1. G. Orfanos, ComNets, RWTH Aachen University Multihop MAC Protocol for MC-CDMA based WLANs confidential Georgios Orfanos RWTH Aachen University, Chair of Communication Networks 31.03.2006 ComNets FFV

2. G.Orfanos, ComNets, RWTH Aachen UniversityOutlook MC-CDMA C-DCF Smart Backoff Parallel transmission MAC layer relaying function Multihop guard interval, extended NAV Simulated scenario and parameters Simulation results Comparison with DCF Conclusions

3. G.Orfanos, ComNets, RWTH Aachen University MultiCarrier – Code Division Multiple Access Combination SS and OFDM Frequency spreading Frequency diversity IFFT / FFT realization of multicarrier modulation Multipath robustness –Cyclic prefix Simultaneous transmissions in the same frequency, through division of the spectrum in parallel channels => codechannels Spreading factor 4

4. G.Orfanos, ComNets, RWTH Aachen UniversityC-DCF CSMA / CA with 4 parallel codechannels –multichannel system Selection of codechannel –random –first transfer on cch1 Data transfer: DCF NAV per codechannel –each station monitors optionally one or all codechannels Power control over RTS / CTS –for all data frames

5. G.Orfanos, ComNets, RWTH Aachen University Smart Backoff Backoff procedure spanning over many cchs Backoff Time = Random · aSlotTime 1.Another cch seems idle 2.Another cch is determined idle 3.No cch is idle

6. G.Orfanos, ComNets, RWTH Aachen University Parallel transmission 1 codechannel =1/4 of frequency channel capacity Parallel (multichannel) transmission for high load

7. G.Orfanos, ComNets, RWTH Aachen University MAC layer relaying function Multihop connections up to 3 hops Fig. multihop connection from station 1 to station 4 Multihop packet handled per station as own packet MAC header contains the addresses of all forwarding stations Spatial reuse possible Frame Control Duration / ID Address 1 Address 2 Address 3 Sequence Control Address 4 Frame Body FCS 2 66 6 6260-23124 Mac frame Format

8. G.Orfanos, ComNets, RWTH Aachen University Multihop guard interval, extended NAV Multihop guard interval to prioritize forwarder –Duration of one complete transmission window Smart Backoff at forwarders for bottleneck avoidance –Combined with parallel transmission Extended NAV –Duration, cch, MSs

9. G.Orfanos, ComNets, RWTH Aachen University Simulated scenario and parameters ParameterValue Max. TxPower17dBm Spreading Factor4 Cwmin31 slots Cwmax255 slots Number of Subcarriers48 Data + 4 Pilot Subcarrier Spacing0.3125 MHz Channel Bandwidth20 MHz Carrier Frequency5.25 GHz Noise Level-93dBm Path loss Factor3.5 TxRate Data12 Mbps TxRate Control12 Mbps RTS/CTSenabled Symbol Interval4 µs = 3.2 µ + 0.8 µs Guard Interval0.8 µs Preamble16 µs Max. Propagation Delay0,15 µs PDU Length1024 Byte

10. G.Orfanos, ComNets, RWTH Aachen University Simulation results (I) Mean values Achievable throughput allies with theoretical calculation: 2,5 Mbit/sec/cch Depends on number of hops

11. G.Orfanos, ComNets, RWTH Aachen University Simulation results (II) CDF of delay per hop left: 1,25 Mbit/sec right: 0,75 Mbit/sec (saturation throughput)

12. G.Orfanos, ComNets, RWTH Aachen University Simulation results (III) CDF of end-to-end delay per connection left: 1,25 Mbit/sec right: 0,75 Mbit/sec (saturation throughput)

13. G.Orfanos, ComNets, RWTH Aachen University Comparison with DCF (I) Throughput

14. G.Orfanos, ComNets, RWTH Aachen University Comparison with DCF (II) End-to-end delay

15. G.Orfanos, ComNets, RWTH Aachen UniversityConclusions Multihop guard interval: –prioritizes the relaying MS on medium access –reduces the end-to-end delay of the multihop connection Smart Backoff at forwarding MSs: –reduces the medium access time –enables parallel transmission in many cchs, that increases the available capacity and reduces the bottleneck effect. In multi-channel, multihop environments applying carrier sensing NAV timer per cch (channel) is not enough: –the cch specific NAV per cch and MS proposed is then necessary.

16. G.Orfanos, ComNets, RWTH Aachen University Thank you for your attention ! Georgios Orfanos orf@comnets.rwth-aachen.de Any questions?