1. 1 UCAN: A Unified Cellular and Ad-Hoc Network Architecture Rick Szcodronski ECE 256 February 12, 2008 Published by: Haiyun Luo, Ramachandran Ramjee, Prasun Sinha, Li (Erran) Li, Songwu Lu

2. 2 Cellular vs. 802.11 Networks Range = 250 m. 1 - 11 Mbps CSMA/CD A A 802.11b 1xEV-DO (HDR) Range = 20 km. 38.6 Kbps – 2.4 Mbps CDMA / TDMA

3. 3 Recall: Rate Control CE A D B Rate = 20 Rate = 10 Both 802.11 and HDR use Rate Control to transmit data

4. 4 Motivation for UCAN A B 38.6 Kbps 2.4 Mbps 11 Mbps

5. 5 Simple Test Layout B R D HDR 802.11b

6. 6 Simple Test Results

7. 7 UCAN Architecture 3 Challenges Arise –Who is the best proxy? –What happens when route breaks? –Why should I forward your packets?

8. 8 Proxy Discovery 1.HDR Channel Rate Drops 2.D Sends Route Request Using 802.11 3.RTREQ propagates using “Proxy Discovery” protocol 4.P sends proxy application to Base 5.Base updates proxy tables 6.Base routes packets for D via P D 2.4 Mbps 38.6 Kbps R R P RTREQ Proxy Application

9. 9 Greedy Proxy Discovery Proxy Discovery Process –Periodic broadcast of HDR rate to neighbors –Client Unicasts RTREQ –Once TTL=0 or no better rate, proxy sends RTREQ to base Advantages –Easy to implement –Low uplink overhead Disadvantages –May not find best proxy! –High energy consumption

10. 10 On-Demand Proxy Discovery –Broadcast RTREQ until TTL=0 –Send RTREQ to base if rate > previous –Clients/Base compare Seq_NO from previous entry Advantages –Finds best proxy –Lower energy consumption Disadvantages –High HDR uplink contention –Higher 802.11 congestion for large number of clients 3 Challenges Arise –Who is the best proxy? –What happens when route breaks? –Why should I forward your packets?

11. 11 Routing Failures P,R,D are mobile and can break the relay path R moves, P tells Base Base clears proxy table Base sends packets direct to D via HDR D can re-initiate “proxy request” D R R P Failure!

12. 12 Proxy Maintenance Long Term Maintenance –P,R,D are mobile! –P piggybacks its rate on packets –D compares P’s rate to a threshold of its own –D requests new proxy Short Term Maintenance –Base station can send packet to any client on D’s route –Increased Channel Diversity D R R P R=100 R=30 R=60 R=10

13. 13 HDR Scheduling http://en.wikipedia.org/wiki/Evolution-Data_Optimized D B C A DRC = 1 DRC = 3 DRC = 6 DRC = 12 Q: How do slots get scheduled fairly? A: Proportional Fairness Scheduling

14. 14 Proportional Fairness Scheduling 2 Goals –Maximize cell throughput –Maintain minimum individual Quality of Service How can this extend to UCAN? Proportional Fairness Scheduling T k (t) = Average Throughput R k (t) = Instantaneous Rate Slot Winner = min{T k (t)/R k (t)} Time D B C A DRC = 1 16 slots DRC = 3 4 Slots DRC = 6 1 Slot DRC = 12 1 Slot AAAABBBCCD

15. 15 UCAN Scheduling HDR uses proportional fairness scheduling –Maximize throughput, maintain minimum QoS –Client scheduled when downlink rate is high UCAN Scheduling –Using Proxy’s R k (t): unfair throughput gain –Using Destination’s R k (t): distributed gain B A R=2 R=1 12 12 AB*B*A 3 AB 12 AB*B* R=2R=1 * Packets received using Proxy A R=2 No Relay Relay w/ Prxy’s R Relay w/ Dst’s R

16. 16 Secure Crediting Why should I forward your packets? –Throughput gains for Active Clients –Wasted energy for Non-active Clients Solution for Non-Active Clients –Award credits –Problem: Watch out for credit scam –Solution: Piggyback Message Authentication Code (MAC) in RTREQ

17. 17 UCAN Performance Evaluation HDR downlink degrades rapidly with distance Average data rate = 600 Kpbs Instantaneous Rate varies a lot in small time scale Motivation for UCAN!

18. 18 UCAN Performance Evaluation Single Destination Client –Static destination =.8R –Mobile Relays –Variables Relay Speed Relay Density UDP vs. TCP Greedy vs. On-Demand D R R P

19. 19 UCAN Throughput Evaluation Throughput Trends –Gain over No-Relay stays constant with varying speed –Throughput Gain: On-Demand > Greedy –Gain over No-Relay increases with increased clients

20. 20 UCAN HDR Uplink Evaluation On-Demand’s higher throughput comes at the price of increased HDR uplink overhead

21. 21 UCAN Energy Evaluation Energy Trends –Energy increases as clients increase –Energy increases as speed increases –Energy Comparison: Greedy > On-Demand

22. 22 UCAN Multiple Client Evaluation Multiple Client Setup –80 Clients (5 Destination Clients) –ALL Clients are mobile –TTL = 1-4

23. 23 UCAN Review Questions –What is the energy comparison between Active UCAN Clients and Non-Active HDR Clients? –What happens when > 5 Clients are Active? –How will credits be implemented? –Can UCAN work across carriers (e.g. Verizon, Cingular, US Cellular)? –Can the HDR uplink support VOIP while using UCAN? Promising Future –310% Single User Gain –60% Multiple User Gain –Always-on Internet (Indoors, Train, Car, etc.)

24. 24 Questions or Comments?