High-speed CAN communication system using passband modulation

Disclosed is a high-speed controller area network (CAN) communication system, which is compatible with a CAN communication system, using passband modulation. The system includes: a high-speed CAN controller configured to provide a standard CAN transmission bit stream and a high-speed CAN transmission bit stream; and a high-speed CAN transmitter configured to synthesize a passband CAN signal obtained by modulating the high-speed CAN transmission bit stream in a passband and a standard CAN signal based on the standard CAN transmission bit stream and to transmit it to a CAN bus.

CROSS REFERENCE TO PRIOR APPLICATION

This application is a National Stage Patent Application of PCT International Patent Application No. PCT/KR2014/009258 (filed on Oct. 1, 2014) under 35 U.S.C. § 371, which claims priority to Korean Patent Application No. 10-2013-0117684 (filed on Oct. 2, 2013), which are all hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The following description relates to a controller area network (CAN) communication system, and more particularly, to a high-speed CAN communication system in which an existing standard CAN transmission signal is transmitted with a modulated signal in order to obtain higher transmission rate while maintaining compatibility with an existing CAN communication system.

BACKGROUND ART

A controller area network (CAN) communication system is an in-vehicle network system for providing digital serial communication between various measurement and control apparatuses in a car. The CAN system reduces the weight and complexity by replacing complex electric wirings and relays of electric components in the car with efficient serial communication lines. The CAN system was developed using a network protocol for cars in 1980. Its protocol has excellent real-time control performance, is easy-to-implement, and widely used in the manufacturing industry, aviation, railways, and vehicles. CAN is established as a standard ISO 11898 by the International Organization for Standardization (ISO).

A typical structure of a CAN message includes a 1-bit start of frame (SOF) field, a 12-bit arbitration field, a 6-bit control field, a maximum 64-bit data field, a 16-bit cyclic redundancy check (CRC) field, a 2-bit acknowledge (ACK) field, a 7-bit end of frame (EOF) field, and a 3-bit inter frame space as illustrated inFIG. 1. The number of bits in each field is assigned according to the standard. Bits specified by 0 and 1 in a frame of the CAN message ofFIG. 1are transmitted on the CAN bus with a value specified in the standard. The standard allows for using a total 29-bit identifier by adding 18 bits to the 11-bit arbitration field.

The SOF field is transmitted first to indicate the start of the frame. The arbitration field following the SOF field includes either an 11-bit identifier or a 29-bit extended identifier and a remote transmission request (RTR) bit. The identifier field specifies a processing priority of the CAN message frame transmitted when communicating in the CAN. In order for the arbitration field to determine the priority, a unique identifier or identification number is assigned for each message of CAN data generated in each CAN controller. When the RTR bit has a value of “0” (default), it means that the CAN message contains data frame, and when the RTR bit has a value of “1,” it means that the CAN message contains remote frame. A remote frame is used when one node on a CAN bus requests data transmission from another node, and does not include a data field.

The control field is configured of 6 bits including 4 bits of data length code (DLC) which indicates the number of bytes of the data field and reserved bits R1and R2having a value of “0” to be used later.

The data field includes data to be transmitted from one node to another node with a maximum of 64 bits in length. The CRC field are used for checking cyclic redundancy and is made of 15 bit code and one delimiter bit having a value of “1” which indicates the end. The ACK field is composed of 2 bits. A receiver which has received a valid message correctly reports this to the transmitter by sending a value of “0” during the first slot bit. The second bit has a value of “1.”

The EOF field is configured of 7 bits all having values of “1.” The 3-bit inter frame space all having values of “1” follows the EOF field. After the 3-bit inter frame space, any node seeking to transmit may use the CAN bus. The node seeking to transmit may attempt to secure the bus by transmitting the SOF field. Following the SOF field, 11-bit or 29-bit identifier is transmitted to the CAN frame. Based upon the identifier, only related receiving nodes are enabled for reception while the other nodes go inactive unless exceptional event such as error occurs.

