Patent Application
20160292472
This application claims priority from Italian Patent Application No. MI2015A000401, filed Mar. 17, 2015, and from Italian Patent Application No. MI2015A000404, filed Mar. 17, 2015, both of which are incorporated by reference in their entireties.
The invention relates to a device and a short-range secure radiocommunication system, and to a secure radio communication method that uses such a device.
It is known, in the technical field of short-range near filed communication (NFC) wireless transmissions, that the same are used for a wide variety of operations.
For example, in the field of financial transactions, there is a growing desire to implement payment devices that allow payment through the exchange of payment information via radio between a security data device carrier and a corresponding reader with POS functionality.
Examples of devices that use such communications are data carriers, such as ID cards, ID badges, credit cards, ATM cards and similar; there are more and more used in various services sectors, but also in companies, in order to keep data (especially sensitive data) to be transmitted via radio, by establishing a short-range connection with respective receiver devices (such as card readers, POS with wireless/contactless technology and similar).
Similar considerations apply to the technical field of smartphones, which implement transceiver technologies in the field of proximity (NFC) which allow the exchange of data with similar devices, and even to carry out financial transactions and/or identification by communicating via radio with reader devices via NFC connection.
It is also known that all short-range transceiver technologies used today for these purposes are deemed unsafe and for this reason are greatly limited in possible uses; consider, for example, the very stringent limits imposed on the amount of financial transactions that can be performed with contactless credit cards that integrate appropriate transceiver apparatus.
The reasons for this lack of security are manifold:
As illustrated in
This implies that an eavesdropper in any position, who is able to receive a portion of the signal with sufficient power, is thereby capable of intercepting the short-range communication, and then take possession of sensitive data; for example (
On the other hand, increasing the number of data channels, using standards beams as carriers, does not increase security, but only the interference between channels on a same frequency, which are not independent one another; therefore, complex processing encryption mechanisms are used, requiring a high capacity for pre- and post-processing (and therefore complex and expensive circuitry difficult to implement within the dimensional limits imposed for the devices) and any way not guaranteeing security against eavesdroppers equipped with adequate capacity for post-processing the intercepted signals.
YAN YAN ET AL: “High-capacity millimetre-wave communications with orbital angular momentum multiplexing” (NATURE COMMUNICATIONS, vol. 5, 2014 Sep. 16, p. 4876), discloses a bidirectional link between two data centers equipped with apparatus for transmission/reception of superimposed co-polar EM beams with the same frequency and with different values of the Orbital Angular Momentum (OAM) topological charge, wherein different data channels are associated with respective carriers comprising EM Beams with value of the OAM topological charge different from zero and one from the other.
WO 2014/104911 discloses generating beams with value of the OAM topological charge different from zero by means of circular arrays of antennae.
U.S. Pat. No. 7,701,381 B2 describes a system and method of OAM diverse signal processing using classical beams for applications in which OAM signal character is controlled such as optical tagging and applications in which OAM signal character is not controlled such as clutter mitigation and interference cancellation for target detection, identification etc. This is accomplished by transmitting a source beam having a prescribed state with one or more non-zero OAM components, reflecting the beam off a ‘tagged’ or ‘untagged’ target and receiving the return beam in the direct return path to measure the one or more OAM components to identify the target. According to U.S. Pat. No. 7,701,381 B2, OAM processing provides additional degrees of processing freedom to enhance the processing capabilities to detect and identify both ‘tagged’ and ‘untagged’ targets. The target may be an RF or Optical OAM tag comprising a grating or a hologram, respectively, for reflecting and/or diffracting the transmitted beam towards the receiver. The reflective/diffractive hologram or grating may be incorporated in a credit card. The proposed diffractive grating cannot be made to fit in the size of a credit card at frequencies substantially lower than 100 GHz.
The technical problem which is posed, therefore, is that of providing telecommunication methods, devices and systems for short-range transmission, which can ensure improved security of data exchanged by reducing the possibility of eavesdropping by third parties, as well as short-range telecommunications devices and systems that implement this method.
