Decode-and-forward Protocol Research Articles

Short-Packet Communications in IoT-Aided Cellular Cooperative Networks With Non-Orthogonal Multiple Access

This paper investigates short-packet communications (SPCs) of a cooperative non-orthogonal multiple access (NOMA) Internet-of-Things (IoT)-based cellular network where an IoT master node acts as: (1) a relay for the cellular system and (2) a source for the IoT system. Accurate and asymptotic closed-form expressions for the average block error rates (BLERs) of cellular user (CU) and IoT user (IU) are derived in the presence of imperfect successive interference cancellation (SIC) and channel state information (CSI). Notably, numerical results show that: (i) IUs' performance is significantly improved by exploitation of NOMA technique and is not dominated by decode-and-forward (DF) or amplify-and-forward (AF) relaying protocol; (ii) CUs' performance may not perform well compared with orthogonal multiple access (OMA)-based systems for both AF and DF protocols; (iii) higher antenna configuration at the cellular transmitter results in a rapid BLER convergence for CU.

Integrated Satellite-Terrestrial Networks With Coordinated C-NOMA and Relay Transmission

For the cooperative nonorthogonal multiple access (C-NOMA)-aided integrated satellite-terrestrial network (ISTN), an outage is inevitable if the channel from the satellite to the weak user is in deep fade. To handle this issue, this article proposes to deploy relay nodes to assist the communication, specifically, the relay and strong user forward information, which is sent from the satellite, to the weak user. After that, the weak user can boost its received signal strength by utilizing maximum ratio combining. In this context, we further study two kinds of relay protocols, i.e., decode-and-forward (DF) and amplify-and-forward (AF). For each protocol, the closed-form and asymptotic expressions of the outage probability (OP) are derived and then, based on the asymptotic OP, the diversity order is analyzed. Results indicate the DF protocol is preferable to the AF from the OP aspect although it incurs more computational load. Besides, the diversity order of the proposed ISTN is identical to that of C-NOMA and twice that of the relaying network. Simulation results clarify the superiority of the proposed scheme.

Average Age of Information in Wireless Powered Relay Aided Communication Network

In order to satisfy timeliness requirements arising from environmental sensing applications, Age of Information (AoI) was proposed to characterize the freshness of the received updates. In this article, we consider a wireless powered relay aided communication network (WPRCN), in which a relay wirelessly powered by a hybrid-access point (H-AP) receives environmental monitoring information update from a sensor and forwards it to the H-AP. The long-term average AoI is studied since the decision correctness depends on the update timely uploaded by the relay. The wireless powered relay adopts either a decode-and-forward (DF) or an amplify-and-forward (AF) protocols, respectively, subject to the energy causality. We also consider the decoding cost of DF protocol owing to the relay’s limited energy storage. Since the expression of the average AoI is nonelementary, we propose a Taylor approximation-based algorithm to obtain its integral. We optimize the transmit power/the equivalent average power consumption of the relay for the sake of minimizing the average AoI in the whole WPRCN with different forwarding protocols. Our simulation results demonstrate the accuracy of the theoretical analysis, while the average AoI of the WPRCN is optimized by our power allocation scheme at the relay. The proposed algorithm is verified to achieve a great approximation effect.

Performance Evaluation of a Wireless Cooperative Network with Maximal Ratio Combining Technique

Research on wireless communication is on the rise due to its capability in improving communication in terms of spectrum efficiency, power and communication reliability. In wireless network, power is consumed mostly in the process of data transmission, hence, the need for cooperative relay protocol and technique to improve systems’ performance through power management and quality of service (QoS). Although, there are various cooperative protocols which include: amplify-and-forward, decode-and-forward among others. However, by using these cooperative protocols, the amount of power consumed and QoS still require improvement. Thus, in this work the quest for incorporation of Maximal Ratio Combining (MRC) technique with the Decode-and-Forward (DF) relay protocol in cooperative network. The cooperative network with DF protocol considered consists of the source, destination and relay(s) nodes. The MRC was incorporated at the destination just to combine the received signals from the relay nodes. Moreover, the system’s simulation was carried out by using MATLAB R2020a and evaluated using bit error rate and power consumption as the performance metrics. The obtained results showed that the QoS and power consumption of the considered cooperative network was considerably improved when MRC was employed in the network in comparison with an existing work.

