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UCAN: A Unified Cellular and Ad-Hoc Network Architecture

Rick Szcodronski

ECE 256February 12, 2008

Published by: Haiyun Luo, Ramachandran Ramjee, Prasun Sinha, Li (Erran) Li, Songwu Lu

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Cellular vs. 802.11 Networks

• Range = 250 m.• 1 - 11 Mbps• CSMA/CD

A

A

802.11b1xEV-DO (HDR)

• Range = 20 km.• 38.6 Kbps – 2.4 Mbps• CDMA / TDMA

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Recall: Rate Control

C EA

D

B

Rate = 20

Rate = 10

Both 802.11 and HDR use Rate Control to transmit data

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Motivation for UCAN

A B

38.6 Kbps

2.4 Mbps 11 Mbps

11 Mbps

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Simple Test Layout

B

R

D

HDR

HDR

802.11b

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Simple Test Results

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UCAN Architecture

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

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Proxy Discovery

1. HDR Channel Rate Drops2. D Sends Route Request Using

802.113. RTREQ propagates using “Proxy

Discovery” protocol4. P sends proxy application to Base5. Base updates proxy tables6. Base routes packets for D via P

D 2.4 Mbps

38.6 Kbps

R

R

P

RTREQ

RTREQ

RTREQ

Proxy Application

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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

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On-Demand Proxy Discovery

• 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?

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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!

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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

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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

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Proportional Fairness Scheduling

• 2 Goals– Maximize cell throughput– Maintain minimum individual

Quality of Service

• How can this extend to UCAN?

Proportional Fairness Scheduling• Tk(t) = Average Throughput• Rk(t) = Instantaneous Rate• Slot Winner = min{Tk(t)/Rk(t)}

Time

D

B

CA

DRC = 116 slots

DRC = 34 Slots

DRC = 61 Slot

DRC = 121 Slot

A A A AB B BC CD

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UCAN Scheduling

• HDR uses proportional fairness scheduling

– Maximize throughput, maintain minimum QoS

– Client scheduled when downlink rate is high

• UCAN Scheduling– Using Proxy’s Rk(t): unfair

throughput gain

– Using Destination’s Rk(t): distributed gain

BA

R=2R=1

)(

)(

tR

tT

k

k

1 2

1 2

A B*A

3

A B

1 2

A B*

R=2 R=1

* Packets received using Proxy A

R=2 R=2

R=2 R=2 R=2

No Relay

Relay w/ Prxy’s R

Relay w/ Dst’s R

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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

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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!

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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

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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

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UCAN HDR Uplink Evaluation

On-Demand’s higher throughput comes at the price of increased HDR uplink overhead

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UCAN Energy Evaluation

• Energy Trends– Energy increases as clients increase– Energy increases as speed increases– Energy Comparison: Greedy > On-

Demand

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UCAN Multiple Client Evaluation

• Multiple Client Setup– 80 Clients (5

Destination Clients)– ALL Clients are mobile– TTL = 1-4

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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.)

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Questions or Comments?