Chapter 2
GSM Call Mode Operation
System parameters
106
4460 GSM System Option and 4468 EDGE System Option
Version 12.20
Phase RMS
The RMS phase error is calculated from the phase errors of
all bits within a burst, using the root mean square func-
tion. This value is always positive.
Uplink Time
Timing of the mobile in relation to the 4400. Downlink
and uplink are shifted by three time slots in GSM, and
there is also the timing advance the mobile is commanded
to use. Therefore, the mobile’s burst should arrive at the
4400 with a time delay of three time slots minus timing
advance.
The tolerance limit for this timing delay is entered here in
μs.
Note:
A bit period in GSM is 48/13 μs (roughly 3.7 μs).
Frequency
Err 900
The frequency error is computed as the slope of the
regression line of the phase error over time. It tells you
how well a mobile can synchronize to a base station.
This entry field allows you to specify the symmetrical limit
for GSM 900 systems. GSM 900 specifications specify a
maximum permissible frequency error of about ±90 Hz.
Note:
This field is also applicable to GSM 850 systems.
Frequency
Err 1800
The frequency error is computed as the slope of the
regression line of the phase error over time. It tells you
how well a mobile can synchronize to a base station.
his entry field allows you to specify the symmetrical limit
for GSM 1800/1900 systems. GSM 1800 specifications
specify a maximum permissible frequency error of about
±180 Hz.
Note:
This field is applicable to GSM 1800 and GSM 1900
systems.
Burst
Length
The length of a burst is critical in GSM. If a burst is too
short, not all data transmitted by the mobile can be
received. If it is too long, interference will be caused in
the subsequent time slot.
A standard GSM burst contains 148 bits, with a bit period
of 48/13 μs. Consequently, a normal burst is some
546.5 μs long and has to fit into a time slot with a dura-
tion of 577 μs.
BER Ia
The
B
it
E
rror
R
atio is defined as the ratio of falsely
decoded bits in relation to all bits transmitted. It is calcu-
lated for the three different bit classes separately.
In this entry field, you enter the upper limit for the BER on
class Ia bits.
BER Ib
The
B
it
E
rror
R
atio is defined as the ratio of falsely
decoded bits in relation to all bits transmitted. It is calcu-
lated for the three different bit classes separately.
The maximum value for the BER on class Ib bits is entered
in this entry field.