Performance analysis of dual-hop mixed radio frequency/free space optical transmission systems based on partially coherent beams over F-distribution channel models

The performance of dual-hop mixed radio frequency (RF)/free space optical (FSO) communication system with partially coherent beams (PCBs) is investigated on the basis of decode-and-forward (DF) protocol. Specifically, both the RF and FSO channels are assumed to follow F-distribution with proper selection of parameters. Taking the path loss, atmospheric turbulence, and pointing errors into consideration, the closed-form expressions for the probability density function (PDF) and cumulative distribution function of the received signal-to-noise ratio are derived in terms of hypergeometric function in RF and FSO links, respectively. Subsequently, the closed-form expressions for outage probability, average bit error rate, and ergodic channel capacity of this system with M-ary phase-shift keying and M-ary quadrature amplitude modulation schemes are obtained on the basis of DF protocol. The results show that shadowing in RF link as well as the pointing error and atmospheric turbulence in FSO link would result in significant performance deterioration in dual-hop mixed RF/FSO system, while PCB can bring significant performance improvement of mixed RF/FSO systems with pointing errors over weak to moderate turbulence. Furthermore, the correctness of the analytical expressions is verified by Monte Carlo simulations. This work would benefit the design and development of the mixed RF/FSO systems.

Emerging cooperative MIMO-NOMA networks combining TAS and SWIPT protocols assisted by an AF-VG relaying protocol with instantaneous amplifying factor maximization

In this study, we examine an emerging Multiple-Input-Multiple-Output (MIMO) Non-Orthogonal Multiple Access (NOMA) network which combines Transmit Antenna Selection (TAS) and Simultaneous Wireless Information and Power Transfer (SWIPT) protocols. A pre-coding channels matrix was designed to aid the TAS protocol. We deployed a strong user as a relay to assist a weak user. Three cooperative MIMO-NOMA network scenarios were investigated. In the first scenario, we assumed the relay was deployed with (i) Decode-and-Forward (DF), (ii) Amplify-and-Forward (AF) with Fixed Gain (FG) and (iii) AF with a Variable Gain (VG) protocols to improve system performance over the first scenario. In scenario (iii), we investigated an amplify coefficient based on the maximum of instantaneous CSI and obtained the Outage Probability (OP) in novel closed form. The analytical results showed that although the Base Station (BS) sent information and energy at the same instant, the OP performance at the relay was sufficient due to assistance from multi-antennas and the TAS protocol. However, the OP performance at the user under cooperation with a relay using the AF-VG protocol achieved better system performance than the DF and AF-FG protocols. We proved and verified the analytical results with Monte Carlo simulations.

Hybrid AF/DF Cooperative Relaying Technique with Phase Steering for Industrial IoT Networks

For the next generation of manufacturing, the industrial internet of things (IoT) has been considered as a key technology that enables smart factories, in which sensors transfer measured data, actuators are controlled, and systems are connected wirelessly. In particular, the wireless sensor network (WSN) needs to operate with low cost, low power (energy), and narrow spectrum, which are the most technical challenges for industrial IoT networks. In general, a relay-assisted communication network has been known to overcome scarce energy problems, and a spectrum-sharing technique has been considered as a promising technique for the radio spectrum shortage problem. In this paper, we propose a phase steering based hybrid cooperative relaying (PSHCR) technique for the generic relay-assisted spectrum-shared WSN, which consists of a secondary transmitter, multiple secondary relays (SRs), a secondary access point, and multiple primary access points. Basically, SRs in the proposed PSHCR technique operate with decode-and-forward (DF) relaying protocol, but it does not abandon the SRs that failed in decoding at the first hop. Instead, the SRs operate with amplify-and-forward (AF) protocol when they failed in decoding at the first hop. Furthermore, the SRs (regardless of operating with AF or DF protocol) that satisfy interference constraints to the primary network are allowed to transmit a signal to the secondary access point at the second hop. Note that phase distortion is compensated through phase steering operation at each relay node before second-hop transmission, and thus all relay nodes can operate in a fully distributed manner. Finally, we validate that the proposed PSHCR technique significantly outperforms the existing best single relay selection (BSR) technique and cooperative phase steering (CPS) technique in terms of outage performance via extensive computer simulations.

