GB2361794A - Data transmission between vehicles and a control centre - Google Patents
Data transmission between vehicles and a control centre Download PDFInfo
- Publication number
- GB2361794A GB2361794A GB0109837A GB0109837A GB2361794A GB 2361794 A GB2361794 A GB 2361794A GB 0109837 A GB0109837 A GB 0109837A GB 0109837 A GB0109837 A GB 0109837A GB 2361794 A GB2361794 A GB 2361794A
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- vehicles
- centre
- event
- control centre
- transmission
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- G—PHYSICS
- G07—CHECKING-DEVICES
- G07C—TIME OR ATTENDANCE REGISTERS; REGISTERING OR INDICATING THE WORKING OF MACHINES; GENERATING RANDOM NUMBERS; VOTING OR LOTTERY APPARATUS; ARRANGEMENTS, SYSTEMS OR APPARATUS FOR CHECKING NOT PROVIDED FOR ELSEWHERE
- G07C5/00—Registering or indicating the working of vehicles
- G07C5/008—Registering or indicating the working of vehicles communicating information to a remotely located station
-
- G—PHYSICS
- G08—SIGNALLING
- G08G—TRAFFIC CONTROL SYSTEMS
- G08G1/00—Traffic control systems for road vehicles
- G08G1/09—Arrangements for giving variable traffic instructions
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Mobile Radio Communication Systems (AREA)
- Traffic Control Systems (AREA)
Abstract
A method of controlling the data transmission from vehicles to a control centre comprises the vehicle receiving an interrogation message and using a statistical distribution function to delay the transmission from each vehicle to avoid exceeding the available bandwidth of the communication network. The interrogation message maybe a broadcast or multicast message. The statistical function contains a free parameter which is controlled by the control centre and is transmitted to the vehicle. The value of the parameter is set such that within a predetermined time period a sufficient number of vehicles have responded to ensure that the detection of an event by the vehicles is a statistical certainty. When the point of certainty has been reached the control centre notifies the vehicles and further transmissions are inhibited. The control centre may also set a maximum time for reply by the vehicle. The interrogation message my include a transmission control signal to request vehicles to transmit either on a positive occurrence of an event, constantly or both.
Description
2361794 METHOD OF DATA TRANSMISSION BETWEEN VEHICLES AND A CONTROL CENTRE
The present invention relates to a method of controlling the instants of transmission of data concerning events detected by vehicles of a vehicle group, especially a random sample vehicle group, to a control centre.
Road traffic services exist based on transmission to a control centre of data which arise or are ascertained in the vehicle and which were not previously used or were used only locally in the vehicle. In the control centre such data are linked with data from other vehicles and conclusions are derived. The vehicles are, for example, random sample vehicles of a vehicle group which can comprise not only vehicles connected in organisatorial manner, but any desired vehicles, for example all vehicles simultaneously travelling on a given road network. Examples of corresponding services include: traffic jam detection, accident detection and provision of data to enable conclusions to be drawn about the state of the weather. Services of that kind are termed "Floating Car Data".
The certainty of the conclusions can be increased if reference is made to a large number of vehicles. On the other hand, interrogations of that kind are problematic, as costly mobile radio technologies, which are limited in their capacity, have to be used. Thus, a compromise is necessary between the number of transmission and the level of certainty.
Transmission of the results of the evaluations of the control centre to the vehicles (this transmission is termed "downlink" in the following) can be sent by way of either a broadcast channel (for example, DAB, GSIVISIVIS-CI3) or a point-to-point connection (for example, mobile radio, GSMBS, GSM-SMS-PtP). These transmissions in downlink can also be used for control of the transmissions from the vehicles to the control centre (termed "uplink" in the following).
Control of uplink transmissions can firstly be organised periodically, for example if vehicles transmit their data according to a defined, service-specific time period or path. Secondly, uplink transmissions can be undertaken in event-controlled manner, perhaps when defined events are detected by the vehicle, for example travel standstill on the motorway. Periodic or event-controlled organisation of the uplink transmission is described in, for example, DE-C-195 13 640.
