Title: Jie Wu
1COT 6930 Ad Hoc Networks (Part I)
- Jie Wu
- Department of Computer Science and Engineering
- Florida Atlantic University
- Boca Raton, FL 33431
2Table of Contents
- Introduction
- Infrastructured networks
- Handoff
- location management (mobile IP)
- channel assignment
3Table of Contents (contd.)
- Infrastructureless networks
- Wireless MAC (IEEE 802.11 and Bluetooth)
- Security
- Ad Hoc Routing Protocols
- Multicasting and Broadcasting
4Table of Contents (contd.)
- Infrastructureless networks (contd.)
- Power Optimization
- Applications
- Sensor networks and indoor wireless environments
- Pervasive computing
- Sample on-going projects
5Classification 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
6Wired/Wireless Networks
7Wireless 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)
8Samples
- Portable phones (home cordless, cellular, PCS)
- Paging (one-way service)
- Personal digital assistants (PDAs)
- Wireless LANs (small service area with
high-bit-rate services)
9Samples (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
10Wireless 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
11Infrastructured Networks
- Cellular architecture
- Base station
12Infrastructured 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)
13Infrastructured Networks
14Infrastructured Networks
- Different generations
- 1G (analog)
- 2G (digital)
- 2.5G (digital)
- 3G (cdma2000 in US and W-CDMA in Europe and
Japan)
15Infrastructured Networks
16Infrastructured 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)
17Infrastructured Networks
- Issues to be covered
- Celluar Concept
- Mobility Management
- Handoffs
- Location Management
- Channel Assignment
18Celluar 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.
19Cellular 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.
20Cellular Call (Contd)
21Cellular Call (Contd)
22Cellular Call (Contd)
23Cellular Call (Contd)
24Cellular Call (Contd)
25Cellular Call (Contd)
26Cellular Call (Contd)
- Information flow for conventional call
27Cellular Call (Contd)
- Information flow for cellular telephone call
28Cellular Concept
- Cell hexagon
- Cluster a set of cells that you utilizes the
entire available radio spectrum - Channel Interference
- Cochannel interference
- Adjacent channel interference
29Cellular 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
30Cellular 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
31Cellular 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)
-
32Cellular Concept
- Cochannel reuse for N1, 3, 4, 7, 9, 12, 13, 16
33Cellular Concept
34Cellular Concept
- Signal-to-Interference Ratio
- S Pdesired / Pinterference
- a path-loss gradient (between 2 and 4)
- signal strength , where d is distance
-
-
35Cellular 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
-
36Cellular Concept
37Cellular Concept
- 120 degree directional antennas (3-sector cells)
-
38Cellular Concept
- Different arrangements of directional antennas
-
39Handoff
- Mobility Management
- Handoff management
- Location management
40Handoff
- Handoff provide continuous service by supporting
handover from one cell to another. - Hard handoff break before make
- Soft handoff make before break
-
41Handoff
- Handoff Initiation
- Relative signal strength
- Relative signal strength with threshold
- Relative signal strength with hysteresis
- Relative signal strength with hysteresis and
threshold
42Handoff
- Handoff Decision
- Network-controlled handoff
- Mobile-assisted handoff
- Mobile-controlled handoff
43Location 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
44Location 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
45Location Management
- Location area (LA) a set of cells controlled by
a MSC
46Location 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
47Location Management
- Avoiding the ping-pong effect
48Location 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
49Location Management
- Location update vs. paging
- Trade-off between the cost of the nature, number,
and frequency of location updates, and the cost
of paging
50Location Management
- Location information dissemination the
procedures that are required to store and
distribute the location information relate to the
MSs
51Location 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)
52Location Management
- Mobile IP (home agent, foreign agent, and care-of
address)
53Location 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
54Location 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
55Location 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.
56Location Management
- A sample Markov walk model
57Location 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
58Location 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
59Location 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
60Location 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.
61Location 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
62Channel Assignment
- Channel assignment assigns the required number
of channels to each cellular region such that - Efficient frequency spectrum is utilized.
- Interference effects are minimized.
63Channel 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.
64Channel 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.
65Channel 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.
66Channel 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.
67Channel 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
68Channel 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
69Channel 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.
70Channel Assignment
- Heuristic techniques
- Neural networks
- Evolutionary algorithms Genetic algorithm
- Fuzzy logic
- Simulated annealing
- Tabu search
- Swarm intelligence (collective behavior of
animals)
71Channel 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.
72Channel 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.
73Channel 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.
74Channel 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.
75Channel 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.
76Table of Contents
- Introduction
- Ad Hoc Wireless Networks
- Routing in Ad Hoc Wireless Networks
- Dominating-set-based Routing
- Open Problems and Opportunities
- Conclusions
77Domination-set-based Routing (Wu and Li, FAU)
School bus routing
78Properties
- 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.
79Other 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
80Other 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
81Simulation
(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.
82Switching-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.
83Switching-off (Contd.)
Figure 17 mobile host v switches off
84Hierarchy of Dominating Sets
Figure 18 A sample ad hoc wireless network
85Maximum Hierarchical Level
Figure 19 Maximum hierarchical levels relative
to the number of hosts v
86Power-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)
87Power-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
88Dominating-set-based and GPS-based Routing
- Dominating-set-based routing does have drawbacks
in highly dense networks where communication
complexity is high.
89Dominating-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.
90Table of Contents
- Introduction
- Ad Hoc Wireless Networks
- Routing in Ad Hoc Wireless Networks
- Dominating-set-based Routing
- Open Problems and Opportunities
- Conclusions
91Open 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
92Opportunities
- 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.
93Table of Contents
- Introduction
- Ad Hoc Wireless Networks
- Routing in Ad Hoc Wireless Networks
- Dominating-set-based Routing
- Open Problems and Opportunities
- Conclusions
94Thin 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
95Fat 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.
96Technology 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
97Any Questions ?