Jie Wu

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COT 6930 Ad Hoc Networks (Part I)

• Jie Wu
• Department of Computer Science and Engineering
• Florida Atlantic University
• Boca Raton, FL 33431

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Table of Contents

• Introduction
• Infrastructured networks
• Handoff
• location management (mobile IP)
• channel assignment

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Table of Contents (contd.)

• Infrastructureless networks
• Wireless MAC (IEEE 802.11 and Bluetooth)
• Security
• Ad Hoc Routing Protocols
• Multicasting and Broadcasting

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Table of Contents (contd.)

• Infrastructureless networks (contd.)
• Power Optimization
• Applications
• Sensor networks and indoor wireless environments
• Pervasive computing
• Sample on-going projects

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Classification of Communication Networks

• Scale
• LAN, MAN, WAN, Internet
• Transmission technology
• broadcast
• point-to-point
• Service
• single service
• integrated service
• Transmission medium
• wired networks
• wireless networks

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Wired/Wireless Networks
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Wireless Networks

• 200 million wireless telephone handsets
  (purchased annually)
• A billion wireless communication devices in use
  (in near future)
• anytime, anywhere
• manytime, manywhere (in many applications)

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Samples

• Portable phones (home cordless, cellular, PCS)
• Paging (one-way service)
• Personal digital assistants (PDAs)
• Wireless LANs (small service area with
  high-bit-rate services)

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Samples (Contd.)

• Satellites (ubiquitous coverage with low-bit-rate
  services)
• Two-way comm. between satellites and vehicles
  (and ships)
• One-way comm. Global Positioning Systems (GPS)
• Wireless loops (local or metropolitan)
• Wireless ATM
• Mobile IP

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Wireless Network Applications

• Positioning method using Cell-id
• Local weather forecast
• Nearest vacant parking garage
• Events today in the city
• Personalized service M-business
• E-mail
• Mobile gaming
• Mobile advertising

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Infrastructured Networks

• Cellular architecture
• Base station

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Infrastructured Networks

• Cell (hexagon with 2-10 km radius)
• Cellular System Infrastructure
• MS (mobile system)
• BS (base station)
• BSC (base station controller)
• MSC (mbile switching center)
• PSTN (public switched telephone network)

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Infrastructured Networks
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Infrastructured Networks

• Different generations
• 1G (analog)
• 2G (digital)
• 2.5G (digital)
• 3G (cdma2000 in US and W-CDMA in Europe and
  Japan)

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Infrastructured Networks

• Frequency hopping

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Infrastructured Networks

• Multiplexing techniques
• FDMA (frequency division multiple access)
• TDMA (time division multiple access)
• CDMA (code division multiple access)
• CDMA
• Direct sequence
• Frequency hopping
• (GSM is based on TDMA)

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Infrastructured Networks

• Issues to be covered
• Celluar Concept
• Mobility Management
• Handoffs
• Location Management
• Channel Assignment

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Celluar Call a sample

• Susans telephone tunes to the strongest signal.
• Her request includes both her and Bills
  telephone numbers. BS relays the request to the
  switch.
• The switch commands several BSs to transit
  paging messages containing Bills number.
• Bills phone responds to the paging message by
  informing the system of its location.

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Cellular Call (Contd)

• The switch commands Susans phone to tune to
  channel X and Bills phone to channel Y.
• The cellular phone conversation starts.
• During the conversation, Bill moves to a new
  cell. The system rearranges itself to maintain
  the conversation.

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Cellular Call (Contd)
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Cellular Call (Contd)
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Cellular Call (Contd)
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Cellular Call (Contd)
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Cellular Call (Contd)
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Cellular Call (Contd)
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Cellular Call (Contd)

• Information flow for conventional call

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Cellular Call (Contd)

• Information flow for cellular telephone call

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Cellular Concept

• Cell hexagon
• Cluster a set of cells that you utilizes the
  entire available radio spectrum
• Channel Interference
• Cochannel interference
• Adjacent channel interference

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Cellular Concept

• Importance of Celluar Topology
• U of users
• W available spectrum
• B bandwidth per user
• N frequency reuse factor (size of cluster)
• M of cells required to cover an area
• U M W / N B

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Cellular Concept

• Cellular Hierarchy
• To extend the coverage area
• To serve areas with higher density
• Picocells local indoor
• Microcells rooftops of buildings
• Macrocells metropolitan areas
• Megacells nationwide areas

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Cellular Concept

• Cochannel reuse ratio
• D distance between cochannel cells
• R cell radius
• N cluster size
• (N can only take on values of
• for integers I and J)

