Media Access and Routing Protocols for Power Constrained Ad Hoc Networks

1. Media Access and Routing Protocols for Power Constrained Ad Hoc Networks Carlos Pomalaza-Ráez Centre for Wireless Communications – University of Oulu and Indiana University - Purdue University, USA carlos@ee.oulu.fi http://www.cwc.oulu.fi

2. Outline • Introduction • Main features of power constrained networks • Design considerations • MAC layer • Routing algorithms • Physical layer issues • Cross-Channel design • Final observations

3. Main Features of Ad Hoc Networks • Dynamic topology • Bandwidth-constrained and variable capacity links • Energy-constrained operations • Limited physical security

4. Mobility in Ad Hoc Networks

5. Dynamic Routing

6. Route Maintenance

7. Sensing Networking Computation Wireless Sensor Networks (WSN) New technologies have reduced the cost, size and power of micro-sensors and wireless interfaces Circulatory Net EnvironmentalMonitoring • Benefits from 3 technologies • digital circuitry • wireless communication • silicon micro-machining

8. Applications • Battlefield • Detection, classification and tracking • Habitat Monitoring • Micro-climate and wildlife monitoring • Examples: • ZebraNet (Princeton) • Seabird monitoring in Maine’s Great Duck Island(Berkeley & Intel)

9. Applications • Structural, seismic • Bridges, highways, buildings • Examples: Coronado Bridge San Diego (UCSD), Factor Building (UCLA) • Smart roads • Traffic monitoring, accident detection, recovery assistance • Examples: ATON project (UCSD) highway camera microphone • Contaminants detection

10. Sensor Nodes

11. Sensor Node Evolution

12. Typical Features of WSN • Relatively large number of nodes • Low cost, size, and weight per node • Energy constrained • Prone to failures • Almost static topology • More use of broadcast communications instead of point-to-point • Nodes do not have a global ID • Limited security

13. Design Considerations • Fault tolerance • Scalability • Cost • Power consumption • Hardware and software constraints • Topology maintenance • Deployment • Environment

14. Node Energy Consumption Projections 10,000 1,000 100 10 1 .1 • Deployed (5W) Average Power (mW) • (50 mW) (1mW) 2000 2002 2004

15. Node Hardware In-node processing Wireless communication with neighboring nodes Event detection Acoustic, seismic, magnetic, etc. interface Electro-magnetic interface sensors radio CPU battery Limited battery supply

16. Energy Limitations • Each sensor node has limited energy supply • Nodes may not be rechargeable • Energy consumption in • Sensing • Data processing • Communication (most energy intensive) 20 15 10 Power (mW) 5 0 Sensing CPU TX RX IDLE SLEEP Power consumption of node subsystems

17. A Layered Approach Network MAC PHY

18. Code Time Frequency Media Access Control MAC: Let multiple radios share the same communication media • Local Topology Discovery and Management • Media Partition By Allocation or Contention • Provide Logical Channels to Upper Layers Application Network MAC Physical

19. Channel Access in Multi-hop Networks Large number of short range radios in a wide area Cons: Hidden Terminal-CSMA is not appropriate - No Global Synch Pros:Channel Reuse C B E D A

20. Which MAC is Good for WSNs? • Most existing MACs are targeted for • One-hop, centralized control network: cellular network, 802.11, Bluetooth… • Bandwidth hungry application, strict QoS requirement • Existing MACs are based on existing radios • More than 90% of power is burned when radio is idle “Energy efficient” WSNs built using existing MACs might not be that efficient

21. Two Possible Approaches • Modify or enhance current protocols to make them more energy aware • For example use the power control mechanism present in the IEEE 802.11 standard • Develop and implement new protocols that take into account full consideration of the network constraints

22. IEEE 802.11 Standard • PCF (Point Coordination Function) • Centralized medium access control • DCF (Distributed Coordination Function) • Distributed medium access control

23. 802.11 DCF: RTS-CTS-DATA-ACK A (Sender) DATA RTS ACK CTS B (Receiver)

24. Four Way Handshake RTS-CTS-DATA-ACK • A sender node waits for DIFS( Distributed Inter-Frame Space) before making an RTS attempt • A node enters a SIFS ( Short Inter Frame Space) before sending an ACK, DATA or CTS frame • NAV (Network Allocation Vector) indicates the duration of the current transmission

25. Four Way HandshakeRTS-CTS-DATA-ACK DIFS SIFS RTS DATA Sender node SIFS SIFS CTS ACK Receiver node NAV(CTS) NAV(RTS) Others NAV- Network Allocation Vector

26. Simple Power Control RTS C D A B CTS

27. Simple Power Control DATA C D A B ACK

28. Power Levels (simple power control) Pmax Pi 0 ACK RTS CTS DATA

29. Ranges • Transmission range • Receive and correctly decode packets • Carrier sensing range • Sensing the signal • Carrier sensing zone • Sensing the signal, but cannot decode it correctly • Can interfere with on-going transmission

