Relay Communication System Research Articles

Technical characteristics of the relay communication satellite “Queqiao” for Chang’e-4 lunar farside exploration mission

Chang’e-4 (CE-4) is a mission that probes land softly on the farside of the Moon to peform scientific exploration for the first time in the world. The relay communication for the lander and the rover on the lunar farside to maintain contact with the Earth stations during their landing and surface operation is a key problem to be resolved. As an important part of Chinese Chang’e-4 farside exploration mission, Queqiao relay communication satellite provides relay communication support for the lander and the rover on the lunar farside. Different from other spacecraft for lunar mission, a Halo orbit around the Earth-Moon liberation point 2 is used first in the world to provide a continuous communications links to the lander and the rover on the farside of the Moon. A series of technical challenges have to be faced. Based on the analysis to the mission characteristics and mission requirements, the technical difficulties are identified and solutions for these problems are given, including selection and design of mission orbit, the relay communication system design trade-off, onboard instruments’ adaptibility to the very low on-orbit temperature environments, etc. The system design overview and flight profile of the Queqiao are given in this paper. Technical characteristics and technical innovation of the Queqiao satellite are summarized. The future technical development prospect or lunar relay communication missions is also given in this paper.

Transceiver design for multiple‐input multiple‐output full‐duplex amplify‐and‐forward relay communication systems

This study examines the linear source and relay precoder and destination combiner design for multiple-input multiple-output full-duplex (FD) relay communication systems. The effect of the residual interference due to the imperfect loop interference cancellation is considered in the design. Two design algorithms are proposed to minimise the mean squared error of the received signal at the destination. The first is a tri-step alternating iterative algorithm while the second is a bi-step iterative algorithm, which has lower complexity and performance comparable to that of the first algorithm. The convergence of these algorithms is evaluated. Results are presented, which show that the proposed FD relay system can provide approximately double the achievable rate of the corresponding half-duplex system if the residual interference is not high.

Precoding Design for Two-Way MIMO Full-Duplex Amplify-and-Forward Relay Communication Systems

Full duplex (FD) multiple-input multiple-output (MIMO) relaying can significantly increase the spectral efficiency of cooperative communication systems. This paper examines the problem of linear source and relay precoder and destination combiner design for two-way MIMO FD amplify-and-forward (AF) relay communication systems. The effect of the residual loop interference (LI) due to imperfect LI cancellation is considered in the design. Two algorithms are proposed to minimize the mean squared error (MSE) of the received signals at the destinations. The first is a tri-step alternating iterative algorithm and the second is a bi-step iterative algorithm. The convergence and complexity of these algorithms are analyzed. Simulation results are presented, which show that the proposed two-way FD system provides approximately double the achievable rate of the corresponding half-duplex (HD) system when the residual LI is low. Furthermore, the bi-step algorithm shows comparable performance to the tri-step algorithm and has a lower computational complexity.

Data Exchange of Relay Transmission and Information Scheduling in Shared Networks

With the diversification of the kinds of wireless transmission service, the transmission rate and reliability of wireless communication have been demanded sharply. The shortage of resources of spectrum has become continuously prominent. These are bottlenecks to restrict the development of wireless communication. The current multi-antenna cooperative relay communication system can’t sense complex communication scenes agilely, and adjust the strategy of interference suppression according to the signal characteristics adaptively, and optimize the resource of the system dynamically. Moreover, the degree of freedom and transmission system reliability should have been further improved. Aiming at the above problems, this paper extracts the features of the combined signal from different degrees of freedom, considering the influence and effect of the distribution characteristics of the signal on its separability, and signal spatial structure to enhance the ability to adapt to complex environmental interference. It explores multiple interactive cooperative transmission scheduling to optimize the wireless resource dispatching and new network coding jointly, and get a unified multi antenna relay transmission processing standards and to improve the efficiency of information transmission. It carries out theoretical studies of interference coordination algorithms which can acquire higher forwarding efficiency at relay in the view of energy efficiency and spectral efficiency.

UAV Relay Flight Path Planning in the Presence of Jamming Signal

The flight path of the unmanned aerial vehicle (UAV) relay can significantly affect the performance of the wireless relay communication system. In this paper, we investigate the optimization of the UAV flight path in a wireless relay communication system, when a jamming or interference signal is present. The UAV flight path is optimized to maximize the signal-to-interference-plus-noise ratio (SINR), and the required parameters are estimated. The simulation results show that the proposed method can achieve performance close to an ideal SINR optimization and also highlight the benefits of optimizing the SINR instead of the signal-to-noise ratio (SNR) when a jamming or interference signal is present.

