1. National Taiwan University Department of Computer Science and Information Engineering The Broadcast Function in Wireless Ad-Hoc Network 2002.9.2 Speaker:peter

2. National Taiwan University Department of Computer Science and Information Engineering Outline  An overview of the broadcast function  Difference between wired and wireless networks  The essence of broadcast problem  Categorization of present protocols  Ultra WideBand technology  Broadcast protocol for Ultra WideBand ?

3. National Taiwan University Department of Computer Science and Information Engineering Broadcast  Function: paging a particular host sending an alarm signal finding a route to a particular host  Two type: Be notified -> topology change Be shortest -> finding route  Objective: Reliability (all nodes have received the broadcast packet) Optimization

4. National Taiwan University Department of Computer Science and Information Engineering The difference of two type source Be notifiedBe shortest 5 forwarding nodes 4 hop time source 6 forwarding nodes 3 hop time

5. National Taiwan University Department of Computer Science and Information Engineering Difference between wired and wireless networks  Broadcast property  Reliability: CSMA/CD vs. CSMA/CA RTS/CTS/data/ACK procedure is too cumbersome to implement for broadcast Simultaneous transmission and hidden node problem  Expensive bandwidth  Therefore the flooding which is the simple broadcast mechanism in wired networks is not suitable in wireless networks (broadcast storm problem)

6. National Taiwan University Department of Computer Science and Information Engineering Broadcast Storm  Many retransmissions are redundant Because radio propagation is omnidirectional and a physical location may be covered by the transmission ranges of several nodes  Heavy contention could exist Because retransmitting nodes are probably close to each other  Collisions are more likely to occur Because the RTS/CTS dialogue is inapplicable and the timing of retransmissions is highly correlated

7. National Taiwan University Department of Computer Science and Information Engineering The essence of broadcast problem  Reliability Reliable MAC negotiation Collision avoidance  Reduce redundant rebroadcasts  Avoid Simultaneous transmission  Optimization Minimize the forwarding nodes Minimize the power consumption

8. National Taiwan University Department of Computer Science and Information Engineering Reliable MAC negotiation  Extend RTS/CTS for broadcast Waiting for all neighbors to be ready  RTS collision ?  Forwarding ? Sending broadcast packets anyway  Affect other transmission Repeatedly broadcast until all neighbor received  Acknowledgement A The neighborhood state of mobile nodes is under control by RTS/CTS

9. National Taiwan University Department of Computer Science and Information Engineering Collision avoidance  Reduce redundant rebroadcasts (minimize forwarding nodes) Be shortest  minimum forwarding set Be notified  minimum broadcasting set  Avoid Simultaneous transmission Different timing of rebroadcasts

10. National Taiwan University Department of Computer Science and Information Engineering Minimum Forwarding Set Problem  Define: Given a source A let D and P be the sets of k and k+1 hop neighbors of A Find a minimum-size subset F of D such that every node in P is within the coverage area of at least one node from F  In general graph: NP-complete: reduce “ Set Cover ” to it Approximation ratio: logn  In unit disk graph: Unknown Approximation ratio: constant (by reference [1])

11. National Taiwan University Department of Computer Science and Information Engineering Minimum Broadcasting Set Problem  Define: Given a source A Find a spanning tree T such that the number of internal nodes is minimum  In general graph: NP-hard: hard to “ Minimum Connected Dominating Set ” Approximation ratio: log ( is the maximum node degree)  In unit disk graph: NP-hard Approximation ratio: constant (by reference [2])

12. National Taiwan University Department of Computer Science and Information Engineering Optimization  Minimize the power consumption (Minimum-Energy Broadcast Tree Problem)  Define: Given a wireless ad hoc network M = (N,L) A source node s to broadcast a message from s to all the other nodes such that the sum of transmission powers at all nodes is minimized  Same as the Steiner Tree problem in directed graph: NP-complete: reduce “ 3-CNF SAT ” to it Approximation ratio: n

13. National Taiwan University Department of Computer Science and Information Engineering Categorization of present protocols  Simple flooding  Area based method (by reference [3]) Counter based scheme Distance based scheme Location based scheme  Neighbor knowledge method Neighborhood base Set cover base MCDS base

14. National Taiwan University Department of Computer Science and Information Engineering Flooding  Each node forwarding the broadcasting packets exactly one time Using Process ID

15. National Taiwan University Department of Computer Science and Information Engineering Area Based Method 1

16. National Taiwan University Department of Computer Science and Information Engineering Area Based Method 2  Maximum additional coverage of previous transmission:  Average additional coverage: ≈ 0.41  r 2  Average additional coverage after having received a broadcast message twice: ≈ 0.19  r 2

17. National Taiwan University Department of Computer Science and Information Engineering Area Based Method 3 The expected additional coverage after hearing the message k times, is expected to decrease quickly as k increases.

