Wireless Mesh Networks: First part: an Overview - PowerPoint PPT Presentation

Loading...

PPT – Wireless Mesh Networks: First part: an Overview PowerPoint presentation | free to download - id: 1790ba-ZDc1Z



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Wireless Mesh Networks: First part: an Overview

Description:

... to the Water Filling Approach when perfect Channel estimation is considered. ... for the general case of imperfect channel estimations and spatially colored MAI. ... – PowerPoint PPT presentation

Number of Views:314
Avg rating:3.0/5.0
Slides: 89
Provided by: womenproje
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Wireless Mesh Networks: First part: an Overview


1
Wireless Mesh NetworksFirst partan Overview
2-nd
Workshop

on
WOMEN Project
University of Rome La Sapienza, INFOCOM Dept.
(Faculty of Engineering)
Rome September 8-th, 2006
2
Outline
  • Wireless Mesh Network Definition and
    Characteristics

Wireless Mesh Networks application scenarios
MAC layer solutions currently adopted
Slotted Seeded Channel Hopping (SSCH)
Network layer solutions currently adopted
Dynamic Source Routing (DSR)
Conclusions and future researches
3
Wireless Mesh Networks Definition

A Wireless Mesh Network is a multi-hop
distributed mesh topology system, with
self-configuration and self-organization
capabilities, where each node is potentially able
to forward Informative Units toward other nearby
nodes
I.F. Akyildiz, X. Wnag, W. Wang, Wirless Maesh
Netowrks a survey , Computer Netwroks No.47,
pp. 445-487, 2005.
4
Wireless Mesh Networks Characteristics (1/2)
  • 1. Auto-configuration all network nodes are
    designed to self-discover their neighbors and
    paths without needing of any centralized network
    entity
  • Auto-organization nodes can autonomously
    resolve Out-of-Service events, due to
    temporary off or congested radio links, by
    exploiting the Mesh Topology
  • Scalability the covered area can be extended by
    simply adding new nodes to the current Mesh
    Network
  • Mobility the nodes can move on a limited area
    and keep the connectivity with (at least) a
    network node

5
Wireless Mesh Networks Characteristics (2/2)
  • Mesh Clients mobile and peripheral nodes able to
    communicate with other nodes only through radio
    interfaces. Minimal routing functions are solved
    by them. Moreover, they
    are power constrained, typically low cost and
    developed on already existing Wireless Cards
    (e.g., 802.11a/b/g Network Interface Cards (NIC)
    )
  • Mesh Routers nodes with minimum (or null)
    mobility, constituting the network backbone, with
    radio interfaces towards the mesh clients and
    mesh routers and wired interfaces towards the
    outside network.
    They are not power constrained, can process
    the most of network traffic and results more
    expensive than the mesh clients.
  • Additional features of the Wireless Mesh
    Networks Currently there is no standard, and
    open questions are related to the security
    aspects and to proper MAC protocol developments

6
Wireless Mesh Networks architectures
(1/3)(Infrastructure/backbone)
IEEE 802.16
  • This architecture is composed by mesh routers
    which are employed for the wireless backbone and
    mesh clients are excluded by the mesh topology
  • Connections among the mesh routers are realized
    with IEEE802.16 technology
  • Mesh routers function also as gateway for
    Internet access

7
Wireless Mesh Networks architectures
(2/3)(Client-Mesh)
IEEE 802.11
  • This architecture is composed by
    self-configured Mesh Clients with routing
    functions
  • It represents the mesh network operating in
    ad-hoc mode
  • Currently wireless links are IEEE 802.11 based

8
Wireless Mesh Networks architectures
(2/3)(Hybrid-Mesh)
IEEE 802.16
IEEE 802.11
  • This architecture given by combing the two
    previous ones
  • Mesh Clients can access at the network through
    mesh routers as well as directly with other mesh
    clients

9
Application Scenarios (1/2)
Community Networking
Broadband home networking
  • Low cost alternative to link difficult areas to
    be cabled
  • Alternative to
  • IEEE 802.11 and Bluetooth standards

