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Recently, a number of empirical models have been introduced in the literature for the behavior of direct path used in the design of algorithms for RF based indoor geolocation. Frequent absence of direct path has been a major burden on the performance of these algorithms directing researchers to discover algorithms using multipath diversity. However, there is no reliable model for the behavior of multipath components pertinent to precise indoor geolocation. In this dissertation, we first examine the absence of direct path by statistical analysis of empirical data. Then we show how the concept of path persistency can be exploited to obtain accurate ranging using multipath diversity. We analyze the effects of building architecture on the multipath structure by demonstrating the effects of wall length and wall density on the path persistency. Finally, we introduce a comprehensive model for the spatial behavior of multipath components. We use statistical analysis of empirical data obtained by a measurement calibrated ray-tracing tool to model the time-of- arrival, angle-of-arrival and path gains. The relationship between the transmitter-receiver separation and the number of paths are also incorporated in our model. In addition, principles of ray optics are applied to explain the spatial evolution of path gains, time-of-arrival and angle-of-arrival of individual multipath components as a mobile terminal moves inside a typical indoor environment. We also use statistical modeling for the persistency and birth/death rate of the paths.

Our increased reliance on localization devices such as GPS navigation has led to an increased demand for localization solutions in all environments, including indoors. Indoor localization has received considerable attention in the last several years for a number of application areas including first responder localization to targeted advertising and social networking. The difficult multipath encountered indoors degrades the performance of RF based localization solutions and so far no optimal solution has been published. This dissertation presents an algorithm called Coherent Array Reconciliation Tomography (CART), which is a Direct Positioning Algorithm (DPA) that incorporates signal fusion to perform a simultaneous leading edge and position estimate for a superior localization solution in a high multipath environment. The CART algorithm produces position estimates that are near optimal in the sense that they achieve nearly the best theoretical accuracy possible using an Impulse Radio (IR) Ultra-Wideband (UWB) waveform. Several existing algorithms are compared to CART including a traditional two step Leading Edge Detection (LED) algorithm, Singular value Array Reconciliation Tomography (SART), and Transactional Array Reconciliation Tomography (TART) by simulation and experimentation. As shown under heavy simulated multipath conditions, where traditional LED produces a limited solution and the SART and TART algorithms fail, the CART algorithm produces a near statistically optimal solution. Finally, the CART algorithm was also successfully demonstrated experimentally in a laboratory environment by application to the fire fighter homing device that has been a part of the ongoing research at Worcester Polytechnic Institute (WPI).

The Internet has become one of the most widely used forms of communication available. Many applications used on the Internet require the user to interact constantly with the network. For example web browsing where the user will expect the browser to respond quickly, to finish loading pages quickly and to do all of this at an equal level for all users. The network's performance is dependant on the protocols it uses and how the resources of the network are distributed. This is why TCP (Transmission Control Protocol) is one of the most important protocols, because it controls the amount of data entering the network and provides reliability to most interactive applications. The thesis starts by introducing a basic TCP model which is later extended to model the effects of burstiness produced by TCP. Burstiness can cause a routers buffer to unnecessarily overflow. These overflows cause TCP connections to under-utilise link bandwidth because of unnecessary packet retransmissions. A model to define a quantitative measure of both burstiness and throughput of a system of TCP connections is introduced. The model gives insight into how the TCP protocol causes burstiness and can be used to find scenarios where burstiness is decreased. This helps to improve the utilization of links by reducing the burstiness of protocols. An important performance metric for interactive traffic is user perceived delay, the delay that an end user would encounter when using an application. An example of user perceived delay is the time a user waits before a HTML web page starts loading. The retransmission delays are the most important type of delay for interactive traffic because they are usually very large. A dynamic priority RED Queue (DPRQ) is introduced which changes the priority of the queues based on the goodput (throughput of succesfully transmitted packets) threshold of the interactive traffic. Using dynamic priority allows packet loss to be reduced by up to eight times for interactive traffic, which intern reduces retransmission delay. Fairness measures how equally network resources are allocated amongst different connections. When a link with TCP connections is overloaded each connection on the link will reduce its throughput to allow all the connections to have approximately equal load. This does not take into account that other links may be under utilized. The fairness issue is addressed by introducing Multipath TCP (MATCP) which allows path selection to occur at the TCP layer. This allows each unique flow to take a different path, instead of all the flows of one source using the same path. Using MATCP, a finer grain of load-balancing can be achieved and the complexity and state required in the network is greatly reduced. Two analytic models are provided in chapters three and four, which investigate slow start and TCP burstiness. In chapter five the DPRQ queue is introduced to reduce user perceived delay. An analytic model of the DPRQ is provided and verified through experimental simulation. In chapter six an analytic model of Multipath TCP is provided, which is also verified by simulation.

As multiprocessor system size scales upward, two important aspects of multiprocessor systems will generally get worse rather than better: (1) interprocessor communication latency will increase and (2) the probability that some component in the system will fail will increase. These problems can prevent us from realizing the potential benefits of large-scale multiprocessing. In this report we consider the problem of designing networks which simultaneously minimize communication latency while maximizing fault tolerance. Using a synergy of techniques including connection topologies, routing protocols, signalling techniques, and packaging technologies we assemble integrated, system-level solutions to this network design problem.

