Title: Method and radar system for transmitting information

The invention relates to a method and radar system for transmitting information.

It has been known for a long time, that a radar system can be used for communication purposes. For example, GB 247,126 discloses a radar system including means for generating radar signal pulses, and means for producing frequency modulation of the carrier frequency of the pulses in accordance with communication signals.

A more advanced prior art system is known from DE2808544A1, teaching to apply binary phase encoding of a message into an unmodulated radar pulse sequence (of a pulse Doppler radar), so that radar operation to detect targets can be achieved at the same time as transmission of messages. However, this system is relatively complex and expensive, and can only achieve relatively low data transfer rates.

US 4,291,309 discloses a method, wherein a carrier wave is modulated in amplitude during short intervals of interruption of detecting a beat frequency. The intervals are timed to occur when the beat frequency would be abnormal. In this prior art system, the radar and communication functionalities can not be performed simultaneously. Besides, the achievable communication data-rate of this know system is very small. The present invention aims to provide an improved method and radar system for transmitting information.

According to an embodiment, there is provided a method for transmitting information, comprising:

-providing a first radar signal generator, which provides a continuous wave radar signal having a first modulation;

-modulating the radar signal with the information, to be transmitted using a second modulation;

-transmitting the continuous wave radar signal modulated with the information;

-providing a first radar signal receiver, which seeks reflected continuous wave radar signal parts relating to the transmitted radar signal, modulating the radar signal with the information.

For example, the method can include: providing a second radar signal receiver, receiving the transmitted continuous wave radar signal; and -processing the continuous wave radar signal, received by the second radar receiver, to obtain the information therefrom. Also, according to an embodiment, there is provided a radar system configured to transmit information during radar operation, particularly being configured to carry out the method according to the invention, the system comprising:

- a first radar signal generator, configured to provide a continuous wave radar signal having a first modulation;

-a modulator to modulate the radar signal, provided by the first radar signal generator with the information to be transmitted using a second modulation;

-a transmitter to transmit the continuous wave radar signal modulated with the information; and

- a first radar signal receiver configured to receive reflected continuous wave radar signal parts relating to the transmitted radar signal.

For example, the system can comprise one or more second radar signal receivers, being spaced-apart from the first receiver, to receive the transmitted continuous wave radar signal, wherein each the second radar signal receiver can comprise a processor to process the continuous wave radar signal, received by the second radar receiver, to obtain the information therefrom.

The present method and system can provide a reliable means to communicate using radar signals, during (i.e., simultaneously with) radar

operation, using relatively inexpensive means, wherein relatively high data rates (i.e. transmission of large amounts of information) can be achieved.

In a preferred embodiment, the first modulation of the continuous wave radar signal is a frequency modulation. For example, the frequency modulated continuous wave radar signal as such can comprise an array of subsequent radar signal parts, each radar signal part having a continuously rising and/or falling frequency, for example broadband signal parts, particularly a continuous array of chirps having linear frequency slopes (with slope angle α). As an example, each subsequent radar signal part can be frequency modulated between a first (minimum) and second (maximum) frequency, having for example a certain high carrier frequency (for example at least in the MHz range or GHz range) and a relatively narrow bandwidth (for example below the MHz range, or below the GHz range in the case that the carrier frequency is in the GHz range). In a more preferred embodiment, the second modulation of the radar signal, to modulate the signal with the information, is amplitude modulation. In this way, particularly, an FM radar signal can be AM modulated with information, to be transmitted, which can be carried out simply by the application of a suitable AM modulator. In case of a first radar signal receiver detecting radar targets, via radar signal reflections, interference between the AM information containing part and target detection information can be avoided in a simple manner.

Also, a remote radar signal receiver can process the AM-FMCW (i.e. Amplitude Modulated Frequency Modulated Continuous Wave) radar signal to acquire the transmitted information there-from, using relatively inexpensive means. Particularly, the AM part in the transmitted radar signal can be demodulated there-from in a simple manner.

In an alternative embodiment, the second modulation of the radar signal, to modulate the signal with the information, can be a frequency modulation, for example by the application of a frequency modulator.

