties and an effective iterative optimization algorithm is developed. Simulation results are provided to demonstrate the effectiveness of the proposed scheme. [ABSTRACT FROM PUBLISHER]

We analytically study the achievable rates of full-duplex massive multiple-input multiple-output (MIMO) relay systems over Rician fading channels. The decode-and-forward protocol is adopted at the relay station, where the channel state information (CSI) is assumed to be imperfect. We demonstrate that the system bottleneck, self-interference (SI), can be significantly canceled by zero-forcing (ZF) processing at the relay station, which is equipped with massive receive and transmit arrays. Because no active SI cancellation is deployed at the relay station, there is no need for SI channel estimation. We derive an approximate closed-form achievable rate expression for ZF processing with statistical CSI. When the number of antennas of the transmit and receive arrays at the relay station is sufficiently large, the transmit powers of each source and the relay station can be significantly scaled down proportionally to the number of antennas. Since Rayleigh fading is a special case of Rician fading, the results in this paper hold for Rayleigh fading channels. The theoretical analysis is verified by the numerical results. [ABSTRACT FROM PUBLISHER]

In this paper, we examine the physical layer security for cooperative wireless networks with multiple intermediate nodes, where the decode-and-forward protocol is considered. We propose a new joint relay and jammer selection (JRJS) scheme for protecting wireless communications against eavesdropping, where an intermediate node is selected as the relay for the sake of forwarding the source signal to the destination and meanwhile, the remaining intermediate nodes are employed to act as friendly jammers, which broadcast the artificial noise for disturbing the eavesdropper. We further investigate the power allocation among the source, relay and friendly jammers for maximizing the secrecy rate of proposed JRJS scheme, and derive a closed-form sub-optimal solution. Specifically, all the intermediate nodes, which successfully decode the source signal, are considered as relay candidates. For each candidate, we derive the sub-optimal closed-form power allocation solution and obtain the secrecy rate result of the corresponding JRJS scheme. Then, the candidate, which is capable of achieving the highest secrecy rate, is selected as the relay. Two assumptions about the channel state information (CSI), namely the full CSI (FCSI) and partial CSI (PCSI), are considered. Simulation results show that the proposed JRJS scheme outperforms the conventional pure relay selection, pure jamming, and generalized singular-value-decomposition-based beamforming schemes in terms of secrecy rate. Additionally, the proposed FCSI-based power allocation and PCSI-based power allocation schemes both achieve higher secrecy rates than the equal power allocation scheme. [ABSTRACT FROM PUBLISHER]

We propose a composite decode-forward (DF) scheme for the two-way relay channel in the full-duplex mode by combining coherent, independent, and partial relaying strategies. The relay partially decodes each user’s information in each block and forwards this information coherently with the source user to the destination user in the next block as in block Markov coding. In addition, the relay independently broadcasts a binning index of both users’ decoded information parts in the next block as in independent network coding. Each technique has a different impact on the relay power usage and the rate region. We further consider the independent and partial DF scheme for its more practical channel state information requirements, and derive in closed-form link regimes when this scheme achieves a strictly larger rate region than just time sharing between its constituent techniques, direct transmission, and independent DF relaying, and when it reduces to a simpler scheme. The analytical approach is based on maximizing the weighted composite DF sum rate and comparing with the outermost time-sharing line connecting corner points of rate regions of the constituent techniques. Numerical results demonstrate significant rate gains by performing link adaptation of the composite scheme based on the identified link regimes. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the capacity of the Gaussian two-hop full-duplex (FD) relay channel with residual self-interference. This channel is comprised of a source, an FD relay, and a destination, where a direct source-destination link does not exist and the FD relay is impaired by residual self-interference. We adopt the worst case linear self-interference model with respect to the channel capacity, and model the residual self-interference as a Gaussian random variable whose variance depends on the amplitude of the transmit symbol of the relay. For this channel, we derive the capacity and propose an explicit capacity-achieving coding scheme. Thereby, we show that the optimal input distribution at the source is Gaussian and its variance depends on the amplitude of the transmit symbol of the relay. On the other hand, the optimal input distribution at the relay is discrete or Gaussian, where the latter case occurs only when the relay-destination link is the bottleneck link. The derived capacity converges to the capacity of the two-hop ideal FD relay channel without self-interference and to the capacity of the two-hop half-duplex (HD) relay channel in the limiting cases when the residual self-interference is zero and infinite, respectively. Our numerical results show that significant performance gains are achieved with the proposed capacity-achieving coding scheme compared with the achievable rates of conventional HD relaying and/or conventional FD relaying. [ABSTRACT FROM AUTHOR]