Two or more nodes may start the transmission simultaneously. In this case, the CAN standard provides multiple access arbitration scheme on the CAN bus. In the CAN standard, a carrier sense multiple access with bitwise arbitration (CSMA/BA) method is used for multiple access. Each of the nodes transmits the identifier after the SOF transmission, and drives the CAN bus with a logic level 0 or 1 according to a value of the identifier. The logic level 0 is referred to as dominant, and the logic level 1 is referred to as recessive. For example, it is assumed that the first node drives the identifier bit with dominant, and the second node drives the identifier bit with recessive. Thus, when two nodes drive the identifier bit with dominant and recessive at the same time, the state of the bus becomes a dominant state. The second node detects that the transmitted bit and the bit received from the bus are different indicting that its message has lower priority and subsequently stops the driving of the bus. As a result, it may be seen that a message having a small value of the identifier (ID) has a higher priority.

The node which obtains right to use the bus through the identifier competition may transmit a maximum of 64 bits during the data field. In order to determine a sampling time during the bit interval, the receiver detects bit transition from the logic level 0 to 1 or from the logic level 1 to 0. In order to ensure that the transition always occurs in a predetermined interval, when the same five or more bits are transmitted, a bit transition of different value is inserted after 5 consecutive same bit transmission. For example, when five bits of “1” are transmitted consecutively, a single bit transmission of “0” is transmitted on the CAN bus after 5 bit transmission and is removed in the receiver. The receiver detects the edge using a change of the bit transmission, and performs the bit detection by sampling after a predetermined offset time. The offset should be set to an appropriate value according to a delay of the system and the like.

Recently, demand for high-speed data transmission, specifically in vehicles including multimedia devices and the like, is increasing. Introduction of an additional high-speed standard transmission method other than the existing CAN interface may be considered. However, new scheme requires additional cable installation increasing vehicle weight and manufacturing costs. Therefore, recently, methods of increasing the data transmission rate based on the CAN standard have been proposed.

First, in order to improve the data transmission efficiency while maintaining the transmission rate of 1 Mbps in the CAN communication system, an efficient scheduling method through a channel delay analysis has been proposed. Additionally, methods for transmitting data at high speeds by overclocking have been proposed. In these methods, the data rate is increased during the overclocking period. However, the period for high data transmission is decreased compared to other standard CAN transmission period. Hence, the overall transmission rate is not increased significantly. In order to perform the high-speed transmission by increasing the data transmission interval by overclocking, a technique related to a CAN with flexible data-rate (CAN-FD) has been proposed. This is a technique in which the overclocking is performed with a maximum of 16 MHz in the data field after acquiring the bus right through the SOF and identifier transmission. After the data field transmission is completed, the rate is returned to an existing CAN rate of 1 Mbps. When CAN-FD devices operate along with the existing CAN devices, existing CAN receivers detect multiple edges in one-bit interval of 1 μs in CAN standard and report errors. Since the compatibility with the existing CAN receivers is not maintained, the CAN-FD scheme should be used between the nodes that support the CAN-FD method.

A method for maintaining the compatibility with the existing CAN receiver during high-speed transmission by overclocking like the CAN-FD method has been proposed. In this method, a high-speed clock is not transmitted over the entire bit interval of 1 μs. Instead, the clock is increased only in a gray zone where the existing CAN nodes do not perform the edge detection in order to maintain compatibility. However, since the data is not transmitted at high speeds over the entire bit interval, the rate is lower than that in the CAN-FD scheme.

All the above-proposed methods increase the rate by overclocking. However, since there is a limit to increasing the clock in the transmission method through the edge detection and the sampling according to the CAN standard and a response of a high-frequency band is limited due to a general frequency characteristic of a channel, it is difficult to ensure reliable reception when using the high-speed clock. In order for the receiver to perform the edge detection and the sampling, the receiver should receive a waveform as close to a rectangular one as possible. When using the high-speed clock, it is difficult for the receiver to completely receive the rectangular waveform, and thus the edge detection and bit detection performance is degraded. Therefore, a maximum rate of the CAN-FD that is being proposed currently is about 16 Mbps.