Also, an embodiment can provide digital machine readable instructions, particularly software code, configured to cause a machine to carry out a method according to the invention when executed by the machine, particularly to provide a system according to the invention. Further advantageous embodiments of the invention are described in the dependent claims. These and other aspects of the invention will be apparent from and elucidated with reference to non-limiting embodiments described hereafter, shown in the drawings.

Figure 1 schematically depicts a system and respective method according to an embodiment of the invention;

Figure 2 shows a radar signal transmission/receiving part of the system shown in Fig. 1;

Figure 3 shows a target detection result of the transmission/receiving part of the system of Fig. 1; Figure 4 shows a radar signal information receiving part of the system shown in Fig. 1;

Figure 5 shows a frequency spectrum of an example of a radar signal received by the information receiving part of Fig. 4;

Figure 6 shows an example of a processed radar signal spectrum, processed by the information receiving part of the system;

Figure 7 depicts a further embodiment of the invention; and

Figure 8 depicts an alternative of the embodiment shown in Fig. 2.

Corresponding or similar features are denoted by corresponding or similar reference signs in the present patent application. Figures 1-2 show a non-limiting embodiment of a radar system configured to transmit information during radar operation. According to a preferred embodiment, a primary part of the system is based on commonly known Frequency Modulated Continuous Wave (FMCW) radar technology. Thus, the radar system provides various advantages over, for example, pulsed Doppler radar systems, for example concerning the complexity and costs.

Moreover, the present FMCW radar system can detect both location (i.e. distance) and velocity of a target Ta, as is known to the skilled person. Since FMCW radar technology as such is known from the prior art, its details will not be explained in the present patent application. The present FMCW radar system has been adapted to provide a communication means as well, above its normal radar functionality. This will be explained in the following, regarding the embodiments shown in figures 1-8. For example, the system can comprise a first radar signal generator 1, for example being part of a first radar station Rl (for example a mobile, movable or location-fixed radar unit), configured to provide a continuous wave radar signal Sl having a frequency modulation. The radar signal generator 1 is associated with a transmitter 7 to transmit the continuous wave radar signal, and with a first radar signal receiver 2 (being part of the first radar station Rl, or at least being located near the first radar signal generator 1) configured to (continuously, i.e., uninterruptedly) receive reflected continuous wave radar signal parts relating to the transmitted radar signal (as follows from Fig.l, one or more remote targets Ta can induce the mentioned reflected radar signals). In the present embodiment, the transmitter 7 is an antenna, which is also used for receiving reflected radar signals; alternatively, different antennas can be provided for the transmission and receiving of signals.

The frequency modulated continuous wave radar signal Sl as such can be frequency modulated in various ways. According to a simple and efficient embodiment, the first signal generator 1 is configured to generate a signal consisting of a continuous array of subsequent sine wave radar signal parts, each sine wave radar signal part for example having a continuously rising and/or falling frequency, for example broadband signal parts, particularly a continuous array of chirps (for example being frequency modulated between a minimum frequency Fl and maximum frequency F2). The radar system can also be called a "chirped radar system", using a linear chirp waveform.

For example, as will be appreciated by the skilled person, the first radar signal generator 1 can be configured to employ a continuous wave radar signal used to determine the velocity of one or more targets Ta. The first radar signal generator 1 can also be configured to modulate the continuous wave signal with a modulation resulting in the frequency modulated continuous wave (FMCW) radar signal Sl, having the first modulation, used to determine the distance to the one or more targets Ta.

In an embodiment, the FM modulated radar signal Sl can have a carrier wave frequency of about IGHz (some GHz) or higher, however, other frequency ranges (for example in the MHz range) can also be applied if desired. Also, the frequency sweep F of the FM modulated radar signal can be in the range of about several Mhz up to several GHz, or be a different frequency sweep.