18. National Taiwan University Department of Computer Science and Information Engineering Area Based Method 4  Counter based scheme: Using “ Random Assessment Delay ” (RAD) The counter is incremented by one for each redundant packet received If the counter is less than a threshold value when the RAD expires, the packet is rebroadcast. Otherwise, it is simply dropped

19. National Taiwan University Department of Computer Science and Information Engineering Area Based Method 5  Distance based scheme: Using “ Random Assessment Delay ” (RAD) Estimating the distance d between sender and receiver by signal strength Calculate the additional coverage by d (additional coverage = ) If the additional coverage which is calculated by the minimum distance is more than a threshold value when the RAD expires, the packet is rebroadcast. Otherwise, it is simply dropped

20. National Taiwan University Department of Computer Science and Information Engineering Area Based Method 6  Location based scheme: Using “ Random Assessment Delay ” (RAD) Adding location information to the header of the broadcast packets Calculate the additional coverage by k location information which are received during RAD  Difficult to calculate exactly  Using grid-filling approximation If the additional coverage is more than a threshold value, the packet is rebroadcast. Otherwise, it is simply dropped

21. National Taiwan University Department of Computer Science and Information Engineering Neighbor Knowledge Method  Neighborhood information  How to decision forwarding nodes Neighborhood base  SBA, Self pruning Set cover base  Multipoint relaying, Dominant pruning, AHBP MCDS base

22. National Taiwan University Department of Computer Science and Information Engineering Scalable Broadcast Algorithm (SBA)  Information: Hello message (2-hop)  Forwarding node decision: Node v j who receives the packet from v i checks whether the set N(v j )-N(v i )-{v i } is empty Node v j schedules the packet for delivery with a RAD (Random Assessment Delay) Dynamically adjust the RAD to (nodes with the most neighbors usually broadcast before the others)

23. National Taiwan University Department of Computer Science and Information Engineering Self pruning  Information: Hello message (1-hop) Piggyback adjacent node list in broadcast packets (2-hop) Store adjacent node list in cache  Forwarding node decision: Node v j who receives the packet from v i checks whether the set N(v j )-N(v i )-{v i } is empty vivi vjvj

24. National Taiwan University Department of Computer Science and Information Engineering Multipoint relaying  Information: Hello message (2-hop)  Forwarding node decision: The sending node A selects forwarding nodes from it ’ s adjacent nodes A select a minimum node set F  N(A) such that: A node set U = N(N(A)) – N(A) Piggyback forward list in “ Hello ” packets

25. National Taiwan University Department of Computer Science and Information Engineering Dominant pruning  Information: Hello message (2-hop)  Forwarding node decision: The sending node selects forwarding nodes from it ’ s adjacent nodes Node v j who receives the packet from v i, v j select a minimum node set F  N(v j ) - N(v i ) such that: A node set U = N(N(v j )) – N(v i ) – N(v j ) Piggyback forward list in broadcast packets

26. National Taiwan University Department of Computer Science and Information Engineering Dominant pruning vivi vjvj N(N(v j )) B(v i,v j ) U N(v i ) N(v j )

27. National Taiwan University Department of Computer Science and Information Engineering The drawback of present set cover based protocols 1 … i-1 i i+1 i+2 v i-1 vivi s When a node v i received the broadcast packet from node v i-1, it will select some forwarding nodes from N(v i )-N(v i-1 ) to cover all nodes in U. However, some nodes in U are not i+2 level nodes, and some nodes in N(v i )-N(v j ) are not i+1 level nodes.

