1、中文 3255 字， 1965 单词 英文翻译 下属学院 理工学院 专 业 电子信息工程 班 级 2012 年 3 月 8 日 A LOW COST REAL-TIME INTELLIGENT TAXIMETER SENSOR1 ABSTRACT A taximeter smart sensor system possessing immunity to fraud is introduced. The system is based upon embedded controllers employed to perform the crypto-operation between the s
2、ensor and taximeter using the standard RC5 algorithm. Special emphasis is given to promote highest system integrity while keeping complexity, size and cost to minimum. Preliminary practical implementation and verification of the system installed and tested under real taxicab environment promises its
3、 feasibility to cope with fraud in processing taxi fare. 1. INTRODUCTION For more than a decade, taximeter has been conceived as a ubiquitous device that allows cap passengers in big cities around the globe to avoid the hassle of begin overcharged. Practically all the meters implemented these days,
4、are based upon micro-controller systems. To process taxi fares, a motion sensor (such as a Hall-effect device) is installed between the gearbox and speedometer and whenever the vehicle is in motion it generates electrical pulses to the micro-controller based taximeter for fare calculation. The perio
5、ds of the generated pulse stream are inversely proportional to the vehicle instantaneous speed and the actual proportional constant depends upon the car model. As a result, the number of pulses released from the sensor over a certain time interval reflects the distance and this is employed by the me
6、ter to compute the fares 1,2. In fact, the integrity of the current taximeters has so long been in question due to the fact that the adopted system in use nowadays exhibits a critical loophole that may cause unreliability and allow faulty operation. The drawback is the system susceptibility to inter
7、ference either created by the nearby engine or artificially induced. This interference coupling onto the pulse cable routing between the sensor and the taximeter produces additional pulses superimposed on the original sensor signal. In this way, faked pulses created and injected at some points along
8、 the cable routing can effectively raise the taxi fare making the system vulnerable to fraud. To combat the pitfall, a real-time intelligent taximeter sensor system immune to the interference or fraud pulses is developed in this paper. The principal and detailed operations of the proposed system are
9、 outlined. Issues concerning synchronisation and implementation are also addressed. Finally, practical results and testing of the smart system in real environment are discussed. 2. SYSTEM OVERVIEW The overall block diagram of the introduced system is shown in Fig. 1. Essentially, the principle behin
10、d the development is to embed a small micro-controller into the sensor to allow the encryption of the sensors pulse stream before being transmitted along the routing cable. At the other end, another micro-controller of a similar type is also introduced to enable the decryption of the encrypted pulse
11、s. Principally, any type of encryption algorithms can be employed but the obvious criterion is to choose the one that would result in a minimum hardware burden but yet provide an acceptable security level. The proposed encryption process relies on the sampling of the original pulses over a chosen pe
12、riod by the encryption or transmitting controller. Subsequently, two sets of data are generated by encrypting the sampled pulses using two unique keys (denoted as A and B in Fig.1). For our 1 S.Jantarang, P.Potipantong, A.Worapishet. A LOW COST REAL-TIME INTEL LIGHT TAXIMETER SENSORJ. Circuits and S
13、ystems, 2002(2):217-220. designed system, key A and key B are selected pseudo-randomly from a set of 16 unique keys for good security, The resulting pair of encrypted data is then transmitted sequentially to the decryption or receiving controller along with the key number. With the assigned informat
14、ion of key A and key B, the receiving end is able to reconstruct the incoming sets of data. If there is no information distorted by any means along the transmission cable, the two sets of reconstructed pulses will be perfectly matched and one of them will then be delivered to the taximeter for furth
15、er fair processing. However, any discrepancies are detected between the two reconstructed pulses；the output to the taximeter will be kept at logic “0” ceasing the increment of the fare as if the vehicle is immobile. Eventually, the whole process repeats for the next collection of the sampled pulses
16、in the transmitting controller. 3. DETAILED OPERATION AND TRANSMISSION PROTOCOL Most of the pre-installed sensors for taxis in the designated Bangkok metropolitan area typically output the pulse steam at the maximum of 6,750 pulses per km.If the highest car speed is limited to 200 km/hr, the shortes
17、t pulse period released is 2.67ms. This has been rounded down to 2ms giving the maximum pulse frequency of 500Hz. Illustrated in Fig.2 is the detailed transmission operation of the encryption controller where the original pulse stream from sensor is sampled at the intervals of 250us using the contro
18、llers interrupts. The intervals between each interrupt are denoted as “Slot”. The RC5 algorithm employed requires 16 sampled pulses per one encryption and this sets the number of slots in one transmitting cycle (and the receiving cycle) to 16 indicated as Slot 0 to Slot 15 in Fig2 and thus the perio
19、d per one cycle is 4ms. The transmitter begins with idle state at Slot 0. During Slot 2 and 4, the stored 16-bit sensor data sampled in the previous operating cycle is encrypted using the pre-assigned key A and key B respectively, resulting in two sets of 16-bit encrypted data. Each key is 64-bit lo
20、ng and is selected in a pseudo-random fashion from the total of 16 unique keys. The resulting RC5-encrypted data is subsequently arranged into four collections of 8-bit data before being transmitted along with the associated key numbers (0-15) to the receiving controller at Slot 3, 5, 9 and 11. Fig.
21、3 shows the data frame for each transmission slot, starting with a start bit followed by the (high or low byte) 8-bit encrypted data, (high or low byte) 2-bit key number and ending with a stop bit. The data transfer rate is 100 kbitskec. To facilitate synchronisation betwem the two ends, a synchroni
22、sing data is generated during ,Slot 6.Upon completing the transmission cycle, the sync data is forwarded to the receiving-end controller during Slot 15 to align the start of the next decryption operation in the receiving end with that in the transmitting encl. The detailed synchronisation operation will be discussed in the next section. From Fig.2, it can be seen that the remaining of the
