This mode
of operation is called full rate. The half-rate mode is achieved when users occupy a single time slot
during the 40-msec frame.
the cell boundary. A method used to quantify the voice quality is to subject listeners to various samples
of voice recordings under various channel conditions and then rate the voice quality on a scale
from 1 to 5. This is commonly called the Mean Opinion Score (MOS1) for that particular vocoder.
When we are close to the base station, the analog system produces slightly better voice quality
since the digital vocoder is a lossy compression algorithm. However, as we travel away from the cell
site, the performance of the digital system is better because the system characteristics (i.e., error correction,
interleaving) are able to compensate for multipath fading errors. Lastly, as we travel to the
edge of the cell, depending on the system planning, the digital system has a sharper roll-off than the
analog system. A reason for this is that the error correction technique used begins to break down.
In other words, the amount of errors present exceeded the error correction capability of the code.
The time-slot structures for both uplink and downlink are given in Fig. 1.4. Each time slot contains
324 bits which is equivalent to 6.
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