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UCAN: A Unified Cellular and UCAN: A Unified Cellular and Ad-Hoc network ArchitectureAd-Hoc network Architecture

By

H. Luo, S. Lu

Computer Science Department

UCLA

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What is new?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

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Comparison of Wide-area wireless network Comparison of Wide-area wireless network and Local-area wireless networkand Local-area wireless network

Wide-area wireless network

Local-area wireless network

Coverage Up to tens of kilometers, e.g., 20kms.

Up to hundreds of meters, e.g., 250m for Wi-Fi

Throughput Low.

Up to 2Mbps, mainly for voice

High.

11Mbps for 802.11b, 54Mbps for 11a/11g

Organization Infrastructure mode, one hop.

Ad-hoc, multi-hops

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Requirement for UCANRequirement 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

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Organization of this paperOrganization 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

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Background knowledgeBackground 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

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Related work of combing two wireless Related work of combing two wireless networksnetworks

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.

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Motivated by a simple exampleMotivated by a simple example

Non-relay case:

Relay case:

FTP ServerLaptop inside roomHDR cellualr link

HDR cellualr link

FTP Server

802.11 link

Relay client

in corridor,

better HDR DL

Laptop inside room

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Throughput comparison of the simple exampleThroughput comparison of the simple example

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Architecture of UCAN 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.

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Issues need to be addressed in UCAN systemIssues 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

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Proxy Discovery and Routing: Greedy algoProxy 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.

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Proxy Discovery and Routing: On-demand algoProxy 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.

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Route and Proxy Maintenance -1Route 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

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Route and Proxy Maintenance -2Route and Proxy Maintenance -2 Route consistency and loops

• Solution is to include the entire relay path in the RTREQ message to exclude route loop

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Refining scheduling algo in HDRRefining 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 Tk(t)/Rk(t), where Tk(t) means the avearage throughput of the kth user in time t (with an arbitary window size of w), and Rk(t) is the current DL channel rate of user k at time t.

Refined scheduling algo in UCAN• Tk(t) is represented by the number of bits received by destination

client within the arbitary window size• How to represent Rk(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

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Refining scheduling algo in HDR-exampleRefining 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

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Allow diversity in UCANAllow 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

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Secure Crediting mechanismSecure 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

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EExperiments and pxperiments and performance evaluations-1erformance evaluations-1 HDR Channel model

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EExperiments and pxperiments and performance evaluations-2erformance evaluations-2 HDR Channel Rate: instant and average

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EExperiments and pxperiments and performance evaluations-3erformance 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

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EExperiments and pxperiments and performance evaluations-4erformance evaluations-4 The relationship of the packet size vs relay hops

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EExperiments and pxperiments and performance evaluations-5erformance 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

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EExperiments and pxperiments and performance evaluations-6erformance evaluations-6 Single destination client : HDR uplink overhead

• The ratio of on-demand / greedy proxy discovery algorithms

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EExperiments and pxperiments and performance evaluations-7erformance evaluations-7 Single destination client : Energy consumption

• The energy consume ratio of on-demand / greedy proxy discovery algorithms

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EExperiments and pxperiments and performance evaluations-8erformance 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

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EExperiments and pxperiments and performance evaluations-9erformance 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

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DiscussionsDiscussions 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

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Summary of UCANSummary 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

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THANK YOU !THANK YOU !