+ 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 60’s it allowed for full duplex transmission and reduced the FM channel band- width to KHz (narrowband FM). Analog Cellular (first generation) - Advanced Mobile Phone Sys. (AMPS) In the late 60’s early 70’s 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. Digital cellular (second generation) - GSM, IS 54, IS 136, IS 95 In the late 80’s the idea of digital cellular emerged. Now both the voice and the control were digital. Digital voice allows for error control and pre and post processing of the signal thereby reducing the effects of noise, so common in wireless systems. By 1991 digital cellular service began to emerge. GSM is the European standard that has become the most popular due to its early introduction. IS 54 is the TDMA digital standard that uses the old AMPS system for transmission. IS 136 is the new TDMA standard and IS 95 is the CDMA based standard. All 4 systems are in operation in the US!

Personal Communications Systems (third generation) - DECT, DCS1800 In the early 90’s 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 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.