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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
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Overview
Motivation and Problem
Frequency Usage of IEEE802.11a
New MAC Protocol
Simulation Results
Conclusion
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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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 couplingCoverage extension is attractive to reduce installation costs. In large WLAN hotspots ¾ of the total costs are caused by the fixed infrastructure.
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Motivation for Multi Hop Networks
€
Time
Return of Investment
Cost without multi hop
Cost with multi hop
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Problems for multi-hop networks with IEEE802.11 WLAN
Many researchers report about the problem of IEEE802.11b in multi-hop networksReason: RTS /CTS exchange blocks ongoing communicationExample: Simple line communication
DC E FCTSCTSBRTSRTS
A
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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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 topologiesThe bandwidth is not use efficiently IEEE802.11a offers higher transmission rates, but the bandwidth inefficiency remains the sameThe problem resides in the MAC design
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Data Rate versus Range IEEE802.11a
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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5GHz ISM Frequency Bands
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Channel Structure IEEE802.11a
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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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 problemlow connectivity (N channels result in connectivity level of 1/N)routing over different channels is difficult
All terminals use the same channel - STATIC APPROACHInefficiency 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 connectivitySolution need!!!
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Proposed MAC Scheme
Use of a common signaling channelOnly for RTS/CTS exchange4 way handshake with probingData and ack on dedicated channel
Sender Receiver
signaling channel
dedicated channel
RTS1 CTS1 RTS2CTS2
probe data S2R ack
RTS1RTS2probe data S2RCTS1CTS2ack
NAVchannel
NAVchannel
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Proposed MAC Scheme with Collisions
Sender 1 Receiver 1
signaling channel
dedicated channel
RTS1 CTS1 RTS2CTS2
probe data S2R ack
RTS1 CTS1 RTS2CTS2
probe data S2R
Sender 2 Receiver 2RTS1 CTS1
probe
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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First Simulation Results
Based on a MATLAB model by D. Angelini, University of Ferrara Only MAC performance No real multi hopPackets are generated in a CBR fashion and send randomly to one of the neighborsPacket length 4kbyte (reservation phase)Surface area 30x30m²We distinguish two different approach
static approachdynamic approach
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Throughout for the dynamic, static and 802.11b standard approach
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Intermediate Discussion
Dynamic approach yields better results than the static or the IEEE802.11b approachBut, 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-NICDo we need the probing packet?
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Possible Improvements
No probing packet assuming that the modulation and coding settings can be derived from the signaling channelRate controlled hand-shake New calculation of the congestion window
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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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)
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Multi-Hop Performance
Real Multi-Hop Scenario Model based on C++ Implementation by F. Bertocchi, University of Ferrara 60 wireless terminalsSender chooses receiver randomly for one packetShortest path routing for multi hop communicationMetric:
Packet Delivery: Ratio of send and received packetsTransmission Delay: Delay between sender and receiver
Three approaches under investigationStatic ChoiceRandom ChoiceDynamic Choice (Our MAC)
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Multi Hop Performance – Packet Delivery
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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Multi Hop Performance – Transmission Delay
IEEE Wireless Communication Magazine: Design and Performance of an Enhanced IEEE802.11 MAC Protocol for Multihop Coverage Extension
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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