However, to the best of our knowledge, the secrecy performance has not been well studied for cooperative systems, as most of the existing works focus on traditional relay schemes, e.g., amplify-to-forward and DF schemes. In this work, a dual-hop cooperative system, in which there are a Source- Destination (S-D) pair, a relay node (R) and an eavesdropper (E), which attempts to eavesdrop the confidential message sent by S and forwarded by R, is considered. R tries to coordinate the processes of information decoding from the received signal, by recoding and forwarding the received messages to D. Further, R adopts threshold DFrelaying scheme to decide whether to aid S-D pair’s information transmission or not, aiming to enhancing the system performance and save the system resource. The main contributions of this work are listed as follows:
For relay-aided OFDM(A) systems, the authors in  and  have proposed two efficient types of relaying, namely amplify and forward (AF) and decode and forward (DF). Recently, the DFrelaying is receiving a lot of interest due to its simple processing at the relay. With DFrelaying, symbols are transmitted in two time slots (TSs). During the first TS, the source broadcasts symbols on all sub- carriers with the relay keeping quiet. During the second TS, except from the relay, the source might also broad- cast symbols on subcarriers not used by the relay, as will be elaborated later. Adopting DFrelaying, the authors in [4-23] have studied the RA problems for downlink OFDMA intensively.
Concerning relay aided OFDM(A) transmissions, two low-complexity yet efficient types of relaying have been proposed in  and , namely amplify-and-forward (AF) and decode-and-forward (DF). Recently, the DFrelaying is receiving a lot of interest due to its simple processing at the relay. To better apply it,  and  have further proposed the ML decoding to address the error propa- gation issue. With DFrelaying, symbols are transmitted in two time slots (TSs). During the first TS, the source broadcasts symbols on all subcarriers with the relay keep- ing quiet. During the second TS, except for the relay, the
In this paper, we investigated the effects of the source-relay distance and fast/slow-fading CCIs on the performance of the DF-relaying OC system. Con- ditioned on the probability of symbol errors at the relay, we first developed the MGF of the instantan- eous maximum output SINR. Using the total prob- ability theorem, we then derived closed-form expressions for the OP and the average SER at the destination. With these analytical expressions, it was shown that the performance of the large distance be- tween the source and the relay is better than that of the small distance, regardless of interference fading speed at the destination. Furthermore, we also showed that given the distance, the performance of slow-fading interference is basically better than that of fast fading, except in the low SNR regime for the
Considering the CCI, system models in multi-cell DF relay-aided OFDMA become quite interesting and chal- lenging. With multi-cell DF relay-aided OFDMA systems,  and  have discussed RA algorithms when the powers are uniformly allocated to all stations. For multi- cell OFDMA systems without DFrelaying, several RA algorithms have been proposed in [29-32]. However, these methods cannot be extended directly to solve RA prob- lems jointly optimizing transmission mode selection, sub- carrier assignment (MSSA), as well as power allocation (PA) in multi-cell OFDMA systems with opportunistic DFrelaying. Concerning the opportunistic DF protocol in multi-cell relayed OFDMA systems,  and  have recently proposed joint RA schemes to maximize the sum rate over all cells and the weighted sum of each cell min-rate, respectively. However, the proposed centralized algorithms (CAs) seem to be quite heavy to implement in practice.
