Adaptive Relay Research Articles

Efficient and adaptive resource scheduling in IEEE 802.16j transparent relay networks

Relaying is regarded as a promising technique for enhancing the system throughput and coverage of emerging broadband wireless access networks. While next generation broadband wireless standardization bodies (e.g., LTE-advanced and IEEE 802.16j) have specified the support of relays in general terms, the problem of allocating network resources in an efficient and effective manner remains a challenging issue. In this study, the utility-based resource scheduling optimization problem for IEEE 802.16j transparent relay networks is formulated mathematically and proven to be NP-hard. Two efficient heuristic algorithms, namely Relay Resource Scheduling (RRS) and Adaptive Relay Resource Scheduling (ARRS), are proposed to resolve the resource scheduling problem. RRS maximizes the system utility in networks containing direct and relay mobile stations by exploiting the benefits of optional transmissions. ARRS enhances upon the performance of RRS by adaptively determining the split ratio between the access zone and the transparent zone in the downlink subframe. The computational complexities of both algorithms are shown to be polynomial and proportional to the number of links and subchannels in the network. The simulation results show that the proposed algorithms achieve significantly better throughput and fairness performance than existing schemes such as Partial Proportional Fairness (PPF) and GenArgMAX.

An Adaptive Relaying Scheme for Fuse Saving in Distribution Networks With Distributed Generation

In some situations, utilities may try to “save” the fuse of a circuit following temporary faults by de-energizing the line with the fast operation of an upstream recloser before the fuse is damaged. This fuse-saving practice is accomplished through proper time coordination between a recloser and a fuse. However, the installation of distributed generation (DG) into distribution networks may affect this coordination due to additional fault current contributions from the distributed resources. This phenomenon of recloser-fuse miscoordination is investigated in this paper with the help of a typical network that employs fuse saving. The limitations of a recloser equipped with time and instantaneous overcurrent elements with respect to fuse savings, in the presence of DG, are discussed. An adaptive relaying strategy is proposed to ensure fuse savings in the new scenario even in the worst fault conditions. The simulation results obtained by adaptively changing relay settings in response to changing DG configurations confirm that the settings selected theoretically in accordance with the proposed strategy hold well in operation.

LLR-aware smart link-adaptive strategy for decode-and-forward cooperative communication

Error propagation seriously degenerate the diversity order of Decode-and-Forward (DF) cooperative communication. To address this problem, a novel Log Likelihood Ratio (LLR)-based Link Adaptive Relaying (LAR) is proposed to promote adaption accuracy at relay. The instantaneous Bit Error Probability (BEP) is calculated according to the LLR of the received signals firstly, then based on it, the equivalent Signal-to-Noise Ratio (SNR) is employed to operate dynamic power scaling by relay. It is theoretically proved that the full diversity order can be attained by the scheme. Besides, the power sensitivity is also analyzed. Simulation results show that the proposed scheme outperform the conventional LAR and can achieve full diversity order. Moreover, its strong adaptation to SNR fluctuation is validated.

Round-Robin Relaying With Diversity in Amplify-and-Forward Multisource Cooperative Communications

In this paper, a round-robin-based relay protocol dubbed round-robin relaying with source selection protocol (R3SSP) is proposed to achieve full cooperative diversity in multisource cooperative communication networks. In R3SSP, all the sources transmit their individual information in turn. The relays then forward the messages of some specific sources in a fixed order according to the limited feedback information. Compared with traditional relay selection-based protocols, R3SSP is based on round-robin relaying, thus avoiding relay selection and requiring no specific channel state information feedback. R3SSP can therefore be implemented with lower complexity. Furthermore, the exact and asymptotic expressions of the outage probability are derived. The diversity-multiplexing tradeoff (DMT) performance is also analyzed. Theoretical analysis shows that R3SSP achieves full cooperative diversity and provides better DMT performance than relay selection-based protocols in a system where the number of sources is higher than that of the relays. Based on the DMT analysis, we further propose an adaptive relay activation scheme that is capable of achieving higher DMT by dynamically selecting the number of relays to be activated in the entire network. Simulation results also verify the validity and superiority of R3SSP.

Jointing Adaptive Modulation Relay Selection Protocols for Two-Way Opportunistic Relaying Systems with Amplify-and-Forward Policy

Two novel best-relay selection protocols, the jointing adaptive modulation max---min (AM-MM) protocol and the jointing adaptive modulation maximum harmonic mean (AM-MHM) protocol, are proposed for ...

