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SELF-CONFIGURABLE WIRELESS LAN SYSTEMS. Mathilde Benveniste, Ph.D. [email protected] Introduction. Contiguous coverage is desirable with WLANs in order to attract mobile applications; e.g. phone calls The limited number of ‘channels’ available imposes the need for RF planning

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Self configurable wireless lan systems

SELF-CONFIGURABLE WIRELESS LAN SYSTEMS

Mathilde Benveniste, Ph.D.

[email protected]

M. Benveniste


Introduction
Introduction

  • Contiguous coverage is desirable with WLANs in order to attract mobile applications; e.g. phone calls

  • The limited number of ‘channels’ available imposes the need for RF planning

  • To maintain the ‘plug-and-play’ nature of 802.11 WLANs, it is important to make extended WLAN systems ‘self-configurable’

M. Benveniste


Outline
Outline

  • RF Planning functions

  • Self-configurable wireless systems

  • Examples: Cellular and Indoor Wireless

  • Challenges for 802.11

M. Benveniste


Rf planning
RF Planning

  • Infrastructure multi-BSS WLANs resemble cellular systems and indoor wireless systems

  • Both operate on a limited RF spectrum

  • Channel losses permit channel reuse

  • Components of RF planning

    • Cell coverage and power setting

    • Channel assignment (FDMA/TDMA)

M. Benveniste


Rf planning approaches

Traditional RF Planning

Map Studies

Digitized maps are generated with empirical models from large computer data bases with propagation descriptors

Field-strength surveys

Field-strength surveys used to calibrate empirical models

Iterative Coverage Estimation and power setting

Manual Neighbor Lists

Regular fixed channel assignment

Best approximation regular N=7

Assumes regular cell grid and uniform traffic

Self-Configuration

Adaptive LearningProcess

Signal-strength measurements are collected continually by both mobile stations and base stations

Self characterization

Neighbor Listsand Re-use Criteriaderived from these measurements and updated adaptively

Optimized RF planning

The derived parameters employed by optimal algorithms for power settingand channel assignment

RF Planning Approaches

M. Benveniste


Self configurable indoor wireless

Signal-strength measurements are collected continually with standard equipment exploiting features of standard air interfaces

Base Stations -- equipped to measure uplink and downlink channels

Mobiles (report measurements through MACA and MAHO functions)

These enable system to adapt to

base station service interruption

return of base station to service

offered load

addition of new base stations

lay-out changes

*Prototype developed by author for an IS-136 system, while with AT&T

Self-Configurable Indoor Wireless*

active

stations

MAHO measurement

base station (AP)

inactive

stations

MACA measurement

base station (AP)

M. Benveniste


Maca maho functions
MACA/MAHO functions

Mobile Assisted Channel Assignment (MACA)

  • The base station sends to a ‘registered’ station a list of channel numbers on which to measure signal strength

  • The station takes the measurements and reports them to the base station

    Mobile Assisted Hand Over (MAHO)

  • The base station sends to an ‘active’ station a list of channel numbers on which to measure signal strength

  • The station takes the measurements and reports them to the base station

M. Benveniste


Channel assignment
Channel Assignment

  • Flexible (slowly changing over time) but static channel assignment enables a station to monitor a single channel

  • Optimized fixed or adaptive non-regular channel assignment can be used to meet various objectives; e.g. load balancing

  • Optimization is based on reuse criteria, which specify whether a channel may be used by a pair of cells

M. Benveniste


8-Base -Station Example

Graph

B

A

G

A

G

F

C

H

B

F

E

D

C

E

H

D

Interference Matrix

Reuse Criteria

M. Benveniste


Graph coloring for channel assignment

‘Balanced’ Graph Coloring

A

B

G

F

H

C

D

E

2 co-channel base stations

per channel

Graph Coloring for Channel Assignment

Heuristic methodbalances co-channel sets of nodes

Objective is to

  • balance color sets

  • impose color set size restrictions

M. Benveniste


Power

Margin

Contiguity

Requirement

Coverage

Requirement

Power Setting with Contiguity Requirement

Attenuation

Data

3

1

3

3

1

B1

3

3

3

3

B3

3

3

1

3

3

3

3

2

3

3

3

2

3

B2

Mobile Locations

2

M. Benveniste


Challenges with wlan systems
Challenges with WLAN systems

  • Insufficient channels available to obtain contiguous interference-free coverage

    (3 channels of 802.11b are not enough for 3-D coverage)

  • Problem becomes more serious with ad hoc placement of APs by independent LAN owners

    (8 channels of 802.11a may not be enough for 3-D coverage)

  • Problem can be remedied by allocating channel time among co-channel BSSs

    • Bandwidth allocation may be either fixed or dynamic

    • Distributed dynamic bandwidth allocation is more consistent with current channel access mechanism

M. Benveniste


Cellular system - Centralized

Air interface

All measurement data is forwarded to a central controller for processing. Decisions are made by the controller and sent to the base stations

Wired link

MTSO

Control Architecture

Wireless LANs - Distributed

Wireless Link

Multiple ownership of independent LANs and the lack of coordination between different APs makes channel assignment/ bandwidth allocation more difficult to optimize

Some signaling capability may be desirable (wired, over the air, or …)

  • Wired link

Air Interface

Switch

APs

M. Benveniste


The good news is
The Good News is...

  • Because the cellular standard that we worked with was established, we were restricted to using the available functions for goals other than their intended use. That was tough!

  • The goal is to have the 802.11 standard provide the ‘hooks’ in the PHY and MAC layers that will enable one to provide, through higher layers, the self-configuration capability for 802.11 WLANs.

M. Benveniste


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