To overcome finite lifetime bottleneck in the ubiquitous deployment of low-power wireless devices in Internet-of-Things, we propose a novel integrated information relay and energy supply (i2RES)-assisted RF harvesting co-operative communication model. i2RES aids the communication between two distant energy-constrained wireless nodes by: 1) RF energy transfer to the source and 2) relaying source data along with supplying energy to the destination. To enable efficient i2RES-powered information transfer to the destination, we first derive and then maximize the delay-limited achievable throughput over Rician channels by jointly optimizing time allocation for information and energy transfer along with relative position of i2RES between source and destination. Although the throughput maximization problem is nonconvex and highly nonlinear, we prove its generalized-convexity and obtain the global-optimal numerical solutions. To gain analytical insights, we also derive tight closed-form approximation for the optimized solutions. Numerical results validate the analysis and demonstrate significant gain in throughput performance via our proposed optimization schemes under practical hardware constraints. Finally, we discuss how the analysis and optimization results can be extended to general RF-EH system settings with relaxed constraints. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of primary transmissions on the performance of a dual-hop bidirectional cognitive radio system. The secondary users (SUs) communicate with each other in an underlay mode with the assistance of amplify-and-forward (AF) relays in the presence of primary users (PUs). Depending on whether there exists interference at the secondary transceivers, originating from the primary transmissions, or there is a possibility of employing the best relay selection technique at the secondary side, two operating cases are considered for the secondary network (SN). For both cases, tight lower bounds on the outage probability (OP) and the average symbol error probability (SEP) are derived in closed form. Moreover, a novel and general closed-form expression for the bit error rate (BER) of $M$-ary square quadrature amplitude modulation (QAM) for both single- and multiple-relay systems, under additive white Gaussian noise (AWGN) when Gray coded bit mapping is employed, is presented. In addition, we provide an upper bound and closed-form approximate expression for the ergodic capacity (EC). Numerical results provide important insights into the impact of system parameters on performance; for instance, it is demonstrated that, in both cases, under consideration of power constraints on the secondary nodes as dictated by the underlay mode of operation, the SN always achieves the full diversity order similar to the noncognitive counterpart. [ABSTRACT FROM PUBLISHER]

Applying data buffers at relay nodes significantly improves the outage performance in relay networks, but the performance gain is often at the price of long packet delays. In this paper, a novel relay selection scheme with significantly reduced packet delay is proposed. The outage probability and average packet delay of the proposed scheme under different channel scenarios are analyzed. Simulation results are also given to verify the analysis. The analytical and simulation results show that, compared with non-buffer-aided relay selection schemes, the proposed scheme has not only significant gain in outage performance but also similar average packet delay when the channel signal-to-noise ratio (SNR) is high enough, making it an attractive scheme in practice. [ABSTRACT FROM PUBLISHER]

In conventional energy harvesting amplify-and-forward relaying, only the relay harvests energy from the source. In this paper, a new energy harvesting relaying protocol is proposed, where the source also harvests energy from the relay, in addition to the energy harvesting relay. The performances of the new protocols using two different strategies are analyzed. Numerical results show that the new protocols have certain gain over the conventional protocol. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a novel relay selection scheme for orthogonal frequency-division multiplexing systems by combining conventional bulk and per-subcarrier selection schemes and analyze its outage performance over equally spatially correlated channels. Specifically, the combined selection scheme selects only two relays at the first attempt and performs per-subcarrier selection over these two relays. We analyze the asymptotic outage performance of the combined selection scheme in the high signal-to-noise ratio (SNR) region and prove a generalized theorem. This theorem states that the combined selection can achieve an optimal outage probability equivalent to the per-subcarrier selection at a high SNR without using the full set of available relays for selection. This unique property is termed the equivalence principle, and it holds for all correlation conditions. To explore this principle, we consider three examples: decode-and-forward, fixed-gain amplify-and-forward (AF), and variable-gain AF relay systems. Furthermore, two extended applications, i.e., antenna selection and branch selection, are also considered to reveal the feasibility and the expandability of the equivalence principle. Our analysis is verified by Monte Carlo simulations. The proposed combined selection and the proved theorem provide a general and feasible solution to the tradeoff between system complexity and outage performance when relay selection is applied. [ABSTRACT FROM AUTHOR]

