columbia/ecsma2006111715200611172006-11-27columbia/ecsmaSensor network dataset for enhancing CSMA MAC protocol.This dataset contains packet transmission traces collected
from an experimental wireless sensor network testbed, where E(Enhanced)-CSMA
MAC protocol is implemented using TinyOS on Mica2 motes.the initial version2006-11-172006-03-262006-04-0859http://www.crawdad.org/columbia/ecsmahttp://www.crawdad.org/wiki/pmwiki.php?n=Main.Dataset.Columbia-ecsmasensor networkNetwork Performance AnalysisMAC Protocol DevelopmentCSMA MACsensor networkE(Enhanced)-CSMA is a fully distributed MAC framework targeted
at increasing the chance of successful packet reception in wireless
sensor networks using carrier sensing.
To show the performance enhancement, the authors conducted packet
transmission experiments on a 31 node sensor network testbed based on
TinyOS running on Mica2 motes.The testbed comprises 31 Mica2 motes arranged in a roughly rectangular grid.
The motes are connected to MIB600 Ethernet interface boards which are mounted
across a suspended ceiling hanging about 4ft from the concrete structural
ceiling (nodes 1-6 are instead mounted on the dry wall) of a roughly 1600ft2
room of our research center.
The motes hang approximately 10ft above a metal tile raised floor.
A line of heavy-duty rigging for electrical conduits and throw
switches hangs approximately 2ft from the suspended ceiling between
nodes 28-31 and the rest, offering substantial reflective surface area.
The Mica2s are powered from the MIB600s, which in turn are powered
by a 802.3af Power over Ethernet hub via standard CAT5E cables.
The Ethernet back channel is used for mote programming,
experimental parameter configuration and data collection,
and as the feedback channel for the ideal feedback scheme described
in the paper. Motes use a frequency of 914.077MHz and are equipped with
standard quarter wave whip antennas.The Ethernet back channel is used for mote programming, experimental
parameter configuration and data collection. The motes are configured
by prior to each experimental run via the ethernet back channel by
shell script wrappers around applications running on a central server.
These applications send experiment control/config messages that are
handled by message handlers implemented in TinyOS on the motes.
Data is gathered on the motes (stored in RAM) and then offloaded via
the same backchannel in response to a query after the experimental run.24200611172006-11-27columbia/ecsma/feedbackTraceset of packet transmissions with different feedback mechanisms of E(Enhanced)-CSMA protocol.This traceset contains the packet transmission data collected from
the experiments of applying three feedback mechanisms - ideal, positive
and periodic, to demonstrate the potential and feasibility of E-CSMA.the initial version2006-11-172006-03-262006-04-08MAC Protocol DevelopmentWith respect to a given transmitter, the state of the wireless
channel at each potential receiver in its radio range is unique.
Therefore, the authors propose to measure the existing correlation
empirically by employing in-band feedback mechanisms to create
a probability distribution of successful reception.
The authors further propose that a transmitter maintains such a distribution
for each of its potential receivers (i.e., one hop neighbors).
This traceset contains the packet transmission data collected from
the experiments applied by three feedback mechanisms - ideal, positive
and periodic, to demonstrate the potential and feasibility of E-CSMA.
For this traceset, the authors use 'Outlier Magnitude' as the input
value set, and use 'per-neighbor' probability distributions for
maintaining channel status.columbia/ecsma59200611172006-11-27columbia/ecsma/feedback/idealTrace of packet transmission experiments with ideal feedback mechanism of E(Enhanced)-CSMA MAC protocol.Trace of packet transmission experiments with ideal feedback mechanism of
E(Enhanced)-CSMA MAC protocol.the initial versionfalse2006-11-172006-03-262006-04-08With Ideal feedback, a receiver sends back
an acknowledgment for each packet received. Per receiver,
per bin (i.e., bins for RSS value), the transmitter keeps
a FIFO queue of the M most recent feedback results, where
a result is 1 if an acknowledgment is received for a given
packet and 0 otherwise. The instantaneous estimate of the
success probability to a given receiver with channel conditions
mapping to a given bin is calculated as a function (e.g., average)
of these M most recent feedback results, where clearly M controls
the granularity of the stored probability.
Ideal feedback is sent out-of-band over an Ethernet back channel
(for experimental comparison only).
