Building Robust Wireless LAN for Industrial Control with DSSS-CDMA Cell Phone Network Paradigm

1. Building Robust Wireless LAN for Industrial Control with DSSS-CDMA Cell Phone Network Paradigm Qixin Wang Department of ComputingThe Hong Kong Polytechnic University

2. The demand for real-time wireless communication is increasing. Mechanical Freedom / Mobility Ease of Deployment / Flexibility

3. The demand for real-time wireless communication is increasing. Cables for connecting various monitors to anesthesia EMR

4. The demand for real-time wireless communication is increasing. Reduce the risk of tripping over wires Future Today

5. What is real-time? Robotic Surgery: each task is a continuous loop of sensing (or actuating) jobs Each job: 1. Must catch deadline 2. Does not have to be fast

6. What is real-time? Aviation and Industrial Control: each task is a continuous loop of sensing (or actuating) jobs Each job: 1. Must catch deadline 2. Does not have to be fast

7. What is real-time? A typical real-time task is a continuous loop of periodic jobs. Job: (Period, Exe. Time, Deadline) A Job Deadline Exe. Time Exe. Time Exe. Time Time Period

8. What is real-time? A typical real-time task is a continuous loop of periodic jobs. Job: (Period, Exe. Time, Deadline) Real-time = each job catches deadline Real-time ≠ running fast A Job Deadline Exe. Time Exe. Time Exe. Time Time Period

9. Reliability and Robustness is the top concern for real-time wireless communication. Cannot back off under adverse wireless channel conditions

10. Reliability and Robustness is the top concern for real-time wireless communication. Cannot back off under adverse wireless channel conditions

11. Reliability and Robustness is the top concern for real-time wireless communication. • Adverse wireless medium • Large scale path-loss • Multipath • Persistent electric-magnetic interference • Same-band / adjacent-band RF devices

12. Nowadays wireless LANs are NOT real-time. IEEE 802.11b IEEE 802.11g IEEE 802.11e MACAMACAW IEEE 802.11a IEEE 802.15.1 IEEE 802.15.4 1994 2005 2003 1999 2002

13. Nowadays wireless LANs are NOT real-time. IEEE 802.11 packet loss rate in an industrial environment [Willig02] Trace ID (87sec/trace)

14. Nowadays wireless LANs are NOT real-time. IEEE 802.11 packet loss rate in an office environment [Ploplys04]

15. Nowadays wireless LANs are NOT real-time. IEEE 802.11 packet loss rate in an office environment [Ploplys04] Why?

16. Design philosophy mismatch: pursuing large data throughput & short delay

17. Design philosophy mismatch: pursuing large data throughput & short delay Signal Energy Time

18. Design philosophy mismatch: pursuing large data throughput & short delay Send packet fast Do not spend much time accumulate strength Signal Energy Time

19. Design philosophy mismatch: pursuing large data throughput & short delay Signal Energy Time

20. Design philosophy mismatch: pursuing large data throughput & short delay Signal Energy Time

21. Design philosophy mismatch: pursuing large data throughput & short delay Signal Energy Time

22. Observation: Real-time communications are usually persistent connections with low data rate Typical inter-node traffic: 100~200 bit/pkt, 10~1 pkt/sec per connection.

23. Observation: Real-time communications are usually persistent connections with low data rate Typical inter-node traffic: 100~200 bit/pkt, 10~1 pkt/sec per connection. Information Theory: Lower data rate  higher robustness.

24. Observation: Real-time communications are usually persistent connections with low data rate Typical inter-node traffic: 100~200 bit/pkt, 10~1 pkt/sec per connection. Information Theory: Lower data rate  higher robustness. Direct Sequence Spread Spectrum (DSSS) Technology: Lower data rate  Higher robustness

25. Tutorial on DSSS

26. Tutorial on DSSS Data stream, a.k.a bit stream. Bit rate: rb .

27. Tutorial on DSSS Pseudo Noise Sequence (PN) Stream, a.k.a chip stream. Chip rate: Rc. Data stream, a.k.a bit stream. Bit rate: rb .

28. Tutorial on DSSS Pseudo Noise Sequence (PN) Stream, a.k.a chip stream. Chip rate: Rc. Definition: Processing Gaing := Rc/rb . Data stream, a.k.a bit stream. Bit rate: rb .

