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This letter proposes non-orthogonal multiple access (NOMA) based coordinated direct and relay transmission (CDRT) and hybrid multiple access (HMA) protocols for a general CDRT system, where a base station directly serves cell-center users (CCUs), while it communicates with cell-edge users (CEUs) via a relay. The ergodic sum capacity (ESC), capacity scaling and the number of successive interference cancellation (SIC) operations are derived correspondingly. If the number of CCUs is less than that of CEUs and the interference level of imperfect SIC is small, the proposed NOMA-based CDRT can achieve much better ESC than HMA. Otherwise, the proposed HMA achieves a better performance-complexity tradeoff. Numerical results verify the effectiveness and superiority of the proposed protocols.

In this paper, the cooperative electronic relay in device to device (D2D) communication system will be used which is not clarified until now. A scenario in our work will be made by using three types of cooperative diversities together that are compress and forward relay, decode and forward relay (DF) and amplify and forward relay (AF). Numerical results show that, the D2D outage probability of the proposed scheme is lower than that of the traditional relay transmission, which is further reduced with an increasing number of the electronic relays, therefore utilizing number of the electronic relay equal to 8 relays will reduce the outage probability by 0.0024 than using previous relays channel. Moreover using our proposed relay at SNR equal to 25 dB resulting in reducing BER by 4 dB. Moreover, the comparison between using proposed relay and previous research like AF relay with variable gain and DF relay will be carried out, where outage ratio will reduce to 15 dB using our proposed the electronic relay.

In this paper, we investigate the resource optimization algorithm design in a multicarrier relay system with simultaneous wireless information and power transfer (SWIPT). The relay is capable of harvesting energy from the source's signals by using the power splitting method. The non-ideal energy consumption including both the non-ideal power amplifier and non-ideal circuit power consumption is considered. First, we study the transmission rate maximization problem (TRMP) in an asymmetric decode-and-forward (DF) relay transmission, where the transmission power at the source, the transmission power at the relay, the power splitting ratio, and the transmission time are jointly optimized. The formulated problem is a non-convex problem, and it is generally quite difficult to solve it. By exploiting the structure of the problem, we propose two methods (logarithmic operation on constraints and logarithmic change of variables) to transform it into the corresponding difference of convex (DC) optimization problems. Then, we extend the TRMP to an amplify-and-forward (AF) relay transmission. Furthermore, we propose an effective algorithm to solve the DC optimization problem and prove that the algorithm can converge to a stationary point. Finally, extensive simulations are conducted to verify the performance of the proposed algorithm. The simulation results show that the asymmetric DF relay transmission achieves the highest sum rate and the AF relay transmission achieves a much lower sum rate than both the asymmetric and symmetric DF relay transmissions under different conditions.

In this work, two signal-space diversity (SSD) based schemes are proposed for a system where one user is directly in contact with both the base station and the relay, while the other user is only in contact with the relay. The first scheme combines the coordinated direct and relay transmission (CDRT) technique with SSD to improve the achievable sum-rate of the system and is called the SSD-based CDRT (SSD-CDRT) scheme. On the other hand, the second scheme exploits only the SSD technique to improve the diversity order of one of the users and is termed SSD based non-CDRT (SSD-nCDRT). Various performance metrics such as outage probability, system outage throughput, diversity order, and achievable sum-rate are evaluated in closed-form for both schemes to compared them with their counterparts non-orthogonal multiple access (NOMA) based schemes, i.e., NOMA-CDRT and NOMA-nCDRT schemes. The comparative study confirms that the proposed SSD-CDRT and SSD-nCDRT are superior to NOMA-CDRT and NOMA-nCDRT, respectively, in terms of all the considered performance metrics.

A coordinated direct and relay transmission is proposed using uplink non-orthogonal multiple access (UP-NOMA). A two-user UP-NOMA scenario is considered, where a cell-center user directly communicates with a base station (BS), whereas a cell-edge user needs the assistance of a half-duplex decode-and-forward relay to communicate with the BS. The ergodic sum capacity of UP-NOMA is analyzed under both perfect and imperfect successive interference cancellation. The superiority of UP-NOMA over conventional multiple access is demonstrated through simulation and analysis.

