1. 1 UCAN: A Unified Cellular and Ad-Hoc network Architecture By H. Luo, S. Lu Computer Science Department UCLA

2. 2 What is new? The goal is to improve the throughput performance of the wide-ares wireless network by taking advantage of the adhoc network. Try to take the benifits of both networks: 3G cellular network and adhoc network 3G BTS forward packets to proxy client with better quality Proxy clients use adhoc network to forward packets to destination client Maintaining fairness by refining the 3G BTS scheduling algorithm Develop greedy and on-demand protocol: UCAN Develop a secure crediting mechanism to motivate users

3. 3 Comparison of Wide-area wireless network and Local-area wireless network Wide-area wireless network Local-area wireless network CoverageUp to tens of kilometers, e.g., 20kms. Up to hundreds of meters, e.g., 250m for Wi-Fi ThroughputLow. Up to 2Mbps, mainly for voice High. 11Mbps for 802.11b, 54Mbps for 11a/11g OrganizationInfrastructure mode, one hop. Ad-hoc, multi-hops

4. 4 Requirement for UCAN It requires that the mobile terminals are equipped with two interfaces: 3G & IEEE802.11b A fundamental question: why should a mobile user relay traffic for other users ? Contributions of this paper: A novel architecture of UCAN Develop protocols including new proxy discovery, ad-hoc routing; Refining scheduling algo for 3G BTS to balance traffic Sercure crediting to encourage relaying Increase single / aggregate HDR downlink throughput

5. 5 Organization of this paper Sec1: introduction Sec2: background fo HDR, 11b, and related work Sec3: motivation to develop UCAN with examples Sec4: architecture of UCAN Sec5: proxy discovery and adhoc routing Sec6: enhance of scheduling algorithm of 3G BTS Sec7: secure credit to motivate relay Sec8: simulation results Sec9: related discussions Sec10: conclusion

6. 6 Background knowledge HDR—anywhere, always on Part of 3G CDMA2000 standard, for burst data. UL 154k, DL: 2.4M, shared in TDMA mode. Duration of each user in DL is defined by the scheduling algo: Propotional scheduling algo. IEEE802.11b—named as Wi-Fi most popular among the 802.11 family 2 modes: infrastructured mode and ad hoc mode using routing protocol to relay data: multi-hop

7. 7 Related work of combing two wireless networks Category: traffic model -- peer-peer, infrastructure mode relay model -- stationary, mobile # of interface – one or two UCAN: infrastructure mode traffic, two interface, and mobile relays. Disavantages of other options: peer-peer traffic: inefficient to provide high availability service one interface: throughput limited by the bandwidth limited cellular system Stationary relays: iCar system, increased cost.

8. 8 Motivated by a simple example Non-relay case: Relay case: FTP Server Laptop inside room HDR cellualr link FTP Server 802.11 link Relay client in corridor, better HDR DL Laptop inside room

9. 9 Throughput comparison of the simple example

10. 10 Architecture of UCAN HDR DL quality is measured by clients within BTS’s coverage When the DL quality is below a certain level,HDR will forward the data through possible Proxy client, Relay clients. Clients should be able to operate in dual mode: HDR and 11b.

11. 11 Issues need to be addressed in UCAN system How does the HDR BTS disceovery a proxy server? Proxy discovery and routing How does the HDR BTS maintain fairness among mobile nodes? HDR Scheduling algorithm How are the mobile nodes encouraged to paticipate in the traffic relaying? Secure crediting algorithm

12. 12 Proxy Discovery and Routing: Greedy algo Proactive; unicast from destination client;route recorded in the RTREQ message until until it reaches proxy client, and then forwared to HDR BTS via a proxy application.

13. 13 Proxy Discovery and Routing: On-demand algo Reactive; broadcast from destination client;route recorded in the RTREQ message until it reaches proxy client candidates, and then forwarded to HDR BTS via independent proxy applications.

