Maximum entropy based analysis of a DS/SSMA diversity system

D.Ing.This thesis sets out to propose and analyze a cellular Direct Sequence Spread Spectrum Multiple Access (DSjSSMA) system for the Indoor Wireless Communication (IWC) Nakagami fading channel. The up- and downlink of the system implement Differential Phase Shift Keying (DPSK) and Coherent Phase Shift Keying (CPSK) as modulation schemes respectively, and are analyzed using Maximum Entropy (MaxEnt) principles due to its reliability and accuracy. As a means to enhance system capacity and performance, different forms of diversity are investigated; for the up- and downlink, respectively, RAKE reception and Maximum Ratio Combining (MRC) diversity together with Forward Error Control (FEC) coding are assumed. Further, the validity of the Gaussian Assumption (GA) is quantified and investigated under fading and non-fading conditions by calculating the missing information, using Minimum Relative Entropy (MRE) principles between the Inter- User Interference (IUI) distribution and a Gaussian distribution of equal variance

IR-UWB for multiple-access with differential-detection receiver

Impulse-Radio Ultra-Wideband (IR-UWB) emerged as a new wireless technology because of its unique characteristics. Such characteristics are the ability to support rich-multimedia applications over short-ranges, the ability to share the available spectrum among multi-users, and the ability to design less complex transceivers for wireless communication systems functioning based on this technology. In this thesis a novel noncoherent IR-UWB receiver designed to support multiple-access is proposed. The transmitter of the proposed system employs the noncoherent bit-level differential phase-shift keying modulation combined with direct-sequence code division multiple-access. The system is investigated under the effect of the additive white Gaussian noise with multiple-access channel. The receiver implements bit-level differential-detection to recover information bits. Closed-form expression for the average probability of error in the proposed receiver while considering the channel effects is analytically derived. This receiver is compared against another existing coherent receiver in terms of bit error rate performance to confirm its practicality. The proposed receiver is characterized by its simple design requirements and its multiple-access efficiency

A spatial diversity scheme for fixed point indoor wireless communication

The ease with which indoor wireless systems can be installed has become their main selling feature. A desirable application for wireless systems is the transmission of compressed digital music in an indoor shopping mall environment. The indoor environment, with its many walls and highly reflective surfaces, has a high level of multipath. High levels of slowly changing multipath can cause deep fades, and therefore reduce the reliability of the system. The proper use of multiple receiving elements is one way to mitigate the deep fades caused by multipath. The main objective of this thesis is to study a simple and cost effective approach to combining the signals from several receiving elements. A novel diversity combining approach using 2 receiving elements is presented. The novel diversity combining approach consists of periodically changing the phase of one of the two received signals. A set of simulations was developed to study the effectiveness of the novel diversity combining method in mitigating deep multipath fades. The relative performances of two different implementations of the diversity combining were compared to a baseline test case that did not include diversity combining. In both of the simulated implementations, the diversity combining approach proved to be an effective means of mitigating the multipath fading phenomenon. A proof-of-concept, bench-top hardware prototype was also developed. The transmitter and receiver were implemented in Field Programmable Gate Arrays (FPGAs). The laboratory testing of the hardware successfully illustrated the feasibility of the proof-of-concept system

COSSAP simulation model of DS-CDMA indoor microwave ATM LAN

This thesis presents an original work in the area of designing and implementing a simulation testbed for modelling a high speed spread spectrum Asynchronous Transfer Mode (ATM) Local Area Network (LAN). The spread spectrum technique used in this LAN model is Direct Sequence Code Division Multiple Access (DS-CDMA). The simulation model includes at least a physical layer of such a LAN, embedded into the COSSAP1 simulation environment, and has been fully tested. All the newly developed building blocks are comprised of standard blocks from the COSSAP libraries or compatible user-built primitive blocks (only where it is absolutely necessary), and are flexible enough to allow the modification of simulation or model parameters; such as the number of signal channels, modulation method used, different spreading code sequences and so on. All these changes can be made with minimal effort. Another significant contribution made in this thesis is the extended research into evaluating the Bit Error Rate (BER) performance of different spread spectrum COMA coding schemes for an indoor microwave A1M LAN [8]. Different spread spectrum CDMA coding schemes are compared for their transmission error rate in Additive White Gaussian Noise (AWGN) channel with varying transmitted signal power and at different channel Signal to Noise Ratio (SNR) levels. Since a wireless microwave channel is very prone to transmission errors, a major contribution of the simulation testbed developed in this thesis is its use in the finding of an optimal physical layer transmission scheme with the best Bit Error Rate (BER) performance in an indoor environment

DS-CDMA with power control error using weighted despreading sequences over a multipath rayleigh fading channel

In this paper, closed-form solutions for the average bit error rate (BER) performance of a direct-sequence codedivision multiple-access system with imperfect power control are derived for both coherent and noncoherent receptions operating over a multipath Rayleigh fading channel. The RAKE structure receivers under consideration employ despreading sequences weighted by adjustable exponential chip waveforms optimized for multiple-access interference rejection. The chip-weighting waveforms employed are determined only by one parameter γ which leads to easy tuning of the waveforms in practice to achieve the best performance. The results indicate that the number of active users supported at a given BER for the case of γ tuned to maximize the average signal to interference plus noise ratio H is much larger than the case of γ = 0 (fixed or rectangular despreading sequence). It is shown that imperfect power control affects the irreducible BER for the case of γ = 0. On the other hand, the effect of imperfect power control on BER performance for the case of γ tuned to maximize Ĥ is equivalent to a reduction in the average signal-to-noise ratio, and, hence, system performance can be compensated by increasing the transmitter power. It is further shown that the effect due to imperfect power control on BER performance is significant while that on the maximum value of Ĥ obtained by tuning γ is rather insignificant. Index Terms-Code-division multiple access, RAKE receivers, spread-spectrum communication. © 1999 IEEE Publisher Item Identifier S 0018-9545(99)05722-9.published_or_final_versio