This trace contains the results of experiments with different
source rates (0.25, 0.5, 1, 2, 3, 4, 5, packets/sec).
Each experiment consists of five trials where (regardless of
source rate) 200 packets are transmitted by each of the 31
transmitters.
Actual packet transmissions at rate r_src = 1/t_src are randomized
within the interval t_src. Thus, every time t = n*t_src the start
of the next transmission is set as t+rand(0, t_src-PKT_TX_TIME),
where rand(min, max) returns a number chosen uniformly at
random in the supplied interval, and PKT_TX_TIME is the
time necessary to transmit a packet at the specified rate r_src.Trace includes directories of different source rates (e.g., rate-0.25pps).
In each rate-[RRR]pps directory, you can find
- aggrSummary.trial[N].txt: summary file for trial N
(e.g., aggrSummary.trial1.txt for trial 1)
- summary-[nn].txt: summary file for mote nn
(e.g., summary-03.txt is for mote 3)
- rate-[RRR]pps.trial-[N]: directory for trial N of source rate RRR experiment
In each rate-[RRR]pps.trial-[N] directory, you can find
- tx-[nn]: log file directory for mote nn
(e.g., txt-03 for mote 3)
In each tx-[nn] directory, you can find
- beta-[T].alpha-[A].log: log file of the exp with duty fraction T and
decision threshold A
Each summary file consists of the values for the following variables:
- beta: 'T' in the paper
- txns: # of transmitted packets
- txECSMA: # of transmitted packes using ECSMA
- rcvd: # of received packets
- avgDelay: avg delay for transmitting one packet
Each log file consists of the values for the following variables:
- numTxnsToNeighbor: # of tx'ed packets to each neighbor
- numBkoffsWhenSendingToNeighbor: # of backoffs when sending to each neighbor
- avgDelayWhenSendingToNeighbor: # of delays when sending to each neighbor
- numEcsmaYesCsmaNo: # of times (pkts) the ECSMA algorithm said tx
while the plain CSMA algorithm said backoff.
- numEcsmaNoCsmaYes: reverse of the previous
- numReceptions: # of packets received by each neighbor
- numSentWithCSMA: # of packets sent with CSMA to each neighbor
- numSentWithECSMA: # of packets sent with ECSMA to each neighbor
- numSuccessesInBin: # of reception successes to each neighbor in each bin
- numFailuresInBin: # of reception failures to each neighbor in each bin
- successRatioTraceInBin: previously this was a trace of how the probability
in each bin evolved. we started out looking at the first 20 samples, but
it was using up to much space in memory so we just chopped it to
the last value in each bin./download/columbia/ecsma/feedback-ideal.tar.gzcolumbia/ecsma/feedback60200611172006-11-27columbia/ecsma/feedback/positiveTrace of packet transmission experiments with Positive feedback mechanism of E(Enhanced)-CSMA MAC protocol.Trace of packet transmission experiments with Positive feedback mechanism of
E(Enhanced)-CSMA MAC protocol.the initial versionfalse2006-11-172006-03-262006-04-08With Positive feedback, a receiver sends back
an acknowledgment for each packet received. Per receiver,
per bin (i.e., bins for RSS value), the transmitter keeps
a FIFO queue of the M most recent feedback results, where
a result is 1 if an acknowledgment is received for a given
packet and 0 otherwise. The instantaneous estimate of the
success probability to a given receiver with channel conditions
mapping to a given bin is calculated as a function (e.g., average)
of these M most recent feedback results, where clearly M controls
the granularity of the stored probability.
Positive feedback is sent inband over the wireless channel.
This trace contains the results of experiments with different
source rates (0.25, 0.5, 1, 2, 3, 4, 5, packets/sec).
Each experiment consists of five trials where (regardless of
source rate) 200 packets are transmitted by each of the 31
transmitters.
Actual packet transmissions at rate r_src = 1/t_src are randomized
within the interval t_src. Thus, every time t = n*t_src the start
of the next transmission is set as t+rand(0, t_src-PKT_TX_TIME),
where rand(min, max) returns a number chosen uniformly at
random in the supplied interval, and PKT_TX_TIME is the
time necessary to transmit a packet at the specified rate r_src.Trace includes directories of different source rates (e.g., rate-0.25pps).
