Relay Terminals Research Articles

Analytical BER Calculation of TAS/MRC-Based Two Hop UWB Communication System Over IEEE 802.15.4a Channel

ABSTRACTIn this paper, we calculate the bit error rate (BER) of the orthogonal binary signals in the two hop ultra-wideband (UWB) communication system with the transmit antenna selection scheme at the source and the relay terminals. In the two hop UWB system, relay is configured to perform the decode and forward cooperative strategy. In order to calculate the BER of the investigated UWB system, we consider the characteristic function- based approach to model the sum of path gains of the IEEE 802.15.4a channel. We assume that all the IEEE 802.15.4a channel links are independent and identically distributed and perfect channel state information is available at the transmitter. The results exhibit that the derived BER is a good match with the simulations and it has been significantly improved over the BER of the conventional UWB systems.

Connectivity Restoration in Wireless Sensor Networks via Space Network Coding

The problem of finding the number and optimal positions of relay nodes for restoring the network connectivity in partitioned Wireless Sensor Networks (WSNs) is Non-deterministic Polynomial-time hard (NP-hard) and thus heuristic methods are preferred to solve it. This paper proposes a novel polynomial time heuristic algorithm, namely, Relay Placement using Space Network Coding (RPSNC), to solve this problem, where Space Network Coding, also called Space Information Flow (SIF), is a new research paradigm that studies network coding in Euclidean space, in which extra relay nodes can be introduced to reduce the cost of communication. Unlike contemporary schemes that are often based on Minimum Spanning Tree (MST), Euclidean Steiner Minimal Tree (ESMT) or a combination of MST with ESMT, RPSNC is a new min-cost multicast space network coding approach that combines Delaunay triangulation and non-uniform partitioning techniques for generating a number of candidate relay nodes, and then linear programming is applied for choosing the optimal relay nodes and computing their connection links with terminals. Subsequently, an equilibrium method is used to refine the locations of the optimal relay nodes, by moving them to balanced positions. RPSNC can adapt to any density distribution of relay nodes and terminals, as well as any density distribution of terminals. The performance and complexity of RPSNC are analyzed and its performance is validated through simulation experiments.

Distributed space-time coding scheme with differential detection and power allocation for cooperative relay network

By introducing orthogonal space-time coding (STC) scheme in wireless cooperative relay network, two distributed differential STC (DSTC) schemes based on the amplify-and-forward (AF) and decode-and- forward (DF) methods are, respectively, developed. The scheme performance is investigated in symmetric and asymmetric wireless relay networks. The presented schemes require no channel information at both relay terminals and destination terminal, and have linear decoding complexity when compared with the existing scheme. Moreover, they are suitable for the application of different constellation modulations and DSTC schemes, and thus provide more freedoms of design. Besides, the power allocations between source and relay terminals are jointly optimized to minimize the system pairwise error probability for symmetric and asymmetric networks, and two practical methods are presented to solve the complicated optimized problem from asymmetric network. Simulation results show that the scheme with DF method has better performance than that with AF method due to no amplification of noise power, but the performance superiority will decrease at high SNR due to the error propagation of decoding at the relays. Furthermore, the distributed DSTC schemes with optimal power allocation have better performance than those with conventional fixed power allocation.

Mitigating Packet Drop and Energy Consumption in Wireless Sensor Networks Using Network Level Optimized Relay Election Protocol

Mitigating Energy Consumption and improving data delivery are the primary constraints in wireless sensor networks. It can be achieved by improving the efficiency of transmission by establishing coordinated communication across relay terminals. Complexity of interaction among accessing the medium is an erroneous source in relay. First an effective relay must be chosen under proper coordination among the entire network for excellent data broadcasting and delivery. Second requirement is to allocate proper time management schedules. The relaying technique is to minimize the energy consumption and to avoid data loss by mitigating packet drop. It is achieved by implementing NLORE protocol which aims at providing high energy conservation and improves the throughput. We use TDMA scheduling for managing the time slot. This scheduling aims at providing proper coordination in the network. Network coordination is necessary not just to reduce the packet drop but also to reduce retransmission of redundant data. NLORE and TDMA are implemented to work in hand with each other to meet the primary goal.