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Cellular Concept

• Cochannel reuse for N1, 3, 4, 7, 9, 12, 13, 16

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Cellular Concept

• Cochannel reuse for N7

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Cellular Concept

• Signal-to-Interference Ratio
• S Pdesired / Pinterference
• a path-loss gradient (between 2 and 4)
• signal strength , where d is distance

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Cellular Concept

• Capacity Expansion
• Additional spectrum for new subscribers (20
  billion for PCS bands)
• Change the cellular architecture cell splitting
  and directional antennas
• Nonuniform distribution of the frequency bands
• Change the modem and access technology

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Cellular Concept

• Cell Splitting

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Cellular Concept

• 120 degree directional antennas (3-sector cells)

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Cellular Concept

• Different arrangements of directional antennas

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Handoff

• Mobility Management
• Handoff management
• Location management

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Handoff

• Handoff provide continuous service by supporting
  handover from one cell to another.
• Hard handoff break before make
• Soft handoff make before break

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Handoff

• Handoff Initiation
• Relative signal strength
• Relative signal strength with threshold
• Relative signal strength with hysteresis
• Relative signal strength with hysteresis and
  threshold

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Handoff

• Handoff Decision
• Network-controlled handoff
• Mobile-assisted handoff
• Mobile-controlled handoff

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Location Management

• Location management
• Activities a wireless network should perform in
  order to keep track of where the MS is
• Location updates
• Paging
• Location information dissemination

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Location Management

• Location update
• Messages sent by the MS regarding its changing
  points of access to the fixed network
• Static location update the topology of the
  cellular network decides when the location update
  needs to be initiated
• Dynamic location update the mobility of the
  user, as well as the call patterns, is used in
  initiating location updates

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Location Management

• Location area (LA) a set of cells controlled by
  a MSC

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Location Management

• Location update
• Each BS in the LA broadcasts its id number
  periodically
• An MS is required to continually listen to the
  control channel for the LA id
• When the id changes, the MS will make an update
  to the location by transmitting a message with
  the new id to the database containing the
  location information

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Location Management

• Avoiding the ping-pong effect

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Location Management

• Paging broadcasting a message in a cell or a
  group of cells to elicit a response from the MS
  for which a call or message is incoming
• Blanket paging with an LA (used in GSM)
• Closest-cells first with ring search
• Sequential paging

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Location Management

• Location update vs. paging
• Trade-off between the cost of the nature, number,
  and frequency of location updates, and the cost
  of paging

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Location Management

• Location information dissemination the
  procedures that are required to store and
  distribute the location information relate to the
  MSs

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Location Management

• Location information dissemination
• Each MS is associated with a home network and a
  home database
• The home database keeps mobile id, authentication
  keys, accounting, and location
• The location of MS is maintained in terms of
  visiting network (where the MS is located) and a
  visiting database (which keeps track of the MSs
  in its service area)

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Location Management

• Mobile IP (home agent, foreign agent, and care-of
  address)

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Location Management

• Mobile IP
• Server X transmits a message for mobile node A
  and the message is routed to As home network
• The home agent encapsulates the entire message
  inside a new message which has the As care-of
  address in the header and retransmits the message
  (called tunneling)
• The foreign agent strips off the outer IP header
  and delivers the original message to A

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Location Management

• Common Assumptions
• Network topology
• 1-D networks linear array and ring
• 2-D networks hexagon and mesh
• Call arrival probability
• Known call arrival time (can update location just
  before the call arrival)
• Poisson process

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Location Management

• Mobility models
• Fluid flow model continuous movement with
  infrequent speed and direction changes
• Random walk model time is slotted. The
  probability that the subscriber remains in the
  current cell is p and to a neighbor is (1-p)/n,
  where n is the number of neighbors (memoryless)
• Markov walk model the current move is dependent
  on the previous move.

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Location Management

• A sample Markov walk model

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Location Management

• Normal walk model The I th move, M(I), is
  obtained by rotating the (I-1) th move,
• M(I-1), counterclockwise for T(I) degrees,
  where T(I) is normally distributed with zero mean

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Location Management

• Location Management Schemes
• Location areas (LA)
• Optimal location area configuration
• Optimization store the ids of two most recently
  visited location area
• Reporting cells (RC)
• Dominating set each cell is either in the set or
  a neighbor of a cell in the set
• K-hop dominating set

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Location Management

• Update Strategies
• Time-based
• When a MS enters a new cell, it needs to find out
  the number of cells that will be pages if an
  incoming call arrive and the resulting cost for
  the network to page the mobile station.
• The weighted paging cost is the paging cost
  multiplied by the call arrival probability.
• A location update will be performed when the
  weighted paging cost exceeds the location update
  cost

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Location Management

• Movement-based
• Each MS keeps a count (init. 0) after each
  location update.
• The count is increased by one when NS crosses the
  boundary between two cells.
• When the count reaches a predefined threshold,
  the MS updates its location and resets the count
  to 0.

