By: Jianming Zhu
Advisor: Dr. Yeheskel Bar-Ness
Department of Electrical and Computer Engineering

Time: 11:00 - 12:45 PM, Wednesday, April 20th, 2005
Place: Room 202, ECE Center, New Jersey Institute of Technology (NJIT), Newark NJ. Directions

Abstract

This dissertation addresses two topics regarding MC-CDMA system in details: the rate capacity and the adaptation of users' signature sequences. Both of them are studied for the downlink communication scenario under multi-code scheme.

The purpose of studying rate capacity is to understand the potential of applying MC-CDMA technique for high speed wireless data communications. It is shown that, to maintain high speed data transmission under multi-code scheme, each mobile's should cooperatively decode its desired users' encoded data symbols which are spread with distinct signature sequences. Higher data rate can be achieved by implementing dirty paper coding (DPC) to cooperatively encode all users' data symbols at the base station. However, the complexity of realizing DPC is prohibitively high. Meanwhile, it is found that the resource allocation policy has profound impact on the rate capacity which can be maintained in the system. The widely adopted proportional resource allocation policy is only suitable for the communication scenario in which the disparity of users' channel qualities is small. When the difference of users' channel qualities is large, non-proportional assignment of power and signature sequences has to be resorted.

Both centralized and distributed adaptation schemes are developed to adapt users' signature sequences in the downlink of MC-CDMA system. With the centralized scheme, the base station collects complete channel state information of the system and iteratively adapts all users' signature sequences to optimize an overall system performance objective function, e.g. the weighted total mean square error (WTMSE). Since the proposed centralized scheme is designed such that each iteration of signature sequence adaptation decreases the WTMSE which is bounded from below, the convergence of the proposed centralized scheme is guaranteed.

The distributed signature sequence adaptation refers to the scenario in which each user's signature sequences are independently adapted to optimize the associated user's individual performance objective function with no regard to the performance of other users in the system. Two distributed adaptation schemes are developed. In one scheme, each user adapts its signature sequences under a pre-assigned power constraint which remains unchanged during the process of adaptation. In the other scheme, pricing methodology is applied such that the transmission power at the base station can be properly distributed among users when users' signature sequences are adapted. The stability issue of the distributed adaptation schemes is analyzed with game theory frame work. It is proven that there always exists a set of signature sequences at which no user can unilaterally adapt its signature sequences to improve its individual performance, given the signature sequences chosen by other users in the system.

Committee Members:

Dr. Y. Bar-Ness, Advisor, Distinguished Professor, New Jersey Institute of Technology
Dr. A. Haimovich, Professor, New Jersey Institute of Technology
Dr. A. Abdi., Assistant Professor, New Jersey Institute of Technology
Dr. R. You, Assistant Professor, New Jersey Institute of Technology
Dr. N. Mandayam, Professor, Rutgers University