The present invention is a method in which a passband modulation signal for high-speed data transmission is transmitted in addition to the existing CAN signal that is transmitted in the same way as the CAN standard, and the compatibility with the existing CAN is maintained while enabling high-speed data transmission.

According to the increase of the bandwidth requirement for a vehicle and a controller, multimedia applications that cannot be supported by the existing CAN communication system are on the rise. The installation of a high-speed network in order to address this problem is very expensive. Specifically in the case of a vehicle, the increase in the weight and cost of the vehicle due to installation of additional cables can be prohibitive.

As vehicles become more sophisticated, electronic control apparatuses and multimedia apparatuses increase, and a huge amount of cabling is required to connect these separate apparatuses with each other. The cables take a significant part of the overall vehicle weight and manufacturing costs, posing issues in the reliability and component quality management. Hence, fundamental countermeasures are necessary to meet the challenges.

FIG. 2illustrates a CAN communication system used in a conventional vehicle and the like. Each node on the CAN communication system includes a CAN controller, and the CAN controller may perform transmitting and receiving of a standard CAN bit stream, and serves to generate a standard CAN frame, process an identifier, transmit data, and perform error processing, and the CAN transceiver serves to load actual bits with dominant and recessive bits onto a CAN bus. In general, a differential signal is used for robustness to errors. When the recessive bit is transmitted, in general, the corresponding node does not drive the bus, and thus a state of the bus is set to return to a default value. When another node drives the bus in this state, the state of the bus changes to the one that the driving node specifies.

FIG. 3illustrates a bus driving signal of the CAN transceiver illustrated inFIG. 2. The dominant signal corresponds to a bit0, and the recessive signal corresponds to a bit1. When the dominant signal is transmitted, the corresponding node transmits the signal to the bus, and when the recessive signal is transmitted, the corresponding node does not load the signal onto the bus. When the CAN nodes simultaneously drive the dominant and the recessive in the same bit interval, the state of the CAN bus becomes a dominant state. During the arbitration period, the node that transmits the dominant bit acquires the right to transmit the data on the bus, and the node that transmits the recessive bit waits until the bus is available later.

DISCLOSURE

Technical Problem

The present invention is directed to providing a high-speed controller area network (CAN) communication system in which an existing CAN transmission bit is transmitted in the standard CAN signal and high speed data bits are transmitted in a passband CAN signal obtained by modulating the data in a passband that is synthesized with the standard CAN signal, the synthesized signal is delivered to a CAN bus, and data transmission rate is increased while maintaining the compatibility with an existing CAN communication system in order to address the above-described problems.

Technical Solution

One aspect of the present invention provides a high-speed controller area network (CAN) communication system compatible with the existing CAN communication system. The high-speed CAN communication system using passband modulation includes a CAN controller which provides a standard CAN transmission bit stream and a high-speed CAN transmission bit stream and a CAN transmitter which synthesizes a passband CAN signal obtained by modulating the high-speed CAN transmission bit in a passband and a standard CAN signal to deliver them to a CAN bus.

Meanwhile, a high-speed CAN receiver on the bus receives the synthesized high-speed CAN signal and demodulates the passband signal among them, supporting high data rate.

Advantageous Effects

The technique to be described below significantly improves data transmission rate compared to the existing controller area network (CAN) system while it does not cause significant cost increase due to its compatibility with the existing CAN system, resulting in contribution to weight saving and data rate increase of target CAN system.

In the existing CAN standard, when the receiver receives a frame incompatible with the CAN standard, the receiver can transmit an error frame to stop the transmission. In the technique to be described below, the high-speed CAN communication system using passband modulation transmits a passband signal to only a dominant bit interval with limited amplitude. Accordingly, conventional CAN receivers located on the same bus receive the combined high-speed CAN signal as the standard CAN signal without generating frame error. Meanwhile, the high-speed CAN receiver that supports the high-speed CAN communication system recognizes and receives the passband signal in the high-speed CAN signal, and thus it is possible to receive data at a high speed. As a result, in the technique to be described below, the compatibility with the existing CAN standard is maintained.