In connection with this problem it is particularly desirable to restrict the area in which an eavesdropper is able to intercept and discriminate the signals exchanged between the transceivers that communicate via short-range transmissions.
It is also required that the new solution be suitable to be carried out in a simple and economical way, using technical production in current use and without departing from the dimensional requirements imposed by international standards for the different devices.
These results are obtained according to the present invention by a device according to the claims, by a system according to the claims and by a method according to the claims.
Further details may be obtained from the following description of non-limiting examples of embodiment of the subject matter of the present invention provided with reference to accompanying drawings in which:
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With reference to
The term “beam” indicates a set of paraxial waves, i.e. waves which have directions of propagation which diverge only slightly from the direction, z, along which the entire beam is propagated. Said beam is monochromatic (the waves forming the beam are sinusoids with the same frequency) and coherent (said sinusoids have phases in a deterministic relationship with each other).
Electromagnetic beams with non-zero orbital angular momentum are characterized by the presence of a singularity, where at the contributions of the EM field with different phases interfere destructively so that the beam intensity is substantially zero and the phase is indeterminate.
The simplest case, widely described in the literature, of an EM field in a “pure” OAM state (or mode), i.e. one characterized by a unique integer value of its Orbital Angular Momentum, is known in the literature as Laguerre-Gaussian (LG) beam. The pure LG states or modes are paraxial beams obtained by appropriate superposition of plane waves, characterized by the presence of a central phase singularity. The intensity distribution of a generic pure LG mode presents a rotational symmetry about its axis of propagation z and is characterized by two integer indexes, l e p:
l is the azimuthal index, also called OAM topological charge or, generically, value of OAM, and it univocally defines the angular dependence of the phase of the field. It indicates the number of interlaced helices that make up the wave front. These helices have a pitch equal to the wavelength λ;
p is the radial index: it represents the number of radial nodes of the LG beam, i.e. the number of points (at a finite distance from the centre) at which the field is zeroed. This is equivalent to saying that p+1 is the number of relative maximums (alternately, positive and negative) of the field amplitude, succeeding each other along the radial direction, starting from the central singularity in which the origin of the coordinates, r=0, is placed.
The complex amplitude of the field of a LG beam in cylindrical coordinates (r, φ, z) is described by
with w=w0√{square root over (1+(z/zR)2)}, where w0 is the beam waist radius, R the radius of curvature of the wavefront, zR the so-called Rayleigh distance (Rayleigh range), L|l|p(2r2/w2) the associated Laguerre polynomial and (2p+|l|+1)arctan(z/zR) the so-called Guoy phase. The term exp(−ilφ) describes the azimuthal dependence of the phase.
The LG beams with integer and non-zero OAM present an intensity distribution characterized by a donut shape: the maximum intensity falls within an annular region, in the center of which the intensity of the electromagnetic field is zero (
The module and sign of the OAM topological charge (or azimuthal index) l can be schematically represented, respectively, by the number of rotations of a suitable vector V around the z axis and by the direction of rotation—clockwise or counterclockwise—of the vector on a generic plan γ perpendicular to the propagation direction z, when the z coordinate increases by a wavelength λ (
Moreover the EM field of an LG beam with non-zero Orbital Angular Momentum has, in a generic observation plane perpendicular to the axis of propagation, a phase which is variable with continuity upon variation of the angular coordinate in the plane itself; this means that it has a well-defined and unique periodic spatial structure called “phase profile” which, if measured, may be used for discriminating wave beams with different OAM.
Beams with the same carrier frequency, having same polarization (for brevity hereinafter called co-polar) and substantially coaxial, characterized by different values of OAM, are orthogonal, and so independent of each other; as a consequence, they remain intrinsically separated from each other during propagation and therefore they can be exploited as carriers for independent channels in radio communication. The expression “data transmission channel” (or in short “data channel”) is used here to indicate any signal which carries information, without any limitation as to the type of said information or the technology used for the (analog or digital) generation/encoding thereof and for its transmission (modulation method).