investigated the performance by optimizing the transmit power factor . The study impacts of relay selection of cooperative NOMA on the performance system . the authors in  proposed a novel best cooperative mechanism (BCM) for wireless energy harvesting and spectrum sharing in 5G network. The - include amplify-and-forward (AF) and decode-and-forward (DF) relaying. In , it showed that a dual-hop power line communication (PLC) system can improve the system capacity compared to direct-link (DL) transmission. And M. Rabie et. al.  proposed using Multi-hop relay instead of use one hop relay or dual-hop relays. This study, the authors investigated the energy efficiency over PLC channels with assuming log-normal fading. The studies  and  analyzed the system performance of multi-hop AF/DFrelaying over PLC channels in terms of average bit error and ergodic capacity. These studies showed that the system performance can be improve by increasing the number of relaying. In addition, The authors in  studied the impact of relay selection (RS) on system performance. The compared results on two-stage versus max-min RS showed that cooperative NOMA system over Rayleigh fading channels with two-stage RS is better than max-min one. We hypothesized that there are N users with the Nth user at the far end from BS with the worst channel condition. The QoS of the Nth user can be improved with the N-1 user’s cooperation instead of just receiving a relay cooperation. At each node perform the best neighbor selection to forward the signal next neighbor. The best selection of neighbors is repeated until the signal reaches the destination
Motivated by the interest of two-way relay-assisted sys- tem, as our major contribution, we will derive closed-form expressions of the ergodic rate for the proposed relay- assisted strategy, and investigate the effects of noise, the predetermined ratio, the received power of signals includ- ing the desired signal, and the interference. Two cases in which the relaying terminal has the same (symmetric) and different (asymmetric) received power from the two ter- minals exchanging information are considered. We then study the performance for the weak interference case and high signal-to-noise ratio (SNR) case. The approximations of ergodic rate for these cases are derived respectively. Based on these approximations, we present closed-form power allocation strategies which involve several key sys- tem coefficients and can be easily implemented. Numer- ical results confirm the accuracy of the analysis results and show the tightness of our approximate results. The improvement of the ergodic rate by using the power allo- cation strategy also can be found from the numerical results. To the best of our knowledge, this is the first ana- lytical result that is applicable for D2D communication with two-way DFrelaying.
In terms of modern applications of wireless sensor networks in smart cities, relay terminals can be employed to simultaneously deliver both information and energy to a designated receiver by harvesting power via radio frequency (RF). In this paper, we propose time switching aware channel (TSAC) protocol and consider a dual-hop full-duplex (FD) relaying system, where the energy constrained relay node is powered by RF signals from the source using decode- and-forward (DF) relaying protocols. In order to evaluate system performance, we provide an analytical expression of the achievable throughput of two different communication modes, including instantaneous transmission and delay- constrained transmission. In addition, the optimal harvested power allocation policies are studied for these transmission modes. Most importantly, we propose a novel energy harvesting (EH) policy based on FD relaying which can substantially boost the system throughput compared to the conventional half-duplex (HD) relaying architecture in other transmission modes. Numerical results illustrate that our proposed protocol outperforms the conventional protocol under the optimal received power for energy harvesting at relay. Our numerical findings verify the correctness of our derivations and also prove the importance of FD transmission mode.
Specifically, in the seminal paper , energy harvesting was applied to amplify-and-forward (AF) relaying. In , the total energy harvested from multiple sources was optimally allocated among different destinations. In , the effect of large-scale network interference on energy harvesting decode- and-forward (DF) was considered. Reference  studied the effect of the random location of the relay on DFrelaying. Fur- thermore, reference  maximized the achievable throughput of an AF energy harvesting system. A similar problem was studied in  for DF. In , the achievable throughput of an AF energy harvesting system was optimized. In all these works, the conventional energy harvesting relaying protocol was assumed, where in the broadcasting phase, the source transmits signal to the relay for energy harvesting. This can be further improved by allowing the source to harvest energy from the relay during the relaying phase to maximize the energy use. In this work, a new energy harvesting AF relaying protocol is proposed where the relay harvests energy in the broadcasting phase and the source harvests energy in the relaying phase. The harvested energy at the source is either used immediately in the next transmission or accumulated to conduct more transmissions. The performances of these two strategies are analyzed and compared with the conventional protocol. Nu- merical results show that the new protocols can achieve certain throughput gain due to the extra energy harvested at the source.
In order to overcome these challenges, cooperative communication has been considered as an effective solution, either as mixed RF/FSO systems or as serial FSO systems – using either amplify-and-forward (AF) or decode- and-forward (DF) relaying scheme. In , for FSO based relay systems, outage analysis is performed using both AF and DFrelaying techniques, binary pulse position modulation, and direct detection, where optical links are characterized by Log-normal distributed irradiance and path loss. Error rate analysis is studied for MIMO (multiple input multiple output) based FSO system employing a simple modulation technique such as on-off keying (OOK) and direct type of detection ,
• In chapter 4, a multi-hop DFrelaying system is considered where there exist multiple non-colluding eavesdroppers. The contributions related to this system are stated at this point: (i) Inspired by , a new way of using cooperative jamming is extended to the aforementioned system to enhance the secrecy. In the proposed strategy, on the contrary with traditional cooperative jamming, extra helper is not needed and the transmitter cre- ates the intentional jamming. (ii) Secrecy performance of the aforementioned system is analyzed. (iii) Power allocation strategies are presented to improve the security by optimally allocating the power to the friendly jamming and the primary signal. It is illus- trated that using the optimal power assignment boosts the ergodic secrecy capacity. (iv) It is shown that diverse parameters impact the optimal power allocation factor among which channel state information (CSI) of the adversary nodes must be noted particularly. (v) Since accessing the CSI of the adversary nodes may not be feasible in many cases, the sub-optimal solution is given which does not require the CSI of the adversary nodes. The sub-optimal solution can be considered as close bound for the optimal solution if the illegitimate entity is close to the transmitter.
