Green Data Acquisition

Developing energy-efficient signal processing hardware is crucial for advancing environmental sustainability in modern Information Processing Systems (IPSs). Our focus is on leveraging signal processing innovations to mitigate energy consumption, thereby fostering the green evolution of technology. Analog-to-Digital-Converters (ADC) are crucial hardware components in modern IPSs. Global clock, dynamic range, and application dependency are three major factors that govern the performance and power of an ADC. This proposal introduces methods to reduce power in the field of ADCs by improving upon their governing factors. Specifically, we introduce three energy-efficient ADCs, referred to as "Green ADCs": Time-Encoding-ADC, Modulo-ADC, and Task-Based-ADC, by incorporating optimized analog pre-processing and digital post-processing techniques. Particularly, time-encoding-ADC eliminates the need for a global clock by encoding time intervals between events and converting them into digital signals. This greatly simplifies the ADC's design and reduces the power consumption and required bits while still ensuring optimal signal recovery. Modulo-ADC addresses the dynamic range issue by using the non-linear modulo operator. This reduces the requirement for ADCs with high dynamic range, leading to lower power consumption and a lower bit rate while again enabling optimal recovery. Task-Based-ADC is designed to optimize the ADC for a specific application, resulting in lower overall design complexity and power consumption. We believe that the deployment of Green-ADCs holds significant promise for enhancing the environmental sustainability of modern IPSs by reducing the power consumption of digital systems across different silos including medical applications, communication, radar, defense technologies and more. 


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 Prototype
           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.

                 Unlimited Dynamic Range ADC Prototype
              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 Pre-Coder for Task Based Quantization Prototype
           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-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.

                                                                       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.

                                   Cognitive Sub-Nyquist Collocated MIMO Radar Prototype