This paper investigates distributed linear constellation precoding (DLCP) for two-way relaying communication systems in conjunction with the techniques of bit-interleaved coded modulation (BICM) and BICM with iterative decoding (BICM-ID). First, a decoding strategy for the relay node that is based on quaternary code representation is developed. Then, the union bounds (for the case of BICM) and error-free feedback bounds (for the case of BICM-ID) on the quaternary digit error probability and bit error probability under network coding in the multiple-access (MA) phase are obtained. Based on the obtained bounds, the impact of DLCP on the error performance is analyzed by considering three error types in the MA phase. It is shown that type-3 errors need to be carefully taken into account in the design of a DLCP scheme. By developing a performance metric related to type-3 errors, the design parameter of DLCP is optimized when BICM is used, whereas it is shown that DLCP is not needed when BICM-ID is used. Extensive simulation results are provided to corroborate the analysis and demonstrate the performance superiority of the proposed decoding strategy over the one that directly decodes the exclusive-OR (xor) code. For the case of BICM, the performance advantage achieved by properly designing DLCP is also illustrated. [ABSTRACT FROM AUTHOR]

In this paper, we consider the relay selection and power allocation (RSPA) problem in amplify-and-forward (AF) relaying networks. The objective is to minimize the outage probability at the receiver, assuming that only the mean channel gain information is available. By taking advantage of its special structure, we propose to decompose the RSPA problem into two tractable subproblems, which can be implemented in a semidistributed manner. For the relay selection (RS) subproblem, a relay-ordering-based scheme is designed to incrementally select a subset of relays from the candidate nodes according to a specific metric in a centralized manner, which is dominated by the mean channel gain of each individual nodes. For the power allocation (PA) subproblem, a source-driven iterative algorithm is proposed for each relay to decide its optimal transmit power locally by exploiting the convexity of this subproblem. Simulation results are provided to evaluate the outage and signal-to-noise-ratio (SNR) performance of the proposed scheme under different channel conditions. It is shown that the proposed scheme can dynamically select relays and adjust power allocation according to the SNR and channel conditions. It outperforms the other two benchmark schemes, and the performance is close to the optimal scheme with exhaustive search, but the computational complexity is significantly reduced. [ABSTRACT FROM AUTHOR]

In this paper, the performance of a nonregenerative relaying network of multiple-antenna terminal nodes is analyzed with respect to the power allocation issue. Assuming that complete channel state information (CSI) of all links is known at the destination terminal, an optimal power allocation (OPA) approach is investigated subject to constant total power with the objective of maximizing the instantaneous signal-to-noise ratio (SNR) at the destination. Generally, by this OPA approach, the total available power in the system is appropriated to source and relay nodes proportional to channel properties with the aim of coordinating the source–relay and relay–destination hop quality. Closed-form expressions for the outage probability are analytically derived, considering both conventional and maximized SNRs. It is shown that OPA outperforms the conventional uniform power allocation, although the achieved improvement is more significant if the number of destination antennas is less than the number of source antennas. Moreover, the results indicate that the effect of OPA on the performance improvement is significant if the relay node is close to the source terminal. Moreover, it is seen that the minimum number of the source and destination antennas is a determinant parameter in the evaluation of the outage probability. Hence, it is demonstrated that for an efficient system design, the number of source antennas should be as close as possible to that of the destination antennas. In addition, the relay selection scheme is considered to further improve the performance of the system. Finally, simulation results are presented, which confirms the validity of the analysis. [ABSTRACT FROM PUBLISHER]