2 The known methods work well in many applications, but there are also applications which are inadequate or break down. In particular, in the case of interrogations sent by the control centre to the vehicles the risk exists in the organisation of the data transmissions that numerous vehicles occupy the mobile radio system within a short time and the vehicles transmit corresponding reports about an actual event to the control centre. Narrow-band mobile radio services can thereby be overloaded, but transmission systems with sufficient performance capability would cause high transmission costs.
Moreover, the known methods generate a very high management and processing cost.
It would thus be desirable to achieve a reduced loading of the transmission system with a data certainty which is as high as possible.
According to the present invention there is provided a method of controlling the instant of transmission to a control centre of data concerning events detected by vehicles of a vehicle group, especially a random sample vehicle group, characterised in that the control centre communicates an interrogation message to vehicles of a vehicle group and each vehicle on the interrogation message transmits the data to the control centre delayed in time in correspondence with a statistical distribution function.
The reference "event" comprehends a change in state, for example if a state detected by vehicles no longer corresponds with data transmitted by the control centre to the vehicles.
Thus, in response to an interrogation by the control centre, new data are transmitted to the centre not immediately, but delayed by a time period established on the basis of a distribution function, i.e. produced randomly or calculated pseudo-randomly. The interrogation is realised by transmission of an interrogation message by the control centre to the vehicles to be interrogated. Due to the simultaneous or largely simultaneous interrogation of a number of vehicles the detection of events by the individual vehicles is triggered and the ascertained data is transmitted to the control centre with a delay. By virtue of this method not only the number of transmissions, but also the operating effort for management of the data, vehicles and states can be substantially reduced by statistical displacement of the transmission times into the future. As the statistical distribution function according to which this happens is known in the control centre, the centre can recognise a reported event as correct after relatively few reports.
3 The interrogation message from the control centre to the vehicles of a vehicle group is preferably carried out in the form of a broadcast message or in the form of a multicast message.
In the case of the broadcast message, all vehicles in the reception range of the interrogation message are addressed, insofar as they fulfill the necessary technical and organisatorial requirements, and are prompted by the interrogation message to detect relevant events and to communicate ascertained data concerning the events to the control centre in statistical distribution and delayed in time. If the interrogation message is in the form of a broadcast message, a Wide-ranging random sample vehicle group is addressed and accordingly the uplink transmission channels are substantially loaded, but by virtue of the random time delay this loading can be kept to an acceptable level. For example, the traffic density or the number of road users in the reception range can also be calculated or estimated in advantageous manner by an interrogation message in the form of a broadcast message.
If the interrogation message has the form of a multicast message, a subquantity of all possible vehicles in the reception range can be addressed. The vehicle group addressed by a multicast message thereby represents a proportion of the vehicle group addressed by a broadcast message. The realisation of a multicast message preferably takes place on the basis of a selective criterion which is transmitted to the vehicles in the reception range together with the interrogation message and by means of which only the vehicles satisfying the selection criterion are selected and thus only those vehicles transmit the relevant data to the control centre by way of their uplink channel. A possible example of an interrogation message in the form of a multicast message has the following content: 1f the vehicle is located on a motorway, transmit the actual vehicle speed to the control centre". Through this form of interrogation it is ensured that only vehicles located on a motorway transmit their speed data - detected, for example, by a navigation apparatus as a sensor - to the control centre. Apart from this form of conditional multicast message, other forms of a multicast message are possible.
In one preferred variant of data detection, data are ascertained by an appropriately constructed sensor directly before the random transmission instant, which is individual to the vehicle, to the control centre. In another preferred variant the data for detection of the interrogation message are obtained by the sensor and are transmitted to the control centre at a random later instant individual to the vehicle. In the case of the first variant, the most 4 up-to-date data are transmitted on each occasion, which is of significance especially for rapidly changing events, whilst in the case of the other variant it is ensured that the instant of detection of the event by the sensors of the addressed vehicle group is uniformly fixed. Thus, a snapshot of the events is obtained.
In a preferred example of the method the statistical distribution function is a predetermined distribution function with at least one free parameter for which the control centre selects a concrete parameter value which it transmits to the vehicles. It is thereby possible to manage with one basic distribution function for all kinds of events, which function can be readily adapted to the special requirements for correct recognition of specific events.
