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Jan 6th, 2013 at 7:40pm
An iDirect remote site will typically have 6 dB of uplink power control range.
When initially commissioned the nominal BUC power and bit rate towards the hub adjusts itself so that the correct C/N is achieved at the teleport hub site.
If the design good and the equipment provided is good (adequate dish size and BUC power rating) and dish pointing accurate, we hopelfully get a result like:
Modem output power is such that the BUC power is 6 dB lower than is maximum possible BUC power.
Example:
Transmit BUC maximum rated power output (at -1 dB gain compression test) = 2W or +3 dBW or +33 dBm
Actual BUC power (clear sky set up) = 0.5W or -3 dBW or +27 dBm.
In service, if it rains at the remote site, the receive signal quality at the teleport will decrease, the hub will then tell the remote site to increase its level and will continue doing this until it is told to transmit at its maximum power, as determined during the commissioning -1dB gain compression test. The system will therefore continue to operate normally even when the uplink rain fade at the remote is 6 dB.
It does assume that your antenna is pointed perfectly and that your dish and BUC power rating are adequate. Note that it is very tempting to use cheap (smaller dish/lower power BUC) and poor alignment accuracy and waste some or all of the ULPC range in a poor installation. Such sites may well work perfectly in clear sky but will have rain outages for a higher proportion iof the year.
How often you get fades deeper than 6 dB at 30 GHz depends on your rain. During such times it is possible to mitigate (i.e. make less bad) the problem by reducing your terminal transmit bit rate, rather than loosing service altogether. Approx 3 dB of benefit can be achieved by each halfing of the transmit bit rate. This is called adaptive modulation/coding. This technique is used in Hughes HX, HN9000 etc but I'm not sure about iDirect.
Best regards, Eric.
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