On the Capacity of Full‐Duplex AF/DF Relay System with Energy Harvesting for Vehicle‐to‐Vehicle Communications

This paper studies the ergodic capacity (EC) of full‐duplex (FD) amplify‐and‐forward (AF) and decode‐and‐forward (DF) relay system with energy harvesting (EH) for vehicle‐to‐vehicle (V2V) communications. Unlike previous works on FD‐EH systems, we consider the case that both relay and destination are mobile vehicles while the source is a static base station. We mathematically derive the exact closed‐form expressions of ECs of both AF and DF protocols of the considered FD‐EH‐V2V relay system over cascade (double) Rayleigh fading. Our numerical results show that the ECs in the case of the V2V communication system are reduced compared to those in the case of stationary nodes. Also, with a specific value of residual self‐interference (RSI), the ECs of the considered FD‐EH‐V2V relay system can be higher or lower than those of half‐duplex‐ (HD‐) EH‐V2V system, depending on the average transmission power of the source. Furthermore, when the transmission power of the source and RSI are fixed, the ECs of the considered system can achieve peak values by using optimal EH time duration. On the other hand, the ECs of both AF and DF protocols reach the capacity floors in the high signal‐to‐noise ratio (SNR) regime due to the RSI impact. Also, the effect of RSI dominates the impact of cascade Rayleigh fading in the high SNR regime. Finally, we validate our analysis approach through Monte‐Carlo simulations.

SINR and Delay Analyses in Two-Way Full-Duplex SWIPT-Enabled Relaying Systems

We first investigate the accumulated loopback self-interference (ALSI) under amplify-and-forward (AF) protocol in two-way full-duplex (TWFD) relaying systems with simultaneous wireless information and power transfer (SWIPT). We analyze how SWIPT affects ALSI and establish the condition for ALSI to converge when there is no energy buffer. Unlike ALSI in TWFD relaying without SWIPT (Chang et al., 2019), ALSI in TWFD relaying with SWIPT always converges and does not grow unbounded. In addition, we study the delay performance in such a system under AF and decode-and-forward (DF) protocols. In AF protocol, the condition for successful signal transmissions is provided. When that condition is met, the received signals at the relay can always get through the channels but experience delays. Otherwise, the outage event occurs. In DF protocol, the best-effort scenario (having no energy buffer) and the QoS scenario (having energy buffer) are discussed. The probability of successful transmissions and the distribution of the delay in both scenarios are derived. Simulation results of DF protocol show that the best-effort scenario is suitable for the delay-tolerant service and the QoS scenario is suitable for the delay-sensitive service. Furthermore, AF protocol is more suitable for the service with less QoS demanding.

Outage probability of dual-hop cooperative communication networks over the Nakagami-m fading channel with RF energy harvesting

Cooperative communication systems with wireless power transfer are being investigated for future advanced wireless networks. In this research, we propose applying a wireless power transfer to dual-hop cooperative communication systems, in which a relay node harvests the energy from the radiofrequency in order to forward the received signal, and a source node can communicate with a destination node directly or through the selected relay nodes. The system performance is evaluated by an outage probability that is calculated over independent and identically distributed (i.i.d) Nakagami-m distributions in two scenarios, i.e., integer m and arbitrary m. Furthermore, the closed forms of the outage probability expressions are derived in the case of both the amplify-and-forward (AF) and decode-and-forward (DF) protocols. The Monte Carlo method is utilized to simulate the system with the aims of evaluating the system performance and verifying the theoretical analysis. The numerical results highlight that the proposed calculation method and the closed form of the outage probability are accurate. We also compare the system performance of both the AF and DF protocols and show the effect of parameter m on the performance of the system.

Performance analysis of NOMA-based cooperative networks with relay selection

Non-orthogonal multiple access (NOMA) technique is an expert on channel differences exploiting. In this paper, a dual-hop NOMA-based cooperative relaying network where a best relay is selected as an active node to accomplish the communication between a source and a destination is discussed. We assume that both decode-and-forward (DF) and amplify-and-forward (AF) protocols are applied to the selected relay. The metrics that ergodic sum-rate and outage probability are investigated, and the closed-form expressions of the latter for DF and AF protocols are derived. Numerical and simulation results are conducted to verify the validity of the theoretical analysis, in which we can see that the NOMA based DF relaying is better than the NOMA based AF relaying and other existing NOMA-based cooperative communication schemes.

Interference alignment in two‐hop multiple‐input multiple‐output interference channel under various CSI and antenna correlation

In this paper, the problem of interference management is investigated in the downlink of multi-user multiple-input multiple-output two-hop interference channel under various scenarios of channel state information (CSI) and antenna correlation. Interference alignment (IA) in the space dimension is a powerful tool to solve this problem. Iterative IA algorithms are adopted in both the first and the second hops transmissions independently. After aligning interfering signals, the recovery of the transmitted signal vector is performed based on zero-forcing and semi-definite relaxation detectors. Furthermore, the impacts of the imperfect CSI and antenna correlation on sum-rate are investigated for decode-and-forward (DF) and amplify-and-forward relaying protocols. When the system is proper but IA is not completely feasible, the performance of minimum interference leakage (MIL) is compared with rank-constrained rank minimisation (RCRM) algorithm in DF protocol. RCRM algorithm is more sensitive to CSI such that the channel uncertainty easily leads to an increase in the interference matrix rank. According to the simulation results, for the case of perfect CSI, RCRM makes further interference-free dimensions which leads to better performance than MIL, but for the case of imperfect CSI, close performance is observed.

