NNSquad - Network Neutrality Squad
[ NNSquad ] Lightsquared
(For NNSQUAD if you wish). One detail that needs to be mentioned about the decisions involved in the design of GPS receivers that might have made existing receivers significantly more vulnerable to overload by powerful transmitters on nearby frequencies as planned by Lightsquared is that both of the re-purposed bands in which Lightsquared intends to locate powerful terrestrial signals are internationally allocated essentially world wide for Mobile Satellite Service uplinks and downlinks and have been in that status for around 30 years. Specifically the band from 1525-1559 MHz immediately below the GPS L1 allocation has been (and still is) allocated and used more or less exclusively for weak downlink signals from geo synchronous mobile communications satellites. None of these signals much exceed around -110 DBM on omni antennas and pose no interference problem at all to GPS receivers at the 1575.42 MHz L1 frequency. And until Lightsquared proposed 1500 watt terrestrial signals in that band it would have been quite a safe assumption that few high powered signals were to be found there world wide as they would seriously interfere with mobile satellite reception. Lightsquared, of course, proposes to handle this over the USA by making deals with the (other) mobile satellite providers to use much less spectrum for USA aimed mobile satellite downlinks so their terrestrial base stations can fill the rest of the downlink spectrum with high powered local signals. And the bands immediately above the GPS L1 frequency - including the uplink band for geosync mobile satellite at 1626-1660 MHz that may also have some Lightsquared terrestrial signals in it under their proposals - were previously occupied under international allocations by relatively low powered uplinks from widely and very thinly dispersed mobile satellite terminals transmitting occasionally - and for the higher powered signals - mostly via highly directional dish or flat plate type antennas aimed directly at the satellite from user platforms. While these signals would be much stronger for a nearby GPS receiver than the downlink band signals, they are further away in frequency and not very common in typical areas where consumer GPS is most often used. In contrast - in addition to some possible Lightsquared base signals in this band - there may be MANY hundreds of thousands of mobile transmitters transmitting from omnidirectional antennas and much more of the time in this band and commonly from around areas where consumer GPS is used. While one might argue that designing more bulletproof GPS front ends would have been a good idea (but hardly cost effective in a cost sensitive market) it was a pretty reasonable assumption that both of those adjacent bands had low probabilities of containing strong persistent interfering signals more or less world wide because of what they were internationally allocated for. And Lightsquared is radically changing this, long after many hundreds of millions of GPS receivers have been designed with these assumptions in mind, deployed and are in daily use. -- Dave Emery N1PRE/AE, die@dieconsulting.com DIE Consulting, Weston, Mass 02493 "An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either."