Download Infostations: A New Design for Wireless Computing

Infostations:
A New Design
for Wireless Computing
Christopher Crammond
Charuhas Pandit
Yaling Yang
Computing Trends
1980s
1990s
200?
Desktop
Laptop
Network
Wireless
The Downfall of 3G
• 3G clearly addresses the issue of
increased data rate.
• What about ...
– System Asymmetry
– Cost per Bit
3G: System Asymmetry
• Voice - equal amounts of traffic on both
uplink and downlink
• Data - produces more traffic for downlink
• 3G wastes bandwidth
3G: Cost Analysis
• Voice requires 10 Kbit/s at v cents/min
• Implying a data rate of 1 MByte/s
corresponds to 13v cents/MByte
• if v = 10, require $1.30 per Mbyte
• 3G is expensive
Exit 3G, Enter Infostations
• Infostation: an isolated pocket of high
bit-rate coverage
• Smaller areas of coverage
• Lower Transmit Power
• Lower cost per bit
Infostation: The Premise
• Designed to account for system
asymmetries
• Acknowledges data is bursty.
• Tolerate longer delays.
• Disjoint pockets of coverage allow for
reducing the reuse factor N = 1.
• Use unlicensed frequency band.
Achievable Data Rates
• Optimistically: 500 Mbit/s in 100 MHz Band
– Preliminary analysis under ideal conditions
• Realistically: 4 Mbit/s in 1 MHz Band
– Infostations at 100 meter intervals
– Using current technology
– Iacono August 1998
Mathematical Justification
• Optimization Problem:
– With finite energy, when to transmit?
Water-filling Principle
• Solution:
– For optimum throughput, transmit the most
power to the user with the best channel
– Implies use of smaller coverage i.e., (r/R)<1
Calculations: Infostations
• No need for ubiquitous coverage
• Better SIR conditions
• Smaller cluster size
• More bandwidth available gives higher
data rate
SIR in 2D Infostation system
n
d
P 
r

