Relay Communication System Research Articles

Adaptive interference compensation method

The article is devoted to the consideration of the method of adaptive compensation of interference to information transmission systems using space-time coding technology. When such systems use two or more antennas for transmitting information and the same number of antennas for receiving, it becomes possible to compensate for interference signals. The investigated compensation method is based on the introduction of adaptive filters into each of the input channels of the information transmission system. Adaptive filters are tuned to the process of the mixture of the useful signal and interference so that after the processing the sum of the interference components at the output of the compensator is minimized, and the useful signal does not deteriorate on average. The expressions that determine the algorithm of the adaptive noise compensator are given. The compensator for interference signals coming from a powerful airfield radar was built for the ground radio relay communication system with double antenna spacing. It has been shown experimentally that the compensator suppresses radio impulse interference from 30 to 40 decibels in different frequency channels of the microwave link.

Multi-Layer Bilinear Generalized Approximate Message Passing

In this paper, we extend the bilinear generalized approximate message passing (BiG-AMP) approach, originally proposed for high-dimensional generalized bilinear regression, to the multi-layer case for the handling of cascaded problem such as matrix-factorization problem arising in relay communication among others. Assuming statistically independent matrix entries with known priors, the new algorithm called ML-BiGAMP could approximate the general sum-product loopy belief propagation (LBP) in the high-dimensional limit enjoying a substantial reduction in computational complexity. We demonstrate that, in large system limit, the asymptotic MSE performance of ML-BiGAMP could be fully characterized via a set of simple one-dimensional equations termed state evolution (SE). We establish that the asymptotic MSE predicted by ML-BiGAMP' SE matches perfectly the exact MMSE predicted by the replica method, which is well-known to be Bayes-optimal but infeasible in practice. This consistency indicates that the ML-BiGAMP may still retain the same Bayes-optimal performance as the MMSE estimator in high-dimensional applications, although ML-BiGAMP's computational burden is far lower. As an illustrative example of the general ML-BiGAMP, we provide a detector design that could estimate the channel fading and the data symbols jointly with high precision for the two-hop amplify-and-forward relay communication systems.

Optimizing Energy Harvesting Decode-and-Forward Relays With Decoding Energy Costs and Energy Storage

Energy harvesting (EH) relay communication systems with decoding energy costs in multiple block cases have not been widely studied. This paper investigates the relay network with a decode-and-forward relay powered by EH. Unlike other works, we consider the relay with energy decoding costs which harvests random energy from both a dedicated transmitter and other ambient radio-frequency (RF) sources. The EH relay adopts a harvest-receive-forward time-switching architecture. We optimize the time fractions of the three phases and the reception rate at the relay to maximize the offline throughput for single and multiple block cases under two EH scenarios. The multi-block optimization problem constitutes a complex non-convex problem, which we decouple into a single block problem with two auxiliary variables determined by an outer optimization problem. The original problem is finally solved at the cost of linear optimization after series of tricks. Several conclusions are derived: (i) energy storage is necessary (unnecessary) when the relay harvests energy from the transmitter (ambient RF sources), (ii) the optimal reception rate remains unchanged, while the optimal time fractions vary with the energy harvested from ambient RF sources leading to different average throughput. We give numerical simulations to verify our theoretical analysis.

Tradeoff analysis of SWIPT-Based regenerative relay communication system

It has been brought to attention that the energy-carrying relay system can not only increase the energy harvesting of the system but also reduce the energy loss of the system at the same time. In this paper, a trade-off metric is incorporated in the power allocation of the energy-carrying relay system, which can substantially meet the energy harvesting and data transmission requirements of various application scenarios in a more flexible manner. Subsequently, a trade-off metric is proposed, and an optimization problem for maximizing the trade-off metric value is constructed. Eventually, the optimal solution for optimizing the trade-off metric is obtained by applying Lagrangian multiplier method. It has been shown in experimental simulations that the trade-off metric has the minimum value of 0.4073 when ω=0.54, which represents the intersection of the three curves. It implies that the proposed trade-off metric can precisely describe the relationship between the probability of successful information transmission and the energy harvesting power. Most importantly, the trade-off metric proposed in this paper can well illustrate the relationship between energy harvesting and information transmission. Whether it is a symmetrical channel or an asymmetrical channel, where the optimal solution derived through theoretical calculations is consistent with the experimental result.