In that case, the concrete parameter value is preferably selected so that, within a predetermined time after detection of an event by several vehicles, statistically so many vehicles transmit data with respect to the event that there exists in the control centre a predetermined statistical certainty that the event has actually occurred.
A negative exponential or equipartitioned distribution function is preferably used as the statistical distribution function.
As soon as the control centre has received such a number of reports concerning an event that the predetermined statistical certainty exists that the event has actually occurred, it can feed back a stop report to the vehicles. Vehicles which detect this and have not yet transmitted then no longer transmit, so as to avoid redundant reports in the uplink.
Alternatively, it is possible to manage without a stop report to the vehicles if the control centre establishes in advance a maximum delay time for the transmission of data and communicates this to the vehicles and W vehicles which establish a delay time longer than the maximum delay time do not transmit.
According to one preferred example of the method the interrogation message contains a control signal by which the vehicles are so controllable that they undertake a data transmission to the control centre only in the case of positive ascertaining of an event to be detected. In this case, no data transmission from the vehicles to the control centre takes place in the absence of the positive event. Through this formation of the interrogation message together with a corresponding control signal it is possible to further reduce the number of uplink data transmissions in conjunction with the statistically delayed data transmission in a specific time period. As this procedure corresponds with the detection of states of a randomly drawn sample from a quantity of vehicles, conclusions about the states of the entire quantity can be drawn by means of suitable statistical methods, for example, hypothesis tests.
According to another advantageous example of the method there is transmitted with the interrogation message a control signal by which it is ensured that the vehicles transmit to the control centre the data, which are ascertained by virtue of the interrogation message, independently of the kind of data. A high degree of data reliability is thereby achieved. Moreover, a reliable estimation of the number of interrogated vehicles is obtained. This magnitude is of significance for the establishing of the predetermined distribution function, which preferably takes place by way of a free parameter, which is defined by the control centre and transmitted to the vehicles, of the function.
It has proved particularly advantageous to provide the interrogation message with a control signal by which the vehicles are controllable in such a manner that they communicate event-related data to the control centre either only in the case of presence of a positive event or constantly, thus independently of the presence of a positive event. Through this alternative possibility of control of the detection and transmission units in the vehicles, the respective advantages of the two modes of operation can be selected in dependence on the particular form of event detection.
Examples of the present invention will now be more particularly described with reference to the accompanying drawings, in which:
Fig. I is a diagram showing the basic sequence of a method exemplifying the invention; and Fig. 2 is a flow chart showing the sequence for determination of parameters of a random distribution by which vehicles calculate transmission time instants in performance of the method.
In the following description the basic method is a "Floating Car Data" service in which vehicles transmit data (uplink) when they have been required to do so by a control centre by means of an interrogation message (downlink). In that case the uplink communications
6 are transmitted from the vehicles to the control centre delayed in time on each occasion in correspondence with a statistical distribution.
When the control centre receives communications, it waits until such a number of communications has been received as to permit conclusions to be made with a sufficiently high statistical certainty. In that case, the transmissions must arrive within a servicespecific time period. The control centre then signals to the vehicles a recognised change in state. All vehicles which have not transmitted up to then do not transmit.
For the avoidance of cumulative or avalanche-like transmissions on the uplink channels it is ensured that the transmission instants of the vehicles are randomly delayed. Through statistical displacement of the transmission instants into the future in combination with a time limit after which transmission no longer takes place (for example, stop report), a significant reduction in the transmission volume on the uplink channel can be achieved.
The vehicles delay the instant of transmission on the basis of a statistical distribution which is known to the vehicles and the control centre and the parameter of which is calculated by the control centre and communicated to the vehicles.
Through the known statistical distribution and the parameter settings, which are known not only to the vehicles but also to the control centre, of the distribution, the control centre can calculate a statistical certainty for the occurrence of the event.