10
Application Scenarios (2/2)
Metropolitan Wireless Mesh Networks
  • They can be view as a low cost solution of wide
    band access networks

11
MAC layer solutions
  • Mac protocol for Wireless Mesh Networks has to
    consider several differences with those employed
    by the WLANs
  • 1) The multi-hop environment
  • 2) All the architectures are distributed and
    each node is involved to the cooperation of the
    network traffic management
  • Currently, the proposed MAC protocols are mainly
    based on two methods
  • Virtual MAC protocols working on the top of
    existing MAC protocols
  • P.Bahl, R. Chandra, SSCH Slotted
    Seeded Channel Hopping for Capacity Improvement
    in IEEE 802.11 Wireless ad-hoc networks
  • Innovative MAC protocols with features similar to
    those proposed for ad-hoc wireless networks
  • J.W. Kim, N. Bambos, Power Efficient MAC
    scheme using Channel Probing in Multirate
    Wireless Ad-hoc Networks

12
Slotted Seeded Channel Hopping(SSCH)
  • SSCH is a protocol for ad-hoc wireless networks
    using IEEE 802.11 standard and exploits IEEE
    802.11 MAC layer service
  • It can be simply implemented via software into a
    device equipped with a Wireless Network Interface
    Card (NIC) and IEEE 802.11 standard compliant
  • Its task is to extend the channelization of the
    IEEE 802.11a (13 channels), IEEE 802.11 b/g (11
    channels) standard to the ad-hoc networks so to
    increase the throughput of each node
  • Each node is equipped with a Channel Scheduler
    for the channel/frequency hopping
  • Each node is equipped with a Packet Scheduler
    where the flow management is given by
    per-neighbor FIFO queues which are maintained in
    a priority queue ordered by perceived neighbor
    reachability

13
SSCH Performances
Disjoint flows
Non-disjoint flows
  • As the number of flows increases, SSCH
    considerably exceeds the IEEE 802.11a performances

14
Dynamic Source Routing (1/2)
  • Routing protocol for ad-hoc wireless networks
    with low mobility nodes
  • Differently to Distance vector or Link State
    based protocols, Dynamic Source Routing does not
    use periodic routing advertisement messages
  • It is based on Source Routing technique before
    transmitting, each node evaluates the nodes
    sequence (hop) through which the packets are
    forwarded toward the destination node
  • Route
    Discovery
  • A control procedure is adopted for the correct
    packet reception and is based on data link
    acknowledgement between two adjacent nodes
  • Route
    Maintenance

15
DSR Performances
  • Routing length between a factor 1.01 and 1.09
    from the optimal case
  • Overhead ratio from 1.01 to 2.6 from the optimal
    case

16
Conclusions
  • Wireless Mesh Networks are considered as a
    flexible, performing and low cost alternative to
    current WLANs
  • Currenlty, the proposed solutions are of
    proprietary type (MIT, Roofnet, Nokia, Mesh
    Connectivity Layer) and are essentially based on
    the IEEE 802.11 a/b/g standards
  • The MAC (SSCH) and routing (DSR) protocols
    currently adopted result to be extremely simple
    to be implemented
  • By the end of 2006 IEEE 802.11s Mesh standard is
    expected to be ratified

17
Wireless Mesh NetworksSecond
PartPublications
18
Title of Paper Optimized Power Allocation for
Multi-Antenna Systems impaired by Multiple-Access
Interference and Imperfect Channel-Estimation
WOmEn Project First Publication

Authors E.Baccarelli, M.Biagi, C.Pelizzoni,
N.Cordeschi
Accepted on IEEE Tr. On Vehicular Technology
19
Outline
  • System Model (Wireless MIMO channel)
  • Mean Mutual Information
  • Power-Constrained Maximization of the Mean Mutual
    Information
  • System Nodes Interaction the Game Theory
    Approach
  • Spatial-Power Allocation Multi-Antenna (SPAM)
    Game for Ad -hoc networks
  • SPAM game-vs.-collision-free Access strategies
  • Conclusions

