8
Above is a table that shows the relative frequency plans of the three GSM networks: GSM900, DCS1800
and PCS1900.
The frequency range of the Uplink and Downlink show how the two bands are split into the two directions,
rather than an uplink being followed by a downlink 200kHz later. Another difference is that the channel
numbers are different. Remember this if you write any test control software and want to port from one system
to another, as the channel numbers must be changed for correct operation.
2
）：
GSM FDMA and TDMA
：
GSM uses TDMA (Time Division Multiple Access) and FDMA (Frequency Division Multiple Access). The
slide shows part of one of these bands. Each band is divided into 200kHz slots called ARFCN’s (Absolute
Radio Frequency Channel Numbers).
As well as dividing up the frequency, the ARFCN is also divided in time into 8 Timeslots (TS), each TS
being used in turn by a different MS. The 8 TS’s together are known as a Frame.
3
）：
Physical Channel
：
The combination of a TS number and ARFCN is called a physical channel. The corresponding Number is
called ARFCN (Absoluteness RF Channel Number). One ARFCN assert a pair of channels, one is uplink, the
other is downlink. This pair of channels is called physical channel.
In GSM system , the frequency interval is 200kHz.
The ARFCN of PGSM is 1~124
，
the center frequency of CH1 uplink is 890.2MHz. When the value of
ARFCN is equal to n, center frequency uplink channel is fn=f1+(n-1)
200kHz
。
The center frequency of
corresponding downlink channel need to add duplex frequency separation, PGSM is 45MHz.
We need declare that, because of the PCD system is only used in North American, and no DCS system
used, these two systems can not be exist at the same area, the ARFCN of DCS and PCS system can overlap
with each other.
4
）：
Modulation Mode
：
Now the signal can be modulated with a 0.3GMSK modulation scheme.
5
）：
TDMA Burst
：
The burst can be divided into three distinct areas:
• Ramp Up
• Useful Part of the Burst
• Ramp Down
All of these levels are controlled by the GSM standard.
The Useful Part of the Burst is the area where the modulated data is present. There are 148 bits (each bit is
represented by a single symbol in 0.3GMSK modulation) which will be examined more closely in a later
section.
GSM is part of
TDMA
system
，
6
）：
Duplex
Timing
：
Downlink and Uplink
Uplink Lags Downlink by 3 Timeslot periods
Uplink and Downlink use same Timeslot Number
Uplink and Downlink use same Channel Number (ARFCN)
Summary of Contents for W420
Page 1: ...Voxtel Repair Manual Item W420 ...
Page 23: ...23 3 LDO circuit ...
