Efficient Data Acquisition

Efficient data acquisition is key in diverse fields such as bio-medical applications, radar, communications, image processing and more. We develop efficient sensing approaches based on either rethinking the hardware components, improving the dynamic range,  optimizing for a relevant task, or taking the signal structure into account. Several examples of our new sensing devices are given below.

 

Time Encoding Machine (TEM)

The time encoding machine (TEM) is an asynchronous event-driven method that samples and quantizes timings rather than amplitudes. Since TEM is not dependent on a global clock, it consumes less power. Furthermore, in contrast to traditional ADCs, increasing the signal's amplitude reduces the timing quantization dynamic range, cutting the number of bits per sample required. Thus, we can reduce power and bits while leveraging low-cost and simple hardware by combining TEM sampling with our robust recovery algorithms for a variety of signals.

TEM
                                         TEM Prototype
TEM_GUI_2021
           TEM Prototype Graphic User Interface

                                         

 

   

    

 

 

 

 

Unlimited Dynamic Range ADC

Transmission medium or processing devices have limited dynamic range, meaning that signals beyond a certain dynamic range are clipped. A modulo operation can be used to limit the dynamic range prior to transmission. We suggest a robust modulo operation and recovery method with high accuracy, which enables sampling and processing signals of wide dynamic range using a small number of bits.

Modulo
                 Unlimited Dynamic Range ADC Prototype
Modulo_FRI_GUI_2021
              UDR Prototype Graphic User Interface

 

 

 

 

 

 

 

 

 

Analog Precoder 16X4

Another aspect we address in the lab is taking the specific task into account in order to reduce both sampling and quantization rates. Conventional ADCs are designed to facilitate recovery of the received signals by sampling at the Nyquist rate and using high resolution quantizers. However, to meet the ever-increasing demand for higher data rates nowadays, the dimensionality and bandwidth of the received signals can be extremely high. To address this issue, we propose efficient task-based quantization using the fact that, in practice, signals are often acquired in order to extract some underlying information, i.e., for a specific task. Our task-based approach first introduces an analog combiner which reduces the dimensionality of the input and then scalar quantizers are employed considering practical hardware limitations, followed by a digital domain processing module. This allows the acquisition of many classes of signals using low bit systems.

analog
Analog Pre-Coder for Task Based Quantization Prototype
ask_Based_GUI_2021
           Task Based Quantization Graphic User Interface

       

 

 

 

 

 

 

 

Sub-Nyquist Sampling

Finally, by exploiting structure in a wide class of analog signals, we can reduce sampling and processing rates to far below the Nyquist rate. Our approach relies on modeling the structure as a union of subspaces, and then designing preprocessing that aliases the signal prior to sampling. The aliased signal has lower dimension and can therefore be sampled at a low sub-Nyquist rate. Compressed sensing methods are then used to recover the underlying signal. Examples of this approach include low-rate sampling of pulse streams for radar and ultrasound and low-rate sampling of multiband signals for cognitive radio.

Sub-Nyquist sampling

    sub
                                                                                  Sub-Nyquist sampling systems in a variety of applications

     

    Sub-Nyquist Radar Prototype

    We designed a Xampling-based hardware prototype that allows sampling of radar signals at rates much lower than Nyquist. We demonstrate by real-time analog experiments that our system is able to maintain reasonable detection capabilities, while sampling radar signals that require sampling at a rate of about 30MHz at a total rate of 1Mhz, namely, at 1/30 of the Nyquist rate even in the presence of strong noise and clutter.

    prototype
                                                                       Sub-Nyquist Radar Prototype

    Sub-Nyquist Radar with Distorted Pulse Shape

    The radar prototype below can be extended to the blind setting where the pulse shape is not known by adding an additional receiver. The performance with two sub-Nyquist receivers is the same as that of a single sub-Nyquist system with a known pulse.

    Sub-Nyquist sampling
    Sub-Nyquist Radar with Distorted Pulse Shape Prototype
    Sub-Nyquist sampling
    Sub-Nyquist Radar with Distorted Pulse Shape Prototype

     

     

     

     

     

     

     

     

    Multiple-Input Multiple-Output (MIMO) radar

    Extending the ideas to a collocated multiple-input multiple-output (MIMO) radar. The setup allows reduced rate sampling in both the spatial and spectral domains at rates much lower than dictated by the Nyquist sampling theorem. We use frequency division multiplexing (FDM) to achieve the orthogonality of MIMO waveforms and apply the Xampling framework for signal recovery.

    cog
                                   Cognitive Sub-Nyquist Collocated MIMO Radar Prototype

     

    References