Sharif Digital Repository

This paper studies the energy-limited performance of multi-relay networks. Taking the properties of the power amplifiers (PAs) into account, we derive closed-form expressions for the optimal power allocation, the outage probability and the throughput in the cases with a sum consumed energy constraint. Moreover, we analyze the diversity and the multiplexing gains of the PA-aware systems. Finally, we investigate the performance of large-scale multi-relay networks and develop efficient multi-relay systems with low cooperation overhead. The numerical and the analytical results show that the inefficiency of the PAs affects the outage probability and the throughput of the multi-relay systems... 

This paper investigates the performance of a smart distribution system comprised of multi-microgrids during emergency conditions. It also proposes a hierarchical scheme for outage management in such a system to enhance the security of supply during contingencies. This goal is achieved through sharing the available generation and storage capacities among different microgrids. In this regard, at first, a well-organized framework is devised in order to introduce the roles and tasks of each player in operation stage of a multi-microgrids system. Based on this framework, the general optimization model that needs to be evaluated in the proposed outage management scheme is formulated. Then, various... 

This paper proposes a novel optimization based home load control (HLC) to manage the operation periods of responsive electrical appliances, determine several recommended operation periods for nonresponsive appliances, and schedule the charge/discharge cycling of plug-in hybrid electric vehicle (PHEV) considering various customer preferences. The customer preferences are in the format of payment cost, interruption cost, and different operational constraints. The projected algorithm is online, in which household appliances are initially scheduled based on the payment cost, and when the home load is interrupted, the scheduling will be updated to minimize customer interruption cost. Due to... 

In this study, a new two-way relaying scheme based on compute-and-forward (CMF) framework and relay selection strategies is proposed, which provides a higher throughput than the conventional two-way relaying schemes. Two cases of relays with or without feedback transmission capability are considered. An upper bound on the computation rate of each relay is derived, and based on that, a lower bound on the outage probability of the system is presented assuming block Rayleigh fading channels. Numerical results show that while the average sum rate of the system without feedback, named as max-CMF (M-CMF), reaches the derived upper bound only in low SNRs, that of the system with feedback, named as... 

Cognitive radio and cooperative networks are increasingly regarded as revolutionary technologies that utilise the radio spectrum efficiently. In this study, spectrally encoded (spread-time) code division multiple access (SE-CDMA) scheme is proposed as a flexible and adaptable technique for physical layer of cognitive relay networks. All primary and secondary users transmit their signals to a common base station (BS) and then the BS selects one of the cognitive secondary users based on feedback information to relay the primary user's (PU's) data. To study the efficiency of the system, two scenarios are considered. In the first scenario, the secondary users transmit their information using the... 

This study presents an efficient fractional frequency reuse scheme for macrocell network which uses six directional antennas to cover the outer region and analyses the performance. Cross-tier interference between macrocell and femtocell networks leading to throughput and outage probability degradation is a major issue in two-tier networks when femtocells are deployed in co-channel with macrocells. In this study, the received interference from the macrocell network to femtocell network is analysed. Then, based on the degree of received interference, an algorithm for orthogonal resource allocation to femtocells with low cross-tier interference is presented. According to the introduced scheme,... 

Competition in the electric power industry urges utilities to not only reduce the investment costs, but also to reasonably cut the operation and maintenance expenses as much as possible, while keeping both power quality and reliability requirements met. Reliability-centred maintenance (RCM) has been proven to be in response to this dilemma in power systems and has been yet successfully applied in various engineering contexts. This study introduces a novel approach, as of the first steps of RCM implementation in composite power generation and transmission systems, to identify the critical components for the main sake of a more focused maintenance management. Criticality evaluation is, here,... 

Distribution automation (DA) application for fault management in the electricity distribution networks is one of the main potential remedial actions to reduce customers' outage times and hence improve service reliability. As a result, various automation schemes have been developed and introduced in different countries and by different venders. The impacts of implementing a specific automation scheme on reliability indices of a given distribution system can be different from other available automation schemes. For this reason, when comparing the available automation schemes with each other or with the other reliability improvement measures, it is necessary to perform a course of reliability... 

An algorithm for determining optimal reserve capacity in a power market is presented in this paper. Optimization process in the proposed algorithm is based on the cost-benefit trade off. Market clearance is executed with consideration of uncertainties of power system components in an aggregated environment. It is assumed that both generating units and interruptible loads participate in the reserve market. In addition, customers' reliability requirements are considered as constraints for decision making process of ISO. The rendered method considers random outages of generating units and transmission lines and determined outage of interruptible loads and employs Monte Carlo Simulation (MCS)... 

Despite their attractive features, free-space optical (FSO) communications suffer from several challenges in practical deployment; the major of them is fading or scintillation. To overcome such limitations, multiple input multiple output (MIMO) and cooperative techniques have been proposed. Although the promising effects of cooperative transmissions in radio frequency (RF) communications have greatly been investigated, there have not been remarkable researches on cooperative transmissions in FSO communications. In this study, the authors consider a relay-assisted FSO communication and investigate the outage performance of two well-known cooperative protocols, namely amplify-and-forward (AF)... 

