1. 1 Photo: San Onofre Nuclear Generating Station Radio Channel Quality in Industrial Sensor Networks Daniel Sexton, Jay Werb SICon 05 February 9 th 2005

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3. 3 “Generic” Mesh Network Features Bi-directional  Acknowledgements and commands Multi-hop  Extend solutions and resiliency Self-healing  Reliable and flexible Standards  IEEE 802.15.4 Secure  Symmetric link to link encryption

4. 4 Anatomy of an installed system Bridge nodes interface the sensor network to the IP world Mesh nodes form a reliable backbone for routing sensor data Sensors connect to end nodes to access the network

5. 5 Value Proposition Motor Replaced Δ = 25.61°C

6. 6 IEEE 802.15.4 Standard Desirable features –250 kbps → Flexibility, low duty cycle –2.4 GHz → International –Lightweight MAC → low complexity –Simple ASIC → many sources → low cost –Network Security But will it work in a harsh factory environment?

7. 7 Does the promise match the reality? Research focuses on radio reliability in factories –Channel fading & multipath –Channel coherence –Radio performance In simulation On the wire Statistical: lost packets in factories Will channel diversity help?

8. 8 Channel Fading Multipath effects –Varies by position –Varies by frequency –Varies over time Overcome with diversity –Path diversity Costs more routing nodes –Frequency diversity Free with certain protocols

9. 9 Fading Factors Path Loss: L(dB) = 40 +10*N*LogD L= path loss at 2.4GHz D = distance in meters N=Exponential Path Loss Factor N=2 for free space Observed values of N: 1.3<N<3.7 Factors: Building Construction, Channel Obstructions This equation represents a single static channel L(dB) = 40 +10*N e *LogD N e = Value based on installation type Small Scale: L(dB) = 40 +10*N e *LogD + L s + L l L s = RV based on measured Channel Characteristics Both in time and space (Rayleigh, Rician, Nakagami, etc). Large Scale:L(dB) = 40 +10*N e *LogD + L l L l =RV based on loss from Obstructions (Walls, Doors, Ceilings) L l usually a log normal distribution – from installations of same type The better we characterize N e the less variance in L l

10. 10 Frequency Diversity In situ experiment 1 4 3 2 6 5 IEEE 802.5.4 Channels

11. 11 Diversity Gains Frequency Diversity (Greater than Coherence Bandwidth) Good Margin for fading and interference Path Diversity (Greater than 1 wave length) Good Margin for fading, some for interference Time Diversity (Greater than Coherence Time) Good Margin for interference, some for fading Methods to Obtain Diversity Gain (Small Scale) We use all Three Need to quantify Large Scale Diversity Gain NLOS Channel Rayleigh Faded

12. 12 Power Level How much power is enough? –1 mW (0 dBm) is typical power level for 802.15.4 Not enough for target 100 meter range Especially when no line of sight available –Interference from Bluetooth and WiFi Need similar power level to be heard Supporting tests and simulations to be published –Regulatory limits 36 dBm in US; 20 dBm in Europe (FH); 10 dBm some countries –Transmitter energy consumption Transmitter percentage ~35% at 15 dBm; inflection point Tested at 15 dBm –Seems about right; more field experience needed

13. 13 Covering the Bases Static Multipath Time Variant Multipath Static Interference (e.g. Microwave) Time Variant Interference (Other Networks) Spatial Diversity (Mesh Routing)  Frequency Diversity (Channel Hopping)  Temporal Diversity (Retries)   Transmit Power (15 dBm)  Overall Risk Coverage  Assumptions –Spatial diversity supports a few paths –Frequency diversity supports many channels –Path diversity directs signal away from interferers –Interference is channel limited

14. 14 Early Results Summary Industrial protocols should support diversity –Diversity gains >>10 dB –Frequency diversity is “free” –Some path diversity also provides redundancy Increase 2.4 GHz radio power to about 15 dBm –Bluetooth/WiFi coexistence –Hostile radio environment, line of sight often unavailable –Range consistent with scale of industrial applications Likely range somewhat less than 100 meters –Multihop architecture is necessary More testing needed in a wider variety of sites