In each rate-[RRR]pps directory, you can find
- aggrSummary.trial[N].txt: summary file for trial N
(e.g., aggrSummary.trial1.txt for trial 1)
- summary-[nn].txt: summary file for mote nn
(e.g., summary-03.txt is for mote 3)
- rate-[RRR]pps.trial-[N]: directory for trial N of source rate RRR experiment
In each rate-[RRR]pps.trial-[N] directory, you can find
- tx-[nn]: log file directory for mote nn
(e.g., txt-03 for mote 3)
In each tx-[nn] directory, you can find
- beta-[T].alpha-[A].log: log file of the exp with duty fraction T and
decision threshold A
Each summary file consists of the values for the following variables:
- beta: 'T' in the paper
- txns: # of transmitted packets
- txECSMA: # of transmitted packes using ECSMA
- rcvd: # of received packets
- avgDelay: avg delay for transmitting one packet
Each log file consists of the values for the following variables:
- numTxnsToNeighbor: # of tx'ed packets to each neighbor
- numBkoffsWhenSendingToNeighbor: # of backoffs when sending to each neighbor
- avgDelayWhenSendingToNeighbor: # of delays when sending to each neighbor
- numEcsmaYesCsmaNo: # of times (pkts) the ECSMA algorithm said tx
while the plain CSMA algorithm said backoff.
- numEcsmaNoCsmaYes: reverse of the previous
- numReceptions: # of packets received by each neighbor
- numSentWithCSMA: # of packets sent with CSMA to each neighbor
- numSentWithECSMA: # of packets sent with ECSMA to each neighbor
- numSuccessesInBin: # of reception successes to each neighbor in each bin
- numFailuresInBin: # of reception failures to each neighbor in each bin
- successRatioTraceInBin: previously this was a trace of how the probability
in each bin evolved. we started out looking at the first 20 samples, but
it was using up to much space in memory so we just chopped it to
the last value in each bin./download/columbia/ecsma/feedback-positive.tar.gzcolumbia/ecsma/feedback61200611172006-11-27columbia/ecsma/feedback/periodicTrace of packet transmission experiments with Periodic feedback mechanism of E(Enhanced)-CSMA MAC protocol.Trace of packet transmission experiments with Periodic feedback mechanism of
E(Enhanced)-CSMA MAC protocol.the initial versionfalse2006-11-172006-03-262006-04-08With Periodic feedback, receivers return the number of
packets successfully received (per neighbor, per RSS bin) in the
previous interval, and may optionally return the number of
packets with failed CRCs over the same interval. Transmitters
count the number of packets they send (per neighbor, per
RSS bin) over the same interval to compare with the information
fed back from the receivers. This feedback interval can be
defined in terms of time or number of packets. In the former
case, the receiver sends back the aggregated acknowledgment
every specified time period; in the latter, the receiver
must successfully receive a specified number of packets before
sending the acknowledgment. Motivations for a non time-based
approach include removing any synchronization requirement,
allowing for simpler protocol correctness verification
(e.g. FSM analysis), and not depending on a periodic
workload to keep the overhead low.
This trace contains the results of experiments with different
source rates (0.25, 0.5, 1, 2, 3, 4, 5, packets/sec).
Each experiment consists of five trials where (regardless of
source rate) 200 packets are transmitted by each of the 31
transmitters.
Actual packet transmissions at rate r_src = 1/t_src are randomized
within the interval t_src. Thus, every time t = n*t_src the start
of the next transmission is set as t+rand(0, t_src-PKT_TX_TIME),
where rand(min, max) returns a number chosen uniformly at
random in the supplied interval, and PKT_TX_TIME is the
time necessary to transmit a packet at the specified rate r_src.Trace includes directories of different source rates (e.g., rate-0.25pps).
In each rate-[RRR]pps directory, you can find
- aggrSummary.trial[N].txt: summary file for trial N
(e.g., aggrSummary.trial1.txt for trial 1)
- summary-[nn].txt: summary file for mote nn
(e.g., summary-03.txt is for mote 3)
- rate-[RRR]pps.trial-[N]: directory for trial N of source rate RRR experiment
In each rate-[RRR]pps.trial-[N] directory, you can find
- tx-[nn]: log file directory for mote nn
(e.g., txt-03 for mote 3)
In each tx-[nn] directory, you can find
- beta-[T].alpha-[A].log: log file of the exp with duty fraction T and
decision threshold A
Each summary file consists of the values for the following variables:
- beta: 'T' in the paper
- txns: # of transmitted packets
- txECSMA: # of transmitted packes using ECSMA
- rcvd: # of received packets
- avgDelay: avg delay for transmitting one packet
Each log file consists of the values for the following variables:
- numTxnsToNeighbor: # of tx'ed packets to each neighbor
- numBkoffsWhenSendingToNeighbor: # of backoffs when sending to each neighbor
- avgDelayWhenSendingToNeighbor: # of delays when sending to each neighbor
- numEcsmaYesCsmaNo: # of times (pkts) the ECSMA algorithm said tx
while the plain CSMA algorithm said backoff.