A Novel Low-Complexity GFDM Relay Communication System: Relay Selection and Filter-and-Forward

In this paper, we develop a low-complexity cooperative relay network based on generalized frequency division multiplexing (GFDM) system. In this network, multiple relay nodes (RNs) are used to relay GFDM symbols from a source node (SN) toward a destination node (DN). We propose three methods to design the RNs based on the minimization of the total power of the noise after symbol estimation at the DN. In the first method, only one node is selected among all RNs to forward the signal from the SN to the DN. In the second and third methods, a filter-and-forward (FF) scheme is used, such that at each RN, the received GFDM signal from the SN is circularly convolved with a finite impulse response (FIR) filter and then, forwarded to the DN. The FIR filter's coefficients are represented as a circulant matrix. Since a circulant matrix is characterized by its eigenvalues, we obtain the eigenvalues of the FIR coefficient matrices for all RNs. The difference between the second and third methods is that in the former, the eigenvalues of the filter matrices are restricted to be one or zero, however, in the later, the eigenvalues are determined with no restrictions. Simulation results are provided to demonstrate the performance of the proposed methods in terms of bit error rate (BER). Moreover, we show that because of using circular convolution, the proposed methods can be implemented with a low complexity.

Investigation of possibilities of replacement of cable lines by radio relays in difficult­-accessible and «problem» areas

The article considers the routes of cable systems of the telecommunication network, for each its advantages and features are determined. The key trends and prospects for the development of radio relay communication in Ukraine are noted. The analysis of the current state of digital radio relay communication systems in the market of information and telecommunication services is given, indicating their tactical and technical characteristics, their peculiarities of use are given. A detailed analysis of the possibilities of replacing cable communication lines in hard-to-reach and «problematic» environments with the latest digital radio relays and replacing the «problem» area with other promising wireless transmission systems. Promising systems of wireless information transmission are analyzed. The analysis showed that the decision to partially replace certain network components with more convenient ones should be implemented. To address the goal set in the article, the following steps are considered, namely: reducing maintenance costs, increasing the simplicity and speed of construction of the communication network, increasing network survivability to the detriment of simplicity, clarifying the possibility of compensating the data exchange rate, autonomy of the network structure from other public or private institutions. Recommendations for the use of the obtained results are the expediency of replacing cable communication lines with radio relays in hard-to-reach and problem areas and as an alternative, laser data transmission is chosen, which allows to significantly speed up information exchange between two stations on the «problem» area. any network flow. Laser receivers, due to their low power, do not pose a health hazard.

Joint Position and Time Allocation Optimization of UAV‐Aided Wireless Powered Relay Communication Systems

The Internet of things (IoT) has emerged as a platform for connecting massive physical devices to collect and analyze data for decision‐making. Wireless devices in IoT are usually energy‐constrained and thus need to be powered by a stable and reliable energy source in order to maintain a long network lifetime. An unmanned aerial vehicle (UAV) as an energy source is a proper and applicable way to supply energy to wireless devices in IoT, due to its flexibility and potential of providing line‐of‐sight (LOS) links for wireless air‐to‐ground channels. In this paper, a UAV‐aided wireless powered relay communication system is presented, where a UAV firstly emits energy to a source and a relay, and then, the source and relay cooperatively transmit information to their destination. To explore the performance limit of the system, a problem is formulated by jointly optimizing the position of the UAV and time allocation to maximize the achievable information rate of the system. By deriving the explicit expressions of the optimal position of UAV and optimal time fraction, the nonconvex optimization problem is efficiently solved. Simulation results show that our proposed method significantly outperforms the benchmark methods.

Enhanced Tensor-Based Joint Channel and Symbol Estimation in Dual-Hop MIMO Relaying Systems

In this letter, an enhanced alternating least squares (EALS) algorithm for joint channel and symbol estimation is proposed in a dual-hop multiple input multiple output (MIMO) relaying communication system based on a simplified Khatri-Rao space-time (KRST) coding at the source node. The proposed method exploits the parallel factor (PARAFAC) and PARATUCK2 models at the relay node and the destination node, respectively. Exploiting the structure of these tensor models, we present an iterative alternating estimation scheme using optimized step size factors for accelerated convergence and lower overall complexity compared to conventional approaches. Identifiability conditions and computational complexity are analyzed, and simulation results are provided to corroborate the effectiveness of the proposed algorithm.

Analysis of Asymmetric Dual-Hop Energy Harvesting-Based Wireless Communication Systems in Mixed Fading Environments

This work investigates the performance of a dual-hop energy harvesting-based fixed-gain amplify-and-forward relaying communication system, subject to fading impairments. We consider a source node ( S) communicating with a destination node ( D), either directly or through a fixed distant relay ( R), which harvests energy from its received signals and uses it to amplify and forward the received signals to D. We also consider maximal-ratio combining at D to combine the signals coming from S and R. Both power-splitting and time-switching energy harvesting protocols are investigated. The S - R link is modeled by Nakagami- m fading model, while the R - D and S - D links experience α- μ fading. Closed-form expressions for the statistical properties of the total signal-to-noise ratio are derived, based on which novel closed-form expressions are then derived for the average symbol error rate as well as for the average channel capacity, considering four different adaptive transmission policies. The derived expressions are validated through Monte Carlo simulations.