A fundamental model which defines magnitudes necessary for calculations and illustrates the mathematical equations describing an example of the method is described in the following:
Fig. 1 illustrates, by way of a model, the steps of the method:
1. A number N of vehicles is disposed in a relevant geographical region reachable by a transmitted interrogation message from the control centre. Triggered by the interrogation message received at an instant to, the vehicles detect, with the aid of appropriate sensors, an event which triggers a transmission to the control centre of data within a "Floating Car Data" service.
7 2. The vehicles transmit the demanded and ascertained data delayed in time to the control centre. An algorithm determines the delay in time by generating a pseudo random number in correspondence with the known distribution function. The control of the parameter of this algorithm is carried out as described further below. The delay time of the individual vehicles is moreover described by a random variable T , The control centre has a sufficiently accurate estimation value N of the number of vehicles, for example through a previous recording of the vehicles at the control centre. By way of example, transmission time instants of individual vehicles are denoted in Fig. 1 by arrows perpendicular to the time axis.
3. The control centre receives communications from the vehicles and waits until a sufficiently large number a of communications has been received in order to detect the event with sufficient statistical certainty cr. The instant at which the control centre recognises the event as statistically certain is denoted in Fig. 1 by td. The control centre then transmits a state change report back to the vehicles.
4. At an instant tf in Fig. 1, all vehicles have received the report back. If a vehicle has not transmitted the uplink communication up to then, the transmission is inhibited.
As an alternative to the active feedback to the vehicles from the control centre, it is also possible for the centre to preset a time up to which the vehicles transmit. This means that the control centre determines a sufficiently long time period T, and transmits this to the vehicles participating in the service, for example together with the parameter values for calculation of the pseudo random number. The vehicles transmit only when the ascertained delay times are smaller than T, All transmission processes moreover take place delayed in time. In this manner the vehicles are independent of the feedback of the changed state from the control centre.
Calculation of the parameters of the random distribution, by which the vehicles calculate the transmission instant, in the control centre is now described by reference to Fig. 2.
If the vehicles, triggered by the interrogation message communicated by the control centre, detect an event, inclusive of a change in state relative to an earlier state, then they do not transmit immediately, but calculate on the basis of a distribution function a pseudo random number which represents a measure for delay of the data transmission.
8 In general the distribution function must have a free parameter 1 which is preset by the control centre for control of delay times. The distribution function can be realised by, for example, a negative exponential distribution with the parameter 1.
The parameter A. is calculated by the control centre and communicated to the vehicles as follows:
The control centre defines a time period td (detection time) within which at least a number a of the N vehicles should have reported the event with the probability a to the control centre. % depends on the kind of service and on the distribution of the time which elapses until the vehicles detect the event. A longer detection time is made possible for a rain warning than for, for example, an emergency call.
2) Based on the given parameters N (number of vehicles), a (number of required reports for the detection), td (maximum time period for recognition of the event with the probability a) and the given distribution for the time T, the control centre can calculate the parameters for control of the probability distribution (here X).
3) The calculated parameter values are now communicated to the vehicles in the area concerned together with the interrogation message.
4) Subsequently, the event is detected by means of sensors in the vehicles and the thereby ascertained data are transmitted to the control centre by the vehicles, which detect this event, delayed in accordance with a statistical distribution function in such a manner that within the time tdat least the given number a of reports with the probability ain arrive at the control centre.
The control centre thus controls the calculation of the waiting times of the vehicles in such a manner that within the time td at least a vehicles have transmitted the communications with the probability a.
The procedure described here is in principle suitable for the determination of a degree of freedom of any desired random distribution.
9 Thus, not all N vehicles transmit the detected event. The number n of transmitting vehicles must be greater than a. How large the number n is depends on: the distribution according to which the transmission time instant of the data is determined, the duration until the control centre has received the a communications, processed them and transmitted the report back to the vehicles or until these have been evaluated by the vehicles, and the transmission duration of the communications in the uplink.
The starting point in this model is that the control centre either knows the number N of the vehicles concerned or has at least an estimated value N.
Table I below provides an overview of the magnitudes used in the above calculation of L Table 1
Magnitude Description Commentary
N Number of vehicles concerned Control centre detects N, for example through recording of the vehicles at the control centre a Necessary number of reports Control centre ascertains this value. The for detection of the event value a depends on the form of the service and on N.
