User Manual

Architecture
Nortel Networks Confidential
3–48
PE/DCL/DD/0063
411–9001–063
Standard 12.07/EN September 2000
GSM/BSS V12
If there is a failure or other problem, it generates an alarm:
microprocessor fault
frequency range not respected (if the frequency to synthesize as requested by the
DRX digital part is incorrect)
PLL loss of alignment (if one of the receiver PLLs is not aligned)
3.4.2.3 Transmitter unit (TX)
The Transmitter unit has two main parts:
IF and RF chains
gain control loop (or Automatic Level Control)
IF and RF Chain
An I/Q modulator with a Local Oscillator (LO) phase–locked on a reference
frequency transposes the two baseband I/Q signals into the IF chain.
This 125 MHz local oscillator (LO_IF) phase–locked on a 13 MHz signal translates
the baseband signals into an intermediate frequency. (The IF is 125 MHz in
GSM 900, 286 MHz in GSM 1800 and 299 MHz in GSM 1900).
The second LO is used for up conversion from IF to RF.
The up–conversion is followed by bandwidth filter, amplifier stages, variable
voltage attenuators, and digital attenuators.
Gain Control Loop (or Automatic Level Control)
The driver transmit chain upholds the accuracy of the transmission power
compatible with the GSM recommendations against time.
The control dynamics use two components: one voltage variation attenuator (VVA)
and a step–by–step digital attenuator taking target attenuation into account and
compensating for it.
The Automatic Level Control also includes the PA.
3.4.3 DRX shutting down
3.4.3.1 DRX soft blocking
The DRX soft blocking consists in setting a DRX “out of service” without stopping
the calls established on this DRX. If possible, an intra–cell handover is performed
for those calls to release the DRX more quickly. Otherwise, the DRX will be
released after the normal completion of the calls.