1. TiZo-MERLIN The TIME-ZONE MAC ROUTING AND LOCALIZATION INTEGRATED protocol for wireless sensor networks Master student: Antonio Ruzzelli Supervisor : Paul Havinga This work is performed as part of the EYES Project.

2. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusion intro 2 Index WSN Overview Requirements Assumptions Related work Merlin design The idea Data traffic Mac and Routing Details Scheduling Initialization Multipath and Overhearing Simulation Liftime Latency Bandwidth Comparison of schedue tables Comparison with related protocols Conclusion

3. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 3 Wireless Sensor Networks Application specific wireless networks for monitoring, smart spaces, medical systems and robotic exploration Large number of distributed nodes and self organizing Normally battery operated and hence power limited For these important reasons we make the following requirements:

4. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 4 Design Requirements Energy efficiency often difficult recharge batteries or replace them so prolonging the life-time is important Scalability to the change in network size, node density and topology some nodes may die over time new nodes may join later Lightweight protocol Limited memory capacity of cheap sensors Ability to reduce the latency if necessary Include data queries These requirements leads us to the following network assumptions:

5. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 5 Network assumptions Composed of many small nodes deployed in an ad hoc manner Most communication will be between nodes as peers, Packets hop from a node to node till it gets the gateway (beacon). Nodes must self-configure Nodes must save energy →TDMA approach assumed

6. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 6 Related WSNs MAC protocols SMAC : High latency due to data forwarding interruption problems (RTS/CTS) TRAMA : Good solution. Complex in terms of slot assignment EMACS : High latency and very tight synchronization DMAC : Only unidirectional communication. It does not support multiple gateways. Some inconsistency in the forwarding msg activity.

7. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 7 What is the main IDEA behind this new MAC? Gateway Node Why Time Zones? Nodes with the same color are in the same time zone Nodes within the same subset belong to the same gateway (Paul Havinga et al.)

8. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 8 Time zones : Number of hops to get the closest gateway Nodes in the same zone have same hop count Set up periodically by subnet flooding and local broadcast Nodes features : Nodes within a time zone own the same slot Nodes belong to one gateway only Nodes store the number of hops to the closest gateway

9. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 9 Data traffic 1.Subnet flooding by gateway: Gateway msgs are forwarded to all nodes in the subnet 2.Local broadcast by node : Nodes send msgs to all of the direct neighbours. No forwarding is performed. 3. To gateway Transmission by node : Nodes closer to the gateway forward msgs until it reaches the gateway.

10. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 10 Transmission Mechanism Every slot has a contention period; Nodes pick up a random time “t” in Contention Period; Start listen to the channel at “t”; Channel is Free  Start sending the packet ; Channel is busy  Turn off the radio until the next scheduled Slot DATACP AB SLOTSLOT 1.Nodes in the same zone transmit and receive simultaneously 2.Nodes in the neighbouring zone are listening 3.Nodes 2 hops away are switched off Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 A AB B

11. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 11 Collision reporting Collision reporting takes place in the end of the slot just before the next contention period; After transmitting, Tx node listens for a collision report; In case of collision Rx node broadcasts a collision report; In case of collision the packet is sent again after a random exponential backoff time. The collision report is a short burst msg. PacketCP CR

12. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 12 Initialization: Gateways flood their sub network simultaneously; Nodes set their hop count number and forward the msg. Nodes include their hop count number in forwarded messages...............................

13. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 13 1- Sub-network Set-Up Useful for initializing and updating the network Gateways flood the network as follow: 2 2 2 1 1 1 3 2 3 4 4 5 4 5 4 3 Zone 1 Zone 3 Zone 2 Zone 4 Zone 5

14. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 14 Example of scheduling tables (1) X-schedule vs. V- Schedule Listen-only mode Transmit-only mode Sleep mode slots Frame is divided in 4 slots; Nodes in the same zone transmit simultaneously After the transmission nodes switch off immediately Contention period is performed among nodes in the same zone (same hop count) FrameTime Space

15. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 15 Implicit Multiple path Performing 1 2 3 3 4 45 5 6 6 7 6 Forwarding “Transmission to Gateway” results in multiple copies of the same msg; Nodes can detect copies of arriving msgs by combination of Source ID and message ID contained in the msg; Messages arriving at gateway follow multiple paths. Pro : Greater reliabilty! Con : Increase overhead! 7 9 8 How to reduce this overhead?

16. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 16 Overhearing Nodes not getting the channel keep on listening to the beginning of other’s transmitting packet then switch off. Packets start with an index containing the ID of included msg; Nodes discard the msgs already fowarded Pro : Reduce overhead in transmission! Con : Small increase of node activity; Increase complexity. Channel contention messages Msg-index Discard msgs already forwarded P a c k e t

17. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 17 Implementation Nodes with the same colors are in the same zone (same hop Count Number). Number slot /frame = 4 Contention period = 31ms DataRate = 115200 bits/sec DataSize = 16+8 Bytes (data + 3 bytes preamble + starting code) ParametersValues Energy Transmitting21 mW Energy Receiving14.4 mW Energy stand-by15 µW Switch time Tx/Rx518 µs Switch time Rx/Tx12 µs Switch stanby/Rx518 µs Switch stand-by/Tx15 µs Eyes node

18. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 18 Network setup Time Calculated running several static networks Frametime = 1 sec The sensor radio range is kept to a minimum in the way that allows the network to be still connected 4 gateways are placed in the corners The area network is 4000 m^2 Comparison: V-schedule has double setup time than X-schedule

19. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 19 Sensor signal range 1.The graph shows a linear behaviour of the lowest signal strength in order to keep the network connected 2.The graph is the statistical result of running several static networks. 3.Topology: 800*500 m^2 area network 4 beacons in the corners In order to save energy and prevent collisions, it is necessary to keep to a the signal strength of nodes to a minimum !

20. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 20 V-schedule v.s. X-schedule lifetime and bandwidth 1 Gateway 100 Nodes random distributed 800*500 area network Minimal signal strength (12 m) 50 msg/min generated by 5 random nodes Static network Lifetime calculated considering a linear battery depletion 50 msgs/min generated by 5 random nodes Number of msg received running 1Joule battery energy 3.36 %coll 1 gateway 4.47 % coll 1 gateway 4.47 %coll 4 gateways 5.60 %coll 4 gateways

21. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 21 Static Network Lifetimes normalized to SMAC MERLIN tuning 2 sec. Frametime X-schedule 45 nodes 1 Gateway 5 random nodes generate msgs periodically Msg size 16 bytes (+8 bytes preamble and starting code) 40 nodes assisting the forwarding Statisticallly obtained running several random networks Network is considered to fail when 30% of nodes is depleted

22. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 22 MERLIN Implementation Result: The X-schedule performs better than the V-schedule in terms of latency The V-schedule performs better than the X-schedule in terms of energy consumption and number of collisions. V-schedule is more suitable for low traffic WSNs with multiple gateways. Low latency of MERLIN can be used as a trade-off to extend the node lifetimes The performance in terms of energy consumption and latency is optimize acting to the slot length. Some collisions occur on the border of gateway subsets and around gateways. Msgs are recovered by the collision reporting + retransmission after a random back-off time. MERLIN with static network has given good results in terms of number of collisions without the need of a handshake mechanisms among nodes; The protocol is suitable for static and low mobility networks.

23. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 23 Summary of TiZo-MERLIN features Suitable for mobile sensor networks with a number of fixed gateways; TDMA based; No explicit RTS/CTS among nodes; Implicit handshake mechanism; Contention period among nodes ; Collision report in the end of a slot; Reliability achieved by multi-paths; High Latency and low bandwidth;

24. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 24 Conclusion Future work recommended: Improve the behaviour with mobile nodes using: The RSSI also used for localization A table of neighbours An improved routing protocol as an upper layer It can check the best neighbour based on the energy level Investigate “Down-Up-Up” asymmetric scheduling Investigate the usage of two different frequencies for “Flooding” and “To gateway” transmission The solution can avoid collision and decrease the retransmission in the subnet border.

25. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 25 Questions Thank you for your attention!

26. energy efficient sensor networks Features & Data trafficArchitectureSchedulingMultipathImplementationConclusionintro 26 Using two different frequencies : f1 = Frequency 1f2 = Frequency 2 f1 f2 f1 f2 f1f2 f1 f2 f1 Collisions at the border can be eliminated by using 2 frequencies If a subnet uses f1 for “to gateway” transmission, then adjacent subsets use f2 If a subnet uses f2 for “subset flooding” then adjacent subnets use f1 Subnet 1Subnet 2 Subnet 3