The low latency is a prime concern for large Network-on-Chips (NoCs) typically used in chip-multiprocessors (CMPs) and multiprocessor system-on-chips (MPSoCs). A significant component of overall latency is the serialization delay for applications which have long packets such as typical video stream traffic. To address the serialization latency, we propose to exploit the inherent path diversity available in a typical 2-D Mesh with our two novel router architectures, Dual-path router and Dandelion router. We observe that, in a 2-D mesh, for any source-destination pair, there are two minimal paths along the edges of the bounding box. We call it XY Dimension Order Routing (DOR) and YX DOR. There are also two non-minimal paths which are non-coinciding and out of the bounding box created by XY and YX DOR paths. Dual-path Router implements two injection and two ejection ports for parallel packet injection through two minimal paths. Packets are split into two halves and injected simultaneously into the network. Dandelion router implements four injection and ejection ports for parallel packet injection. Packets are split into smaller sub-packets and are injected simultaneously in all possible directions which typically include two minimal paths and two non-minimal paths. When all the sub-packets reach the destination, they are eventually recombined. We find that our technique significantly increases the throughput and reduces the serialization latency and hence overall latency of long packets. We explore the impact of Dual-path and Dandelion on various packet lengths in order to prove the advantage of our routers over the baseline. We further implement different deadlock free disjoint path models for Dandelion and develop a switching mechanism between Dual-path and Dandelion based on the traffic congestion.

In this thesis, the blind phase estimator algorithms are studied, including Histogram Algorithm (HA), Modified Histogram Algorithm (MHA), Maximum Likelihood (ML), 4th power-law and modified 4th power-law to compare their performance under quadrature amplitude modulation and additive white gaussian noise(AWGN) channel. Owing to the development of wireless communication, I used the fading channel of wireless communication and studied the performance of all algorithms again. After differential encoding and quadrature amplitude modulation, signals enter additive white gaussian noise(AWGN), constant phase offset and fading channel. At receiver, I use the above estimator to find the phase offset. If there is not line of sight under fading channel, all estimators performance are not good from simulation results, if there is a strong line of sight, all estimators performance are good and approximate to the AWGN channel.

OFDM-based WLAN systems are originally used for nearly static environment. But in the trend of user-convenience, if we want to support mobility, the most important issue is the Doppler effect caused by the object velocity. We investigate how the Doppler effect, signal-to-noise ratio (SNR) and imperfect estimation of channel impulse response (CIR) and the maximum Doppler shift fd influence the final bit error rate (BER) under the simulation environment, modified WLAN 802.11a specification. For these effects, we give some simulation results and conclusions. If CIR and df are known with the same number of multipath, we can see some phenomenon. First, the BER is dominated by AWGN noise. Second, under the same channel delay spread, the higher the object velocity is, the more serious the BER is. Third, under the same the object velocity, the more serious the BER is. If CIR is known instead of fd, under the same error percentage of fd and the same number of multipath, the lesser the velocity is the lesser the BER curve changes. If fd is known instead of CIR with the same number of multipath, the longer the channel delay spread is, the more serious the BER is.

A review of adaptive decorrelating detector techniques for direct-sequence code division multiple access (CDMA) signals is given. The goal is to improve CDMA system performance and capacity by reducing interference between users. The techniques considered are implementations of multiuser receivers, for which background material is given. Adaptive algorithms improve the feasibility of such receivers. An adaptive multiuser receiver for CDMA system has been proposed to increase system capacity. The adaptive decorrelator can be used to eliminate interference from known interferers, though it is prone to noise enhancement. However the receiver is basically designed for synchronous CDMA over AWGN channels. In order to confirm the robustness of the receiver for the asynchronous cases, experimental evaluations are displayed when the relative user delays are small compared to the symbol duration and when the channel is Rayleigh multipath fading as in micro-cellular scenarios. In addition to the efficient implementation of the decorrelating detector of [1], the receiver also can be adapted to incorporate decision feedback. Successive interference cancellation techniques reduce interference by cancellation of one detected signal from another. And an efficient incorporation of decorrelator with RAKE and (DF) decision feedback receiver for frequency-selective Rayleigh fading multipath channels is also proposed. Performance evaluation of the detector via computer simulation scenarios is conducted to substantiate it's potential for real-time operation.

In this thesis, we take an application of multiple symbol differential detection (MSDD) technique in direct-sequence code division multiple access (CDMA) system. It is well- known that MSDD is an effective noncoherent demodulator which outperform the conventional M-ary differential phase shift keying (MDPSK) in additive white Gaussian noise (AWGN) channel. Take MPSK demodulator into consideration, the performance of MSDD based on noncoherent demodulation approaches the performance of coherent demodulation. However, there is little research about MSDD in frequency-selective fading channel. We are now combining the MSDD and Rake receiver to be the signal demodulator. In conventional, there are two kinds of Rake receivers. One is coherent demodulator. Another is noncoherent demodulator. For coherent demodulation, it needs to have channel estimation at each path. The advantage is that the performance will be improved. On the other hand, the disadvantage is complexity and operation will increase. On the contrast, for noncoherent demodulation, it is the performance degradation and complexity simplification. In this thesis, We suggest a multiple symbol differential detection on Rake receiver for CDMA system. From our computer simulation, only for hard decision, the performance is improved and the improvement is proportional to the number of multipath and the number of the length of multiple symbol. This will not happen in conventional MDPSK. However, from our observation, the improvement of performance is degrading as the number of multipath increase. Thus, we employee the technique of Viterbi decoding differential detection (VDDD) to demodulate the differential sequence. By the property of decision interval, the VDDD can obtain additional improvement.