Performance Analysis of Hybrid Protocol Based Two-Way Decode-and-Forward Relay Networks

Joint relay-user selection in energy harvesting relay network with direct link

This paper studies the outage performance of the hybrid amplify-and-forward (AF) relaying protocol in simultaneous wireless information and power transfer (SWIPT) systems with direct link. In the hybrid power-time switching based relaying (HPTSR), the block time T is divided into two parts. One is used for energy harvesting and information processing, and the other is used for information transmission from relay to destination node. During the part of energy harvesting and information processing, one portion of the received signal is used for energy harvesting (EH) and the other portion of the received signal is used for information processing. An analytical expressions for outage probability is derived in the hybrid AF-based relay network. Our numerical results verify our analytical expressions and shows that the proposed system performance of the hybrid protocol in the presence of the direct link outperforms the hybrid protocol without direct link.

This paper evaluates the throughput and outage probability (OP) of a secondary user (SU) in a cognitive relay network with an energy harvesting (EH) decode-and-forward (DF) relaying scheme. A potential relay, selected from a set of relays using a proactive relaying scheme, harvests energy. The power transmitted by source and relay nodes are constrained by an interference threshold of the primary receiver. Two schemes of relaying, a time switching based relaying (TSR) and a power splitting based relaying (PSR) are studied. Considering EH and cognitive constraint at the relay node, we analyse the achievable throughput and outage performance of a cognitive DF relaying network. We study the impact of EH time, power splitting ratio, number of relays and tolerable interference threshold of PU on the throughput and outage performance of SU.

This paper investigates the performance of amplify-and-forward (AF) cognitive relay networks with partial relay selection (PRS) in a spectrum-sharing context. The PRS schemes can be divided into two different types: source-relay PRS and relay-destination PRS, which are respectively called SR-PRS and RD-PRS for short. Different from most of the existing studies which only consider interference power constraint on secondary source and relay nodes, transmit power constraint on secondary relay nodes is further considered in our work. In this condition, we derive the lower bound on symbol error rate and the upper bound on ergodic capacity of the two schemes aforementioned over Rayleigh fading channels, which has never been studied before. According to the analyses, the power constraints and the number of secondary relay nodes are the main factors affecting the system performance. Furthermore, the performances of the two schemes are compared by simulations and the correctness of the analytical results are verified by Monte Carlo simulations.

In this paper, we study the performance analysis of a cooperative terrestrial-underwater visible light communication (UWVLC) system, considering energy harvesting at a decode and forward (DF)relay onthe ship.The transmitter tothe shiplink is modelled by shadowed Rician fading channel, while the UWVLC link is characterised by mixture exponential generalized gamma (EGG) distribution. The energy constrained relay harvests energy from the received signal based on power splitting (PS) scheme, assuming a part of received power is used for energy harvesting. Energy harvesting at the relay node makes the system sustainable by reducing the carbon footprints. We derive novel closed form expressions for bit error rate (BER), outage probability and ergodic capacity for the considered system at the underwater node, considering the effects of various parameters that include bubble level, temperature and salinity

Wireless energy transfer cooperative communication systems are analyzed in this paper. In these systems, a source node can communicate with a destination node directly or via the selected relay nodes, while relay nodes harvest energy from radio frequency for forwarding the received signal. In addition, the decode and forward (DF) protocol is applied to relay nodes, and selection combination technique is employed at the destination in order to select the best relay node. The system performance is presented by outage probability expressions over independent and identically distributed (i.i.d) Nakagami-m channel model. The theoretical analysis and the close-form expression of outage probability are derived and compared with the Monte Carlo simulation. The perfect match of calculation and simulation results verifies our theoretical analysis.

