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In this thesis a new type of ¡§Parallel Combinational CDMA System¡¨ will be introduced. The proposed scheme is one kind of multi-code CDMA systems, which can greatly increase the bandwidth efficiency of a communication system. We also propose a detection method, which in particular suits well the signal detection in a CDMA system based on the parallel combinational architecture. The proposed high bandwidth-efficient CDMA system can be used for any type of wireless communication systems with only a limited increase in hardware complexity, that is the need of a bank of correlator receiver in parallel to perform the signal detection. Both multiple access interference and multipath interference will be considered in the analysis given in this thesis. The study on the subject will also be accompanied by computer simulation, which will be used as a benchmark to the results obtained from the analysis. It is concluded from this thesis that the proposed new type of ¡§Parallel Combinational CDMA System¡¨ has a great potential for the applications in the future wireless communications.

Bandwidth estimation has been extensively researched in the past. The majority of existing methods assume either negligible or fluid cross-traffic in the network during the analysis. However, on the present-day Internet, these assumptions do not always hold right. Hence, over such paths the existing bandwidth estimation techniques become inaccurate. In this thesis, we explore the problem assuming arbitrary cross-traffic and develop a new probing method called Envelope, which can simultaneously estimate bottleneck and available bandwidth over an end-to-end path with multiple heavily congested links. Envelope is based on a recursive extension of the stochastic queuing model first proposed by Kang, Liu, Dai and Loguinov (2004), and a modified packet-train methodology. We use two small packets to surround the probing packet-trains and preserve the inter-packet spacing of probe traffic at each router in the path-suffix. The preserved spacings are then used by the receiver to estimate bandwidth. We first reproduce results for a single congested router case using the model proposed by Kang et al. Next, we extend it to the case of multiple congested routers with arbitrary cross-traffic and develop the methodology Envelope. We evaluate the performance of Envelope in various network path topologies and cross-traffic conditions through extensive NS-2 simulations. We also evaluate various probe-traffic parameters which affect the accuracy of this method and obtain the range of values for these parameters that provide good estimation results. Finally, we compare the bandwidth estimation results of our method with the results of other existing methods such as IGI (2003) , Spruce (2003), Pathload (2002), and CapProbe (June 2004) using simulation in Network Simulator (NS-2) with varied network topologies and cross-traffic.

Bandwidth estimation has been extensively researched in the past. The majority of existing methods assume either negligible or fluid cross-traffic in the network during the analysis. However, on the present-day Internet, these assumptions do not always hold right. Hence, over such paths the existing bandwidth estimation techniques become inaccurate. In this thesis, we explore the problem assuming arbitrary cross-traffic and develop a new probing method called Envelope, which can simultaneously estimate bottleneck and available bandwidth over an end-to-end path with multiple heavily congested links. Envelope is based on a recursive extension of the stochastic queuing model first proposed by Kang, Liu, Dai and Loguinov (2004), and a modified packet-train methodology. We use two small packets to surround the probing packet-trains and preserve the inter-packet spacing of probe traffic at each router in the path-suffix. The preserved spacings are then used by the receiver to estimate bandwidth. We first reproduce results for a single congested router case using the model proposed by Kang et al. Next, we extend it to the case of multiple congested routers with arbitrary cross-traffic and develop the methodology Envelope. We evaluate the performance of Envelope in various network path topologies and cross-traffic conditions through extensive NS-2 simulations. We also evaluate various probe-traffic parameters which affect the accuracy of this method and obtain the range of values for these parameters that provide good estimation results. Finally, we compare the bandwidth estimation results of our method with the results of other existing methods such as IGI (2003) , Spruce (2003), Pathload (2002), and CapProbe (June 2004) using simulation in Network Simulator (NS-2) with varied network topologies and cross-traffic.

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Video streaming is an increasingly popular Internet application. However, despite its popularity, real-time video streaming still remains a challenge in many scenarios. Limited home broadband bandwidth and mobile phone 3G bandwidth means many users stream videos at low quality and compromise on their user experience. To overcome this problem, we propose CStream, a system that aggregates bandwidth from multiple co-operating users in a neighborhood environment for better video streaming. CStream exploits the fact that wireless devices have multiple network interfaces and connects co-operating users with a wireless ad-hoc network to aggregate their unused downlink Internet bandwidth to improve video quality. CStream dynamically generates a streaming plan to stream a single video using multiple connections and continuously adapts to changes in the neighborhood and variations in the available bandwidth. We have built CStream and evaluated it on a controlled test-bed of computers with various performance measures. The results show linear increase in throughput and improved video streaming quality as the number of cooperating users in a neighborhood increase.

The rapid increase in demand for bandwidth in optical networks over the last two decades has led to the development of wavelength division multiplexing where multiple channels are transmitted simultaneously at different wavelengths over a single optical-fiber to maximize the usage of the bandwidth available in fiber. Increasing demand for bandwidth has led to narrower channel spacing and the use of advanced modulation schemes that are more spectrally efficient than traditional on-off keying techniques [1]. Nonlinearities and dispersion effects in fiber accumulate over a long distance and can adversely affect the quality of a channel. Hence the ability to measure detailed features of the optical spectrum is crucial to study the performance of a communication link. A conventional optical spectrum analyzer (OSA) based on a diffraction grating has a wide wavelength or frequency scanning range, but suffers from poor frequency resolution. The narrowest resolution bandwidth reported for a grating based OSA is - 0.06nm or 7.5GHz at 1550nm [1]. Various spectral features of interest, such as the transmission spectrum of a laser and modulation spectrum of a channel require sub-picometer resolution, which cannot be achieved by conventional methods using a diffraction grating. High resolution spectrum analyzers (HRSAs) have been built based on heterodyne detection where a portion of the optical spectrum is converted to radio-frequency (RF) with DC corresponding to the local-oscillator (LO) central frequency [3-6]. This is a common technique used in RF-spectrum analyzers. The resolution bandwidth is determined by the electrical bandwidth of the optical receiver. The lowest resolution bandwidth reported is of the order of tens of MHz [6]. Widespread implementation of these instruments however, has been limited owing to their cost and size, one of the major factors being the external cavity (ECT) lasers used as the local-oscillator source in such instruments. We have built a coherent-channel analyzer (CCA) based on balanced coherent detection using a commercial distributed-feedback (DFB) laser as the LO. The use of a DFB laser for the CCA has the potential of reducing the cost of the instrument by at least one-tenth of the price of an HRSA. In this thesis we describe the working of the CCA. We provide an end-to-end system model, analyze the resolution and sensitivity performance of the system, and demonstrate a frequency resolution of 100MHz over the DFB tuning range of 200GHz with a sensitivity of -95dBm. The CCA provides a practical, cost and size effective alternative to the HRSA at the cost of tunability. / Graduate

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Recently an efficient multicasting protocol has been reported which uses a concept known as pseudo diameter to reduce the number of duplicate packets generated during multicasting in wide area networks (WANs). This work is superior to the Distance Vector Multicast Routing protocols (DVMRP) from the viewpoint of better bandwidth utilization. In this thesis security aspect of the above mentioned multicast protocol has been considered. Asymmetric key cryptography concept has been used effectively to design the protocol.