DSP of Wideband Signals

On Sat, 05 Apr 2008 20:55:16 -0400, Randy Yates <yates@ieee.org>
wrote:

>Eric Jacobsen <eric.jacobsen@ieee.org> writes:
>> [...]
>
>Thanks for the feedback/references Eric.
>
>> It's wasn't the same signal as the current standard, 
>
>What do you mean by "current standard?" 

The IEEE 802.15.4a standard.

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org

Randy Yates wrote:
> Dave <dspguy2@netscape.net> writes:
> 
>> On Apr 4, 8:56 am, Randy Yates <ya...@ieee.org> wrote:
>>> In wideband systems such as CDMA (DSSS) and IR-UWB, the analog signal at
>>> the receiver is very wide even though the datarate may be relatively
>>> small. Therefore in order for demodulation and detection to be performed
>>> in the digital domain, very fast ADCs and front-end DSP must be
>>> utilized. In some modern IR-UWB systems, this may not be feasible due to
>>> the extreme bandwidth (>1 GHz) of the signals.
>>>
>>> Since the underlying data rate is relatively low, much of this bandwidth
>>> is "redundant" in some sense. My question is this: do techniques exist
>>> in which some of the initial demodulation is performed in the analog
>>> domain, the output of which is a much smaller bandwidth signal that can
>>> then be more tractably (and economically!) converted and processed in
>>> the digital domain?
>>>
>>> I'd love to hear ideas on this.
>>> --
>>> %  Randy Yates                  % "So now it's getting late,
>>> %% Fuquay-Varina, NC            %    and those who hesitate
>>> %%% 919-577-9882                %    got no one..."
>>> %%%% <ya...@ieee.org>           % 'Waterfall', *Face The Music*, ELOhttp://www.digitalsignallabs.com
>> Randy,
>> While not in the communications fields, Radar systems often LFM /
>> Chirp waveforms which can have a wide bandwith. To ease the ADC
>> requirements Stretch processing is often performed in the analog
>> domain.
>>
>> Instead of mixing the received signal with a constant frequency
>> sinusoid it is mixed with a signal whose frequency changes linearly
>> with time - usually the chirp rate matches that of the transmitted
>> signal.
>>
>> For radar signals a target at a specific range appears as a constant
>> frequency (different ranges appear at different frequencies). To
>> complete the pulse compression / matched filter, you simply perform an
>> FFT, and you can relate the frequency bins to particular ranges.
>>
>> Not sure if that helps or not - or if it was what you were looking
>> for.
> 
> All suggestions welcome and potentially useful. Thanks much for your
> suggestion and your time to respond, David.

In the 70s the analogue chirping and dechirping for radars was general 
achieved with SAW devices. I think some of the spread spectrum radios at 
that time may have used similar techniques.

Regards,
Steve