Since the proposed high-speed CAN communication system is compatible with existing CAN communication apparatuses which are installed and in operation, applications that require high data rate such as multimedia can be gradually added thereto while maintaining compatibility with the existing CAN system in operation, and thus manufacturers such as car manufacturers can easily introduce and use them.

MODES OF THE INVENTION

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the accompanying drawings, only main components are illustrated in larger sizes for clarity of the present invention and additional components are omitted, and thus the drawings should not be interpreted as limiting.

FIG. 4illustrates a high-speed controller area network (CAN) communication system according to the present invention, and the high-speed CAN communication system includes a high-speed CAN controller100and a high-speed CAN transmitter200. The high-speed CAN controller100transmits a high-speed CAN transmission bit stream according to the present invention as well as a standard CAN transmission bit stream which is an existing CAN message frame to the high-speed CAN transmitter200.

The standard CAN transmission bit stream refers to data transmitted based on the CAN standard, and the high-speed CAN communication bit stream refers to data transmitted from the high-speed CAN communication system using passband modulation. The standard CAN transmission bit stream includes a start of frame (SOF) field, an arbitration field, a control field, a data field, a cyclic redundancy check (CRC) field, an acknowledge (ACK) field, an end of frame (EOF) field and an inter frame space field which are defined in the CAN standard.

Data transmitted at a high speed in passband may be a message frame based on any protocol. Further, it is also possible to use an interleaver and an error correction code for the reliable transmission and reception. Various formats may be used for the data transmitted using the high-speed CAN communication system transmitted in passband.

The standard CAN transmission bit stream is input to a passband CAN signal generator210, a signal synthesizer220, and a signal converter230.

The high-speed CAN transmitter200includes the passband CAN signal generator210, the signal synthesizer220, and the signal converter230.

The passband CAN signal generator210receives the high-speed CAN transmission bit stream to convert to a passband CAN signal. Since the standard CAN transmission bit is transmitted through a CAN bus5only when the standard CAN transmission bit is a dominant bit, that is, a bit0, the passband CAN signal generator210is enabled to receive the high-speed CAN transmission bit only when the CAN transmission bit is a dominant bit.

In the signal synthesizer220ofFIG. 5, a passband CAN transmission signal is input to the first signal selector222after being multiplied by a weight ASSin a multiplier221. The first signal selector222receives the standard CAN transmission bit stream as a control input, and outputs input port 0 when the control bit of the received bit stream is 0 and outputs input port 1 when the control bit of the received bit stream is 1. The standard CAN transmission bit stream is delivered as a control input of the second signal selector223, and outputs 1 V of the input port 0 when the control bit is 0 and outputs 0 V of the input port 1 when the control bit is 1. The output of the second signal selector223constitutes the existing standard CAN transmission signal. The standard CAN transmission signal is based on the standard CAN transmission bit stream delivered from the high-speed CAN controller100.

The outputs of the first signal selector222and the second signal selector223are combined in an adder224, and an output of the adder224constitutes the high-speed CAN transmission signal.

The signal converter230drives the bus only when the standard CAN transmission bit stream is in a dominant bit interval, and converts a single-ended signal to a differential signal to be delivered to the CAN bus5. The signal converter230stops the driving of the CAN bus5when the standard CAN transmission bit stream is in a recessive bit interval.

FIG. 6illustrates the passband CAN signal generator210illustrated inFIG. 4, and the passband CAN signal generator210includes a serial-to-parallel converter211, an I-signal mapper212, a Q-signal mapper213, the first pulse shaping filter214, the second pulse shaping filter215, a high-speed CAN signal modulator216, and a carrier wave generator217.

The high-speed CAN bit stream which is an input of the signal generator is input with a rate R (R>1 Mbps) higher than a rate of 1 Mbps of the standard CAN bit stream. The serial-to-parallel converter converts the high-speed CAN bit stream to two streams for passband transmission, the first stream is applied to In-phase (I) signal mapping, and the second stream is applied to Quadrature (Q) signal mapping. One or more bits may be loaded to an I-signal and a Q-signal according to a passband modulation method. For example, one bit may be loaded to each of the I-signal and the Q-signal when using a QPSK modulation method and two bits may be loaded to each of the I-signal and the Q-signal when using 16QAM. The symbol rate, fs, of each of the I-signal and the Q-signal becomes R/2 when using the QPSK, and becomes R/4 when using the 16QAM signal.