Wireless-Powered Cooperative Multi-Relay Systems With Relay Selection

In this paper, a wireless-powered cooperative multi-relay network is investigated to enhance the communication quality between two end users. Multiple intermediate relay terminals, which are off-grid and randomly spread within a certain cooperating area, attempt to decode-and-forward the source information to the destination by using the energy scavenged from the source radio-frequency signals. A power splitting architecture is adopted at each relay, where the received signal observation from the source is adaptively divided into two portions for information decoding and energy collection. Then, a single best relay (or relays), according to five different criteria, is selected to forward the decoded source signal to the destination. In view of the spatial randomness and the energy causality at the intermediate relays, stochastic geometry is applied to characterize the end-to-end outage probability of the cooperative multi-relay system considered, based on which the asymptotic outage performance in the high signal-to-noise ratio regime is analyzed. Simulation results demonstrate that with only nominally more knowledge, e.g., locations and charging status of relays, available for relay selection, the communication quality of the system can be substantially improved compared with an arbitrarily random relay selection.

Distributed relay selection strategy based on physical‐layer fairness for amplify‐and‐forward relaying systems

For relay terminals in wireless communication systems, the difference of the power consumed for relaying signals means unfairness, which may reduce the network lifetime when the system is energy-constrained. Classic opportunistic relay selections always cause unequal power consumption among all relays. In this study, the authors propose a novel distributed relay selection strategy, named the fair opportunistic relay selection (FORS) strategy, for amplify-and-forward (AF) opportunistic cooperative systems. The FORS strategy is designed based on physical-layer fairness that means all available relays cumulatively consume equal power. They use a set of weight coefficients to adjust the channel fading coefficients effectively and then change the selection probabilities for all relays on the basis of proportional fair scheduling. Considering that the ‘optimal’ relay can be selected proactively in quasi-static Rayleigh fading channels based on local channel state information, the overhead of the proposed scheme is small. Then, they analyse the performance of the FORS strategy and provide an exact analytical expression for the outage probability (P out) and the average symbol error probability. Numerical simulation results validate their analysis. The results show that the FORS strategy approximately achieves the upper bound of physical-layer fairness in the AF relaying system.

Design and Analysis of Broadband Amplify-and-Forward Cooperative Systems: A Fractionally-Spaced Sampling Approach

In this paper, we propose novel fractionally-spaced frequency-domain equalizers for the amplify-and-forward cooperative systems. In the proposed equalization schemes, the sampling rate of the received signal remains at least as high as the Nyquist rate within the digital processing chain of the relay node(s), upon which a true fractionally-spaced equalization becomes feasible at the destination. Based on minimum-mean-square-error (MMSE) criterion, different equalization structures (linear and non-linear) are designed, and approximations for their bit error rate (BER) performance are presented. The BER performance of the proposed schemes are further lower bounded through a matched-filter bound (MFB) analysis which provides insight into system design such as optimum power allocation and relay selection strategy. Our results show that, under certain channel realizations and sampling phase errors (that may occur in the relay and destination terminals), the performance of the conventional symbol-spaced cooperative systems reduces to that of no relay scenario. However, the performance of cooperative systems with the proposed fractionally-spaced equalizers is independent of the samplers' phases, and as a result, full benefit of cooperation is retained.

GUARANTEEING THE TROUBLE-FREE OPERATION OF CAPACITOR BANKS IN POWER-SUPPLY SYSTEMS OF INDUSTRIAL ENTERPRISES

Purpose. The problem of resonance phenomena in power systems of industrial enterprises using capacitor banks for reactive power compensation was detected. Circuit of the capacitor banks tier to downshift main substation tires is present. But there is no common algorithm to calculate and avoid such trouble. The main goal of this article is to introduce some basics for power supply systems with possible resonant circuits engineering. Methodology. At the first step the data on the change of the current in the chemical company network when changing capacitor banks value are received. For these purposes the oscilloscope function of digital protection relay was used. Current data samples were analyzed by spectrum detection software. Most significant levels of the 3rd and 5th harmonics were achieved. Comparison of harmonic distortion levels with and without capacitor bank is given. Results. Achieved data allow making conclusion about overloading reasons of capacitor banks while higher harmonics currents presence. A voltage and current harmonious composition measuring in the absence of power quality analyzers using digital protection relay terminals or emergencies registers are proposed. The necessity of power quality monitoring near capacitor banks connections to avoid resonance phenomena (current and voltage resonance) in industrial power supply systems is proven. The control algorithm of capacitor banks to provide electromagnetic compatibility, while various modes of nonlinear load operation is given. Originality. Using of digital protection relay oscilloscoping for current resonant detection can allow to significally reduce time and cost of solution. Replacement parallel circuit comprising a branch and one active-inductive load to another branch network in the presence of higher harmonics source are proposed. Practical value. A sequence for measuring the levels of harmonic components at the connections of capacitor banks in the absence of specialized instruments is proposed. The algorithm to avoid possible resonance currents in the presence of condensing units is proposed.

