Abstract:
An Intelligent Transportation Systems (ITS) device is described. The ITS device ( 400 ) includes: radio resources including a receiver ( 402 ) adapted to receive a radio signal in at least two frequency bands; a channel detector ( 410 ) arranged to analyse a signal received in a first frequency band to determine the presence of a transmission in that frequency band; a controller ( 402 ) configured to control assignment of radio resources, and in the event that the channel detector detects a signal in the first frequency band, to prevent transmission of a potentially interfering radio signal. The first frequency channel can be part of another radio communications system, such as a RTTT1 SSRC radio system.

Description:
PRIORITY CLAIM TO RELATED APPLICATIONS 
     This application is a national stage application under 35 U.S.C. §371 of PCT/AU2011/000951, filed Jul. 28, 2011, and published as WO 2012/012836 A1 on Feb. 2, 2012, which claims priority to Australian Application No. 2010903357, filed Jul. 28, 2010, which applications and publication are incorporated by reference as if reproduced herein and made a part hereof in their entirety, and the benefit of priority of each of which is claimed herein. 
     FIELD OF THE INVENTION 
     The present invention relates to radio devices enabling the coexistence of wireless communications systems. The illustrative embodiment is presented in the context of an intelligent transportation system. 
     BACKGROUND OF THE INVENTION 
     Intelligent Transport Systems (ITS) are systems that sense, gather and communicate data in a transportation setting. The aim of such systems is to aid transportation systems to operate more safely, efficiently or cost effectively, and to aid in the planning and management of transportation systems. Exemplary uses of ITS include traffic flow monitoring, variable tolling, emergency vehicle tracking and deployment and dynamic traffic control, to name a few. 
     Some components of ITS are affixed to moving vehicles. These devices communicate with each other and/or fixed components of the system wirelessly. ITS typically operate at 5.9 GHz, and may be compliant with draft standards such as ETSI TS 202 663 or IEEE 1609/802.11p for example. 
     However, one potential issue for deployment of ITS is the requirement of coexistence between the already deployed Road Transport and Traffic Telematics (RTTT) Dedicated Short Range Communication (DSRC) devices and other similar systems and ITS devices. 
     RTTT-DSRC devices include systems that are used to collect road tolls, such as the system illustrated in  FIG. 1 . These devices typically operate at 5.8 GHz. 
     The RTTT-DSRC system of  FIG. 1  includes road side equipment (RSE)  102  and one or more RTTT-DSRC devices  104 ,  104 A, such as those carried by vehicles  106 ,  106 A. Typically RTTT-DSRC devices  104  are low power devices capable of running off batteries for long periods. The device  104  operates in a very low power mode listening for signals from road side equipment  102  (e.g. a toll gantry). When the RTTT-DSRC device  104  “hears” a signal it “wakes up” and enters a higher power mode and attempts to execute a transaction with the RSE  102 . The wireless connectivity range for RTTT-DSRC devices  104 ,  104 A is typically short, say less than 100 m. The RTTT-DSRC will only operate over the zone  108  in which it is capable of communicating with the RSE  102  as the vehicle  106  moves past it. Thus, in  FIG. 1  the RTTT-DSRC device  104  can communicate with the RSE  102 , but RTTT-DSRC device  104 A is out of range. 
     On the other hand, ITS devices can have higher transmit powers and may be active continuously. In  FIG. 1  each vehicle  106 ,  106 A has an ITS device  110 ,  110 A affixed to them. 
       FIG. 2  is a schematic block diagram of the ITS device  110 . The device  110  has an ITS radio component  204  which is effectively the physical transmitter and receiver of the device  110 . Operation of the device  110  is controlled via a manager component  202 , and it runs a protocol stack  206 . As noted above the device  110  will typically operate on a channel at 5.9 GHz, and will be compliant with draft standards such as ETSI TS 202 663 or IEEE 1609/802.11p for example. 
     Despite the fact that they operate at slightly different carrier frequencies, interference can result between the systems. Interference has the potential to disrupt communication via the RTTT-DSRC. 