- numEcsmaNoCsmaYes: reverse of the previous
- numReceptions: # of packets received by each neighbor
- numSentWithCSMA: # of packets sent with CSMA to each neighbor
- numSentWithECSMA: # of packets sent with ECSMA to each neighbor
- numSuccessesInBin: # of reception successes to each neighbor in each bin
- numFailuresInBin: # of reception failures to each neighbor in each bin
- successRatioTraceInBin: previously this was a trace of how the probability
in each bin evolved. we started out looking at the first 20 samples, but
it was using up to much space in memory so we just chopped it to
the last value in each bin./download/columbia/ecsma/feedback-periodic.tar.gzcolumbia/ecsma/feedback25200611172006-11-27columbia/ecsma/predict-inputTraceset of packet transmissions with different predict inputs of E(Enhanced)-CSMA protocol.This traceset contains the packet transmission data collected from
the experiments of applying different predict inputs - e.g., 'Raw RSS' to demonstrate
the potential and feasibility of E-CSMA.the initial version2006-11-172006-03-262006-04-08MAC Protocol DevelopmentIn order to compare the E-CSMA performance achieved when using
the Raw RSS value as the input value to the decision process,
versus using the Outlier Magnitude, that is, the difference
between the Raw RSS value and an adaptive estimate of the noise
floor value observed by the transmitter, the authors present
this data using 'Raw RSS' as the input value set.
To eliminate any biasing effect of a particular in-band
feedback mechanism, the authors compare these two input sets
using the ideal feedback scheme.
For this traceset, the authors use 'Raw RSS' as the input
value set, and use 'per-neighbor' probability distributions
for maintaining channel status.columbia/ecsma62200611172006-11-27columbia/ecsma/predict-input/raw-rssTrace of packet transmission experiments with 'Raw RSS' input of E(Enhanced)-CSMA MAC protocol.Trace of packet transmission experiments with 'Raw Rss' input of
E(Enhanced)-CSMA MAC protocol.the initial versionfalse2006-11-172006-03-262006-04-08With Ideal feedback, a receiver sends back
an acknowledgment for each packet received. Per receiver,
per bin (i.e., bins for RSS value), the transmitter keeps
a FIFO queue of the M most recent feedback results, where
a result is 1 if an acknowledgment is received for a given
packet and 0 otherwise. The instantaneous estimate of the
success probability to a given receiver with channel conditions
mapping to a given bin is calculated as a function (e.g., average)
of these M most recent feedback results, where clearly M controls
the granularity of the stored probability.
Ideal feedback is sent out-of-band over an Ethernet back channel
(for experimental comparison only).
This trace contains the results of experiments with different
source rates (0.25, 0.5, 1, 2, 3, 4, 5, packets/sec).
Each experiment consists of five trials where (regardless of
source rate) 200 packets are transmitted by each of the 31
transmitters.
Actual packet transmissions at rate r_src = 1/t_src are randomized
within the interval t_src. Thus, every time t = n*t_src the start
of the next transmission is set as t+rand(0, t_src-PKT_TX_TIME),
where rand(min, max) returns a number chosen uniformly at
random in the supplied interval, and PKT_TX_TIME is the
time necessary to transmit a packet at the specified rate r_src.Trace includes directories of different source rates (e.g., rate-0.25pps).
