Performance Of Relay System Research Articles

Multimode Antenna Selection for MIMO Amplify-and-Forward Relay Systems

Obtaining the most from multiple-antenna relay systems requires algorithms that configure the source and relay adaptively to instantaneous channel conditions. In this paper, we define an antenna selection mode of operation as the number of selected transmit antennas at the source (which is equal to the number of data substreams), the substream-to-antenna mapping at the source, the number of selected transmit antennas at the relay, and the substream-to-antenna mapping at the relay. We develop dualmode and multimode antenna selection algorithms to choose the mode that is most likely to deliver the lowest vector symbol error rate assuming the overall data rate is fixed. The effective condition numbers of both the two-hop channel and the relay channel are derived to give intuition on how the spatial characteristics of the constituent channels affect mode selection and to derive low complexity algorithms. Link-level simulations show that our proposed algorithms usually select the best mode, thus improving the diversity performance of spatial multiplexing relay systems and providing array gains over the existing single-stream relay transmission strategies. The two-hop multimode algorithms are shown by system-level simulations to improve the reliability of transmission and extend spatial multiplexing capability to cell-edge users in a multi-cell network.

Half-duplex relaying with serially concatenated low-density generator matrix (SCLDGM) codes

Recently, the integration of cooperation with coding has proven to be a very useful technique to enhance relay system performance. Relay systems based on low-density parity-check (LDPC) codes have the potential to approach the theoretical information limits very closely. However, LDPC codes have a disadvantage in that the encoding complexity is high. To solve this problem, serially concatenated low-density generator matrix (SCLDGM) codes are attracting attention owing to their low encoding complexity. However, the performance of SCLDGM coded relaying has not been investigated. In this paper, we apply SCLDGM codes to relay channel with the motivation of lowering the encoding complexity. Since SCLDGM codes are concatenated codes, we cannot use the same method as LDPC coded relaying. We propose a new relaying system and three cooperation protocols suited for SCLDGM codes. Computer simulation results show that the bit error rate (BER) performance of the proposed system is equal to that of conventional LDPC coded relaying system.

Frame Resource Allocation Schemes that Improve System Capacity and Latency Performance of Time-Division Duplex Multihop Relay Systems

This paper proposes two novel frame resource allocation schemes: Mixed bidirectional allocation scheme and Offset allocation scheme. They improve system capacity and latency performance unlike the conventional time-division duplex relay scheme which divides the frame structure into time segments for the access zone and time segment for the relay zones as in IEEE802.16j (WiMAX) systems. Computer simulations confirm that the two proposed schemes outperform the conventional schemes in terms of throughput and latency. An evaluation of the offset allocation scheme confirms that it improves the total throughput by about 85%, and reduces latency by about 72%, compared to the conventional schemes.

Performance of OFDM-Based Dual-Hop Amplify-and-Forward Relaying

In this letter, the end-to-end BER performance of a dual-hop OFDM-based relay system is investigated. The relay terminal operates in the amplify-and-forward (AF) mode. We derive the bit error rate (BER) of AF relaying with average power scaling (APS) constraint valid for source-relay link high signal- to-noise ratio conditions. We also study a frequency diversity technique that improves the performance of single antenna AF-APS relaying. The theoretical BER expressions are verified by computer simulations for a 4-QAM modulated OFDM system.

Blackouts and relaying considerations - Relaying philosophies and the future of relay systems

This paper addresses the broad question of relaying philosophies, modes of operation of relays under abnormal system conditions, the categories of their failure modes, and advances made possible by modern technology in computer relays, adaptive relaying, and the use of wide-area measurements for improved protection and the ability to mitigate wide-area outages. It is hoped that this discussion will lead to a dialogue among system planners, relay engineers, and operating personnel to explore the realities of relay system performance under stressed system conditions and to adapt solutions made possible by new technological innovations

A physical laboratory for protective relay education

Undesirable but unavoidable natural events or human errors will occur to disrupt normal power system operation. Engineers must apply protective relay systems for the most probable events based on practical judgment to minimize service interruptions and damage to the equipment. Understanding the performance and limitations of different protective relay systems is vital in their application. One can explain the philosophy of system protection, the basic theory of a protective relay system, and the relay algorithms from classroom sessions and/or computer simulation. However, it is difficult, if not impossible, to evaluate the actual performance and possible misoperation of a relay in the field just through computer simulation or benchtop testing. This paper introduces the usage of the Power System Simulation Laboratory at the Energy Systems Research Center to enhance the teaching and research activities in relay education. A brief description of the laboratory configuration and the design of the relay testing station are presented. Some sample examples to illustrate the use of this facility for undergraduate and graduate education in protective relay systems are also included in this paper.

