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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
2
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
3
Recall: Rate Control
C EA
D
B
Rate = 20
Rate = 10
Both 802.11 and HDR use Rate Control to transmit data
4
Motivation for UCAN
A B
38.6 Kbps
2.4 Mbps 11 Mbps
11 Mbps
5
Simple Test Layout
B
R
D
HDR
HDR
802.11b
6
Simple Test Results
7
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
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
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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
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
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
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
21
UCAN Energy Evaluation
• Energy Trends– Energy increases as clients increase– Energy increases as speed increases– Energy Comparison: Greedy > On-
Demand
22
UCAN Multiple Client Evaluation
• Multiple Client Setup– 80 Clients (5
Destination Clients)– ALL Clients are mobile– TTL = 1-4
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
Questions or Comments?