Bi-directional relay network employing signal space diversity

Abstract In this work, signal space diversity (SSD) method is exploited for a simple two-way relay channel (TWRC) with two end users mutually exchanging information. In order to ensure simplicity, the same rotation angle and interleavers are used under SSD framework. Also the well known decode-and-forward (DF) and amplify-and-forward (AF) protocols are adapted for the proposed TWRC. The analytical symbol error rate (SER) performance of the proposed scheme is evaluated for DF and AF protocols individually and evaluated through simulation results. The proposed scheme is shown to improve the performance of TWRC in terms of SER for both two protocols.

Outage Analysis of RF Energy Harvesting Cooperative Communication Systems Over Nakagami-$m$ Fading Channels With Integer and Non-Integer $m$

The study of the effects of Nakagami- $m$ fading channels with both integer and non-integer $m$ plays an important role in the design of practical wireless systems. In this paper, we investigate a dual-hop cooperative communication system, where source node communicates with destination node through direct and relaying paths. Partial relay selection (PRS) scheme is used to select the best relay among $N$ relays which are capable of harvesting energy from radio frequency (RF) signals. At the destination, selection combining (SC) technique is employed to combine the signals of the direct path and the relaying path. We consider two relaying protocols, i.e. amplify-and-forward (AF) and decode-and-forward (DF). For both AF and DF protocols, we derive the tight lower-bound closed-form approximate expression and the exact closed-form expression of the outage probability (OP) over Nakagami- $m$ fading channels with both integer and non-integer $m$ . Moreover, the optimal energy harvesting duration which minimizes the OP is also determined. Numerical results show that, the OP of DF protocol and its minimum value is lower than those of AF protocol for the same parameter settings. Moreover, the time switching ratio which gives the smallest OP in the case without direct path is larger than the case with direct path.

A Relay-Assisted OFDM System for VLC Uplink Transmission

Uplink transmission is an issue for visible light communications due to the unpleasant irradiance from the source light when placed close to the users. To overcome this problem, this paper proposes the use of relays to lower the required source optical power. A popular multi-carrier modulation scheme, termed direct-current biased optical orthogonal frequency division multiplexing, is employed to achieve high spectral efficiency. In addition, both amplitude-and-forward (AF) and decode-and-forward (DF) protocols are used. The theoretical models of AF and DF protocols are also obtained and verified by simulations. To minimize the source optical power while satisfying reliable communications, this paper formulates the associated optimization problems for AF and DF protocols. Exhaustive search is first used to obtain the optimal configuration for the system. As exhaustive search requires high computation efforts and can be time-consuming, two low-complexity suboptimal designs for AF and DF protocols are then proposed, and the proposed suboptimal designs can approximate the performance of exhaustive search in high signal-to-noise ratio regions. Numerical and experimental results indicate that when compared with the counterpart without a relay, the proposed relay-assisted system requires much lower source optical power under the constraints of reliable transmissions.

Cooperative secrecy transmission in multi‐hop relay networks with interference alignment

In this study, the authors consider the secrecy communication of one source-destination pair in a wireless multi-hop relay network, where each node is equipped with multiple antennas. They use the method of interference alignment for secrecy transmission in the presence of an eavesdropper. Firstly, they propose a decode-and-forward (DF) relaying protocol and give a new result on the joint probability density function of the first, second, horizontal ellipsis , kth ($k=1, 2,\ldots $k=1,2, horizontal ellipsis ) largest eigenvalues of the complex Wishart matrices $\boldsymbol{H} \boldsymbol{H}H$HHH, where $\boldsymbol{H}$H is an matrix whose elements are independent identically distributed complex Gaussian variables with zero mean and unit variance. They then utilise this result to characterise the legitimate outage probability and the diversity order of the proposed DF protocol. The case where the relay works in the amplify-and-forward (AF) mode is considered at last, and the diversity order of the proposed AF protocol is given.