Process map for collision avoidance based on information exchange for autonomous navigation of vessel

A reliable collision avoidance method is essential when operating an autonomous vessel. For this to become a reality, a number of researches have been conducted in order that the autonomous vessel could take an action for collision avoidance by herself. However, it may lead to dangerous situation without knowing the navigation intention of target-ships. In order to solve the issue, we developed the process map for collision avoidance based on information exchange via the communication relay system as follows: (i) the navigation situation analysis of the autonomous vessel was conducted based on manned ship voyage definition; (ii) the sequence diagram for information exchange was developed based on the autonomous vessel’s navigation context and the communication relay system, and (iii) the process map for collision avoidance based on information exchange was proposed based on the developed sequence diagram and the existing collision avoidance method. It would be expected that the autonomous vessel could avoid collision more safely than taking an action by herself.

Proactive optimization of transmission power and 3D trajectory in UAV-assisted relay systems with mobile ground users

In this paper, an Unmanned Aerial Vehicle (UAV)-assisted relay communication system is studied, where a UAV is served as a flying relay to maintain a communication link between a mobile source node and a remote destination node. Specifically, an average outage probability minimization problem is formulated firstly, with the constraints on the transmission power of the source node, the maximum energy consumption budget, the transmission power, the speed and acceleration of the flying UAV relay. Next, the closed-form of outage probability is derived, under the hybrid line-of-sight and non-line-of-sight probability channel model. To deal with the formulated nonconvex optimization, a long-term proactive optimization mechanism is developed. In particular, firstly, an approximation for line-of-sight probability and a reformulation of the primal problem are given, respectively. Then, the reformulated problem is transformed into two subproblems: one is the transmission power optimization with given UAV’s trajectory and the other is the trajectory optimization with given transmission power allocation. Next, two subproblems are tackled via tailoring primal–dual subgradient method and successive convex approximation, respectively. Furthermore, a proactive optimization algorithm is proposed to jointly optimize the transmission power allocation and the three-dimensional trajectory. Finally, simulation results demonstrate the performance of the proposed algorithm under various parameter configurations.

Automatic UAV Relay Communication System Based on Microwave Directional Antenna

To tackle the communication problem of unmanned aerial vehicle (UAV) complex aerial operations, we propose an automatic UAV relay communication system based on microwave directional antenna. Our system is organized by the design scheme, overall structure and working process. The system has the ability to transmit information at a distance, which solves the problem of limited communication distance caused by the transmission power limitation of UAV communication system. The system can automatically switch into different communication mode according to communication network environments to improve the communication quality. In addition, it increases the mobility and enhances endurance in severe environment to meet the emergency communication covered on demand.

Resource Optimization for Time Slot-Split Noma in Full-Duplex Cooperative Communications

A time-slot-split non-orthognal multiple access (TSS-NOMA) scheme for full-duplex (FD) relaying communication systems is proposed to improve frequency resource utilization. Aiming at the problem of low bandwidth efficiency when users pairing, TSS-NOMA divides the whole time slot into several parts to improve the matching process, where users can occupy all bandwidths in different time slots. TSS-NOMA decodes the information symbols of relay and re-encodes the messages through the new power allocation factors of successfully matched users. The mixed symbols are sent to increase the proportion of central users’ own signals received by themselves, thus improving the performance of the system. To maximize the minimum achievable rate of the system, TSS-NOMA optimizes the power allocation at the base station and the relay. Numerical results show that TSS-NOMA can achieve higher spectral and energy efficiency than some existing schemes.

Placement optimization of caching UAV-assisted mobile relay maritime communication

Recently, due to the deployment flexibility of unmanned aerial vehicles (UAVs), UAV-assisted mobile relay communication system has been widely used in the maritime communication. However, the performance of UAV-assisted mobile relay communication system is limited by the capacity of wireless backhaul link between base station and UAV In this paper, we consider a caching UAV-assisted decode-and-forward relay communication system in a downlink maritime communication. For the general case with multiple users, the optimal placement of UAV is obtained by solving the average achievable rate maximization problem through the one-dimensional linear search. For a special case with single user, we derive a semi closed-form expression of the optimal placement of UAV. Simulation results confirm the accuracy of analytical results and show that the optimal placement of UAV and the average achievable rate significantly depend on the cache capacity at UAV We also show the difference between the performances of the air-to-ground model and the air-to-sea model.

