Cooperative Analog and Digital Signal Processing : Georgia Institute of Technology  
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Probabilistic Computing

Abstract

Biological systems hold the key to ultra-powerful computing using just microwatts of power; this research explores emulating this behavior in electrical systems. A novel, biologically inspired computing paradigm is being developed which could fundamentally change scientific and multimedia computing. This new computing approach simultaneously addresses a looming problem in semiconductor systems and many nano-electronics systems; that is, as feature sizes in computer chips are scaled down further, ideal behavior cannot always be guaranteed. In these systems, results of individual operations are described only statistically or probabilistically. A principal point of this research is to embrace probabilistic computing elements rather than to devise ways to make them ideal or deterministic. Recent research suggests that biological and other natural systems are probabilistic in nature. Thus, probabilistic technology provides a novel method to simulate biological, chemical, and neurobiological systems to reach previously unattainable simulation speeds and complexity. Additionally, many multi-media signal processing systems can take advantage of this computing approach to achieve tremendous gains in efficiency at the cost of imperceptible degradation in quality.

 

Probabilistic CMOS (PCMOS) allows a computing circuit to operate probabilistically and, as a result, achieve extreme power savings. A PCMOS circuit is a digital circuit where the supply voltage is lowered to sub-threshold levels; the output of the circuit is correct with some probability p < 1. The probabilistic nature of the computation may be artificially imposed or it may be a inevitable result of extreme semiconductor scaling. Furthermore, p can be precisely controlled using extant analog floating gate technology. This research uses PCMOS to perform computations and simulations that either require or can tolerate probabilistic behavior, specifically simulation of biological processes which can be extended to Monte Carlo simulations for any dynamical system. These methods allow orders-of-magnitude speed-up and substantially reduced power consumption. The research involves hardware, algorithmic, and theoretical aspects of probabilistic computing.

 

 

Support

  • This work is supported by the National Science Foundation awards #0726969 and #0937177

Publications

  • Bo Marr, Jason George, David V. Anderson, and Paul Hasler, "Increased Energy Efficiency and Reliability of Ultra-Low Power Arithmetic", International Midwest Symposium on Circuits and Systems (MWSCAS), p. 366-369, vol. , (2008). Published, 10.1109/MWSCAS.2008.4616812
  • Bo Marr, Brian Degnan, David V. Anderson, and Paul Hasler, "Asynchronously Embedded Datapath for Performance Acceleration and Energy Efficiency," Proceedings of the IEEE International Symposium on Circuits and Systems (ISCAS), p. 3046-3049 , (2009). Published
  • Bo Marr, Stephen Brink, David V. Anderson, Paul Hasler, "A Reconfigurable Analog System for Efficient Stochastic Biological Computation", International Symposium on Biomedical Circuits and Systems, p. 293, vol. , (2008). Published, 10.1109/BIOCAS.2008.4696932
  • Jason George, Harry B. Marr, Bilge Akgul, and Krishna Palem, "Probabilistic Design for Ultra-Low Energy Embedded Computing", Transactions on Embedded Computing, (2008). Accepted,
  • Richie Wunderlich, Bo Marr, Brian Degnan, Paul Hasler, "A Low Power Floating-Gate FPGA", Custom Integrated Circuits Conference (CICC), p. , vol. , (2009). Submitted,
  • Bo Marr, Arindam Basu, Stephen Brink, Paul Hasler, "A Learning Digital Computer", Design Automation Conference (DAC), (2009). Accepted,
  • Bo Marr, Jason George, Brian Degnan, Paul Hasler, David V. Anderson, "Error Immune Logic for Low Power Probabilistic Computing", Journal of VLSI Design, (2009). Submitted,
  • Bo Marr, Stephen Brink, Paul Hasler, David V. Anderson, "A Reconfigurable, Probabilistic Hardware for Fast Dynamical Systems," IEEE Transactions on Circuits and Systems I, (2009). Submitted,

Findings and Resources

Probabilistic Computing Resources

  • The VISEN Center at Rice University is directed by co-PI Krishna Palem

Recent Findings

  • A General Theory of Probabilistic Dynamical Systems: any dynamical system can be represented by a PCMOS system, both those that are random and deterministic by nature including biological, chemical, and nuclear systems [as reported in submitted TCAS I paper]. This theory was proven by implementing this on a reconfigurable chip, the Reconfigurable Analog Signal Processor (RASP) where probabilistic computation was successful.
  •  Neuromorphic and bio-inspired structures have been developed where the hardware itself 'learns' using floating gate technology [Marr et al, DAC, 2009]. The hardware learns and improves errors, power, and speed based on results from inputs. A chip has been produced with this technology.
  • A plot of real data from a probabilistic circuit on the reconfigurable RASP chip can be seen in [Marr et al, TCAS I, 2009] shows that we can control p, the probability of correctness for a single gate, to within about +/-2% error.
  • A prototype chip 'Reaction Gates' has been built. With the RASP reconfigurable chip, individual units do a single operation that simulates a reaction have been built that have resulted in 130X performance improvement over biological system simulations [Marr et al., BioCAS, 2008],[Marr et al., TCAS I, 2009 (submitted)].