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Location Management

• Distance-based
• Each MS keeps track of distance between the
  current cell and the last reported cell.
• The MS updates its location if the distance
  reaches a predefined threshold.
• Other tracking strategies
• Profile-based
• Topology-based
• Load-sensitive-based

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Channel Assignment

• Channel assignment assigns the required number
  of channels to each cellular region such that
• Efficient frequency spectrum is utilized.
• Interference effects are minimized.

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Channel Assignment

• Three constraints in channel assignment
• Frequency constraints the number of available
  frequencies (channels) in the radio spectrum.
• Traffic constraints the minimum number of
  frequencies required by each station.
• Interference constraints the constraints on the
  placement of frequencies at different stations.

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Channel Assignment

• Three types of interference constraints
• Cochannel constraints
• Adjacent channel constraints
• Cosite constraints any pair of channels assigned
  to a radio cell must occupy a certain distance in
  the frequency domain.

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Channel Assignment

• Channel assignment algorithms
• Fixed channel assignment (FCA) channels are
  nominally assigned to cells in advance according
  to the predetermined estimates traffic intensity.
• Dynamic channel assignment (DCA) channels are
  assigned dynamically as calls arrive.

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Channel Assignment

• Other extensions and combinations
• Hybrid channel assignment (HCA) channels are
  divided into two groups one uses FCA and the
  other uses DCA.
• Borrowing channel assignment (BCA) channel
  assignment is still fixed, but each cell can
  borrow channels from its neighboring cells.

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Channel Assignment

• Models
• Cellular network graph G(V, E)
• Interference constraints compatibility matrix C
  cij
• cij gives separation between cell i and cell j
• cij 0 (no constraint in channel reuse)
• cij 1 (cochannel constraints)
• cij 2 (adjacent channel constraints)
• cii k (cosite constraints)
• Channel requirement vector

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Channel Assignment

• Channel Assignment as a mapping problem
• Optimization problem (NP-complete)
• Sample combinatorial formulations
• Heuristic techniques
• Graph coloring problem (with cochannel
  constraints only)
• Graph models
• Lower bounds

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Channel Assignment

• Combinatorial formulations
• Minimum order FAP minimize the number of
  different frequencies used.
• Minimum span FAP minimize the span (difference
  between max and min frequency used).
• Minimum (total) interference FAP minimize the
  total sum of weighted interference.
• Minimum blocking FAP minimize the overall
  blocking probability of the cellular networks.

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Channel Assignment

• Heuristic techniques
• Neural networks
• Evolutionary algorithms Genetic algorithm
• Fuzzy logic
• Simulated annealing
• Tabu search
• Swarm intelligence (collective behavior of
  animals)

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Channel Assignment

• A new heuristic is acceptable if
• It can produce high-quality solutions more
  quickly than other methods,
• it identifies higher-quality solutions better
  than other approaches,
• it is easy to implement, or
• it has applications to a broad range of problems.

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Channel Assignment

• Graph model multicoloring
• Weighted graph (G(V, E), w) and color set C
• Function f assigns each v in V a subset of f(v)
  of C such that
• For all f(v)w(v) each node gets w(v) colors.
• For all (u,v) in E, f(u) and f(v) have no common
  element two neighboring nodes get disjoint sets
  of colors.

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Channel Assignment

• Graph model multicoloring with reuse distance of
  r.
• Define G(V, E) based on G(V, E) such that
• VV and
• Any pair of nodes at distance d lt r in G is
  connected by an edge in G.

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Channel Assignment

• Lower bounds
• Clique a complete subgraph.
• Weighted clique number ?(G, w)
• Maximum weight of any maximal clique in the
  graph.
• Weighted clique number is a lower bound for the
  multicoloring problem.

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Channel Assignment

• Lower bounds
• Minimum odd cycle n
• Another lower bound ?(G, w) (n/n-1)
• The maximum size of an independent set in an
  n-node off cycle is (n-1)/2.
• Hexagon with reuse distance 2
• ?(G, w)5/4, where n5.
• Hexagon with reuse distance 3
• ?(G, w)9/8, where n9.