Since transmitting an integer number of passband symbols in 1-bit intervals of the standard CAN signal helps simplify the transmission system, it is advantageous for fsto set to n1MHz (where, n1is an integer of two or more). When using the QPSK, the bit0is mapped to 1, and the bit1is mapped to −1. When using the 16QAM, the bit00is mapped to −1, the bit01is mapped to −⅓, the bit10is mapped to ⅓, and the bit11is mapped to 1.

The pulse shaping filter is used to limit the out-of-band radiation of the passband signal, and a root raised cosine (RRC) filter or various pulse shaping filters may be used according to a frequency characteristic of the bus and the passband CAN standard modulation method. The mapped signal, which passes through the filer, is converted to SI(t) and SQ(t) which are band-limited signals. According to the CAN standard, since all nodes on the CAN bus5may drive the bus only when transmitting the dominant signal, the passband CAN signal is generated and transmitted only in the dominant bit transmission interval of the standard CAN signal.

The carrier wave generator217generates a carrier wave signal for a passband frequency fcof the passband CAN signal. As the passband frequency fcis increased, the separation between the standard CAN signal and passband signal in frequency domain is increased, reducing mutual interference. However, too high fcmay cause the signal to be severely attenuated due to high frequency attenuation effect of the channel. Therefore, the passband frequency fcneeds to be set to an appropriate value according to system requirements.

The modulator216performs the modulation as in Equation 1. φ represents a phase of the carrier wave. While fcmay be set to any value as an operation frequency of the carrier wave, it is advantageous for fcto be set to n2MHz (where, n2is an integer of two or more) in order to simplify the system. In this case, the carrier wave of the n2cycle fits into one standard CAN bit interval. For convenience of description, it is assumed that SSS(t) is normalized so that a maximum value is 1 V and a minimum value is −1 V.
sSS(t)=sI(t)*cos(2πfct+φ)+sq(t)sin(2πfct+φ)  [Equation 1]
The standard CAN signal inFIG. 5has a value of 1 V when the standard CAN transmission bit is 0 (dominant), and has a value of 0 V when the standard CAN transmission bit is 1. When it is assumed that the 1-bit interval of the standard CAN signal is TCANand the standard CAN bit is bkin (k−1)TCAN<t<kTCANinterval, the standard CAN signal SCAN(t) is expressed as Equation 2.

The signal synthesizer220may combine the passband CAN signal multiplied by the weight and the standard CAN signal, expressed as the following Equation 3.
ŝSS(t)=sCAN(t)+ASSsSS(t)  [Equation 3]

ASSrepresents the weight of the passband CAN signal, and in this case, it may be seen that the passband CAN signal has a maximum value of ASSV and a minimum value of −ASSV. The high-speed CAN signal ŜSS(t) which is the sum of the standard CAN signal and the passband CAN signal has the minimum value of 1−ASSV in an interval in which the passband signal is transmitted. Therefore, an appropriate ASSwhich satisfies a condition of 1−ASS>0.5 V should be selected so that the existing CAN nodes on the bus do not erroneously detect the signal as the recessive bit.

The signal converter230converts the single-ended signal to the differential signal to load it onto the bus as illustrated inFIG. 7.FIG. 7illustrates an example of the case of using the QPSK modulation as the passband modulation method.

In general, an amplitude of the CAN standard signal is 1 V based on the single-ended signal and is 2 V based on the differential signal. The passband CAN signal of the present invention is built such that the amplitude of ASSSSS(t) has a value in a range of tens of mV to hundreds of mV which is smaller than the CAN standard signal level of 1V. Accordingly, when the existing CAN nodes of the CAN bus5receive the passband CAN modulation signal during the dominant bit transmission interval, the level of the received signal does not become so small to cause erroneous detection. Since the transmitter drives the bus only when the CAN signal is in the dominant bit interval according to the CAN standard, the passband CAN signal is not loaded when the CAN signal is in the recessive bit interval. The signal synthesizer220synthesizes the passband CAN signal only in the dominant bit interval of the standard CAN bit stream for the compatibility with the CAN standard nodes, and does not synthesize the passband CAN signal in the recessive bit interval.

