Motorola TALKABOUT T2688, Руководство по обслуживанию

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Topaz T2688/T200, T2988/T205 L3 Circuit Description
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Motorola Proprietary Information
21. Within Gemini general GSM processing takes place, such as:
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De-Interleaving : Interleaving is a way in which the information that is to be
transmitted is jumbled around before it is sent i.e.
If we wish to send the information
‘They must read this’
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However if we jumble the bits around that make up the words, i.e. transmit in a
different order.
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Channel De-Multiplexing – this is where we decode the signal that was transmitted,
encryption at the transmitter ends is usually done by X-ORing the information.
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Forward Error Correction Decoding – This is where the redundant bits of data that
were added in the transmitter are removed, and the information that is received can be
processed. The redundant bits are added in various quantities dependent upon the
signal quality. This means if some data is lost whilst travelling OTA then, for
example, instead of 8 bits of speech data being lost, only 4 bits of speech and 4 bits of
redundant data.
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De-Segmentation and CRC Attachment analysis . – During the transmission
process the data is broken into packets of various lengths (N
o
of bits). These packets
are then processed to give a checksum of what should be expected at the receiver.
Once in the GEMINI the information received is processed, and the two checksums
compared. From the analysis, the correct algorithm for repairing any data corruption
can be implemented.
22. The processed digital audio from the Gemini is then returned to the VEGA IC on the
Voice-band serial interface VDX ( GEMINI Pin 85 to VEGA Pin 14 ) clock,
VCLKRX and Frame synchronisation signal, VFSRX .
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And we lose the information during the time
that
‘must’ is being sent. Then we will lose a
whole word.
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If now during the same time frame we lose the same
amount of information, and then we will only lose a small
part of each word