20
System Model-(MIMO Wireless Ad-Hoc Network)
(1/2)
21
System Model (2/2)
Multiple Access Interference (MAI)
Tx0-Rx0 Reference link
22
Payload Phase (Tx0-Rx0 reference link)
  • The overall observed signal vector during the
    payload phase
  • The information stream is power constrained as

23
User Information Throughput and Capacity
The choice of is finalized to
reach the system capacity

We adopt Gaussian distributed input signals for
computing the following information throughput

Under some conditions we have derived the
Gaussian Throughput is equal to the Capacity
24
Mean Mutual Information
Such expression is valid under some conditions we
have derived and reported into the Paper
25
Maximization of the User Information Throughput
Problem evaluate and
  • It has been derived the Power Allocation
    Algorithm in order to find the optimal
    expressions of P(1).P(s). It reduces to the
    Water Filling Approach when perfect Channel
    estimation is considered.

26
Modelling of the Nodes Interaction (1/2) Game
Theory Approach
The Game Theory is adopted in order to consider
the node interaction and the dynamic ad hoc
network topology
F.R. Farrokhi, etc Link-Optimal Space-Time
Processing with Multiple Transmit and Receive
Antennas IEEE Commmunications Letters, Vol.5
March 2001.
27
Modelling of the Nodes Interaction (2/2)Game
Theory Approach
  • MIMO ad-hoc network may be modelled as
    Noncooperative
  • Strategic Game
  • - set of
    pair (players set)

  • - Action Set of node

  • - Utility Function of
    node .





There have been found Existence and Uniqueness
Conditions for the Nash
Equilibrum
28
Spatial Power Allocation for Multi-Antenna (SPAM)
Systems
  • Setup Phase (Eigenvalues and Nash Equilibrium )
  • While
  • Evaluate
  • 3. Shape
  • 4.
  • 5. If

    go to 6
  • else go to 2
  • 6. Evaluate the Throughput

29
SPAM Game-vs.-collision free access strategies
(Examples of Throughput Regions for an
hexagonal network)
SNR5dB, tr4. F.R. Farrokhi,
etc Link-Optimal Space-Time Processing with
Multiple Transmit and Receive Antennas IEEE
Commmunications Letters, Vol.5, March 2001.
30
Conclusions
  • The information throughput has been expressed
    in closed form for the general case of imperfect
    channel estimations and spatially colored MAI.
  • The power allocation and spatial shaping have
    been accomplished via the SPAM Game.
  • 3. The SPAM game is fully distributed,
    asyncronous, scalable access schemes.
  • 4. The SPAM game allows point-to-point throughput
    higher than those attainable via conventional
    orthogonal (e.g., collision-free) access schemes.

31
Title of Paper Interference Suppression in
MIMO Systems for ThroughputEnhancement and Error
Reduction
WOmEn Project Second Publication

Authors E.Baccarelli, M.Biagi, C.Pelizzoni,
N.Cordeschi
Proc. of IEEE International Wireless
Communications and Mobile Computing Conference,
3-6 July 2006, Vancouver, pp.611-616.
32
Outline
  • Reference MIMO Model
  • Transmission Rate and Error Rate in multi-user
    environment
  • Throughput enhancement and error reduction via
    interference cancellation
  • Performances
  • Impact on MAC and Routing of the pursued aproach
  • Conclusions and work in progress

33
Reference MIMO Model
  • We consider a scenario where a mesh router
    receives information bits in the presence of
    multi-user interference from different mesh
    clients

34
Reference MIMO Model
  • The packet structure

35
Reference MIMO Model
  • The received sequence, once acquired information
    about channel state (perfect CSI assumed) and
    interference is (under no CSI at the Tx)

36
Reference MIMO Model
  • The interference is generally spatially
    colored since it depends on topology, so this
    last heavily influences the behavior of the system

37
Transmission Rate and Error Rate in multi user
environment
  • The final goal should be to transmit at high
    rate with very low bit error rates
  • By defining the net throughput also known as
    gooput
  • We have to maximize throughput and minimize error
    probability

Double goal High throughput with Low
BER RequirementHigh interference suppression
capability since the transmission is simultaneous
(collision)
38
Transmission Rate and Error Rate in multi user
environment
  • The throughput enhancement in the sense of
    information rate can be achieved by estimating
    interference at receiver side and by subtract it
    since interference reduces the capacity region

