March 2002

M. Benveniste

Slide 1

doc.: IEEE 802.11-02/211r0

Submission

SELF-CONFIGURABLE WIRELESS LAN SYSTEMS

Mathilde Benveniste, Ph.D.benveniste@ieee.org

March 2002

M. Benveniste

Slide 2

doc.: IEEE 802.11-02/211r0

Submission

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’

March 2002

M. Benveniste

Slide 3

doc.: IEEE 802.11-02/211r0

Submission

Outline

• RF Planning functions

• Self-configurable wireless systems

• Examples: Cellular and Indoor Wireless

• Challenges for 802.11

March 2002

M. Benveniste

Slide 4

doc.: IEEE 802.11-02/211r0

Submission

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)

March 2002

M. Benveniste

Slide 5

doc.: IEEE 802.11-02/211r0

Submission

RF Planning ApproachesTraditional 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 Learning Process

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

• Self characterization

Neighbor Lists and Re-use Criteria derived from these measurements and updated adaptively

• Optimized RF planning

The derived parameters employed by optimal algorithms for power setting and channel assignment

March 2002

M. Benveniste

Slide 6

doc.: IEEE 802.11-02/211r0

Submission

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

base station (AP)

base station (AP)

active

stations

MACA measurement

MAHO

mea

sure

men

t

inactivestations

March 2002

M. Benveniste

Slide 7

doc.: IEEE 802.11-02/211r0

Submission

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

March 2002

M. Benveniste

Slide 8

doc.: IEEE 802.11-02/211r0

Submission

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

March 2002

M. Benveniste

Slide 9

doc.: IEEE 802.11-02/211r0

Submission

8-Base -Station Example

A

B

H

C

F

G

D

E

Interference MatrixA B C D E F G H

A 0 1 0 0 0 1 0 0

B 1 0 1 0 0 0 0 0

C 0 1 0 1 0 0 0 1

D 0 0 1 0 1 0 0 0

E 0 0 0 1 0 1 0 0

F 1 0 0 0 1 0 1 0

G 0 0 0 0 0 1 0 0

H 0 0 1 0 0 0 0 0

Reuse Criteria

HG

A B

F

E D

C

Graph

March 2002

M. Benveniste

Slide 10

doc.: IEEE 802.11-02/211r0

Submission

Graph Coloring for Channel Assignment Graph Coloring for Channel Assignment Heuristic method balances co-channel sets of nodes

Objective is to – balance color sets– impose color set size restrictions

2 co-channel base stationsper channel

G

B

H

A

D

F

E

C

‘Balanced’ Graph Coloring

March 2002

M. Benveniste

Slide 11

doc.: IEEE 802.11-02/211r0

Submission

Power Setting with Contiguity RequirementPower Setting with Contiguity Requirement

B3

1

2

1

3

2

33

33 3 3

3

3 3

3

3

1

3

3

3

33

Mobile Locations

B1

B2

CoverageRequirement

ContiguityRequirement

Power Margin

2

AttenuationData

March 2002

M. Benveniste

Slide 12

doc.: IEEE 802.11-02/211r0

Submission

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

March 2002

M. Benveniste

Slide 13

doc.: IEEE 802.11-02/211r0

Submission

Control ArchitectureControl ArchitectureCellular system - CentralizedCellular system - Centralized

MTSO

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

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

Air interface

Wireless LANs - DistributedWireless LANs - Distributed

Switch

Air InterfaceWired link

APs

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 …)

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 …)

March 2002

M. Benveniste

Slide 14

doc.: IEEE 802.11-02/211r0

Submission

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.