Multihop Cognitive Relaying Over Composite Multipath/Shadowing Channels

The composite multipath/shadowing model is key to accurate modeling of real-world wireless channels, due to the combination of the effects of both fading and shadowing. However, the fundamental limits of spectrum-sharing cognitive radio have not been studied for such propagation conditions, leaving a gap in the analysis of these systems and, hence, the communication strategies that can be built upon toward improving performance. In this paper, we consider a primary/secondary spectrum-sharing network and study the performance of the secondary's multihop link by taking the composite multipath/shadowing model, which is described by the generalized- $K$ distribution, for the radio channels. In the multihop system, communication between secondary users (SUs) is assisted by intermediate relay terminals, under coexistence constraints with the primary users (PUs) . We assess the performance of the multihop system, first by deriving the moment generating function (mgf) and the probability density function (pdf) of the upper bounded end-to-end signal-to-noise ratio in closed form. The result is then used to obtain closed-form expressions of bounds on the ergodic capacity and the average bit error rate (ABER) , under the resource sharing constraints. The theoretical results are assessed with numerical analysis for different operating conditions.

모바일 인스턴스 메신저를 이용한 양방향 검색 알고리즘의 설계 및 구현

In this paper, we design and implement a two-way search algorithm that can provide a customized service through the user with real-time two-way communication using a mobile instant messaging service. Therefore, we design and implement the automative search system which enables delivering message to each user mobile terminal from a plurality of relay mobile terminals by utilizing the mobile instant messenger, not to deliver a message from the main server to the mobile instant messenger user directly. Two-way search system using the mobile instant messenger can be immediately collect the user's response is easy to identify the orientation of each user, and thus can be provided to establish a differentiated service plan. Also, It provides a number of services(text, photos, videos, etc) in real-time information to the user by utilizing the mobile instant messenger service without the need to install a separate application. Experiment results, data processing speed of the category processing way to search for the data of the DB server from a user mobile terminal is about 7.06sec, data processing number per minute is about 13 times. The data processing speed of the instruction processing way is about 3.10sec, data processing number per minute is about 10 times. The data processing speed of the natural language processing way is about 5.13sec, per data processing number per minute is about 7 times. Therefore in category processing way, command processing way and natural language processing way, instruction processing way is the most excellent in aspect of data processing speed, otherwise in aspect of per data processing number per minute, the category processing way is the best method.

Improving the Network Lifetime of MANETs through Cooperative MAC Protocol Design

Cooperative communication, which utilizes nearby terminals to relay the overhearing information to achieve the diversity gains, has a great potential to improve the transmitting efficiency in wireless networks. To deal with the complicated medium access interactions induced by relaying and leverage the benefits of such cooperation, an efficient Cooperative Medium Access Control (CMAC) protocol is needed. In this paper, we propose a novel cross-layer distributed energy-adaptive location-based CMAC protocol, namely DEL-CMAC, for Mobile Ad-hoc NETworks (MANETs). The design objective of DEL-CMAC is to improve the performance of the MANETs in terms of network lifetime and energy efficiency. A practical energy consumption model is utilized in this paper, which takes the energy consumption on both transceiver circuitry and transmit amplifier into account. A distributed utility-based best relay selection strategy is incorporated, which selects the best relay based on location information and residual energy. Furthermore, with the purpose of enhancing the spatial reuse, an innovative network allocation vector setting is provided to deal with the varying transmitting power of the source and relay terminals. We show that the proposed DEL-CMAC significantly prolongs the network lifetime under various circumstances even for high circuitry energy consumption cases by comprehensive simulation study.

Performance Analysis of Cooperative Vehicular Systems with Co-channel Interference Over Cascaded Nakagami-m Fading Channels

In this paper, we investigate a dual-hop decode-and-forward (DF) relaying vehicular system in the presence of co-channel interference, in which source, relay and destination terminals are composed ...