The high-speed CAN transmitter200may use a guard interval at the start portion and end portion of a consecutive transmission interval of the passband CAN signal. During the guard interval, the passband CAN signal may not be transmitted as in the example ofFIG. 8, or contain fixed signal as in the example ofFIG. 9, or repeat part of the passband CAN signal as in the example ofFIG. 10. The guard interval protects the passband CAN signal from interference caused by the abrupt transmission changes of the dominant bits and recessive bits at the start and end of consecutive transmission interval. The length of the guard interval may be changed according to the delay characteristic of the channel.FIG. 8illustrates the case in which the passband CAN signal is not transmitted during the guard interval.FIG. 9illustrates the case in which the fixed signal is transmitted during the guard interval.FIG. 10illustrates the case in which, when the passband CAN signal includes a signal1, a signal2, and a signal3, the signal3is repeated at the start portion and the signal1is repeated at the end portion. The guard interval may be present at both of the start portion and the end portion, or may be present at any one portion thereof.

FIG. 11illustrates a method of building a high-speed CAN signal generated by combining a standard CAN signal and a passband CAN signal. A fixed amplitude modulation method and a variable amplitude modulation method may be used as methods of modulating the passband CAN signal. However, the high-speed CAN signal generated by combining the passband CAN signal and the standard CAN signal should be restricted by adjusting the amplitude of the passband CAN signal so that the existing CAN nodes are protected against false detection of bits and edges in interval of 1 μs.

A minimum level Sminduring the dominant bit transmission is equal to 1−ASSV based on the single-ended signal as illustrated inFIG. 12. As the ASSis reduced, the difference between the minimum value Sminand 0 V is increased. Therefore, the possibility of erroneous detection of the dominant bit as the recessive bit at the existing CAN node receiver is reduced. On the other hand, when the weight ASSof the passband CAN signal is increased, while there is an advantage of the increase of a signal-to-noise ratio of the passband CAN signal, the minimum value Sminis reduced, and thus the possibility of erroneous detection of the bit and edge by the existing CAN nodes which receive the high-speed CAN signal is increased.

The weight ASSof the passband CAN signal is a system parameter to be adjusted according to the modulation method, the channel characteristic, and the transmission rate of the passband CAN signal generator. The weight ASSmay be set differently for each fields in the standard CAN frame and each data group within data field. For example, the ASScan be set to be small such that the signal is transmitted with small amplitude in the SOF field and arbitration field intervals in order to facilitate the interoperability with the existing CAN nodes, and the ASSmay be set to be large in the other intervals including the data field.

The variable amplitude modulation method used by the passband CAN signal generator210has an advantage of high-speed data transmission by increasing the spectral efficiency. Modulation schemes such as 16QAM, 32QAM and 64QAM may be used according to the characteristic of the channel. The passband CAN signal transmitted using the variable amplitude modulation method has various amplitude vertex values according to the transmission bit stream as illustrated inFIG. 13. The passband CAN signal generator210may find the lowest value of all the vertex values of the passband CAN signal, and limit the weight ASSbased on the lowest value in order to ensure the compatibility with the existing CAN transmission apparatus.

Both frequency modulation and phase modulation may be used as the fixed amplitude modulation method used by the passband CAN signal generator210. BPSK, QPSK, OQPSK, or π/4-DQPSK method may be used as the phase modulation method. FSK, CPM, or the like may be used as the frequency modulation method.