29. Tutorial on DSSS Pseudo Noise Sequence (PN) Stream, a.k.a chip stream. Chip rate: Rc. Definition: Processing Gaing := Rc/rb . Data stream, a.k.a bit stream. Bit rate: rb . DSSS Modulated Stream, a.k.a Scrambled Stream DSSS Modulated Stream, a.k.a Scrambled Stream

30. Tutorial on DSSS Pseudo Noise Sequence (PN) Stream, a.k.a chip stream. Chip rate: Rc. Definition: Processing Gaing := Rc/rb . Same PN Sequence Data stream, a.k.a bit stream. Bit rate: rb . DSSS Modulated Stream, a.k.a Scrambled Stream DSSS Modulated Stream, a.k.a Scrambled Stream

31. Tutorial on DSSS Pseudo Noise Sequence (PN) Stream, a.k.a chip stream. Chip rate: Rc. Definition: Processing Gaing := Rc/rb . Same PN Sequence Data stream, a.k.a bit stream. Bit rate: rb . DSSS Modulated Stream, a.k.a Scrambled Stream DSSS Modulated Stream, a.k.a Scrambled Stream Original Data

32. Tutorial on DSSS Pseudo Noise Sequence (PN) Stream, a.k.a chip stream. Chip rate: Rc. Integration = gEc for each bit (Ec is the energy of a chip) Definition: Processing Gaing := Rc/rb . Same PN Sequence Data stream, a.k.a bit stream. Bit rate: rb . DSSS Modulated Stream, a.k.a Scrambled Stream DSSS Modulated Stream, a.k.a Scrambled Stream Original Data

33. Tutorial on DSSS If a different PN Sequence is applied … +1 +1 +1 -1 -1 -1 +1 +1 +1 +1 -1 -1

34. Tutorial on DSSS If a different PN Sequence is applied … +1 +1 +1 -1 -1 -1 +1 +1 +1 +1 -1 -1 Another scrambled sequence

35. Tutorial on DSSS If a different PN Sequence is applied Integration = Gaussian Noise … +1 +1 +1 -1 -1 -1 +1 +1 +1 +1 -1 -1 Another scrambled sequence

36. Observation Bit Error Rate Processing Gain • DSSS Technology: Larger Processing Gain g Lower data rate  Lower Bit Error Rate (Higher robustness)

37. Observation: DSSS can exploit low data rate to achieve higher robustness DSSS BER Upper Bound

38. Observation: DSSS can exploit low data rate to achieve higher robustness Bit Error Rate DSSS BER Upper Bound

39. Observation: DSSS can exploit low data rate to achieve higher robustness Bit Error Rate DSSS BER Upper Bound Constant

40. Observation: DSSS can exploit low data rate to achieve higher robustness Processing Gain Bit Error Rate DSSS BER Upper Bound Constant

41. Observation: DSSS can exploit low data rate to achieve higher robustness Processing Gain Bit Error Rate DSSS BER Upper Bound Constant Bit Rate

42. Observation: DSSS can exploit low data rate to achieve higher robustness Processing Gain Bit Error Rate DSSS BER Upper BoundLower data rate rb Constant Bit Rate

43. Observation: DSSS can exploit low data rate to achieve higher robustness Processing Gain Bit Error Rate DSSS BER Upper BoundLower data rate rb Larger Processing Gain g Constant Bit Rate

44. Observation: DSSS can exploit low data rate to achieve higher robustness Processing Gain Bit Error Rate DSSS BER Upper BoundLower data rate rb Larger Processing Gain g Lower Bit Error Rate PBER(higher robustness) Constant Bit Rate

45. Key Idea: How to configure for max robustness for adverse wireless medium?

46. Key Idea: How to configure for max robustness for adverse wireless medium? Answer: Use DSSS, deploy as slow data rate rb (i.e., as large processing gain g) as the application allows.

47. Solution Heuristics DSSS with low data rate for high robustness PHY:DSSS

48. Observation: Centralized, last-hop wireless scheme is preferred Centralized: Economical & Simple PHY:DSSS

49. Observation: Centralized, last-hop wireless scheme is preferred Centralized: Economical & Simple Last-Hop: reuse legacy wired backbone PHY:DSSS

50. Solution Heuristics DSSS with low data rate for high robustness Centralized WLAN paradigm PHY:DSSS