30. Ranges Carrier Sensing Zone Transmission Range A B C D E Carrier Sensing Range

31. Variation of 802.11 DCF SRC DATA RTS SIFS DIFS DST ACK CTS SIFS DIFS SIFS TX range NAV (RTS) NAV (CTS) CS zone NAV (EIFS) NAV (EIFS) NAV (EIFS) Defer Channel Access

32. Improved Power Control Less than EIFS Pmax Pi 0 ACK RTS CTS DATA

33. Revisiting the CDMA Multi-Channel Problem 7 6 2 1 5 8 4 3 Nodes use different channels (codes) to transmit data The codes are locally unique with global reuse • Parallel transmission without synch • Implicit local address is the channel

34. Channel Assignment in Cellular Networks • Same frequency can be used in all cells of the same color • Minimize number of frequencies (colors) • The topology is static

35. Code Assignment = Graph Coloring Graph G = (V,E) Δ is the maximum degree For any node, all its neighbors have different colors OR All two-hop neighbors have different colors Number of colors needed <= min {Δ(Δ-1)+1, |V|} Brook and Vizing theorem

36. Code Assignment in Ad Hoc Networks • There is no base station • Nodes are free to connect or disconnect • Nodes move about • Increase or decrease their transmission range These features call for distributed,dynamic, power aware code assignment algorithms

37. Routing Multihop Routingdue to limited transmission range Routing Issues • Low mobility • Power aware • Irregular topology • MAC aware • Limited buffer space Application Network MAC Physical

38. Proactive routing maintains routes to every other node in the network Regular routing updates impose large overhead Suitable for high traffic networks Reactive routing maintains routes to only those nodes which are needed Cost of finding routes is expensive since flooding is involved Good for low/medium traffic networks Routing Proactive vs. Reactive

39. Ad-hoc On-demand Distance Vector Protocol (AODV) Sourcebroadcasts a route packet neighbors re-broadcastthe packet till it reaches the destination RREQ source destination reply packet follows thereverse path of the route request packet recordedin broadcast packet RREP nodes discard thepackets havingbeen seen

40. Traditional Reactive Protocols Finds the best route Destination Source and then uses it as much as possible • But that is NOT a good solution! • Energy depletion in certain nodes • Creation of hotspots in the network

41. Application aware communication primitives (expressed in terms of named data not in terms of node who requests data) Achieve locality for decision making (and reduce the communication) Application centric, data-driven networks Achieve desired global behavior through localized interactions, without global state New Approaches

42. Directed Diffusion Gradient represents both direction towards data matching and status of demand with desired update rate Application-aware communication primitivesexpressed in terms of named data This process sets up gradients in the network to draw events matching the interest Nodes diffuse the interest towards producers via a sequence of local interactions Consumer of data initiates interest in data with certain attributes The choice of path is made locally at every node for every packet Every route has aprobabilityof being chosen Probability  1/energy cost Collect energy metrics along the way Four-legged animal Source Sink

43. Directed Diffusion Reinforcementand negative reinforcement used to converge to efficient distribution Has built in tolerance to nodes moving out of range or dying Source Sink

44. Directed Diffusion • Pros • Energy – much less traffic than flooding – • Latency – transmits data along the best path – • Scalability – local interactions only – • Robust – retransmissions of interests– • Cons • The set up phase of the gradients is expensive

45. SPINSensor Protocol for Information via Negotiation • Basic idea • Exchange data when needed • Save energy by being resource aware • Data negotiation • Meta-data (data naming) • Application-level control

46. SPIN • SPIN messages • ADV- advertise data • REQ- request specific data • DATA- requested data • Resource management • Nodes decide their capability of participation in data transmissions ADV A B REQ A B DATA A B

47. SPIN-BC (broadcast) It sends meta-data to neighbors Sensor broadcasts data A node senses something “interesting” Neighbor sends a REQ listing all of the data it would like to acquire The process repeats itself across the network Neighbors aggregate data and broadcast (advertise) meta-data ADV REQ DATA

48. SPIN-BC (broadcast) Advertise meta-data Advertise Send data Send data Advertise meta-data I am tired I need to sleep … Send data Advertise Send data Request data Nodes do need not to participate in the process Request data Request data

49. SPIN • Pros • Energy – more efficient than flooding – • Latency – converges quickly – • Scalability – local interactions only – • Robust – immune to node failures – • Cons • Nodes always participating

50. Some Physical Layer Issues • Frequency selection • Carrier frequency generation • Signal detection • Modulation • Binary and M-ary modulation schemes • Binary modulation scheme is deemed to be more energy-efficient • Low transmission power and simple transceiver circuitry make Ultra Wideband (UWB) an attractive candidate • Hardware design, e.g. wake-up radio Application Network MAC Physical