Distributed Processing for Multi-Relay Assisted OFDM With Index Modulation

Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) has become a high-profile modulation scheme for the fifth-generation (5G) wireless communications and has thus been extended to multi-hop scenarios in order to improve the network coverage and energy efficiency. However, the extension of OFDM-IM to multi-relay cooperative networks is not trivial, since it is required that a complete OFDM block should be received and decoded as an entity in one node. This requirement prevents the employment of multiple relays to forward fragmented OFDM blocks on individual subcarriers. In this regard, we propose a distributed processing scheme for multi-relay assisted OFDM-IM, by which multiple relays are selected to forward signals in a per-subcarrier manner to provide optimal error performance for two-hop decode-and-forward (DF) OFDM-IM systems. Specifically, a single selected relay only needs to decode partial information carried on certain active subcarriers and forward just as for traditional OFDM systems without IM. After receiving all signals on active subcarriers forwarded by different relays, the destination can reconstruct the complete OFDM block and retrieve the full information. We analyze the average block error rate and modulation capacity of the two-hop OFDM-IM system employing the proposed distributed DF protocol and verify the analysis by numerical simulations.

Performance Analysis of Two-Way Relaying in Cooperative Power Line Communications

This paper studies the performance of a half-duplex (HD) two-way relay (TWR) in power line communication (PLC) over a log-normal fading channel with impulsive noise. We consider the two common relaying protocols: amplify-and-forward (AF) and decode-and-forward (DF). For the DF relaying, we apply physical-layer network coding (PNC) and analog-network coding (ANC) to the PLC TWR. We derive analytic expressions for the average sum capacity and the outage probability of the system. The Monte Carlo simulations are provided throughout to validate our analysis. The analytical results show a tight approximation to the simulation results. We compare the one-way relay (OWR) to the TWR and show that the HD spectral efficiency loss incurred by the OWR can be sufficiently mitigated in PLC. However, the outage probability of the TWR is inferior to that of the OWR. To enhance the outage performance of the PLC TWR, we implement a hybrid PLC/wireless (HPW) system, where all nodes are equipped with the PLC and wireless capabilities. Data transmission occurs over the two parallel links. The diversity in the transmission allows the TWR to improve its outage performance in the AF and DF protocols. The impact of the impulsive noise, inherent to the PLC channels, is also highlighted in the simulation results. It is shown that the impulsive noise severely impairs system performance.

Performance Analysis and Power Allocation for NOMA-Based Hybrid Satellite-Terrestrial Relay Networks With Imperfect Channel State Information

In this paper, we study the multiple-user non-orthogonal multiple access (NOMA) scheme in the hybrid satellite-terrestrial relay networks (HSTRN). The proposed system model takes into account both the decode-and-forward (DF) and amplify-and-forward (AF) protocols at the relay and the imperfection of channel state information (CSI) at all nodes. We analyze the outage performance and investigate the power allocation problem to ensure fairness among users. Specially, we derive the closed-form expressions and the asymptotic expressions at high signal-to-noise-ratios (SNR) region for the outage probability of each user. Based on the asymptotic expressions, the considered non-convex power allocation problem is approximated to a generalized linear fractional programming problem. A low-complexity algorithm is developed to yield an optimal solution. Simulation results demonstrate the validity of theoretical results. The impacts of the channel estimation error and channel fading parameters on the outage performance are analyzed. Comparisons between NOMA and orthogonal multiple access (OMA), as well as between DF and AF protocols are also shown.

Outage Performance for Multiuser Threshold-Based DF Satellite Relaying

Satellite communication plays an important role in future seamless wireless network. In this paper, we investigate the system outage performance of a multiuser threshold-based decode-and-forward (DF) satellite relaying network, where the satellite employing spot beam technology is used as an aerial relay to assist the signal transmission between the terrestrial equipments with multi-antenna. Assuming that maximum ratio transmission (MRT) and maximum ratio combining (MRC) are utilized to achieve the optimal performance, we first obtain the equivalent output signal-to-noise ratio (SNR) expression of the considered system, where frequency division multiplexing access (FDMA) scheme is exploited in the uplink. Then, we derive the closed-form system outage probability (SOP) expression for the considered system, where both uplink and downlink are subject to shadowed-Rician (SR) fading with path loss and antenna gain being considered. The main advantage of our theoretical formula is that it can be used in the case of integer and rational Nakagami-m fading parameters. Furthermore, asymptotic SOP formula at high SNR is also presented to show the diversity order and coding gain of the considered system. Finally, simulation results are provided to verify the correctness of the exact and asymptotic SOP expressions and reveal the effects of representative parameters on the system outage performance of the satellite relaying system with threshold-based DF protocol.