Clock Synchronization Subsystem BSC6900

The clock synchronization subsystem provides clock signals for the BSC6900, generates the RNC Frame Number (RFN), and provides reference clock signals for base stations.

(RFN Generation and Reception

RNC Frame Number (RFN) is used to synchronize NodeBs with the BSC6900. The node synchronization frames from the BSC6900 to the NodeBs carry the RFN information. Figure 1 shows the process of RFN generation and reception. This figure takes the GCUa board as an example.)

Functions

The clock synchronization subsystem provides the following clock sources for the BSC6900 and ensures the reliability of the clock signals:

• Building Integrated Timing Supply System (BITS) clock
• Global Positioning System (GPS) clock
• External 8 kHz clock
• LINE clock

External Clocks

The external clocks of the BSC6900 are of two types:

· BITS Clock

§ The BITS clock signals are of three types: 2 MHz, 2 Mbit/s, and 1.5 Mbit/s. The 2 MHz and 2 Mbit/s clock signals are E1 clock signals, and the 1.5 Mbit/s clock signals are T1 clock signals.

§ The BITS clock has two input modes: BITS0 and BITS1. BITS0 and BITS1 correspond to the CLKIN0 and CLKIN1 ports on the GCUa/GCGa board respectively. The BSC6900 obtains the BITS clock signals through the CLKIN0 or CLKIN1 port.

· External 8 kHz Clock

Through the COM1 port on the GCUa/GCGa board, the BSC6900 obtains 8 kHz standard clock signals from an external device.

LINE Clock

The LINE clock is an 8 kHz clock that is transmitted from an interface board in the MPS to the GCUa/GCGa board through the backplane channel. The LINE clock has two input modes: LINE0 and LINE1.

LINE0 and LINE1 correspond to backplane channel 1 and backplane channel 2 respectively.

The BSC6900 provides reference clock sources for base stations. Clock signals are transmitted from the BSC6900 to base stations over the Abis/Iub interface.