Engineering Commons^™

On The Optimization Problems In Multiaccess Communication Systems, Gangsheng Wang

Dissertations

In a communication system, the bandwidth is often a primary resource. In order to support concurrent access by numerous users in a network, this finite and expensive resource must be shared among many independent contending users. Multi-access protocols control this access of the resource among users to achieve its efficient utilization, satisfy connectivity requirements and resolve any conflict among the contending users. Many optimization problems arise in designing a multi-access protocol. Among these, there is a class of optimization problems known as NP-complete, and no polynomial algorithm can possibly solve them. Conventional methods may not be efficient arid often produce …

Numerical Simulation Of Clipping Distortion In Lightwave Catv Systems, Luay Al-Nadi

Theses

Clipping induced distortion is an essential limit for modulation depth and number of channels in subcarrier multiplexed lightwave video transmission systems. Two different types of laser clipping are compared (single-clipping vs. double-clipping). In this work, the distortion limits imposed by clipping effects, in both directly (single-clipping) and externally (double-clipping) modulated systems, are examined. Numerical simulations were performed to test the efficiency of Saleh's Model. A comparison of results with clipping induced distortion in directly modulated lightwave systems (single-clipping) and clipping induced distortion in externally modulated lightwave systems (double-clipping) is presented, it is shown through numerical simulation that the total non-linear …

Asynchronous Multiuser Decorrelating Detector For Awgn Channel, Ashwini A. Borkar

Theses

Decorrelating detector is one of the sub-optimum detectors for CDMA applications that generally has better performance than the conventional detector and is near-far resistant. Synchronous decorrelating detector employing DPSK modulation is considered and its simulation results are presented.

Attention is focussed on one-shot decorrelating detector for a two user case for asynchronous transmission, where each symbol interval is considered seperately. Initially the performance of the detector with exact estimation of the relative delay is analyzed and then the effect of inaccurate estimation on the probability of error is discussed.

Theory, Design And Applications Of Linear Transforms For Information Transmission, Adil Benyassine

Dissertations

The aim of this dissertation is to study the common features of block transforms, subband filter banks, and wavelets, and demonstrate how discrete uncertainty can be applied to evaluate these different decomposition techniques. In particular, we derive an uncertainty bound for discrete-time functions. It is shown that this bound is the same as that for continuous-time functions, if the discrete-time functions have a certain degree of regularity.

This dissertation also deals with spectral modeling in filter banks. It is shown, both theoretically and experimentally, that subspectral modeling is superior to full spectrum modeling if performed before the rate change. The …

Design Of A Lapd Interface Using The T7130 Multichannel Lapd Controller And The T715a Synchronous Protocol Data Formatter, Hopeton Saint John Walker

Theses

As the ISDN telecommunications standard gains acceptance, there is an ever increasing need for intelligent interfaces to implement the L2 protocol known as LAPD. The T7130 MLC, the T7115A SPYDER-T and the MC68020 microprocessor were used to design a LAPD Interface that conforms to the LAPD protocol as specified by CCITT.

The LAPD Interface utilizes a Shared Memory Array which is attached to the Data Link Processors in a single bus configuration. The SMA Arbitration Control allows access to the SMA on a prioritized basis and was implemented as a state machine using PAL's. L2 drivers and L3 management software …

Soft Decision Adaptive Multiuser Cdma Detector For Asynchronous Awgn Channels, Frank Viehofer

Theses

A multiuser detector in an asynchronous, additive white Gaussian noise, codedivision multipleaccess (CDMA) channel is proposed and analyzed. It employs a combination of a decorrelator and a nonlinear multiuser interference canceler that utilizes soft tentative decisions. The weights of the canceler are adaptively adjusted, in a manner that renders the knowledge of received signal energies and the use of training sequences unnecessary. The steady state error performance of the detector is obtained and found to be superior to the performance of the same detector that utilizes hard tentative decisions.

Adaptive Receivers For Direct-Spread And Multi-Carrier Code Division Multiple Access Systems, Xiangqun Liu

Theses

In this thesis, the detection of Direct Sequence Code Division Multiple Access (DS-CDMA) signals in an AWGN channel and Multi-Carrier (MC) CDMA signals in a time-dispersion channel is discussed.

The DS-CDMA receiver employs an adaptive multiuser interference canceler that utilizes deadzone limiters in the tentative decision stage. With weights adjusted adaptively, the prior knowledge of signal powers is unnecessary. The steady state error performance of this receiver is obtained and found to be superior to the performance of the same receiver using hard limiters for tentative decisions. The channel is considered non-fading in. this receiver.

Modeling the frequency selective channel …

Blind Detection In Channels With Intersymbol Interference, Raafat Edward Kamel

Dissertations

In high speed digital transmission over bandlimited channels, one of the principal impairments, besides additive white Gaussian noise, is intersymbol interference. For unknown channels, adaptive equalization is used to mitigate the interference. Different types of equalizers were proposed in the literature such as linear, decision feedback equalizers and maximum likelihood sequence estimation. The transmitter embeds sequences with the data regularly to help the equalizer adapt to the unknown channel parameters.

It is not always appropriate or feasible to send training sequences; in such cases, self adaptive or blind equalizers are used. The past ten years have witnessed an interest in …

Integrated Voice/Data Services On Multihop Radio Networks, Chialun Lu

Theses

Integrated voice/data is the first step toward Integrated Services Digital Networks (ISDN). Various techniques have been proposed and analyzed for multiplexing voice and data over a large bandwidth channel. Network efficiency is what we are most concerned about. In this paper, we address the problem of determining optimal access policies for a tandem ISDN network by using Dynamic Programming. Computer simulation shows that optimal policy minimizes the data delay.

Statistical Multiplexing Of Video Sources For Packet Switching Networks, Krishna Kancherla

Theses

Communication networks are fast evolving towards truly integrated networks handling all types of traffic. They employ integrated switching technologies for voice. video and data. Statistical or asynchronous time division multiplexing of full motion video sources is an initial step towards packetized video networks. The main goal is to utilize the common communication channel efficiently, without loosing quality at the receiver. This work discusses the concept of using statistical multiplexing for packet video communications. The topology of a single internal packet network to support ISDN services has been adopted. Simulations have been carried out to demonstrate the statistical smoothing effect of …