     It is thus desirable to have ITS devices avoid causing interference around RTTT-DSRC signalling zones. To date several solutions have been proposed for this problem:
         The RSE can be fitted with an ITS radio device. This ITS radio device transmits a message, the reception of which by a vehicle&#39;s ITS device indicates that the vehicle&#39;s receiver is in the vicinity of a RTTT-DSRC zone. The message can include a message type indicating that this message is to be interpreted as transmitted from a RTTT-DSRC location. The vehicle&#39;s ITS receiver may then determine that it is in a RTTT-DSRC zone simply because it received a message of this type. The message may also include the position of the gantry. This is helpful if the vehicle&#39;s ITS device is position aware, e.g. if it has GPS positioning capabilities or across to GPS data from another source. If the vehicle is told where the RTTT-DSRC zone is and it knows its own location in the same co-ordinate system then it can determine whether or not it is in the RTTT-DSRC zone. The dimensions of the RTTT-DSRC zone can also be included in the message transmitted by the RSE&#39;s ITS radio. The message could also include authentication data to validate the message as a countermeasure to spoofing attacks aimed at ITS devices.   The vehicle&#39;s ITS device can be provided with means for receiving RTTT-DSRC signals. The ITS device can then receive RTTT-DSRC signals. The reception of the DSRC signal would indicate to the ITS device that it is in the vicinity of a RTTT-DSRC zone. The reception means includes a dedicated hardware subsystem, radio equipment able to receive and decode the DSRC signal. This subsystem is connected to the ITS device management system which can suspend ITS transmission when the RTT DSRC radio system indicates that it is in a RTTT-DSRC zone.       

     It is an object of the present invention to provide an alternative mechanism to avoid interference between an ITS device and other radio systems such as RTTT-DSRC systems. 
     Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. 
     SUMMARY OF THE INVENTION 
     In a first aspect the present invention provides an Intelligent Transportation Systems (ITS) device including: radio resources including a receiver adapted to receive a radio signal in at least two frequency bands; a channel detector arranged to analyse a signal received in a first frequency band to determine the presence of a transmission in that frequency band; a controller configured to control assignment of radio resources, and in the event that the channel detector detects a signal in the first frequency band, to prevent transmission of a potentially interfering radio signal. 
     In preferred embodiments the transmissions to be prevented are transmissions from the ITS system in a second frequency band. In some embodiments the first frequency band is a frequency band not used by the ITS for transmission of signals. Preferably it is a frequency band used by a RTTT-DSRC. 
     The controller can be configured to cause the receiver to be tuned to the first frequency from time to time to enable the channel detector to attempt detection of a transmission in the first frequency band. The controller can further be configured to cause the receiver to be tuned to a second frequency band and to decode a plurality of received channels transmitted on the second frequency band, according to a predetermined access scheme applied to transmissions on the second frequency band. 
     In the event that the predetermined access scheme applied to transmission on the second frequency band assigns a first transmission of a first type to a first logical channel, and a second transmission of a second type to a second logical channel, the controller can be configured to assign radio resources to the first frequency during at least some periods in which a transmission on the second logical channel of the second frequency band could be received. The predetermined access scheme can include a plurality of second logical channels. In this case the controller can be configured to assign radio resources to the first frequency during at least some periods in which a transmission on one of the second logical channels of the second frequency band could be received. 
     The channel detector can be arranged to analyse a received signal to detect the presence of a transmission in the first frequency band without decoding the received signal in the first frequency band. 
     The channel detector can be arranged to analyse a power level of a received signal in the first frequency band, and in the event that the received power level is above a threshold, determine that a transmission in the first frequency band is detected. The channel detector can be arranged to detect a predetermined transmission structure in the first frequency band. The channel detector can be arranged to detect a predetermined modulation scheme in the first frequency band. 
     The channel detector can include: a time domain correlator for detecting a modulation scheme in the first frequency band; and or a spectral analyser to determine a power level at at least one frequency in the first frequency band. 
     The ITS device preferably includes shared radio resources that are used for reception of signals on the first and second frequency bands. 
     In a second aspect the present invention provides a method in a transceiver operating in an Intelligent Transportation System (ITS). The method includes: enabling reception of a radio transmission in at least one ITS frequency band; enabling reception of a radio transmission in at least one first non-ITS frequency band; analysing a signal received in the first non-ITS frequency band to detect the presence of a transmission in that frequency band; and in the event that a signal in the first non-ITS frequency band is detected; preventing transmission of a potentially interfering radio signal, by the transceiver. 