A high-speed railway system equipped with moving relay stations placed on the middle of the ceiling of each train wagon is investigated. The users inside the train are served in two hops via orthogonal frequency-division multiple-access (OFDMA) technology. In this paper, we first focus on minimizing the total downlink power consumption of the base station (BS) and the moving relays while respecting specific quality-of-service (QoS) constraints. We first derive the optimal resource-allocation solution, in terms of OFDMA subcarriers and power allocation, using the dual decomposition method. Then, we propose an efficient algorithm based on the Hungarian method to find a suboptimal but low-complexity solution. Moreover, we propose an OFDMA planning solution for high-speed trains by finding the maximal inter-BS distance, given the required user data rates to perform seamless handover. Our simulation results illustrate the performance of the proposed resource-allocation schemes in the case of Third-Generation Partnership Project (3GPP) Long-Term Evolution Advanced (LTE-A) and compare them with previously developed algorithms, as well as with the direct transmission scenario. Our results also highlight the significant planning gain obtained, owing to the use of multiple relays instead of the conventional single-relay scenario. [ABSTRACT FROM PUBLISHER]

Due to the distributed nature of cooperative communications systems, the cooperative signals arriving at the destination may not be perfectly aligned, i.e., the system is inherently asynchronous, and signal coordination among multiple relay nodes is imperative. In this paper, we propose a distributed space–time transmission scheme for a general asynchronous cooperative relay network. The scheme provides asymptotic full cooperative diversity, even when the signals arrive at the receiver asynchronously, which can be achieved by a low-complexity minimum-mean-square-error (MMSE) decision feedback equalizer (DFE) instead of the maximum-likelihood (ML) detector. Furthermore, signal coordination is no longer required, which avoids extra coordinating overhead. The proposed scheme applies for both general amplify-and-forward (AF) and decode-and-forward (DF) cooperative communications networks, such as coordinated multipoint/networked multiple-input–multiple-output (MIMO) systems, distributed antenna systems, and relay architecture for cellular systems. Simulation results confirm our analytical results. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel relay-aided successive aligned interference cancellation (RaSAIC) method for a \text2\times K $X$ channel with L$ full-duplex relays, each of which is fully connected to the channel. The core idea of the RaSAIC is to apply a cooperative relays' precoding technique that aligns interference signals at unintended receivers while creating an Alamouti structure for the desired signals. With the proposed cooperative relay transmission technique, it is shown that both the optimal sum degree of freedom (sum-DoF) gain of \text{2}K/(K+\text{1}) and the diversity gain of two are achievable for both constant and time-varying channels when the numbers of relays' antennas are enough to meet the derived conditions, without requiring channel state information (CSI) at transmitters, but with global CSI at relays. Furthermore, it is demonstrated that the same sum-DoF and diversity gain are attainable, even in the presence of interrelay interference due to a full-duplex relaying operation if the memory at the relay nodes is exploited in the proposed manner. [ABSTRACT FROM AUTHOR]

Intermittently connected vehicular networks (ICVNs) consist of stationary roadside units (RSUs) deployed along the highway and mobile vehicles. ICVNs are generally infrastructure constrained with a long inter-RSU distance, leading to large dark areas and transmission outage. In this paper, we propose a novel cooperative store–carry–forward (CSCF) scheme to reduce the transmission outage time of vehicles in the dark areas. The CSCF scheme utilizes bidirectional vehicle streams and selects two vehicles in both directions to serve as relays successively for the target vehicle via inter-RSU cooperation. Compared with the existing schemes, simulation results demonstrate that the proposed CSCF scheme has a great advantage in reducing transmission outage time. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a novel mobile relaying technique, where the relay nodes are mounted on unmanned aerial vehicles (UAVs) and hence are capable of moving at high speed. Compared with conventional static relaying, mobile relaying offers a new degree of freedom for performance enhancement via careful relay trajectory design. We study the throughput maximization problem in mobile relaying systems by optimizing the source/relay transmit power along with the relay trajectory, subject to practical mobility constraints (on the UAV’s speed and initial/final relay locations), as well as the information-causality constraint at the relay. It is shown that for the fixed relay trajectory, the throughput-optimal source/relay power allocations over time follow a “staircase” water filling structure, with non-increasing and non-decreasing water levels at the source and relay, respectively. On the other hand, with given power allocations, the throughput can be further improved by optimizing the UAV’s trajectory via successive convex optimization. An iterative algorithm is thus proposed to optimize the power allocations and relay trajectory alternately. Furthermore, for the special case with free initial and final relay locations, the jointly optimal power allocation and relay trajectory are derived. Numerical results show that by optimizing the trajectory of the relay and power allocations adaptive to its induced channel variation, mobile relaying is able to achieve significant throughput gains over the conventional static relaying. [ABSTRACT FROM AUTHOR]

