[Ronja] Trying out a FPGA

[Gregory Maxwell]

On Thu, Mar 13, 2008 at 3:00 PM, Saad Shakeel
<hybrid.parameter at yahoo.com> wrote:
> Hi everyone,
>
> Just got a SPARTAN 3-E FPGA..... and was wondering if i can implement the
> some parts of the RONJA on it as well....
> I came across the SPIDER project, which was implemented on a CPLD, but i'm
> not sure if a CPLD code is compatible with an FPGA too?

If you have a DAC and ADC chips you could implement the pretty much a
complete signal chain... QAM (de)modulation on the FPGA, error
correction, equalization, etc.

A ronja type device could consist of little more than:

[ethernet mac] - [fpga] - [dac] - [voltage to current amp] - [Tx LED]
                                  - [adc] - [preamp] - [RX sensor]
                                  - [small dac] / < AGC

A digital signal chain like this is, in my opinion, the most cost
effective way to achieve speeds of 100mbit without switching to laser
diodes.

QAM 16 would should be able to fit 100mbit into the (post
equalization) bandpass or the LEDs being used for 10mbit ronja today,
though I do not know what the SNR is like on real paths.