User guide

Understanding Synchronization Link Characteristics

pmp-0229 (Mar 2013)

o enable their SMs first for 2X operation.

• When you have deployable P7 and P8 SMs, do not deploy CSM 130s, CSM 09130s, or CSM

120 P9s beyond half the distance range of the AP. At this distance, steady and reliable 2X

operation typically is not achievable. Deploy the P7 and P8 SMs here.

• Wherever practical, implement

o 10 MHz of channel separation for 3X operation.

o 25 MHz of channel separation for 2X operation.

Understanding Synchronization

The system uses Time Division Duplexing (TDD) - one channel alternately transmits and receives

- rather than using one channel for transmitting and a second channel for receiving. To accomplish

TDD, the AP must provide sync to its SMs – it must keep them in sync. Furthermore, co-located

APs must be synced together - an unsynchronized AP that transmits during the receive cycle of a

co-located AP can prevent that second AP from being able to decode the signals from its SMs. In

addition, across a geographical area, APs that can “hear” each other benefit from using a common

sync to further reduce self-interference within the network.

GPS Synchronization

The Navigation Satellite Timing and Ranging (NAVSTAR) Global Positioning System (GPS)

uses 24 satellites to relay information for precise derivation of position and time.

The cluster management module (CMM) contains a Cambium Oncore GPS Receiver. The CMM

is a critical element in the operation of the system. At one AP cluster site or throughout an entire

wireless system, the CMM provides a GPS timing pulse to each module, synchronizing the

network transmission cycles.

The Oncore GPS Receiver tracks eight or more satellites. The CMM uses the signal from at least

four of these satellites to generate a one-second interval clock that has a rise time of 100 nsec. This

clock directly synchronizes APs and BHMs which, in turn, synchronize the SMs and BHSs in the

network.

The Oncore GPS Receiver also provides

• the latitude and longitude of the GPS antenna (co-located with the CMM)

• the number of satellites that are being tracked

• the number of satellites that are available

• the date

• the time in Universal Coordinated Time (UCT)

• the altitude of the GPS antenna

• other information that can be used to diagnose network problems.