Power Allocation for Conventional and Buffer-Aided Link Adaptive Relaying Systems with Energy Harvesting Nodes

In this paper, we consider optimal power allocation for conventional and buffer-aided link adaptive energy harvesting (EH) relay systems, where an EH source communicates with the destination via an EH decode-and-forward relay {over fading channels}. In conventional relaying, source and relay transmit signals in consecutive time slots whereas in buffer-aided link adaptive relaying, the state of the source-relay and relay-destination channels {as well as the amounts of energy available at source and relay} determine whether the source or the relay is selected for transmission. Our objective is to maximize the system throughput over a finite number of transmission time slots for both relaying protocols. In case of conventional relaying, we propose an offline and several online joint source and relay transmit power allocation schemes. For offline power allocation, we formulate {a convex optimization problem} whereas for the online case, we propose a dynamic programming (DP) approach to compute the optimal online transmit power. To alleviate the complexity inherent to DP, we also propose several suboptimal online power allocation schemes. For buffer-aided link adaptive relaying, we show that the joint offline optimization of the source and relay transmit powers along with the link selection results in a mixed integer non-linear program which we solve optimally using the spatial branch-and-bound method. We also propose efficient online power allocation schemes for buffer-aided link adaptive relaying. Simulation results show that buffer-aided link adaptive relaying provides significant performance gains compared to conventional relaying but requires a higher complexity for computation of the power allocation solution. We also show that buffer-aided link adaptive relaying is more robust to changes in the EH rate than conventional relaying.

Information Theoretical Optimization Gains in Energy Adaptive Data Gathering and Relaying in Cognitive Radio Sensor Networks

Cognitive radio (CR) technology helps mitigate wireless resource scarcity problem by dynamically changing frequency spectrum, power and modulation type. Opportunistic spectrum access increases the network capability and quality. Recently, CR applied to wireless sensor networks (WSNs) generated the paradigm of cognitive radio sensor networks (CRSNs) overcoming the challenges posed by event-driven traffic demands of WSNs. To realize advantages of CRSN, spectrum and power allocation, and routing must be jointly considered to maximize the information capacity, resource utilization and the lifetime. In this paper, power and rate adaptation problem is analyzed for a multi-hop CRSN in an information theoretical (IT) capacity maximization framework combined with energy adaptive (EA) mechanisms and utilization of sensor data information correlations (ICs). CRSN characteristics, i.e., fast data aggregation, bursty traffic and node failures, are considered. The capacity optimization problem is defined analytically and practical local schemes are presented showing the superiority of objective functions utilizing ICs and EA mechanisms in terms of the resulting maximum information rate at sink, i.e., Rmax, lifetime, and energy utilization. Furthermore, dependence of performance on total bandwidth and various relay energy distributions is explored observing the logarithmic dependence of Rmax on total bandwidth.

Principles of designing adaptive relay systems for stratospheric power transmission

Problems of designing laser power transmission systems in a turbulent atmosphere using relay mirrors mounted on a stratospheric airship are analyzed. It is shown that such a system can be designed using a high-power ground-based ytterbium fiber laser, relay mirrors for transmitting highpower laser radiation, and an adaptive optical system for correcting the phase distortions of laser beams due to atmospheric turbulence. A model of a laser power transmission system was designed and tested under laboratory conditions; the tests confirmed the possibility of correcting atmospheric-turbulence distortions during guiding and high-accuracy stabilization of laser beams.

Two-way denoise-and-forward network coding opportunistic relaying with jointing adaptive modulation relay selection criterions

To improve the performance of the two-way denoise-and-forward network coding opportunistic relaying systems (TW-DNF-OR), two novel best-relay selection criterions are presented, which are the jointing adaptive modulation max-min criterion (AM-MM) and the jointing adaptive modulation maximum harmonic mean criterion (AM-MHM). In the proposed AM-MM and AM-MHM criterions, the effect of the modulation schemes used at both sources is exploited perfectly by integrating the adaptive modulation with the max-min and maximum harmonic mean criterions. On the basis of the proposed AM-MM and AM-MHM criterions, the authors analyse the symbol error probability (SEP) of the TW-DNF-OR systems under independent and non-identically distributed Rayleigh fading channels, and obtain the analytical expressions to the approximate upper bounds of the overall average SEPs. The comparison analyses show that the average SEP of TW-DNF-OR is improved greatly when the proposed jointing adaptive modulation best relay selection criterions are used. Moreover, in certain channel realisations or signal-to-noise ratio regions, the adaptive modulation non-selection TW-DNF-OR systems outperform the conventional best relay selection systems in which the adaptive modulation is not integrated with the best relay selection criterions.

Study of Micro Grid Safety & Protection Strategies with Control System Infrastructures

Microgrids have been proposed in order to improve reliability and stability of electrical system and to ensure power quality of grid. Microgrid consists of low voltage distribution systems with distributed energy resources, such as wind turbine and photovoltaic power systems, together with storage devices. It is essential to protect a micro grid in both the grid-connected and the islanded mode of operation against all different types of faults. This paper describes micro grid protection and safety concept with central control and monitoring unit where multifunctional intelligent digital relay could be used. This central control & monitoring infrastructure is used for adaptive relay settings strategy for micro grid protection. Also operational safety design concept and fault mitigation technique is proposed to ensure confidence in protection system.