At the same time, the error reduction can be
obtained by reducing the effect of interference
that, generally, increases BER
39
Throughput enh. and error red. via interference
cancellation
  • The transmitter avoids to transmit for TL slots
    so the receiver can estimate the statistical
    feature of V (multi-user interference) and the
    linear estimator is given by

Reference signal And channel
40
Throughput enh. and error red. via interference
cancellation
  • The performances in terms of estimation error
    variance can be evaluated in the following way

41
Throughput enh. and error red. via interference
cancellation
  • The error variance reduces itself to
  • for high noise
    and/or high level of reference signal
  • for low noise and low
  • level of reference signal

42
Throughput enhancement and error via
interference cancellation
  • The parameter that influences the performance is
    the SIR after cancellation

43
Throughput enhancement and error via
interference cancellation
  • To increase network rate means

44
Throughput enhancement and error via
interference cancellation
  • to reduce the error probability means to
    minimize

q takes into account for the cardinality of
modulation format
45
Performances
  • performances in terms of BEP for different q
    (modulation formats)

46
Performances
  • Net throughput for t2, and different values of r

47
How interference Suppression can aid MAC?
  • Approaches as CSMA usually tries to avoid
    collisions

The packet is NOT dropped (MIMO)
The packet is dropped (SISO)
48
Impact on MAC
  • For sure the effect of interference suppression
    SIMPLIFIES the MAC procedures and the
    architecture
  • The MAC may operate in severe interference
    suppression conditions that means when
    interference is comparable with the main signal

49
Impact on Routing
  • Preliminary results show that MIMO system allows
    power saving strategies (SISO same performance
    with low power emission) and interference
    suppression allows us to consider
    quasi-orthogonal transmission
  • This suggests that multi-hop approach is
    unnecessary in this operating conditions

50
Conclusions
  • Interference suppression allow the system to e
    more simple at upper layers
  • Without decreasing transmission rate (due to
    multi-user interference) we are able to assure
    good performances in terms of BER
  • This does not require severe hardware complexity.

51
WOmEn Project Third Publication

Fast Downloading of Large Files via Multi-Channel
Wireless Mesh Networks
Enzo Baccarelli, Mauro Biagi, Nicola Cordeschi
Cristian Pelizzoni,
First International Workshop on "Wireless mesh
moving towards applications" ( WiMeshNets 2006 ),
(Co-located with QShine 2006, Waterloo, Ontario,
Canada) August 10, 2006
52
Outline
  • System Model and Problem Setup
  • The constrained Minimization Problem, the
    fundamental trade-off Time-minimization, Budget
    Constraints, and QoS client Requirements
  • The possible strategies Single-channel v.s.
    Multi-channel, Optimal and Sub-optimal approach
    the On-Off policy
  • Optimal energy-allocation policy and Throughput
    performance of the system the general framework
    and two specific rate-functions of practical
    interest
  • An application example. The Broadcast MIMO
    systems the Dirty Paper strategy
  • Conclusions and Works in Progress

53
Problem Setup
  • The last-hop of Wireless Mesh Networks,.
  • Broadcast-type multi-channel Wireless Application
    scenarios fading affected-links
  • Energy-limited (battery powered) Wireless Mesh
    Router
  • Multi-flows and Multimedia applications the
    large (and increasing) size of multimedia
    objects.
  • Clients demand for fast-downloading Guaranteed
    QoS and maximum allowed Download-Time.
  • Conventional current proxies inadeguate to solve
    the problem.