Probability by which an event This value is preset. It depends on the within a predetermined time form of service.
has to be detected td Time after which an event with Depends on the form of service.
the probability a has to be detected tf Time until report back of the Depends on the speed of the return event in downlink channel.
In summary, the afore-described example of the method may enable a reduction in the number of transmissions in uplink in the case of substantially simultaneous detection of events, in that, in response to an interrogation message in downlink the vehicles transmit not immediately, but statistically delayed in time. This method is advantageous in order to reduce the expensive communication by way of mobile radio systems, to not overload narrow-band communication systems and to nevertheless allow the control centre a statistical certainty about the detection of an event.
11
Claims (10)
1. A method of data transmission between vehicles and a control centre, comprising the steps of transmitting an interrogation message from the centre to vehicles in a vehicle group and transmitting data relating to events detected by the vehicles to the centre in response to the message, but with a delay in time dependent on a statistical distribution function.
2. A method as claimed in claim 1, wherein the interrogation message is a broadcast message or a multicast message.
3. A method as claimed in claim 1 or claim 2, wherein the function is a predetermined function with at least one free parameter for which the centre selects and transmits to the vehicles a concrete value.
4. A method as claimed in claim 3, wherein the value is selected so that within a predetermined time after detection of an event by a plurality of vehicles/ transmission of data concerning the event to the centre will have been undertaken by such a number of the vehicles that a predetermined statistical certainty that the event has actually occurred will exist in the centre.
5. A method as claimed in claim 4, comprising the steps of transmitting from the centre to the vehicles a notification of the existence of said certainty and inhibiting further transmission of said data concerning the event from the vehicles to the centre in response to receipt by the vehicles of the notification.
6- A method as claimed in any one of claims 1 to 4, comprising the step of transmitting from the centre to the vehicles a maximum delay time determined in advance by the centre and inhibiting transmission of data concerning the event to the centre from vehicles establishing a delay time longer than the maximum delay time.
7. A method as claimed in any one of the preceding claims, wherein the function is negatively exponential or equipartitioned.
8. A method as claimed in any one of the preceding claims, comprising the step of so controlling the vehicles by way of a control signal included in the interrogation message 12 that the vehicles transmit data to the centre only in the case of positive presence of a predetermined event condition.
g. A method as claimed in any one of claims 1 to 7, comprising the step of so controlling the vehicles by way of a control signal included in the interrogation message that the vehicles constantly transmit data concerning the event to the centre.
10. A method as claimed in any one of claims 1 to 7, comprising the step of so controlling the vehicles by way of a control signal included in the interrogation message that the vehicles transmit data concerning the event to the centre either constantly or only in the case of presence of a positive event.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10020253A DE10020253A1 (en) | 2000-04-25 | 2000-04-25 | Method for controlling the transmission times of data relating to events that are detected by vehicles |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB0109837D0 GB0109837D0 (en) | 2001-06-13 |
| GB2361794A true GB2361794A (en) | 2001-10-31 |
| GB2361794B GB2361794B (en) | 2002-05-22 |
Family
ID=7639888
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0109837A Expired - Fee Related GB2361794B (en) | 2000-04-25 | 2001-04-20 | Method of data transmission between vehicles and a control centre |
Country Status (3)
| Country | Link |
|---|---|
| DE (1) | DE10020253A1 (en) |
| FR (1) | FR2808110B1 (en) |
