On the Implementation of Differential Encoder for Spectral Shaping in 56Kbps Embedded Modems

Present paper deals with the simulation and implementation of two functional units, parse-to-shaping-frame and differential encoder, for spectral shaping in 56Kbps digital modem transmitter. The idea behind spectral shaping is to adapt the shape of the transmitted signal, to conform to the shape or spectral limitations of the channel, without changing the basic pulse shape or peak-to-average-ratio. This unit suppresses the signal component close to dc to minimize the effect of ac couplings or to provide sufficient data transitions for reliable clock recovery. A combined algorithm for implementation of the parse-to-shaping-frame and differential encoder functions utilized in transmitter of 56Kbps digital modem has been presented. An algorithm to perform parse-to-shaping-frame and differential encoding functions has been developed during present study. Proposed algorithm has been simulated and implemented on the Digital Signal Processor. Practical results obtained have been found almost similar to the theoretical and simulated results.