Target Design of the Optimal
Energy-allocation-Policy How Much and How
Distribute The Minimization of Download-Time of
huge-size data.
54
System Model The Channel
State of the i-th sub-channel
The overall Multi-Channel State
  • Continuous-state slotted wireless links.
  • Slow faded downlink sub-channels the Block
    fading model.
  • Multiple Orthogonal Sub-channels
  • (time, frequency, code, spatial domain).
  • Current value of link-state over slot t
    known at the mesh-router slot-by-slot
  • Probability density function known
    at the mesh-router

Random Sequence
55
System Model Budget Constraints and QoS
Requirements
  • Multi-channel system constituted by
    orthogonal sub-channels a mesh-router serves
    clients requiring the download

Information Units (IU) to transfer to the clients
  • Overall available energy

Upper bound on the allowed peak-energy per slot
Minimum energy to be radiated over i-th
sub-channel
QoS Client requirements
56
The Considered Family of Rate-Fuctions
  • We assume
  • is in over
  • non decreasing both for and
  • strictly concave over
  • non
    decreasing for

How to choose?
budget state download state
channel state
57
The optimal allocation of
The System Rate-Function The Throughput
performance of the considered System
How much Energy and How distribute it
How much Energy to radiate
58
Related Works
Energy Allocation and Trasmission Scheduling in
Satellite and Wireless Networks, A. Fu, Phd
Thesys, Massachusetts Institute of Technology,
January 2003
  • Single Client
  • No QoS constraints are accounted for
  • Single channel discrete state link
  • Linear rate-function
  • Our Work
  • Multiple traffic-flows, multiple Clients
  • QoS Requirements
  • Continuous state multiple-orthogonal sub
    channels
  • The rate-function a general framework

59
The constrained Optimization Problem
How Much energy has to be radiated in the current
slot How distribute energy between the M
Sub-Channels How take into account for the
QoS-Client requirements
60
The Optimization Problem and its Restatement
(Low of Large Number)
61
The Optimal Energy-allocation Policy (1/3)
Form of the Optimal Policy strongly depends on
the Average available energy for the download of
a single IU

Total energy not sufficient to meet QoS
Maximal energy policy

Single channel Optimal Policy
62
The Logarithmic rate-function - 1
(Shannon capacity)
(Rayleigh channel)
63
The Logarithmic rate-function - 2
On-Off policy only sub-optimal very poor
performance in strongly energy-limited
application scenarios
Optimal Policy On-Off Policy
Average download time (slot)
Optimal Policy On-Off Policy
64
The Optimal Energy-allocation Policy (2/3)
Full Allocation Sub-Region
Not-Full Allocation Sub-Region
65
The Optimal Energy-allocation Policy (3/3)
66
Case of the Logarithmic Rate-function
67
Case of the -powered Rate-Function
68
An Application Example the Broadcast MIMO System
(1/3)
Mesh Router Multi-Antenna
Mesh Clients Mono-Antenna
Dirty-Paper Strategy 1) Channel Matrix
QR-factorization, 2) Orthogonal Pre-coding,
3) Iterative Interference pre-subtraction
69
An Application Example the Broadcast MIMO System
(2/3)
70
An Application Example the Broadcast MIMO System
(3/3)
Average download time (slot)
71
Conclusions and Works in Progress
  • The Multi-channel Optimal Energy-allocation
    Policy has been derived for the general framework
    we considered
  • An efficient Algorithm for its computation has
    been derived, and comparisons with sub-optimal
    approaches has been carried out
  • Performance evaluations in single-link systems
    and broadcast system application scenarios have
    been carried out
  • How can the Considered Strategy take into account
    for real-time multimedia applications
    (not-elastic traffic)?

Thinking about.
72
WOMEN projectproviding QoS with channel state
dependent scheduling in WMNs
University of Rome La Sapienza Presented by
Tiziano Inzerilli 8/9/2006
73
Contents
  • Models and basic assumptions
  • Approach for QoS provision
  • traffic control scheduler design
  • Statistics

74
Contents
MODELS BASIC ASSUMPTIONS
  • Models and basic assumptions
  • Approach for QoS provision channel state
    dependent scheduling
  • Statistics

75
Network model
  • MR (mobile routers) BS (base stations)
  • quasi static nodes
  • Point-to-multipoint transmission
  • IEEE802.16/ IEEE802.11
  • MC (mobile nodes)
  • Fast moving
  • Point-to-point transmission
  • IEEE802.11

MR
link
BS
MC
channel
76
Link model
Errors in different Channels statistically
independent
Rec. Node 1
Trans. node
  • Bandwidth allocation

