Search

This paper investigates the relay-assisted wireless information and power transfer enabled hybrid visible light communication (VLC)-radio frequency (RF) network, where a light emitting diode (LED) access point (AP) serves multiple information users (IUs) and multiple energy harvesting users (EHUs). IUs are allowed to receive information from the LED AP through time-division-multiple-access (TDMA) manner by either the single-hop VLC-ONLY mode or the relay-assisted dual-hop VLC-RF mode, while EHUs harvest energy via the VLC links. An optimization problem is formulated to maximize the achievable information rate of IUs by jointly optimizing the access mode selection, the direct current (DC) offset at the LED AP, the peak amplitude of the alternating current (AC) component at the LED AP, the electrical power allocated to the LED AP and the power allocation at relay, subject to the energy harvesting (EH) requirement constraints of EHUs. To tackle the non-convex problem with binary variables, we first decompose it into two subproblems in terms of the two access modes. Then, the subproblems are equivalently transformed and solved by the proposed successive convex approximation (SCA)-based algorithms. Simulation results show that significant performance gain can be achieved by optimizing the DC offset. It is also observed that the area where the VLC-ONLY mode is superior to the VLC-RF mode is enlarged with the decrease of the minimal EH requirement. Besides, the achievable information rate of IUs by the VLC-RF mode first increases and then decreases with the increment of the distance between the relay and the LED AP. [ABSTRACT FROM AUTHOR]

This article investigates the simultaneous wireless information and power transfer-wireless powered communication network systems, where a multiantenna source transmits information to a multiantenna destination with the assistance of multiple single-antenna energy-constrained relays. For such a system, a transmission protocol is presented based on the $J$ th best relay selection and the transmit antenna selection such that the information and power are transferred over the channel with the largest instantaneous power gain. Time switching receiver architecture is adopted at the relays for information decoding and energy harvesting (EH). The system information transmission performances in Rayleigh fading are analyzed with the nonlinear EH model and imperfect channel state information (CSI), and the closed-form expressions of the system outage probability and reliable throughput are derived. In order to provide more concise results, the corresponding approximate expressions are also derived at low and high signal-to-noise ratio. Numerical results show that our obtained theoretical results match Monte Carlo simulation results very well, demonstrating the effectiveness of our obtained analytical results. Besides, it also shows that the imperfect CSI of the source-to-relay link has greater impact on the system performance than that of the relay-to-destination link. Additionally, by using the nonlinear EH model, the false performance caused by the linear EH model can be reduced. [ABSTRACT FROM AUTHOR]

This paper investigates the link scheduling for relay-aided high-mobility vehicular networks, where the vehicles with good vehicle-to-infrastructure (V2I) links are employed as cooperative relay nodes to help forward information to the ones with poor V2I links over vehicle-to-vehicle (V2V) links. To overcome the inefficiency of current instantaneous information rate based link scheduling (IIR-LS) method, especially in high-mobility scenarios, we propose a mobile service amount based link scheduling (MSA-LS) for high-mobility vehicular networks. We formulate an optimization problem to maximize the MSA of MSA-LS by jointly scheduling the V2I and V2V links. Since the resulted combinational optimization problem is too complex to solve, we design an efficient low-complexity algorithm, where Sort-then-Select, Hungarian algorithm, and Bisection search are employed. Simulation results demonstrate that our proposed MSA-LS is able to achieve new optimal performance. It is also shown that our proposed MSA-LS is much more efficient for high-mobility vehicular systems, which can improve the system average throughput with increment of about 13% compared with existing IIR-LS and with about 22% increment compared with traditional non-cooperation scheduling. [ABSTRACT FROM PUBLISHER]

