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Wireless Mesh Networks: First part: an Overview. 2-nd Workshop on WOMEN Project. University of Rome “La Sapienza”, INFOCOM Dept. (Faculty of Engineering). Rome September 8-th, 2006. Outline. Wireless Mesh Network: Definition and Characteristics.

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wireless mesh networks first part an overview

Wireless Mesh Networks:First part:an Overview

2-nd Workshop


WOMEN Project

University of Rome “La Sapienza”, INFOCOM Dept. (Faculty of Engineering)

Rome September 8-th, 2006


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

wireless mesh networks definition
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 Unitstoward other nearby nodes

I.F. Akyildiz, X. Wnag, W. Wang, “Wirless Maesh Netowrks: a survey” , Computer Netwroks No.47, pp. 445-487, 2005.

wireless mesh networks characteristics 1 2
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
wireless mesh networks characteristics 2 2
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
wireless mesh networks architectures 1 3 infrastructure backbone
Wireless Mesh Networks: architectures (1/3)(Infrastructure/backbone)



  • 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
wireless mesh networks architectures 2 3 client mesh
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

Wireless Mesh Networks: architectures (2/3)(Hybrid-Mesh)



  • 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

IEEE 802.11

application scenarios 1 2
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


Application Scenarios (2/2)

They can be view as a low cost solution of wide band access networks

Metropolitan Wireless Mesh Networks

mac layer solutions
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“

s lotted s eeded c hannel h opping 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

Slotted Seeded Channel Hopping(SSCH)
ssch performances
SSCH Performances



  • As the number of flows increases, SSCH considerably exceeds the IEEE 802.11a performances



dynamic source routing 1 2
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

dsr performances
Routing length between a factor 1.01 and 1.09 from the optimal caseDSR Performances
  • Overhead: ratio from 1.01 to 2.6 from the optimal case


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


WOmEn Project First Publication

Title of Paper :“Optimized Power Allocation for Multi-Antenna Systems impaired by Multiple-Access Interference and Imperfect Channel-Estimation”

Authors: E.Baccarelli, M.Biagi, C.Pelizzoni, N.Cordeschi

Accepted on IEEE Tr. On Vehicular Technology



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


system model 2 2
System Model (2/2)

Multiple Access Interference (MAI)

Tx0-Rx0 Reference link


Payload Phase (Tx0-Rx0 reference link)

  • The overall observed signal vector during the payload phase
  • The informationstream is power constrained as:
user information throughput and capacity

The choice of is finalized to reach the system capacity

User Information Throughput and 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

mean mutual information

Mean Mutual Information

Such expression is valid under some conditions we have derived and reported into the Paper

maximization of the user information throughput

Problem: evaluate and

Maximization of the User Information Throughput

  • 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.
modelling of the nodes interaction 1 2 game theory approach

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.

modelling of the nodes interaction 2 2 game theory approach

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

spatial power allocation for multi antenna spam systems

Spatial Power Allocation for Multi-Antenna (SPAM) Systems

Setup Phase (Eigenvalues and Nash Equilibrium )



3. Shape


5. If go to 6

else go to 2

6. Evaluate the Throughput


SPAM Game-vs.-collision free access strategies(Examples of Throughput Regions for anhexagonal network)

SNR=5dB, t=r=4.

F.R. Farrokhi, etc…

“Link-Optimal Space-Time Processing with Multiple Transmit and Receive Antennas”

IEEE Commmunications Letters, Vol.5, March 2001.

  • 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.

WOmEn Project Second Publication

Title of Paper :“Interference Suppression in MIMO Systems for ThroughputEnhancement and Error Reduction”

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.



