An optimum algorithm

for reporting of automobile position

Nguyen Thanh Hung i, Hideto Ikeda', Kuribayasi Kenzil, Nikolaos Vogiatzis11 and Zin Lin''Computer Science Department, Ritsumeikan University

1-1-1 Noji-Higashi, Kusatsu Shi 525-8577 JapanEmail: {hungnt, hikeda, kenzi, zinlin}gcyber.cs.ritsumei.acjp

Transport Systems Centre, University ofSouth Australia, AUSTRALIA;Email: nikolaos.vogiatzisgunisa.edu.au

Abstract- This paper presents a car navigation system for afuture integrated transportation system as an IntelligentTransportation System- ITS. The system focuses on themechanisms how to detect the current position of each vehicleand to navigate each vehicle. The individual vehicular data iscollected using Global Positioning System - GPS for location dataand then transmitted to the control center by the mobile phone.For the purpose of this paper, the device will be referred to"Reporting Equipment for current geographic Position" or REP.In the case where every vehicle within the transportationnetwork is equipped with a REP it will be referred to as"Comprehensive REP Environment" or CREPE. If a greatnumber of cars report their positions to the control center, itcauses a heavy load of network. This paper proposes analgorithm to reduce the network load. If a car skips some reports,the control center cannot estimate its correct position. Thealgorithm aims to decrease the frequency of the reportingwithout sacrificing the proper level of accuracy for the position.The effectiveness is evaluated as 1/2 or 2/3 times compared toperiodical reporting algorithms.

Keywords- Navigation; Integrated transportation system; GPS;Network load; Timing; Locality and Scope.

I. INTRODUCTION

In present traffic system, car navigation systems have beeneffectively put to practical use [1, 2]. Traffic is controlled byrecognizing road conditions such as the waiting time ofvehicles (as seen by queue lengths) at intersections or tollgates, the distance detection between vehicles, etc by means ofinfrared sensors and the camera located on roads or fromsatellites. However, these systems only acquire the roadconditions like construction, traffic incidents, and congestion,etc., and cannot get the vehicle information in real time. Toprovide enough data for navigation, the system have to acquirethe current information of all vehicle running on road.

To provide en-route vehicular navigation information todrivers and the appropriate control strategies to control trafficefficiently, a comprehensive environment has been defined ina paper written by Hung, Ikeda, Vogiatzis and Zin (2006) [5].In that paper, the authors described a new environment inwhich the real-time information is reported from a new type ofdevice which will be referred to "Reporting Equipment forcurrent geographic position" (REP) equipped in each vehicle.

At the core of the REP is GPS which provides position, speedand direction information, and the mobile phone networkwhich provides device level communications. The REPterminal uses the information from the mobile phone networkto allow the Control Center to provide information/instructions to the individual drivers. The environment inwhich all vehicles are equipped with a REP is referred to theComprehensive REP Environment or CREPE. If a CREPE inoperation, then the number of REP terminals, will have theeffect of increasing significantly the network load and thisneeds to be considered since the current mobile network isvery limited in its communication channels.

This paper proposes an optimum algorithm to reduce thenetwork load. The algorithm aims to decrease the frequency ofreporting with a proper accuracy of vehicle position. Toevaluate the algorithm, we established experiments to analyzethe accuracy of reports in different cases such as theperiodically reporting and the changing of vehiclecharacteristics like speed or direction in different trafficsituations. In the experiment, each REP terminal equipped invehicle has to provide necessary information to the controlcenter. The experiment results show us the optimum algorithmfor reporting to reduce the frequency of report, naturally reducethe load of the mobile network.

Figure 1: Three layered model ofIMAGINATION

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II. CREPE ARCHITECTURE

A. CREPEnvironment andIMAGINATIONIn order to improve traffic network systems and to co-

ordinate the network of moving units, and integrate variouskinds of transportation systems, Vogiatzis, Ikeda et alproposed an Integrated Transportation System -

IMAGINATION [3, 4] that takes into account all aspects of atransportation management system, using artificial intelligence,data streaming management systems, and GPS. The threelayered ofIMAGINATION is shown in figure 1.

The lowest layer manages specific controllers in locationsof intersection, acquires data from those locations and controlsthe environment. Data is acquired by a local unit called front-end components-fix point sensors; data is then transmitted tothe data management system or related to control centers.Some data is used specifically for the control of individuallocations whereas other data is locally summarized and thentransmitted to the middle layer. Besides information collectedfrom the front-end components, the REP terminal providesfunctionality for reporting and receiving information betweenthe vehicle and the control center.