LEVEL CROSSING RATE OF PRODUCT OF TWO NAKAGAMI-m RANDOM VARIABLES AND RAYLEIGH RANDOM VARIABLE

In this paper, the level crossing rate of product of two Nakagami random variables and Rayleigh random variable will be calculated. This result can be used in the performance analysis of wireless relay communication system with three sections: Nakagami-m fading is present in the first and second section and Rayleigh fading is present in the third section. Also, the obtained result can be used for calculation of the level crossing rate of the product of three Rayleigh random processes, and the level crossing rate of the product of two Rayleigh random processes and Nakagami-m random process. The influence of the parameter m on the level crossing rate is analysed and considered. Key words: Level crossing rate, Nakagami-m random variable, Rayleigh random variable

Stem cells repurpose proliferation to contain a breach in their niche barrier.

Adult stem cells are responsible for life-long tissue maintenance. They reside in and interact with specialized tissue microenvironments (niches). Using murine hair follicle as a model, we show that when junctional perturbations in the niche disrupt barrier function, adjacent stem cells dramatically change their transcriptome independent of bacterial invasion and become capable of directly signaling to and recruiting immune cells. Additionally, these stem cells elevate cell cycle transcripts which reduce their quiescence threshold, enabling them to selectively proliferate within this microenvironment of immune distress cues. However, rather than mobilizing to fuel new tissue regeneration, these ectopically proliferative stem cells remain within their niche to contain the breach. Together, our findings expose a potential communication relay system that operates from the niche to the stem cells to the immune system and back. The repurposing of proliferation by these stem cells patch the breached barrier, stoke the immune response and restore niche integrity.

Research and Analysis for Relay Communication System of Chang'e-4 Lunar Relay Satellite

In order to realize the landing mission of Chang'e-4 satellite on the far-side of the Moon,a lunar relay communication satellite is developed to provide relay communication service between the ground station and the lander as well as the rover of Chang'e-4 on the farside of the Moon. The relay communication system is the main payload and the key to accomplish mission objectives of the relay satellite.The technical scheme of the relay communication system is studied and analyzed in this paper.

The Development Overview and Prospect of Lunar Relay Communication Satellite System

The relay communication is a key problem for lunar exploration missions,especially the landing and cruising on the lunar farside and polar areas,as well as the manned lunar exploration missions. The research and development status are analized about lunar relay communication satellite system throughout the world. Based on the analysis on the requirements for lunar relay communication missions,the implementation approach are analyzed for relay communication system scheme,orbit selections,etc. The technical development trends for future lunar relay communication satellite system are also given in this paper.

Outage and error analysis of three hop hybrid VLC/FSO/VLC–based relayed optical wireless communication system

AbstractIn this paper, we consider a three hop hybrid visible light communication/free space optical/visible light communication (VLC/FSO/VLC) system in which the information is transmitted from a room inside the building on a VLC link toward the decode and forward (DF) relay attached to that building. The relay maps the incoming signal on the FSO link and forwards it to the other DF relay attached to the second building, which further passes it down to the user inside the room onto the VLC downlink. The VLC and FSO links follow the Lambertian emission model and Gamma‐Gamma fading statistics, respectively, under the impact of atmospheric turbulence, pointing errors, semiangle, and field of view of the detector. The performance of the three hop hybrid system is derived in terms of the closed‐form expression for the outage probability. The error performance is analyzed in terms of average symbol error probability of the considered hybrid system. Furthermore, an expression for asymptotic outage probability of the system is derived to investigate the behavior of the system at high signal‐to‐noise ratio (SNR) regimes. The impact of variation in the parameters on the hybrid VLC/FSO//VLC communication system performance is illustrated by the numerical plots.

RADIO RELAY SYSTEM WITH TWO-SECTION PERFORMANCE IN THE PRESENCE OF NAKAGAMI-M FADING AND RICIAN CO-CHANNEL INTERFERENCE

Wireless mobile relay communication system with two sections operating over short term fading channel in the presence of co-channel interference subjected to small scale fading has been considered. Desired signal experiences Nakagami-m fading and co- channel interference experiences Rician fading. Desired signal at output of the second section has Nakagami-m*Nakagami-m distribution. The signal-to-interference ratio of product of two Nakagami-m random variables and Rician random variable has been presented. In this paper, closed form expresions for moments of signal- to-interference ratio of considered system are calculated. The influence of Nakagami-m short term fading severity parameter and Rician κ factor on presence is analysed and discussed. Mobile relay communication system with two sections can lead to a more reliable and efficient transmission, which is of great importance in the risky environments. Key words: Nakagami-m fading, Rician fading, moment, mobile relay communications system