Relay Selection for Simultaneous Information Transmission and Wireless Energy Transfer: A Tradeoff Perspective

In certain applications, relay terminals can be employed to simultaneously deliver information and energy to a designated receiver and a set of radio frequency (RF) energy harvesters, respectively. In such scenarios, the relay that is preferable for information transmission does not necessarily coincide with the relay that is preferable for energy transfer, since the corresponding channels fade independently. Relay selection thus entails a tradeoff between the efficiency of the information transmission to the receiver and the amount of energy transferred to the energy harvesters. The study of this tradeoff is the subject on which this work mainly focuses. Specifically, we investigate the dependence of the ergodic capacity and the outage probability of the information transmission to the receiver on the amount of energy transferred to the RF energy harvesters. We propose a relay selection policy that yields the optimal tradeoff in a maximum capacity/minimum outage probability sense, for a given energy transfer constraint. We also propose two suboptimal relay selection methods that apply to scenarios with limited availability of channel state information. Additionally, we propose a suboptimal scheme which approximates the optimal scheme for the special case of two relays and facilitates performance analysis. Interesting insights on the aforementioned tradeoffs are unveiled.

Decode-and-forward relaying based on orthogonalcomplementary codes

In this note, we propose a full-duplex decode-and-forward cooperative diversity scheme based on code division with orthogonal complementary codes. We consider a simple case in which a single user is assisted by a single relay to achieve cooperative diversity. When the cooperation is full-duplex, the operational delay of the relay makes the channel asynchronous and this may cause multiple-access interference (MAI) between the user and relay. The orthogonal complementary codes have perfect autocorrelation and cross-correlation properties that provide MAI-free operation in asynchronous channels. In the proposed scheme, the user and relay terminals spread their messages with complementary codes and the spread messages can reach the destination without interfering with each other. The numerical results reveal that the proposed scheme reaches the same bit-error-rate performance in both synchronous and asynchronous channels. The results are also compared with the conventional orthogonal code sets, such as Hadamard sets, which fail to provide diversity.

A SURVEY ON INCREMENTAL RELAYING PROTOCOLS IN COOPERATIVE COMMUNICATION

Cooperative communication is one of the latest techniques in wireless communication to form virtual antenna arrays. Cooperative communication is an alternative method for MIMO (Multiple input multiple output) system. This scheme assumes TDMA (Time division multiple access) channel accessing and divides the communication into two phases which includes direct transmission and retransmission by the relay terminal. A few cooperative diversity protocols ,for example fixed relaying, selection relaying and incremental relaying are used in order to perform different sorts of processing by the relay terminals, and combining at the destination terminals. Each diversity protocol exhibits its own unique performance. Fixed relaying can be further classified into amplify and forward (AF) relaying and decode and forward (DF) relaying. In AF , relay users amplifies the signal and retransmits it, and in the case of DF, the relay users decodes and retransmits the signal. The Selection relaying is performed by taking the fading coefficient into account. In this report, the recent works on incremental relaying protocol has been summarized. Incremental relaying is based on the feedback mechanism. In this scheme, relay users perform retransmission only if needed, based on the received SNR (Signal to noise ratio) or decoding error that occurs during direct transmission. It is used in cooperative communication in order to attain efficient use of degrees of freedom and to overcome bandwidth inefficiency. The authors have presented a number of protocols such as Incremental selection amplify and forward (ISAF), Joint incremental selection relaying (JISR), Fractional Incremental relaying (FIR), Selective Fractional Incremental relaying (SFIR) and Efficient Incremental relaying (EIR).

Improvement in Channel Estimation and Error Rate Performance in Mobile Cooperative OFDM Systems with Intercarrier Interference

In mobile cooperative orthogonal frequency division multiplexing (OFDM) systems with amplify-and-forward (AF) relays, in which the source and relay terminals are moving, Doppler frequency might become very large due to the formation of double-hop channels, possibly causing very large intercarrier interference (ICI). Therefore, ICI mitigation technique capable of reducing the impact of high Doppler frequency is required. This paper reports the study of ICI mitigation technique that uses frequency domain equalizer (FDE) with improvements in three aspects, namely, better channel estimation using cubic-spline approximation, use of selection combining to utilize cooperative diversity in order to suppress ICI, and simple error correcting code with double interleaving to suppress errors due to residual ICI. By using the proposed ICI mitigation technique, error rate performance of mobile cooperative OFDM systems can be improved significantly. Even at high Doppler frequencies, error floors due to residual ICI can be decreased by up to two decades.