Reference MIMO Model

Transmission Rate and Error Rate in multi-user environment

Throughput enhancement and error reduction via interference cancellation


Impact on MAC and Routing of the pursued aproach

Conclusions and work in progress

reference mimo model

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

reference mimo model1

Reference MIMO Model

The packet structure

reference mimo model2

Reference MIMO Model

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

reference mimo model3

spatially white noise

Possible spatial coloration

Induced by the channel

Orthogonal STBC

of n-th user

Reference MIMO Model

The interference is “generally” spatially colored since it depends on topology, so this last heavily influences the behavior of the system

transmission rate and error rate in multi user environment

Transmission Rate and Error Rate in multi user environment

Double goal:

High throughput with


Requirement:High interference suppression capability since the transmission is simultaneous (collision)

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

transmission rate and error rate in multi user environment1

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

throughput enh and error red via interference cancellation



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

throughput enh and error red via interference cancellation1

Throughput enh. and error red. via interference cancellation

The performances in terms of estimation error variance can be evaluated in the following way

throughput enh and error red via interference cancellation2

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

throughput enhancement and error via interference cancellation

Throughput enhancement and error via interference cancellation

The parameter that influences the performance is the SIR after cancellation

throughput enhancement and error via interference cancellation1

Throughput enhancement and error via interference cancellation

To increase network rate means

throughput enhancement and error via interference cancellation2

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



performances in terms of BEP for different q (modulation formats)



Net throughput for t=2, and different values of r

how interference suppression can aid mac



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)

impact on mac

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

impact on routing

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



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.


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



  • 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
problem setup
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.


Design of the Optimal Energy-allocation-Policy: ‘’How Much’’ and ‘’How Distribute’’

The Minimization of Download-Time of huge-size data.


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:


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?

channel state

budget state download state


Single-Channel Optimal Design

Multi-Channel Optimal Design

The optimal allocation of

The System Rate-Function:

The Throughput performance of the considered System

How much Energy


How distribute it

How much Energy

to radiate


The On-Off Policy


The Optimal Policy

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
  • QoSRequirements
  • Continuous state multiple-orthogonal sub channels
  • The rate-function: a general framework

For , we have the following equivalent, simpler form:

The Optimization Problem and its Restatement

(Low of Large Number)


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 sufficientto meet QoS

“Maximal energy” policy

Single channel Optimal Policy


The Logarithmic rate-function - 1

(Shannon capacity)

(Rayleigh channel)


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


The Optimal Energy-allocation Policy (2/3)

FullAllocation Sub-Region

Not-Full Allocation Sub-Region



Space-Orthogonal Sub-Channels

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


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….

women project providing qos with channel state dependent scheduling in wmns

WOMEN project:providing QoS with channel state dependent scheduling in WMNs

University of Rome La Sapienza

Presented by Tiziano Inzerilli


  • Models and basic assumptions
  • Approach for QoS provision:

traffic control & scheduler design

  • Statistics



  • Models and basic assumptions
  • Approach for QoS provision: channel state dependent scheduling
  • Statistics
network model
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






link model
Link model

Errors in different

Channels statistically



Node 1

  • Bandwidth allocation



C1,, BER1



Channel 1


Node 2

C2,, BER2



Channel 2


Node N

  • Varibility due to
  • channel impairments
  • MAC




Channel N

channel model
Channel model








Traffic control


Gilbert channel






channel model gilbert channel
Channel model: Gilbert Channel
  • Every Tslot a transition occurs.









  • 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
channel model types of channels
Channel model: types of channels

No MAC contention

No channel errors

No MAC contention

Channel errors

MAC contention

Channel errors

channel state dependent csd independent csi scheduling model
Channel State Dependent (CSD) & Independent (CSI) Scheduling Model

Flow N

Flow N

Flow 2

Flow 3

Flow 4

Flow 5

Flow 2

Flow 3

Flow 4

Flow 5

Flow 1

Flow 1

CSD Packet


CSI Packet


Error Correction:






Channel K

Channel 1

Channel 2

Channel 3




Wireless Link

Wireless Link



traffic control & scheduler design

  • Models and basic assumptions
  • Approach for QoS provision: channel state dependent scheduling
  • Statistics
metrics constraints
Metrics & Constraints

Delay Constraint (only real-time traffic)

Bandwidth Allocation Metrics

Data Loss Metrics

Link Utilization Metric

design of traffic control
Design of traffic control

Mean link

Capacity over


Flow Classification







Instantaneous channel state vector


With time




Without time






Web br.


File transf




other design options
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
    • Computational cost
    • Optimize metrics


  • Models and basic assumptions
  • Approach for QoS provision: channel state dependent scheduling
  • Statistics
simulation scenario
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




error prone channel subscenario

Theoretical curve

Experimental curve

Link Utilization Efficiency

% data loss

Error-prone channel subscenario

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)