1. Distribution of precise frequency
Requirement for e.g. WCDMA/UMTS transport equipment: 15 parts per billion (ppb)
This means: OK to deliver up to a dozen too many/too few clock cycles every day (for a 8kHz reference frequency).
2. Distribution of locked frequency with tight phase control
Requirement for e.g. Fixed WIMAX transport equipment 4.3 micro seconds
This means: The precise number of clock cycles has to be delivered every year. It is OK to lead or lag up to a dozen of degrees at any time (also for a 8kHz reference)
3. Distribution of time of day
Requirement for e.g. radio interface of CDMA/CDMA2000: 1 micro second.
This means: Time carrying signal cannot be sent more than 150 m without compensating for transport delay. That would be one city block(!)
To measure time in distance of speed of light, and frequency wander in lost clock cycles, put the hard mobile infrastructure requirements on frequency, phase and time of day distribution into perspective. For those interested in more details, I recommend taking a look at Xelerated’s precision time solution white paper.
More on this topic will also be presented at the upcoming MPLS & Ethernet World Congress 2010 and Ethernet Wholesale Summit 2010 in Paris, February 9-12, 2010. Xelerated will be there as well as many of our industry peers.
Look forward to seeing you there!JV