For example, the first radar signal generator 1 can comprise a first direct digital synthesizer (DDS), to generate a very stable radar signal. In a further embodiment the generator 1 comprises or is connected to a sweep generator Ia. In the present embodiment, the sweep generator Ia produces a continuous chirps wave, having linear slopes for each chirp between a minimum and maximum frequency (the frequency range, between a first frequency Fl and second frequency F2, i.e. the bandwidth of the signal, being indicated by an arrow F in Fig. 2), and a time period (length) of each chip being indicated by arrow T in Fig. 2. Each chirp preferably is a sine wave having a linearly changing frequency. An amplitude -time graph of a chirp of the resulting signal Sl is also shown in Fig. 2. The skilled person will appreciate that the mentioned direct digital synthesizer can be part of this sweep generator, or be connected thereto to drive the sweep generator Ia.

Also, in the present embodiment, the sweep generator Ia has been linked to the radar signal receiver 2. The radar signal receiver can use the signal provided by the sweep generator Ia in the processing of detected radar signal reflections, to detect targets (i.e. target distance and speed), particularly

during (i.e. simultaneously with, instantaneously with) the transmission of the modulated signal Sl' (and receiving and processing the modulated signal Sl' by one or more remote receivers 3), as will be appreciated by the skilled person. Figure 3 shows an example of an output that can be generated by the radar signal receiver 2, indicating a plot (spectrum) of frequency versus amplitude, wherein two target related frequency peaks fti and ft2, relating to two different targets can be discerned. Such target related peaks are also commonly known as "target beat notes" (i.e., beat frequencies). Due to its configuration, the radar system can discern targets up to a maximum beat note (in a target information band), which has been indicated by fmax in Fig. 3. Then, according a preferred embodiment, the system also comprises a modulator 5 to modulate the FMCW radar signal Sl, provided by the first radar signal generator 1 with the information to be transmitted using a second modulation. In the present embodiment, the modulator 5 is an amplitude modulator. Part of a resulting AM-FMCW modulated signal Sl' has been depicted in Fig 2, in a time-amplitude diagram, and in Figure 5 in a frequency- spectrum.

Also, for example, the modulator 5 can provide a continuous AM modulation of the FMCW radar signal Sl during a time period of at least one FMCW modulation period (T), resulting in the AM-FMCW signal Sl', as follows from Fig. 2.

For example, the system can include one or more information ("data") providing or generating components 20, which can communicate or transmit information to be transmitted to the modulator 5 to modulate that information into the radar signal Sl. Figure 8 depicts a further embodiment, wherein the information providing or generating components 20 as such is a data modulator configured to provided a data modulated signal S3. Particularly, such a data modulator 20 can be configured to modulate the information (data) onto a data signal carrier ("carrier", in Fig. 8) of a

given/predetermined frequency fd with a third modulation, resulting in the data modulated signal S3. The third modulation can be amplitude, frequency or phase modulation (e.g. AM, FM, FSK, QPSK, QAM, or OFDM). In the embodiment of Fig. 8, the downstream amplitude modulator 5 can be configured to modulate the radar signal Sl, provided by the first radar signal generator 1, with the data modulated signal S3 received from the data modulator 20.

Information (data) to be transmitted can involve many types of information, for example audio, video, multimedia, pictures, target related information and/or other information. The information as such, for example, can be or include unprocessed data, pre-processed data, modulated data, scrambled or coded data, digital data, analogue data, and/or a combination thereof and/or other data, as will be appreciated by the skilled person.

Besides, advantageously, in the embodiment of Fig. 2, the modulator 5 is preferably configured to modulate the radar signal using an amplitude modulation data signal frequency fd satisfying the condition: fd>2f _m ax (i.e., fd is larger than two times fmax). As a non-limiting example, in case the possible target frequencies are in the range of 1-100 kHz, the frequency fd of the AM modulation of the FMCW signal (leading to the AM-FMCW signal Sl') is larger than 200 kHz. Using such relatively high data modulation frequencies can provide relatively large data transmission rates. Also, in a further embodiment (as is shown in fig. 2), the AM modulation can involve modulating an AM sinus wave (having the mentioned data signal frequency fd as carrier frequency, and having an amplitude that contains the information/data/message to be transmitted) to the FMCW signal.

Regarding the further embodiment shown in Fig. 8, for example, the carrier frequency fd (of the data signal carrier) can satisfy the condition:

λ > 2-/ _max +—

where fmax is a maximum target beat frequency that can be detected and BW is a bandwidth of the data modulated signal S3.

