700 Mhz Spectrum Auction

Ian Stirling OpenMoko at mauve.plus.com
Mon Aug 6 04:36:25 CEST 2007

kenneth marken wrote:
> On Sunday 05 August 2007 20:21:57 Derek Pressnall wrote:
>>On 8/2/07, Ian Stirling <OpenMoko at mauve.plus.com> wrote:
>>>Wolfgang S. Rupprecht wrote:
>>>However, the signals from distant stations still interfere, and increase
>>>the channel noise level, reducing range.
>>>With planned networks, this is all managed.
>>>With unplanned networks, it could in principle auto-configure, but only
>>>if everyone implements the same fairness protocol.
>>I had an idea that may help reduce radio interference in point to
>>point communications.  Lets say if one end (the base) was set up to
>>broadcast using multiple antennas aranged in some sort of pattern,

Beamforming antennas are a big future topic.
In principle, you can trade off number and arrangement of antennas so 
that you can, both reject noise in certain directions, and send less of 
your signal in different directions.
> sounds like a cross between mimo and direction finding to me.
> would be interesting to try it :)

The limit of this is pretty much the size of the device.
It can work _really_ well with devices not constrained too much in size.

For example, at 700Mhz, the wavelength is some 40cm.
With a cylindrical antenna a metre or so in diameter and a meter tall, 
you can get around a beam of 30 degrees or so.

With 1/12th the actual power needed to talk to a mobile device.

On the device itself, options are very limited.
You can accurately point the antenna (electrically) at an interfering 
source, and have the device not be interfered with it by then - but 
actually positively pointing isn't really favoured by the physics.
That only really happens when the size of the device gets over the 

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