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In today’s wireless communication system, one of the major challenges is to maintain good quality of recovered speech at receiver with unpredictable variations and behavior in channel conditions. Modeling of channel is always a difficult task and channel condition is a decisive factor for quality of speech being reproduced at receiver. Till date many techniques have been evolved to mitigate the effect of channel. GSM Adaptive Multi Rate (AMR) 06.90 is one of such technique which counteracts the deleterious effect of channel on speech signals. This technique employs variable bit rate that dynamically switches to specific modes of operation (switching bit rates – called modes of operation) depending upon the channel conditions.
This paper yields development of AMR coder based on Code Excited Linear Prediction algorithm. By affecting some of the key parameters of CELP coder, variable bitrates of AMR coder can be achieved tuning to different channel conditions. An e-test bench using Simulink is created in order to implement AMR coder based on CELP algorithm, and the same studied and investigated through series of simulations. Subsequently Subjective (Mean Opinion Score) and Objective (Perceptual Evaluation of Speech Quality, Signal to Noise Ratio, Segmented SNR) analysis have been carried out on proposed algorithm to evaluate its performance for various bitrate modes. The obtained results clearly advocate significant improvement (for each Subjective and Objective analysis parameters) over [17] while implemented in Simulink. It also reveals the fact that speech quality improvement is evident with respect to increase in bitrate modes. In next phase real time implementation of proposed coder on TMS320C6713 DSP Kit using Simulink Real Time Workshop (RTW) and Code Composer Studio has been discussed. The goal of real time implementation of the proposed coder is to observe the feasibility of coding and decoding of the proposed coder on DSP TMS320C6713 kit.
