SatSig topic:

COTM using Spread Spectrum

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Sep 13^th, 2008 at 6:13pm

COTM using iDirect Spread Spectrum, how do we calculate or know whether this will cause interference to the adjacent satellite?

By the way what the ITU Spec for adjacent satellite interference?

Sep 13^th, 2008 at 11:03pm

Ask your satellite operator if your proposed parameters will comply with the intersystem coordination agreements they have reached with other nearby satellites.

They will need to know your proposed power into the feed of your transmit earth station and your actual transmit carrier bandwidth (including spreading) and how many earth stations will be transmitting on the same frequency. They will need to know the transmit main beam and sidelobe envelope of your transmit antennas.

Best regards, Eric.

Sep 14^th, 2008 at 12:11am

What kind of platform do you intend to communicate on-the-move from? Vessel? Aircraft? Vehicle?

There are a variety of antennas on the market (phase array, stabilized parabolics, VICTS, etc) and anyone interested in tackling COTM should ensure they do the necessary homework prior to engaging such a task. Matter of fact, I would recommend getting ahold of iDirect in Herndon and have them assist you with your efforts, so you don't recreate some of the lessons they have already learned (antennas specifically). The nice thing about iDirects direct sequence spread is that it is TDMA, so only one system is transmitting at a time in the SS inbound(s)...whereas CDMA requires you to keep track of everyone in that upstream.

As Eric said, get ahold of your BW service provider (Intelsat, SES, Eutelsat, etc) and have them run some budgets based on your platform specifics (make sure you have the specs on your system readily available when you call them). Lastly, expect to be challenged by the laws of physics.

Sep 14^th, 2008 at 4:18pm

Hi,

thanks.

cotm will be using on vehicle.

Some questions:
1) iDirect modem give Rx SNR value. What this SNR relationship to Eb/No ?
2) How do we calculate the spreading gain (dB) ?

regards,
w