UCLA ENGINEERING Computer Science School of EECS, Peking
University On Heterogeneous Neighbor Discovery in Wireless Sensor
Networks Lin Chen , Ruolin Fan , Kaigui Bian Lin Chen #, Mario
Gerla , Tao Wang and Xiaoming Li Peking University, Beijing, China
Yale University, New Haven, CT, USA * UCLA, Los Angeles, CA, USA #
University Paris-Sud, Orsay, France
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UCLA ENGINEERING Computer Science School of EECS, Peking
University A BRIEF INTRODUCTION TO NEIGHBOR DISCOVERY
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UCLA ENGINEERING Computer Science School of EECS, Peking
University Find the Neighbors to Form a Network
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UCLA ENGINEERING Computer Science School of EECS, Peking
University Power Conservation Keep radios off, turn on
periodically
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UCLA ENGINEERING Computer Science School of EECS, Peking
University ND Protocol Determines the Pattern by Which Each Radio
Turns ON or OFF 000001000001000001 010000001010000001 Node A (6)
Node B (2, 9) Duty Cycle: Percentage of 1 period in which a
sensor/radio is active Node As DC = 1/6; Node Bs DC = 2/9 Period =
6 Period = 9
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UCLA ENGINEERING Computer Science School of EECS, Peking
University 010000001010000001 ND Protocol Determines the Pattern by
Which Each Radio Turns ON or OFF 000001000001000001 Node A (6) Node
B (2, 9) A viable neighbor discovery protocol must either implement
clock synchronization or be robust in the face of clock drifts
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UCLA ENGINEERING Computer Science School of EECS, Peking
University Goals 1.Guarantee neighbor discovery within a reasonable
time frame 2.Minimize the number of time slots for which the node
is awake to save energy 3.Match the nodes awake-sleep schedules
with their heterogeneous battery duty cycles as closely as possible
(ie. Finer duty cycle granularity)
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UCLA ENGINEERING Computer Science School of EECS, Peking
University SOME EXISTING ND PROTOCOLS
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UCLA ENGINEERING Computer Science School of EECS, Peking
University ND Protocol Types Probabilistic Protocols Exploits the
birthday paradox Non-deterministic: No upper bound on discovery
latency Quorum Based Protocols Exploits the geometry of a 2-D array
Co-primality Based Protocols Exploits the Chinese Remainder Theorem
(CRT)
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UCLA ENGINEERING Computer Science School of EECS, Peking
University Quorum ND Protocols 1111 1 1 1 11 1 Period = 16 Duty
Cycle = 7/16 Arrange time slots into a matrix formation Choose 1
row and column as the on slots This ensures that nodes operating on
the same duty cycle (ie. Homogeneous nodes) will discover each
other within bounded time Latest development: Searchlight
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UCLA ENGINEERING Computer Science School of EECS, Peking
University Co-Prime ND Protocols Theorem: A Co-primality based
neighbor discovery protocol guarantees discovery for any two nodes
for any amount of clock drifts if the associated integer sets of
the nodes in this network satisfy the co-prime pair property, with
the worst-case discovery delay bounded by the product of the two
smallest co-prime numbers, one from each set
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UCLA ENGINEERING Computer Science School of EECS, Peking
University Co-Prime ND Protocols Example from the theorem: 2 nodes
with wakeup schedules of 3 and 2, respectively 100100 101010010101
Time drift by 1 time slot A: 3 B: 2 In reality, each node chooses 2
different numbers and combine their wake-up slots Solves the
problem of 2 nodes choosing the same number Latest development:
Disco (only choose prime numbers)
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UCLA ENGINEERING Computer Science School of EECS, Peking
