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## PowerPoint Slideshow about ' The Broadcast Function in Wireless Ad-Hoc Network' - wendy-donovan

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### Ultra WideBand Technology(UWB)

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 ?

OutlineThe difference of two type

5 forwarding nodes

4 hop time

6 forwarding nodes

3 hop time

source

source

Be notified

Be shortest

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)

Difference between wired and wireless networksMany 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

Broadcast StormReliability

Reliable MAC negotiation

Collision avoidance

Reduce redundant rebroadcasts

Avoid Simultaneous transmission

Optimization

Minimize the forwarding nodes

Minimize the power consumption

The essence of broadcast problemExtend 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

Reliable MAC negotiationA

The neighborhood state of mobile

nodes is under control by RTS/CTS

Reduce redundant rebroadcasts

(minimize forwarding nodes)

Be shortest minimum forwarding set

Be notified minimum broadcasting set

Avoid Simultaneous transmission

Different timing of rebroadcasts

Collision avoidanceDefine:

Given a source A

let D and P be the sets of k and k+1 hop neighbors of A

Find a minimum-size subsetF 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])

Minimum Forwarding Set ProblemDefine:

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])

Minimum Broadcasting Set ProblemMinimize 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

OptimizationSimple 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

Categorization of present protocolsArea Based Method2

- Maximum additional coverage of previous transmission:
- Average additional coverage:

≈ 0.41r2

- Average additional coverage

after having received a broadcast

message twice: ≈ 0.19r2

Area Based Method3

The expected additional coverage after hearing the message

k times, is expected to decrease quickly as k increases.

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

Area Based Method4Area Based Method5

- 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

Area Based Method6

- 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

Neighborhood information

How to decision forwarding nodes

Neighborhood base

SBA, Self pruning

Set cover base

Multipoint relaying, Dominant pruning, AHBP

MCDS base

Neighbor Knowledge MethodScalable Broadcast Algorithm (SBA)

- Information:
- Hello message (2-hop)
- Forwarding node decision:
- Node vj who receives the packet from vi checks whether the set N(vj)-N(vi)-{vi} is empty
- Node vj 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)

Information:

Hello message (1-hop)

Piggyback adjacent node list in broadcast packets

(2-hop)

Store adjacent node list in cache

Forwarding node decision:

Node vj who receives the packet from vi checks whether the set N(vj)-N(vi)-{vi} is empty

Self pruningvj

vi

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

Dominant pruning

- Information:
- Hello message (2-hop)
- Forwarding node decision:
- The sending node selects forwarding nodes from it’s adjacent nodes
- Node vj who receives the packet from vi , vj select a minimum node set F N(vj) - N(vi) such that:
- A node set U = N(N(vj)) –N(vi) –N(vj)
- Piggyback forward list in broadcast packets

The drawback of present set cover based protocols1

When a node vireceived

the broadcast packet from

node vi-1, it will select

some forwarding nodes

from N(vi)-N(vi-1) to

cover all nodes in U.

However, some nodes

in U are not i+2 level

nodes, and some nodes

in N(vi)-N(vj) are not i+1

level nodes.

vi

vi-1

s

…

i-1

i

i+1

i+2

The drawback of present set cover based protocols2

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 ?

vi2

vi-1

s

vi1

…

i-1

i

i+1

i+2

Forwarding Set Problem in unit disk graph

Fiis the output of the -approximation

algorithm which select some nodes in

blue area to cover all nodes in Qi

OPTi is the optimal solution of Forwarding

Set problem and lie on Ai

Q1

Q2

A2

A1

A4

A3

Q3

Q4

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])

MCDS based algorithmIdea:

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])

MCDS based algorithm in unit disk graph1MCDS based algorithm in unit disk graph2

- 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
- v1,v2,…,v|T| be an arbitrary preorder traversal of T
- Ui is the set of nodes in U that are adjacent to vi but none of v1, v2,…,vi-1
- Then U1,U2,…,U|T| form a partition of U
- |U1|5, |Ui|4, 2i|T|

MCDS based algorithm in unit disk graph3

at most 240

vj

vi

j=1~i-1

Ui lie in a sector of at most 240

degree within the coverage range

of node vi, this implies that |Ui|4

A node is adjacent to at

most five independent

nodes in unit disk graph

Comparison

350x350 r:100

By Chiang Jui-Hao

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

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

UWB in Short Range Wireless

- Spatial capacity : (bps/m2)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]

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

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.

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]

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

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

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]

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

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