Vehicular networks require a reliable and efficient one-hop broadcast service to disseminate delay sensitive messages for high-priority safety applications. However, frequent link breakage in the dynamic networking conditions, in the presence of high relative mobility and channel fading, poses technical challenges in satisfying the strict service requirements. Makeup transmissions can improve the performance through repetitive broadcasting of packets before detecting a transmission failure. In this paper, we introduce a node cooperation based makeup strategy for vehicular networks, referred to as cooperative relay broadcasting (CRB), such that neighboring nodes rebroadcast the packet from a source node, increasing the reliability of the broadcast service. The decision to perform CRB is taken proactively and based on the channel conditions between the relaying nodes and the target one-hop neighbors. We propose an optimization framework that provides an upper bound on the CRB performance with accurate channel information. Further, we propose a channel prediction scheme based on a two-state first-order Markov chain to select the best relaying node for CRB. We study the reliability of the broadcast service in terms of packet received rate and packet delivery rate. Through extensive simulations, we demonstrate that the proposed CRB scheme provides a more reliable broadcast service, as compared with existing approaches. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate a multiuser multiple-input single-output relay system with simultaneous wireless information and power transfer, where the received signal is divided into two parts for information decoding and energy harvesting (EH), respectively. Assuming that both base station (BS) and relay station (RS) are equipped with multiple antennas, we study the joint transceiver design problem for the BS beamforming vectors, the RS amplify-and-forward transformation matrix, and the power splitting (PS) ratios at the single-antenna receivers. The aim is to minimize the total transmission power of the BS and the RS under both signal-to-interference-plus-noise ratio and EH constraints. First, an iterative algorithm based on alternating optimization (AO) and with guaranteed convergence is proposed to successively optimize the transceiver coefficients. This AO-based approach is then extended into a robust transceiver design against norm bounded errors in channel state information (CSI), by using semidefinite relaxation and the S-procedure. Second, a novel design scheme based on switched relaying (SR) is proposed that can significantly reduce the computational complexity and overhead of the AO-based designs while maintaining a similar performance. In the proposed SR scheme, the RS is equipped with a codebook of permutation matrices. For each permutation matrix, a latent transceiver is designed, which consists of BS beamforming vectors, optimally scaled RS permutation matrix, and receiver PS ratios. For the given CSI, the optimal latent transceiver with the lowest total power consumption is selected for transmission. We propose concave-convex procedure-based and subgradient-type iterative algorithms, respectively, to design the latent transceivers under perfect and imperfect CSI. Simulation results are presented to validate the effectiveness of all the proposed algorithms. [ABSTRACT FROM PUBLISHER]