The DBS (Database Management System) in the middlelayer also manages data from individual controller andsystem-wide data for the purpose of resource management,analysis and transport facilities planning. The data in themiddle layer are used for establishing new knowledge rules,supporting activities of managing transport office, registrationof vehicles, the administrating of roads, etc.

In the top layer, KS (Knowledge System) manages thecontrol/behavioral rules associated with the environment suchas intersections, facilities and appropriate rules for conditionssuch as accident wardens, traffic congestion etc.

Finally, control centers are established for specific purposessuch as a fire control center, highway monitoring center, roadtraffic monitoring etc. Each control center connects to therelated local units to get appropriate data for its controlmechanism. From the idea of integrated systemIMAGINATION, a new environment called CREPEis defined by Hung, Ikeda et al (2006) [5]. The 7=CREPE which stands for Comprehensive REP 5Environment is an environment in which all vehiclesare equipped with a REP terminal to acquire vehicle Functioi

information and report to control centers. Base on thedata acquired, control centers can estimate futurelocation of all vehicles running on road by its micro-simulation system and control the traffic ofautomobile in real time [5]. Since theIMAGINATION collects real-time traffic data fromeach REP terminal to construct and validate trafficcontrol algorithms, it can efficiently control traffic

oiland navigate each vehicle. 4

The architecture of CREPE is described in figure2. The REP terminals received the current position ofvehicle from GPS satellite then report that data

GSatellite *;=G PS Satellite

IREP IREP 1IREP1terminal terminal ... terminal

Mobile network Mobile networkcenter center

q t W14Automobile Control Center- -Automobile Control Center-

Figure 2: Architecture of CREPE

including others vehicle information such as speed, direction,etc. to the control centers through mobile phone networks.

B. Reporting loadIn CREPE, it is possible to cause a heavy load to the

network since the REP terminals always get the current vehicleposition by GPS and it have to judge whether to report to thecontrol centers. Control centers analyze all reports and controltraffic.

Thus, the load at automobile control centers is alwayshigh, especially during peak periods (morning peak, typicallybetween 8am and 9am and afternoon peak between 4pm and6pm, and localised during special events such as sporting orcultural events) because the control centers have to acquire theinformation from vehicle and then to estimate each movementof all vehicles to control traffic in real time. That problem issolved by deployment of local control centers usingdistributed computing geographically decomposed (Hung etal., 2006) (figure 3)[5].

The frequency of report from REP terminals also affects themobile network centers network load since theircommunication channels are limited. Each REP terminal mayhave to decrease the frequency of its report but still can provideenough information to control center. However, if the

_ll. ..........................

{ ] * 1l g * ~~~~~~~~~~~~~~~~~~~Toplayerf Scope Central ll .-Traffic regulations::|*-Congestion *=

Specified Accident|*-Specified incident * /...........................jill | 11( 1 f f .~~~ Higher layer

on H * 1 * IWider areaX X w 1< W < i ~~~~~~~~~~~~~~-Weatheriv71~~~~ ~ ~ ~ ~~~~~~~~~~~~~~~~~~.. .

A' ] X n////=w /gggggai~~~~~~~~~~~~~~~~Cotriolglersl

_Signal timing

Geographical decomposition

Figure 3: Deployment a decentralized system ofCREPE

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Figure 4: Use case diagram ofREP terminal

frequency of report is decreased, the accuracy of the actualroad situation as reported to the control center also be effected,especially as the control center cannot estimate the correctpositions of each vehicle on road and it cannot assist in thenavigation for drivers or control the traffic network correctly.To achieve the requirement, the following section discussesimplementation ofREP terminals.

III. IMPLEMENTATION OF REP TERMINAL

A. Requirements ofreportfunctionWe consider the following requirements:

- The current position of all cars can be acquired.- The acquired data have an acceptable accuracy.

