Cambium Networks PMP 450, Руководство по планированию

Страница: 125 / 223

PMP 450 Planning Guide
Configuration options for TDD synchronization
The PMP 450 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, collocated APs must be synced together - an
unsynchronized AP that transmits during the receive cycle of a collocated 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.
The configuration options available for synchronization on the PMP 450 Access Point are:
•
AutoSync : The AP automatically receives sync from one of the following sources:
o
GPS Sync over Timing Port (UGPS, co-located AP GPS sync output, or “Remote AP” feed from a
registered SM’s GPS sync output)
o
GPS Sync over Power Port (CMM)
o
On-board GPS (internal GPS)
Upon AP power on, the AP does not transmit until a valid synchronization pulse is received from one of the
sources above. When there are synchronization sources on both the timing port and the power port, the power
port GPS source will be chosen first.
If there is a loss of GPS synchronization pulse, within two seconds the AP automatically attempts to source
GPS signaling from another source. On-board GPS (internal GPS) is the last source checked for GPS signaling
if there is no receipt of signaling from the timing port or from the power port. AutoSync will source timing
from the on-board GPS if a valid synchronization pulse is detected (the on-board GPS module should not be
used as the primary timing source). If no valid GPS signal is received, the AP ceases transmission and SM
registration is lost until a valid GPS signal is received again on the AP.
•
Au Free Run : This mode operates similarly to mode “AutoSync”, but if a previously received
synchronization signal is lost and no GPS signaling alternative is achieved (from the timing port, power port, or
on-board GPS), the AP automatically changes to synchronization mode “Generate Sync”. While SM
registration ins maintained, in this mode there is no synchronization of APs that can “hear” each other; the AP
will only generate a sync signal for the local AP and its associated SMs. Once a valid GPS signal is obtained
again, the AP automatically switches to receiving synchronization via the GPS source and SM registration is
maintained.
In mode Au Free Run, if a GPS signal is never achieved initially, the system will not switch to “Free
Run” mode, and SMs will not register to the AP. A valid GPS signal must be present initially for the AP to switch
into “Free Run” mode (and to begin self-generating a synchronization pulse).
•
Generate Sync (factory default): This option may be used when the AP is not receiving GPS synchronization
pulses from either a CMM or UGPS module, and there are no other APs active within the link range. Using this
option will not synchronize transmission of APs that can “hear” each other; it will only generate a sync signal
for the local AP and its associated SMs. See Advantage of GPS synchronization on page 1-117.
pmp-0047 (March 2014)
1-115