in-pavement wireless sensor network for vehicle classification
DESCRIPTION
In-Pavement Wireless Sensor Network for Vehicle Classification. Authors:Ravneet Bajwa , Ram Rajagopal , Pravin Varaiya and Robert Kavaler Presenter: Xiangyi Gu. Outline. Motivation Introduction Description Communication Protocol Design Experiment Setup Performance - PowerPoint PPT PresentationTRANSCRIPT
AUTHORS:RAVNEET BAJWA, RAM RAJAGOPAL, PRAVIN VARAIYA AND
ROBERT KAVALER
PRESENTER: XIANGYI GU
In-Pavement Wireless Sensor Network for
VehicleClassification
Outline
MotivationIntroductionDescriptionCommunication Protocol DesignExperiment SetupPerformanceConclusion & Future Work
Outline
MotivationIntroductionDescriptionCommunication Protocol DesignExperiment SetupPerformanceConclusion & Future Work
Motivation
Intrusive technologies Piezoelectric sensors, inductive loops (examples) High installation and maintenance costs
Non-intrusive technologies Infrared, video imaging(examples) Sensitive to traffic and weather condition
Propose an alternative system base on a WSN that is both cost effective and insensitive to environmental conditions
Transportation agencies collect vehicle classification information to plan highway maintenance programs, evaluate highway usage and optimize the deloyment of various resources on the road
MotivationIntroductionDescriptionCommunication Protocol DesignExperiment SetupPerformanceConclusion & Future Work
Problem Statement
Cars, buses, three-axle single unit trucks, and five-axle single trailer trucks (classifying vehicles)
A vehicle travels in a traffic lane at some varying speed and we wish to count the number of axles and the spacing between each axle in an accurate manner
Proposed WSN System
Vibration sensor (accelerometer) embedded in the road Calculate the axle spacings
Vehicle detection sensor (magnetometers) Report the arrival and departure times of a vehicle
Access point (AP) Send commands to sensors Log the incoming data
First in-pavement, easyto deploy, WSN basedsystem for counting axlesand axle spacing
Outline
MotivationIntroductionDescriptionCommunication Protocol DesignExperiment SetupPerformanceConclusion & Future Work
Wireless Vehicle Detection Sensor
Measures the changes in magnetic field to infer the local presence of a vehicle
Synchronous Nanopower Protocol(SNP), aTDMA based protocol Last 10 years with a single 7200 mAhr battery
Given the arrival times tai and taj at the twosensors i and j, the speed v will bev = dij / |taj – tai|
Estimate the length(L) of the vehicleL = v(tdj - taj)
Wireless Vibration Sensor
Sensor needs to be insensitive to the vehicles traveling in the neighboring lanes
Sample fast enough to capture the transient vibrations
Insensitive to the truck engine and environmental noise
The sensor has to be well coupled to the road way and be resistant to heavy vehicle traffic
Challenges
•Sample the analog output of an accelerometer and transmit the data via a radio•Designing a sensor that measures pavement vibrations for axle detection have many unique challenges
•Sensor resolution target is 500ug•Bandwidth 50Hz•Sampling frequency 512 Hz( > 5 times Nyquist Frequency)-Power consumption increases for higher sampling rates
Axle detection and counting
Given vehicle speed measurement and reliable measurement from the wireless vibration sensor, we still need to construct an axle detection algorithm that has good performance
There are two important challenges in detecting individual axles:
A B.The vibration
signals from successive axles tend to blend.
In wide highway lanes, vehicles can experience significant wander
Sensor Design
Resolution:Selecting an accelerometer
SD1221-005 has higher sensitivity and lower noise density
However, it consumes more than 20 times the current than MS9002.D and has to be operated at higher voltage
Both devices achieved the aimed minimum resolution of 500 ug Select MS9002.D due to its low operating voltage and low
current consumption
Noise: Filters for mitigating sound noise
Accelerometer is sensitive to soundMS9002.D behaves like a microphone under
the device’s bandwidth3rd order low-pass filter with cutoff
frequency of 50 Hz is sufficiently aggressive to filter out most of the sound in the audible spectrum
Casing
Sound isolationProtect the electronics from
rain water and oil spill on theroad
Circuit Description
2.5 V supply voltageAmplifier with gain 10The gain of 10 reduces the range of the accelerometer to ≈±225mgThis is necessary in order to ensure
that the quantization noise from the ADC is less than the noise from the accelerometer Otherwise, the resolution of the system will be limited by
ADC noiseThe reduced range is still sufficient
For heavy trucks ± 200 mg
Outline
MotivationIntroductionDescriptionCommunication Protocol DesignExperiment SetupPerformanceConclusion & Future Work
Communication Protocol Design
MAC Layer TDMA based Time is divided into multiple frames with each
frames about 125 ms long Each frame is further divided into 64 time slots Slot 0 is used by AP to send clock synchronization
information and other commands to the sensors AP assigns every node unique time slots and a
node ID to communicate with it.