     The step of, enabling reception of a radio transmission in at least one ITS frequency band can include, tuning a receiver of the transceiver to the ITS frequency band; and the step of, enabling reception of a radio transmission in at least one first non-ITS frequency band includes, tuning the same receiver to the non-ITS frequency band. 
     The transmissions received on the ITS frequency band can be arranged according to a predetermined access scheme applied, such that the ITS frequency band includes a first logical channel and second logical channel. In this case the method can also include, enabling reception of a radio transmission in at least one of the first non-ITS frequency band during at least some periods in which a transmission on the second logical channel could be received. 
     The access scheme can include a plurality of second logical channels. In this case the method can include enabling reception of a radio transmission in the first non-ITS frequency band during at least some periods in which a transmission on one of the second logical channels could be received. 
     The method can also include analysing a received signal in the non-ITS channel to detect the presence of a transmission without decoding the received signal. The step of analysing a signal received in the first non-ITS frequency band to detect the presence of a transmission in that frequency band, can include: analysing a power level of a received signal in the non-ITS frequency band; and in the event that the received power level is above a threshold, determining that a transmission in the non-ITS frequency band is detected. The step of analysing a signal received in the first non-ITS frequency band to detect the presence of a transmission in that frequency band, can include: analysing the received signal to detect a presence or absence of a predetermined transmission structure in the received signal. 
     The predetermined transmission structure can include a predetermined modulation scheme. The method as may include, conducting time domain correlation to detecting a modulation scheme in the received signal. 
     The method can also include, conducting spectral analysis of the received signal to determine a power level at, at least one frequency in the non-ITS frequency band. 
     The step of preventing transmission of a potentially interfering radio signal, by the transceiver includes any one or more of the following: 
     preventing transmission by the device; 
     preventing transmission by the device in one or more selected frequency bands; 
     preventing transmission by the device having a power level above a predetermined power level. 
     The method can further include, ceasing prohibition of transmissions of a potentially interfering radio signal. 
     For example the step of ceasing prohibition of transmissions of a potentially interfering radio signal could occur after any one or more of the following criterion are fulfilled: 
     a predefined time has elapsed; 
     the transceiver has moved a predefined distance; 
     a subsequent analysis of a signal received in the first non-ITS frequency band fails to detect the presence of a transmission in that frequency band. 
     As used herein, except where the context requires otherwise, the term “comprise” and variations of the term, such as “comprising”, “comprises” and “comprised”, are not intended to exclude further additives, components, integers or steps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described by way of non-limiting example only, with reference to the accompanying drawings. In the drawings: 
         FIG. 1  illustrates a Road Transport and Traffic Telematics, Dedicated Short Range Communications system in which a device operating in accordance with the present invention can be operated: 
         FIG. 2  illustrates a conventional Intelligent Transport Systems device; 
         FIG. 3  illustrates an embodiment of an Intelligent Transport Systems transceiver made in accordance with the present invention; 
         FIG. 4  is a diagram illustrating the time periods in which an Intelligent Transport Systems, made in accordance with an embodiment of the present invention, receives an ITS service channel and time periods in which it attempts to detect RTTT-DSRC communications. 
         FIG. 5  is a diagram illustrating the time periods in which an Intelligent Transport Systems device, made in accordance with another embodiment of the present invention, receives an ITS service channel and time periods in which it attempts to detect RTTT-DSRC communications. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In broad concept, the preferred embodiments of the present invention re-use radio resources of the ITS radio system to assist in detection of transmission on another radio communications system such as a RTTT-DSRC system. Most preferably this can be performed without decoding the RTTT-DSRC transmissions. 
       FIG. 3  illustrates schematically, selected components of an ITS transceiver  400 . In particular the receiver components of the transceiver are illustrated. The ITS device  400  includes an ITS receiver component  404  adapted to receive a radio signal via antenna  405  and output a demodulated signal to an ITS baseband processor  408 . Higher level processing of the demodulated signals is performed by according to the protocol stack  406 . 
     The transceiver  400  also includes a detector  410  configured to analyse the signals received by the receiver  404  and determine whether or not the received signal includes transmission on a predetermined non-ITS channel—namely a channel associated with an RTTT-DSRC system. 
