1. VTC 2004 Spring, Milan, Italy Complementing 3G Cellular Networks by Multi Hop Capabilities of an Enhanced MAC Protocol for Wireless LAN Frank H.P. Fitzek, Federico Bertocchi and Michele Zorzi Department of Communications Technology, Aalborg University Neils Jernes Vej 12, 9220 Aalborg Øst, Denmark, e-mail: ff@kom.auc.dk University of Ferrara, Via Saragat 1, I-44100 Ferrara, Italy, e-mail: [fbertocchi|zorzi]@ing.unife.it

2. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 2 Overview 3G/WLAN Coupling Motivation Architecture Problem of IEEE802.11 MAC IEEE802.11a introduction New MAC Protocol Simulation Scenario Simulation Results Conclusion

3. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 3 3G/WLAN Coupling 3G and WLAN (IEEE802.11) have disjunctive advantages 3G backbone (services, billing, etc) 3G coverage WLAN data rate (allows to create new services) 3GPP propose the 3G/WLAN coupling 3G investments were incredible high and the installation of WLAN hotspots has to come at a minimum price. 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. 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 Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 4 Motivation for Multi Hop Networks from the cost perspective Cummulative cost/return € Time Return of Investment Cost without multi hop Cost with multi hop

5. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 5 Possible Architecture for 3G/WLAN Coupling InternetCore SGSN GGSN Chat MMS IMS MBMS application servers ERAN BTS NodeB UTRAN BSC RNC Packet Data Gateway WT VAP AP Switch VAP AP location X location Y location Z

6. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 6 Problems for multi-hop networks with standard 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

7. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 7 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

8. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 8 Data Rate versus Range IEEE802.11a

9. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 9 5GHz ISM Frequency Bands

10. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 10 Channel Structure IEEE802.11a

11. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 11 Possible Approaches For Spectrum Usage Divide collision domain into smaller groups by assigning all different channels randomly– 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) higher connectivity Standard IEEE802.11 Communicate the usage of the assignment of the channels to all wireless nodes – DYNAMIC APPROACH higher connectivity Solution need!!!

12. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 12 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

13. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 13 Simulation Model and Metric Simulation Model Four different topologies Senario A/1R/1S/5S Assuming video services Source: 24 “Friends” episodes VBR traffic peak/mean ~ 20 Random length and starting phase Randomly chosen sender and transmitter Shortest path routing Metric Delivery ratio of send and received packets Delay of received packets including retransmissions and multi hop

14. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 14 Scenario A: Delivery

15. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 15 Scenario A: Delay

16. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 16 Scenario 1R: Delivery

17. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 17 Scenario 1R: Delay

18. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 18 Scenario 1S: Delivery

19. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 19 Scenario 1S: Delay

20. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 20 Scenario 5S: Delivery

21. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 21 Scenario 5S: Delay

22. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 22 Conclusion and Outlook 3G/WLAN coupling enables new services for the customer Multi Hop WLAN allows low cost installation of WLAN Important in the initial phase New proposed MAC protocol for Multi Hop yields high performance in terms of delivery ratio and delay even for real time video services. Small changes to the standard IEEE802.11 MAC protocol. Further improvements were already investigated. Future work should include TCP traffic.

23. VTC 2004 Spring, Milan, Italy Thanks for your attention! Q/A ff@kom.aau.dk zorzi@ing.unife.it

24. IEEE Semiannual Vehicular Technology Conference May 17-19, 2004, Milan, Italy 24 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