Wireless Sensor Networks

Transcription

1 Wireless Sensor Networks Office Hours: Tuesday 5 Main Building, third fllor Credits: 6

2 Protocol Stack Time Synchronization Energy Efficiency Distributed Processing Application Layer Network Layer MAC Layer PHY Layer

3 Outline 1. Zigbee Upper Layers 2. Zigbee Tree-based Topology. Zigbee Mesh Topology

4 Outline 1. Zigbee Upper Layers 2. Zigbee Tree-based Topology. Zigbee Mesh Topology 1. AODV-based Mesh 2. Many-to-One Routing. Performance

5 Outline 1. Zigbee Upper Layers 2. Zigbee Tree-based Topology. Zigbee Mesh Topology 1. AODV-based Mesh 2. Many-to-One Routing. Performance

6 Mesh Topologies Nodes work in non Beacon-Enabled mode Need of defining a Routing Protocol Zigbee Coordinator ZigBee Router ZigBee End Device Communications flow

7 Zigbee Mesh Topology Based on AODV or Many-to-One The path, P, minimising the total path cost, C(P), is selected C( l) min 7, 1 4 p s 1 C(P 1 )= 2 Generally, p s =p CON 1 1 C( P) L 1 i 1 C( l i ) 2 C(P 2 )=4

8 Zigbee Mesh Topology Cost of a generic link: C(l) 7 C( l) min 7, 1 4 p s Generally, p s =p CON = Prob{P r >= P rmin } P r [dbm]

9 Zigbee Mesh Topology: AODV

10 Zigbee Mesh Topology: AODV Route-Discovery Table entry

11 Zigbee Mesh Topology: AODV Route Request Command frame format Route Reply Command frame format

12 Zigbee: AODV an example ZC 12

13 Zigbee: AODV an example ZC 1

14 Zigbee: AODV an example C Route Request Broadcast Packet, sent in an instant randomly and uniformly distributed within a given interval A 0 C C: path cost 7 5 B 2 ZC 14

15 Zigbee: AODV an example C Route Request Broadcast Packet C: path cost A: PC = 0 + B: PC = A 5 B 0 2 C ZC 15

16 Zigbee: AODV an example C Route Request Broadcast Packet C: path cost A: PC = 0 + B: PC = A 5 B 2 2 C ZC 16

17 Zigbee: AODV an example C Route Request Broadcast Packet C: path cost A: PC = 0 + B: PC = ZC: PC = min 7 + (from A) + 2 (from B) 7 A 5 B 2 C ZC 2 17

18 Zigbee: AODV an example Route Reply Unicast Packet on the selected path, sent through CSMA/CA C: path cost A: PC = + 7 B: PC = 2 + ZC: PC = min 7 + (from A) + 2 (from B) 7 A 5 B 2 C ZC 18

19 Outline 1. Zigbee Upper Layers 2. Zigbee Tree-based Topology. Zigbee Mesh Topology 1. AODV-based Mesh 2. Many-to-One Routing. Performance

20 Zigbee: Many-to-One routing 20

21 Zigbee: Many-to-One an example ZC 21

22 Zigbee: Many-to-One an example ZC 22

23 Zigbee: Many-to-One an example C Many-To-One Route Request. Broadcast Packet C: path cost A C B 0 ZC 2

24 Zigbee: Many-to-One an example C Many-To-One Route Request. Broadcast Packet C: path cost A C B 0 ZC 24

25 Zigbee: Many-to-One an example C Many-To-One Route Request. Broadcast Packet C: path cost A C B ZC Each node selects the next-hop toward the ZC 25

26 Zigbee: Many-to-One an example C C: path cost Many-To-One Route Request. Broadcast Packet A: PC = B: PC = A 5 B 2 C ZC Each node selects the next-hop toward the ZC 26

27 Zigbee: Many-to-One an example C Many-To-One Route Request. Broadcast Packet C: path cost A: PC = B: PC = 0 + C: PC = min 7 + (from A) + 2 (from B) 7 A 5 B 2 C 5 ZC Each node selects the next-hop toward the ZC 27

28 Zigbee: Many-to-One an example C Many-To-One Route Request. Broadcast Packet C: path cost A: PC = B: PC = 0 + C: PC = min 7 + (from A) + 2 (from B) 7 A 2 B 2 C 5 ZC Each node selects the next-hop toward the ZC 28

29 Zigbee: Many-to-One an example ZC sends RREQ If B retransmits RREQ before A A selects B as next hop A C ZC RREQ received by A and B B RREQ A RREQ If A retransmits RREQ before B A selects ZC as next hop 7 2 B 2 Instant of transmission randomly distributed t Selected Paths are affected by MAC randomness ZC 29