     The controller also includes a controller  402 . The controller  402  is responsible for scheduling the use of the radio resources of the device  400  between the competing RTTT-DSRC detector  410  and ITS Radio functions. In the event that the channel detector  410  detects a RTTT-DSRC signal, the controller  402  prevents transmission of potentially interfering ITS signals. 
     The controller  402  is configured to cause the receiver  404  to be tuned to the ITS frequency band and to decode the received channels according to the ITS access scheme, and also to cause the receiver to be tuned to the RTTT-DSRC frequency from time to time to enable the channel detector to attempt detection of a RTTT-DSRC transmission. In this way the sharing of ITS Radio resources between the RTTT-DSRC detection and ITS communications functions is achieved. 
     In time periods where the radio resources are allocated to receiving the RTT DSRC frequency the RTTT-DSRC detector  410  processes the received signal. During this period the ITS Baseband processor  406  may be unable to receive ITS signals, unless the transceiver is arranged to have multiple ITS receivers. 
     The RTTT-DSRC detector  410  informs the controller  402  if it determined that a RTTT-DSRC signal is present. The RTTT-DSRC detector  410  may be disabled while the ITS Radio RF  404  is tuned to ITS frequencies. 
     The RTTT-DSRC channel detector  410  is arranged to analyse a received signal to detect the presence of a RTTT-DSRC transmission without necessarily decoding the received signal. The RTTT-DSRC detector  410  may use several techniques to determine if a RTTT-DSRC signal is present, for example analysing the power and/or the transmission structure of a signal received in the RTTT-DSRC frequency band. 
     In one embodiment, the detector  410  analyses the received signal and if the power in the frequency band where RTTT-DSRC signals are transmitted is above a threshold level the RTTT-DSRC detector  410  determines that it is in a RTTT-DSRC zone. For example, the received signal can be analysed to determine the power level at selected frequency or over a frequency band. This power spectral density approach can be used to calculate the total RTTT-DSRC in-band signal power. This value can be compared to a threshold to decide if there is a RTTT-DSRC signal present. 
     In another embodiment, the detector  410  checks for the one or more predetermined signal or transmission structures that are expected to be used in RTTT-DSRC waveforms. For example, the preamble of a RTTT-DSRC signal can be transmitted using 2-level Amplitude Modulation at 500 or 250 kbps. If this signal structure is expected on the RTTT-DSRC frequency, the RTTT-DRSC detector  410  can include an element sensitive to this structure. For example the detector  410  can include a time domain correlator to detect the AM signal at the chosen frequency. 
     In a preferred embodiment, in addition to the reuse of the ITS Radio receiver  404  the RTTT-DSRC detector  410  also reuses elements of the ITS Radio Baseband processor  408  resources. 
     As will be appreciated, because the ITS and RTT DSRC are not synchronised with each other, the ITS device may switch into the RTTT-DSRC detection mode part way through a transmission on the RTTT-DSRC. In the case that the RTTT-DSRC detector  410  begins processing part way through a RTTT-DSRC message, Power Spectral Density techniques can be used to detect the presence of the RTTT-DSRC signal. The RTTT-DSRC detector  410  is able to use FFT or DFT resources from the ITS Radio baseband processor  408  to assist with these Power Spectral Density measurements. 
     In a preferred form, the controller  402  allocates the radio resources of the receiver according to a predefined scheme. In one form, the allocation scheme leverages the timing scheme used in ITS transmissions to provide an acceptable trade off between RTTT-DSRC detection speed and acceptable ITS signal reception. 
     In ITS two types of logical channels are commonly defined. One or more service channels (SCH) and a control channel (CCH). The CCH is used for critical safety services whereas the SCH is used for other services such as traffic probe snapshots. More specifically, in the SAE J2735, IEEE 1609/802.11p family of standards Basic Safety Messages are broadcast on the CCH several time per second from each vehicle. All vehicles within range can then receive this broadcast message and obtain the position of the transmitter from the message payload. In a single radio system, the ITS radio resources are tuned some of the time to the CCH frequency and some of the time to an SCH. In devices with multiple radios it is possible to operate on both CCH and SCH channels simultaneously. 