In this paper, we offer the secrecy outage probability of the amplify-and-forward (AF) transmission, which consists of one source, one destination, one relay, and one passive eavesdropper. Particularly, we consider that the relay is equipped with multiple antennas while other terminals is utilized with single antenna and apply diversity techniques (for both the reception and the transmission) at the relay to achieve gains in a secrecy outage performance. Additionally, we analyze the exact secrecy outage probability of the proposed systems in a one-integral form. Finally, some numerical examples are given to verify our provided analytical results for different system conditions.

The Internet of Things (IoT) depicts a bright future, where any devices having sensorial and computing capabilities can interact with each other. Among all existing technologies, the techniques for the fifth generation (5G) systems are the main driving force for the actualization of IoT concept. However, due to the heterogeneous environment in 5G networks and the broadcast nature of radio propagation, the security assurance against eavesdropping is a vital yet challenging task. In this paper, we focus on the transmission design for secure relay communications in IoT networks, where the communication is exposed to eavesdroppers with unknown number and locations. The randomize-and-forward relay strategy specially designed for secure multi-hop communications is employed in our transmission protocol. First, we consider a single-antenna scenario, where all the devices in the network are equipped with the single antenna. We derive the expression for the secrecy outage probability of the two-hop transmission. Following this, a secrecy-rate-maximization problem subject to a secrecy-outage-probability constraint is formulated. The optimal power allocation and codeword rate design are obtained. Furthermore, we generalize the above analyses to a more generic scenario, where the relay and eavesdroppers are equipped with multiple antennas. Numerical results show that the proper use of relay transmission can enhance the secrecy throughput and extend the secure coverage range.

In a polarized MIMO transmission, performances of the system deteriorates due to the difference between the transmission characteristics of horizontal polarization and vertical polarization. In this paper, we will examine the influence of a relay station position on channel capacity for relay transmission in polarized MIMO. As a result, it is clarified that a high channel capacity is stably obtained when the relay station and the reception point is in the line-of-sight environment.

In this paper, high frequency (HF) transmission over relay channels is investigated. A three node system in which a relay node assists the transmission from the source to the destination is considered. To extract the multipath diversity for the HF channels, orthogonal frequency division multiplexing transmission scheme is applied. It is assumed that exact channel knowledge is not available at destination, and channel estimation is applied by transmitting pilot symbols. Different methods of interpolation are discussed in obtaining channel estimation. Simulations results are shown to compare the performance of different HF channels in low latitudes and mid-latitudes.

Multi-hop relay transmissions achieve high quality and vast area communications by using several relay nodes. For the relay method based on an amplify-and-forward (AF), channel estimation (CE) is only demanded in the destination node. In the single-hop AF relay transmission for orthogonal frequency division multiplexing (OFDM) systems, we have proposed the CE by using the pilot signal based on the time frequency interferometry (TFI). However, in the multi-hop AF relay transmission, the conventional TFI method degrades the system performance due to a null signal and the overlapped channel. To solve this problem, in this paper, we propose the CE based on the real and imaginary TFI pilot signals in the three hop AF relay transmission for OFDM systems.

Relay communication network is a technique to obtain spatial diversity by using one or more relay terminals in order to improve the transmission performance. Amplifty-and-forward (AF) and decode-and-forward (DF) are two kinds of fixed relaying protocols and widely researched now. In this paper the performance of AF and DF in terms of the outage probability and the symbol error rate (SER) is analysed. We also introduce and analyse a protocol of hybrid AF and DF (HADF) which is a new relaying protocol based on AF and DF. HADF protocol can choose the right protocol (AF or DF) that should be used in the relay transmission. In this paper, we compare HADF with AF and DF respectively, and the simulation results show that the performance of HADF protocol has been greatly improved with respect to outage probability and SER.

In this paper, we investigate the relay nodes (RNs) deployment optimization to improve the energy efficiency in wireless sensor networks (WSNs). First, the energy dissipation model of multi-hop relay transmission scheme with random RNs deployment under a given BER requirement is established. Then, we present the optimal RNs deployment to minimize the energy dissipation, which the position of RNs, the number of RNs and modulation sizes are optimized by two steps optimization. Numerical results show that, optimal RNs are deployed on the line between source node and destination node with the same hop distance. Meanwhile, RNs deployment with joint optimization can further reduce the energy dissipation in comparison with single parameter optimization.

