Relay Technique Research Articles

Power and Trajectory Optimization for UAV-Enabled Amplify-and-Forward Relay Networks

Unmanned aerial vehicle (UAV) is suitable to improve connectivity of wireless communication networks in harsh environment due to its flexible deployment and high mobility. In this paper, we consider the case that a UAV is employed as a mobile relay to ferry data between two disconnected ground nodes. The amplify-and-forward mobile relay technique is studied. By exploiting the channel state variation induced by the movement of UAV, we consider maximizing the end-to-end throughput of this mobile relay system by optimizing the source/relay power allocation, as well as the UAV’s trajectory. However, the formulated problem is non-convex and intractable to solve. To address this non-convex problem, we propose two iterative algorithms to optimize the source/relay power allocation with the fixed UAV’s trajectory and the UAV’s trajectory with fixed power allocation, by successive convex optimization, respectively. Then, an iterative algorithm is proposed to optimize the source/relay power allocation and UAV’s trajectory in an alternate manner. By exploiting the predictable channel variation via the proposed power and trajectory optimization scheme, numerical results show that significant throughput gains can be achieved.

Localizing Noncooperative Receiver Through Full-Duplex Amplify-and-Forward Relay

Localizing noncooperative transmitter (Tx) and receiver (Rx) that belong to another system is important in many scenarios, e.g., interference management in cognitive radio systems and user behavior learning in ad hoc wireless networks. However, obtaining the locations of these nodes in particular in frequency-division duplex systems is challenging, since the localization network usually does not know the spectrum that the Rx uses for backward transmission. In this paper, we propose to use the full-duplex relay technique to localize a noncooperative Rx, which does not require the knowledge of the Rx’s backward transmission spectrum. In the proposed method, localization sensors alternatively act as a full-duplex amplify-and-forward relay to trigger the power control of the Tx–Rx link. Then, by detecting the power adjustment of the Tx, each localization sensor can estimate the time difference of arrival between the direct and relay signals. Finally, the Rx location can be calculated from triangulation. Simulation results show that the proposed method can effectively localize the Rx, which validates its potential for receiver-aware applications and services.

Modern methods of design, analysis, optimization and implementation of conventional control algorithms for processes with finite and infinite degrees of freedom

This paper presents characterization methods for a large class of industrial processes using a critical experiment as well asmodern methods of design, analysis, optimization and implementation of conventional control algorithms. Special attention is set to theprocess characterization methods using relay techniques and phase-locked loops in order to form a general process model which servesas a base for adequate controller design. This general process model adequately approximates processes which behaviour can bedescribed with linear mathematical models with finite and infinite degrees of freedom including conventional finite dimension systems,time-delay systems, systems whose behaviour is dominated by a wave and transport problems such as mass and energy transfer,systems described with fractional differential equations etc. Based on characterization, an important accent is also put on the design ofPI/PID controller due to their large application in industry which exceeds 93% compared to all the other controllers according toHoneywell's surveys. In order to illustrate validity of characterization model and effectiveness of presented design method, the paperprovides an example of optimal PID controller designed under constraints on robustness and sensitivity to the measurement noise.Digital implementation is considered for both the controllers with rational and those with non-rational transfer functions. At the end,controller analytical design methods are elaborated and analytical formulae for PI/PID controllers tuning are presented.

Relay Technology with Unequal Emission Power: Multi-mode Relay

Relay technology can enlarge the coverage of cellular network, improve the spectral efficiency, and enhance the robustness of communication system. It has been one of the most striking areas in recent years. In this paper we discussed the relay technology with one-way relay and two-way relay, introduced two kinds of relay techniques: amplify-and-forward (AF), and Decode-and-Forward (DF). Then based on two-way amplify-and-forward relay, we derived the amplify factors of unequal emission power relay.

Region based cooperative routing in underwater wireless sensor networks

Cooperative routing is an appealing challenge in underwater wireless sensor networks (UWSNs). In this paper, we propose a region based cooperative routing protocol (RBCRP) for amplify and forward (AF) technique over Rayleigh faded channels in UWSNs. The source node sends the sensed signal to the destination and available relay nodes. At the destination node, bit error rate (BER) is checked on the basis of which, either positive or negative acknowledgement (ACK or NACK) is sent to the source and relay nodes. We also use mobile sinks (MSs) and energy harvesting techniques to further prolong the network lifetime and maximize the throughput. Our derived mathematical equations for the SNR gain and outage probability are verified by simulations. Results show that RBCRP performs better than the existing incremental best relay technique (IBRT) in terms of throughput, network lifetime and outage probability.