Performance analysis of two‐way opportunistic decode‐and‐forward based systems in Nakagami‐ m fading environments

This paper studies the performance of a two-way relay-based communication system with opportunistic relay selection in Nakagami-m fading environments. The authors consider a two-way wireless communication system where two nodes, acting as sources and using different modulation schemes for transmission, are unable to exchange data because of deep fading on their direct link and proceed via L relay terminals. They provide closed-form expression for the probability density function of the link between the ‘selected’ best relay and each source, and use this result to derive a closed-form expression for the average symbol error probability which, to the best knowledge of the authors, has never been done before. This result is further approximated for the high signal-to-noise ratio regions and used to develop closed-form expressions for the optimised power allocated to each node involved in the communication process. The authors asset their formulae with numerical results and interpretations to complete this work.

Impact of the External Co-channel Interferences Over Multiuser Bi-directional Wireless Relaying Networks-Part I: System Description and Outage Analysis

This paper investigates the impact of co-channel interferences (CCIs) caused by the external terminals over multiuser bi-directional amplify-and-forward (AF) relaying. The investigation considers multiuser pair and single bi-directional AF based relay and finite numbers of external interference terminals in the system model. Simultaneous transmission model, which is default mode, creates CCIs that is caused by the other user-pairs (internal terminals) in the system model. The opportunistic source-pair selection (OSPS) strategy achieves near-optimal solution for the internal CCIs challenge and also achieves diversity order in high SNR regimes. However, external terminals' CCIs are inevitable and degrades the system performance. The main aim of this paper is to clearly state the impacts of external CCIs both for simultaneous and OSPS methods. According to the simulation results, in the case that the external terminals' transmit powers are identical and non-identical to each other, and if the external terminals' transmit powers are proportional with SNR, this results on the degradation of the achievable diversity order from $$N$$ N to 0 while also affecting the coding gain. The results also show that, when the external terminals have fixed transmit power values rather than proportional with SNR, in this circumstance, external terminals interference does not affect the achievable diversity order but it affects the system coding gain.The results also show that, when the number of external terminals which affect the user-pairs and relay terminals increase, for both identical and non-identical cases, the losses at the system coding gain exponentially decay. On the other hand, if the external terminals have non-identical transmit powers and if the relay terminal is interfered with more transmit power in comparison with what interferes with the user-pairs, this gives better performance values.

Real-time exploration of a multi-robot rescue system in disaster areas

A system procedure is proposed for a multi-robot rescue system that performs real-time exploration over disaster areas. Real-time exploration means that every robot exploring the area always has a communication path to human operators standing by at a base station and that the communication path is configured by ad hoc wireless networking. Real-time exploration is essential in multi-robot systems for USAR (urban search and rescue) because operators must communicate with every robot to support the victim detection process and ad hoc networking is suitable to configure a communication path among obstacles. The proposed system procedure consists of the autonomous classification of robots into search and relay types and behavior algorithms for each class of robot. Search robots explore the areas and relay robots act as relay terminals between search robots and the base station. The rule of the classification and the behavior algorithm refer to the forwarding table of each robot constructed for ad hoc networking. The table construction is based on DSDV (destination-sequenced distance vector) routing that informs each robot of its topological position in the network and other essentials. Computer simulations are executed with a specific exploration strategy of search robots. The results show that a multi-robot rescue system can perform real-time exploration with the proposed system procedure and reduce exploration time in comparison with the case where the proposed scheme is not adopted.

Relay Beamforming Design with SIC Detection for MIMO Multirelay Networks with Imperfect CSI

In this paper, we consider a dual-hop multiple-input-multiple-output (MIMO) wireless multirelay network, in which a source-destination pair, both equipped with multiple antennas, communicates through multiple half-duplex amplify-and-forward (AF) relay terminals, which are also with multiple antennas. Since perfect channel-state information (CSI) is difficult to obtain in a practical multirelay network, we consider imperfect CSI for all channels. We focus on maximizing the signal-to-interference-plus-noise ratio (SINR) at the destination. We propose a novel robust linear beamforming at the relays, based on the QR decomposition filter at the destination node, which performs successive interference cancellation (SIC). Using the law of large numbers, we obtain the asymptotic rate in the presence of imperfect CSI, upon which the proposed relay beamforming is optimized. Simulation results show that the asymptotic rate matches with the ergodic rate well. Analysis and simulation results demonstrate that the proposed beamforming outperforms the conventional beamforming schemes for any power of CSI errors and SNR regions.