Motorola PTP 800, User Manual

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User Guide: PTP 800 Licensed Ethernet Microwave Wireless operation
phn-1478_005v000
Apr 2010
1-23
PTP 800 uses Low Density Parity Check (LDPC) forward error correction (FEC)
coding. The code rate is calculated as the ratio between the un-coded block size
and the coded block size. FEC code rate in PTP 800 varies between 0.76 and 0.94
depending on channel bandwidth and modulation mode.
For more information, see Capacity, transmit power and sensitivity on page 4-39.
Adaptive coding and modulation
PTP 800 supports both Fixed Modulation and Adaptive Coding and Modulation
(ACM) modes. In ACM mode, the PTP 800 selects the modulation mode according
to the quality of the received signal. The selection criterion is to provide the highest
link capacity that can be achieved while keeping the communication error free.
When compared with Fixed Modulation operation, ACM can increase either link
availability, or average wireless link capacity, or both.
Wireless link capacity
The maximum data throughput capacity of the PTP 800 wireless link is the lower of
the wireless link capacity and the data capacity limit set by the PTP 800 license
key.
All PTP 800 CMUs are shipped with a factory-set 10 Mbit/s capacity limit, meaning
that capacity is restricted to a maximum of 10 Mbit/s at the data port. Users can
purchase capacity upgrades in nine steps between 20 Mbit/s and unlimited
capacity. For more information, see
Capacity upgrades on page 1-36 .
NOTE
Purchasing a capacity upgrade will not necessarily lead to an increase in
data capacity, as capacity also depends on channel bandwidth and
modulation mode. For more information, see
Capacity, transmit power
and sensitivity on page 4-39 .
Automatic transmitter power control
PTP 800 provides closed-loop automatic transmitter power control (ATPC). ATPC
avoids overload of the receivers in links with low link loss by automatically
adjusting transmitter power. The ATPC threshold is –40 dBm received power. ATPC
has no effect in links where the received power is lower than the threshold.
Automatic adjustment of the transmitter can be enabled or disabled using the
Automatic Transmitter Power Control attribute on the Configuration page of the
web-based interface. This attribute must have the same setting at both ends of the
link.