In 14th August 2003, the Northeast USA suffered its worst power outage event in history. The power disturbance spreading through the system caused mal-trips of the distance relay remote back-up protections, which indeed contributed to the power outage cascading a wide area. The power outage in the Northeast USA was constrained by the presence of HVDC interconnections between the HVAC networks in Ontario and New York. The system collapse did not progress beyond the HVDC interconnection interface with Quebec. The HVDC link can regulate the voltage and current therefore impacts on the performance of the protection and system stability. The distance relay mal-operations were one of the main cause of the Northeast USA blackout as well as the other recent major large area blackouts which were pointed out by the previous papers. This thesis is focus on investigate how HVDC interconnections contribute to maintaining the power system stability. The research work investigated the performance of a distance relay to faults and disturbance on networks containing HVDC interconnection. The research work was carried out by modelling and testing a classic signal processing distance relay in a simple AC network which was based on Kunder’s two areas system using MATLAB/SIMULINK at first. Then the modeled distance relay’s performance was investigated by combining the distance relay and a simple HVDC link based on the Kunder’s two areas system. The research work firstly combined the signal processing distance relay and the HVDC link together to investigate the distance relay’s performance when the protected feeder containing DC link. The distance relay’s performance was investigated when the protected feeders containing HVDC link under fault conditions and power swing conditions. For comparison, a similar power system without HVDC link was also simulated.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Reliable System Services Corporation (RSS Corp.) presents the feasibility of a low cost, low power, high capacity, robust RF Communications Network using SATCOM and UAV relays. The developed architecture will be suitable for OTH Large Area Test and Training exercises as well as applications for OTH Digital Battlefield scenarios. A specific application is shown for the planned Littoral Combat Ship (LCS) missions, although the developed architecture will have broader applications for any surface combatant requiring an Over-the-Horizon (OTH) data link to distributed players and sensors. A conceptual design for the IP network radio system will implement RSS Corp. developed secure IRIDIUM global full duplex data links and Harris Corp. developed long range high bandwidth 802.11 full duplex data links. The results will be significant, and the developed system could be a cornerstone of the future digital battlefield combat communications architecture. The developed technology will also have significant use in any application for Test, Evaluation and Training Ranges requiring net centric, command/control and wide bandwidth TLM data collection from distributed remote players and sensors.

International Telemetering Conference Proceedings / October 26-29, 1987 / Town and Country Hotel, San Diego, California / Engineering requirements and design characteristics of the coherent throughput relay system which supports East Coast pre-launch checkout of NASA's Space Shuttle and its Payloads are presented. The Relay system is required to provide communications through NASA's Tracking and Data Relay Satellite System for the Shuttle and Payload-Users while they are encapsulated in the launch preparation facilities at the John F. Kennedy Space Center and the Eastern Test Range, Florida. The Relay system is required to be transparent to its users' data at all rates up to three MB/s at S-band and 300 MB/s at Ku-band. Noise and group-delay distortion are major contributors to wide band RF signal degradation. These were major factors in the Relay system design. Antenna design, pointing angle and location were constrained by the need to maximize end-to-end RF signal isolation at both S-band and KU-band, simultaneous forward and return frequencies. System characteristics and link analysis are also presented. In addition, a similar Data Relay located at Vandenberg Air Force Base is briefly described.

International Telemetering Conference Proceedings / October 17-20, 1988 / Riviera Hotel, Las Vegas, Nevada / This paper discusses one approach to determine a characteristic of West - Java's air and ground segment as a block-box to accomodate radio waves propagation, especially in L-band ranges, by evaluating both the topographical data and radio reception pattern as measured from ground based telemetry receiving-end system. All the measured signals are random and assumed to be stationair and ergodic. In order to characterize the channel for polarization diversity reception, some statistical analysis are applied to the signal strength measured of both - RHCP and LHCP components of 1531 MHz propagated waves as transmitted fr om NC212-200 PK-NZJ-aircraft. Some computer calculated correlograms of measured data are shown herewith, it is focused for a certain radio corridor at radial 265E relative to the ground based receiving antenna. More over some curves of predicted multipath gain factor are also presented to gain more theoretical back ground. When this paper is written, a further field experiments on the matter concerned is beeing conducted.