| GB (1) | GB2361794B (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1912191A1 (en) * | 2006-10-12 | 2008-04-16 | Aisin AW Co., Ltd. | Navigation system |
| WO2009049969A1 (en) * | 2007-10-10 | 2009-04-23 | Robert Bosch Gmbh | Method for detecting information |
| WO2015042776A1 (en) * | 2013-09-24 | 2015-04-02 | Harman International Industries, Incorporated | Message broadcasting in vanet |
| GB2543888A (en) * | 2015-07-30 | 2017-05-03 | Ford Global Tech Llc | Improvements in or relating to distributed vehicular data management systems |
| DE102016003969A1 (en) * | 2016-04-01 | 2017-10-05 | Audi Ag | Method for acquiring environmental data by means of several motor vehicles |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10126618B4 (en) * | 2001-05-31 | 2007-03-08 | Siemens Ag | Method for exchanging status information via direct radio links between subscriber terminals |
| DE10315164A1 (en) * | 2003-04-02 | 2004-10-14 | Endress + Hauser Gmbh + Co. Kg | Method for the approximate determination of a measurement time and corresponding device |
| DE10359836A1 (en) * | 2003-12-19 | 2005-07-21 | Daimlerchrysler Ag | Data transmission method for transferring information between a motor vehicle's networked terminals and a mainframe located outside the vehicle uses a mobile telephone network log-in routine |
| KR20200029201A (en) * | 2018-09-10 | 2020-03-18 | 현대자동차주식회사 | Method and apparatus for v2v communication |
Citations (3)
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|---|---|---|---|---|
| US5164904A (en) * | 1990-07-26 | 1992-11-17 | Farradyne Systems, Inc. | In-vehicle traffic congestion information system |
| US5812069A (en) * | 1995-07-07 | 1998-09-22 | Mannesmann Aktiengesellschaft | Method and system for forecasting traffic flows |
| US6061625A (en) * | 1996-02-08 | 2000-05-09 | Mannesmann Ag | Process for obtaining traffic data |
-
2000
- 2000-04-25 DE DE10020253A patent/DE10020253A1/en not_active Withdrawn
-
2001
- 2001-04-20 GB GB0109837A patent/GB2361794B/en not_active Expired - Fee Related
- 2001-04-25 FR FR0105549A patent/FR2808110B1/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5164904A (en) * | 1990-07-26 | 1992-11-17 | Farradyne Systems, Inc. | In-vehicle traffic congestion information system |
| US5812069A (en) * | 1995-07-07 | 1998-09-22 | Mannesmann Aktiengesellschaft | Method and system for forecasting traffic flows |
| US6061625A (en) * | 1996-02-08 | 2000-05-09 | Mannesmann Ag | Process for obtaining traffic data |
Non-Patent Citations (4)
| Title |
|---|
| IEICE Transactions on Communications July 1994 Japan ISSN 0916-8516 Vol E77-B Pages 934-938 * |
| Pacific Rim Transtech Conference 1995 - SM Turner & D J Holdener * |
| Performance Analysis of Road Traffic Data Collection - J-P Linnartz & M Westerman * |
| Probe Vehicle Sample Sizes for Real Time Information: The Houston Experience. ISBN 0-7803-2587-7 * |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1912191A1 (en) * | 2006-10-12 | 2008-04-16 | Aisin AW Co., Ltd. | Navigation system |
| US8364391B2 (en) | 2006-10-12 | 2013-01-29 | Aisin Aw Co., Ltd. | Navigation system |
| WO2009049969A1 (en) * | 2007-10-10 | 2009-04-23 | Robert Bosch Gmbh | Method for detecting information |
| US8874309B2 (en) | 2007-10-10 | 2014-10-28 | Robert Bosch Gmbh | Method for acquiring information |
| WO2015042776A1 (en) * | 2013-09-24 | 2015-04-02 | Harman International Industries, Incorporated | Message broadcasting in vanet |
| US10097964B2 (en) | 2013-09-24 | 2018-10-09 | Harman International Industries, Incorporated | Message broadcasting in vanet |
| GB2543888A (en) * | 2015-07-30 | 2017-05-03 | Ford Global Tech Llc | Improvements in or relating to distributed vehicular data management systems |
| DE102016003969A1 (en) * | 2016-04-01 | 2017-10-05 | Audi Ag | Method for acquiring environmental data by means of several motor vehicles |
| DE102016003969B4 (en) | 2016-04-01 | 2019-02-21 | Audi Ag | Method for acquiring environmental data by means of several motor vehicles |
Also Published As
| Publication number | Publication date |
|---|---|
| GB0109837D0 (en) | 2001-06-13 |
| GB2361794B (en) | 2002-05-22 |
| FR2808110B1 (en) | 2005-12-30 |
| DE10020253A1 (en) | 2001-12-06 |
| FR2808110A1 (en) | 2001-10-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20060420 |