In a warehouse, because there exist frequent changes of stock status and the quality of some contents are influenced by the environment such as temperature, fast and accurate management of the warehouse's environment is very important for Warehouse Management Systems. However, due to the absence of a unified standard for the communication protocol between RFID nodes and centralized MAC schemes for RFID communications in previous studies have severe problems. Therefore, in this paper, we propose a WiMedia MAC based RFID cooperative relay transmission scheme for warehouse management system applications.

A decode-and-forward two-way relay system benefits from orthogonal frequency division multiplexing (OFDM) and relay transmission. In this paper, we consider a decode-and-forward two-way relay system over OFDM with two strategies: A joint subcarrier matching algorithm and a power allocation algorithm operating with a total power constraint for all subcarriers. The two strategies are studied based on average capacity using numerical analysis by uniformly allocating power constraints for each subcarrier matching group. An optimal subcarrier matching algorithm is proposed to match subcarriers in order of channel power gain for both transmission sides. Power allocation is defined based on equally distributing the capacity of each hop in each matching group. Afterward, a modified water-filling algorithm is also considered to allocate the power among all matching groups in order to increase the overall capacity of the network. Finally, Monte Carlo simulations are completed to confirm the numerical results and show the advantages of the joint subcarrier matching, power allocation and water filling algorithms, respectively.

The WiMedia Alliance has specified a Distributed Medium Access Control (D-MAC) protocol based on UWB for high speed wireless home networks and WPANs. In this paper, firstly, a time slot reservation protocol for relay transmission is proposed. Furthermore, we propose a novel relay node selection algorithm adaptive to current UWB link transmission rate. The proposed relay node selection algorithm has compatibility with current WiMedia D-MAC standard and is executed at each device according to the SoQ as a QoS criterion.

In a warehouse, because there exist frequent changes of stock status and the quality of some contents are influenced by the environment such as temperature, fast and accurate management of the warehouse`s environment is very important for Warehouse Management Systems (WMS). However, due to the absence of a unified standard for the communication protocol between RFID nodes, the connection between RFID nodes can be broken in case of movement of a RFID reader to a region with a different protocol. Moreover, centralized MAC schemes for RFID communications in previous studies have severe problems. For an example, if a cluster header disappears from the cluster due to the cluster header`s movement or bad channel conditions, the RFID member nodes of the cluster waste lots of time and energy to re-elect a new cluster header. Therefore, in this paper, we propose a WiMedia Distributed MAC (D-MAC) scheme for RFID communications and its cooperative relay transmission scheme for WMS applications Simulation results show performance improvement at the RFID node by using the proposed cooperative relay transmission scheme.

Recently, multi-hop relay transmission has drawn much attention owing to its advantage of coverage extension at low power consumption. In this paper, we derive a performance bound of multi-hop communication systems with multiple amplify-and-forward relays when the optimal path is selected. The bound is derived in generalized Nakagami fading channels with different parameters for each hop by applying the geometric mean bound to the path signal-to-noise ratio (SNR) and obtaining the moment generation function of the bound. It is shown that the bound based on the geometric mean is closer to the actual performance of optimal path selection when the fading effect is small.

In this paper we present the performance analysis of a novel channel assignment scheme where two non-cooperative independent users simultaneously communicate with their destination through a single relay by using only two frequency channels. The analytic derivation of the probability of symbol error for two main relay techniques will be provided, namely Amplify-and-Forward (AF) and Decode-and-Forward (DF). As shown by the obtained results, our switched-frequency approach results in a model that can achieve full- diversity by means of maximum-likelihood decoding at the receiver. Our results are especially important in the DF case, since in traditional techniques (such as half-duplex two-time slot approaches) two sources si-multaneously transmit on the same channel through the first time slot, which necessitates some sort of su-perposition coding. However, since in our scheme both users transmit over orthogonal channels, such a coding scheme is not required. In addition, it is shown that the DF approach based on our novel channel assign-ment scheme outperforms the AF scheme, especially in scenarios where the relay is closer to the receiver.