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Table of Contents

• Introduction
• Ad Hoc Wireless Networks
• Routing in Ad Hoc Wireless Networks
• Dominating-set-based Routing
• Open Problems and Opportunities
• Conclusions

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Domination-set-based Routing (Wu and Li, FAU)
School bus routing
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Properties

• Property 1 V is empty if and only if G is a
  complete graph otherwise, V forms a dominating
  set.
• Property 2 V includes all the intermediate
  vertices of any shortest path.
• Property 3 The induced graph G GV is a
  connected graph.

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Other Results

• Dominating set reduction
• Wu and Li, Dial M 1999
• Extended marking process (Rule-k)
• Dai and Wu, FAU TR, 2001
• Localized maintenance
• Wu and Dai, I-SPAN 2002
• Networks with unidirectional links
• Wu, IEEE TPDS 2002
• Scalable design hierarchical routing
• Wu and Li, Telecomm. Sys. J. 2001

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Other Results (Contd.)

• Mobility management
• Wu and Li, Telecomm. Sys. J. 2001
• Power-aware routing and power-aware broadcasting
• Wu, Dai, Gao, and Stojmenovic, J. Comm. and
  networks, 2002
• Wu, Wu, and Stojmenovic, WOC'2002
• Dominating-set- and GPS-based routing
• Datta, Stojmenovic, and Wu, IPDPS workshop, 2001
• Wu, IEEE TPDS 2002

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Simulation
(a) (b) (c)
Figure 14(a) and (b) Average numbers of gateway
hosts generated from different methods. (C)
Average numbers of rounds needed for different
methods.
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Switching-off

• Only gateway neighbors need to update their
  status!
• Mobile host v broadcasts to its neighbors about
  its switching off.
• Each gateway neighbor exchanges its neighbor set
  with its neighbors.
• Each gateway neighbor changes its marker to false
  if all neighbors are pair wise connected.

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Switching-off (Contd.)
Figure 17 mobile host v switches off
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Hierarchy of Dominating Sets
Figure 18 A sample ad hoc wireless network
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Maximum Hierarchical Level
Figure 19 Maximum hierarchical levels relative
to the number of hosts v
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Power-Aware Routing and Broadcasting

• Power consumption should be minimized and
  balanced among nodes to prolong the life span of
  each node.
• Minimum total transmission power routing (MTPR)
• Minimum battery cost routing (MBCR)

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Power-Aware Activity Scheduling

• MTPR is achieved by routing within dominating set
  only.
• MBCR is achieved by selecting gateways based on
  energy levels.

Figure 20 power-aware activity scheduling
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Dominating-set-based and GPS-based Routing

• Dominating-set-based routing does have drawbacks
  in highly dense networks where communication
  complexity is high.

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Dominating-set-based and GPS-based Routing
(Contd.)

• Use GPS information to reduce the density of the
  network
• Remove nodes 2-D grid and Yao graph.
• Remove links Gabriel graph and RNG graph.

Figure 21 (a) 2-D grid. (b) Gabriel graph. (c)
RNG graph. (d) Yao graph.
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Table of Contents

• Introduction
• Ad Hoc Wireless Networks
• Routing in Ad Hoc Wireless Networks
• Dominating-set-based Routing
• Open Problems and Opportunities
• Conclusions

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Open Problems

• Multicast
• Including multicast membership dynamics
• QoS support
• Plain resource reservation vs. Adaptive QoS
  approach
• Power-aware routing
• Routing traffic based on host's power metrics
• Other applications
• Sensor networks

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Opportunities

• There is no standard for routing in ad hoc
  wireless networks.
• Several routing proposals are currently being
  evaluated by Internet Engineering Task Force
  (IETF)'s MANET working group.

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Table of Contents

• Introduction
• Ad Hoc Wireless Networks
• Routing in Ad Hoc Wireless Networks
• Dominating-set-based Routing
• Open Problems and Opportunities
• Conclusions

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Thin Computing Network and Mobile Computing

• Wireless ubiquitous computing pervasive
  computing
• Currently, 98 of all processors are in household
  appliances, vehicles, and machines on factory
  floors.
• Radically new challenges await us when there are
  hundreds or thousands of computers per human.
• Wired and wireless networks co-existence

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Fat Computing Massive Parallel Computing

• DOE's Accelerated Strategic Computer Initiative
  (ASCI)
• COTS machines with teraflops and beyond.
• Cray's SV1 and SV2 (scalable vector) and IBM's
  Blue Gene.

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Technology and Strategic Convergence

• Similar Disciplines
• Parallel processing, Distributed processing, and
  Network processing
• Different Disciplines 3C convergence
• Computer, Communication, and Consumer electronics
• Strategic Convergence
• Higher Education, Government, Business Industry

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Any Questions ?