2. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 1 SELF-CONFIGURABLE WIRELESS LAN SYSTEMS Mathilde Benveniste, Ph.D. benveniste@ieee.org

3. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 2 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’

4. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 3 Outline RF Planning functions Self-configurable wireless systems Examples: Cellular and Indoor Wireless Challenges for 802.11

5. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 4 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)

6. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 5 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 Learning Process Signal-strength measurements are collected continually by both mobile stations and base stations Self characterization Neighbor Lists and R e-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

7. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 6 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) active stations MACA measurement MAHO measurement inactive stations

8. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 7 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

9. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 8 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

10. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 9 8-Base -Station Example A B H C F G D E Interference Matrix Reuse Criteria H G A B F E D C Graph

11. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 10 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 stations per channel G B H A D F E C ‘Balanced’ Graph Coloring

12. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 11 Power Setting with Contiguity Requirement B3 1 2 1 3 2 3 3 3 3 3 3 3 3 3 3 3 1 3 3 3 3 3 Mobile Locations B1 B2 Coverage Requirement Contiguity Requirement Power Margin 2 Attenuation Data

13. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 12 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

14. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 13 Control Architecture Cellular 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 Wired link Air interface Wireless LANs - Distributed Switch Air Interface Wired 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 …)

15. doc.: IEEE 802.11-02/211r0 Submission March 2002 M. BenvenisteSlide 14 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.