Joint subcarrier and power allocation for df-based multiuser two-way relay networks

Two-way decode-and-forward (DF) relay technique is an efficient method to improve system performance in 5G networks. However, traditional orthogonal frequency division multiplexing (OFDM) based two-way relay systems only consider a per-subcarrier relay strategy, which treats each subcarrier as a separate channel, which results in significant sum rate loss, especially in fading environments. In this paper, a joint coding scheme over multiple subcarriers is involved for multi-pair users in two-way relay systems to obtain multiuser diversity. A generalized subcarrier pairing strategy is proposed to permit each user-pair to occupy different subcarriers during the two transmission phases, i.e., the multiple access and broadcast phases. Moreover, a low complexity joint resource allocation scheme is proposed to improve the spectrum efficiency with an additional multi-user diversity gain. Some numerical simulations are finally provided to verify the efficacy of our proposal.

Multiuser MIMO Precoders With Proactive Primary Interference Cancelation and Link Quality Enhancement for Cognitive Radio Relay Systems

A novel multiuser multiple-input multiple-output (MU-MIMO) cognitive radio (CR) system with an improved received signal-to-interference-noise ratio (SINR) and enhanced primary user (PU) interference suppression is proposed for systems with the independent parallel streams of CR multiusers communication. In the overlay CR system with a licensed PU and unlicensed CR users (CUs), the performance of PU tends to be degraded by the interference of CU. Likewise, the transmission efficiency of CU tends to be reduced by the interference of PU. In conventional MU-MIMO systems, precoding techniques are mainly designed to constrain the CU transmitted power, which can prevent interference to PU. However, the transmitted signal of PU unavoidably induces some interference to CUs. In performance studies of the conventional CR systems, the signals of PU interference are regarded as white noise. In the paper, a cooperative MU-MIMO CR relay technique is proposed to improve the quality of the CR transceiver via the relay station canceling the PU interference in two time slots. Specifically, the relay station applies MU-MIMO precoding scheme to carry multiple negative PU signals to CUs for canceling PU interference and to acquire an improved received SINR. Furthermore, the proposed MU-MIMO CR relay system is simulated to confirm the performance being better than a conventional CR system. Besides, the sum rate linear growth of the proposed system is due to its robustness against strong interference from the PU, against interference from multiple CUs, and against stream interference.

A new digital filter directional relay technique using active/reactive power portrait

The present paper discusses some conventional directional relay drawbacks, which are based on the relationship between voltage and current, in order to determine fault direction. In addition, it presents a new fault detection technique based on instantaneous active and reactive energy that is measured and analysed at the relaying point. This energy has a distinct characteristic which is used to distinguish the fault direction. The suggested relay has determined the fault direction in a rather short time after fault occurrence, even in 2–5ms, depending on the characteristics of the fault generated travelling waves. The algorithm used in this method has been modified in order to improve the performance of the relay. Simulation studies showed that the directional relay based on this new technique has fast speed operation with reliability and dependability.

Opportunistic scheduling for a two‐way relay network using Markov decision process

In this study, the authors study transmission scheduling for a two-way relay network in time-varying fading channels, where the relay node can opportunistically use traditional one-way relay technique or network coding to forward traffic to the end nodes. They formulate a stochastic dynamic programme with the objective of minimising the long-run cost, defined as a function of both the transmission power and data transmission delay. An unconstrained Markov decision process model is developed and solved for the average and discounted cost problems. The optimal solution requires high computational and modelling complexity when the state space is large. For this reason, they develop heuristic solutions with lower complexity. For the discounted cost problem, a simulation-based dynamic programming algorithm is proposed that not only simplifies the modelling process and reduces the computational complexity, but also achieves close-to-optimum cost. For the average cost problem, a heuristic scheduling scheme is proposed, which makes transmission decisions based on estimated costs in the current and next time slots. The heuristic scheme achieves close-to-optimum cost performance while greatly reducing the computational complexity.

Estimate the Primary-Link SNR Using Full-Duplex Relay for Underlay Spectrum Sharing

In cognitive radio networks, the signal-to-noise ratio (SNR) of the primary receiver (PR), called primary-link SNR, is critical for underlay spectrum sharing. However, it is very difficult for the cognitive user (CU) to obtain the primary-link SNR. In this letter, we propose a new method to let the CU autonomously estimate the primary-link SNR, where the full-duplex relay technique is used. Then, the CU can conduct the underlay spectrum sharing more efficiently. Simulation results indicate the effectiveness of the proposed method.