14. 14 Route and Proxy Maintenance -1 Route Failures and Recovery 11b Mac layer generate a callback function to inform the client such failures Client reports the failure to HDR BTS HDR BTS use HDR DL in replacement of the relay path, eliminate the Proxy table A new route request may be initiated: proxy re-discovery Proxy Maintenance If the HDR DL of the proxy degrades, this proxy should be replaced Not a good idea to initiate proxy discovery periodically: too much overhaed and difficult to determine the interval Solution is to pigggy back the channel rate of the proxy client to the destination client, and let the destination client to decide whether or not to initiate a new round of proxy discovery

15. 15 Route and Proxy Maintenance -2 Route consistency and loops Solution is to include the entire relay path in the RTREQ message to exclude route loop

16. 16 Refining scheduling algo in HDR Original shceduling of HDR Tradeoff between throughput and fairness: DL channel is shared by users in TDMA mode BTS selects the minimum T k (t)/R k (t), where T k (t) means the avearage throughput of the kth user in time t (with an arbitary window size of w), and R k (t) is the current DL channel rate of user k at time t. Refined scheduling algo in UCAN T k (t) is represented by the number of bits received by destination client within the arbitary window size How to represent R k (t)? Choice one : use that of the proxy client, or Choice two: use that of the destination client The key idea is to maintain fairness between clients and encourage mobile nodes to become proxy clients

17. 17 Refining scheduling algo in HDR-example Suppose DL channate rate of destination and proxy client node is 1:2 When no relay is used, slot scheduling between destination and proxy client is 1:1 When relay is used, use proxy’s rate as criterion, slot scheduling between destination and proxy client is 1:1, resulting in unfairness When relay is used, use client’s rate as criterion, slot scheduling between destination and proxy client is 1:2, no unfairness

18. 18 Allow diversity in UCAN Due to fast fading, max average channel rate may not stand for the max instant channel rate In UCAN, allow HDR BTS to forward data to the client along the relay path with the highest data rate, instead of the proxy server. The HDR BTS need to know the complete relay path Additional processing is needed to keep the packets in order

19. 19 Secure Crediting mechanism The goal is to enourage clients to act as proxy client for other nodes Extra incentive is givne to the proxy client and all the clinets along the relay path by accumulating credits for the them, besides the refining scheduling algorithm Detailed crediting is discussed in other papers Focus on authentications of clients along the relay path The basic idea is to include an authentication key between two neighbouting clients in the relay path, and forward the keys to the HDr BTS HDR BTS can discriminate the cheating clients by requesting the compuataion of the authentication keys

20. 20 Experiments and performance evaluations-1 HDR Channel model

21. 21 Experiments and performance evaluations-2 HDR Channel Rate: instant and average

22. 22 Experiments and performance evaluations-3 Simulator: ns-2 Application: FTP/TCP and CBR/UDP Speed of mobile clients: 0, 2, 5, 10, 15m/s Radius of HDR Cell: 500m, only one cell Number destination clients : one or more Number of other relay/proxy clients: 30~100 Two srecial techniques: Aggregate of data frames at the proxy client: because each HDR DL frame is 128 bytes in average at speed of 600kbps and 1.67 ms per slot. Inefficiency in IP. Scoped Neighborhood advertisement: In greedy proxy discovery algorithm, use TTL in HDR DL channel rate advertisement to reduce the overhead

23. 23 Experiments and performance evaluations-4 The relationship of the packet size vs relay hops

24. 24 Experiments and performance evaluations-5 Single destination client : throughput gain client placed at d = 400m to the HDR BTS, channel rate=340kbps radius of 802.11b is 115m at 11Mbps, so 3 hops are expected, with channel rate = 1.25Mbps

25. 25 Experiments and performance evaluations-6 Single destination client : HDR uplink overhead The ratio of on-demand / greedy proxy discovery algorithms

26. 26 Experiments and performance evaluations-7 Single destination client : Energy consumption The energy consume ratio of on-demand / greedy proxy discovery algorithms

27. 27 Experiments and performance evaluations-8 Multiple destination clients : greedy algorithm Use variable TTL (from 1 to 4) in RTREQ thus result in different length of relay path All the max/min throughput gains are greater than 1

28. 28 Experiments and performance evaluations-9 Multiple destination clients : On-demand algorithm Use variable TTL (from 1 to 4) in RTREQ thus result in different length of relay path All the max/min throughput gain ratios are greater than 1

29. 29 Discussions Strategies used in UCAN and some open issues Frugal Usage of HDR Links Base Station Pull v.s. Client Push Variable Data Rate and Transmit Range in 802.11 HDR Uplink Proxy Co-located HDR BS and IEEE 802.11 AP Interaction with Peer-to-Peer Traffic HDR Scheduling and End-to-end Delay Multiple Cell Relay Application Scenarios In Section

30. 30 Summary of UCAN Unified Cellular and Adhoc Network to improve the throughput of cellular system Two approaches: greedy / on-demand proxy discovery Slightly better performance of on-demand with substantial higher signaling overhead, compared with greedy algo. The deficiency of greedy algo is consuming more power than on-demand algo. Refining scheduling algo for HDR Secure crediting system

31. 31 THANK YOU !