On Full-Duplex Relaying for Optical Wireless Scattering Communication With On-off Keying Modulation

We address full-duplex relaying for optical wireless communication with stochastic and non-negligible self-interference at the relay node with on-off keying modulation. Assume a relay communication system with a source node, a relaying node, and a destination node, where there is no interference at the source and destination nodes, since they merely transmit or receive. We propose two full-duplex relay protocols, namely, the detect-and-forward relaying protocol and the decode-and-forward relay protocol. For the former, the relay node performs the symbol detection and forwards the detected symbols to the destination node, and for the latter, the relay node performs block decoding and forwards the re-encoded block to the destination node. We prove that for sufficiently high self-interference intensity, the achievable transmission rate of the full-duplex relay system can be lower than that of the half-duplex relay system without self-interference for the detect-and-forward relay protocol. We also prove that for the decode-and-forward relay protocol, the full-duplex relay system always has a larger transmission rate compared with the half-duplex relay system. This can be justified by the fact that, for the decode-and-forward protocol, the source-relay link adopts two codebooks in the scenarios with and without self-interference. The performance of the two proposed protocols is evaluated by the numerical results.

Probability-based pilot allocation for MIMO relay Distributed compressed sensing channel estimation

Multiple-Input Multiple-Output (MIMO) relay communication systems are used as an efficient system in spectral efficiency and power allocation view point. In these systems, some of the facilities need channel state information (CSI). Besides, new estimation methods based on compressed sensing (CS) are well known for their spectral efficiency and accuracy. In this paper, we have used a Distributed CS-based channel estimation method to improve the accuracy and spectral efficiency of channel estimation for MIMO-Orthogonal Frequency Division Multiplexing relay network. Specifically, using Least Squares (LS) estimation increases the accuracy of well-known Compressive Sampling Matching Pursuit (CoSaMP) algorithm and proposes Block-verified CoSaMP (B-vCoSaMP). To improve the accuracy of estimation, we are encountered with a combinatorial optimization which is dealt with probability-based approaches in this paper. More particularly, three probability-based optimization methods have been proposed to optimize the mutual coherence of measurement matrix called Sequential Cross-Entropy (SCE), Extended Estimating of Distribution Algorithm (EEDA), and Parallel Cross-Entropy (PCE). All these methods are based on sampling from a Probability Density Function (PDF) which is updated in each iteration using elite samples of the population. The simulation results represent the accuracy and speed of the proposed methods, and the comparison is expressed as well.

Performance analysis of cognitive underlay two-way relay networks with interference and imperfect channel state information

In this paper, we evaluate two-way relay communication systems in cognitive radio environments. The proposed model includes two subsystems: a primary system and a secondary system. The primary system consists of a primary transmitter and a primary receiver while the secondary includes two terminals exchanging their data via an intermediate relay node. Each network node is equipped with a single antenna and operates under a half-duplex mode. The channel state information (CSI) interference from the secondary node to the primary receiver is assumed imperfect. Using analytical methods, this paper derives the interference probability from the secondary system to the primary receiver and an optimal back-off control power coefficient for the secondary transmitter. To evaluate the secondary system quality, an explicit expression for the system outage probability (OP) and its closed form in the high signal-to-noise region (SNR) is presented. Theoretical results are verified using Monte-Carlo simulation.

Multi‐relay cooperative transmission based on rateless codes and adaptive demodulation

A rate adaption scheme is given at the receiver using rateless codes and log-likelihood ratio (LLR) threshold-based adaptive demodulation (ADM). The received bits with LLR absolute values higher than the preset threshold are demodulated by the receiver, otherwise, deleted. Through the theoretical analysis of the average mutual information (MI) of the demodulated bits, the method is obtained to calculate the LLR demodulation threshold under the required error performance after decoding and the constraint of codeword length for decoding. Then, the rate adaption scheme is applied in a parallel multiple relay wireless communication system. The LLR threshold is set according to the instantaneous SNR of the received signals in order to keep the average MI per demodulated bit of each relay link the same. The demodulated bits coming from all links are combined for decoding. The 256-QAM constellation and Raptor code are then considered as a special case to design a sample scheme. Simulation results prove the correctness of the theoretical analysis and the feasibility of the proposed scheme, and when it is employed by a multi-relay transmission system, the diversity gain can be obtained, and the anti-fading and the anti-jamming abilities of the system are promoted.