SIR 
n
6
d 
P  

i 1
 Di 
1  3N R 

SIR  
6  r 
n
D1
D2
D6
R
r
D5
D4
D3
Which system is better?
2M bps
6M bps
Answer: Depends!
• User Density
• Importance of throughput vs. delay
• Type of application offered
Queuing Analysis
•
Modeled as M/M/1 queue with reneging
•
If coverage (r/R) increases,
–
Worst case SIR decreases, so data rate
available decreases, so m decreases.
–
Dwell time in area increases, so reneging
rate (n) decreases
–
Arrival rate (l) increases
Relating l, n, m to r/R
•
Arrival rate l = pruE[v]
u = mobile user density
v = mobile speed
•
Reneging rate n = 2E[v]/pr
•
Service rate m related to data rate, c,
related to modulation scheme
•
Performance of modulation scheme
related to r/R.
Mailbox accumulation –
performance parameter
• Between infostations, mailbox accumulates
messages
• X = accumulated mailbox size between
successive infostation visits (random variable)
• E[X] = lu tc (m/c), where lu is the messages
per user per second and tc is the average time
between visits to Infostations.
• tc= (pR2)/(2r E[V])
2D Numerical Example
Modulation
BPSK
QPSK
16 QAM
64 QAM
N
1
1
3
1
3
4
7
1
3
4
7
12
c
1
2
0.67
4
1.33
1
0.57
6
2
1.5
.86
0.5
r/R
0.66
0.56
.97
0.37
0.64
0.74
0.99
0.25
0.42
0.49
0.65
0.85
E[X]
9.52
5.61
9.72
4.25
7.36
8.49
11.11
4.19
7.48
8.55
11.28
14.78
l
0.26
0.22
0.38
0.15
0.25
0.29
0.39
0.10
0.16
0.19
0.26
0.33
u=(0...0.0004), R=500, E[V]=2.5, m=2e6, lu=0.01
What Does it all Mean?
• Lowest E[X] for r/R = .25 (reduced
coverage) and 64 QAM (high modulation)
• Thus justifying the use of infostations
• For 1D, delay is also better (WPMC ‘99)
Infostation Protocol Layering
• Intelligent transmission protocol for Infostations.
Application
Application
Transportation
Wireless TCP for
Infostations
Network
Mobile IP
Data Link Control
Media Access
Control
WINMAC
Physical
Physical
WINMAC
• Support both fairness and preemptive service
• Multiple access & channel resource allocation
• Transmission rate switching
• Retransmission scheme
Multiple Access Protocol
• Slot Allocation Algorithm: When a mobile with higher
priority arrive, assign it most of the channel resources.
Otherwise provide fair service.
• TDMA/TDD configuration: A frame consist of a number
of time slot and each slot can carry one packet
• Reservation and Transmission:
• Look for beacons
• Choose a rate based on the highest rate and the the largest
# of available slots
• Send reservation and registration request
• Transmit data
Transmission Rate
•
Rate Switching algorithm (suppose 3 rates):
–
Listen to beacons of 3 data rates
–
Monitor Packet Error Rate of current channel
condition
–
Suppose transmission in rate 2 and find out that
2 out of 3 recent beacons of rate 3 is heard and
PER<0.1 then switch to rate 3. Otherwise, if less
or equal to one beacon out of 3 is heard of rate
2 and PER>0.5, then switch to rate 1.
Retransmission Scheme
• Combine SR (selective repeat) & GBN (Go
back N) ARQ.
• SR: Only require sender to retransmit the
lost packet.
• GBN: Require the sender to retransmit all
the packet after the error or lost packet.
• Using SR within the processing ability of
hardware or software and use GBN beyond
the ability.
Architecture
UMTS
SS7 signaling
Network
Infostation Controller
Radio Port
Proxy Cache
Radio Port
Internet
ATM or Frame Relay
Radio Port
Radio Port
Infostation and Mobile IP
• Current
Proposals
for Mobile
IP fit well
into the
Infostation
concept.
Correspondent Host
Home Agent
Mobile Host
Foreign Agent
Infostations and Mobile IP I
• When the mobile recognizes that it is no
longer connected to its home network, it
is assigned a care-of-address from the
network it is visiting. In an infostation
system, the IC will assign the care-ofaddress to the mobile .
• The mobile then informs the home agent
about its current location to allow
packets to be forwarded to it.
Infostations and Mobile IP II
• The mobile can also inform the other
party of its current care-of address,
which the other party can use to directly
communicate with the mobile.
• When a mobile enters the RP of another
Infostation it would register there, obtain
a new care-of-address, and continue the
session using the new Infostation.
TCP Solution
• Split Connection: A TCP connection
between a fixed host and mobile host is
split into two connections at the BS.
• End-to-End approach-TCP smart: The
snoop agent in the Infostation Controller
(IC) monitors all of its TCP connections.
The IC will cache all segments received
from the fixed Host and not yet
acknowledged by the MH.
Application Design for a
Network of Infostations
• Example: A map service for vehicles on a highway.
High bandwidth
info-station coverage
Open Infostation Research
• Transmitting in unlicensed bands
• Randomized movement of mobile.
• Data transfers over multiple sessions.
• All the hassles of increased bit-rate.
Infostation Downside
• Difficult to track down explicit numbers.
• Exclusively at WINLAB.
• Lack of commercial interest.
• Dependent of failure of 3G.
Bibliography
•
Borras, Joan and Roy D. Yates. "Infostation Overlays in Cellular Systems." IEEE WCNC (1999): 495-9
•
Elaoud, Moncef and Parameswaran Ramanathan. "TCP-SMART: A Technique for Improving TCP
Performance in a Spotty Wide Band Environment." IEEE (2000): 17-83-7
•
Goodman, David. "The Wireless Internet: Promises and Challenges." computer.org 2/01
•
Frenkiel, Richard, B.R. Badrinath, Joan Borras, and Roy D. Yates. "The Infostations Challenge:
Balancing Cost and Ubiquity in Delivering Wireless Data." IEEE Personal Communications (2000): 6671.
•
Iacono, Ana Lucia and Christopher Rose. "Minimizing File Delivery Delay in an Infostation System."
WINLAB, 1998.
•
Irvine, J., D. Pesch, D. Robertson, and D. Girma. "Efficient UMTS Data Service Provision using
Infostations." IEEE (1998): 2119-23.
•
Yates, Roy D., Narayan B. Mandayam. "Challenges in Low-Cost Wireless Data Transmission." IEEE
Signal Processing (2000): 93-102.
•
Wu, Gang, Churng-Wen Chu, Kevin Wine, James Evans, and Richard Frenkiel. "WINMAC: A Novel
Transmission Protocol for Infostations." IEEE VTC'99. 1999.
•
Ye, Tao, H. Arno Jacobsen, and Randy Katz. "Mobile Awareness in a Wide Area Wireless Network of
Info-stations." Berkeley.