الفهرس Only 14 pages are availabe for public view
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Abstract
Error control codes have become a vital part of modern digital wireless systems, enabling reliable transmission to be achieved over noisy and fading channels. Over the past decade, turbo codes have been widely considered to be the most powerful error control code of practical importance. In the same time, mixed voice/data networks have advanced further and the concept of global wireless networks, integrating satellite and terrestrial links, has emerged. Such networks present the challenge of optimizing error control codes for different channel types, and for the different qualities of service demanded by voice and data.
This thesis introduces the topic of turbo codes. The relative performances of the principle turbo decoding MAP and SOVA algorithms are evaluated by simulation. The MAP algorithm is shown to have the better performance in comparison to the SOVA algorithm. Matlab simulation program is used to calculate the HER performance with different frame sizes, different code rates and different number of iterations.
A DC-free error correcting codes scheme, based on either convolutional codes or turbo codes, is presented. The proposed scheme achieves the DC-free and error correcting capability simultaneously. The scheme has a simple cascaded structure of running digital sum (RDS) control encoder and the conventional encoder of channel coding. It is well known that a given sequence becomes DC-free if and only if the absolute RDS value of the sequence is bounded by a constant for any time instant. The RDS control encoder generates a sequence which gives the required coded sequence with a bounded RDS value. The structure allows us to exploit efficient soft decision decoding which attains additional coding gains compared with hard decision decoding over an additive white Gaussian noise (AWON) channel.