User's Manual

Advanced Configuration Features

Horizon Compact Release 1.01.01 Wireless Ethernet Product User Manual – Volume 1

Table 11-2 Time Sources

Index Stratum

Source

IP Address

Source

1 2 199.212.17.15 Industry Canada

2 2 199.212.17.20 Industry Canada

3 1 192.5.41.40 U.S. Navy

4 1 192.5.41.209 U.S. Navy

5 2 129.132.2.21 Switzerland

11.11 Automatic Adaptive Modulation (AAM)

The two principal modulation schemes used on the Horizon Compact system are QPSK and QAM. QPSK

(the lowest modulation scheme) is ideal for long distance, but has the lowest throughput capability.

Higher throughputs are achieved by using more complex modulation schemes e.g. 16-QAM, 32-QAM,

64-QAM, 128-QAM, 256-QAM. The higher numbers indicate a progressively more complex scheme and a

higher bandwidth (throughput) capability e.g. 256-QAM is more complex than 128-QAM and provides a

higher throughput. More complex modulation schemes are susceptible to noise and thus require a

stronger signal for the demodulator to accurately decode the data stream. Consequently, the more

complex the modulation scheme used, the shorter the distance limitation of the radio link.

If a system is using a given modulation scheme and weather conditions cause signal levels to deteriorate

below acceptable levels (risking a link failure), changing the modulation scheme to a less complex

scheme, will allow the link to remain functional, although the throughput will be low er, until weather

conditions improve. The modulation scheme can then be returned to the original scheme and the

throughput returned to normal levels.

The Horizon Compact system can be configured to automatically change modulation schemes if

environmental conditions deteriorate to the point where a wireless link may otherwise fail. This feature is

called A utomatic Adaptive Modulation (AAM). Note that AAM cannot be invoked if RLS is enabled.

The current modulation scheme (determined by the configured system mode parameter) will switch to the

lowest modulation scheme available (a number of system modes, which includes the modulation scheme,

are available for any given radio band, see Section 6.2), if the Horizon Compact units detect errored, but

corrected, frames (caused by reduced RSL levels). The original modulation scheme will be restored once

preset parameters indicate that conditions are suitable for returning to the original modulation scheme

(and return to the original bandwidth). The total outage time due to modulation downshift is

approximately 50 to 100 mS on average, with upshift down time at approximately 75 mS.

All radio bands available with the Horizon Compact support AAM.