الفهرس 
Beyond the Fourth GenerationOnly 14 pages are availabe for public view
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Abstract
AIN SHAMS UNIVERSITY
FACULITY OF ENGINEERING
Abstract
Name: Ahmed Hassan Ahmed Mansour
Thesis: Enhancement of OFCDMA Systems Performance Using MIMO Techniques
Degree: Doctor of Philosophy in electrical engineering
(Electronics and Communications engineering
department)
The optimization of a communication system becomes a difficult objective if distinct techniques are utilized to resolve different problems of the same system. Accordingly, the main target of future mobile communication systems (e.g. 5G) is to integrate different techniques under a unified framework for the optimization purpose.
Orthogonal Frequency Code Division Multiple Access (OFCDMA) system is one of the most promising multi-user wireless communications systems that outperforms Orthogonal Frequency Division Multiplexing (OFDM) and Multi-Carrier code division multiple access (MC-CDMA). This is achieved through the utilization of two-dimensional spreading.
This study proposes a downlink air interface that targets data rate increase and bit error rate (BER) performance enhancement with low complexity receiver. The proposed system is an integration of space-time spreading (STS) and OFCDMA that exploits transmit diversity needed for BER enhancing and data rate boosting with low complexity advantage. Further BER improvement was achieved through applying an effective Iterative Interference Cancellation (IIC) algorithm at the receiver. Analytical and complexity analyses are presented for the proposed system performance in addition to simulation results. The proposed system attained better performance with lower system complexity compared to the STS-aided multi-carrier direct sequence CDMA that uses beamforming as a closed-loop transmit diversity. Moreover, for maximum supported data rare, an integration of a Full Loaded (FL) multi-code transmission OFCDMA and STS is proposed. This system exploits transmit diversity needed for BER enhancement and data rate optimization. Further BER improvement was achieved through applying an effective IIC in the space domain combined with Multi-Code Interference (MCI) suppression algorithm at the receiver. The BER performance improvement was emphasized through comparing the proposed system with a similar system that uses joint iterative detection. A considerable improvement was also obtained by increasing the number of IIC iteration loops. In addition, the effect of Frequency Domain (FD) spreading factor with different number of iteration loops was investigated.
The achieved BER performance outperforms the Maximal Ratio Receive Combining (MRRC) diversity system performance with 1Tx and 8Rx. Moreover, the system performance was enhanced significantly with the FD spreading factor increase.
Finally, A combination between STS-Aided-OFCDMA and Complete Complementary Codes (CCC) was proposed for asynchronous uplink transmission. The results proved that there is BER improvement compared with systems that depend on traditional codes.
Thesis Supervisors:
1- Prof. Dr. Salwa Hussein El-Ramly
2- Dr. Mona Zakria Saleh