1. IEEE Wireless Communication Magazine Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension Frank H.P. Fitzek, Diego Angelini, Gianlucca Mazzini, and Michele Zorzi Universita di Ferrara, Italy

2. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 2 Overview Motivation and Problem Frequency Usage of IEEE802.11a New MAC Protocol Simulation Results Conclusion

3. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 3 Motivation for Multi Hop Networks Multi hop networks are a viable option for installation of a network where it is missing/incomplete or as a complement to existing cellular systems. Example: 3G/WLAN coupling Coverage extension is attractive to reduce installation costs. In large WLAN hotspots ¾ of the total costs are caused by the fixed infrastructure.

4. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 4 Motivation for Multi Hop Networks € Time Return of Investment Cost without multi hop Cost with multi hop

5. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 5 Problems for multi-hop networks with IEEE802.11 WLAN Many researchers report about the problem of IEEE802.11b in multi-hop networks Reason: RTS /CTS exchange blocks ongoing communication Example: Simple line communication DCE F CTS B RTS A

6. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 6 Problems for multi-hop networks with IEEE802.11 WLAN Simple example shows the throughput degradation for multi- hop network operation (6 terminals are blocked while one packet is transmitted) Well documented and reported for IEEE802.11b even for more sophisticated network topologies The bandwidth is not use efficiently IEEE802.11a offers higher transmission rates, but the bandwidth inefficiency remains the same The problem resides in the MAC design

7. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 7 Data Rate versus Range IEEE802.11a

8. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 8 5GHz ISM Frequency Bands

9. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 9 Channel Structure IEEE802.11a

10. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 10 Possible Approaches For Spectrum Usage Divide collision domain into smaller groups: assign all wireless terminals randomly to different channels – RANDOM APPROACH reduce the RTS/CTS problem low connectivity (N channels result in connectivity level of 1/N) routing over different channels is difficult All terminals use the same channel - STATIC APPROACH Inefficiency in the bandwidth usage (N channels result in a bandwidth efficiency of 1/N) full connectivity Communicate the usage of the assignment of the channels to all wireless nodes – DYNAMIC APPROACH full connectivity Solution need!!!

11. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 11 Proposed MAC Scheme Use of a common signaling channel Only for RTS/CTS exchange 4 way handshake with probing Data and ack on dedicated channel Sender Receiver signaling channel dedicated channel RTS1 CTS1 RTS2 CTS2 probe data S2Rack RTS1RTS2 probe data S2R CTS1CTS2 ack NAV channel NAV channel

12. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 12 Proposed MAC Scheme with Collisions Sender 1 Receiver 1 signaling channel dedicated channel RTS1 CTS1 RTS2 CTS2 probe data S2Rack RTS1 CTS1 RTS2 CTS2 probe data S2R Sender 2 Receiver 2 RTS1 CTS1 probe

13. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 13 First Simulation Results Based on a MATLAB model by D. Angelini, University of Ferrara Only MAC performance No real multi hop Packets are generated in a CBR fashion and send randomly to one of the neighbors Packet length 4kbyte (reservation phase) Surface area 30x30m² We distinguish two different approach static approach dynamic approach

14. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 14 Throughout for the dynamic, static and 802.11b standard approach

15. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 15 Intermediate Discussion Dynamic approach yields better results than the static or the IEEE802.11b approach But, the dynamic approach uses 8 channels, while the static approach is using only one. Fairness of the comparison! Improvement of the dynamic scheme Collisions may occur due to missing information from the signaling channel if terminals are transmitting on a dedicated channel. Solution: 2nd W-NIC Do we need the probing packet?

16. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 16 Possible Improvements No probing packet assuming that the modulation and coding settings can be derived from the signaling channel Rate controlled hand-shake New calculation of the congestion window

17. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 17 Impact of the number of dedicated channels for one and two W-NICs 1 Wireless NIC 2 Wireless NIC Larger number of dedicated channels help to improve throughput, but gain decreases for each additional channel (bottleneck of signaling channel)

18. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 18 Multi-Hop Performance Real Multi-Hop Scenario Model based on C++ Implementation by F. Bertocchi, University of Ferrara 60 wireless terminals Sender chooses receiver randomly for one packet Shortest path routing for multi hop communication Metric: Packet Delivery: Ratio of send and received packets Transmission Delay: Delay between sender and receiver Three approaches under investigation Static Choice Random Choice Dynamic Choice (Our MAC)

19. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 19 Multi Hop Performance – Packet Delivery

20. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 20 Multi Hop Performance – Transmission Delay

21. IEEE Wireless Communication Magazine Thanks for your attention! zorzi@ing.unife.it frank@fitzek.net

22. IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension 22 Further Reading F.H.P. Fitzek, P. Seeling, M. Reisslein, and M. Zorzi, "Visualisation Tool for Ad Hoc Networks - ViTAN", IEEE Network Magazine, software tools for networking, p. 9, Vol.17, No. 4, July/August 2003 F.H.P. Fitzek, D. Angelini, G. Mazzini, and M. Zorzi, "Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Ad Hoc Networks", In Proceedings IEEE VTC 2003, Wireless Communications: 3G and Beyond Symposium, October 6-9, 2003, Orlando, Florida, USA F.H.P. Fitzek, G. Schulte, and M. Zorzi, "Connectivity, Multi Hop, and Upper Bound Capacity Calculation for Multi-Rate Terminals in Ad-Hoc Networks“, In Proceedings of Wireless World Research Forum 9, (WWRF9), July 1-2, 2003, Zürich, Switzerland