Relay Users Research Articles

A novel scheduling framework for QoS-aware OFDMA resource allocation in a network with small relay cells and macro users

Relaying is a convenient way to provide full coverage in cellular networks. In particular, small relay cells can be used as a cost-effective solution for indoor coverage in MIMO–OFDM systems. The small relay cells would need to cater for indoor users’ quality of service (QoS) expectations. One key QoS objective is delivering stable data rates for multimedia applications, which we refer to as guaranteed data rates. In this article, we consider optimization for delivering guaranteed data rates in a network with multiple relays and a macro base station, in a scenario when there are both macro users and relay users to be served. A novel scheme called cell-guaranteed bit rate by relay scheduling is proposed, with both optimal and heuristic scheduling methods. To perform the optimization we exploit resource block allocation, and parameters such as relaying duration and relay bandwidth allocation. Interference between relays and macro is avoided through time domain orthogonalization. Another key aspect of the scheme is inter-frame scheduling, wherein relay feeder links can be flexibly scheduled in any time slot along with macro users. Performance evaluation is presented using real-time indoor measurement channels and a sample test scenario. Results show the heuristic method can improve performance by 89.47% as compared to round-robin scheduling at relays and is within a 5% gap to optimal scheduling.

Channel Aligned Beamforming in Two-Way Multi-Pair Decode-and-Forward Relay Down-Link Channels

We consider the down-link of multi-pair two-way decode-and-forward (DaF) relay channel with multiple antennas at all the nodes. We propose schemes composed of relay pre-coder and user receive beam-formers to support 2M degrees of freedom when M antennas are employed at the relay. A channel aligning technique, where the channel vectors of a pair are forced to be aligned, is introduced so that we can use, at the relay, the well-known pre-coder like zero forcing (ZF) or the regularized channel inversion (RI) from the cellular down-link channels. Alternation based optimization of the pre-coder and the beam-formers searches the channel aligned vector space to further enhance the performance of the scheme in the low and mid SNR range.

Energy- and Cost-Efficient Mobile Communication Using Multi-Cell MIMO and Relaying

In this paper, relaying and multi-cell MIMO transmission are investigated as approaches for improving resource reuse and more flexible organization of cellular networks. The analysis focuses on approaches for future cellular systems, which jointly exploit relaying and multi-cell MIMO transmission. Possible candidate approaches are identified, simplified for practical applications and evaluated using a system-level model from the European research project WINNER. Their achievable throughput is analyzed under practical constraints using three different normalization approaches: cost-normalization, energy-normalization, and joint cost-energy-normalization. It can be shown that the combined approach of relaying and multi-cell MIMO provides significant gains for the uplink communication. The selected approach exploits cooperative multi-cell MIMO processing between base stations and relay nodes, and uses a resource coordination technique on the links between relay nodes and user terminals. If a relay-based deployment is subject to a cost- and energy-normalization, multi-cell MIMO outperforms relaying with respect to achievable downlink throughput.

Bit Concatenation Based User Relaying in MIMO Broadcast Channels

A novel user relaying scheme based on bit concatenation is proposed for multiple-input multiple-output (MIMO) broadcast channels. In a broadcasting phase, a part of information for a destination user is concatenated to data for a relaying user and transmitted to the relaying user. The destination user receives the part of information via the relaying user in a relaying phase in addition to the data in the broadcasting phase. An achievable rate region for the proposed scheme is derived and an algorithm to characterize the boundary of the rate region is proposed. Our analysis shows that the proposed user relaying in a MIMO BC expands the achievable rate region for the zero-forcing dirty paper coding (ZF-DPC) in the MIMO BC without relaying. It is also shown that the proposed user relaying scheme always outperforms a superposition coding (SC) based user relaying scheme. Optimal and suboptimal user pair scheduling algorithms are investigated for a two-user MIMO BC and the proposed suboptimal user pair scheduling scheme is shown to approach the optimal scheduling when the relaying channel gain is large.