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

This paper investigates the simultaneous wireless information and power transfer (SWIPT) in cooperative relay networks, where a relay harvests energy from the radio frequency (RF) signals transmitted by a source and then uses the harvested energy to assist the information transmission from the source to its destination. Both source and relay transmissions use rateless codes (RCs), which allow the destination to employ any of the two information receiving strategies, i.e., the mutual information accumulation (IA) and the energy accumulation (EA). The SWIPT-enabled relay employs three different SWIPT receiver architectures, the ideal receiver, and two practical receivers (i.e., the power splitting (PS) receiver and the time switch (TS) receiver). Accordingly, three relaying protocols, namely, the ideal protocol, PS protocol, and TS protocol, are presented. To explore the system performance limits with these three protocols, optimization problems are formulated to maximize their achievable information rates. For the ideal protocol, explicit expressions of the optimal solutions are derived. For the PS protocol, a linear-search algorithm is designed to solve the nonconvex problems. For the TS protocol, two solving methods are presented. Numerical experiments are carried out to validate our analysis and algorithms, which show that, with the same SWIPT receiver, the IA-based system outperforms the EA-based system, whereas with the same information receiving strategy, the PS protocol outperforms the TS protocol. Moreover, compared with nonrateless-coded systems, the proposed protocols exhibit considerable performance gains. Moreover, the effects of the relay position on system performance are also discussed, which provides insights on SWIPT-enabled relay systems. [ABSTRACT FROM AUTHOR]

In 5G heterogeneous networking, it is promising to integrate different wireless networks to provide higher data rate. This paper models the integrated system as a receiver frequency division relay channel (RFDRC) and studies how to improve the transmission rate by combining decode-forward (DF), compress-forward (CF), and amplify-forward (AF) schemes. First, we establish clear criterions on how to select a relay scheme among DF, CF, and AF schemes and prove that the CF outperforms AF for all possible configurations. Based on the scheme selection criterions, we propose a hybrid DF–CF scheme which takes advantage of both DF and CF schemes in RFDRC. A near-optimal resource allocation is presented for the DF–CF-based system, leading to a new achievable rate for RFDRC. For ease of implementation, we further put forward a hybrid DF–AF scheme and reconsider the joint bandwidth and power allocation. Two suboptimal resource allocation solutions are established. In particular, when source frequency band and relay frequency band have equivalent bandwidth, we show that the proposed hybrid DF–AF scheme can achieve the concave envelope of the maximum between DF rate and AF rate. Numerical results show that the proposed schemes bring significant gains for RFDRC. [ABSTRACT FROM AUTHOR]

For a two-way relay network (TWRN) with three nodes, we discuss the performance optimization of digital network coding (DNC) and physical network coding (PNC) schemes under the energy harvesting (EH) constraints and peak power constraints. We also consider the energy transfer between nodes, which is referred to as energy co-operation. To find the maximal achievable performance, we first consider the case of offline scheduling, formulate the corresponding optimization problems, find the optimal solutions, as well as present some useful theoretical properties on optimality. Then we move to the online scheduling, and propose both dynamic programming and some intuitive policies to approach the performance of its offline counterpart. Numerical results show that PNC outperforms DNC due to the higher spectrum efficiency and the intrinsic coding gains, under the same conditions. Furthermore, it is observed that if the relay harvests much more energy and shares it with the two source nodes, DNC with energy co-operation scheme has the potential to perform comparable to or even better than PNC without energy co-operation scheme, which validates the importance of energy co-operation in contemporary communication systems. [ABSTRACT FROM AUTHOR]

This paper investigates the energy efficiency (EE) in multiple relay-aided OFDM systems, where decode-and-forward (DF) relay beamforming is employed to help the information transmission. In order to explore the system performance behavior with user fairness for such a system, an optimization problem is formulated to maximize the EE by jointly considering multiple factors, i.e., the transmission mode selection (DF relay beamforming or direct-link transmission), the helping relay set selection, the subcarrier assignment and the power allocation at the source and relays on subcarriers, under nonlinear proportional rate fairness constraints, where both transmit power consumption and linearly rate-dependent circuit power consumption are taken into account. To solve the nonconvex optimization problem, we propose a low-complexity scheme to approximate it. Simulation results demonstrate its effectiveness. The effects of the circuit power consumption on system performance is also studied and it is observed that with either the constant or the linearly rate-dependent circuit power consumption, system EE grows with the increment of system average channel-to-noise ratio (CNR), but the growth rates show different behaviors. For the constant circuit power consumption, system EE increasing rate is an increasing function of the average CNR, while for the linearly rate-dependent one, system EE increasing rate is a decreasing function of the average CNR. This observation is very important, which indicates that by deducing the circuit dynamic power consumption per unit data rate, system EE can be greatly enhanced. Besides, we also discuss the effects of the number of users and subcarriers on the system EE performance. [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]