Abstract —This paper investigates the performance of a max- imum energy selection receiver of an adaptive decode-and- forward (DF) relaying scheme for a cooperative wireless system. In particular, a close-form expression for the bit-error-rate (BER) is analytically derived when the system is deployed with binary frequency-shift keying (BFSK) modulation. The thresholds used at the relays to address the issue of error propagation are opti- mized to minimize the BER. While finding the optimal thresholds requires information on the average signal-to-noise ratios (SNRs) of all the transmission links in the system, the approximate threshold at each relay that requires only information on the average SNR of the source-corresponding relay is investigated. It is also shown that the system achieves a full diversity order with the approximate thresholds . Both analytical and simulation results are provided to validate our theoretical analysis.
Energy harvesting improves the performance of wireless relaying by relieving the energy consumption burden at the relays. Several works have been conducted in this area. In their seminal paper , the authors proposed two methods of signal relaying based on energy harvesting using time-switching (TS) and power-splitting (PS). The harvested energy was then used to forward the received signal to the destination. In , assuming that the relay does not have any energy storage capacity, the optimum tradeoff between harvesting time and relaying time has been studied. In , assuming multiple energy harvesting relays are available, the allocation policies of the total energy harvested from multiple sources have been studied among different relays. Reference  used PS to study the outage performance and the averaged harvested energy for both non-cooperative and cooperative systems suffering from large-scale network interference. Reference  used stochastic geometry to study the effect of random relay location on the performance of decode-and-forward (DF) relaying. In , the throughput was analyzed for a DFrelaying system. In , a joint power splitting and antenna selection scheme was considered to maximize the achievable rate for amplify-and- forward (AF) relaying.
sity technique to exploit fading channels  . In , the symbol error probability was derived for dual hop with single antenna in Rayleigh and Nakagami m-fading channels and the outage performance of communica- tion system was investigated for AF and DFrelaying network. Cooperative communication for a multi-relay network with multiple-input multiple-output network to exploit spatial diversity is investigated in . Here, the relays and users cooperate in sharing information which in turn increases capacity and coverage area of wireless communications. Other techniques utilizing relays equipped with multi-antennas and multi-relay network are investigated where an infrastructure-based relaying deploying multi-antennas on a relay is presented in the work of Adinoyi et al. . To decrease number of relay nodes and thus reducing cost, a single antenna is deployed at source and destination while multi-antennas are fixed on receiver side of relays. The receiver criterion is based on threshold relaying with MRC and selection combining. Also cooperative communication is studied when re- lay selection scenario applied for the best relay link. It was shown that selection relaying can achieve same di- versity order as AF -. Furthermore, deploying multi-antennas at the source or relays receiver side shows improvement as number of antennas increased from 1 to 2 for high and low SNR but increasing antennas more than 2, did not add significant improvement in performance at high SNR  .
Abstract— Cooperative communication has recently been considered as a key technology for modern wireless standards and next generation wireless networks to improve the quality-of-service (QoS) and extend transmission coverage in a cost-effective manner. For designing the efficient OFDM-based relay communication systems, there are various relaying schemes are used. Distributed coding schemes employ two major relaying protocols, decode and forward (DF) and amplify and forward (AF). They suffer from a disadvantage of either noise ampliﬁcation or error propagation. An adaptive relaying protocol (ARP) for general relay networks is proposed here. For the proposed approach, all relays are included into one of two relaying schemes, referred to as a DF relay and an AF relay. All relays, which decode correctly, are included in the DFrelaying scheme, and other relays, which could not decode correctly, are included in the AF relay scheme. Performance improvement analysis of the proposed scheme is carried out, and compared with other relaying protocols. Simulation result demonstrates the proposed method to give better performance when compared with the conventional techniques in terms of SNR and BER.