In conventional digital communication systems, the quality of the received signal does not improve beyond a certain level as the channel quality increases. Such kind of quality saturation effect is caused by the unrecoverable quantization errors produced by source coding. The Hybrid Digital-Analog (HDA) transmission, where the quantization errors are transmitted in an analog mode along with the quantized data in a digital mode, has been recognized as an effective technique to combat the quality saturation effect. In this paper, we introduce HDA transmission in Wireless Relay Networks (WRNs) over Rayleigh slow-fading channels to eliminate the quality saturation effect and achieve graceful improvement for the better channel quality. Our goal is to minimize the end-to-end distortion by optimal power allocation. We note that digital-analog power allocation involved in HDA transmission is coupled with source-relay power allocation in WRNs. Therefore, the joint power allocation problem should be considered. We investigate this problem for two kinds of relays in WRNs, i.e., Amplify-and-Forward (AF) relays and Decode-and-Forward (DF) relays. In the case of AF relays, we find that the joint power problem is concave and thus derive the explicit expressions of the optimal solution. In the case of DF relays, we formulate the joint power allocation problem as a nonlinear fractional programming problem and then propose an efficient algorithm to search the optimal solution. Simulation results show that the proposed joint power allocation schemes outperform existing schemes in terms of end-to-end distortion in both WRNs with AF relays and that with DF relays under various channel conditions.

In this paper, a distributed power control algorithm is proposed for wireless relay networks in interference-limited environments. The objective is to minimize the total transmission power while satisfying the signal-to-interference-plus-noise ratio (SINR) requirements. Two forwarding techniques, i.e., decode- and-forward (DF) and amplify-and-forward (AF), are considered. The proposed algorithm only requires locally measured SINR on the relay nodes (RNs) and the destination nodes (DNs), based on which each cooperation unit (defined as one source node (SN) and DN pair with the RN associated to it) iteratively updates the transmission power of the SN and the RN by solving a local optimization problem. We prove that the convergence is guaranteed when the parameters adopted in the algorithm are sufficiently large, and then a parameter adjusting method is also designed. Simulation results indicate that the proposed algorithm converges fast and leads to only 7% more power consumption than the optimal power allocation in the considered scenarios. It is also shown that even in interference-limited environments, relaying can still improve system performance substantially in terms of outage and power consumption.

In this work, the ergodic capacity performance for multiple-input/single-output (MISO) free-space optical (FSO) communications system with equal gain combining (EGC) reception is analyzed over gamma-gamma and misalignment fading channels, which are modeled as statistically independent, but not necessarily identically distributed (i.n.i.d.). Novel and analytical closed-form ergodic capacity expression is obtained in terms of H-Fox function by using the well-known inequality between arithmetic and geometric mean of positive random variables (RV) in order to obtain an approximate closed-form expression of the distribution of the sum of M gamma-gamma with pointing errors variates. In addition, we present an asymptotic ergodic capacity expression at high signal-to-noise ratio (SNR) for the ergodic capacity of MISO FSO systems. It can be concluded that the use of MISO technique can significantly reduce the effect of the atmospheric turbulence as well as pointing errors and, hence, provide significant capacity gain over the direct path link (DL). The impact of pointing errors on the MISO FSO system is also analyzed, which only depends on the number of laser sources and pointing error parameters. Moreover, it can be also concluded that the ergodic capacity performance is dramatically reduced as a consequence of the severity of pointing error effects. Simulation results are further demonstrated to confirm the analytical results.

In this paper, we propose a new non-orthogonal multiple access (NOMA)-aided Single-Input Multiple-Output (SIMO) multi-hop relay scheme using wirelessly energy harvesting (EH) andFountain Codes (FCs). Specifically, a single antenna source node employs NOMA to transmit two data streams to two multiple antenna destinations with the assistance of N intermediate multiple antenna Decode-and-Forward (DF) relays. The destinations accumulate received information until sufficient data is gathered to successfully recover the original data. This configuration ensures the SIMO structure is maintained across all hops, as the relays utilize multiple antennas for reception and a single antenna for transmission. To enhance channel capacity at the relay and destination nodes, the selection combining (SC) technique is applied. For data transmission, both the source and relay nodes harvest wireless energy from a power station deployed within the network, follows a time-switching approach. We first derive exact expressions for the end-to-end (e2e) instantaneous signal-to-interference-plus-noise ratios (SINRs) at both destinations, along with their corresponding cumulative distribution functions (CDFs) over Rayleigh fading channels. Then, we derive analytical expressions for the average channel capacity (ACC-e2e) and outage probability (OP-e2e) at each destination and validate their accuracy through Monte Carlo simulations.

