الفهرس 
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Abstract
Error control codes have become a vital part of modem digital wireless systems, enabling reliable transmission to be achieved over noisy channels. Over the past decade, turbo codes have been widely considered to be the most powerful error control code of a practical importance. In the same time, mixed voice/data networks have advanced further and the concept of global wireless networks has emerged. Such networks present the challenge of optimizing error control codes for noisy channel at different quality of services demanded by voice and data. This thesis introduces the topic of turbo code and its application in the networks which supports delivering of VolP such as WiMAX technology and UMTS (3G mobile communication) networks which is predicted to support VolP in the near future.
The thesis can be divided into three parts. The first part discusses the channel coding theorems and gives a general overview about the convolutional codes as an introduction to turbo codes. Then turbo codes’ performance in terms of Bit Error Rate (BER) is introduced. Turbo code BER is close to the Shannon limit. For binary modulation, several authors use BER = 10-5 and signal to noise ratio (Et/No) = 0.2 dB as a pragmatic Shannon limit reference for a rate 1/2 code. Thus, the error performance of a turbo code at BER = 10-5 is within 0.5 dB of the (pragmatic) Shannon limit.
The relative performance of the principle turbo decoding MAP and SOY A algorithms are evaluated by simulation. The MAP algorithm is shown to have a better performance compared with the SOYA algorithm. MATLAB simulation program is used to calculate the BER performance with different frame sizes, different code rates and different number of iterations.
The second part focuses on the VoIP technology and gives a brief explanation about this technology; how is it useful, its advantages, disadvantages and the concept of mobile V oIP. Then, the concept of broadband wireless access (BW A) networks is discussed and the WiMAX technology is introduced as an example of BW A. A general technical understanding of WiMAX standards is given fIrst, and then a technology comparison among WiMAX and DSL, Wi-Fi and 3G is presented. The aim of this comparison is to fInd out the advantage feasibility of the WiMAX service.
The third (and last) part of the thesis discusses the turbo code applications in both WiMAX and UMTS standards. This discussion is given by illustrating the turbo encoder used in each standard and then showing the BER performance of the turbo code using a MA TLAB simulation. Finally, a new turbo decoding scheme is applied for the UMTS system. This new scheme aims to minimize the decoding complexity (the great number of calculations) especially for large frame sizes.