ABSTRACT Transmission of information has become a key feature of the

modern way of life. The possibilities ordered by telecommunications are

changing the way how people work, shop, spend their leisure time etc. The

advancing communication and information processing technologies create

more markets for new communication services and products. In particular,

the demand for wireless communication services has increased rapidly and

the trend is excepted to continue. Therefore, stringent requirements on the

capacity of communication systems are posed in terms of the number of

users a system can serve simultaneously. In other, and more appropriate,

words, as much information as possible should be transferred. This goal can

be achieved by designing efficient source coding methods to compress the

non-systematic redundancies in the information, by using smaller cells in

cellular systems, by utilizing spatial signal processing techniques, and by

designing efficient multiple-access techniques and transceivers for them.

The topic of this thesis is to analyze demodulation techniques which

demodulate multiple users of a communications system jointly increasing

the capacity of communication systems. The approach is called multiuser

demodulation (MUD) or multiuser detection. Receivers applying multiuser

demodulation are called multiuser receivers.

The partial parallel interference cancellation (PPIC) scheme

can give an optimal IC by adding a partial cancellation weight (PCW) to

each interference cancellation path, in which case the PCW is a fraction of

one and reflects the reliability of the tentative decision. Then, that the fuzzy-

based PPIC (FB-PPIC) outperforms the conventional PIC and constant

weight PPIC over flat fading channels .However, the real situation of the

channel is a frequency selective fading channel in the wireless DS-CDMA

communication system. Therefore, in this paper, we further investigate the

performance of FB-PPIC over frequency selective fading channels.

Simulation results show that with a scaling factor, the FB-PPIC can then

outperform the CPIC and CW-PPIC over multipath time-varying frequency

selective fading channels.

We investigate the technologies of multiuser interference

cancellation technique for DS-CDMA radio systems. One of main factors

that affect the performance of DS-CDMA systems is the multiple access

interferences (MAIs). Multiuser interference calculation technique can

eliminate the MAIs and boost high spectral efficiency radio

communications. Several suboptimal multiuser interference cancellation

schemes have been proposed. Among the suboptimal multiuser interference

cancellation schemes, the multistage interference cancellation scheme

cancels the MAIs by parallel way and performs very well. In this dissertation

the performance for that suboptimal multiuser interference cancellation with

multistage interference cancellation will be investigated. Based on the study

results, we try to design a new multiuser interference cancellation scheme

using neuro-fuzzy theory that is suitable for realization by using DSP

processors or VLSI.

In a multi-user environment, Multi-user signal processing

schemes provide a way to overcome the ejects of MAI and improve

performance. Demodulators based on the Minimum Mean Squared Error

(MMSE) criterion are optimal for ‘ideal’ AWGN channels. However, in the

case of multiple accesses wireless multi-path channels, wherein MAI and ISI

are inherent.