A novel orthogonal frequency division multiple access-based cognitive cooperative relaying scheme is proposed in which cognitive users assist primary users (PUs) by relaying their information. Both PUs and cognitive users communicate to a common base station. Based on the received feedback, cognitive users relay data of PUs. Two different schemes of relay assignment and power allocation are considered. Probability of error of PU and outage probabilities of both primary and cognitive users are investigated. Our analyses show substantial improvements in the probability of error and outage probability of PU while the outage probability of the cognitive user does not change significantly. We... 

Distribution automation application for fault management in the electricity distribution networks is one of the main potential remedial actions to reduce customers' outage times and hence improve service reliability. For this purpose, various automation schemes have been developed and introduced in different countries and by different venders. However, the challenge for electric utilities, especially in today's competitive electricity market, is to identify and evaluate potential reliability reinforcement schemes. Accordingly, appropriate schemes must be determined and prioritized for implementation. In this context, reliability cost/worth assessment plays an important role. A comprehensive... 

In the United States electricity market standard, when several transmission service requests (TSRs) are made for a specific pair of power injection/extraction points, the independent system operator (ISO) must allocate the available transmission capability (ATC) associated with the pair to the requests. An ATC allocation must determine the amount of accepted requests as well as the priority of the accepted requests during emergencies. The requests could have different types (recallable/non-recallable), tariffs, and time frames and these factors must be properly considered in ATC allocation. This paper proposes a method for optimal ATC allocation in the planning horizon which incorporates the... 

In this paper, we present a novel and rather simple method for calculating reverse-link outage probability in signal-to-interference ratio (SIR)-based power-controlled direct-sequence code-division multiple access (DS-CDMA) systems. We obtain outage probability for a single-service system using the interference-to-received-signal-power ratio. We extend our method to the multiservice case using the uplink load factor, which is the ratio of the interference to the interference plus noise. Unlike most of the previous works, we employ the 2-D Poisson point process to model the spatial distribution of mobile users in the network coverage area. We approximate the... 

This paper investigates the outage probability and the throughput of relay networks with joint information and energy transfer where the relay harvests energy from transmitted radio-frequency (RF) signal of the source. Considering different power consumption models, we derive the outage probability of the systems for both adaptive and non-adaptive power allocations at the relay. With a total energy consumption constraint at the source, we provide closed-form expressions for the optimal time sharing and power allocation between the source energy and information transfer signals. The analytical and simulation results demonstrate the efficiency of joint energy and information transfer systems... 

In recent years, STT-RAMs have been proposed as a promising replacement for SRAMs in on-chip caches. Although STT-RAMs benefit from high-density, non-volatility, and low-power characteristics, high rates of read disturbances and write failures are the major reliability problems in STTRAM caches. These disturbance/failure rates are directly affected not only by workload behaviors, but also by process variations. Several studies characterized the reliability of STTRAM caches just for one cell, but vulnerability of STT-RAM caches cannot be directly derived from these models. This paper extrapolates the reliability characteristics of one STTRAM cell presented in previous studies to the... 

In this letter, we introduce a decentralized compute-and-forward (DCMF) protocol to solve the rank failure problem in compute-and-forward (CMF) ad hoc multi-user multi-relay networks without a central coordinator. In sufficiently strong inter-relay links, we show that the DCMF scheme can reach the same achievable rate as in the successive centralized CMF (SCCMF), which is a modified version of the previously introduced centralized CMF in using our proposed successive method for a fair comparison. We evaluate the outage probability and rate of the proposed strategy, and compare the results with those of the conventional CMF and decode-and-forward, and the SCCMF  

Reliability of the power distribution unit (PDU) is very important in electrical systems. Since any failure in this unit leads to system failure. A commonly used method for increasing the reliability of a dc PDU is using the redundant modules. If a fault occurs in a voltage regulator of PDU, it is replaced by its redundant module. In conventional redundancy, each dc voltage regulator has its exclusive redundant modules. Therefore, if both a regulator and its redundant modules fail, the system is stopped. It is an important drawback since the exclusive redundant modules of other voltage regulators may not be used, but, the PDU cannot use them instead of faulty regulators. In this paper, the... 

This paper proposes a hierarchical outage management scheme to enhance the resilience of a smart distribution system comprised of multi-microgrids against unexpected disaster events. In this regard, after identifying the main features and requirements for a resilient outage management scheme, an appropriate framework is devised and the roles and tasks of different management entities in a multi-microgrids system are introduced. Based on this framework, the microgrids schedule their available resources in the first stage using a novel model predictive control-based algorithm. In the second stage, distribution system operator coordinates the possible power transfers among the microgrids and... 

This paper deals with the application of Fast Fourier Transform Base Method (FFTBM) with signal mirroring (FFTBM-SM) to assess accuracy of MELCOR code. This provides deeper insights into how the accuracy of MELCOR code in predictions of thermal-hydraulic parameters varies during transients. The case studied was modeling of Station Black-Out (SBO) accident in PSB-VVER integral test facility by MELCOR code. The accuracy of this thermal-hydraulic modeling was previously quantified using original FFTBM in a few number of time-intervals, based on phenomenological windows of SBO accident. Accuracy indices calculated by original FFTBM in a series of time-intervals unreasonably fluctuate when the...