How Voice Signal Processing in GSM

How Voice Signal Processing in GSM, radio channel, code stream, channel coding, burst formatting, interleaving, voice, radio, interferences.

The radio channel is quite different from the wired channel. First, the radio channel has a distinct time-change characteristic. The radio channel is exposed to the air, so it is vulnerable to the  interferences in the air. The signal is influenced by various interferences, multi-path fading and shadow fading, so the error bit ratio is rather high.

Voice Signal Processing

To solve the problems mentioned above, a series of forward and backward(uplink & downlink) transmission techniques are applied. The original subscriber data or signaling data are transformed before being carried by the radio waves. And at the other end of the transmission, a reverse transforming will be done.

This can provide necessary protection to the transmitting signal. The transformation methods roughly include the channel coding/decoding, interleaving/de-interleaving, burst formatting, encryption/decryption, and modulation/demodulation. For the voice, to pass an analog-to-digital converter is actually a sampling process in the rate of 8KHz,

after quantification each 125μs contains 13bit of code stream; then speech coding is performed  with every 20ms as a segment and the code transmission rate is reduced to 13Kbit/s, which becomes 22.8Kbit/s after the channel coding; then the voice becomes a code stream at 33.8kbit/s after code interleaving, encryption and burst formatting and is transmitted finally. The processing at the terminal is just the reverse of the above procedures.

Article Topics :

radio channel, code stream, channel coding, burst formatting, interleaving, voice, radio, interferences, encryption, fading gsm, gsm basic, how signal processing is done in gsm, interleaving, signaling processing of gsm, uplink