Wireless Performance Prediction – Rationale and Goals

1. IEEE 802.11 Study Group on Wireless Performance Prediction Wireless Performance Prediction – Rationale and Goals David G. Michelson University of British Columbia Department of Electrical and Computer Engineering 15 March 2004 Dave Michelson, University of British Columbia.

2. Background • In recent years, IEEE 802.11 wireless LANs have grown beyond their original role as extensions to wired LANs that provide isolated islands of wireless connectivity. • As IEEE 802.11 wireless LANs are increasingly used to provide ubiquitous coverage in campus-wide environments, it has become desirable to predict their performance before access points are deployed or usage ramps up. • Current IEEE 802.11 standards address the implementation of wireless devices and the operation of wireless networks, but do not address the needs of those who plan the deployment of such networks. Dave Michelson, University of British Columbia.

3. Background (cont.) Our own interest in wireless performance prediction has been motivated by: • deployment of one of the world’s largest campus wireless LANs (1500+ access points covering over one million m2) at the University of British Columbia, and • the needs of our colleagues in the University Networking Program’s Wireless LAN Project Dave Michelson, University of British Columbia.

4. The Role of Wireless Performance Prediction When would one want to predict wireless system performance? Ans. • Planning Stage - when access point locations are being chosen. • Commissioning Phase - after access points have been installed, but before usage ramps up. • Maintenance Phase – after access points have been added or their locations changed, or after the environment has been changed or altered due to construction renovation, etc. cf. Operations Phase – performance can be measured directly but any corrective action is reactive rather than proactive . Dave Michelson, University of British Columbia.

5. Wireless Performance Which wireless performance parameters might be of interest to designers and operators? Ans. • Coverage • Link reliability • Throughput (as a function of traffic load) • Latency (as a function of traffic load) • PESQ* (VoIP) (as a function of traffic load) *Perceptual Evaluation of Speech Quality Dave Michelson, University of British Columbia.

6. Issues in Wireless Network Deployment • The ultimate limits to the performance and capacity of most modern wireless networks, including IEEE 802.11 wireless LANs, are set by: • propagation impairments, – contention, • MAC overhead, – mutual interference. • Assuring adequate coverage and link reliability through correct access point placement is necessary but not sufficient • Wireless networks generally perform well when traffic (i.e., contention and co-channel interference) is light; the trick is to maintain and ensure good performance when traffic (i.e., contention and co-channel interference) is heavy Dave Michelson, University of British Columbia.

7. Client Access Point • Link Level • MAC overhead • propagation impairments • device placement • transmit power settings • Cell Level • usage • contention • QoS settings • RTS/CTS • Three Views of a Wireless Network • including principal impairments, and • mitigation techniques • Network Level • mutual (co-channel) interference • transmit power settings • channel assignments Dave Michelson, University of British Columbia.

8. Modeling Wireless Performance Metrics • Our goal is to model wireless performance metrics in terms of network layout, usage, and equipment performance parameters. • These metrics and parameters can be expressed on either a point (deterministic) or area (statistical) basis. • We need to capture the complex manner in which wireless performance metrics depend upon network parameters. • Measurement-based modeling is well-suited to capturing our intuition and understanding in a form amenable to analysis and simulation. Dave Michelson, University of British Columbia.

9. Wireless Performance Predictionusing Measurement-based Models Propagation Models Network Layout Equipment Performance Models Wireless Performance Metrics Usage Usage Models Equipment List Dave Michelson, University of British Columbia.

10. Test and Measurement to Support Wireless Performance Prediction • Lab tests – Equipment Performance • typically conducted in controlled environments by vendors • characterize the performance of access points and client devices in the presence of propagation impairments and interference in a deterministic manner • Field tests – Propagation and Interference • typically conducted in deployed networks by operators • characterize the propagation and interference environments in a statistical manner Dave Michelson, University of British Columbia.

11. Propagation Modeling in Support of Wireless Performance Prediction • Site-general models for use at the planning stage, e.g., ITU-R P.1238 (Indoor), COST-231 (Indoor), and ITU-R P.1411 (Outdoor). • Site-specific models based upon data collected by the deployed network itself at the commissioning and maintenance stages, • E.g., on command, each access point in a network emits a test signal that the other access points measure in order to construct a mutual interference matrix Dave Michelson, University of British Columbia.

12. WPP Recommendations and Standards • Will capture our knowledge and intuition regarding the manner in which IEEE 802.11 wireless network performance depends upon physical design parameters • Will provide network designers and implementers with traceable methods for comparing alternative network layouts and designs. • Will stimulate development of new and better methods for wireless performance prediction by providing a benchmark against which alternative methods can be compared Dave Michelson, University of British Columbia.

13. Task Group on Wireless Performance Prediction Proposed Purpose • Develop a set of models and methods for predicting wireless performance metrics, including coverage and throughput, on either a point or area basis given certain information concerning the layout, usage, and devices of an IEEE 802.11 wireless LAN. • Benefit those who: • plan wireless local area networks • install wireless local area networks • maintain or upgrade wireless local area networks • develop wireless local area network planning and optimization tools Dave Michelson, University of British Columbia.

14. Task Group on Wireless Performance Prediction Proposed Scope • Identify: (a) scenarios in which wireless performance prediction might be performed and (b) specific wireless performance metrics useful in wireless network planning and optimization. • Identify network layout, usage, and device parameters that affect the wireless performance metrics identified in Item 1. • Develop a set of models and methods for predicting particular wireless performance metrics on either a point or area basis given the parameters identified in Item 2. Dave Michelson, University of British Columbia.

15. Task Group on Wireless Performance Prediction Proposed Scope (cont.) • Specify lab measurements that will sufficiently characterize device performance (access point and clients) in the presence of propagation impairments and interference for use in Item 3. • Specify site-general usage, propagation, and interference models for use in Item 3. • Specify methods or features that vendors might incorporate into access points (and possibly client devices) in order to facilitate site-specific characterization of usage, propagation, and interference for use in Item 3. Dave Michelson, University of British Columbia.

16. Acknowledgements The contributions of: • Shailesh Sheoran and Jamie Caplan (UNP research engineers) • Haynes Cheng, Arnel Lim, and Michael Weatherby (Engineering Physics senior project students) are gratefully acknowledged. Dave Michelson, University of British Columbia.