When the passband CAN signal generator210uses the fixed amplitude modulation method, information is not carried in the amplitude of the passband signal. Therefore, it is possible to transmit the passband signal by limiting (clipping) as illustrated inFIGS. 14 and 15. In this case, the complexity of the signal synthesizer220and the signal converter230may be reduced. The clipping of the passband signal uses the outputs of the pulse shaping filters214and215. When there is no pulse shaping filter for the passband CAN signal, the outputs of the signal mappers212and213are clipped as illustrated inFIG. 14 or 15. InFIG. 14, when the passband CAN signal is greater than 0, the passband CAN signal is simplified to 1, and when the passband CAN signal is smaller than 0, the passband CAN signal is simplified to −1, and thus the passband CAN signal generator210, the signal synthesizer220, and the signal converter230may be easily implemented. The clipping method ofFIG. 14can be further simplified as inFIG. 15when the passband signal is fixed to 1 for the passband signal greater than 0, and the passband signal is fixed to 0 for the passband signal smaller than 0. In this case, the output of the passband CAN signal generator210has one of the two values 1 and 0 without any negative value. Therefore, the passband CAN signal generator210may be further simplified fromFIG. 5, and the signal synthesizer220and the signal converter230may be further simplified.

FIG. 16illustrates an example of frequency spectrum of the high-speed CAN signal of the proposed method. An RRC (root raised cosine) filter with a roll-off factor of 0.3 is used as a pulse shaping filter of the passband CAN signal. The passband CAN signal has a carrier frequency fcof 24 MHz, a symbol ratio fsof 16 MHz, and an amplitude ASSof 100 mV, and uses a QPSK method as a modulation method. The radiation characteristic of the passband CAN signal in frequency domain may be adjusted by using appropriate the pulse shaping filter depending upon the radiation condition and the modulation method.

The passband transmission signal may be variously configured according to the modulation method, carrier frequency, and symbol rate. Table 1 illustrates some examples of the passband CAN transmission system.

It is possible to transmit the passband CAN signal during the entire CAN frame as long as the node is allowed to drive the CAN bus5. For example, the passband CAN modulation signal can be transmitted in the SOF field, the arbitration field, the control field, the data field, and the CRC field in the CAN message frame structure ofFIG. 1when dominant bits are transmitted. However, the passband CAN signal is not transmitted to the ACK field, the EOF field and the inter frame space.

FIG. 17illustrates an example of a standard CAN signal bit stream and corresponding passband CAN signal transmission for a standard CAN frame. The length of data field is set to 32 bits.FIG. 18illustrates an example of using an extended frame with data field length set to 8 bits, where the transmission of passband CAN signal is turned on and off according to the standard CAN signal bit stream.

FIG. 19shows the case when two CAN nodes start transmission at the same time. A high-speed CAN node A transmitted 8 bits of identifier bits and is about to transmit ninth bit of a recessive bit as illustrated inFIG. 19, when another node B (the node B may be an standard CAN node or may be the high-speed CAN node according to the present invention) drives the bus to the dominant state. In this case, the node A loses right to drive the bus, and accordingly the high-speed CAN transmitter200of the node A should stop the transmission both of the standard CAN signal and the passband CAN signal from the next bit interval.

In order to maximize the passband CAN transmission interval in the standard CAN frame, all the bit fields in the standard CAN bit stream can be assigned to be dominant bits. Since the arbitration field of the variable fields is a unique identifier in the node, it is not allowed to change the field arbitrarily. Other than the arbitration field, it is possible to change the data field so that the number of dominant bits is maximized. To this end, the DLC bit is fixed to “1000,” setting the length of the data transmission interval to 64 bits which is the longest interval in the standard CAN frame. The resulting bit transmission of the CAN bus has repeated pattern of 5 dominant bits and 1 recessive bit during the data field.FIG. 20illustrates an example in which the passband CAN signal interval is maximized using the repeated pattern of the 5 dominant bits and the 1 recessive bit when 64-bit data is transmitted using the standard CAN frame. The DLC field is set to a bit1, a bit0, a bit0, and a bit0, and all bits of the 64-bit data field are set to 0 to have a maximum number of dominant bits. According to the CAN standard, since a bit1is inserted automatically after the consecutive 5 bits of 0's, the actually transmitted bit stream becomes “100000” starting from the DLC field. It may be seen that the 13-bit recessive bit is inserted in the data bit interval. According to the CAN standard, since the CRC bit is changed according to the data configuration of the entire frame, the dominant bit may not be assigned arbitrarily. The maximum number of dominant bits is 67 bits (3 bits+64 bits) which is the sum of the DLC field and the data field. This means that passband CAN signal can be transmitted at least for the 67-bit interval regardless of the identifier values.