In this paper, we propose a novel buffer-aided cooperative phase steering (B-CPS) technique for delay-tolerant wireless networks (DTNs). In the proposed B-CPS technique, all relay nodes (RNs) that succeed in data decoding from a source node (SN) deliver the original signal of SN to a destination node (DN) with a decode-and-forward (DF) manner. With the property of DTNs, the signal from the SN is allowed to be delayed at RNs, and thus all the RNs that succeeded in decoding wait until a certain condition is satisfied, which the minimum channel gain from the RNs to the DN exceeds a threshold. When the condition is satisfied, all the RNs send the received signal to the DN with the CPS technique. Simulation results show that the proposed B-CPS significantly outperforms the conventional CPS technique in terms of outage probability.

Orthogonal frequency-division multiplexing (OFDM) transmission is considered for a medium-voltage (MV) power-line access network (AN). In this paper, we analyze the channel capacity of OFDM-based two-hop relaying systems over MV power lines, where a single relay node is used between the source and destination nodes in an effort to enhance the channel capacity using either cooperative relaying (CR) or noncooperative relaying protocols. For each relaying protocol, the relay node operates in either the amplify-and-forward (AF) or the decode-and-forward (DF) mode. Numerical results show that the channel capacity of the CR protocol in the DF mode is superior to that in the AF mode, as well as to the NCR protocol in the AF and DF modes.

Through simultaneous energy and information transfer, radio frequency (RF) energy harvesting (EH) reduces the energy consumption of the wireless networks. It also provides a new approach for the wireless devices to share each other’s energy storage, without relying on the power grid or traffic offloading. In this paper, we study RF energy harvesting enabled power balancing within the decode-and-forward (DF) relaying-enhanced cooperative wireless system. An optimal power allocation policy is proposed for the scenario where both source and relay nodes can draw power from the radio frequency signals transmitted by each other. To maximize the overall throughput while meeting the energy constraints imposed by the RF sources, an optimization problem is formulated and solved. Based on different harvesting efficiency and channel condition, closed form solutions for optimal joint source and relay power allocation are derived.

This paper proposes an optimal power allocation method for two-way decode-and-forward (DF) relay networks when transmit power values at source nodes are the same. In this paper we consider the multiple access (MAC) capacity for DF relaying scheme. Using case studies, it analytically determines the optimal power values for the two source nodes and one relay node. The achievable sum rate is maximized under a sum power constraint for given squared magnitude of the channel coefficients. Finally, numerical results show that the achievable sum rate for proposed optimum power allocation is greater than or equal to that for equal power allocation.

We investigate the Ergodic capacity (EC) performance of device-to-device (D2D) Internet of Things (IoT) relay non-orthogonal multiple access (NOMA)- simultaneous wireless information and power transfer (SWIPT) systems where the relayed communication is supported with direct link. A two-user case is considered in which a base station transmits symbols to two NOMA users, and the energy harvesting (EH) based relay node via a direct link. The EH based relay node harvests the energy from the BS’s signal and again transmits a superimposed composite NOMA signal intended for the user with poor channel condition and for its D2D user to offload its data traffic. A D2D user offloading is considered to further enhance the spectral efficiency of the system. We derive the analytical expressions for the EC of each of the user and the ergodic sum capacity (ESC) of the system and validate them with simulation results. In such settings, our results demonstrate that the EC of a node and the ESC of the system can be improved through the maximal ratio combining (MRC) scheme compared to a system with single signal decoding scheme. Our results also indicate that the overall ESC of the NOMA-SWIPT system can be improved by having a direct link for a user in the system.