Energy efficiency and its optimization constitute critical tasks in the design of low-power wireless networks. This paper is devoted to the error rate analysis and energy efficiency optimization of regenerative cooperative networks in the presence of multipath fading under spatial correlation. To this end, exact and asymptotic analytic expressions are first derived for the symbol error rate (SER) of $M$-ary quadrature amplitude and $M$-ary phase-shift keying modulations ( $M$-QAM and $M$- PSK), respectively, assuming a dual-hop decode-and-forward (DF) relay system, spatially correlated Nakagami- $m$ multipath fading, and maximum ratio combining (MRC) at the destination. The derived expressions are subsequently employed in quantifying the energy consumption of the considered system, incorporating both transmit energy and the energy consumed by the transceiver circuits, and in deriving the optimal power allocation (OPA) formulation for minimizing energy consumption under certain quality-of-service (QoS) requirements. A relatively harsh path-loss (PL) model, which also accounts for realistic device-to-device communications, is adopted in numerical evaluations, and various useful insights are provided for the design of future low-energy wireless networks deployments. Indicatively, it is shown that, depending on the degree of spatial correlation, severity of fading, transmission distance, relay location, and power allocation strategy, target performance can be achieved with much overall energy reduction compared with direct transmission (DT) reference. [ABSTRACT FROM AUTHOR]

This paper studies the performance of two traditional schedulers, namely, proportional fair (PF) and round robin (RR), in the context of relay-enhanced Long-Term Evolution Advanced (LTE-A) networks. These two schedulers are natural candidates for implementation in relay nodes (RNs), and following the results obtained in single-hop networks, mobile operators could be tempted to adopt PF because of the good tradeoff it offers between cell capacity and fairness. Based on a statistical throughput evaluation model, we show that this is not necessarily the right option. The number of RNs, their locations in the cell, and backhaul link quality have a decisive influence on scheduler choice. In some scenarios, it is even not desirable to deploy relays as they degrade the network performance compared with the no-relay case. For the purpose of performance evaluation, we develop a realistic and computationally tractable statistical network model that takes into account fast fading, multiple interferers, cell range expansion bias, backhaul link quality, and traffic load. We also propose optimization of the radio frame structure and a suboptimal RN placement scheme to fairly compare RR and PF. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the multiservice delivery between the source–destination pairs in distributed selfish wireless networks (SeWN), where selfish relay nodes (RN) expose their selfish behaviors, i.e., forwarding or dropping multiservices. Owing to the effect of the RNs’ node-selfishness on the multiservices, a distributed framework of the node-selfishness management is constructed to manage the RN’s node-selfishness information (NSI) in terms of its available resources, the employed incentive mechanism and the quality-of-service (QoS) requirements, and the other RNs’ NSI in terms of their historical behaviors. In this framework, the RNs’ NSI includes the degree of node-selfishness (DeNS), the degree of intrinsic selfishness (DeIS) and the degree of extrinsic selfishness (DeES). Under the distributed node-selfishness management, a path selection criterion is designed to select the most reliable and shortest path in terms of RNs’ DeISs affected by their available resources, and the optimal incentives are determined by the source to stimulate forwarding multiservices of the RNs in the selected path. Our simulation results demonstrate that this framework effectively manages the RNs’ NSI, and the optimal strategies of both the path selection and the incentives are determined. [ABSTRACT FROM AUTHOR]

We consider a three-node buffer-aided relaying network with statistical quality-of-service (QoS) constraint in terms of maximum acceptable end-to-end queue-length bound outage probability. In particular, we study the adaptive link selection relaying problem that aims to maximize the constant supportable arrival rate $\mu$ to the source (i.e., the effective capacity). Fixed and adaptive source and relay power allocation are investigated. By employing asymptotic delay analysis, we first convert the QoS constraint into minimum QoS exponent constraints at the source and relay queues. We then derive the link selection and power allocation solutions as functions of the instantaneous link conditions and QoS exponents using Lagrangian approach. Solutions for various special cases of link conditions and QoS constraints are presented. Moreover, we compare the effective capacities of the proposed relaying schemes and other existing schemes under different link conditions and QoS constraints. Illustrative results indicate that the proposed schemes offer substantial performance gains, and power adaption outperforms fixed power allocation at low signal-to-noise power ratio (SNR) region or under loose QoS constraints. [ABSTRACT FROM AUTHOR]