Energy Efficient Cooperative Multicast Scheme Based on Selective Relay

Multicast communication has been researched for many years in efforts to simultaneously achieve high throughput and good fairness, which have a trade-off relationship. Recently, a cooperative multicast scheduling scheme was proposed. It is considered a promising solution owing to its trade-off characteristics realized by promoting user cooperation among group members. However, it requires significant relay power consumption for user cooperation, since all group members in a good channel condition should relay without checking whether there is at least one user requesting a relay in the transmission boundary. Therefore, in order to resolve this inefficiency, we proposed an energy efficient cooperative multicast scheme (EECM) based on selective relay. We can achieve reduced unnecessary relay power expenditure by selecting relay users with consideration of the condition of nearby users. The performance results derived from a numerical analysis reveal that the proposed scheme requires less energy consumption than the existing solution with almost the same throughput performance.

Research on Cooperative User Relaying Assisted Load Balance Scheme in OFDMA Networks

In OFDMA networks with the frequency reuse factor equaling to one, such as LTE networks, handover based load balance is a commonly used scheme for balancing the unevenly distributed traffic among different cells in order to improve the spectrum utilization. However, edge users shifted from the heavy-loaded cell to the light-loaded cell usually suffer from SNR degradation. In this paper, a user relaying assisted load balance scheme is proposed to overcome this problem. In the proposed scheme, the shifted user can select another user in the light-loaded cell as the relay node for cooperative transmission. By selecting the appropriate ‘user relay’, the SNR degradation can be effectively avoided. In the paper, an analytical model is developed, the necessary condition of the cooperative user selection is analyzed and the optimal user selection criteria for capacity maximization are derived. Numerical results show that the derived cooperative user selection criteria can increase the shifted users’ maximum average mutual information which indicates the SNR degradation problem has been solved.

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.

Research of User Access Problem with Source Users and Relay Users in a Relay Cooperative Network

Research of User Access Problem with Source Users and Relay Users in a Relay Cooperative Network

On the Sum-Rate of Uplink MIMO Cellular Systems with Amplify-and-Forward Relaying and Collaborative Base Stations

Cooperation and relaying are emerging technologies as flexible solutions for improving the capacity of cellular systems. Motivated by this, we investigate the asymptotic achievable sum-rate for multiple-input multiple-output (MIMO) multiple-access cellular systems in the uplink employing cooperative base stations (BSs) and amplify-and-forward (AF) relaying. In our model, the antennas at the user equipments (UEs), relay terminals, and BSs are correlated and there are direct links between UEs and BSs. Using the replica method, we derive the large-system sum-rate for the uplink system using joint optimal decoding (JOD) as well as separate detection and decoding (SDD) and show that each UE's performance can be characterized by a vector Gaussian channel with an appropriate vector input, an effective channel gain, and a vector Gaussian noise. Based on the asymptotic result, we also devise an efficient algorithm to determine the asymptotic optimum transmit matrices for the UEs and relays that can maximize the sum-rate of the MIMO multiple-access cellular network if the spatial channel covariance information (CCI) is available and exploited at the UEs and the relay terminals.

Effective capacity for interference and delay constrained cognitive radio relay channels

This paper investigates delay constrained performance of a cognitive radio relay network when the cognitive (secondary) user transmission is subject to satisfying spectrum-sharing restrictions imposed by a primary user. The primary user allows a secondary user to gain access to its allocated spectrum band as long as certain thresholds on the interference power, on the peak or average values, inflicted on the primary receiver are not exceeded by the transmission of the secondary users. In addition, we assume that the secondary transmitter benefits from an intermediate node, chosen from K terminals, to relay its signal to the destination. Considering that the transmission of the secondary user is subject to satisfying a statistical delay quality-of-service (QoS) constraint, we study the maximum arrival rate of the secondary user's relay link while the interference limitations required by the primary user are satisfied. Particularly, we obtain the effective capacity of the secondary network and determine the power allocation policies that maximize the effective capacity of the secondary user's relaying channel. In addition, we derive closed-form expressions for the effective capacity of the channel in Rayleigh block-fading environment under peak or average interference-power constraints. Numerical simulations are provided to endorse our theoretical results.