Energy harvesting technique is a potential way for relay node energy supply in cooperative networks with respect to deployment flexibility and maintenance charge reduction. However, unlike traditional power source, it is intuitive that the fluctuation of harvested energy flow can degrade the benefit resulted from relay-aided cooperative transmission. To this end, this paper focuses on the performance analysis of an energy harvesting relay-aided cooperative network under slow fading channel from a perspective of outage behavior and attempts deriving the closed-form expression of outage probability of the proposed cooperative protocol. Compared with simple direct transmission protocol, it is proved that a multiplicative gain for improving system performance in terms of minimizing outage probability can be obtained by energy harvesting relay-aided cooperative transmission. In particular, if there are multiple available relay nodes around the environment or the energy-exhausted probability of relay node is small, it is very profitable to employ relay-aided cooperative transmission protocol. [ABSTRACT FROM PUBLISHER]

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

This paper investigates the simultaneous wireless information and energy transfer for the non-regenerative multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) relaying system. By considering two practical receiver architectures, we present two protocols, time switching-based relaying (TSR) and power splitting-based relaying (PSR). To explore the system performance limits, we formulate two optimization problems to maximize the end-to-end achievable information rate with the full channel state information (CSI) assumption. Since both problems are non-convex and have no known solution method, we firstly derive some explicit results by theoretical analysis and then design effective algorithms for them. Numerical results show that the performances of both protocols are greatly affected by the relay position. Specifically, PSR and TSR show very different behaviors to the variation of relay position. The achievable information rate of PSR monotonically decreases when the relay moves from the source towards the destination, but for TSR, the performance is relatively worse when the relay is placed in the middle of the source and the destination. This is the first time such a phenomenon has been observed. In addition, it is also shown that PSR always outperforms TSR in such a MIMO-OFDM relaying system. Moreover, the effects of the number of antennas and the number of subcarriers are also discussed. [ABSTRACT FROM AUTHOR]

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

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

A relay channel (RC), consisting of a source, a relay, and a destination, is a basic transmission unit of cooperative communication networks. The capacity of an RC is not known in general. In this paper, an SNR decomposition (SD) strategy is presented to implement time sharing, which provides a new tractable and achievable rate for a full-duplex Gaussian RC. More specifically, we first expand the SNR of a relay destination channel (SNR-RD) into two terms under the relay power constraint and divide the system into two subbands. Then, we assign the obtained SNR-RD for each subband and employ decode-forward (DF) or compress-forward (CF) according to the assigned SNR-RD. It is shown that the achievable rate of the SD strategy is competitive with that of superposing CF on DF. As the superposition structure requires a sophisticated codeword design, the SD strategy provides another practical combination structure of DF and CF strategies. Approximations for the SNR-RD and bandwidth allocation for subbands are also given. Based on the obtained results, two application scenarios, i.e., mobile relay and quasi-static fading RCs, are also considered. Finally, various numerical results are shown to support our developed theoretical results. [ABSTRACT FROM PUBLISHER]

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

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

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

The diamond relay network is an efficient cooperative networking configuration in which the source node cooperates with two selected neighbors. For such networks, we investigate the impact of the relay positioning on the performance. In particular, considering an opportunistic protocol based on the use of relaying buffers, we provide sets of constraints which, when satisfied, give sufficient conditions for simultaneously guaranteeing network stability and throughput improvement. These results are given for both symmetric and asymmetric relay locations. In contrast to prior work dealing with the diamond relay network, we also break the strong hypothesis of no interlink interference between the source and relay transmissions. Our results provide design guidelines for relay selection by establishing areas of feasible relay locations, whilst also identifying optimal positions which lead to maximum throughput gain. [ABSTRACT FROM AUTHOR]