Date: Sun, 06 Mar 2011 21:09:52 -0500 From: Etienne Robillard <erob@gthcfoundation.org> To: Bruce Cran <bruce@cran.org.uk> Cc: freebsd-chat@freebsd.org Subject: Re: can somebody explains OFDM in FreeBSD? Message-ID: <4D743E70.50109@gthcfoundation.org> In-Reply-To: <20110306223910.0000745d@unknown> References: <4D73BB23.8020806@gthcfoundation.org> <201103061758.47368.hselasky@c2i.net> <4D73C223.8040009@gthcfoundation.org> <201103061836.39151.hselasky@c2i.net> <4D73F1D2.4000208@gthcfoundation.org> <AANLkTikopx8kmjQGgkaG%2BzE5P8GXehJdQaj462hBr6nn@mail.gmail.com> <20110306223910.0000745d@unknown>
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On 06/03/11 05:39 PM, Bruce Cran wrote: > On Mon, 7 Mar 2011 05:00:42 +0800 > Adrian Chadd <adrian@freebsd.org> wrote: > > >> FreeBSD doesn't implement OFDM in the kernel. >> >> The various chipsets implement OFDM, not FreeBSD. >> >> There's no "software" OFDM. The 802.11 chipsets out there take care >> of it, not FreeBSD. >> > [moved to freebsd-chat] > > OFDM doesn't exist in the digital domain. The furthest you can go in > software is to use the I-Q pairs that represent the modulated (baseband) > data - that is, QPSK, BPSK, QAM etc. If you have a card that makes I-Q > data accessible (and I suspect most wireless cards don't) then you can > demodulate it using general-purpose software such as Matlab or a DSP > library. > > you don't need to make the transformations at the digital domain: only time domain is really what you need in a pure sinusoidal function so you could compute the reverse using sin-1. Therefore no need to go further than the OFDM layer where a custom CPU (the kernel) could 'capture' the raw 802.11 data stream and modulate an invert current according to this variable bitrate in Mb/s. -- Etienne Robillard Company: Green Tea Hackers Club Occupation: Software Developer (and CEO) E-mail: erob@gthcfoundation.org Work phone: 450-936-2123 Website (Company): https://gthc.org/ Website (Blog): https://gthc.org/blog/ PGP public key fingerprint: F2A9 32EA 8E7C 460F 1728 A1A7 649C 7F17 A086 DDEC During times of universal deceit, telling the truth becomes a revolutionary act. -- George Orwell If a free society cannot help the many who are poor, it cannot save the few who are rich. -- John F. Kennedy
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