الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
In digital communication systems effeceint and reliable data transmission is achieved through the use of error correcting codes. The task of these codes is to add redundancy bits to the transmitted data sent over a communication channel in such a way that in the presence of channel noise, errors in corrupted messages can be corrected. As the number of added bits increases, the error correction capability of the code increases. On the other hand increasing redandany requires additional bandwidth for transmission. This increase in bandwidth is an undesirable feature in narrow band systems. In spread spectrum systems, the redandancy added by erorr correcting codes can be used to perform the spreading process. It was proved that spread spectrum CDMA systems can reach thier maximum theoretical capacity when they are combined with low rate (high redundancy) error correcting codes. CDMA is wieldy used as a multiple access technique in satellite communication systems, it provides higher user capacity than the other multiple access techniques and in addition it has the ability to suppress interference and offers good immunity to multipath fading. Orthogonal and super-orthognal convolutional codes are low rate error correcting codes that is applied in CDMA spread spectrum applications to perform both coding and spreading. Powerfull error correcting codes
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can be obtained by connecting more than two simple codes through interleavers which is known as concatenated codes. There are two well known concatenated coding schemes; serail concatation and parallel concatation. In digital satellite communication systems, due to the large distance between transmitter and receiver the transmitted signal is subjected to path loss and atmospheric-induced fading. In order to maintain sufficient received power at the destination, it is required that a high efficiency power amplifier be employed. The high power amplifier introduces nonlinear distortions when it operates in its maximum power efficiency region which ia called saturation region. This results in degradation to the signal-to-noise ratio of the system. In order to compensate for this nonlinear response, two methods are commonly used; employing a linearization technique or to back-off the operating point of the amplifier from saturation to its linear region.
In this research, A new concatenated coding scheme is proposed. The concatenated coding scheme combines the princibles of both parallel and serail concatenation. Performance of the proposed coding scheme is evaluated in an additve white Gaussain noise channel and is compared to that of both serial and parallel concatenated convolutional codes.
Also, a new low rate concatenated coding scheme is proposed The proposed low rate code is suitable for spread spectrum CDMA applications. Performance of the proposed low rate
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coding sheme is evaluated in both additve white Gaussain noise channel channl and satellite channel and nonlinear satellite channel.