Cooperative HARQ protocols using semi-blind relays for underlay cognitive radio networks

In this paper, we evaluate the throughput of cooperative ARQ and HARQ I protocols in underlay cognitive radio networks using semi blind relays. Semi Blind Relays do not require to estimate the channel of the first hop, they use only some channel statistics. Relays help the secondary source to deliver its packet. Only relays that generate an interference to primary receiver lower than a predefined threshold will be activated. Three relay selection techniques are considered: opportunistic relaying, partial and reactive relay selection. Opportunistic relaying consists in selecting the relay that offers the highest end-to-end SNR. Partial relay selection consists in selecting the relay that offers the highest SNR of the first hop. Reactive relay selection consists in selecting the relay that offers the highest SNR of the second hop. This relay is selected among the active ones that generate an interference to primary receiver lower than a predefined threshold. To the best of our knowledge, there are no studies dealing with throughput evaluation of HARQ protocols for cognitive radio networks using opportunistic relaying, partial and reactive relay selection. Besides, this is the first paper to deal with HARQ protocols using semi blind relays. Previous studies dealt with outage, bit and symbol error probabilities evaluation for cognitive radio networks.

Backlash identification for PMSM servo system based on relay feedback

This paper presents a novel method of backlash identification for PMSM servo system based on a relay feedback technique. We develop this method by analyzing the motor velocity signal in time domain under a strong assumption that the speed signal can be viewed as piecewise segments. The proposed approach takes a dead-zone model to describe the backlash and adopts an elastic two-mass model to represent the servo system. In view of response speed and differential noise, the motor velocity has been chosen to be the feedback signal. It should be pointed that particular attention ought to be paid to the choices of the parameters of the delay element and the relay component. This is because undervalued choices may lead to system chaos and thus the failure of identification. Since little knowledge is available about the potential backlash size, the identification procedure is performed iteratively until the identified value converges to its true value. This new strategy only requires one encoder on the motor side, from which the position and speed signals can be acquired. To complete the identification process, however, knowledge of both the motor’s moment of inertia and the load’s moment of inertia is needed. Simulation and experimental results validate that this new strategy is easy and fast to execute with good accuracy.

Development of tunable miniature piezoelectric-based scanners validated by the combination of two scanners in a direct image relay technique.

Miniature piezoelectric actuators are commonly used as a compact means to relay images for numerous endoscopic applications. These scanners normally consist of an electrically driven lead zirconate titanate (PZT) tube that oscillates an optical fiber at its resonant frequency. The diameter and length of the PZT and fiber, the attachment of the fiber to the PZT, as well as the driving signal determine the main characteristics of the scan-frequency and amplitude of vibration. We present a new, robust, and repeatable method for producing miniature PZT actuators. The described technology allows for continuous tuning of the scanner mechanical properties during the assembly stage, enabling adjustment of resonant frequency and subsequent amplitude of vibration without a priori knowledge of the fiber's mechanical properties. The method consists of manufacturing high-precision fiber-holding plastic inserts with diamond turning lathes that allow for the fiber length to be quickly varied and locked during operation in order to meet the preferred performance. This concept of tuned PZTs was demonstrated with an imaging technique that combined two scanners oscillating in unison at the ends of a single optical fiber to relay images without the need to correlate the driving signal with a detector.

Efficient Relay Selection Scheme based on Fuzzy Logic for Cooperative Communication

The performance of cooperative network can be increased by using relay selection technique. Therefore, interest in relay selection is sloping upward. We proposed two new relay selection schemes based on fuzzy logic for dual hop cooperative communication. These relay selection schemes require SNR (signal to noise ratio), cooperative gain and channel gain as input fuzzy parameters for selection of best relay. The performance of first proposed relay selection scheme is evaluated in term of BER (bit error rate) in Nakagami, Rician and Rayleigh fading channels. In second proposed relay selection scheme, threshold is used with the objective to minimize the power consumption and channel estimation load. Its performance is analyzed in term of BER, number of active relays and load of number of channel estimations.

Achieve Secure Handover Session Key Management via Mobile Relay in LTE-Advanced Networks

Internet of Things is expanding the network by integrating huge amount of surrounding objects which requires the secure and reliable transmission of the high volume data generation, and the mobile relay technique is one of the efficient ways to meet the on-board data explosion in LTE-Advanced (LTE-A) networks. However, the practice of the mobile relay will pose potential threats to the information security during the handover process. Therefore, to address this challenge, in this paper, we propose a secure handover session key management scheme via mobile relay in LTE-A networks. Specifically, in the proposed scheme, to achieve forward and backward key separations, the session key shared between the on-board user equipment (UE) and the connected donor evolved node B (DeNB) is first generated by the on-board UE and then securely distributed to the DeNB. Furthermore, to reduce the communication overhead and the computational complexity, a novel proxy re-encryption technique is employed, where the session keys initially encrypted with the public key of the mobility management entity (MME) will be re-encrypted by a mobile relay node (MRN), so that other DeNBs can later decrypt the session keys with their own private keys while without the direct involvement of the MME. Detailed security analysis shows that the proposed scheme can successfully establish session keys between the on-board UEs and their connected DeNB, achieving backward and forward key separations, and resisting against the collusion between the MRN and the DeNB as the same time. In addition, performance evaluations via extensive simulations are carried out to demonstrate the efficiency and effectiveness of the proposed scheme.