Power allocation of cooperative amplify-and-forward communications with multiple relays

Cooperative diversity is one of the most effective ways to mitigate the fading effect of wireless channels and obtain the spatial gain in wireless networks. In this paper, an optimal power allocation (OPA) scheme for a cooperative communication system using the amplify-and-forward (AF) transmit strategy with multiple relay users is proposed by minimizing the bit-error-rate (BER) at the destination under the constraint of the total transmit power of both the source user and the relay users. Simulation results indicate that the proposed power allocation method can achieve significant BER performance improvement than using the equal power allocation (EPA) scheme, while still attains low complexity. The system performance is improved significantly with the increasing of the number of relay users at high signal-noise ratio (SNR). However, at low SNR, the system performance decreases when the relay number increases. Thus, an adaptive relay selection scheme may be used to choose the appropriate relay numbers in different transmission scenarios to provide system performance improvement and keep the power allocation scheme with low complexity.

Diversity-Multiplexing Trade-off in Adaptive Two-Way Relaying

Resource allocation for symmetric half-duplex bidirectional relaying networks is considered. Various decode-and-forward (DF) based relaying strategies that efficiently exploit quantized channel state information (CSI) at the transmitters (CSIT) are investigated. Adapting the number of channel uses for each relaying phase and allocating transmit power based on limited CSIT is shown to result in a significant improvement in the diversity-multiplexing trade-off (DMT). Without a direct link between the sources, power control is instrumental to efficiently exploit CSI feedback from sources to relay, resulting in superior performance that matches corresponding upper bounds in certain cases. With direct links between the sources, it is shown that DF two-way relaying does not suffer from a diversity loss when the multiplexing gain is high, a significant improvement over the dynamic DF protocol for one-way relaying. The best DMT is achieved when each source broadcasts partial CSI to the other nodes in the network, allowing them to adapt their transmit powers.

Third quadrant Nyquist point for the relay feedback autotuning of PI controllers

The original relay feedback autotuning method of Astrom and Hagglund [1] is based on the Nyquist point at the phase angle of −π (the critical frequency). Recently, Friman and Waller [8] showed that the critical frequency is too high to tune PI controllers and proposed an autotuning method that finds a Nyquist point at the third quadrant through the two-channel relay. Here, the method to find Nyquist points in the third quadrant is revisited and adaptive relay feedback method which can be applied to noisy processes is proposed. It is shown that the bandwidths of PI control systems and the first-order plus time delay model identifications support the Nyquist point at the third quadrant. Nyquist points at the third quadrant can be obtained by introducing a filter and hysteresis to the relay feedback loop. However, the filter time constant and the size of hysteresis should be adjusted iteratively because their phase shifts are dependent on the resulting relay oscillation frequency. Simulations show that this adaptive relay feedback method finds a given Nyquist point at the third quadrant accurately under noisy environments and provides excellent PI control systems.

Symbol Error Rate Analysis and Power Allocation for Adaptive Relay Selection Schemes

In this paper, we analyse the symbol error rate (SER) performance of adaptive relay selection schemes (ARS) in a general dual-hop multiple-relay network. Specifically, we provide a closed-form SER expression for ARS which is tight over the whole signal-to-noise ratio (SNR) region. In addition, the derived SER can be readily extended to conventional relay selection schemes, i.e. amplify-and-forward relay selection (AF-RS), perfect decode-and-forward relay selection (PDF-RS), adaptive decode-and-forward relay selection (ADF-RS), and cooperative-maximum-ratio-combining decode-and-forward relay selection (CDF-RS). Transmit power allocation based on the simplified SER is presented to improve the system performance. The analytical results are verified by computer simulations.

A Novel Distributed Simulation Approach in Adaptive Distance Relaying

In this paper, an adaptive distance relaying strategy based on the global network simulation (GNS) concept is presented. The GNS concept is actually a distributed simulation approach (DSA) for piecewise analysis of large-scale power grids using diakoptics and large change sensitivity (LCS) concepts. To set each utility's relays trip settings adaptively in each power system condition, detailed short circuit analysis is run in the GNS environment. It first updates the pre-fault voltage profile across utilities and then modifies their nodal ZBus in such a way to reflect the effect of the whole network in local fault studies performed by individual utilities; hence, presenting an accurate and secure federative approach on a geographically decomposed grid using local information and computational resources. A set of currently experienced rules in distance coordination is outlined and adaptive as well as conventional relay zone settings in each sub-network are calculated based on the selected rules. An efficient easy-to-implement algorithm to consider the effect of zero sequence mutual impedance among parallel lines is also presented and well integrated into the proposed adaptive approach in the GNS environment. The IEEE 14 bus test system and a real version of a large-scale grid with more than 2,600 buses are used to illustrate the characteristics of the proposed adaptive strategy in terms of security and dependability by comparison with conventional distance protection.

