Communication Quality & Measurements Mobile Ad-hoc Network

1. Communication Quality & Measurements • Mobile Ad-hoc Network • Power Control in Cellular Networks • Channel capacity • Routing in Ad-hoc networks 1

2. Power gain • Power gain, in decibels (dB), is defined by the 10 log rule as follows: • Gain  G= 10 log10(Pout/Pin) dB • Where Pin is the power applied to the input and Pout is the power from the output. 2

3. Power Control in Cellular Network 3

4. Power Control in Cellular Network • Near-far Problem • Mobile user near to base station overwhelms the signal coming from faraway users, usually those located near to the cell boundary. • Feedback as solution • Use power control to adjust the transmit power level of each user so that the received powers at the base station are equalized. 4

5. Power Control in Cellular Network • Interference Management • Each user needs to satisfy its SIR requirement. • The network wants to minimize the total power consumption in the network. • What power control algorithm to use? 5

6. Power Control in Cellular Network • Distributed Power Control (DPC) Algorithm • Used in IS-95, CDMA2000 cellular networks • The SIR requirement of the i-th user: • The transmit power of the i-th user at time slot t: • The received SIR of the i-th user at time slot t: 6

7. Power Control in Cellular Network • Channel parameter and SIR requirements: 7

8. Power Control in Cellular Network • First iteration (1st time slot): 8

9. Power Control in Cellular Network • Convergence to equilibrium: 9

10. Power Control in Cellular Network • Inner and outer loop: • Further Reading: • http://scenic.princeton.edu/network20q/lectures/Q1_notes.pdf 10

11. Communication Quality & Measurements • Power Control in Cellular Networks • Channel capacity 11

12. Represents theoretical maximum that can be achieved In practice, only much lower rates achieved Formula assumes white noise (thermal noise) Impulse noise is not accounted for Attenuation distortion or delay distortion not accounted for Shannon Capacity Formula 12

13. Classifications of Transmission Media • Transmission Medium • Physical path between transmitter and receiver • Guided Media • Waves are guided along a solid medium • E.g., copper twisted pair, copper coaxial cable, optical fiber • Unguided Media • Provides means of transmission but does not guide electromagnetic signals • Usually referred to as wireless transmission • E.g., atmosphere, outer space 13

14. Example of Nyquist and Shannon Formulations • Spectrum of a channel between 3 MHz and 4 MHz ; SNRdB = 24 dB • Using Shannon’s formula 14

15. Example of Nyquist and Shannon Formulations • How many signaling levels are required? 15

16. Mobile Ad Hoc Networks • Mobile Ad Hoc Networks • Routing Problems • Routing Algorithms

17. A typical Wireless Sensor Network • Integration of Sensor Nodes (SN) and Gateways (GW) SN SN GW Bluetooth SN GW SN SN SN SN SN SN SN GW GW SN SN WLAN GPRS/3G Ethernet Fr. Schiller

18. Problems • A new area • Many unresolved problems • Communication => Mobile ad hoc networks • Energy issues => to minimize the energy consumption => work longer • Surveillance and monitoring • In-network processing • Query processing • Sensor data aggregation and filtering

19. Sensors Networks • Sensor networks • The network formed by a group of sensors • Wireless sensor networks (WSN) • A group of sensors are connected by a wireless network • The sensors may be fixed/stationary • Ad hoc networks • The connections of a set of nodes (sensors) are not static • No fixed infrastructure (what will be the problems?) • Mobile ad hoc network (MANET) • The nodes in an ad hoc network are mobile • The connections are not static • They are connected by wireless communication

20. Why Wireless Sensor Networks? • Ease/speed of deployment => no infrastructure is needed • Self-adaptive and self-organizing => dynamic topology • Mobility of objects (tracking)

21. Mobile Router MANET Mobile Devices Mobile IP, DHCP Fixed Network Router End system MANET: Mobile Ad-hoc Networking Fr. Schiller

22. Mobile ad-hoc networks (MANET) • Network without infrastructure • Use components of participants • Intermediate nodes for networking • Examples • Single-hop: All partners max. one hop apart • Bluetooth piconet, Smart phones in a room,gaming devices… • Multi-hop: Cover larger distances, circumvent obstacles • Bluetooth scatternet, police network, car-to-car networks…

23. Mobile ad-hoc networks (MANET) • Communication by radio frequency • Provide point-to-point, multicast and broadcast • A large number of mobile (fixed) nodes • No fixed configuration (moving, mobile ad hoc network (MANET)) • They communicate with their neighboring nodes using radio signals • Limited bandwidth and may have collision if no coordination (medium access control protocol) • The neighboring nodes should not be far from it

24. Mobile ad-hoc networks (MANET) • If a node (source node) wants to communicate with another node (destination node), it may rely on relay nodes to forward the message to the destination node • Since the bandwidth is very limited, it is important to find the best route with the smallest number of relay nodes to the destination • Minimize the number of hop counts (energy and bandwidth) • The service area may be divided into grids based on the communication range of the node R (R vs. grid size) • Only one of the nodes in a grid needs to be in active mode of operation • To conserve energy, some of the nodes may switch to doze mode of operation => changing communication path

25. Routing Problem • Routing: finding a route to send data from the source to the destination • How? If multiple exists, which one to choose N7 N6 N6 N7 N1 N1 N2 N3 N2 N3 N4 N4 N5 N5 time = t1 time = t2 good link weak link Changing topology

26. Routing Problems • Asymmetric links • A path from node A to B does not implies that node B can use the same path to send packet to node A • Redundant links • Multiple paths from A to B, which one is the best one (minimizing the number of hops count) and should be chosen • Interference • Collision: neighboring nodes send packets at the same time • Collision -> retransmission (MAC) • Dynamic topology • Changing link quality due to movement • Update of path information in the intermediate nodes • No nodes have a complete information of the status of all the nodes in the system • Changing of a path