Moreover, as follows from Fig. 3, the amplitude modulation of data into the FMCW radar signal can lead to data/target related peaks, being indicated by peaks fd-ft2, fd-fti, fd+fti fd+ft, 2fd-ft2, 2fd-fti, 2fd+fti 2fd+ft in the radar target detection spectrum. However, due to the advantageous application of fd>2fmaχ, these peaks will generally lie above f _max (in the detected signal spectrum), and are thus separated from true target related peaks fti, ft2, (which lie below fmax) so that the AM modulation of the FMCW signal does not interfere with the primary radar operation of the system.

Besides, the system can include a second radar signal receiver 3 (see Fig 1), being spaced-apart from the first receiver 2 (i.e. from the first radar station Rl), to receive the transmitted continuous wave radar signal (particularly simultaneously with the first radar signal receiver 2 processing detected radar signal reflections, to detect targets T).

The second radar signal receiver 3 can be located in a position where it is desired to receive data or information from the first radar station Rl. According to a non-limiting embodiment, the second radar signal receiver 3 can also be part of a (second) radar station, having its own radar signal transmission, receiving and processing components to detect targets, however this is not essential. The second radar signal receiver 3 can also be part of or be associated with units, devices or stations that have no further means to detect remote targets via radar technology. For example, the second receiver can comprise a suitable antenna 16 to receive radar signals Sl'. Figure 4 shows a further embodiment of the second receiver 3, and its operation. The second radar signal receiver 3 preferably comprises a processor 9 to process the continuous wave radar signal Sl', received by the second radar receiver 3, to obtain the information therefrom. Particularly, the following configuration can provide AM information recovery by the receiver 3, in which a desired band limitation of the data signal can be achieved:

The processor 9 preferably comprises a second signal generator 6 configured to provide a second continuous wave signal S2 that has the same configuration as the radar signal Sl provided by the first radar generator 1.

For example, the second radar signal generator 6 can be configured to provide a second continuous wave radar signal S2 that has the same first modulation as the radar signal Sl provided by the first radar generator 1. Herein, preferably, the second radar signal generator 6 comprises a second direct digital synthesizer having the same configuration as the direct digital synthesizer of the first radar signal generator 1. In this way, the second radar generator 6 can preferably produce an exact copy of the FMCW signal generated by the first generator 1.

Also, the processor 9 preferably comprises a loop structure 10, 11, 18, 19 comprising synchronizing means 10, 18, 19, configured to synchronise the received signal Sl ¹ and the generated same signal S2, to delay the signals Sl', S2 with respect to each other such that a frequency difference δf (indicated in frequency-time graph G of Fig. 4) between the signals Sl', S2 becomes and remains equal to an intermediate frequency IF.

For example, the loop part of the processor 9 can comprise a frequency-difference measuring unit 18 to measure the instantaneous frequency difference δf between the received radar signal Sl' and the locally generated second signal S2.

The loop can include an adjustable delayer 10, which can be connected to the frequency-difference measuring unit 18, for example via a synchronisation controller 19, to control the delaying of the signals Sl ¹ , S2 based on the measurement results of the measuring unit 18. In this way, a feedback process/loop can be carried out to automatically provide a desired delaying of the received radar signal Sl', having the information, and the locally generated second signal S2.

Besides, the loop part of the processor 9 can include a multiplier or mixer 11 configured to multiply /mix the thus delayed signals Sl', S2. In the

output spectrum of a resulting mixer signal, an information containing frequency band can be shifted from an intermediate frequency IF, the intermediate frequency being an intermediate (i.e. central) frequency in the frequency sweep F of the initial FM radar signal Sl (i.e. IF=(F2-Fl)/2), as will be explained below. The spectrum of a resulting mixed signal is shown in Fig. 6.

Also, for example, the receiver 3 can comprise a bandpass filter 14 to filter separate an information containing frequency band part from the intermediate frequency. A bandpass filtering of the processes signal is being indicated by BPF in Fig. 6 (in the present case, the data containing part that has been shifted with minus fd from the intermediate frequency is being bandpass filtered from a remaining part of the spectrum).