In each rate-[RRR]pps directory, you can find
- aggrSummary.trial[N].txt: summary file for trial N
(e.g., aggrSummary.trial1.txt for trial 1)
- summary-[nn].txt: summary file for mote nn
(e.g., summary-03.txt is for mote 3)
- rate-[RRR]pps.trial-[N]: directory for trial N of source rate RRR experiment
In each rate-[RRR]pps.trial-[N] directory, you can find
- tx-[nn]: log file directory for mote nn
(e.g., txt-03 for mote 3)
In each tx-[nn] directory, you can find
- beta-[T].alpha-[A].log: log file of the exp with duty fraction T and
decision threshold A
Each summary file consists of the values for the following variables:
- beta: 'T' in the paper
- txns: # of transmitted packets
- txECSMA: # of transmitted packes using ECSMA
- rcvd: # of received packets
- avgDelay: avg delay for transmitting one packet
Each log file consists of the values for the following variables:
- numTxnsToNeighbor: # of tx'ed packets to each neighbor
- numBkoffsWhenSendingToNeighbor: # of backoffs when sending to each neighbor
- avgDelayWhenSendingToNeighbor: # of delays when sending to each neighbor
- numEcsmaYesCsmaNo: # of times (pkts) the ECSMA algorithm said tx
while the plain CSMA algorithm said backoff.
- numEcsmaNoCsmaYes: reverse of the previous
- numReceptions: # of packets received by each neighbor
- numSentWithCSMA: # of packets sent with CSMA to each neighbor
- numSentWithECSMA: # of packets sent with ECSMA to each neighbor
- numSuccessesInBin: # of reception successes to each neighbor in each bin
- numFailuresInBin: # of reception failures to each neighbor in each bin
- successRatioTraceInBin: previously this was a trace of how the probability
in each bin evolved. we started out looking at the first 20 samples, but
it was using up to much space in memory so we just chopped it to
the last value in each bin./download/columbia/ecsma/raw-rss.tar.gzcolumbia/ecsma/predict-input26200611172006-11-27columbia/ecsma/rcv-probablityTraceset of packet transmissions with different receiver probability schemes of E(Enhanced)-CSMA protocol.This traceset contains the packet transmission data collected from
the experiments of applying different receiver probality schemes - e.g., 'Per-Neighborhood'
to demonstrate the potential and feasibility of E-CSMA.the initial version2006-11-172006-03-262006-04-08MAC Protocol DevelopmentIn order to compare a scheme where probability distributions are
not kept per neighbor but per neighborhood, with the ECSMA scheme,
the authors have implemented a variant of E-CSMA, termed ECSMA_neighborhood
that keeps only a single probability distribution at each transmitter
rather than one for each receiver.
The authors present the data here from our experimental testbed
under the same testbed configuration and experimental parameterization as our
per-neighbor data.
For this traceset, the authors use 'Outlier Magnitude' as the input
value set, and use 'per-neighborhood' probability distributions for
maintaining channel status.columbia/ecsma59200611172006-11-27columbia/ecsma/rcv-probablity/per-neighborhoodTrace of packet transmission experiments with per-neighborhood scheme of E(Enhanced)-CSMA MAC protocol.Trace of packet transmission experiments with per-neighborhood scheme of
E(Enhanced)-CSMA MAC protocol.the initial versionfalse2006-11-172006-03-262006-04-08For ECSMA_neighborhood, the authors have implemented three feedback
schemes as follows:
With Ideal feedback, a receiver sends back
an acknowledgment for each packet received. Per receiver,
per bin (i.e., bins for RSS value), the transmitter keeps
a FIFO queue of the M most recent feedback results, where
a result is 1 if an acknowledgment is received for a given
packet and 0 otherwise. The instantaneous estimate of the
success probability to a given receiver with channel conditions
mapping to a given bin is calculated as a function (e.g., average)
of these M most recent feedback results, where clearly M controls
the granularity of the stored probability.
Ideal feedback is sent out-of-band over an Ethernet back channel
(for experimental comparison only).
With Positive feedback, a receiver sends back
an acknowledgment for each packet received. Per receiver,
per bin (i.e., bins for RSS value), the transmitter keeps
a FIFO queue of the M most recent feedback results, where
a result is 1 if an acknowledgment is received for a given
packet and 0 otherwise. The instantaneous estimate of the
success probability to a given receiver with channel conditions
mapping to a given bin is calculated as a function (e.g., average)
of these M most recent feedback results, where clearly M controls
the granularity of the stored probability.
Positive feedback is sent inband over the wireless channel.
