User's Manual

Wireless operation Chapter 1 Product description
phn-2182_002v000
1-18
May 2011
The system provides an adaptive modulation scheme where the receiver constantly
monitors the quality of the received signal and notifies the far end of the link of the
optimum modulation mode with which to transmit. In this way, optimum capacity is
achieved at all times.
NOTE
PTP LINKPlanner includes an estimate of mean data rate, the data rate
provided by each modulation and the percentage of time spent in each
modulation mode.
MIMO
Multiple-Input Multiple-Output (MIMO) techniques provide protection against fading
and increase the probability that the receiver will decode a usable signal. When the
effects of MIMO are combined with those of OFDM techniques and a high link budget,
there is a high probability of a robust connection.
The PTP 250 transmits two signals on the same radio frequency, one of which is
vertically polarized and the other horizontally polarized. The system also has the
ability to adapt between two modes of operation:
• Dual Payload: When the radio channel conditions allow, the system will transmit
two different and parallel data streams, one on the vertical channel and one on
the horizontal channel. This doubles the capacity of the system.
• Single Payload: As the radio channel becomes more challenging, the system has
the ability to detect this and switch to a mode which transmits the same data
stream on both vertical and horizontal channels. This provides polar diversity and
is another key feature which allows the system to operate in challenging radio
channels.
The switching between modes is automatically controlled by the adaptive modulation
feature described in Adaptive modulation on
page 1-17.