Wireless operation Chapter 1: Product description
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phn-2513_004v000 (Oct 2012)
Modulation modes
The PTP 800 wireless link operates using single carrier modulation with the following fixed
modulation modes:
• QPSK
• 8PSK
• 16QAM
• 32QAM
• 64QAM
• 128QAM
• 256QAM
The available selection of modulation modes varies depending on band, region and channel
bandwidth.
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 4-22.
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.
ODU-B offers superior ACM characteristics to ODU-A.
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.
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