With Periodic feedback, receivers return the number of
packets successfully received (per neighbor, per RSS bin) in the
previous interval, and may optionally return the number of
packets with failed CRCs over the same interval. Transmitters
count the number of packets they send (per neighbor, per
RSS bin) over the same interval to compare with the information
fed back from the receivers. This feedback interval can be
defined in terms of time or number of packets. In the former
case, the receiver sends back the aggregated acknowledgment
every specified time period; in the latter, the receiver
must successfully receive a specified number of packets before
sending the acknowledgment. Motivations for a non time-based
approach include removing any synchronization requirement,
allowing for simpler protocol correctness verification
(e.g. FSM analysis), and not depending on a periodic
workload to keep the overhead low.
For each feedback scheme (as in three directories - per-neighborhood-ideal,
per-neighborhood-positive, and per-neighborhood-periodic, respectively),
trace contains the results of experiments with different
source rates (0.25, 0.5, 1, 2, 3, 4, 5, packets/sec).
Each experiment consists of five trials where (regardless of
source rate) 200 packets are transmitted by each of the 31
transmitters.
Actual packet transmissions at rate r_src = 1/t_src are randomized
within the interval t_src. Thus, every time t = n*t_src the start
of the next transmission is set as t+rand(0, t_src-PKT_TX_TIME),
where rand(min, max) returns a number chosen uniformly at
random in the supplied interval, and PKT_TX_TIME is the
time necessary to transmit a packet at the specified rate r_src.There are three directories corresponding to each feedback scheme -
per-neighborhood-ideal, per-neighborhood-positive, and per-neighborhood-periodic.
Each feedback scheme directory includes directories of different source rates
(e.g., rate-0.25pps).
In each rate-[RRR]pps directory, you can find
- aggrSummary.trial[N].txt: summary file for trial N
(e.g., aggrSummary.trial1.txt for trial 1)
- summary-[nn].txt: summary file for mote nn
(e.g., summary-03.txt is for mote 3)
- rate-[RRR]pps.trial-[N]: directory for trial N of source rate RRR experiment
In each rate-[RRR]pps.trial-[N] directory, you can find
- tx-[nn]: log file directory for mote nn
(e.g., txt-03 for mote 3)
In each tx-[nn] directory, you can find
- beta-[T].alpha-[A].log: log file of the exp with duty fraction T and
decision threshold A
Each summary file consists of the values for the following variables:
- beta: 'T' in the paper
- txns: # of transmitted packets
- txECSMA: # of transmitted packes using ECSMA
- rcvd: # of received packets
- avgDelay: avg delay for transmitting one packet
Each log file consists of the values for the following variables:
- numTxnsToNeighbor: # of tx'ed packets to each neighbor
- numBkoffsWhenSendingToNeighbor: # of backoffs when sending to each neighbor
- avgDelayWhenSendingToNeighbor: # of delays when sending to each neighbor
- numEcsmaYesCsmaNo: # of times (pkts) the ECSMA algorithm said tx
while the plain CSMA algorithm said backoff.
- numEcsmaNoCsmaYes: reverse of the previous
- numReceptions: # of packets received by each neighbor
- numSentWithCSMA: # of packets sent with CSMA to each neighbor
- numSentWithECSMA: # of packets sent with ECSMA to each neighbor
- numSuccessesInBin: # of reception successes to each neighbor in each bin
- numFailuresInBin: # of reception failures to each neighbor in each bin
- successRatioTraceInBin: previously this was a trace of how the probability
in each bin evolved. we started out looking at the first 20 samples, but
it was using up to much space in memory so we just chopped it to
the last value in each bin./download/columbia/ecsma/per-neighborhood.tar.gzcolumbia/ecsma/rcv-probablity59columbia/ecsmaShane B. Eisenmanshane@ee.columbia.eduColumbia UniversityElectrical EngineeringGraduate studentDept. of Electrical Engineering, 1300 S.W. Mudd Building, 500 West 120th Street, New York, NY 10027http://comet.columbia.edu/~shane/eisenman-ecsmaShane B. EisenmanAndrew T. CampbellE-CSMA: Supporting Enhanced CSMA Performance in Experimental Sensor Networks using Per-neighbor Transmission Probability ThresholdsProceedings of the 26th IEEE International Conference on Computer Communications (INFOCOM)--05--2007Anchorage, ALhttp://ieeexplore.ieee.org/iel5/4215581/4215582/04215726.pdf?tp=&isnumber=&arnumber=4215726crawdadmeasurementwirelesscolumbia_ecsmacrawdadcolumbia/ecsma20070501