الفهرس 
CDMA FoundationOnly 14 pages are availabe for public view
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Abstract
Over the last few years, wireless communications has experienced rapid growth in the demand for provision of high data rate wireless multimedia services. This fact motivates the need to find ways to improve the spectrum efficiency of wireless communication systems. Application of antenna arrays in wireless communication has been of special interest, particularly in the last two decades.
Code Division Multiple Accesses (CDMA), one of the effective and efficient technologies, is used in 2^nd generation (2G), 3^rd generation (3G) wireless and becomes one of potential candidates for the physical layer of 4G mobile system with the aim of improving cell capacity communication. Under the CDMA System environment the Third Generation (3G) has many advantages such as highly efficient spectrum utilization and variable user data rates. However, in order to achieve this promised high capacity, good techniques are needed to overcome several wireless impairments such as fading and multiuser interference. This is why significant research work is currently being devoted to improve the performance of Direct Sequence Code Division Multiple Access (DS-CDMA) systems using different techniques, such as interference cancellation, array antenna and power control. The antenna array technology is a promising means to overcome signal impairments in wireless personal communications. When special signal processing achieved through array antennas is combined with temporal signal processing, the space-time processing can mitigateeinte reference and multipath to yield higher network capacity, coverage, and quality. It has been shown by many studies that when an array is appropriately employed in a communication system, it helps in improving the system performance by increasing channel capacity and spectrum efficiency, extending range coverage, tailoring beam shape, steering multiple beams to track many subscribers, and compensating antenna aperture distortion electronically. It also reduces multipath fading, co-channel interferences (CCI) and bit error rate (BER).
Antenna arrays are majorly used: Broadside array and End fire array. They are used to radiate their own beam patterns. The antenna arrays with different arrangements: The Spacing of the elements and the Number of elements may produce the diverse radiation properties. The overall radiation pattern results in certain directivity and different lobes with different number of elements and different spacing between them.-Also, array antennas have also emerged as a promising technology to enhance the spectrum efficiency of present and future wireless communications systems by exploiting the spatial domain. Further, all future generation systems are required to support
multiple data rates with good quality of service. Antenna array helps in improving the system performance by increasing channel capacity and spectrum efficiency, extending range coverage, tailoring beam shape, steering multiple beams to track many subscribers, and compensating antenna aperture distortion electronically.
This thesis addresses the problem of using antenna array to improve the performance of CDMA systems by reducing the multipath fading, co-channel interferences (CCI), and bit error rate (BER). The thesis introduces to the following contributions:-
An analytical model for evaluating the mean BER of a DS-CDMA system with QPSK modulation, employing an array antenna and operating in Ricean fading environments has been derived. A closed form expression for coverage, capacity, BER was derived and the analytical solution is valid and verified using Mathcad software package.
The average Bit-Error-Rate (BER) performance for DS-CDMA system with broadside antenna array over both Additive White Gaussian Noise (AWGN) and frequency-selective Rayleigh fading channel was evaluated. We examined the BER performance of Rake Receiver with QPSK and coding, varying the number of users, spreading factor, Rake fingers and the value of directivity of antenna at base Station (number of antenna). A new analytical expression for the outage and bit-
error probability (BEP) of CDMA systems is introduced. An analysis for the uplink outage capacity improvements in CDMA systems using receive antenna array and power control schemes that can track multipath fading is presented Nakagami fading channel was evaluated .
The designed and implementation & Antenna arrays based in single antenna E-shaped patch antenna. Two parallel slots are incorporate into the patch of a microstrip antenna to expand its bandwidth, and designed antenna operates in the frequency range of (1.85 ~1.99) GHz. The antenna is designed using air as a dielectric substrate between the ground plane and substrate patch antenna. The designed (2x2) array antenna depends on E-shaped microstrip patch antenna element; the array antenna is using a separate co-axial probe (Probe feed) to each E-shape patch antenna element for further CDMA applications. Moreover we set our antenna as a single patch, we transformed it to a (1x4) linear array (FR 4 substrate) and finally, we analyzed the (1x5) Edge feed linear microstrip patch array antenna that has been designed with dielectric constants of ε_r=2.2 with fixed substrate height of h=1.5748mm (RT/D5880 substrate).