1. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 1 Ad Hoc/Sensor Networking and Multihop WLANs Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org Date: 2005-05-18 Authors:

2. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 2 Abstract This talk presents problems that will be introduced when current MAC protocols are applied to multihop networking, including mobile ad hoc networks, sensor networks, and multihop WLANs. We point out the issues to be addressed, current status for research and development, and incentives for investigating multihop networking.

3. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 3 Examples for Multihop Networks Ad hoc networks (MANET) Sensor networks Mesh networks Home networks with repeaters Multihop WLANs Others: Multihop cellular networks

4. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 4 Mobile Ad Hoc Networks Mobile stations communicate with each other directly Absence of any predefined infrastructure High mobility possible Every node acts as a router Wireless Link Node

5. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 5 Wireless Sensor Networks Large number of small devices Static stations communicate with each other directly Sinks for gathering data Every relay node acts as a router Sink

6. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 6 Home Networks Intelligent appliances (AIs) communicate with access point (AP) directly or through a repeater IEEE 802.11 or ultrawideband (UWB) may be used

7. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 7 Mesh Networking Mesh points (MPs) communicate with each other wirelessly Only some of the access points have wired connections to the Internet Every node also acts as a router

8. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 8 Multihop WLANs Combining ad hoc networks and wireless LANs Mobile stations communicate with each other directly Packets are routed to APs to access the Internet Each participating node also acts as a router

9. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 9 Ad Hoc Cellular Networks Combining ad hoc networks and cellular networks Mobile stations communicate with each other directly Packets are routed to APs to access the Internet Each participating node also acts as a router

10. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 10 Advantages for Multihop Networking Ad hoc networks –Infrastructureless Sensor networks –Great commercial values WLAN Mesh –Range extension with lower infrastructure cost Multihop WLAN/cellular networks –Range extension without additional infrastructure –Dead zone elimination/mitigation –Lower power consumption –Higher speed (due to shorter distance) –Lower interference and better spatial reuse –Higher throughput (potentially)

11. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 11 Why Commercial Ad Hoc Networking Has Not Happened Routing protocols were not standardized till 2004 The number of laptop computers did not reach a critical mass Lack of killer applications –E.g., ad hoc networking in conference venues is replaced by WLAN coverage Poor performance (in ad hoc networking environments) based on current products Low throughput due to relaying Some problems not solved Difficult configuration

12. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 12 New Driving Forces for Multihop Networking VOIP over WLAN –802.11 becoming available on smart phones Reaching critical mass Extended range beneficial for WLAN access Energy efficiency is critical Proliferation of 802.11 hot spots –Range extension = making more money –Feasible with higher speeds and advanced technology Muni/national WiFi to be deployed –Range extension = infrastructure cost reduction Extending 802.11 to sensor networking –Huge market

13. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 13 Problems with Current WLAN MAC in Multihop Networking Environments High collision rate TCP and 802.11 in multihop networking environments Interference problems –Interference-range hidden/exposed terminal problem –Additive interference problem Problems associated with power control –Heterogeneous hidden/exposed terminal problem –Single-channel MAC difficult QoS and fairness problems –Alternate blocking problems Fairness problems Exposed terminal problem

14. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 14 Interference-range Hidden/Exposed Terminal Problem The interference range is typically larger than that of transmission range A potential transmitter D that cannot be reached by the CTS message of B may send a packet and collide with B’s reception A B A B D A D E B (a) (b) (c) RTS CTS Data D RTS

15. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 15 Additive Interference Problem A receiver is outside the interference radius of any other transmitters (except for its own transmitter), but the sum of nearby interference collide the reception anyway Relatively difficult to solve

16. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 16 Heterogeneous Terminal Problem A B CTS C D E F G H

17. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 17 Alternate Blocking Problem DE CTS BA C

18. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 18 Exposed Terminal Problem (b) (a) BA Data CD CTS CA Data DB CTS

19. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 19 Issues Needed to Be Addressed Resolving/mitigating aforementioned problems Routing Mobility Energy efficiency Security, privacy, and reliability Incorporating emerging technologies Applicability to sensor networks Cooperation from users Billing and Business model

20. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 20 Distinction from TGs TGs focus on the following context: –Residential networks –Office networks –Campus/public networks –Safety/military networks Mesh points are different from laptops/smart phones –Infrastructure –Power supply available –Stationary in nature –Single-hop networking from mobile stations (users) to mesh points Likely TGs outcome –Up to 32 nodes only –Most likely infrastructure mode –Not changed for mobile stations (general users) –minimum changes to current MAC protocol

21. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 21 Distinction from TG5 Current TG5 proposals –Synchronized MAC –Hierarchical architecture –Lower mobility –Smaller range –Relatively lower speed –Not applicable to 802.11 PHY

22. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 22 Current Status in Research and Development Four experimental routing protocol RFCs standardized by IETF in 2004 Numerous ad hoc network testbeds in universities Some commercial products based on AODV Intensively researched in academia and industry –Military applications for about 3-4 decades –Renewed interests for about 1 decade –Mainly focused on routing –Problems well known –Interesting techniques and solutions but some may be complex or even infeasible

23. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 23 Concluding Remarks Everything will be ad hoc in the future Multihop networking will be a norm, rather than an exception Time to look into multihop networking issues Emerging technologies should be incorporated

24. doc.: IEEE 802.11-05/0461r1 Submission May 2005 CH Yeh, Queen's UniversitySlide 24 References Sadeghi, B., IEEE 802.11-05/0065r0. Yeh, C.-H., “The advance access mechanism for differentiated service, power control, and radio efficiency in ad hoc MAC protocols,” Proc. IEEE VTC’03F, 2003.