On 1/03/2016 8:57 AM, Tom Worthington wrote: > > On 28/02/16 13:46, Frank O'Connor wrote: > >> So all the observed trends, the increase in speeds ... aren’t gonna >> appear... > > Speeds will increase, but people want stuff they can carry around with > them, not have it stuck on a desk at home. Only the devices I choose to carry around. I want my TVs, security alarm system, audio system, kitchen appliances stuck at home - and operating connected 24x7, so a docking station system where everything stops when I take the CPU away with me in my pocket need not apply. They are also likely to require far more capacity and speeds than any stuff that is small and light enough that I might carry around.
> > >>> Cell phones were invented to overcome the limited spectrum. >> >> ... I’m interested in knowing EXACTLY what you were trying to say. >> ... > > Cell phones use radio transmission in small geographic areas, called > "cells", which allows the spectrum to be reused. The cells were > originally many kilometers, but now can be tens of meters (for > example covering a few houses in a street): > https://en.wikipedia.org/wiki/Cellular_network#Frequency_reuse When cell-sizes are many kilometres radius, covering areas of up to 100 square kilometres, it is efficient to build the high cost of the central radio transmitters, receivers, masts and mountings, power connection and fibre or microwave backhaul connection, as this cost was very small in comparison to running a real link to each of the locations within the area, or compared to the large number of mobile devices and people that could be served in that area and the costs amortised over. When you shrink the cell-size, so that much the same capacity and radio bandwidth is shared amongst a much smaller set of users, and you then need vastly greater numbers and costs of basestation infrastructure that efficiency evaporates at some point and it becomes more costly (and more prone to failure) to build a gazillion base-stations than to just dig and run a cheap cable. Also, in the context of frequency re-use, the signal strength at the edge of the zone has to be weak so as not to interfere with an adjacent zone using the same frequencies. This means there is a band around the circumference where the signal strength is measurable, but too low to provide satisfactory service - yes the signal extends many kilometres, but the outer half-kilometre is useless. In a large cell this zone is a small proportion of the total area, so is acceptable. As you shrink the cell diameter, that 'useless zone' becomes a larger and larger proportion of the total area of the cell, and the cell becomes less space-efficient. A cell with only 'tens of metres' range, covering a few houses in a street, might provide sufficient signal strength at the street to provide great service to cars and all the letterboxes at the bottom of the driveways - but that's not where people need service. At the actual dwellings at the end of 5- - 15 metre driveways, and with signal levels dropping further through the walls, is precisely where the signal will be weakest and slowest - the useless zone. Paul. _______________________________________________ Link mailing list [email protected] http://mailman.anu.edu.au/mailman/listinfo/link