     In a preferred scheme, the controller  402  causes a receiver  404  of the device  400  to tune to the RTTT-DSRC frequency band in a time period where that receiver would normally communicate on the SCH. During this time the RTTT-DSRC detector  410  can determine the presence transmissions of any RTTT-DSRC devices. The RTTT-DSRC detection phase could also be executed on the CCH, but this is less preferable since the SCH is typically used for lower priority transmissions in the ITS.  FIG. 4  illustrates an example of a timing scheme,  420 , for the reception of signals in a single receiver ITS device, such as that of  FIG. 3 . In this scheme: 
     the time periods  422  indicate periods in which a first logical channel (e.g. the CCH can be received); 
     the time periods  424  indicate periods in which a second logical channel (e.g. the SCH can be received); and 
     the time periods  426  indicate periods in which the receiver can be tuned to another frequency band so the channel detector  410  can scan for transmissions. 
     As can be seen, radio resources are preferentially assigned to the first logical channel and less priority given to the second logical channel and the task of scanning for transmissions on the other frequency band (e.g. the RTTT-DSRC frequency). The relative time allocated to the three reception tasks and the timing of them can be varied from this example, as needed. Moreover, in an ITS with multiple logical channels, it could be decided that the ITS device will not use one of the logical channels and instead additional time allocation is granted to the detection task. In this case, no time periods are be allocated to reception on the excluded logical channel. 
     In the case that the ITS device has two ITS radio receivers, such as that contemplated in draft ETSI ITS standards, the CCH is assigned to one radio while SCH communications assigned to the other Radio. In this case, the RTTT-DSRC detection can be scheduled on either or both of the SCH and CCH radios, however as noted above, the preference is to use the SCH of the ITS radio system as the applications are generally less critical on the SCH than the CCH. 
       FIG. 5  illustrates an example of such a timing where one radio receiver is assigned to the one of the ITS logical channels and periodically used to scan the RTTT-DSRC. The diagram illustrates, the allocation of radio resources of one receiver of the ITS device between an ITS channel (preferably a SCH logical channel) and RTTT-DSRC frequency band. (e.g. this may be one radio of a two-radio ITS device, the sole radio in an ITS device where only one ITS logical channel exists, or where only one ITS logical channel is to be monitored.) 
     In the diagram  500  the time periods  502  represent time periods in which the radio resources are assigned to the ITS logical channel and time periods  504  in which the resources are assigned to an RTTT-DSRC frequency band and during which the detector  410  attempts to detect RTTT-DSRC communications. The timing of the switching from ITS communications mode to RTTT-DSRC mode can be periodic as illustrated in  FIG. 4 , random or varied according to any known scheme. The other receiver could be permanently assigned by the controller  402  to another ITS channel, and thus is not illustrated. 
     The underlying purpose of the detection of the RTTT-DSRC system is to minimize or avoid interference between the ITS and RTTT-DSRC. Avoidance of interference can be achieved by the controller  402  totally preventing transmission by a transmitter of the device  400 . Alternatively, it may be possible to transmit at certain frequencies without unacceptable interference, in this case the controller  402  can restrict transmission to selected frequency bands fulfilling non-interference requirements, or by preventing transmission by the device in one or more frequency bands that are likely to cause interference. In another form, the controller  402  can cause a transmitter of the ITS device to operate at a reduced power level that will not cause unacceptable levels of interference. 
     Once the detector  410  has detected the presence of an RTTT-DSRC transmitter and the controller has put the transceiver into a mode that minimizes or eliminates interference from the ITS transmissions, it will be necessary to return to a mode in which normal ITS transmission can be performed. This can be performed in a number of ways, for example the controller  402  can revert to normal ITS communications after a predefined time has elapsed. If the ITS device is position-aware (e.g. is has a receiver for determining its position by a satellite positioning system) the controller  402  can revert to normal transmission on the ITS device once the transceiver has moved a predefined distance. Alternatively the controller  402  can be configured to allocate the radio resources to the RTTT-DSRC channel, and stay in its detection mode until the RTTT-DSRC detector  410  no longer detects transmission on the RTTT-DSRC frequency. The ongoing analysis of the RTTT-DSRC frequency can be continuous or performed periodically. Once the applied criterion is met the controller  402  will allocate radio resources in the normal manner and normal ITS communications can be resumed. 
     It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.