In this thesis, we address the statistics of mutual information of amplify-and-forward (AF) multiple-input multiple-output (MIMO) two-hop relay channels, where the source terminal (ST), relay terminal (RT) and destination terminal (DT) are equipped with a number of correlated antennas and there is a line-of-sight (LOS) component (Rician fading) of each link. To the best of our knowledge, deriving analytical expressions for the statistics of mutual information of the relay channel is difficult and still unsolvable. To circumvent the mathematical difficulties, we consider this problem under the large-system regimen in which the numbers of antennas at the transmitter and receiver go to infinity with a fixed ratio. In the large-system regimen, this thesis has made the following contributions: 1) We get the mean and the variance of the mutual information of the concerned relay channel. 2) We show that the mutual information distribution converges to the Gaussian distribution. The analytical results are derived by mean of two powerful tools developed in the context of theoretical physics: emph{saddle-point approximation} and emph{superanalysis}. The derived analytical results are very general and can degenerate to several previously results as special cases. From a degenerated case, we realize that the previous result by Wagner {em et al.} cite{Wag-08} is wrong and thus we provide the corrected result. Finally, Simulation results demonstrate that even for a moderate number of antennas at each end, the proposed analytical results provide undistinguishable results as those obtained by Monte-Carlo results.

Cooperative communication is a promising technique to provide spatial diversity in a virtual multi-input and multi-output (MIMO) manner. However, as application evolves toward a more practical situation, realistic constraints and issues such as channel state information (CSI) assumption must be accounted when developing appropriate cooperative schemes. In this thesis, we have addressed delay related problems in both single user pair cooperation (SUPC) and multiple user pair cooperation (MUPC) networks. In SUPC, realizing that the outdated CSI caused by delay between relay selection instant and transmission instant can impair diversity order severely, we propose an opportunistic multiple relay selection (MRS) scheme to achieve desired diversity order and combat the variation of the wireless environment. On the other hand, for multiple user pairs cooperation (MUPC), we start from one of the notable work, two hop opportunistic relaying (THOR), and analyze its the delay related problems. We propose an opportunistic pair scheduling (OPS) scheme which can get rid of the buffer requirement at the relay nodes of THOR and incurs no loss in terms of throughput scaling. Furthermore, we extend OPS to a general scheduling scheme, $L$ scheduling, which can achieve controllable throughput-and-delay trandeoffs. / Graduate

<p>In this thesis, we consider an amplify and forward half-duplex two-way-relay wireless communication system. For such a system, we estimate the channel information using a particular test signal set. The actual transmitted signal from a normalized square QAM constellation is then detected by choosing the symbol in the QAM constellation closest in distance to it. We derive an error probability which is found to be signal dependent for this system. An optimum design problem under a transmission power constraint based on this signal dependent asymptotic formula is then formulated leading to the optimum transmission power condition. Simulations show that under this optimum power transmission condition the system indeed yields optimum performance.</p> / Master of Applied Science (MASc)