- Every vehicle moving on road can receive road informationand control signals from the control center.- The frequency of each REP terminal report can be efficientlydecreased.The implementation of REP terminal is described as

following:

B. Functional architecture

Figure 4 shows the Use case diagram of REP terminal. Thedriver decides the destination by using the navigation systemand keeps driving on road. Information on the vehicle such as

speed, direction, current GPS position is acquired and reportsto the operator at control center by the REP terminal accordingto present circumstances. The latest road information isacquired from the data base system and used for thenavigation. To achieve those functions, we designed thefunctional architecture of REP terminal as shown in figure 5and as following:

GPS receiver receives GPS data using RMC(Recommended Minimum Specific GNSS data) sentencewhich includes angle of deviation, the terrestrial magnetismmode, checksum at the measurement time and status, latitude,the longitude, ground speed, direction and time. The datareceived from GPS is processed and transmitted to the Datareporter. Data reporter judges the timing to report aftercomparing GPS data with the map data and route informationfrom Map manager and Route manager. Log system recordsautomatically the operation of REP. Data transmittercommunicates between REP and control center according tothe provided timing and content of the report from vehicle. Ifthe control center recognizes the map information is notupdated, it will transmit the latest map data to the Datatransmitter and then pass to the Map manager. After updated,the Map manager issues re-detection of route to the Route

I -. Data ----> ControlGPS data acquisition

Figure 5: Functional architecture ofREP terminal

manager. Displaylvoice system navigates driver by image or

voice by the last map and route data.

C. Data structure ofMap data

Due to the limitation of storage, REP cannot use thecurrent map data being use now because it is too large. Wedesign the data structure of Map data which demonstrates infigure 6 with necessary infornation of road and related places.Thus, the proposed data structure of Map can be installed inthe REP memory which similar to current mobile storage. Inthis structure, each Route-Block can be connected to eachother, thus the neighbouring Route-Block IDs are recorded.Beside, some of road infornation is necessary such as

coordinates, surface type, etc., traffic regulations and theireffecting time. The Place table provides the infornation aboutparking, intersections, etc. The adjoining places can besearched by the ConnectedPlacelD, the relation between eachRoute-Block and Place can be found by the "Locate"relationship. Thus, this data structure can provide enoughinformation for road and route detection. Base on the detectedinfornation, the REP can calculate vehicle OD route by itsshortest route finding method.

D. Dataformat ofthe REP report

The data fornat of the REP report is designed into fourtypes:

G>RouteBlock Place

(pk)RouteBflockID (pk)PlaceID(fk)PlaceID (fk)ConnectedPlaceID(fk)FrontRbID ParkingRule(fk)BackRbID Length(fk)LeftRbID Width(fk)RighRbID HeightStartCoordinate FacilitiesEndCoordinate XCoordinateSurfaceType YCoordinateWidthLengthInclinationDirectionDegreeOfCurveTrafficRegulations pk: Primary key

EffectTimeOfReg. fk: foreign key

Figure 6: Data structure of map information

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Display/ voice R m asvstem

L.

Start information: When driving begins

Transmission vehicle ID, driver ID, position, speed,data destination and time

Receive data Congestion and regulation of traffic

Stop information: When driver stop.

Transmission vehicle ID, driver ID, position,data Consolidating data and time

Receive data none

Update information: When REP updates the road situation

Transmission vehicle ID, driver ID, position, time,data consolidating data and destination

Receive data Congestion and regulation of traffic

Incident information: When the car causes the accident, or theother cars cause the accident, or other incidents such ascongestion, earthquake, etc.

Transmission vehicle ID, driver ID, position, time,data status of incident (type, injured person,

present traffic trouble, etc.)

Receive data Incident processing method

Such kind of that information can be reported to the controlcenter by the algorithms below.

IV. REPORTING ALGORITHMS OF REP TERMINAL

which REP reports to the control center.

- Periodical timing

- Different route detected

- When the parameters of car changed such as speed,direction and destination

- When the vehicle going to pass the intersections.

- Assumption. When moving, the vehicle is assumed to carrya vector. If the direction of vehicle changed, the new vectorwill create naturally an angle compared to the previous vector.In this paper, we called that different angle is "angle ofvehicle" or r.

The REP terminal always acquires data from the vehicle anddecides when to report according to the data content from GPSreceiver (figure 7). From those cases, we analyze thefollowing algorithms.

A. Algorithm A. Periodical reportingThe REP terminal will report at interval time (figure 8A).

In this paper, the frequency of report is assumed to be At= 1 to20 second. The shorter frequent to report the higher accuracycan be achieved; however the heavier network load will beoccurred. This algorithm is used as the base to compare withour algorithms for reducing the reporting timing.