Social-Aware Relay Selection Scheme for Relay-Based D2D Communications

In order to improve the communication quality of relay-based D2D communication, this paper proposed a relay selection algorithm with the consideration of the information of the social domain and the physical domain. First, the transmission performance of D2D relay communication in the half-duplex relay mode and the full-duplex relay mode is analyzed separately in the physical domain. Second, we analyzed the user’s history check-in information to obtain the characteristics of user’s mobility and the social relationship strength between users. Finally, we proposed a relay communication gain metric to measure the extent of transmission performance improvement brought by D2D relay communication and developed a relay selection algorithm for maximizing the relay communication gain. The simulation results show that compared with the traditional D2D relay communication scheme, the transmission rate and stability of the transmission link of the D2D relay communication system using the proposed algorithm are greatly improved.

Design of communication relay mission for supporting lunar-farside soft landing

ChangE-IV will be the first soft-landing and rover mission on the lunar farside. The relay satellite, which is located near the Earth-Moon L2 point for relay communication, is the key to the landing mission. Based on an analysis of the characteristics of the task and the technical difficulties associated with the relay satellite system, the overall design scheme of the relay communication mission is proposed in terms of trajectory design and communication system design among other aspects. First, according to the complex dynamic environment, a mission orbit that serves as an uninterrupted communication link is presented. A short-duration and low-energy transfer trajectory with lunar flyby is discussed. Orbital correction and a low-cost control strategy for orbit maintenance in the Earth-Moon L2 point region are provided. Second, considering the existing technical constraints, the requirement of relay communication in different stages and the design schemes of frequency division and redundant relay communication system are introduced. Finally, based on the trajectory design index and the performance of the communication system, the overall design scheme of the relay communication mission is proposed. This mission will provide the technical support and reference required for the ChangE-IV mission.

Secure Energy Harvesting Communications with Relay Selection over Nakagami-m Fading Channels

In this paper, a secure energy harvesting relay communication system with partial relay selection over Nakagami-m fading channels is proposed. A power beacon can provide wireless energy for the source and relay. A time-switching-based (TS) radio frequency energy harvesting technique is deployed at the power beacon. An eavesdropper is able to wiretap to the signal transmitted from the source and the relays. The exact closed-form expression of secrecy outage probability is derived. The results show that with increasing number of relays the system performs better in terms of secrecy outage probability (SOP). In addition, the energy harvesting duration has a significant effect on the secrecy outage probability. There exist an optimal energy harvesting duration that can achieve the lowest SOP and therefore this parameter should be carefully designed.

MIMO-STBC Based Multiple Relay Cooperative Communication Over Time-Selective Rayleigh Fading Links With Imperfect Channel Estimates

This paper analyzes the effect of time-selective fading arising due to node mobility and imperfect channel estimates on the end-to-end performance of multiple-input multiple-output space-time block coded multiple relay cooperative communication systems. Both dual-phase and multi-phase selective decode-and-forward relaying protocols are considered for the end-to-end communication in a multiple relay cooperative system, followed by presentation of complete analyses for the same. For each protocol, closed-form expressions are derived for the per-frame average pair-wise error probability and asymptotic error floor over independent and nonidentical time-selective Rayleigh fading links. A framework is also developed for obtaining the optimal source relay power factors for each of the above protocols, which significantly improve the end-to-end reliability of the system for a given power budget. It is shown that both the multirelay systems achieve the full diversity order (DO) when all the nodes are static and perfect channel estimates are available at each receiving node. The DO of the system reduces to that of the direct source–destination link for a scenario when only the relays are mobile. Interestingly, however, in other mobile scenarios, both the systems are limited by an asymptotic error floor with increasing signal to noise ratio. Further, the impact of DO of the source–relay and relay–destination links on the optimal source–relay power allocation is also explicitly demonstrated. Simulation results yield several important insights into the end-to-end error performance for different mobility conditions and also validate the derived analytical results.

APPLICATION OF LAPLACE APPROXIMATION FORMULA IN PERFORMANCE ANALYSIS OF WIRELESS RELAY COMMUNICATION SYSTEM IN MULTIPATH FADING ENVIRONMENT

In this paper, Laplace approximation formula is efficiently used to calculate infinite-series expression for average level crossing rate (LCR) of the product of Nakagami-m and kappa-mu random processes. The results can be used in performance analysis of dual-hop relay wireless mobile communication system in specific multipath fading environment when the first section is under the influence of NLOS multipath environment while the second section is under the influence of LOS multipath fading environment. The influences of multipath fading parameters on the LCR of the proposed model are examined, graphically presented and discussed. Moreover, analytical approach of applying Laplace approximation formula in multi-hop systems is further considered by obtaining closed form expressions for the LCR of the product of three and four Nakagami-m processes, respectively. Key words: average level crossing rate, kappa-mu multipath fading, Laplace approximation formula, Nakagami-m distribution, relay communications system.