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Transcript of Rate Throughput
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5/28/2018 Rate Throughput
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Sunil Kowlgi, Vacha Dave Univesity of Texasat Austin 1
Effect of Data Rate on
Throughput
Wireless and Mobile Computing Project Presentation
EE 382V project
Sunil KowlgiVacha Dave
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Sunil Kowlgi, Vacha Dave Univesity of Texasat Austin 2
Presentation Outline
Motivation
Methodology Overview
Setup and Environment NS-2
802.11b
Experiments , Results and Analysis Experiments
Results
Analysis Furthering the work
Issues
References
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Sunil Kowlgi, Vacha Dave Univesity of Texasat Austin 3
Motivation
Most wireless cards come with multiple data rates
The commonly held belief is that higher data rate
guarantees higher throughput.
Higher data rates require higher transmit powerwhich means lesser spatial reuse.
We would like to see how spatial reuse is affectedfor different data rates and how this effect manifestsas reduced throughput.
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Methodology Overview
We measured throughput for a single flow ona linear chain topology of nodes.
Measurements were carried out for differentdata rates and transmit power levels.
The number of concurrent successfultransmissions was measured to serve as anindication of spatial reuse.
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Setup and Environment: NS-2 PHY Layer
Phy/WirelessPhy: Frequency2.4GHz (802.11b)
RX thresholdvaried according to data rate
Transmit powerswept over a range 130dBm Carrier sense threshold - 1e-13W
Capture threshold10dB
Propagation/Shadowing: Path Loss Exponent2.0 (free space)
Shadowing deviation4.0 ( outdoor)
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Setup and Environment: NS-2 MAC Layer
Mac/802_11 :
RTS Threshold0 ( RTS/CTS turned on )
Data rate1, 2, 5.5, 11Mbps ( 802.11b)
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Setup and Environment: NS-2 Network
Layer - NOAH
Package that enables static routing for
wireless nodes
Lets you set the routing table by hand for
each node
Queue/DropTail/PriQueueinterface queue
type
Network interface queue length500
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Setup and Environment: Application layer
Constant Bit Rate (CBR) traffic is used
CBR parameters that were set: Time interval between packetsvaried for different
experiments Packet size1456 bytes + 24 MAC hdr + 20 IP hdr
Different transmit data rates can be achieved byvarying CBR parameters
CBR lets you limit the maximum number of packetsthat need to be sent from source to sink.
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Setup and Environment: Testing for
different Power levels
FCC mandates that wireless transmitters limit
power to 30dBm (1W).
Commonly used transmit power level for
wireless cards is 15dBm.
We ran experiments for all power levels in the
range 130dBm.
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Setup and Environment: Measuring
Throughput
Loss Monitor was used to measure the throughput
at the sink, over a given time window.
All simulations were run for 700 seconds
The initial and final 100 seconds of simulation were
excluded from throughput measurement. This is to
ensure that the system was in steady state.
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Experiments carried out
To determine the chain length
To determine of CBR value
To measure the throughput for different
power levels, for 802.11b data rates
Number of concurrent transmissions for
different power levels, for 802.11b data rates
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Experiment: Determining Chain Length
Trying to approximate an infinite chain length, forwhich throughput does not vary significantly withsmall change in number of nodes.
Before carrying out throughput v. data rateexperiments we determined the right chain lengthand that would be valid for different data rates.
Settings: Power level15dBm
Packet size1500 bytes
Distance between nodes550m
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Results: Determining Chain Length
Throughput vs. Number of Nodes for sending rate = 1Mbps,
distance between nodes = 550m
transmit power = 15dBm
0
100200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60 70 80 90Chain Length
Throughput(Kbps)
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Results: Determining Chain Length
Throughput for different number of nodes at 2Mbps Data Rate,
Distance= 550m,
transmit power = 15dBm
0
200
400
600
800
1000
1200
1400
1600
1800
0 10 20 30 40 50 60 70 80 90
Number of Nodes
ThroughputinKbps
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Results: Determining Chain Length
Throughput Vs. Number of Nodes for 11Mbps sending rate,
distance between nodes= 550m
transmit power = 15dBm
0
100
200
300
400
500
600
700
0 10 20 30 40 50 60 70 80 90
Number of Nodes
Throughput(Kbps)
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Analysis: Determining Chain Length
There is a quasi-exponential decay inthroughput as the chain length is increased.
