Source-Channel Codec for a WCDMA Based Multimedia System
The project deals with the operation of a Source-Channel Codec for a WCDMA Based Multimedia System. The system is meant to transfer and receive both digitized speech and still image signals. It uses a part of the WCDMA technology to mix up the transmitted signals throughout the implementation of Direct Sequence Spread Spectrum and Chip Sequencing methodologies. The Walsh code algorithm is used to ensure the orthogonality among different Chip Sequences. On the transmitter side the system first offers the formatting stage where both a speech and a still image signal are digitized. The following stage in the system exhibits a significant degree of data compression applying appropriate compression algorithms: Lempel-Ziv-Welch for the speech signal and Huffman Code Algorithm for the still image. These compression algorithms are implemented in the Source Encoder stage of the system. The system also provides basic FEC (Forward Error Correction) capabilities, using both Linear Block Code and Convolutional Code algorithms introduced in the Channel Encoder stage. The goal of these FEC algorithms is to detect and correct errors during the transmission of data due to the channel imperfections. At the WCMDA stage the two signals are added together forming an aggregated signal that is being transmitted through the channel. On the receiver side a digital demodulator separates the aggregated signal into two signals using the feature of the orthogonality of vectors. Then the Channel Decoder stage follows, where both signals, which have gotten corrupted during the transmission through the channel due to channel imperfections, are recovered. The imperfections in the channel are simulated by random noise that is added to the aggregated signal in the WCDMA stage of the system. The last stage in the system, the Source Decoder stage, deals with the conversion of the received signals from the digital to analog form and reconstruction of the signals in the sense that they can be heard (speech) and seen (still image). Each stage in the system is simulated using MATLAB programming language. The report is formed of three major parts; the theoretical part where the theory behind each stage in the system is explained, the example part where applicable numerical examples are provided and analyzed for better understanding of both the theory and the Matlab code, and the result part where the Matlab results for each stage are analayzed.