bright plasma stems growing from the cathode edge, which sometimes bridged the gap. For mixtures with a higher C 2 H 6 , content, there was no decrease in laser ef iciency with increasing W until the discharge remained stable, and the lengths of the plasma channels were not in excess of d/2. This causes us to anticipate that the increase of the electrical ef iciency with increasing inter-electrode distance takes place because the SIVD becomes more uniform due to a greater overlapping of diffuse channels [5, 7]. In the investigated electrode system, a great enhancement of the electric ield takes place at the gap edge. In such gases as CO 2 , air and N 2 , this results in the discharge concentrat ing at the gap edge . In mixtures of SF 6 with hydrocarbons this is not the case, because of the distinguishing feature of SIVD–even though SIVD originates at the edge, it then dis places into the interior of the gap because of the existence of the mechanisms that limit the current density in a diffuse channel. The SIVD plasma intensity distribution over the optic axis-contained plane parallel to the electrode surfaces is shown in Figure 14. The maximum of the SIVD luminosity intensity is attained at the axis. The radiation energy is also distributed over the laser aperture in a similar manner, i.e. the edge’s electric ield enhancement does not appreciably in lu- ence the distribution of the output laser radiation. By this means, a local illumination of the cathode is quite suf icient to obtain a uniform SSVD in mixtures of SF 6 with hydrocarbons, and the presence of regions displaying high edge non-uniformity does not worsen the SIVD stability and only in luences the distribution of the laser radiation energy over the aperture slightly. Therefore it is possible to use plane electrodes rounded off to small radii along their perimeters. We have not found any appreciable features for the P–P oper ating mode that have not been mentioned previously else- where [27-29]. The radiation divergence was measured in the special case where the laser operated on DF molecules Figure 15. As can be seen from Figure 15, the radiation
The relaying protection of smart substation faces very high real-time requirements in the power system, because the digital transformer is working on digital sampling, it will be affected by the switch, for example, the reception time of the receiver is prolonged, link propagation of the combiner occurs and other factors affect the da- ta transmission . In this process, combiner queuing and switch forwarding are one of the key factors for the time error of the digital transformer. Therefore, it is necessary for relevant operators to develop a scientific and reasonable sampling scheme. Before that, the possible errors should be calculated and then the sampling work should be carried out. The results of calculation and sampling should be or- ganically combined to minimize errors and delays, which is conducive to the im- provement of real-time performance of relay protection in smart substation.
data transmitted for V increases and data transmitted for U decreases but the former is with a higher speed due to a direct transmission compared to a two–hop transmission. When λ = 0, the whole time is used for U and µ is fixed at a value to balance the data transmitted of two hops. When λ increases, the time for U in Reference Scheme is shortened accordingly. However in CDR Scheme 1, the time for U is not changed with a slightly different balance point (µ) because the V’s transmission slightly affects the U’s transmission. In the meantime, transmitted data for V increases therefore the sum–rate increases with a high speed. When λ reaches the balance point of U’s DF transmissions and continues to increases, the time for RS–U has to decreases accordingly to balance with a small data transmitted in BS–RS transmission. With a small inter–user channel, the interference from a user to the other is negligible, CDR Scheme 2’s rates and sum–rate has a quite similar slopes as seen in Fig. 5. In the two figures, AF CDR schemes S 1 , S 2 are worse than their
 Jia Jianbin, Chen Yingwen, Xu Ming, Xia Geming, and Xiao Xiaoqiang(2013), ―Towards the Benefit of Multi-Hop Relaying in Opportunistic Networking‖,IEEE Infocom on Green Computing and Communications and IEEE Internet of Things and IEEE Cyber, Physical and Social Computing.
Relaying can be realized at the diﬀerent layers of the protocol stack. A simple amplifying and forwarding RN can be realized at the Layer 1 (L1) of the protocol stack where the RN is required to have only (some part of) the PHY layer. Layer 2 (L2) RNs, which include the protocol stack up to the Medium Access Control (MAC)/Radio Link Control (RLC) layers, enable the possibility of decentralized radio resource management (RRM). Layer 3 (L3) or higher layer RNs could almost be considered as wireless eNBs and support all the protocol layers of normal eNBs, except that they will not require an expensive backhaul as in a normal eNB (i.e., the backhaul between the RN and the eNB will be based on the LTE air interface instead of microwave or wired interface), and they are assumed to have low transmission power capabilities. Unless otherwise specified, L2 or L3 relays are assumed throughout this paper.