Design Issues for a Multiband Phone
In Chapter 1 we described frequency allocations in the 800, 900, 1800, and 1900 MHz
bands. For a handset to work transparently in Europe, the United States, and Asia, it is
necessary to cover all bands (800 and 1900 MHz for the United States, 900 and 1800
MHz for Europe and Asia).
If we assume for the moment that we will be using the GSM air interface in all bands
(we cover multimode in the next section), then we need to implement the frequencies
and duplex spacings.
Handset outputs for GSM 800 and 900 are a maximum 2 W. A phone working on a
1/8 duty cycle will be capable of producing an RF burst of up to 2 W, equivalent to a
handset continuously transmitting at 250 mW. Multislotting increases the power budget
proportionately. Power outputs for GSM 1800 and 1900 are a maximum 1 W. A
phone working on a 1/8 duty cycle is capable of producing an RF burst of 1 W, equivalent
to a handset continuously transmitting a maximum of 125 mW.
The handsets need to be capable of accessing any one of 995 × 200 kHz Rx or Tx
channels at a duplex spacing of 45, 80, or 95 MHz across a frequency range of 824 to
1990 MHz. Present implementations address GSM 900 and 1800 (for Europe and Asia)
and GSM 1900 (for the United States). GSM 800, however, needs to be accommodated,
if possible, within the design architecture to support GSM GPRS EDGE phones that are
GAIT-compliant (GAIT is the standards group working on GSM ANSI Terminals capable
of accessing a GSM-MAP network) and ANSI 41 (US TDMA) networks.
The design brief is to produce a tri-band (900/1800/1900) or quad band
(800/900/1800/1900) phone delivering good sensitivity and selectivity across all channels
in all (three or four) bands while maintaining or reducing RF component cost and
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