SELF-CONFIGURABLE WIRELESS LAN SYSTEMS

1. SELF-CONFIGURABLE WIRELESS LAN SYSTEMS Mathilde Benveniste, Ph.D. benveniste@ieee.org M. Benveniste

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’ M. Benveniste

3. Outline • RF Planning functions • Self-configurable wireless systems • Examples: Cellular and Indoor Wireless • Challenges for 802.11 M. Benveniste

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) M. Benveniste

5. 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

6. 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

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 M. Benveniste

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 M. Benveniste

9. 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

10. ‘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

11. 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

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 M. Benveniste

13. 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

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. M. Benveniste