Resource Allocation and Relay Selection for Collaborative Communications

We investigate the relay selection problem in a network where users are able to collaborate with each other; decode and forward the messages of each other along with their own messages to the destination. We study the performance obtained from collaboration in terms of (1) increasing the achievable rate, (2) saving the transmit energy, and (3) reducing the resource (time-bandwidth) requirement. To ensure fairness, we assume that the transmit energy to the rate ratio is fixed for all users. We allocate resource optimally for the proposed collaborative protocol (CP) and compare the result with the non-collaborative protocol (NCP) where users transmits their messages directly to the destination. The collaboration gain allows us (1) to decide whether to collaborate or not and (2) to select one relay among the possible relay users. We show that a considerable gain can be obtained if the direct source-destination channel gain is significantly smaller than those of alternative links. We demonstrate that a rate and energy improvement of up to (1+ n?(k/k+1)) can be obtained, where ? is the environment path loss exponent and k is the ratio of the rates of involved users. We also show that the collaboration is only beneficial for the middle range rate ratio.

Research on improving the QoE of relay users in cooperative communication systems

Customers' satisfaction with services is reflected by quality of experience (QoE). Insofar, most studies on cooperative communication have been focused on improving the QoE of source users. However, the improvement of a source user's QoE is obtained at cost of degradation of the relay user's QoE. On the other hand, cooperative communications can achieve performance similar to that of a conventional multiple-input multiple-output (MIMO) system by forming virtual MIMO arrays. Hence, to improve the QoE performance of relay users, this article proposes the concept of a belief threshold at the destination user and a new cooperative scheme based on the belief threshold destination (BTD) technique, while without decaying the BER performance of the communication system.

Studies for the design of the Wendelstein 7-X Thomson Scattering polychromators

The aim of the Thomson scattering system is the measurement of electron temperature and density profiles with high time and spatial resolution. The whole Thomson scattering optical system is optimized to minimize losses of scattered light with wavelengths from 700 nm up to 1064 nm. A five-channel polychromator serves as spectral analyzer of the scattered light. The light is carried to the polychromator input via fiber bundles of 3 mm diameter. High performance dielectric interference filters will be used for spectral analyzing. Their transmission curves will be chosen according to the range of electron temperature that is supposed during W7-X operation (from 10 eV up to 10 keV). The design of the polychromator must be optimized for a high throughput and size compactness. The article describes three possible polychromator setups. The main difference between these designs is the usage of relay and field lenses. The optical properties of the designs will be derived both by measurements and by simulations. Limitations considering high Numerical Aperture (N.A.) and fiber bundle size are discussed.

A comparison of TDMA, dirty paper coding, and beamforming for multiuser MIMO relay networks

A two-hop multiple-input multiple-output (MIMO) relay network which comprises a multiple antenna source, an amplify-and-forward MIMO relay and many potential users are studied in this paper. Consider the achievable sum rate as the performance metric, a joint design method for the processing units of the BS and relay node is proposed. The optimal structures are given, which decompose the multiuser MIMO relay channel into several parallel single-input single-output relay channels. With these structures, the signal-to-noise ratio at the destination users is derived; and the power allocation is proved to be a convex problem. We also show that high sum rate can be achieved by pairing each link according to its magnitude. The sum rate of three broadcast strategies, time division multiple access (TDMA) to the strongest user, dirty paper coding (DPC), and beamforming (BF) are investigated. The sum rate bounds of these strategies and the sum capacity (achieved by DPC) gain over TDMA and BF are given. With these results, it can be easily obtained that how far away TDMA and BF are from being optimal in terms of the achievable sum rate.

Digital relay reports verify power system models

Protective relays continuously monitor the power system to detect abnormal conditions, such as short circuits, that could be damaging to equipment or to the integrity of the system as a whole. They initiate corrective actions (often tripping circuit breakers) to remove the smallest possible portion of the electric system to isolate faulted equipment and allow the remaining part of the system to continue to generate and deliver power. The relay engineer uses "fault studies", or models of the power system operating under normal and short-circuit conditions, to determine what parameters should be measured and what relay settings should be used to discriminate reliably between acceptable and unacceptable system conditions. Like all models, the usefulness of fault study models depends on their validity and accuracy. This article encourages digital relay users to look more closely at their records of disturbances. In addition to the normal use of checking relay performance, these records can also be used to check the accuracy of the power system model.