The chain length for our experiments waspicked from the stable/flat region of thethroughput curve.
We picked a chain length of 60 nodes for allsubsequent simulations.
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Experiment: Determining CBR values
We need to determine the CBR value at
which there are no congestion losses.
For a chain length of 60 nodes, we measured
the throughput for different CBR values. This
was carried out for 1, 2 and 11Mbps data
rates, at a transmit power level of 15dBm.
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Sunil Kowlgi, Vacha Dave Univesity of Texasat Austin 18
Results: Determining CBR values
Throughput for different CB rates, distance between nodes = 550m,
power = 15dBm, 1Mbps data rate
0
5
10
15
20
25
30
35
1 10 100 1000 10000
CBR ( Kbps)
Throughput(Kbps)
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Sunil Kowlgi, Vacha Dave Univesity of Texasat Austin 19
Results: Determining CBR values
Throughput for different CB rates, distance between nodes = 550m,
power = 15dBm, 2Mbps data rate
0
5
10
15
20
25
30
35
40
45
50
1 10 100 1000 10000
CBR ( Kbps)
Throughput(Kbp
s)
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Sunil Kowlgi, Vacha Dave Univesity of Texasat Austin 20
Results: Determining CBR values
Throughput for different CB rates, distance between nodes = 550,transmit power = 15dBm, 11Mbps data rate
0
1
2
3
4
5
6
7
8
1 10 100 1000 10000 100000
CBR (Kbps)
Throughput(Kbps)
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Analysis: Determining CBR Rate
Throughput increases with CBR value until a point, where itstarts to fall.
The reduction in throughput beyond a certain CBR value can beattributed to congestion.
For our subsequent experiments we use CBR values just belowthe inflection point so that it guarantees reasonable throughputwithout the worry of congestion. For 1Mbps31.6 Kbps
For 2Mbps60 Kbps
For 11Mbps60 Kbps
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Sunil Kowlgi, Vacha Dave Univesity of Texasat Austin 22
Experiment: Power Vs. Throughput for a
given Data Rate
Simulations were run to measure the throughput for30 different transmit power levels ( 1- 30 dBm).
These simulations were performed for different datarates1, 2, 11 Mbps.
CBR values determined in the previous experimentwere used ( to avoid congestion-related losses).
Nodes were separated by 550m.
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Result: Power Vs. Throughput for a given
Data Rate
Power v. Throughput for CBR=60Kbps,
chain length = 60, 550m between nodes
-5
0
5
10
15
20
25
30
35
40
0.001 0.01 0.1 1
Power (W)
Throughput(Kbps)
1Mbps
15dBm
15 dBm
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Analysis: Power Vs. Throughput for a
given Data Rate For very low values of transmit power, very few
data packets get across from source to sink, andthroughput is very low.
As the transmit power increases, transmissionsbecome more reliable and the throughput increasestill a point.
There is an inflection point corresponding to acertain transmit power beyond which fewer nodestransmit in a given time interval and thus spatialreuse decreases.
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Result: Putting them All together
Power v. Throughput for CBR=31.6Kbps,
chain length = 60, 550m between nodes
-5
0
5
10
15
20
25
30
35
0.001 0.01 0.1 1
Power (W)
Throughput(Kbps)
1Mbps
2Mbps
11Mbps
15dbm
15 dBm
Power v. Throughput for CBR=60Kbps,
chain length = 60, 550m between nodes
-10
0
10
20
30
40
50
60
70
0.001 0.01 0.1 1
Power (W)
Throughput(Kbps)
1Mbps
2Mbps
11Mbps
15dBm
15 dBm
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Analysis: Putting them All together
For each data rate, throughput increases withincreased transmit power and beyond a certaintransmit power it starts to fall.
The graphs are testament to the fact that for a giventransmit power a higher data rate does not alwaysresult in higher throughput.
The envelope of the curve gives the data rate atwhich transmissions should happen, to achieve thehighest throughput possible for a given transmitpower.
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Analysis: Extrapolating the 11Mbps Curve
The 11Mbps throughput-transmit power curve
appears to flatten out, contrary to intuition!
