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I read that the human range is commonly given as 20Hz to 20,000 Hz. But GSM channels are carrier frequencies of 200 kHz bandwidth. Is that because of SMS part?

It seems for voice 20kHz must be enough. Why 200kHz?

user16307
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You've misunderstood the answer to your previous question. https://electronics.stackexchange.com/questions/166056/how-does-a-base-station-provide-multiple-channels-without-any-interference

It's not tranmitting analog voice. It's transmitting digital data. TDMA is used to share one 200kHz channel among a large number of voice calls. Each voice call is encoded with the AMR codec and ends up as about 10kbit/sec.

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pjc50
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  • i know it is digital. so the bandwidth increases with A/D conversion even though there is speech coding? – user16307 Apr 22 '15 at 13:26
  • @user16307: try sending 20kbit binary data with 20khz bandwidth... – PlasmaHH Apr 22 '15 at 13:34
  • @PlasmaHH do you have formulation for this? am a bit newbie – user16307 Apr 22 '15 at 13:36
  • @user16307: no, I do not have a formula for trying to send 20kbit binary data over 20khz bandwidth... – PlasmaHH Apr 22 '15 at 13:37
  • There are multiple calls per channel. GSM fits 8 calls in one 200kHz channel. http://www.howardforums.com/showthread.php/103872-QUIZ-how-many-calls-per-TDMA-voice-channel – pjc50 Apr 22 '15 at 13:38
  • why does it have to be 20kbit? – user16307 Apr 22 '15 at 13:39
  • so 200 maybe comes from 20X8 = 160 and some other data in between – user16307 Apr 22 '15 at 13:40
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    Actually, the voice channels are band limited to ~300Hz-4kHz, then encoded using an AMR codec which gives about 12kb/s output. Each channel in a TDMA frame has about ~13kb/s throughput, so is large enough to handle the encoded voice. That encoded data is then packed into a streamwith training patterns, guard bits and other overhead giving about 270kb/s total in a TDMA frame (8 channels). – Tom Carpenter Apr 22 '15 at 13:48
  • GSM then uses GMSK as an encoding scheme which fits that data rate into the 200kHz channel (with about 50kHz of side lobe interference between channels) – Tom Carpenter Apr 22 '15 at 14:00
  • i think i gotta read about speech and channel coding for GSM – user16307 Apr 22 '15 at 14:24
  • You will discover that the bandwidth needed for an SMS message is miniscule compared with a voice channel. – cuddlyable3 Apr 22 '15 at 16:57