Also, the processor 9 can include a demodulator 15 to demodulate the information containing frequency band to obtain the information therefrom. As follows from the drawing, the demodulator 15 can be located downstream with respect to the filter unit 14 to receive the filtered part BPF therefrom for further processing, to recover the information from that spectrum part.

Thus, in the receiver configuration of Fig. 4, the same sweep (S2) can be generated as in the remote radar transmitter in order to mix that sweep/signal S2 with the received signal Sl', and fold the data/information back to low frequency. Preferably, the same DDS is used as in the remote transmitter station Rl, in combination with the described loop structure 10, 11, 18, 19, to synchronize the received signal Sl' and the locally generated sweep S2. The frequency difference δf between both sweeps Sl', S2 is being measured and the adjustable delayer 10 can be progressively tuned, such that a lock of the loop is achieved when the frequency difference δf between both sweeps/signals Sl', S2is equal to the desired intermediate frequency IF. By band-pass filtering and simple demodulation, the data can be band limited

first, and recovered thereafter (particularly when the loop lock has been achieved).

During operation the processor 9 of the receiver 3 can to control the loop structure and tune the frequency difference δf between the receive signal Sl ¹ and the locally generated sweep Sl to the intermediate frequency IF. Once the loop is locked (i.e., IF= δf ), one component will appear in the mixer output spectrum (see Fig. 6) in the intermediate frequency IF, plus two data components (at δf=±fd (due to the mixing between δf and the data signal). In this situation, by band-pass filtering one of these data components (IF-fd or IF+ fd) the data can be easily recovered by simple demodulation (for example, a simple envelope detector would suffice).

The operation of the system also follows from Figures 1-6. During operation, the first radar station Rl can operate to detect (i.e. trying to find or locate) targets, by transmitting the first AM-FMCW radar signal Sl'. Particularly, operation can include determination of speed and/or distance of one or more targets Ta simultaneously with the transmission of the modulated continuous wave radar signal.

For example, during operation, the first radar signal generator 1 can employ a continuous wave radar signal suitable to determine the velocity of one or more targets Ta, wherein the first radar signal generator 1 modulates the continuous wave signal with a modulation resulting in a frequency modulated continuous wave (FMCW) radar signal Sl, having the first modulation, used to determine the distance to the one or more targets Ta. Also, during operation, information can be transmitted using the radar signals, for example to transmit a message to one or more remote receivers 3. To this aim, as follows from the drawings, modulating the FMCW radar signal Sl with the information, preferably via AM modulation, to obtain the AM-FMCW radar signal, which signal Sl' is then being transmitted (for example via a suitable antenna 7). Preferably, during operation, the FM continuous wave radar signal Sl is modulated with the data (i.e. information,

or modulated information S2) during a time period of at least one FMCW modulation period T.

During operation of a further embodiment, depicted in Fig. 8, for example, a data modulator 20 modulates the information onto a data signal carrier of frequency fa with a third modulation, resulting in a data modulated signal S3, wherein the AM-modulator 5 modulates the radar signal Sl with the data modulated signal S3.

The first radar signal receiver 2 can (particularly continuously) seek/detect reflected continuous wave radar signal parts Sl' (containing the information), reflected from targets Ta, and relating to the transmitted radar signal Sl'. Receiving of the reflected signal parts by the first receiver 2 is particularly carried out during the above -described (AM) modulating of the FMCW radar signal with the information. Also, the first radar station Rl can process the detected radar echo's to obtain target information (see Fig. 3), for example to determine target speed and/or distance.

Each second radar signal receiver 3 can (for example at the same time as the first receiver 2 seeking reflected signal parts Sl')receive the transmitted continuous wave radar signal Sl' (containing the AM modulated information), and can process the continuous wave radar signal Sl', to obtain the information therefrom. Since the information has been AM modulated, a simple processing can be an envelop-detection processing, wherein the envelop of the amplitude of the detected AM-FMCW signal Sl' is being determined.

