homebrew hardware and WiFi
Wolfgang S. Rupprecht
wolfgang.rupprecht+gnus200702 at gmail.com
Sun Feb 18 19:06:28 CET 2007
Ian Stirling writes:
> Wolfgang S. Rupprecht wrote:
>> Does a GSM/wifi/bluetooth/GPS phone really need
>> 4 different RF chips and associated antennas and cabling?
> There are a large number of reasons why not - firstly, 1GHz A/D
> converter chips are both large, power-hungry, and expensive.
> Secondly, processing the output from them is hard.
> Thirdly, the dynamic range and intermodulation between different radio
> frequencies mean that it's even harder.
One of the GPS manufacturers (Garmin) at one time described their
system as a 1-bit A/D. Unfortunately they didn't say much more, so it
wasn't clear if they mixed the raw 1.5 Ghz down and then "digitized"
that or if they applied the A/D directly to the RF signal stream.
In the GPS case, the further processing involves throwing the
digitized signal at a large number of correlators and then look for a
match with the candidate waveforms. The state of the art has
progressed so much that one company SiRF, is now claiming to have the
equivalent of 200,000 software correlators in their latest Sirf-III
chip. So just thinking out loud, I wonder if it is strictly necessary
to have an 8-bit A/D at Ghz frequencies. A much simpler one might be
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/
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