I hope this adds a bit of light, rather than just heat, to the discussion.
Real global satellite coverage is impossible from the geostationary orbit (GEO) - that position, some 35,000+ KM above the equator, in which a satellite orbits at the same speed as the earth rotates and, therefore, appears to be stationary above a single point on the earth. A little basic arithmetic will show you that the coverage stops will short of e.g. Alert - as others have said.
Most satellites use multiple antennas and multiple signal "shapes" to direct their beams to specific target markets or areas of interest. Some frequency bands are better for wide area coverage, others are better suited to "spot" service. Most satellites operates n the 4-8, and 12-40 GHz bands - subdivided by relatively senseless and non-standard letter codes.
In general, three satellites in GEO (with at least one spare 'parked' in orbit) can cover most of the surface of the planet from 80oN to 80oS - which is pretty nearly global coverage.
To get real global coverage one must use satellites in non-geostationary orbits (NGSO). There are many NGSO schemes: low earth orbit (LEO) (think e.g. Iridium), medium earth orbit (MEO) (think e.g. Globalstar) or high earth or highly elliptical orbit (HEO) and polar orbit, and, and, and ... Each has pros and cons but each requires:
1. A 'constellation' of satellites, say a dozen for MEO and 60+ for LEO to provide near real time, 24/7, global coverage; and
2. Some combination of high power on the satellites - to deal with, say, hand held earth stations, and/or high gain and steerable antennas on earth - to deal with relatively low power satellites.
I no longer know anything about costs, but way back back when, circa 1995, I knew that Motorola spent in excess of $10 billion to launch 66 LEO satellites. I forget how many launches there were (11 or 12, I think) but it was a big expenditure.
Could Canada do such a thing, launch its own military, global satellite constellation? Technically, yes. It is rocket science, but we can do it. Can we afford it? Broadly, yes; Canada can afford it, DND cannot. Could a consortium of nations launch a shared government/military global satellite system? Yes, provided they are really trusted allies - let's say they have not fired shots in anger (at one another) for more than 100 years. The problem with shared systems is that the 'partners' must agree to share control and information - something the US, for example, is always reluctant to do. Can a 'consortium' that does not include the USA design, build, launch and manage really effective, secure, global satellite networks for surveillance and warning and C2? Yes. Much of the technology the USA does not want to share with allies comes from Australian, British, Canadian, Dutch and e.g. Singaporean universities and research centres.
Satellites are not (overly) complicated but they are expensive.
