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March 2002
M. Benveniste
Slide 1
doc.: IEEE 802.11-02/211r0
Submission
SELF-CONFIGURABLE WIRELESS LAN SYSTEMS
Mathilde Benveniste, [email protected]
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.