User`s guide

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GPIB Tutorial and Examples

Example B - Controlling the Mobile

Mobiles need to be tested on a variety of frequency channels (ARFCN) and transmitter

power levels (TX Level). The Agilent 8922M/S uses over-the-air signalling to command

the mobile to any ARFCN or TX Level. ARFCN changes can be made using channel

assignments, with the signalling taking place over the GSM Fast Associated Control

Channel (FACCH). TX Level changes are signalled using the GSM Slow Associated

Control Channel (SACCH). The choice of FACCH or SACCH has been made by the

GSM speciﬁcations.

Before extending your program to control the mobile, press the LOCAL key on the

Agilent 8922M/S and manually establish a call with the mobile. In the MOBILE PHONE

section of the Cell Control screen, use the knob to select TX Level. Using the arrow keys,

quickly change the TX Level from 15, to 14, to 13, to 12, to 10, to 9, to 8, to 7, to 6, to 5

and back down to 15. Notice the mobile’s uplink SACCH reports of TX Level in the

CELL STATUS area of the screen. Notice also the Peak Power measurement in the centre

of the screen. Observe the sequence of events, ﬁrst you command a new TX Level, about

1 second later, the mobile changes its output power, and shortly after, conﬁrms the new

TX Level on the uplink SACCH, to be displayed on the Agilent 8922M/S.

The sequence for ARFCN changes is similar. Because channel assignments use the

FACCH, the process happens more quickly. There is still a perceptible delay from the

channel change being commanded, by changing the Channel value under MOBILE

PHONE, to the TRAFFIC Channel value being conﬁrmed under CELL STATUS.

TX Level Changing

Extend your program, selecting GPIB commands from section “GPIB Commands Used in

Exercises”, to cycle the mobile’s TX Level from 5 to 15 with the following steps:

❒ Establish call as in exercise A.

❒ Set up a loop to count through the TX Levels.

❒ Command the phone to the new TX Level.

❒ Check the reported TX Level, loop until the reported value matches the programmed

value, or too much time has elapsed.

❒ Repeat for the next TX Level.

❒ End call as in Exercise A.