1.1 History and Background Voice Telephony Services

1

• 1.1 History and Background - Voice/ Telephony
  Services
• FM technology - Mobile Telephone Service (MTS)
• Introduced in 1946, it allowed
  telephone calls between fixed stations and mobile
  users. One single
• powerful transmitter/ receiver (base
  station) provided coverage of up to 50km., Based
  on FM technol-
• ogy, each voice channel of 3kHz used
  120KHz of spectrum, and only half duplex service
  was available.
• Blocking probabilities were as high
  as 65 (only 12 simultaneous calls could be
  handled!).
• FM technology - Improved Mobile Telephone
  Service (IMTS)
• Introduced in the mid 60s it allowed
  for full duplex transmission and reduced the FM
  channel band-
• width to 25- 30KHz (narrowband FM).
• Analog Cellular (first generation) - Advanced
  Mobile Phone Sys. (AMPS)
• In the late 60s early 70s work began
  on the first cellular systems. It was obvious
  that IMTS had to be
• organized in a manner that allowed for
  growth in user populations. Two major
  technological improve-
• ments made the cellular concept a
  reality 1) the microprocessor - allowed for
  complex algorithms to
• be implemented, and 2) digital control
  links between base station and mobile unit -
  allowed for
• increased control of the system so
  more sophisticated services could be made
  available.

2

• Personal Communications Systems (third
  generation) - DECT, DCS1800
• In the early 90s the success of cellular
  telephony was obvious and spurred a major effort
  in defining
• the next generation cellular systems that would
  provide ubiquitous access to communications
  services
• any where, anytime for any application. The
  Europeans, motivated by the tremendous success of
  GSM
• defined a new enhanced GSM, called DCS 1800 . It
  will carry both voice and data streams. In
  addition
• they developed a common air interface called DECT
  that will support both data and voice
  transmission
• at 32kbps. In the US the efforts have not
  produced any tangible results as yet, many
  competing stan-
• dards are being pushed and the FCC has taken no
  major role in trying to focus the efforts and
  producing
• a single standard. Several network operators,
  such as Sprint and A. T. T., have started to
  market PCS
• services. These services consist of digital
  cellular in addition to paging and voice mail.
  The cell sizes
• are very small, allowing the portables to be
  small too and lightweight. However what is being
  offered is
• still a far cry from what was promised for PCS.
  It remains to be seen how soon true PCS will be
  offered
• and what it will be based on.