1 / 26

Minimizing 802.11 Interference from ZigBee Medical Sensors

Minimizing 802.11 Interference from ZigBee Medical Sensors. James Hou, Benjamin Chang, Dae-Ki Cho, Mario Gerla BodyNets 2009 April 1, 2009. Introduction. What is ZigBee?. 802.15.4 based standard for wireless personal area networks (WPANs)

nishi
Download Presentation

Minimizing 802.11 Interference from ZigBee Medical Sensors

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Minimizing 802.11 Interference from ZigBee Medical Sensors James Hou, Benjamin Chang, Dae-Ki Cho, Mario Gerla BodyNets 2009 April 1, 2009

  2. Introduction

  3. What is ZigBee? • 802.15.4 based standard for wireless personal area networks (WPANs) • Low cost, low power wireless mesh networking standard • Uses the industrial, medical, and scientific radio (ISM) bands • Designed to be simpler and cheaper than other WPANs such as Bluetooth

  4. Why use ZigBee? • Targeted for RF applications which require: • low data rate • low-cost • low-power (for longer battery life) • mesh-networking • ZigBee used in several medical applications: • Electrocardiogram (ECG) • Arterial blood pressure (ABP) • Central veinous pressure (CVP) • Ventilators • Infusion Pumps

  5. What’s the problem? • 802.11 and ZigBee share the same ISM band • 802.11 CSMA doesn’t accept ZigBee transmissions • Dynamic channel switching not supported • Bottom line – ZigBee transmissions can be lost as a result of local WIFI interference with no resolution scenario

  6. Controversy Two papers claim opposing results • ZigBee and Wireless Radio Frequency Coexistence ZigBee White Paper - June 2007 • “Even in the presence of a surprising amount of interference, ZigBee devices continue to communicate effectively.” • “ZigBee contains a great many features that are designed to promote coexistence and robust operation in the face of interference.” • WLAN Interference to IEEE802.15.4 – Zensys White Paper • Concludes that WLAN causes significant interference against IEEE802.15.4 and thereby also ZigBee devices.

  7. How Does ZigBee Promote Coexistence? • Multiple Channels • 16 non-overlapping channels • 5 MHz apart • Data Rate • Able to transmit up to 250 Kbps. • DSSS • Uses narrow band signals • CSMA

  8. Scenario

  9. WiFi-ZigBee Interference Experiments Setup a test scenario to verify that ZigBee devices can experience severe packet loss as a result of 802.11 traffic ZigBee Client B ZigBee Client A

  10. WiFi-ZigBee Interference Experiment Results Found that a single WiFi device can cause significant loss in Zigbee networks. Could be further influenced by a greater number of nodes Interference is also affected by distance.

  11. Proposed solution

  12. Channel Switching ZigBee switches automatically between multiple frequencies to avoid interference. • Pros: • Out of proposed solutions, easiest to implement. • Cons: • May require hardware modification • If all ZigBee devices used one channel, the single channel could become congested. • This solution will only work in tightly controlled environments and will not work in densely populated dynamic 802.11 environments

  13. Channel Switching could add significant complexity and as a result, cost to these devices. • Instead of modifying the ZigBee stack, somehow have surrounding 802.11 devices cooperate with ZigBee devices. • Solution: devise an external device that will periodically block 802.11 devices to allow ZigBee devices to communicate.

  14. 802.11 Periodic Blocking with RTS/CTS 3rd party system could send CTS packets periodically to 802.11 devices with a long transmission duration. • Pros: • Would block out 802.11 devices for a predictable set period of time. • No need to change 802.11 or ZigBee stack. • External 3rd party device. • Cons: • Some claim windows devices ignore RTS/CTS • Requires special hardware to force an RTS/CTS • May inadvertently block ZigBee and 802.11 networks

  15. Developing the Blocker • Created an application on an Ubuntu machine designed to transmit CTS messages • According to WiFi standard, most WiFi devices will shut off their radio for the duration that is set in an incoming CTS packet • Used the Lorcon library to craft CTS frames and inject or broadcast these packets to the local WLAN • Able to successfully block WiFi devices for a set duration • Verified through WiFi monitor (WildPackets AiroPeek) that most WiFi devices follow desired behavior Can periodically blocking WiFi devices actually help reduce the interference between ZigBee devices?

  16. Experiment

  17. WIFI interferer (Sender) ZigBee Transmitter ZigBee Transmitter WIFI interferer (Receiver) CTS Jammer

  18. Experiment Results with Periodic Blocker

  19. Using our Periodic CTS Blocker • However, in several additional experiments, we found that the jammer only improved ZigBee performance when WiFi used high data rates(700KB/s+) • Jammer decreased performance when WiFi was transmitting at a rate lower than 300KB/s

  20. Controlled blocking with RTS/CTS • Implement a device that uses both WIFI and ZigBee. • When a send is requested, the device will issue a CTS followed by a ZigBee transmission • This will block WIFI for a short duration, enough time to get a ZigBee transmission out.

  21. Experiment Setup for Controlled Blocking Solution WIFI interferer (Sender) ZigBee Receiver Hybrid ZigBee Client/ WiFi Blocker WIFI interferer (Receiver)

  22. Experiment Results with Controlled Blocking Solution

  23. Future work

  24. Gateway • Will passively determine ZigBee transmission intervals • Once intervals are determined, jam 802.11 for just those intervals • Will incorporate an 802.11 chip • Will support multiple ZigBee devices • Ideally located on/near the ZigBee receiver • Will need to support devices joining and leaving • Allows current ZigBee devices to remain unchanged while solving the interference issue

  25. Thank you Key References: • Improving WLAN Performance with RTS/CTS: http://www.wi-fiplanet.com/tutorials/article.php/1445641 • Crossbow Tech. (2005) Avoiding RF interference between WiFi and Zigbee, Crossbow Technical Report. • IEEE 802.15.4: a wireless communication technology for large-scale ubiquitous computing applications. In Proc of . Conference on Mobile and Ubiquitous Systems (CSMU 2006), Guimarães, June 29-30, 2006 • Avoiding Interference in the 2.4-GHz ISM Band: http://www.wirelessnetdesignline.com/60401206;jsessionid=YMLHY4EVLHV2YQSNDLQCKHSCJUNN2JVN?printableArticle=true • Avoiding RF Interference Between WiFi and Zigbee: http://www.xbow.com/Products/Product_pdf_files/Wireless_pdf/ZigBeeandWiFiInterference.pdf • WLAN Interference to IEEE802.5.4: http://www.z-wavealliance.org/modules/iaCM-DocMan/?docId=53&mode=DE

  26. Questions?

More Related