Frame Relay to ATM interworking

Frame Relay is a well-established technology that has attracted a large number of customers world-wide. It is typically used to interconnect large, multi-site company local area networks (LANs). These data connections are usually at low to medium speeds. Asynchronous transfer mode (ATM) is a newer, broadband technology that is capable of very high speed LAN interconnection. In addition, it is arguably an ideal transport medium for legacy protocols such as Frame Relay.This paper describes the data transport features of each technology and discusses how ATM may be used to interconnect existing Frame Relay networks, and how an ATM user may exchange data with a Frame Relay user.

Proposed statistical performance measures for microprocessor-based transmission-line protective relays. I. Explanation of the statistics

The paper presents practical calculations and novel techniques for collecting performance data from protective relays. The methods are focused on, but not limited to, microprocessor-based transmission line relaying systems. Standard definitions are presented for availability, dependability, security, hardware MTBF, relaying MTBF, repair time, and other measures of interest for specific relay types. The paper explains the novel concept of exposures, the key to a standardized security measure. With these standard measures, relay users will be able to compile the first consistent industry-wide data base for relay performance assessment.

Proposed Statistical Performance Measures for Microprocessor-Based Transmission-Line Protective Relays, Part 1: Explanation of the Statistics

The paper presents practical calculations and novel techniques for collecting performance data from protective relays. The methods are focused on, but not limited to, microprocessor-based transmission line relaying systems. Standard definitions are presented for availability, dependability, security, hardware MTBF, relaying MTBF, repair time, and other measures of interest for specific relay types. The paper explains the novel concept of exposures, the key to a standardized security measure. With these standard measures, relay users will be able to compile the first consistent industry-wide data base for relay performance assessment.

ANALISA PROTEKSI HILANG EKSITASI PADA GENERATOR SINKRON DI PLTGU MUARA TAWAR GT UNIT 1.3

One of the operating disruptions that occur in the synchronous generator is the loss of excitation. Where this interference will cause the generated reactive power generator is reduced even lost so that the synchronous generator must absorb the reactive power of the system. If this condition occurs continuously can cause damage to the stator coil, will occur worsening insulation and the stator end iron so as to cause short circuit, or interruption of soil relations in the future. So to anticipate the impact of such disturbances required a protection system. The protection system used in PLTGU Muara Tawar GT unit 1.3 is a minimum reactance relay. This jurnal discusses how to determine the value of loss excitation protection setting using minimum reactance relay and offset relay mho so that synchronous generator can work optimally. From the research calculation the minimum reactance relay usage will work on XA-setting value zone (-2.55 p.u) with 0.5 seconds delay time, XB-setting (offset) of -0.1156 p.u with 0.5 seconds delay time. As for offset relay mho will work on zone 1 and zone 2 for offset value of -0.109 p.u with delay time 0.1 second. As for zone 1 for the base impedance ( ) of -1.0 p.u with a delay time of 0.1 seconds and zone 2 synchronous reactance value ( of 2.423 p.u with a delay time of 0.5 seconds. From those results it is considered sufficient to detect the loss of excitation in the synchronous generator.

Broadcasting Developments Now Taking Place

New developments in broadcasting in the past 20 years are treated from the general allocations development viewpoints including regulatory aspects and the evolution in the broadcast standard, frequency modulation, and television station industry. The prospects for compatible single sideband modulation techniques in standard broadcasting, developments in FM stereo regulations and experimental techniques in the color television field are explored. Brief treatment is accorded the horizon subject of extra terrestrial satellite relay usage in broadcasting as well as the currently developed backbone of international broadcasting. References are included to fundamental explorations of several government-industry engineering committees including the Television Allocations Study Organization, technical study papers issued under the auspices of the Chief Engineer of the Federal Communications Commission, and studies carried on by broadcasters, network organizations, and manufacturers.