<A Globalstar handset in a city would whisper to a nearby terrestrial basestation [not handset - I made a mistake there which made it more unintelligible than it already was without the mistake], not cluttering the space-links of other handsets because the signal would be so weak. When that handset is used in rural areas without terrestrial Globalstar coverage, it would crank up the decibels and call out to a satellite 1414 or 2,000 km away.>
So, in plain American:
If the governments let Globalstar use the spectrum for terrestrial links as well as links to the satellites, that would be good. It would be good because at the moment, a Globalstar phone, using the Globalstar frequencies, can only connect via the satellites. If there is a tree or building or something blocking the signals to and from the satellites, then the phone can't make a connection.
But, if there are base stations built on the ground around cities [or up on buildings, on towers etc, the same as the usual cellphone towers you see around the place], then the Globalstar phone could connect via that ground link rather than through the satellite. That's good because not only would it enable the person to make a call, but it's cheaper to provide ground links in cities and towns than it is to provide satellite service. Which was the idea of the existing Globalstar phones being dual mode or tri mode = so that they could connect via existing cellphone ground links when that method was selected.
But because it will be years before there are enough Globalstar phones in service to justify building terrestrial links in the Globalstar frequency, some terrestrial-only phones might as well be made to use that spectrum which is otherwise going to waste. They could be the usual, small, cellphone [which would not be good enough to connect to satellites]. When QUALCOMM has their RadioOne multimode, multiband phones going, doing this should be a doddle [an easy thing to do]. Multimode means 'can work in the different modes', being CDMA, GSM, cdma2000, 1xRTT, 1xEV, GPRS, W-CDMA. Multiband means 'can work in the different frequencies', from 450 MHz up to, I suppose, 3GHz.
Because spectrum is so valuable, it's a way of making use of the Globalstar spectrum which would otherwise be wasted. It's also a way of providing service to a person who has a single-mode Globalstar phone when they are in urban areas. When Globalstar phones are multimode and multiband, [I suppose in 3 years] they will be able to connect through whatever terrestrial service is available, even if it isn't on the same frequency as Globalstar.
The whispering business is referring to the fact that CDMA phones send a signal which is just strong enough to connect with low error rates. The phone turns it's transmit power up enough to maintain connection to the base station. When the phone is 1 kilometre from a basestation, it takes a very weak signal to maintain connection. But when it has to send the signal at least 1414 kilometres, [the altitude of the satellites] the signal has to be more powerful. But apparently nowhere near as much as you'd think. It's not comparable to shouting 1 kilometre and then shouting 1500 kilometres. [It was Clark Hare who explained that to me]. That's because of antenna gain or whatever it's called [how well the aerial [the antenna by another name] receives the signal]; I suppose that's why the Globalstar phones have big aerials and the satellites have big signal receivers which detect weak signals.
Animals which need to have good hearing [like bats] have big ears which gives them great "antenna gain" because they collect a lot of sound in their big ears.
Because the phones adjust their volume to the right signal level to maintain connection, they aren't polluting the spectrum with more signal than is needed. You probably recall the cocktail party CDMA analogy - if everyone would whisper, the total number of conversations which could be conducted would increase. CDMA spectrum is efficient partly because of this whispering process.
Because CDMA systems are noise-limited [they can only tolerate so much noise and then no more phones can connect because the spectrum is full], this terrestrial use of Globalstar spectrum would enable more ground to satellite links if a lot of Globalstar phones in an area were connecting terrestrially rather than via satellite.
But now that I think more about it, it would be better if the urban phones connected via another frequency band than the Globalstar one, as that will reduce the total noise in the Globalstar system and leave more room for ground to satellite links. But I suppose that depends on how busy those other terrestrial frequencies are. If they are too busy, it would be better to go via the the Globalstar spectrum if it's not busy. We end up back at WackyWireless where the phone connects via whichever system and frequency is available at the cheapest price.
Since this is all stupid and irrelevant over the next couple of years anyway, because almost nobody is using the Globalstar system, it's not going to bring in money or help subscribers any time soon. Globalstar is certainly not in a position to build a bunch of terrestrial base stations in the Globalstar frequencies now.
But in 3 years, the spectrum should be used more effectively and Globalstar phones should be multimode and multiband, connecting [if customers choose that plan] via WackyWireless algorithms to gateways via satellite or direct to terrestrial basestations.
Thank you for making me explain it properly so that I see why it's not such a great idea right now.
I think that explains things quite well. Please tell me to make it simpler if necessary. I still don't think it's very clear.
Pixilated,
Mqurice |