30 Zigbee: Many-to-One source routing If the ZC has to send data to specific nodes in the network Nodes reply to the RREQ with a Route Record packet, where each node in the path includes its network address A 5 2 C 7 B ZC generates a Relay List (Source Routing) ZC

31 Zigbee: Many-to-One an example Each node finds the path at minimum cost toward the ZC 1

32 Zigbee: two options comparison AODV-based routing Limited memory routing tables are an issue Many nodes many broadcasts (route request / route reply) Many-to-One routing Only one route request from Concentrator No routing tables at routers 2

33 Outline 1. Zigbee Upper Layers 2. Zigbee Tree-based Topology. Zigbee Mesh Topology 1. AODV-based Mesh 2. Many-to-One Routing. Performance

34 Throughput: Comparing Tree and Mesh Source Destination Source Relay Destination S R1 R2 R D

35 Throughput: Mesh non BE mode Header = 17 bytes

36 PER: Mesh non BE mode Header = 17 bytes

37 Delay: Mesh topology Nodes generate a packet every T q Query-Based (QB) and non QB applications are considered: QB nodes start the CSMA/CA protocol at the same time, that is when they receive the query Non QB nodes generate the packet in an instant that is uniformed and randomly distributed in Tq retransmissions are allowed Node 1 Node 2 Node 1 Node 2 t T q T q

38 Delay: Scenario

39 Delay: Data Transfer- from ZC to ZED 0 Sleeping ZED 0 ZED 0 polls ZR every 200 ms Data from ZC to ZED 0 18 bytes; Ack=11 bytes. (1) Data () Data Request ZC ZR 0 ZED 0 (2) Ack (4) Ack (5) Data (6) Ack

40 Delay: Data Transfer- from ZED 0 to ZC Data from ZED 0 to ZC 45 bytes; Ack=11 bytes. () Data (1) Data ZC ZR 0 ZED 0 (4) Ack (2) Ack

41 Delay: Results PER QB application No QB application Data from ZC to ZED0 0 0 Data from ZED0 to ZC 8 % 0

42 Topologies: Scenario 1 - Indoor 48 devices deployed at UNIBO Average number of hops 25 m 25 m

43 Topologies: Scenario 2 - Warehouse

44 Topologies: Aims To measure the WiFi coverage Energy detection function: measures the peack of energy received on the channel Frequencies used by the 5 Zigbee networks 4 channels spatially reused f [MHz] b

45 Topologies: Scenario 2 - Warehouse 5 Zigbee Mesh Networks using Many-to-One Routing: 4 networks with 48 nodes 1 network with 6 nodes

46 ZC ZC ZC 1 80 m ZC ZC

47 Topologies: Scenario 2 - Warehouse

48 Topologies: Scenario 2 - Warehouse

49 probabilità probabilità Wireless Sensor Networks Topologies: Results Statistics achieved from 5158 samples in 24 hours Statistics path cost Statistics number of hops path cost Number of hops

50 Topologies: Scenario Smart City 24 lamp posts One G gateway Custom TI CC250-based solution 25 m 50

51 Topologies: Zigbee network IEEE PHY and MAC Pt = 20 dbm Prmin = -96 dbm Zigbee Many-to-One routing Tree topologies 51

52 Topologies: Application Data transmitted every 60 s Commands are sent every 60 s 52

53 Topologies: Results Mean Number of hops Node ID 5

54 Topologies: Results 54

55 Topologies: Results Quasi-stationary environment Are topologies always the same? 55

56 Numerical Results: distance among topologies Considering each topology as a graph, the distance is defined as the number of basic operations (insert or remove a link, change a node position) needed for a topology to became equal to the other under examination

57 Numerical Results: distance among topologies Considering each topology as a graph, the distance is defined as the number of basic operations (insert or remove a link, change a node position) needed for a topology to became equal to the other under examination. 1 2 Operation 1 Operation Distance = 2 57

58 Numerical Results: topologies 58

59 Numerical Results: topologies ZC sends RREQ If B retransmits RREQ before A A selects B as next hop A C ZC RREQ received by A and B B RREQ A RREQ If A retransmits RREQ before B A selects ZC as next hop 7 2 B 2 Instant of transmission randomly distributed t Selected Paths are affected by MAC randomness ZC 59

60 Summing-Up Mesh topologies are more flexible and robust to link failures The average delay is approx. 5 ms per hop Non QB applications (generating asynchronous traffic) perform better than QB applications in terms of packet error rate and delays Topologies are affected by the environment and by MAC randomness

61 Wireless Sensor Networks