Book reviews [8 Reviews

The following books are reviewed: Micro and Nano Energy Harvesting Technologies; Micro- and Nanoelectronics—Emerging Device Challenges and Solutions; Nanomaterials and Devices, Nanotechnology in Advanced Electrochemical Power Sources; Annual Review of Physical Chemistry, Vol. 66; High Power Optics—Lasers and Applications; Electromagnetic Transient Analysis and Novel Protective Relaying Techniques for Power Transformers; Electric Power Distribution Handbook, 2nd Edition

Performance Analysis of Best Relay Selection in Cooperative Wireless Networks

Cooperative communication has been proposed recently in wireless communication systems because of its producing high network reliability and considerable error rate decrease with an extension in the coverage area in wireless networks without need for an increase in the infrastructure. The most challenging problem in implementing cooperation protocols in cooperative wireless networks is the relay selection. This paper proposes a relay selection technique based on Decode-and-Forward (DF) relaying protocol, using the available channel state information (CSI) at the source and the relays. We first establish a closed form symbol error rate (SER) by using the concept of moment generating function (MGF) for both M phase shift keying (MPSK) and M quadrature amplitude modulation (MQAM) signals. By finding the cumulative density function (CDF) and the probability density function (PDF); this facilitated the derivation of a new SER and can propose an optimal power method with relay selection (RS) technique where only the best relay is selected that maximizes the signal-to-noise ratio (SNR) to achieve the transmission process and develop the performance of the system. Finally, simulation results provided good confirmation of the theoretical analysis.

Street Lamps Monitoring System Using Relay Control Technique

This research proposes a simple but very effective method to determine faulty street lamps by utilizing a microcontroller associated with relay control technique to analyze the current consumption of the lamps. With such approach, the lighting system can automatically report the number and the position of the faulty street lamp to the operator in the control room. As a consequence, the faulty street lamp can be quickly repaired. The user interface and controller are programmed in LabVIEW software. The result is verified by modeling street light system using five 100 watts incandescent light bulbs connected in parallel. The results of this research can be applied to improve the existing street light system especially in Thailand. Furthermore, equipment used in this research is cost effective.

Resource Allocation for Cooperative Relay based Wireless D2D Networks with Selfish Users

This paper considers a scenario that more D2D users exist in the cell, they compete for cellular resources to increase their own data rates, which may cause transmission interference to cellular users (CU) and the unfairness of resource allocation. We design a resource allocation scheme for selfish D2D users assisted by cooperative relay technique which is used to further enhance the users’ transmission rates, meanwhile guarantee the QoS requirement of the CUs. Two transmission modes are considered for D2D users: direct transmission mode and cooperative relay transmission mode, both of which reuses the cellular uplink frequency resources. To ensure the fairness of resource distribution, Nash bargaining theory is used to determine the transmission mode and solve the bandwidth allocation problem for D2D users choosing cooperative relay transmission mode, and coalition formation game theory is used to solve the uplink frequency sharing problem between D2D users and CUs through a new defined “Selfish order”. Through theoretical analysis, we obtain the closed Nash bargaining solution under CUs’ rate constraints, and prove the stability of the formatted coalition. Simulation results show that the proposed resource allocation approach achieves better performance on resource allocation fairness, with only little sacrifice on the system sum rates.

Cooperative device-to-device communications in cellular networks

To meet the increasing demand of wireless broadband applications in 4G/beyond 4G cellular networks, D2D communication can serve as a candidate paradigm to improve spectrum efficiency. By reusing the spectrum of cellular users, two D2D users can form a direct data link without routing base stations and core networks; thus, the spectral efficiency can be improved. Further, when the cooperation between cellular users and D2D users is enabled, a win-win situation can be achieved to make all users better off. Thus motivated, we propose a cooperative D2D communication framework in this article, which introduces the cooperative relay technique to conventional underlay/overlay D2D communications. Adaptive mode selection and spectrum allocation schemes are also presented to ensure better performance for both cellular and D2D users. Extensive numerical results show the effectiveness of the proposed framework for a variety of scenarios.