On the outage probability and BER of a DF-based multi-hop system over [formula omitted] and [formula omitted]-extreme fading channels

This paper analyzes the performance of decode-and-forward (DF)-based multi-hop relaying communication systems over α-κ-μ and α-κ-μ-Extreme fading channels. Analytical formulas for the probability density function (PDF) and the cumulative distribution function (CDF) of the received signal-to-noise ratio (SNR) as well as its moment generating function (MGF) are derived. Based on the derived PDFs, novel closed-form expressions for the outage probability (OP), bit error rate (BER) under coherent and non-coherent modulation schemes are derived. Additionally, asymptotic analyses of BER based on Poincare series expansions of SNR PDFs are carried out and results show good approximations for low SNR regimes. Simulations are performed to verify the accuracy and to show the tightness of the theoretical analysis.

First and Second Order Characteristics of a Wireless Three-hop Relay Channel with the Presence of Rayleigh Fading

In this paper, a wireless three-hop relay communication system operating in a Rayleigh multipath fading environment is analyzed. The output signal from such a system is a product of signal envelopes from all sections, meaning that it is actually a product of three random variables (RVs) with Rayleigh distribution. We considered here the first-order characteristics: probability density function (PDF), cumulative distribution function and outage probability (OP). Then, the moments and amount of fading (AoF) were derived in the closed forms. The second order characteristics we present include the following: level crossing rate (LCR) and average fade duration (AFD). A few graphs are given to show the impact of the specific parameters of the wireless three-hop relay system.

Relaying Energy Allocation Scheme Based on Multi-User SWIPT Relaying System

This paper investigates the relay energy allocation scheme based on the time switching (TS) operation strategy in multi-user simultaneous wireless information and power transfer (SWIPT) relaying system, where the relay is energy-constrained and utilizes the energy harvested in the energy harvesting mode to amplify and forward the information of the users. In the multi-user relaying system, the distances of the receivers of the users to the relay may be different. Thus, the total information rate maximization model is proposed and the corresponding energy allocation scheme is derived. After comparing the information rates of users, it is found that the information rates of users who are far from the relay are significantly lower than those of users who are close to the relay, i.e., “far-near” phenomenon. For the “far-near” problem, we propose the common information rate maximization model, and derive the corresponding energy allocation scheme. In this model, the information rates of all users are equal, which ensures the fairness of the information rate in multi-user relaying communication system. The simulation results show that the energy allocation scheme based on the common information rate maximization model can effectively solve the “far-near” problem in multi-user relaying communication system.

Interpretation of AF-DF protocols for FitureMulti Layer-IDMA

In this article, we investigate the bit error rate (BER) performance in a cooperative relay communication system for multilateral IDMA (ML-IDMA) using the maximum ratio combination (MRC) technique. ). ). We investigate the effect of the number of lines on performance and find the average error rate in bits of the AF relay scheme (Amplify and Forward) using the signal-to-noise ratio (SNR) of the relay connection in closed form. The proposed system for evaluating ML-IDMA performance is provided with a different number of layers and a different number of relays in an ML-IDMA cooperative environment. The simulation results show that the BER performance of a 4-relay IDMA double layer system (K = 2) is approximately 4 dB. In addition, the bandwidth saving is 50%. Ultimately, BER performance deteriorates as the number of layers increases and the proposed system increases bandwidth by approximately 1/K.

Performance of the Product of Three Nakagami-m Random Variables

An output signal from a multi-section wireless relay communication system is equal to the product of the signal envelopes from individual sections. In this paper, a three-sections relay system is considered in the presence of Nakagami-m fading at each section. First, random variable (RV) is formed as the product of three Nakagami-m RVs. For such product, the moments are determined in the closed forms. The first moment is the mean of the signal; the second moment is the average power of the signal, and the third moment is skewness. Then, the Amount of Fading (AoF) is calculated. AoF is a measure of the severity effect of fading in a particular channel model. Besides, all system performance are shown graphically and the parameters influence has been analyzed and discussed.

Joint Transmit Power and Placement Optimization for URLLC-Enabled UAV Relay Systems

This letter considers an unmanned aerial vehicle (UAV)-enabled relay communication system for delivering latency-critical messages with ultra-high reliability, where the relay is operating under amplifier-and-forward (AF) mode. We aim to jointly optimize the UAV location and power to minimize decoding error probability while guaranteeing the latency constraints. Both the free-space channel model and three-dimensional (3-D) channel model are considered. For the first model, we propose a low-complexity iterative algorithm to solve the problem, while globally optimal solution is derived for the case when the signal-to-noise ratio (SNR) is extremely high. For the second model, we also propose a low-complexity iterative algorithm to solve the problem. Simulation results confirm the performance advantages of our proposed algorithms.