C1,, BER1
Brec-1
Boff-1
Channel 1
Rec. Node 2
C2,, BER2
Boff-2
Brec-2
Channel 2
Rec. Node N
  • Varibility due to
  • channel impairments
  • MAC

CN,, BERN
Boff-N
Brec-N
Channel N
77
Channel model
Transmitting node
Receiving node
Boff
Btrans
Brec
Gilbert channel model
Traffic control portion
Bqueue-loss
Bchannel-loss
sink
sink
78
Channel model Gilbert Channel
  • Every Tslot a transition occurs.

q
Good Channel
Bad Channel
1-r
1-q
r
  • Rayleigh fading channel average fade duration
    (AFD) and average non-fade duration (ANFD) vs.
    the fade margin M and the Doppler spread fd.
  • Transition Probabilities

79
Channel model types of channels
No MAC contention No channel errors
No MAC contention Channel errors
MAC contention Channel errors
80
Channel State Dependent (CSD) Independent
(CSI) Scheduling Model
Flow 2
Flow 3
Flow 4
Flow 5
Flow N
Flow N
Flow 1
Flow 1
Flow 2
Flow 3
Flow 4
Flow 5
CSD Packet Scheduling
CSI Packet Scheduling
Error Correction FEC, ARQ, interleaving
Wireless Link Monitoring
Channel K
Channel 1
Channel 2
Channel 3
Wireless Link Monitoring
Wireless Link
Wireless Link
81
Contents
APPROACH FOR QOS PROVISION traffic control
scheduler design
  • Models and basic assumptions
  • Approach for QoS provision channel state
    dependent scheduling
  • Statistics

82
Metrics Constraints
Delay Constraint (only real-time traffic)
Bandwidth Allocation Metrics
Data Loss Metrics
Link Utilization Metric
83
Design of traffic control
Mean link Capacity over time
Flow Classification
C(t)
Regulation
Link monitoring
Scheduling
S(t)
Instantaneous channel state vector
84
Classification
Offered traffic
With time constraints
Without time constraints
Non- Real-time
Real-time
video1
Web br.
video2
voice2
File transf
voice1
email
85
Other design options
  • Assessment for channel estimation
  • SNR/SIR, Monitoring ACK reception, RTS/CTS frame
    exchange, BER/BLER measured at destination,
    Ad-hoc probing frames,
  • Regulation strategies
  • Algorithms Dual leaky buckets, markers,
    droppers,
  • Strategies never drop, drop after deadline,
    deadline only for real-time traffic,
  • Scheduling strategies
  • Algorithms Round robin, priority queuing,
    weighted fair schedulers, deadline-based
    schedulers
  • SELECTION CRITERIAS
  • Computational cost
  • Optimize metrics

86
Contents
STATISTICS
  • Models and basic assumptions
  • Approach for QoS provision channel state
    dependent scheduling
  • Statistics

87
Simulation Scenario
  • Main features
  • Multiple real-time and non-real-time flows to
    MC1, MC2, MC3
  • Total capacity 4Mbps
  • Link load 99,1
  • Three subscenarios
  • Error-prone channel
  • Bandwidth variability per MC due to MAC
  • Comparison with WFS
  • Mapping of Flows
  • MC1 video, voice
  • MC2 video, email, FTP
  • MC3 HTTP, email, FTP

BS
MC1
MC2
MC3
88
Error-prone channel subscenario
89
Variable bandwidth subscenario
90
Comp. with WFS subscenarioaverage BAI statistics
91
Comp. with WFS subscenarioLink Utilization
Efficiency
92
Future Ways
  • To evaluate the potentials offered by MIMO-UWB at
    physical layer
  • To consider the joint effect of beamforming and
    interference cancellation in order to aid MAC ad
    routing
  • Performance Analysis of an innovative scheduling
    algorithm for OFDMA based IEEE 802.16a systems
  • Performance analysis of an innovative algorithm
    of Connection Admission Control for IEEE 802.16
    systems
  • To take into account for real-time multimedia
    applications (not-elastic traffic)
About PowerShow.com