University HEDIS (QUORUM) VS TODIS (CO- PRIME)
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UCLA ENGINEERING Computer Science School of EECS, Peking
University HEDIS - The Optimized Quorum Protocol HEterogeneous
DIScovery Protocol Asynchronous periodic slot-based protocol Uses n
x (n-1) time slots n depends upon the desired duty cycle n 2/ Duty
cycle granularity: 2/n The ns must be of the same parity to
guarantee discovery Protocol dictates all odd or all even Example:
even protocol, = 7% = 7/100 2/(7/100) = 200/7 28 = n In this case,
2/n = 2/28 0.071 Radio on for: Slots numbered n x i Slots numbered
(n+1) x i, where i = 0, 1, 2, , n-2
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UCLA ENGINEERING Computer Science School of EECS, Peking
University HEDIS Theorem Theorem: HEDIS guarantees neighbor
discovery within bounded latency for any two nodes with the
same-parity parameters n and m, given any amount of clock drift
between their schedules. The average discovery latency is
O(nm)
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UCLA ENGINEERING Computer Science School of EECS, Peking
University HEDIS Example 0123 4567 891011 n 1 = 4: 4x3 slots 012345
67891011 121314151617 181920212223 242526272829 n 2 = 6: 6x5 slots
01234567891011 012345678910111213141523242526272829 0 0
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UCLA ENGINEERING Computer Science School of EECS, Peking
University TODIS The Optimized Co-Prime Protocol Triple-Odd
DIScovery Protocol Duty cycle granularity too high if only prime
numbers are chosen to ensure co-primality (DISCO) Observation: all
prime numbers (except for 2) are odd Odd integers are likely to be
co-prime Each node chooses consecutive odd integers Example: N a =
{33, 35}; N b = {5, 7} gcd(35, 5) = 5; gcd(35, 7) = 7 gcd(33,5) = 1
=> co-prime; gcd(33, 7) = 1 => co-prime
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UCLA ENGINEERING Computer Science School of EECS, Peking
University TODIS Continued Two consecutive odd integers does not
guarantee co-primality for many number combinations less than 100:
{33, 35}, {75, 77} All possible pairs yield gcd > 1 Three
consecutive odd integers will do the trick Smallest counterexample:
{1600023, 1600025, 1600027} and {2046915, 2046917, 2046919}
Supports duty cycle of 3(n 2 -n-1)/(n(n 2 -4)) 3/n
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UCLA ENGINEERING Computer Science School of EECS, Peking
University PERFORMANCE EVALUATION
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UCLA ENGINEERING Computer Science School of EECS, Peking
University A Comparison of ND Protocols Protocol NameParameter
Restriction Average Discovery Delay Supported Duty Cycles
DISCOPrime p 1, p 2, p 3, p 4 O(min{p 1 p 3, p 1 p 4, p 2 p 3, p 2
p 4 }) 1/p 1 + 1/p 2 U-ConnectPrime p 1, p 2 O(p 1 p 2 )(3p 1
+1)/2p 1 2 SearchlightPower multiples of t 1, t 2 O(t 1 t 2 )2/t 1
2 HEDISSame parity n, mO(nm)2/n TODISOdd n, mO(nm)3(n 2 -n-1)/(n(n
2 -4)) 3/n
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UCLA ENGINEERING Computer Science School of EECS, Peking
University Duty Cycle Matching - Errors Small Duty Cycles: 1, 1/2,
1/3, , 1/100Large Duty Cycles: 0%, 1% 2%, 3%, , 100%
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UCLA ENGINEERING Computer Science School of EECS, Peking
University CDFs of Discovery Latency
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UCLA ENGINEERING Computer Science School of EECS, Peking
University CONCLUSION
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UCLA ENGINEERING Computer Science School of EECS, Peking
University Conclusion We explore the current two main approaches of
designing a heterogeneous ND protocol: quorum and co-primality We
design HEDIS and TODIS, a quorum and co-primality protocol
respectively Both can match battery duty cycles at a high
granularity (2/n and 3/n) HEDIS performs better than TODIS in
discovery latency
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UCLA ENGINEERING Computer Science School of EECS, Peking
University Thank You! Questions?