Relay-based cooperation promises significant gains in a wireless network as it provides an inde-pendent path between a source and a destination. Using simple single antenna nodes, it exploits the spatial diversity provided by the geographically separated nodes in a network to improve the robustness of the communication system against fading. Among the cooperative commu¬nication schemes, the amplify-and-forward (AF) relaying scheme is considered to be easy to implement since the relay does not need to decode its received signal. Instead, it just forwards to the destination the signal it receives from the source. We analyze the performance of fixed-gain AF relaying with imperfect channel knowledge that is acquired through an AF relay-specific training protocol. The analysis is challenging because the received signal at the destination contains the product (or cascade) of source-relay (SR) and relay-destination (RD) complex baseband channel gains, and additional products terms that arise due to imperfect estimation related errors. We focus on the time-efficient cascaded channel estimation (CCE) protocol to acquire the channel estimates at the destination. Using it, the destination can only estimate the product of SR and RD complex baseband channel gains, but not the two separately. Our analysis encompasses a single AF relay system and an opportunistic system with mul¬tiple AF relays, among which one is selected to forward its received signal to the destination, based on its SR and RD complex baseband channel gains. For a single relay system, we first de¬velop a novel SEP expression and a tight SEP upper bound. We then analyze the opportunistic multi-relay system, in which both selection and coherent demodulation use imperfect channel estimates. A distinctive aspect of our approach is the use of as few simplifying approximations as possible. It results in a new analysis that is accurate at signal-to-noise-ratios as low as 1 dB for single and multi-relay systems. Further, the training protocol is an integral part of the model and analysis. Using an insightful asymptotic analysis, we then present a simple, closed-form, nearly-optimal solution for allocation of energy between pilot and data symbols at the source and relay(s). Further, the optimal energy allocation between a source and a relay is characterized when both together operate under a sum energy constraint, as has often been assumed in the literature. In summary, the sum total of the results in this work provides a rigorous and accurate performance characterization and optimization of cascaded channel estimation for AF relaying.

With the ever-growing demand for higher data rate in next generation communication systems, researchers are pushing the limits of the existing architecture. Due to the stochastic nature of communication channels, most systems use some form of adaptive methods to adjust the transmitting parameters and allocation of resources in order to overcome channel variations and achieve optimal throughput. We will study four cases of adaptive transmission and dynamic resource allocation in collaborative systems that are practically significant. Firstly, we study hybrid automatic repeat request (HARQ) techniques that are widely used to handle transmission failures. We propose HARQ policies that improve system throughput and are suitable for point-to-point, two-hop relay, and multi-user broadcast systems. Secondly, we study the effect of having bits of mixed SNR qualities in finite length codewords. We prove that by grouping bits according to their reliability so that each codeword contains homogeneous bit qualities, the finite blocklength capacity of the system is increased. Thirdly, we study the routing and resource allocation problem in multiple collaborative networks. We propose an algorithm that enables collaboration between networks which needs little to no side information shared across networks, but rather infers necessary information from the transmissions. The collaboration between networks provides a significant gain in overall throughput compared to selfish networks. Lastly, we present an algorithm that allocates disjoint transmission channels for our cognitive radio network in the DARPA Spectrum Collaboration Challenge (SC2). This algorithm uses the real-time spectrogram knowledge perceived by the radios and allocates channels adaptively in a crowded spectrum shared with other collaborative networks.

Opportunistic selection algorithms have grown in importance as next generation wireless systems strive towards higher data rates and spectral efficiencies. For example, in orthogonal frequency division multiple access(OFDMA), the system bandwidth is divided into many sub channels. For each sub channel, the user with the highest channel gain is opportunistically assigned to it. .Likewise, in a multi-source, multi-destination (MSD) cooperative relay system, a relay node must be assigned for every source-destination (SD) pair. The assignment decisions are based on local channel knowledge and must be fast so as to maximize the time available for data transmission. We develop novel multiple access based splitting-based selection algorithms for OFDMA and MSD systems. These systems are unique in that the same user and relay can be the most suitable one for multiple sub channels and multiple SD pairs, respectively. For OFDMA systems, we propose an algorithm called Split Select that assigns for every sub channel the user with the highest channel gain over it. For MSD systems, we propose a contention-based en masse assignment (CBEA) algorithm that assigns to each SD pair a relay that is capable of aiding it. Both Split Select and CBEA are fast and scale well with the number of nodes. For example, Split Select requires just 2.2 slots, on average, to assign a sub channel to its best user even when there are an asymptotically large number of contending users. Likewise, CBEA often takes far less than one slot, on average, to assign a relay to each SD pair.