However, during propagation, the transverse section of a beam with nonzero OAM widens (diverges) with increasing distance from the source and in proportion to the value l of the topological charge; it follows that the transverse dimensions of the central “dark area” in the intensity distribution of the beam increase with the distance from the source.
With reference to
a transceiver assembly 1100 (for example a transponder in compliance with RFID standard) comprising:
In more detail, the first transceiver apparatus 1110 of the illustrative device 1000 comprise an array of at least 2l10+1 (in the example of
According to the invention, the first generated/received EM beam from the first EM transceiver apparatus 1110 is associated with a first data channel C1, by means of an appropriate system of coding and modulation.
The second transceiver apparatus 1120 of the illustrative device 1000 comprise a single antenna 1120a disposed in central position with respect to the circumference described by the first transceiver apparatus 1110. The antenna 1120 is arranged to generate a standard EM beam, i.e., with zero OAM (l20=0).
The second EM beam, generated/received by the second EM transceiver apparatus 1120, is associated with a second data channel C2, by means of an appropriate system of coding and modulation.
For example it is assumed that the antennas 1110,1120 may be active or passive radiating elements, for example planar patches or dipoles. These types of antennas allow an easy integration into a security card in accordance with required dimensional standards.
Associating a first channel C1 to an OAM beam with non-zero value of topological charge, a first advantage is obtained that consists in the fact that the difficulty of interception of the channel carried by the first beam rapidly increases with increasing distance from the device 1000 for secure communication. The portion of the γ plan illuminated by the main lobe of the non-zero OAM beam widens, in fact, with increasing distance from the source, and thereby the central area with substantially zero intensity also increases, while the useful power remains confined solely in the crown of the intensity distribution.
Nevertheless, using only the first channel C1 associated with the first beam generated by the first transceiver apparatus 1110, an eavesdropper in a position not correctly aligned with the beam could still intercept sufficient signal power for reconstruction of useful data signal transmitted on channel C1, since, even receiving a signal power low but above the background noise, the intercepted small portion of intensity would carry a not disturbed or interfered signal, which would thus be reconstructable.
According to the invention, the device 1000 includes therefore the second transceiver apparatus 1120 that generate said second EM beam with the same frequency and co-polar, which is associated with a second transmission channel C2 with the aim of interfering with the first channel C1.
The innovative combination advantageously exploits the fact that, in order to exploit at the receiving side the orthogonality of the two received EM beams with different topological charge (OAM), namely to be able to receive and discriminate independent channels C1, C2 associated with the two beams generated, the received field must be completely concatenated, both in amplitude and in phase; in general terms this means that the receiving transceiver apparatus must be able to receive a sufficient portion of the EM field surrounding the beam singularity.
To achieve this concatenation, a receiver must be:
A condition of substantial alignment at a suitable distance is that wherein the receiving transceiver apparatus are arranged:
These two conditions restrict the ability of an eavesdropper to receive and correctly discriminate the information carried on channels C1, C2 associated with the co-polar and the same frequency beams characterized by different OAM, transmitted or received by transceiver apparatus 1110, 1120. These beams, according to the invention, are advantageously used as carriers for data channels C1, C2 for short-range secure communications, whereby a legitimate receiver can easily meet the above conditions, while a fraudulent eavesdropper encounters major difficulties not being able to align itself with nor place itself at a suitable distance from the transceiver, a position in which it would be in any case easily detected.
In this way, the invention advantageously exploits also the fact that the beams with non-zero OAM have a spread (divergence/beam aperture during the propagation) higher than a standard beam, at equal distance of propagation.
The simplest example of exploitation of the two channels C1, C2 associated to the transceiver apparatus 1110,1120 described above is to transmit a single useful signal S1 carried by channel C1 with a non-zero OAM, while on the other channel C2 (in this example, l20=0) a distributing signal with power equal to the useful signal S1 can be transmitted.
