[LINK] tRe: NBN white-elephant-to-be ...

Stilgherrian stil at stilgherrian.com
Thu Aug 26 10:03:07 AEST 2010

On 26/08/2010, at 9:34 AM, Richard Chirgwin wrote:
> Let's pick up cells of max size 500 metres, and ignore two side issues 
> (how much will 100,000 towers in Sydney cost, and will people tolerate 
> wireless towers everywhere?). Let's just stick to performance.
> From page 399 of "3G Evolution: HSPA and LTE for Mobile Broadband", 
> (Dahlman, Parkvall, Skold and Beming, Academic Press, ISBN 
> 978-0-12-372533-2), there is a graph charting LTE capacity.
> If the system is using 5 MHz radio channels, the performance at 500 
> metres from the base station is 20 Mbps; with 10 users, the per-user 
> budget is about 2 Mbps.
> The charts for performance with 20 MHz radio channels are harder to 
> interpret, but the best total throughput of the entire radio channel is 
> about 110 Mbps - about 10 Mbps if there's ten users in the cell (my 
> interpretation of the chart given on page 404 of the same book).
> So: let's assume that whether we're in the city or the country, we can 
> serve almost adequate bandwidth to ten users in one cell; that the total 
> capex of a base station (with three cells) is about $90,000. We get 
> 90/30 or $3,000 capex per household. It's not so much cheaper than 
> pulling fibre.

Richard, your figures are based on 10 active users per cell. But in a 500-metre radius of a tower, in suburban or outer metropolitan areas, surely there would be many more than 10 households in a 500-metre radius of the tower? How does this affect your back-of-envelope model?

Also, if we're talking about wireless as ubiquitous last-mile connectivity, and you can only provide acceptable speeds to 10 simultaneous users per cell, then presumably at peak household broadband times in the evenings that means a cell per every 10 households not for every 10 simultaneous users. Or maybe every 20 households, given non-users and people not at home for the evening and so out.

That brings us back to Narelle Clark's comment, "In order to get those 100 megabit speeds and beyond you'd need to be installing a base station around about on every suburban block," she said. "At the end of every street there'd need to be a base station."


I'm looking at a satellite image of Yagoona in Sydney's west, as random an Australian suburb as any with its streets of red-tiles houses. Counting 10 houses, it does indeed look more like a base station every 100m, not every 500m.

Disclaimer: Due to Bavaria, this morning my arithmetic may not be reliable. Caveat lector.


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