B. Algorithm B. Periodical reporting base on vehicle speedThe report timing is defined as following:

We consider the following cases to analyze timing of Assume At-I, ..., 20s; Av=1,...,50kmls which At is the

Nochange

Report Update information <

Figure 7: Activity diagram of reporting algorithms

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periodical time, Av is the constant ofspeed, v is vehicle speed.

For each At and Av. at each time t, i*At,

if (vti-vtiI>Av) then<Report>else<No-report>.

This definition means the REP recognizes vehicle speedperiodically, it will report if the vehicle speed is bigger than aconstant speed (figure 8B).

C. Algorithm C. Periodical reporting base on vehicledirectionThe report timing is defined as following:

/At =1,...,20s, lAr =1,...,900 which lAr is the constant angle, /Atis periodical time.

For each At and Ar. at each time t,=i*Atj ieN,

if (rtj-rtj l>Ar) then<Report>else <No-Report>.

This definition means the REP recognizes the angle of vehicleperiodically and will report if the angle is bigger than aconstant angle (figure 8C).

D. Algorithm D. Report on speed changed comparing thelast report.The report timing is defined as following:

Using same /At and AIv as Algorithm B,Assume the last time ofreport is ti,if (Vti+]-Vti < Av) then <No-Report>elseif (Vti+2-Vti >Av) then <Report>The speed of vehicle is calculated periodically. The REP onlyreports if the different between the speed of the car when itreported last time at regular interval and the current speed is

Start-to At 2*At i*At

more than a constant speed (figure 8D).

E. Algorithm E. Report on direction changed comparing thelast report.Similar with algorithm D, but in this case, the angle of

the vehicle is recognized periodically. The report timing isdefined as following:

Assume the last time ofreport is ti,

if (rti+,-rti < Ar) then <No-Report>

else if (rti+2-rti > Ar) then <Report>.

The definition means the REP only reports if the differentbetween the angle of the car when it report last time at regularinterval and the current calculated angle is bigger than aconstant defined angle (figure 8E).

F. Algorithm F. Combination D&ECombine two algorithms D and E, the speed and the

direction of vehicle is both calculated periodically. Thealgorithm F is defined as following:

If<AlgorithmD=true>or<AlgorithmE=true>then <Report> else <NoReport>This definition means the REP reports if the speed changedmore than a constant speed value or the angle of car changedmore than a constant value of angle.

G. Algorithm G. Add time delay ofreport to the interval timeIn this algorithm, we add a reporting time of the REP

terminal. Using same interval time At and constant of speed Avas previous algorithms, the report timing is defined asfollowing:

Assume the last time ofreport is tj,if (Vti-vY>Av) then <Report>and<Reset timer to O>

End(i+1)*At (i+2)*At k*At t(s)

A) R

B) vO=0R

C) ro=OR

D) v00°R

D) rO=ORto

G) vO=0R

R R ... R

vA,>Av v2At>Av ... V,At>AvR R R

rAt>Ar r2At>Ar ... riAt>ArR R R

vAf>Av v2At-vA Av ... vitt-vjAt>AvR R R

r>Arr2At-rAt>'Ar ..rA-rJA>A

At 2*At ... i*At

VAi>AvR

At-1,...,20s; Av=

V2At-VAt>AV -. ViAt-VjAt>AVR R

R

V(i,+)At<AVnR

r(+1)At<ArnR

V(i 1)At-Vi t<AvnR

R ... .R

V(,+2)At>Av ...

R

r(,+2)At>Ar ...

R

V(R+2)At-ViAvR

r(,+)At-rniAt<Ar r(,+2)t-r.At>ArnR R

to' At' 2*At'

VO -ViAt<Av vAt-ViAt<AV V2At-ViAt>AVnR nR R ...

vk 0

R

rk=O

... Vk=O

... rk=OR

to,,lo

(kmls)

(degree)

(kmls)

(degree)

t(s)

(kmls)

=1,...,50 kmls; Ar=1,..,900; R: Report; nR: No-Report I Time delay for report ofREPFigure 8: Report timing algorithms ofREP terminal

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else<cNo-Report>The definition means, similar to algorithm D, REP terminalreports when the different between the speed since the lasttime report and current speed is more than a constant definedspeed. After each time of reported, the REP will reset its timer(figure 8G).