Since the CAN standard operates on the bus to which the plurality of nodes are connected, the high-speed CAN signal of the present invention is also received in the existing standard CAN receivers. Since no high-speed CAN signal is delivered in the recessive bit interval, there is no compatibility issues during recessive bit reception period. During the interval in which the dominant bit is received, the received signal level is limited such that it is higher or equal to a predetermined level in the proposed invention, erroneous detection of the dominant bit as the recessive bit does not occur. In the CAN standard, when a frame which is not compatible with the CAN standard is received on the bus, any node on the bus may interrupt the transmission by transmitting an error frame. On the other hand, when the high-speed CAN receiver observes the high-speed CAN signal on the bus, it recognizes high-speed CAN signal in the passband and performs reception of the high-speed CAN data.

FIG. 21is an example illustrating a configuration of a high-speed CAN receiver300of the high-speed CAN communication system, which receives a signal delivered from the bus.

A signal converter310performs differential signal-to-single-ended signal conversion on the signal transmitted from the bus5.

An output of the signal converter310is applied to a standard CAN signal detector320. The standard CAN signal detector320detects a dominant bit when the single-ended signal is increased by more than a predetermined level and outputs a signal which is a logic level 1. On the other hand, when the input single-ended signal is decreased by more than a predetermined value, the output signal is converted to a logic level 0. The standard CAN signal detector320maintains a current output value when the input single-ended signal is not changed beyond a certain threshold value.

The output from the standard CAN signal detector320is delivered to an equalizer350and a decision apparatus360, which will be described below. The standard CAN signal detector determines whether the standard CAN signal delivered from the bus is a dominant bit or a recessive bit.

A passband filter330removes the standard CAN signal and noise from the high-speed CAN signal output from the signal converter310. The output signal from the passband filter330is input to a timing/carrier recovery unit340.

The timing/carrier recovery unit340includes a timing recovery unit (not illustrated) and a carrier recovery unit (not illustrated).

The carrier recovery unit recovers the carrier wave using the high-speed CAN signal output from the signal converter310. The carrier recovery unit corrects a phase and frequency of the high-speed CAN signal in the passband using the recovered carrier wave, and converts the high-speed CAN signal in the passband to a baseband signal.

The timing recovery unit recovers a sampling clock from the high-speed CAN signal, samples down-converted high-speed CAN signal according to the recovered sampling clock and delivers output to an equalizer350.

The equalizer350performs compensation of the channel distortion, and a decision apparatus360outputs the high-speed CAN bit stream by performing decision of symbols for each corresponding modulation method. The equalizer350and the decision apparatus360operate only in an interval in which an output signal value of the standard CAN signal detector320is a logic level 1, and stop the operations in an interval in which the output signal value thereof is a logic level 0.

The high-speed CAN bit stream which is an output of the decision apparatus360is delivered to the high-speed CAN controller100, and the high-speed CAN controller100takes only an input bit stream in the interval in which the output value of the standard CAN signal detector320is a logic level 1, and ignores the output in the interval in which the output value of the standard CAN signal detector320is a logic level 0. The high-speed CAN controller100may perform frame disassemble, de-interleaving, error correction decoding and the like based on a protocol predefined with the transmitter.

The passband filter330, the timing/carrier recovery unit340, the equalizer350, and the decision apparatus360correspond to components which extract the high-speed CAN transmission bit stream from the signal received from the CAN bus5according to whether the standard CAN signal is in the dominant bit region or in the recessive bit region.

While the present invention has been described above with reference to the embodiments, it may be understood by those skilled in the art that various modifications and alterations may be may be made without departing from the spirit and scope of the present invention described in the appended claims.

DESCRIPTION OF REFERENCE NUMERALS OF DRAWINGS