Chapter 3: System planning
Radio Frequency planning
Page
3-22
Frame start
GPS synchronization is a way of guaranteeing that the frame start is the same for all APs. This is what is
used by the Cambium PMP devices.
However, the timing between the GPS signal and the start of the TDD frame is not necessarily the same
for all systems. The Cambium PMP devices and the LTE devices have different start time for their
frames.
The Cambium PMP Radio configuration page offers an LTE co-location option in the GUI Radio page,
that allows the user to co-locate Cambium PMP devices with LTE devices by shifting the start of the
PMP frame to match the start of the LTE frame.
This can be found under Configuration > Radio > Frame Configuration, as shown in below figure.
If the Co-located LTE Frame Configuration Option is selected as Disable, then the Cambium PMP frame
start is not shifted from its legacy timing.
If any of the three other options (LTE Frame Configuration 0, 1 or 2) is selected, the Cambium PMP
frame start is shifted to align to the LTE frame start. Additionally, each Frame Configuration has its
frame start shifted by an integer number of subframes.
The Cambium PMP frame always starts with the downlink portion of the frame, followed by the
turnaround time and then the uplink portion of the frame.
The LTE 10-ms interval however, always starts with subframes D, S and U as the first three subframes,
but it may have additional downlink subframes in the same frame.
For example, in Frame Configuration 1 the 10 ms interval is composed of two repetitions of the following
subframes: D, S, U, U, D. In order to align the Cambium PMP frame to this LTE frame, the downlink start
has to align to the beginning of subframe 4, not subframe 0. With this shift, the sequence of subframes
in the LTE frame becomes D, D, S, U, U, which is the same structure of the Cambium PMP frame
(downlink, turnaround time, uplink).
Содержание PMP 450 AP
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