CHAPTER ONE

INTRODUCTION

1.1   BACKGROUND OF THE STUDY

The introduction of speech coding for mobile communication through security sinusoidal transformation. Speech coding is the application of data compression of digital audio signal containing speech. Speech coding uses speech-specific parameter estimation using audio signal processing techniques to model the speech signal, combined with generic data compression algorithms to represent the resulting modeled parameters in a compact bitstream. The two most important applications of speech coding are mobile telephony and voice over IP.

The techniques employed in speech coding are similar to those used in audio data compression and audio coding where knowledge in psychoacoustics is used to transmit only data that is relevant to the human auditory system. For example, in voice band speech coding, only information in the frequency band 400HZ to 3500Hz is transmitted but the reconstructed signal is still adequate for intelligibility.

Speech coding differs from other forms of audio coding in that speech is a much simpler signal then most other audio signals, and a lot more statistical information is available about the properties of speech. As a result, some auditory information which is relevant in audio coding can be unnecessary in the speech coding context. In speech coding, the most important criterion is preservation of intelligibility and pleasantness of speech, with a constrained amount of transmitted data. The intelligibility of speech includes, the actual literal content, speaker identity, emotions, intonation, timbre etc. In addition, most speech applications require low coding delay, as long as coding delays interfere with speech interaction

Communication is the exchange of thoughts, messages or information, as by speech, signals, writing or behaviour. It is derived from the latin word.

“Communis”, which means to share. Communication requires a sender, a message and a recipient, although the receiver need not be present or aware of the sender’s intent to communicate at the time of communication, thus communication can occur across vast distances in time and space. Communication requires that the communicating parties share an area of communicative commonality. The communication process is complete once the receiver has understood the message of the once the receiver has understood the message of the sender. Feedback is critical to effective communication between participants. Bandwidth is a key concept in many telephony applications. In radio communications, for example, band width is the frequency range occupied by a modulated carrier wave, whereas in optics, it is the width of an individual spectral line or the entire spectral range.

In many signal processing contexts, bandwidth is a valuable and limited range of frequencies. A government agency may apportion the regionally available bandwidth to broadcast license holders so that their signals do not mutually interfere.

For different applications there are different precise definitions for bandwidth. It could be defined as the range of frequencies beyond which the frequency function is zero. This would correspond to the mathematical notion of the support of a function. Bandwidth can also be referred to as the frequencies where the frequency function is small.

Bandwidth typically refers to base band or as a pass band for communication systems.

1.2   CHARACTERISTICS OF MOBILE COMMUNICATION  WITH RESPECT TO SPEECH CODERS

There are a number of additional characteristics of mobile communication, some of which are closely linked with handover.

       The most important characteristics includes:

a)    Adaptive frame Alignment:      Mobile staggers is transmitted by three timeslots after a burst from the base station. This means that there is a nominal delay of three TDM slots between transmit and receive frames at the base station.