27. Routing Problems • May need to traverse multiple links (intermediate nodes) to reach a destination from the source

28. Routing Problems • Mobility causes route changes • Need to maintain (get the latest) the route or to find a route

29. Routing Problems • Routing Problem • To find a route to connect the source node (S) to the destination node (D) through a sequence of relay nodes • The route may just for a one time connection or for a period of time (continuous monitoring) • Issues in routing algorithms: • Minimize message overhead (no. of messages) • On-demand algorithms • Minimize the searching delay • Table-driven algorithms • Route maintenance • Minimize energy consumption rate • Power-aware routing algorithms (choosing high energy nodes as relay nodes • Switching some of the mobile hosts to doze mode to conserve energy

30. Routing Methods • Two types of routing algorithms • On-demand protocols (reactive) • A route is searched upon the receipt a connection request • Table-driven protocols (proactive) • The topology of the whole network is maintained • When a connection is needed, the source node can select the route from its memory directly • Which one is better?

31. Routing Methods • Latency of route discovery • Proactive protocols may have lower latency since routes are maintained at all times • Reactive protocols may have higher latency because a route from X to Y will be found only when X attempts to send to Y • Overhead of route discovery/maintenance • Reactive protocols may have lower overhead since routes are determined only if needed • Proactive protocols can (but not necessarily) result in higher overhead due to continuous route updating • Which approach achieves a better trade-off depends on the traffic and mobility patterns

32. Routing Algorithms • Flooding • Dynamic Source Routing (DSR) • Location-Aided Routing (LAR) • Power-Aware Routing (PAR)

33. Flooding for Data Delivery • Flooding: by broadcast to send the packet to all its neighboring nodes • Sender S broadcasts data packet P to all its neighbors • Each node receiving P forwards P to its neighbors • Sequence numbers used to avoid the possibility of forwarding the same packet more than once • Packet P reaches destination D provided that D is reachable from sender S • Node D does not forward the packet

34. Flooding for Data Delivery Y Represents that connected nodes are within each other’s transmission range Z S E F B C M L J A G H D K I N Represents a node that has received packet P

35. Flooding for Data Delivery Y Represents transmission of packet P Broadcast transmission Z S E F B C M L J A G H D K I N Represents a node that receives packet P for the first time

36. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Node H receives packet P from two neighbors: • potential for collision

37. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Node C receives packet P from G and H, but does not forward • it again, because node C has already forwarded packet P once

38. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Nodes J and K both broadcast packet P to node D • Since nodes J and K are hidden from each other, their • transmissions may collide • =>Packet P may not be delivered to node D at all, • despite the use of flooding

39. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Node D does not forward packet P, because node D • is the intended destination of packet P

40. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Flooding completed • Nodes unreachable from S do not receive packet P (e.g., node Z) • Nodes for which all paths from S go through the destination D • also do not receive packet P (example: node N)

41. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Flooding may deliver packets to too many nodes • (in the worst case, all nodes reachable from sender • may receive the packet)

42. Flooding for Data Delivery: Advantages • Simple • May be more efficient than other protocols when the rate of information transmission is low enough that the overhead of explicit route discovery/maintenance incurred by other protocols is relatively higher • This scenario may occur, for instance, when nodes transmit small data packets relatively infrequently, and many topology changes occur between consecutive packet transmissions • Potentially higher reliability of data delivery • Because packets may be delivered to the destination on multiple paths

43. Flooding for Data Delivery: Disadvantages • Potentially, very high overhead • Data packets may be delivered to too many nodes who do not need to receive them • Potentially lower reliability of data delivery • Flooding uses broadcasting -- hard to implement reliable broadcast delivery without significantly increasing overhead • In our example, nodes J and K may transmit to node D simultaneously, resulting in loss of the packet • In this case, destination may not receive the packet at all • So, what is the actual situation?

44. Flooding of Control Packets • Many protocols perform (potentially limited) flooding of control packets, instead of data packets • The control packets are used to discover routes • Discovered routes are subsequently used to send data packet(s) • Overhead of control packet flooding is amortized over data packets transmitted between consecutive control packet floods

45. Dynamic Source Routing (DSR) • In DSR, it consists of two steps: • Route discovery: a node tries to discover a route to a destination if it has to send something to its destination. How? • Route maintenance: if a node detects the current route has changed, it needs to find a new route • In route discovery, if node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery (small size message) • Source node S floods Route Request (RREQ) • Each node appends own identifier when forwarding RREQ • If a node has already received the request, it will drop the request

46. Route Discovery in DSR Y Z S E F B C M L J A G H D K I N Represents a node that has received RREQ for D from S

47. Route Discovery in DSR Y Broadcast transmission Z [S] S E F B C M L J A G H D K I N [X,Y] Represents list of identifiers appended to RREQ Represents transmission of RREQ

48. Route Discovery in DSR Y Z S [S,E] E F B C M L J A G [S,C] H D K I N • Node H receives packet RREQ from two neighbors: • potential for collision

49. Route Discovery in DSR Y Z S E F [S,E,F] B C M L J A G H D K [S,C,G] I N • Node C receives RREQ from G and H, but does not forward • it again, because node C has already forwarded RREQ once

50. Route Discovery in DSR Y Z S E F [S,E,F,J] B C M L J A G H D K I N [S,C,G,K] • Nodes J and K both broadcast RREQ to node D • Since nodes J and K are hidden from each other, their • transmissions may collide