Wi Fi 802 11b and Bluetooth An Examination of Coexistence Approaches Mobilian Corporation 7431 NW Evergreen Parkway Suite 220 Hillsboro Oregon 97124 503 681 8600 www mobilian com Abstract This paper analyzes different approaches to resolving the interference problems between the Wi Fi and Bluetooth wireless technologies This analysis explores the strengths and weaknesses of these interference mitigation approaches and goes on to explain what is necessary for achieving satisfactory combination performance and true Coexistence without Compromise The contents are based on Mobilian Corporation s coexistence research and development work including a thorough analysis of the problems and various experiments to understand the interference issue In investigating different approaches to interference mitigation this paper gives technical data and uses common wireless technology terms The information presented is targeted to readers who have a basic understanding of wireless networking We recommend that readers without this understanding read Mobilian s first white paper Wi Fi 802 11b and Bluetooth Simultaneous Operation Characterizing the Problem www mobilian com Mobilian TrueRadio Sim OP TrueConnectivity and Coexistence without Compromise are all trademarks of Mobilian Corporation All other trademarks are the property of their respective owners 2001 Mobilian Corporation All rights reserved Page 1 Table of Contents 1 0 Executive Summary 4 2 0 Background 5 2 1 Technical Background 5 2 1 1 Bluetooth Wireless Personal Area Networking WPAN 5 2 1 2 802 11b Wireless Local Area Networking Wi Fi 6 2 1 3 Wi Fi Bluetooth Interaction and Interference 6 3 0 Interference Mitigation Approaches 8 3 1 Collocation without Coexistence Mechanism 9 3 1 1 Overview 9 3 1 2 Analysis 9 3 2 Driver level Modal Switching Between Wi Fi and Bluetooth 10 3 2 1 Overview 10 3 2 2 Analysis Dual mode Radio Switching 11 3 2 2 1 Dual mode Radio Switching 11 3 2 2 2 Leaving the Network without Signaling 11 3 2 2 3 Leaving the Network with Signaling 11 3 2 3 Analysis Driver level Switching 12 3 2 3 1 Throughput and Time delay Concerns 12 3 2 3 2 Impacts of Bluetooth Polling Activities 13 3 3 Adaptive Hopping 13 3 3 1 Overview 13 3 3 2 Analysis 13 3 3 2 1 Adaptive Hopping as Optional Profile Operational Mode 14 3 3 2 2 Adaptive Hopper Must Accurately Sense and Respond to Interferers 14 3 3 2 2 1 Bluetooth Difficulty in Detecting Wi Fi Signal 14 3 3 2 2 2 Congested Wireless Environments are Particularly Troublesome 15 3 3 2 3 Adjacent Channel Noise 17 3 3 2 4 Number of Channels 17 3 4 MAC level Switching 17 3 4 1 Overview 17 3 4 2 Analysis 17 3 5 3 5 1 Simultaneous Operation 17 Overview 17 2001 Mobilian Corporation All rights reserved Page 2 3 5 2 Analysis 19 4 0 Summary 19 5 0 Appendix 1 In band versus Out of band Noise 21 5 1 Signals and Noise 21 5 1 1 5 2 6 0 Types of Noise 21 Bluetooth and Wi Fi Interference Cases 23 Appendix 2 Path Loss Models Employed 24 References 25 Table of Figures Figure 1 Performance Hierarchy of Coexistence Approaches for Collocated Wi Fi Bluetooth 8 Figure 2 Geometry of Measurement and Simulation Environment 9 Figure 3 Measurement of Wi Fi Throughput in the Presence of Collocated Bluetooth 10 Figure 4 Conceptual Wireless System Diagram 11 Figure 5 Basic Geometry of Bluetooth and Wi Fi Penetrated Corporation 15 Figure 6 Likely Location of Two Adaptive Hoppers 16 Figure 7 Simultaneous Operation Covers Entire Conceptual Wireless System Diagram 18 Figure 8 Ganymede Chariot Graph of Mobilian Corporation s TrueRadio Demonstration 19 Figure 9 Mobilian s TrueRadio Performance in Collocated Scenario 20 Figure 10 In Band versus Out Of Band Noise 21 Figure 11 White Noise and Colored Noise are Very Different 22 Figure 12 Typical Transmit Mask 22 Figure 13 Path Loss as a Function of Distance Indoor 2 4 GHz ISM Band 24 2001 Mobilian Corporation All rights reserved Page 3 1 0 Executive Summary Wireless markets from wide area networks to local and personal area networks are widely expected to be the significant market of the 21st Century Investment capital is flowing to wireless companies worldwide and market forecasts consistently project hundreds of millions of installed units With this expansion comes increased opportunity for market innovation and consequently wireless penetration into the core fabric of our everyday lives This growth is spurred by increasing demand for maximum convenience and immediate access to desired information It is facilitated by an unlicensed frequency spectrum providing unlimited free access to whomever wishes to build a wireless device capable of complying with regulatory standards These forces are working together to create traffic and device density in the unlicensed frequencies and consequently opportunities for interference between the protocols using those frequencies As these trends develop the need for multiple wireless devices operating at the same time will increase resulting in still greater potential for interference That is why simultaneous operation is becoming an important topic of discussion in today s market Simultaneous operation is the ability of different fully standards compliant wireless systems to operate simultaneously in any scenario while experiencing minimal or no degradation in performance This definition includes wireless devices that can give the user outstanding performance without a list of operational caveats The device should just work regardless of other devices within its operating environment Wireless local area networking WLAN and wireless personal area networking WPAN are two networks in particular for which simultaneous operation is growing in importance WLAN WPAN simultaneous operation will occur more and more frequently as users begin completing everyday tasks such as copying or printing a file from their WLAN PC while using a WPAN enabled mouse and keyboard Its frequency will continue to grow as personal communication devices and synchronization activities with PCs and networks grow and it will gain even more importance as distributed applications take off the next big thing in software and WPAN devices must coexist with massive amounts of WLAN activity In all these scenarios users will appreciate being able to use whatever wireless devices surround them when they want to and how they want to Users will demand unhindered simultaneous operation and will resist adopting wireless devices as long as there are operational problems or perceived