17-4

GSM Theory

E-GSM, DCS1800 and PCS1900 Systems

E-GSM, DCS1800 and PCS1900 Systems
GSM900 is the original GSM system, using frequencies in the 900 MHz band and
designed for wide area cellular operation. Mobiles with output powers from 1 to 8W are
typical. DCS1800 is an adaptation of GSM900. The term GSM can be used collectively
to describe the GSM900 and DCS1800 standards. Creating DCS1800 involved widening
thebands assigned to GSM and moving them up to 1.8 GHz. TheDCS1800 standard was
created to allow PCN (Personal Communications Networks) to form.
To avoid confusion, the channel numbers (ARFCN) used for DCS run from 512 to 885.
GSM900 channels run from 1 to 124. With wider frequency allocation, leading to more
channels, DCS1800 is able to cope with higher user densities. DCS1800 mobiles are also
designed for lower output powers (up to 1W), so cell sizes have to be smaller, meaning
even higher densities. In all other respects, GSM900 and DCS1800 are the same.
The GSM phase 2 speciļ¬cations brings the two systems even closer. GSM900 gets
additional bandwidth and channels, called E-GSM (Extended band GSM) and lower
powercontrol levels for mobiles, allowing micro-cell operation. Thesetwo features allow
increased user densities in GSM systems.
PCS1900 is in the band around 2 GHz for a PCS (Personal Communications System).
This version of GSM is variously called DCS1900 or PCS1900. In technical terms
PCS1900 is identical to DCS1800 except for frequency allocation.