In a preferred processing of the detected AM-FMCW signal Sl', the second signal generator 6 provides the second continuous wave radar signal S2, as is depicted in the Fig. 4.The receiver 3 synchronises the received radar (data containing) signal Sl' and the generated second signal (S2), by measuring the mentioned frequency difference δf between both signals Sl', S2, and delaying the signals Sl', S2 with respect to each other so that the frequency difference δf becomes equal to the mentioned intermediate frequency IF. For example, in the present embodiment, it is the second signal

S2 that is being delayed with respect to the information containing received radar signal Sl' (alternatively, for example, is the received signal Sl' can be delayed with respect to the second signal S2).

As follows from the above, the delaying is preferably such that in the resulting mixed signal, the information containing frequency band has been be shifted from the intermediate radar frequency IF, to obtain a spectrum as shown in Fig. 6. For example, the frequency-difference measuring unit 18 can measure instantaneous frequency differences δf between the received radar signal Sl' and the locally generated second signal S2, and the synchronisation controller 19 can control the delaying of the signals based on the measurement results of the measuring unit 18, to obtain the desired delay (particularly in an iterative or continuous feedback process)

Then, the bandpass filter 14 and demodulator 15 can recover the information from the mixed signal as has been indicated above, in a relatively simple manner, to obtain the information therefrom.

The method and system according to the invention can be used in many different applications, for example in military and/or civilian applications. In an embodiment, the method and system according to the invention can be used in a traffic regulation and/or controlling system. For example, Fig. 7 shows a traffic regulation and/or controlling system comprising a traffic controller 50. Besides, the traffic regulation and/or controlling can include one or more radar units R, configured to emit radar signals to part of a road 51, and to detect radar reflections relating to passing traffic targets Ta (for example vehicles, trucks and/or other traffic or transportation means). For example, each radar unit can have a configuration that is the same as or similar to the configuration of a first radar signal station Rl as shown in Figures 1-2. Preferably, each traffic radar R can be configured to transmit information during radar operation, and can comprise a mentioned first radar signal generator, a mentioned a modulator to modulate the radar signal and a transmitter to transmit the continuous wave radar signal

modulated with the information, and preferably also with a mentioned first radar signal receiver configured to receive reflected continuous wave radar signal parts relating to the transmitted radar signal.

For example, in an embodiment, each traffic radar station R can be configured to modulate information into a respective radar signal, which information relates to traffic Ta that has been detected by that specific radar station, for example information to the location and/or speed of the detected traffic

In one embodiment, a central traffic controller 50 can be configured to receive the modulated radar signals that are transmitted by the one or more radar stations R. For example, the traffic controller 50 can have a configuration that is the same as or similar to the configuration of the second receiver of the embodiment of Figures 1-6. Particularly, the central controller 50 can have a second radar signal receiver receive the transmitted continuous wave radar signal; and comprising a processor to process the continuous wave radar signal, received by the second radar receiver, to obtain the information (for example speeds and/or locations of detected targets Ta) therefrom.

Thus, the central controller 50 can control the traffic Ta, for example by adjusting or controlling respective traffic signs 52 associated with the road 51, depending on the information received by the various radar stations concerning speeds and/or locations of traffic Ta.

Thus, advantageously, a method and/or system according to the invention can be used to detect vehicles on roads. In an other embodiment, which may be combined with the embodiment of Fig. 7 is desired, the method and/or system can be used to transmit information to passing vehicles Ta. For example, to that aim at least one of the vehicles Ta can be provided with a mentioned second radar signal receiver to receiving the transmitted continuous wave radar signal. In this way, for example, information containing local points of interest, advertisement, navigation information, news, weather

road use information and/or other information can be transmitted to the target vehicles Ta.

Although the illustrative embodiments of the present invention have been described in greater detail with reference to the accompanying drawings, it will be understood that the invention is not limited to those embodiments. Various changes or modifications may be effected by one skilled in the art without departing from the scope or the spirit of the invention as defined in the claims.

It is to be understood that in the present application, the term "comprising" does not exclude other elements or steps. Also, each of the terms "a" and "an" does not exclude a plurality. Any reference sign(s) in the claims shall not be construed as limiting the scope of the claims. Also, a single processor, controller or other unit may fulfil functions of several means recited in the claims, and/or several processors, controllers or other units may fulfil one or more of means recited in the claims.