28. National Taiwan University Department of Computer Science and Information Engineering The drawback of present set cover based protocols 2 … i-1 i i+1 i+2 v i-1 v i1 s When we will select some level i+1 nodes to cover all level i+2 nodes, the number of forwarding nodes selected by distributed algorithm can not be bounded to some ratio of the optimal solution ? v i2

29. National Taiwan University Department of Computer Science and Information Engineering Forwarding Set Problem in unit disk graph Q1Q1 Q2Q2 Q3Q3 Q4Q4 F i is the output of the -approximation algorithm which select some nodes in blue area to cover all nodes in Q i OPT i is the optimal solution of Forwarding Set problem and lie on A i A1A1 A2A2 A3A3 A4A4

30. National Taiwan University Department of Computer Science and Information Engineering MCDS based algorithm  Approximation Algorithm: Definition: A piece is defined as a white node or a black connected component Initialize: all nodes are white Procedure:  At each step we pick a node u that gives the maximum (non-zero) reduction in the number of pieces.  coloring u black and coloring all adjacent white nodes gray.  Recursively connect pairs of black components by choosing a chain of two vertices. Approximation ratio: 3+log (reference [4])

31. National Taiwan University Department of Computer Science and Information Engineering MCDS based algorithm in unit disk graph 1  Idea: Any MIS (maximal independent set) is also a DS, and conversely, any independent DS must be an MIS The size of any MIS in a unit disk graph is at most four times of the size of the MCDS The shortest distance between a node in MIS and it ’ s nearest node in MIS is at most three  Algorithm: Find any MIS Spanning all nodes in MIS  Approximation ratio: 12 (reference [2])

32. National Taiwan University Department of Computer Science and Information Engineering MCDS based algorithm in unit disk graph 2  Lemma: The size of any MIS in a unit disk graph is at most four times of the size of the MCDS  proof: U is any MIS, T is a spanning tree of MCDS v 1,v 2, …,v |T| be an arbitrary preorder traversal of T U i is the set of nodes in U that are adjacent to v i but none of v 1, v 2, …,v i-1 Then U 1,U 2, …,U |T| form a partition of U |U 1 |5, |U i |4, 2i|T|

33. National Taiwan University Department of Computer Science and Information Engineering MCDS based algorithm in unit disk graph 3 A node is adjacent to at most five independent nodes in unit disk graph at most 240  vivi vjvj j=1~i-1 U i lie in a sector of at most 240 degree within the coverage range of node v i, this implies that |U i |4

34. National Taiwan University Department of Computer Science and Information Engineering Comparison 350x350 r:100

35. Ultra WideBand Technology (UWB) By Chiang Jui-Hao

36. What is Ultra Wideband? Originally referred to “baseband”, “carrier-free”, or impulse Any wireless transmission scheme occupies a bandwidth of more than 25% of a center frequency, or more than 1.5GHz

37. Compare with narrowband and wideband UWB systems have two characteristics Bandwidth is much greater, Defined by the Federal Communications Commission (FCC), is more than 25% of a center frequency or more than 1.5GHz Carrierless fashion “narrowband” and “wideband” use RF UWB directly modulate an "impulse" that has a very sharp rise and fall time

38. UWB in Short Range Wireless Spatial capacity : (bps/m 2 ) higher bit rates concentrated in smaller areas For users gather in crowded spaces, the most critical parameter of a wireless system will be its spatial capacity [1]

39. Compare with IEEE 802.11 and Bluetooth (cont.) UWB have greater spatial capacity From the Hartley- Shannon law Potential for support of future high-capacity wireless systems

40. Notice of Proposed Rule Making In May of 2000, the FCC issued a Notice of Proposed Rule Making (NPRM) limit UWB transmitted power spectral density for frequencies greater than 2GHz.

41. Ultra-Wideband transceiver Advantages: UWB is a “carrierless” system,thus we can remove traditional blocks such as carrier recovery loop,mixer…etc. High data rate and number of users. Robustness to multi-path fading. [3]

42. UWB Advantages Extremely difficult to intercept Short pulse excitation generates wideband spectra – low energy densities Low energy density also minimizes interference to other services Multipath immunity Time-gated detector can excise delayed returns - time separation

43. UWB Advantages (cont.) Commonality of signal generation and processing architectures Communications LPI/D, High Data Rates, Multipath Tolerance Radar Inherent high precision – sub-centimeter ranging Wideband excitation for detection of complex, low RCS targets Low cost Nearly “all-digital” architecture Ideal for microminiaturization into a chipset Frequency diversity with minimal hardware modifications

44. UWB Signal in multi-path fading channel Multi-path fading results from the destructive interference caused by the sum of several received paths that may be out of phase with each other.The very narrow pulses of UWB waveforms result in the multiple reflections being resolved independently rather than combining destructively. [4]

45. UWB Applications

46. UWB operation and technology Imaging Systems Ground Penetrating Radar Systems Wall Imaging Systems Through-wall Imaging Systems Medical Systems Surveillance Systems Vehicular Radar Systems Communications and Measurement Systems