In this paper, we re-examine the relay channel under the decode-forward (DF) strategy. Contrary to the established belief that block Markov coding is always the rate-optimal DF strategy, under certain channel conditions (a link regime), independent signaling between the source and relay achieves the same transmission rate without requiring coherent channel phase information. Furthermore, this independent signaling regime allows the relay to conserve power. As such, we design a composite DF relaying strategy that achieves the same rate as block Markov DF but with less required relay power. The finding is attractive from the link adaptation perspective to adapt relay coding and relay power according to the link state. We examine this link adaptation in fading under both perfect channel state information (CSI) and practical CSI in which nodes have perfect receive and long-term transmit CSI, and derive the corresponding relay power savings in both cases. We also derive the outage probability of the composite relaying scheme, which adapts the signaling to the link regime. Through simulation, we expose a tradeoff for relay placement showing that the relay conserves the most power when closer to the destination but achieves the most rate gain when closer to the source. [ABSTRACT FROM AUTHOR]

Multiple access broadcasting (MABC) is a spectral efficient protocol in a two-way relay channel (TWRC). The drawback of this protocol in decode-and-forward (DF) mode is decoding complexity at the relay side. Erroneous decoding at the relay can lead to error propagation that degrades the performance of all relay networks operating in the DF mode. In this paper, a maximum likelihood (ML) detector at the multiple-antenna relay is used, and it is proved that this decoding rule can achieve full diversity order at the multiple access (MAC) phase of the MABC protocol. Then, a new beamforming algorithm named as channel alignment is proposed, and it is shown that it achieves full diversity order. A new relay selection algorithm is proposed, and a tight upper bound for the bit error rate (BER) of this scheme is derived. It is proved that it achieves full diversity order. The analytical results and BER performance of the proposed schemes are investigated and compared through simulations. [ABSTRACT FROM AUTHOR]

The quantize-and-forward (QF) strategy for the half-duplex interleave-division multiple-access relay channel (ID-MARC) is investigated in this paper with multiple users, single relay, and single destination. Different from the orthogonal MARC, multiple users in such an ID-MARC are distinguished by different interleavers. For the case that the relay node cannot recover the initial bits correctly, a denoising mutual-information preserving quantizer (DMIPQ) is proposed, which can remove the noise from the received signal while preserving the useful information. A suboptimal searching algorithm is designed to reduce the complexity of DMIPQ. The approximation of DMIPQ is further discussed to get an analytical solution. It is shown that the approximate DMIPQ is equivalent to the minimum mean square error (MMSE) Lloyd-max quantizer. Numerical results illustrate that the proposed DMIPQ outperforms the MMSE Lloyd-max quantizer. It can be also shown that the bit error rate of the ID-MARC (BER) with DMIPQ is close to its compress-and-forward (CF) bounds. [ABSTRACT FROM AUTHOR]

The outage performance of a dual-hop mobile ad hoc network (MANET), which employs amplify-and-forward (AF) relaying in a Rayleigh fading environment in the presence of a Poisson field of interferers at the destination, is investigated. All mobile users are assumed to follow the Poisson arrival model along the highway and can only communicate with each other via a stationary base station or a mobile relay station. Under this MANET model, a single-integral expression for the exact outage probability and a tight lower bound are both derived. The impacts of transmitting power, path-loss exponent, and spatial density of interferers on the performance of dual-hop systems are found. It is revealed that the outage probability of each hop, as a function of distance, transmitting power, etc., has a different impact on the end-to-end outage probability. The outage probability floor is derived when the transmission power at the source/relay becomes large. The optimal power allocation for the dual-hop link is obtained. The behavior of the outage probability during the communication process between the moving nodes is investigated. The analytical results are validated with Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

We study the capacity region of the parallel Gaussian bidirectional relay channel with $L$ independent sub-channels and propose efficient coding schemes for approaching the capacity limit within a constant gap. A two-step approach is considered. First, the corresponding finite field linear deterministic model is studied, for which linear network coding across sub-channels is shown to achieve the capacity region of the channel. Next, based on the insight obtained, a lattice-based compute-and-forward scheme together with simple linear network coding across sub-channels is proposed and is shown to achieve the capacity region of the Gaussian model to within $L$ bits per user regardless of the channel parameters. Even though coding across different sub-channels is necessary for approaching the capacity region, it is shown that this can be realized through a simple linear network coding scheme (across different sub-channels) at the relay. [ABSTRACT FROM PUBLISHER]