H. Algorithm H. estimate periodically and reportDefinition. Assume the last time ofreport is tj, v is vehicle

speed, pi is vehicle position at time i, P is periodicallyestimation ofvehicle position at At, Ap is constant value I% to10'So, Av is constant speed ] to 50kmls

If(E lPe-Pi >Ap)or(vi-yj>Av)then<Report> else<NoReport>The definition means: we assumed there is a constant

value 10% of error equal to 35m. Algorithm H is to reportcurrent information of the automobile when the sum of errorsof longitude and altitude estimated periodically (At = 1 to 20seconds) is more than a specified constant value 1% to 10% orthe speed is changed Av (1 to 50km/h) comparing to the lastreport.

V. EXPERIMENT AND EVALUATION

To evaluate the algorithms relating to the various reporttimings, we established the experiment as follows. The REPterminal is assumed to use a cellular phone pocket PCMio168RS including GPS, Bluetooth communication. Themobile phone can receive GPS data using RMC sentence andit was programmed to report by the different algorithms withmany cases of traffic situations. Thus, the REP terminal islocated in a vehicle running on 3 different routes at differenttimes. The evaluation data was obtained by collecting GPSdata according to 5 times of the 3 routes for 10 minutes. Inorder to compare reporting timings to periodical reportingalgorithms, each algorithm collected data and evaluated theaccuracy A by the below formula:

A =d(p,t) d(po , t)d(p0,t) *0(0

100

98

96

94

> 92

m 90

< 88

86

84

82

800 6 8 10 12

Frequency of Report

Algorithm A Algorithm B

=Algorithm E --- Algorithm F

-Algorithm C - - Algorithm D

-Algorithm G Algorithm H

In which, Pi is the step of reporting interval with At=lto2Os,po is periodical reporting, d(p,t) is data acquired.The experiment is done with algorithm A, B, C, D, E, F, G andH. Figure 9 shows the result of experiment in the comparisonbetween frequency of report and accuracy. We identified thefollowing points:

To report every time the speed and the direction of vehiclechanged, algorithm B and C cause quite a lot frequency ofreports. When decreasing the frequency of report, the accuracyalso reduced. Using algorithm D and E it is possible to reducethe frequency of report compared with algorithm A, B and Cwith the same accuracy. Algorithm F analyzed speed and thedirection with the constant angle of 0, 45 and 90 degree. Theaccuracy is similar between cases. However, when changingdirection like the car going round a curve or changed the lane,the speed is decreased but the direction angle still less than theconstant angle, thus the algorithm timing becomes dependenton the speed. The algorithm D and G have similar accuracywhile changing the report timing. However, the algorithm D issimpler than G.

The algorithm H is able to decrease the report timing andkeeping the accuracy more than algorithm D. The experimentresult shows that the frequency of report can be optimum ifweaccept an error rate 500 of the sum of errors of longitude andaltitude estimated periodically of At=14s, and the speed ischanged Av=38km/s. The accuracy is kept from 98 to 9900.By the algorithm H, the network load can be able to reduceefficiently.

VI. CONCLUSION

The various algorithms for the report timing of REPterminal is discussed and experimented to resolve the networkload problem. After experiments, we found an optimumalgorithm about focusing on measuring the vehicle speed andits location in each route block, thus the algorithm becomesimple and the frequency to report can be optimum. The paperrevealed a possibility to deploy the REP terminal widely as thefirst step to achieve the implementation of the CREPE forfuture traffic control.

REFERENCES

[1] Matsuda, Roymatsu. 1996. "What is VICS? The New World of CarNavigation." Nikkan Kogyo Shimbun.

[2] Advanced Cruise-Assist Highway System Research Association(http:lwww.ahsra.or.jp)

[3] N. Vogiatzis, H. Ikeda, J. Woolley, Y. He, "Integrated Multi-nodaltraffic Network systems", Journal of the Eastern Asia Society forTransportation Studies, Vol.5,October, pp. 2092-2107 (2003)

[4] H. Ikeda, N. Vogiatzis, W. Wibisono, B. Mojarrabi, and J. Woolley."Three Layer Object Model for Integrated Transportation System". 1stInternational Workshop on Object Systems and Systems Architecture,Victor Habor, Australia, 2004.

[5] Nguyen Thanh Hung, Hideto Ikeda, Nikolaos Vogiatzis and Zin Lin,"New Environment CREPE for transportation control and itseffectiveness", in Proc. IMAIECS 2006 Conf ofEngineers and ComputerScientists, Hong Kong, 2006, ISBN:988-98671-3-3, pp.790-796.

Figure 9: Frequency of report and accuracy

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