Harris Constellation - Threshold-To-Interference (T;I) Ratios; Overview

Constellation® January 2006
7-2 Performance Curves
Threshold-to-Interference (T/I) Ratios
Overview
The T/I curve shows the strength of interference and the frequency away from
the carrier required to degrade the 10
-6
BER (bit error ratio) state threshold
and the 10
-3
BER dynamic/outage thresholds by 1 dB. Measurements were
made by fading the wanted received signal level (RSL) until the 10
-6
BER point
is found (T). A modulated interfering signal is then added until the 10
-6
BER
point is degraded by 1 dB (I). The measurement is also made with a CW
interfering signal which emulates an analog radio FM emission. The ratio is the
T/I. The T/I curve is used for choosing radio frequency assignments and to find
the fade margin in congested areas. T/I curves plotting allowable T/I versus
frequency offset of the interfering signal must be on file with the frequency
search companies and are therefore available for all Harris digital microwave
radios.
Example: if 10
-6
BER threshold is -80 dBm and T/I is 30 dB, then the allowable
interference level at threshold is -80 dBm minus 30 dB = -110 dBm.