In this paper, we provide a comprehensive survey on designs and analyses of various relay-destination transceiving schemes, such as zero-forcing (ZF), minimum mean squared error (MMSE), and maximum information rate (MIR) criteria, in multiple-input multiple-output (MIMO) amplify-and-forward (AF) relaying systems. In the first part of the paper, we suggest a new framework for the transceiver designs utilizing a decomposable property of the error covariance matrix to give a general insight on the system and make the analysis more tractable. Then, in the second part of the paper, we provide an in-depth analysis on their diversity performance. Our analysis embraces two different scenarios, namely, the diversity-multiplexing tradeoff (DMT) and the diversity-rate tradeoff (DRT). First, we derive compact closed-form expressions for the DMT through tight upper and lower bounds. Then, we observe that while our DMT analysis accurately predicts performance of the ZF and MIR schemes, the MMSE-based designs exhibit a complicated rate-dependent behavior and, thus, are very unpredictable via DMT for finite rate cases. Thus, second, we highlight this interesting observation and characterize the diversity of the MMSE schemes at all finite rates. This leads to closed-form expressions for the DRT which reveals relationship between diversity, spectral efficiency, and the number of antennas at each node. The DRT analysis compliments our work on DMT, and thus, the paper provides a complete understanding on the diversity of MIMO AF relaying systems. [ABSTRACT FROM PUBLISHER]

We study the transmission of a set of correlated sources (U1,\ldots ,UK) over a Gaussian multiple access relay channel with time asynchronism between the encoders. We assume that the maximum possible offset \mathsf dmax(n) between the transmitters grows without bound as the block length n \rightarrow \infty , while the relative ratio $ {{ \mathsf {d_{max}}(n) / n}}$ of the maximum possible offset to the block length asymptotically vanishes. For such a joint source-channel coding problem and under specific gain conditions, we derive necessary and sufficient conditions for reliable communications and show that separate source and channel coding achieves optimal performance. In particular, we first derive a general outer bound on the source entropy content for all channel gains as our main result. Then, using Slepian–Wolf source coding combined with the channel coding scheme on top of block Markov coding, we show that the thus achieved inner bound matches the outer bound. As a corollary, we also address the problem of sending a pair of correlated sources over a two-user interference channel in the same context. [ABSTRACT FROM PUBLISHER]

In this paper, a forward decoding procedure is developed for the compress-and-forward (CF) relaying scheme. This procedure uses a layered framework and is based on exploiting a feature of the $N$ -to-1 mapping inherent in the underlying Wyner–Ziv binning. It is shown that exploiting this mapping enables the relaxation of the constraint on the rate of the relay codewords representing the bin indices. For the cooperative multimessage network, the proposed procedure achieves the same rate region as the short-message noisy network coding (SNNC) scheme. However, this procedure is more advantageous for other networks including the two networks presented herein. The first network is a relay chain one with two destinations, whereas the second network is a partially cooperative multimessage one with three destinations. In both networks, side information is available to a subset of the decoding nodes, but not to the rest of the nodes, and in both cases, the network benefits from the relaxation of the rate of the CF bin indices. This relaxation results in rate regions larger than those achieved by the conventional CF and SNNC. [ABSTRACT FROM PUBLISHER]

In this paper, we consider an amplify-and-forward hybrid satellite-terrestrial co-operative network in the presence of cochannel interference (CCI). More specifically, we assume that both the satellite-destination and the satellite-relay links undergo the shadowed-Rician fading and the relay-destination link follows the Nakagami-m fading. By applying the amplify-and-forward (AF) protocol at the terrestrial relay, both the relay and the destination are corrupted by cochannel interference from the terrestrial network. Based on this setup, we first derive the approximate statistical distributions signal-to-interference-plus noise ratio (SINR) and then analyze the system performance. To obtain more insights into the system performance, some asymptotical bit-error rate (BER) results are provided. Moreover, we extend our analysis to a multiple-relay network and analyze the asymptotic performance. Finally, some numerical results are provided to verify our analysis. [ABSTRACT FROM AUTHOR]