User Manual

ArchitectureNortel Networks Confidential 3–43
S8000/S8002/S8006 BTS Reference Manual
When frequency hopping is being used, one of the following occurs:
• The hopping laws authorize permanent BCCH transmission, and all the TRXs
help fill operations.
• The hopping laws do not authorize permanent transmission and a transmitter
is required to enable BCCH “filling” independently and take over when the
hopping laws step down.
Note: That the laws that enables permanent transmission on BCCH are only
accepted by cavity coupling.
Transmitter and receiver control
The SPU controls a transmitter and a receiver. It calculates the frequency hopping
law and determines the frequencies to synthesize.
The transmitter is controlled by the FH bus. The SPU sends the following to the
transmitter:
the power and frequency to use
the bits to send
the time synchronization signal
The SPU sends the following to the receiver:
the frequency to use for the following time slot
the synchronization clock signal
the GSM TIME synchronization signal
The SPU receives the following from the receiver:
digitized samples from the reception channel
the scale factor (gain)
the receiver alarms
Radio measurement processing
The Radio Measurement Processing performed by the BTS ensures that the network
and the mobiles can communicate with each other with minimum interference at the
lowest possible transmission power and with the best transmission quality.
Measurements processed by the BTS include signal strength and signal quality. The
mobile takes measurements in the downlink direction (BTS –> MS), while the BTS
takes them in the uplink direction (MS → BTS). Other measurements include signal
strength on the BCCH frequency of the surrounding cells and the MS_BS distance.
The BTS averages these measurements for each connection. The averaged
measurements are then used as the basis for a decision–making process for the
following: