User Manual

MN021-01
Page 9 of 28
5. Functional description
5.1. Block diagram
Figure 4 Local Unit (TFLF) Block Diagram
The Local unit is the core of the system and provides the following functionalities:
• RF low power interface and optical conversion.
• Power supply distribution and short/surge protection.
• Alarm interface through dry contact.
• Status and alarm LEDs.
• Automatic Level Control (ALC) in Downlink for overdriving and spurious emission control.
• Automatic Gain Control (AGC) for Uplink optical path loss compensation.
• Microprocessor based supervision and data communication.
• “Store” button for software auto configuration and alarm masking.
• Step attenuator for uplink gain setting.
5.2. Down link operations
In the downlink path the TFLF fulfils the following operations:
Power level adjustment: The TFLF local unit is designed to be interfaced with a wide range of
low power BTS and repeaters. For higher power BTS’s an external fixed attenuator is required.
Refer to the Appendix for the typical and maximum allowed input levels. Because the RF port is
duplexed, an external attenuator will add the same downlink loss to the uplink path. To
compensate for this loss, the TFLF uplink gain must be adjusted by means of the UL step
attenuator.
The DL RF power is limited from the ALC to avoid spurious emissions in case of overdriving
inputs.
E/O Conversion: The RF signal modulates the intensity of an optical carrier through an electro-
optic device (laser).
Optical Splitting: The modulated optical carrier is split into 4 ways so that it may be transmitted
on a maximum of 4 optical links.
5.3. Up link operations
O/E Conversion: There are 4 O/E conversion devices, or optical receivers, in the TFLF, one for
each optical link. The modulated optical signal coming from the remote units is detected and
E
O
E
O
AGC
E
O
AGC
E
O
AGC
E
O
AGC
UL manual step
Attenuator, 0-20dB
DL ALC
UL
DL
-48V
DL
UL
Alarm
-48V
DC
DC
microcontroller
..
LEDs
…
Alarm Relays
N.O.
store