User Manual

ArchitectureNortel Networks Confidential 3–47
S8000/S8002/S8006 BTS Reference Manual
3.4.2 DRX radio part
The DRX radio part is composed of a power supply board and of the DRX radio
board.
The power supply is converting common -48 V to specific +5 V/± 12 V power
supply signals for the DRX radio board.
The DRX radio board is composed of three units:
the Frequency reference (Fref) unit
the receiver unit (RX)
the transmitter unit (TX)
3.4.2.1 Frequency reference unit
The reference frequency for all local oscillators is derived from the Fref frequency
supplied by the VCXO, itself derived from the 4.096 MHz signal provided by the
DRX digital part (BCF or CBCF).
It provides a very steady and spurious–free reference clock for the RX/TX hopping
and fixed synthetizers (13 MHz signal).
3.4.2.2 Receiver unit (RX)
The receiver unit (RX) has four main functions. Slot–to–slot frequency hopping is
achieved with a dual synthetizer arrangement (one is active while the other one is
setting to the following frequency):
signal down conversion from radio frequency band to Intermediate Frequency
(IF) then to base band frequency
channel filtering (in IF)
RX–level dynamic management
digitization of the base band signal
The base band signal is then sent in binary form with its scale factor to the DRX
digital part.
Receiver configuration
The receiver configuration is done by the DRX digital part, which sends:
the reception frequency to be used for the following time slot
the synchronization clock signal
the GSM time synchronization signal
Receiver monitoring
The receiver monitors internal equipment: microprocessor and Phase Lock Loops
(PLL).