Application Layer
Sync Application AP sends sync packets on a periodic basis Sensor node listens to sync packets every 125 ms When the clock converges to steady state, then is
listens for a sync packet only once in 30 s Sync application is also used to send commands Set Mode, Reset, Set Timeslot, Set RF, Download
Firmware, Set ID
Application Layer
Accelerometer Application Idle Mode: accelerometer and related circuitry are
turned off by disabling the voltage regulator Once every 30 s, the microcontroller and the transceiver
wake up and acquire the sync packet
Application Layer
Raw Data Mode: microcontroller wake up every 1/512 s, and samples the analog output from accelerometer 32 samples at a sampling freq. 512Hz, and each sample
containing 12 bits of information In every frame(125ms) we accumulate 96 bytes of
information to transmit To have a reasonable packet size, we fragment the data
in two parts, 48 bytes each, and transmit it using two different time slots 62.5ms apart
Application Layer
Download Firmware Application Reprogram the entire flash memory of a sensor
node over the air AP transmits new code repeatedly and the node
updating its code in small pieces Only the data that do not overwrite the current
running program are updated by the node
Axle Detection(ADET) Algorithm
Results of ADET on truck49( two single axles and one tandem axle), a(n) is the measured acceleration in mg, e(n) is the scaled energy in mg2, and s(n) is smooth energy in mg2. The red asterisks on s(n) are the axle locations found by ADET. By reducing the minimum axle sepatation, the individual axles in the tandem axle can also be detected as shown by black circle
Axle Detection(ADET) Algorithm
Using data from 4 trucks at different speeds, we observed the bandwidth of the energy signal and empirically defined by M(v) = 900/v
Low-pass filter is optionalMinimum time separation ζ(v) was chosen by
assuming that the axles are at least 6ft apart
Wide Lane ADET Algorithm
Wander movement in a laneCombining vibration readings from multiple
sensorsDelay Di = di / v sennor2 will measures the peak enery a little later
than sensor 1, so the individual energy measurements nedd to be appropriately delayed
System representation of the adjustment made to correct vehicle wander. The energy if the total signal at time n is the maximum of the energy of the individual signals ei(n) is each sensor i.
Outline
MotivationIntroductionDescriptionCommunication Protocol DesignExperiment SetupPerformanceConclusion & Future Work
Experiment Setup
4 vibration sensors and 4 vehicle detection sensor were installed on California Highway I-680
Vehicles come from Sunol Weigh Station
Slow down at weigh station Easy to collect ground truth
Data from 53 different trucks, rangingfrom pickup trucks to 5-axle commercial trucks
The WSN setup at Suno; site. DHMN are vehicle detection sensors shereas I,J,K,L are vibration sensors
Installation
Boring a 4-inch diameter hole approximately 2.25 inches deep
Installed on a road in less than 20 minutesInstallation of a small sensor is much cheaper and
convenient than installing special material pavements required for piezoelectric sensors
Deployment Challenges
Packet Drops Drop rate was low(1%) (compare 50 feet away)
retransmit packets with a delay of 1 packet drop rate is almost 0 Packet 1, 2, 1again, 2again
Vehicle Wander Because vehicles are not taveling stright in a lane we would like
to choose data from vehicle sensor that was closest to the tires use Wide Lane ADET algorithm
Sensor failure Sensor k did not work Vibration data was available from 3 sensors
Outline
MotivationIntroductionDescriptionCommunication Protocol DesignExperiment SetupPerformanceConclusion & Future Work
Vibration Sensor Performance
Noise with no vehicle in vicinity 414 ug RMS
Truck was parked on top of the sensor with engine were on vs. truck blew its horn 7% vs. 4%
With a heavy truck traveled in the closed lane Sensor did not register any noticeable peaks
Axle Count
Error difference between the ground truth axle count and the estimated axle count
By combining the measurements from all sensors, the algorithm always gives the correct axle count
Error results form the wander movement( Strongly affected by truck wander
Performance of ADET using individual sensors and combinations of sensors. Count Err. Is the difference between the ground truth and ADET estimate. Under each sensor column is the observed frequency of the errors.
Axle Spacing
Left: for tandem axleMiddle: pick up trucks, small two axle
commercial trucksRight: axles of trailers
Distribution of estimated axle spacings. There are three clusters in the data separated by empty bins. The dotted lines represent the means of there clusters
Outline
MotivationIntroductionDescriptionCommunication Protocol DesignExperiment SetupPerformanceConclusion & Future Work
Conclusion
A novel algorithm that estimates the axle count and spacing from pavement acceleration was designed and tested on the collected data
ADET is simple enough to implement a sensor node with limited processing power
Majorities of the existing technologies are wired solutions Both the sensors and the AP are powered by batteries and
consume much less power than other technologiesThe installation procedure and sensors themselves are
much cheaperThere is minimal maintenance compared to other
technologies
Future Work
Find an optimal arrangement of sensors in order to minimize the number of sensors deployed
Reduce the amount of data transmittedReduce the sensor power consumption
Thank you very much!