A possible eavesdropper cannot, in its position, concatenate the whole beam with non-zero OAM delivered by the first channel C1 generated by transceiver 1100, it cannot exploit in reception the phase variation around the singularity of the beam with non-zero l10 OAM to discriminate the first channel C1 from the second co-polar channel C2 with the same frequency. The eavesdropper receives only a portion of the useful signal (therefore, it receives less power) and it is also disturbed by the disturbance signal transmitted on channel C2 (l20=0), which is received superimposed and interfering with the first useful signal on the channel C1 and, not being able to exploit the orthogonality of the different OAM modes, cannot be isolated from the first channel C1 itself.
This embodiment, which envisages the presence of a disturbance signal transmitted on the second channel C2, while meeting the basic requirement of security, implies a waste of power (the power of the disturbance signal), which is not reused in any way for transmission of useful data.
According to a further preferred aspect of the invention useful data signals Si (i=1, 2, . . . ) to be transmitted on channels C1, C2 of the secure communication device 1000 according to the invention are divided between the two channels. For example, if only one useful signal S1 is transmitted, this may be divided at least into two parts, each of which is transmitted on one of the two channels C1, C2. If two or more useful signals S1, S2 are transmitted, these can be divided into the two channels so that each channel C1, C2 transport a composite plot (of parts) of the useful signals S1, S2. In this way, an additional level of security is added, since it is necessary to receive and correctly discriminate all the channels C1, C2 to reconstruct the one or more useful signals S1, S2, and no power is wasted in the transmission.
In
Correspondingly, to secure communication device 1000, the device 2000 includes a transceiver assembly 2100 comprising:
In this example, it is assumed that the transceiver apparatus of a reader device 2000 for secure communication are subjected to dimensional constraints less strict than those required for the device 1000 in the form of security card, for example contained in a circumference of radius between 40 and 70 mm, while for a device such as a security card 1000 one can assume a circumference between 20 and 35 mm in radius.
The antennas of the reader device 2000 can then be implemented for example with arrays of patches, dipoles or coils, possibly coupled with adequate processing means, subject to limitations less stringent than those imposed for a device security card.
A proper configuration of the reader device can thus easily allow also the use of passive elements for the device 1000 in the form of a security card, and preferably the implementation of a minimal pre- or post-processing in security cards, such as a static post-processing preferably implemented with properly dimensioned transmission lines (e.g., microstrip wave guides) that allow the elements of the array to have the corrected phase shifts for transmit and/or receive the predetermined value of OAM.
In the example of
The distance dAB is preferably greater than a minimum distance dAB-min such that the beams with non-zero OAM can develop completely (with donut-shaped intensity distribution and well-defined phase profile), in some cases identified as substantially equal to or slightly greater than the wavelength; for example for a transceiver with dimensions of the order of centimeters, operating at a transmission frequency of 5.8 GHz, typical of RFID applications, a distance dAB-min of a few centimeters is sufficient.
The upper limit of the distance dAB-min depends on various factors, for example on the power of the signal radiated by the transceiver apparatus 1100,2100 of the secure communication devices 1000,2000, on the working frequency, on the size of the transceiver apparatus of both devices 1000, 2000, and on the value of the generated OAM, that affects the enlargement of the antenna lobe, as well as on the signal degradation limits imposed for a correct reception by the devices 1000,2000 (which in turn depend on several parameters such as the post-processing capability). A proper selection of various parameters is within the reach of the designer that implements the different system configurations.
An optimal distance dAB, so preferred, can be one in which the receiving apparatus, if in a position of substantial alignment, are substantially disposed within or around the ring of maximum intensity of the intensity distribution of the OAM beam, preferably placed along the circumference of radius rmax=w√{square root over (l/2)}.
Preferably, the plate 2200 transparent to radio waves is placed at the optimal distance dAB from the radio assembly 2100.
The plate 2200 transparent to radio waves includes means adapted to facilitate alignment between the transceiver apparatus 1110 for transmitting/receiving the OAM beam with non-zero topological charge of device 1000 and the corresponding transceiver apparatus 2110 of the reader device 2000.
