User's Guide Part 1

Table Of Contents

Chapter 1: Product description Wireless operation

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 over a non-line-of-sight path.

The PTP 700 transmits two signals on the same radio frequency, one of which is vertically

polarized and the other horizontally polarized. Depending on the channel conditions, the PTP

700 will adapt between two modes of operation:

•

Dual Payload

: When the radio channel conditions allow, the PTP 700 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 PTP 700.

•

Single Payload

: As the radio channel becomes more challenging, the PTP 700 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 PTP 700 to operate in challenging non- line of sight radio channels.

Lower order modulations (BPSK 0.63 up to QPSK 0.87) only operate in single payload mode.

Higher order modulations (16QAM 0.63 to 256QAM 0.81) are available in single payload mode

and dual payload mode. The switching between modes is automatically controlled by the

adaptive modulation feature described in Adaptive modulation on page 1-12.

Note

The system automatically chooses between dual and single payload to try to increase

the capacity of a link. However the user can disable the dual payload mode, forcing

the more robust option of single payload.