Capacity Analysis of Cooperative Relaying Networks with Adaptive Relaying Scheme Selection

In the present paper, the performance of cooperative relaying networks with adaptive relaying scheme selection is analyzed. Cooperative relaying is a new technique to achieve spatial diversity gain by using neighboring stations. However, when multiple stations transmit simultaneously, the number of interference signals increases. Therefore, the introduction of cooperative relaying in radio communication systems does not always increase the network capacity due to the co-channel interference. Therefore, in order to achieve high spectral efficiency, it is necessary to select cooperative relaying or non-cooperative relaying adaptively. Assuming both centralized and decentralized adaptive controls, the spectrum efficiency is evaluated. The performance under decentralized control is evaluated using a game-theoretic approach. Simulation results show that the introduction of cooperative relaying with centralized control always increases the spectral efficiency. On the other hand, Simulation results also show that, when each source selects a relaying scheme independently and selfishly to maximize its own spectral efficiency, the introduction of the cooperative relaying may reduce the spectral efficiency due to the increase in the number of interference signals.

A relay node deployment method for disconnected wireless sensor networks: Applied in indoor environments

In this paper, a 2-D geometric and adaptive relay node deployment method with polynomial-time complexity is proposed to reduce relay nodes for bridging all disconnected node pairs of a wireless sensor network (WSN). In this method, proper locations for placing relay nodes are discovered on a plane, which gives a much larger degree of freedom to compare with the traditional 1-D search algorithm. In this way, the deployed relay node can bridge as many disconnected node pairs as possible around it. Besides, the method can also adapt to radio environments because that a sophisticated propagation model including large-scale path loss, shadowing, and multipath fading effects is used to estimate link connectivity. Simulation result validates its robustness and efficiency compared with the existing relay node deployment methods. The proposed method significantly reduces the total number of relay nodes compared with the related works in all of the investigated indoor environments.

Adaptive Impedance Relay With Composite Polarizing Voltage Against Fault Resistance

As the conventional relay usually takes the bus voltage as a polarizing voltage, its operating characteristic is fixed and cannot adapt to fault resistance. To enhance the capability against fault resistance, based on the compensated voltage changing with fault resistance, a kind of adaptive impedance relay with composite polarizing voltage is presented in this paper. On the other hand, the operating boundary of the adaptive relay may enter into an ldquoinphaserdquo area along with the increase of fault resistance. To prevent the adaptive relay from maloperation in the ldquoinphaserdquo area, a new additional blocking component is also proposed. Both the adaptive relay and the blocking component were all analyzed in the voltage plane and the impedance plane. Theoretical analyses show that both of them have circular characteristics with greater resistive tolerance. The performance of the relay has been demonstrated on a two-source 500-km line 750-kV system.

Local Coordination Based Routing and Spectrum Assignment in Multi-hop Cognitive Radio Networks

Although Cognitive Radio technology brings efficient spectrum usage and effective interference avoidance, it also brings new challenges to routing in multi-hop Cognitive Radio Networks. Firstly, spectrum assignment is required for each hop in routing; secondly, new delay is introduced during multi-frequency scheduling and frequency switching in each node; thirdly, the intersecting nodes serving multi-frequency traffic is easy to be bottleneck in neighborhood region. In this paper, we analysis and model the pernode delay and the path delay in multi-hop Cognitive Radio Network. Then we propose a framework of local coordination based routing and spectrum assignment to solve above problems, which consists of one protocol for routing path and one scheme for neighborhood region. A on-demand Routing and Spectrum Assignment Protocol is proposed to exchange the local spectrum information and interact with multi-frequency scheduling in each node. A local coordination scheme is presented to support flow redirection at an intersecting node and distribute heavy multi-frequency workload to its neighborhood. We prove the correctness and effectiveness of the protocol by thorough simulations, and find that the proposed solution provides good adaptability to varying spectrum distribution. The end-to-end delay when adaptive relay is cooperating with routing protocol outperforms traditional bare-routing solutions.

System-wide Protection

By its very definition, as applied to power system protection, wide-area measurement systems (WAMSs) are a synergistic combination of relays, measuring instruments, control equipment, automation equipment, monitoring equipment, and communication employed to encompass extensive system elements as opposed to the more traditional view of individual equipment or point-to-point protection. The increasing world-wide application of digital devices and high-speed wideband communication and global positioning systems (GPSs) plus the growing acceptance of adaptive relay protection philosophy and practice have dramatically altered the fundamental role of power-system protection.