RoF relay system can deliver heterogeneous wireless signals to the blind area. Recent wireless systems employ MIMO scheme to achieve high performance. In a conventional combined SDM-MIMO and RoF relay system, multiple RoF links are needed to transmit independent radio signals from multiple antennas, resulting large system complexity and implementation cost. In this paper, we propose a novel combined STBC-MIMO, MRC diversity reception and RoF relay system using only one RoF link. We compare the performance of these two systems by theoretical analysis and computer simulation. It is confirmed that the proposed relay system can achieve better transmission performance than the conventional one.

This paper considers an identification method of the relay transmission characteristics including multipaths and coupling effects at the relay stations of a single-frequency network in an orthogonal frequency division multiplexing (OFDM) system. Estimating the transmission characteristics over the entire frequency range of OFDM transmission paths is extremely difficult because the transmitted signals in an OFDM system are limited to some bandwidth. Therefore, an objective of this paper is to propose a new approach that uses the guard interval feature of the OFDM signal to identify the relay transmission characteristics, multipath characteristics, coupling wave characteristics, and sensitivity characteristic of a closed-loop system including the coupling wave canceler, and evaluate the identification errors. The effectiveness of the proposed method is demonstrated through numerical examples. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 89(12): 10– 19, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20230

This letter reports a performance analysis of a dual-hop relay system composed of asymmetric radio-frequency and free-space optics (RF/FSO) links. This approach is based on the fact that FSO links can provide even wider bandwidths as compared to RF ones. In particular, an exact closed-form expression for the end-to-end outage probability of the RF/FSO relay links is derived. Overall, the RF/FSO links show a slightly worse performance than the RF/RF links, but the performance gap is gradually reduced as the signal-to-noise ratio (SNR) increases. Our mathematical analysis results were verified by exactly matching Monte Carlo simulation results.

In this paper we present analytical model for performance evaluation of dual hop amplify-and-forward relay transmission over non-identical Ricean fading channels on both hops. Probability density function (PDF) and moment generating function (MGF) of total received SNR (signal-to-noise ratio) are presented as fast converging sum. Furthermore, adequate semi-closed form expressions for average bit error rate (BER) and outage probability (OP) are derived. Numerical and simulation results confirm the validity of the proposed analytical model. Additionally, we analyzed the impact of unbalanced SNRs of the two hops on the error performance of the considered relay system.

This paper investigates opportunistic relaying of a half-duplex two-way relay network, where two source users exchange information through a shared amplify-and-forward (AF) relay which is opportunistically selected from a set of candidates. Unlike existing works, in our considered network scenario, the two source users have different target rates. A novel protocol for opportunistic relaying is developed, which adaptively switches between the max-min and the pure-max policies according to the information of system traffic. The performance of the new relaying strategy in terms of the system outage probability is analyzed over Rayleigh fading channels. Simulation results demonstrate that the proposed protocol can implement opportunistic relaying efficiently, and can achieve significant performance gains in terms of the outage probability across all traffics.

For multicell environment, relays introduce additional interferences at the cell edge. To overcome such intercell interferences, we propose the alternate relay transmission schemes. We quantify the ergodic rate performance of the proposed schemes over Nakagami-m fading channel. Numerical results show that the proposed schemes can effectively cancel the inter-cell interference and improve the sum rate performance for cell edge users.

In this paper, we investigate the downlink spectral efficiency of infrastructure relay-enhanced cellular systems. In particular, we use the average achieved spectral efficiency at an arbitrary mobile receiver in presence of co-channel interference, termed as cell spectral efficiency (CSE), to quantify the benefit of relay transmission in terms of lower co-channel interference power. We derive the exact analytical expression of CSE for relay-enhanced system with different transmission strategies while taking into account the random user locations and the impact of pass loss. We show through selected numerical examples that the relay-enhanced systems have the potential to achieve much better CSE performance over the conventional systems Scopus

In order to improve the cell boundary throughput performance and to extend the coverage area, relay transmission with relay stations (RSs) is becoming a promising architecture. However, if RSs are introduced, interference between cells increases and the throughput improvement effect with RSs is prone to be restricted. In this paper, we propose a scheme reducing the interference from other cells by using packet transmission control. The proposed scheme can improve the throughput around the cell boundary and the system throughput considering the users of whole cell by controlling the timing of transmission of each cell.