Applications of microcomputers in power system protection education

The author describes the use of microcomputers to aid instruction in a course on power system protection. The use of the computer is seen in two distinct areas: to promote understanding of relay control; and to aid fault current calculations. The author describes two programs which have been developed specifically for this course, and also discusses the use of a general circuit analysis program for fault current calculations. It is concluded that the use of the computer leads to increased comprehension of the primary course material, which is the design and performance of protective relay systems, the relay settings, and the coordination of the relays. The use of computer animation to demonstrate circuit breaker control and relay-fuse coordination problems is beneficial. >

The performance of digital radio relay systems

This paper outlines some of the different types of digital radio relay systems that are now in worldwide service, identifies the factors which contribute to their performance, and illustrates the performance standards that are currently being achieved. The CCIR performance standards for high capacity digital radio systems are discussed, together with some of the system planning guidelines in current use, and these are compared with worldwide results from a number of system field evaluations. The comparison shows that the CCIR standards can be achieved on established microwave networks, using advanced equipment designs which incorporate diversity and adaptive equalizers to overcome the effects of dispersive fading. The performance and availability of medium and lowcapacity systems are also briefly reviewed, and predictions of non-availability due to rainfall fading are given for some typical systems. The paper concludes that the performance standards for digital radio systems will be in accordance with the highest quality grades required for transmission media in an Integrated Services Digital Network.

Protective Relaying Systems Using Pilot-Wire Channels

This paper has presented a variety of pilot-wire relaying systems. Each has its field of application which is influenced by technical and economic factors, as listed in the previous section. In many cases, particularly where tapped or multiterminal lines are concerned, combinations of the various systems will be necessary for high-speed simultaneous clearing of faults. Experience has indicated that well-designed private-wire circuits are likely to be more reliable than leased circuits. A basic reason for this is the difference in philosophy between communication and power system engineers as to what constitutes a reliable channel. However, given a specific channel, there are no significant differences in the expected reliability of the vanrous relaying systems. The reliability and security of pilotwire relaying can be improved by the following: 1. The use of fault detectors to supervise conventional a-c pilot-wire relay tripping, where their use will not compromise the relay system performance. 2. Supervision of the receiver-relay contact of the transferred-tripping schemes by fault detectors. 3. Channel-failure supervision of the trip circuit with blocking schemes. Table III gives the salient features of the pilot-wire relaying systems described in this paper.

Experimental Transversal Equalizer for TD-2 Radio Relay System

To determine the effect of improved equalization on the performance of TD-2 radio relay systems, an experimental adjustable transversal equalizer has been developed. The equalizer is based on the echo principle as used in transversal filters, and operates in the 60- to 80-mc frequency band. Seven pairs of adjustable leading and lagging echo terms provide flexibility for simultaneous gain and delay equalization. Directional couplers are used for tapping and controlling the echo voltages. Field experiments have shown that system equalization can be improved appreciably by the use of such equalizers.

Performance requirements for relays on unusually long transmission lines

Analysis of fundamental bases of relaying made as part of the engineering for the 270-mile 154-kv interconnection between systems of Nebraska Power Company and Kansas Gas and Electric Company reveals that, of current, phase angle, impedance, and impedance angle, none alone offers satisfactory discrimination among open-circuit, short-circuit, and load conditions. Combination of input-impedance magnitude Z and impedance angle ψ = tan <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> X/R is studied by means of “impedance circle diagrams” of the interconnecting circuit. On these diagrams is charted the dynamic behavior of the interconnected systems during faults and surges of synchronizing power. The desirable areas of trip and no trip are mapped, and general specifications for the performance of relay systems are presented in terms of impedance magnitude and angle, Z ∠ ψ. Thereby full advantage can be taken of all possible synchronizing power inherently available over the interconnection and at the same time faults and approach of out-of-step condition can be recognized properly.

Performance Requirements for Relays on Unusually Long Transmission Lines

Analysis of fundamental bases of relaying made as part of the engineering for the 270-mile 154-kv interconnection between systems of Nebraska Power Company and Kansas Gas and Electric Company reveals that, of current, phase angle, impedance, and impedance angle, none alone offers satisfactory discrimination among open-circuit, short-circuit, and load conditions. Combination of input-impedance magnitude Z and impedance angle ψ = tan−1 X/R is studied by means of “impedance circle diagrams” of the interconnecting circuit. On these diagrams is charted the dynamic behavior of the interconnected systems during faults and surges of synchronizing power. The desirable areas of trip and no trip are mapped, and general specifications for the performance of relay systems are presented in terms of impedance magnitude and angle, Z ∠ ψ. Thereby full advantage can be taken of all possible synchronizing power inherently available over the interconnection and at the same time faults and approach of out-of-step condition can be recognized properly.