Wednesday, July 19, 2017

On Unlimited Sampling

Ayush Bhandari just let me know about the interesting approach of Unlimited Sampling in an email exchange:

...In practice, ADCs clip or saturate whenever the amplitude of signal x exceeds ADC threshold L. Typical solution is to de-clip the signal for which purpose various methods have been proposed.

Based on a new ADC hardware which allows for sampling using the principle 
y = mod(x,L)

where x is bandlimited and L is the ADC threshold, we show that Nyquist rate about \pi e (~10) times faster guarantees recovery of x from y. For this purpose we outline a new, stable recovery procedure.

Paper and slides are here.

There is also the PhysOrg coverage. Thanks Ayush ! Here is the paper:

Shannon's sampling theorem provides a link between the continuous and the discrete realms stating that bandlimited signals are uniquely determined by its values on a discrete set. This theorem is realized in practice using so called analog--to--digital converters (ADCs). Unlike Shannon's sampling theorem, the ADCs are limited in dynamic range. Whenever a signal exceeds some preset threshold, the ADC saturates, resulting in aliasing due to clipping. The goal of this work is to analyze an alternative approach that does not suffer from these problems. Our work is based on recent developments in ADC design, which allow for ADCs that reset rather than to saturate, thus producing modulo samples. An open problem that remains is: Given such modulo samples of a bandlimited function as well as the dynamic range of the ADC, how can the original signal be recovered and what are the sufficient conditions that guarantee perfect recovery? In this work, we prove such sufficiency conditions and complement them with a stable recovery algorithm. Our results are not limited to certain amplitude ranges, in fact even the same circuit architecture allows for the recovery of arbitrary large amplitudes as long as some estimate of the signal norm is available when recovering. Numerical experiments that corroborate our theory indeed show that it is possible to perfectly recover function that takes values that are orders of magnitude higher than the ADC's threshold.

h/t Laurent.

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