Thursday, August 20, 2009

Systems Summary 2


Here we can compare the characteristics of some of the circuit switched systems.

The GSM standard was completed in 1990 with the first networks in operation in 1991. The
maximum user bit-rate for GSM is 9.6 kbps. As GSM is primarily a voice based digital system then no data interface is specified. Remember that because GSM is circuit switched a call setup is required before data is transmitted - this can take up to 40 seconds.

The High-Speed Circuit Switched Data standard was completed in 1997 and Ericsson’s
product is on the market. HSCSD offers higher speeds than GSM by utilizing several timeslots simultaneously; using all 8 timeslots in a single frame means a net bitrate of about 64 kbps. It's envisaged that the market for HSCSD will be quite small. Essentially, HSCSD makes several GSM calls simultaneously which means that a single user can hog a large portion of the air interface. Add that to the fact that making multiple GSM telephone call simultaneously is not a cheap pastime and it is easy to see that HSCSD is likely to be a niche market.

The Universal Mobile Telephone System is scheduled to be specified by 1999. The channel separation is undecided as of yet, but the channel access method will be Wideband-CDMA. The planned net bit-rate is between 144 kbps to 2 Mbps, depending on the users location. Remote areas with lower coverage should offer the minimum bit-rates, while urban areas with higher coverage should provide the higher bit-rates. The plan is to have UMTS in operation by the year 2002. To achieve this ambitious goal and to protect current network operators from capital dis-investment it is likely that UMTS will utilize the existing GSM infrastructure in some way.

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