But, if the curve is extrapolated for transmit
powers up to 5W (!) it shows the degradation
of throughput.
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Sunil Kowlgi, Vacha Dave Univesity of Texas
at Austin 28
Experiment: Measuring Spatial Reuse -
Possibilities Spatial reuse could be quantified in different ways
The minimum distance between nodes at which an optimalFairness Ratio of 1 is achieved is indicative of spatialreuse.
The number of transmissions that complete in a timeinterval ( defined by the transmission time of a standardsize data packet) is indicative of spatial reuse.
Using the queuing theory
First packet 59x , second at 59x + x, and so on
Measuring the deviation from ideal We adopted the second methodology to quantify
spatial reuse.
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Sunil Kowlgi, Vacha Dave Univesity of Texas
at Austin 29
Experiment: Measuring Spatial Reuse
After a simulation run, the trace file was examined
by a script to determine the maximum number of
ACKs in a time interval.
The time interval was determined by measuring time
from sending of RTS to the reception of an ACK, for
a single CBR packet of 1500 bytes.
13 ms for 1Mbps 7.2 ms for 2Mbps
4 ms for 11 Mbps
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Sunil Kowlgi, Vacha Dave Univesity of Texas
at Austin 30
Result: Measuring Spatial Reuse
Power v. Throughput for CBR=60Kbps,
chain length = 60, 550m between nodes
-10
0
10
20
30
40
50
60
70
0.001 0.01 0.1 1
Power (W)
Throughput(Kbps)
1Mbps
2Mbps11Mbps
15dBm
15 dBm
Measure of Spatial Reuse
-1
0
1
2
3
4
5
6
7
0.001 0.01 0.1 1
Power in Watts
NumberofAcksreceived/time
interval 1 Mbps
2 Mbps
11 Mbps
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Sunil Kowlgi, Vacha Dave Univesity of Texas
at Austin 31
Analysis: Measuring Spatial Reuse
Very Jittered Curveseems to follow the
general throughput curve
Binning the values and taking a weighted
average would result in a better curve
Pessimistic boundsince it counts only the
transmissions that have completed during the
given time interval.
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Sunil Kowlgi, Vacha Dave Univesity of Texas
at Austin 32
Furthering the Experiments
Effect of Distance between nodes on the
result
We have maintained a distance on 550 m
between nodes. This is just under thetransmission range for 1Mbps.
More exhaustive sweep over different
Application layer data rates.
Trying out for different packet sizes
Issue with 64 byte packets
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Sunil Kowlgi, Vacha Dave Univesity of Texas
at Austin 33
Some of the Exhaustive Sweep
CBR vs. Throughput (Kbps) for different power levels,
chain length = 60 nodes, 550 m apart
-5
0
5
10
15
20
2530
35
40
45
1 10 100 1000 10000 100000
Constant Bit Rate (Kbps)
Throughput(Kbp
s)
0.001259
0.001585
0.001995
0.002512
0.003162
0.003981
0.005012
0.00631
0.007943
0.01
0.0125890.015849
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Sunil Kowlgi, Vacha Dave Univesity of Texas
at Austin 34
Issues
We could not see any throughput for 5.5 Mbps, forall transmit power levels. Possibly because ofincorrect value of RX threshold.
The default TTL value for IP in NS-2 is set to 32. Aweek was spent in figuring out the mysteriouspacket drops for long chain lengths.
NS-2 simulations took a long time, which preventedus from performing more exhaustive experiments.For instance, sweeping across different CBR ratesfor different power levels.
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Sunil Kowlgi, Vacha Dave Univesity of Texas
at Austin 35
References
The Network Simulator http://www.isi.edu/nsnam/ns/
Capacity of AdHoc Wireless Networks Jinyang Li,
Charles Blake, Douglas S. J. De Couto, Hu Imm Lee,
and Robert Morris , MOBICOM 01
Improving spatial reuse through tuning transmit power,
carrier sense threshold, and data rate in multihop
wireless networks, Kim et al. MOBICOM 2006
An Experimental Evaluation of Several Rate Adaptation
Protocols, Choi et. al.
http://www.isi.edu/nsnam/ns/http://www.isi.edu/nsnam/ns/