System Level Low Power Design: A Case Study

1. System Level Low Power Design: A Case Study SonaliChouhan*, M. Balakrishnan#, and Ranjan Bose* *Electrical Engineering Department #Computer Science and Engineering Department Indian Institute of Technology Delhi, India

2. Outline SLD Workshop Case Study Introduction Problem definition Design space exploration framework Energy models Trade-offs in using error control codes (ECCs) Exploration of the design space Validation

3. SN SN SN SN SN SN CH CH SN SN SN SN SN SN BS BS CH CH SN SN SN SN SN SN SN SN SN SN CH CH SN SN SN SN SN SN SN SN SN SN SN SN Sensor Network SN- Sensor Node CH- Cluster Head BS- Base Station(Sink) SLD Workshop Case Study 3

4. Advantages SLD Workshop Case Study Intimate connection with immediate environment Useful in unsafe and repeated field studies Economical for long term data collection Single deployment, multiple utilization 4

5. Critical Issues Low energy Consumption Low power Consumption SLD Workshop Case Study Requires long life Battery driven 5

6. Wireless Sensor node System Architecture 1 Computing Unit 2 Communication Unit 3 Sensing Unit 4 Power Supply 4 3 1 2 Memory Memory Battery Battery Sensors Sensors ADC ADC MPU MPU Radio Radio Mixer I/P Signal Filter Filter PA LO SLD Workshop Case Study

7. While Taking Design Decisions.. SLD Workshop Case Study • Must consider computation, circuit and signal transmit energies • Application driven parameters are important Bit Error Rate (BER) Inter-node distance Path Loss Exponent

8. Applications & Typical BER SLD Workshop Case Study

9. To Achieve Low BER SLD Workshop Case Study Increase SNR Use Error Control Codes (ECCs)

10. Error Control Codes Redundancy Data Code Word SLD Workshop Case Study • Energy gain • Coding gain saves energy • Energy Cost paid • Transmitting “redundant” bits • Encoding-Decoding

11. Encoding/Decoding Encoding/Decoding Coding Gain Coding Gain > < + + Additional coding bits Additional coding bits SNR Increase v/s ECC Encoding/Decoding Increased SNR Coding Gain Additional coding bits With ECC (Case 2) Without ECC With ECC (Case 1) Computation Energy Circuit Energy Signal Energy Energy Saving Energy Components SLD Workshop Case Study

12. Error Control Codes Encoder Decoder C Model Processor Architecture Performance Model Channel Model Distance Bandwidth Operating Freq Modulation Scheme Computation Energy Model Radio Energy Model Path Loss Exponent Ckt Compo Power Combined Energy Packet Length Exploration Framework BER SNR SLD Workshop Case Study Energy Per Bit

13. Radio Energy Model Power Amp Power Filter Power Circuit Energy Model Circuit Energy Per Bit LNA Power Mixer Power Oscillator Power Total Radio Energy Per Bit Inter-node Distance Bit Error Rate Bandwidth Signal Energy Model Signal Transmission Energy Per Bit Operating Frequency SNR Channel Condition Modulation SLD Workshop Case Study Packet Length

14. Signal Energy Model b – No. of bits B – Bandwidth N0/2 – AWGN PSD NF – Receiver noise figure SNR – Signal to Noise Ratio Gr, Gt – Antenna Gain L – Packet Length – Wavelength d – Inter-node distance SLD Workshop Case Study

15. Circuit Energy Model SLD Workshop Case Study

16. Circuit Energy Model SLD Workshop Case Study • Power Components: • Low Noise Amplifier (PLNA) • Mixer (PMix) • Frequency synthesizer (PFS) • Filter (Pfilter) • IFA (PIFA) • Power amplifier (PPA)

17. Computation Energy Model SLD Workshop Case Study • Sim-Panalyzer’s energy simulator • Cycle accurate • Simulates StrongArm SA1100 processor • Models • Cache power • Datapath & execution unit power • Clock tree power • I/O power

18. Design Space Exploration SLD Workshop Case Study • Error Control Codes • Hamming • Reed-Solomon • Convolution • Application and deployment parameters • Distance • Environment • Bit error rate

19. Exploration Setup SLD Workshop Case Study • Configured computation energy simulator for node • operating frequency • Instruction and data cache • Considered O-QPSK modulation scheme • Considered 2 types of nodes • Type I : decoding done at non-energy constraint end • Type II: decoding done at battery powered node

20. Exploration Results (Type I Node) SLD Workshop Case Study

21. Exploration Results (Type I Node) SLD Workshop Case Study

22. Type II Node Energy SLD Workshop Case Study

23. Node Energy v/s Distance SLD Workshop Case Study

24. Node Energy for Different BER RS Codes SLD Workshop Case Study

25. Effect of Path Loss Exponent RS Codes ~ 60% SLD Workshop Case Study

26. Conclusions SLD Workshop Case Study • Proposed methodology for energy consumption based design space exploration • Trade-off between computation-radio energy • Integrated framework takes into account • Computation energy • Radio energy • Framework is generic, can account for different processors, ECCs, modulation schemes, application parameters

27. Framework for Validation of Computation-Radio Energy Trade-off in Sensor Node

28. Previous Results SLD Workshop Case Study

29. Previous Results • EECC_Coded < Euncoded • Ratio of computation-radio energy varies with ECC • Energy optimal ECC varies with distance • Analyzed ECC energy behavior with its parameters • Validation SLD Workshop Case Study

30. API C# Application Compiler Tools (to see output) Sensor Node (Proc + Radio) USB DMM Sensor Sensor Sensor Node Sensor Node Power Supply Power Supply System and Setup SLD Workshop Case Study

31. System and Setup • imote2 wireless sensor node SLD Workshop Case Study

32. System and Setup • SNR v/s Inter-node distance SLD Workshop Case Study

33. System and Setup • Energy Measurement SLD Workshop Case Study

34. SLD Workshop Case Study