An advantageous aspect of the invention is that determining the point of proper alignment between the two devices is facilitated by the structure of the non-zero OAM beams: thanks to the minimum intensity of the signal located in the center of the antenna lobe radiated by the transceiver apparatus 2110 of the reader device (or by transceiver apparatus 1110 of the security card device 1000) it is simple to configure means for correct alignment between the secure communication devices 1000,2000, for example aligning the respective minimum points of signal intensity.
In the exemplary embodiment shown in
With this configuration, the operation of the secure communication system between the security card device 1000 and the reader device 2000 is the following:
A possible fraudulent eavesdropper E, which for illustrative purposes is supposed equipped with correct transceiver E100 means (for example, a reader equal to the reader 2000) adapted to receive the beams generated by apparatus 1100,2100 of the secure communication devices 1000, 2000, and with a very high post-processing capability of the received signals, is not however able to receive and discriminate the two channels C1, C2 of communication between the devices 1000,2000 beyond a certain angular misalignment limit and/or over a certain lateral translation/offset limit relative to the position of correct alignment, because he can not obtain the orthogonality condition between the two channels.
Security card device 3000 differs from the device 1000 in that it includes third transceivers apparatus 3130 for generating a third EM beam characterized by an OAM with non-zero value l30 (in the example l30=−1) of the topological charge and different from the OAM values l10, l20 of topological charge of the beams generated by the first 3110 and second 3120 transceiver apparatus; the third transceiver apparatus 3130 are correspondingly suitable for reception of an EM beam characterized by the same value l30 of OAM topological charge of the transmitted signal.
The reader device 4000 includes similar third transceiver apparatus 4130 capable of generating and receiving an EM beam the same value l30 of OAM. EM beams transmitted/received by the third transceiver apparatus 3130,4130 are associated to a third secure short range telecommunications channel C3.
The first transceiver apparatus 3110,4110 and the third transceiver apparatus 3130,4130 are implemented by two concentric circular arrays of patch antennas working for example at a frequency of 5.8 GHz (typical RFID standard). The size of the transceiver assembly 4100 of reader device 4000 can be chosen substantially equal to the received/transmitted wavelength (about 50 mm), in order to reduce the secondary lobes, and better focus the power in a main lobe of irradiation of the assembly 4100.
The operating principle of the secure communication system of
For illustrative purposes, it is assumed that the legitimate receiver B, with limited post-processing capability, is not able to properly receive the channels C1,C2,C3 below a threshold value equal to −3 dB compared to the maximum SNIR, and that it must also receive the three channels C1,C2,C3 with the same SNIR in order to be able to properly equalize in reception and thereby reconstruct the at least one useful signal S1 divided on the three channels. With these assumptions, it can be seen in
With reference to
However, the fraudulent eavesdropper E, not being able to be aligned in the correct position with the device 4000 of entity A, is in a tilted orientation and/or in a shifted position with respect to the ideal position occupied by the device 3000 of legitimate receiver B. The angle of inclination (=tilt) and the distance (=offset) of the eavesdropper E from the axis of optimal alignment of the device determine the inability of E to independently receive the three channels associated with beams with different OAM value, so the region of the surrounding space B in which E is able to receive sufficient signal over all three channels C1, C2, C3 results therefore extremely narrow.
The OAM channels received from translated and/or inclined positions with respect to the ideal position, occupied by B, are not received as orthogonal, and even if they were received with a sufficient SNIR, the eavesdropper would need a very high and non-plausible post-processing capability distinguish them to, which he is awarded in the examples only for purposes of illustration.
It is, therefore, clear that the use of communication channels associated with at least two EM beams with different orbital angular momentum values to implement a secure short-range communication guarantees an extremely narrow region of space within which it is possible to properly receive channels, and outside of which the reception becomes very difficult for a possible fraudulent eavesdropper.
According to a preferred embodiment, transceiver assemblies 1100, 3100 of the secure communication devices 1000,3000, for example the security cards of
A further embodiment provides instead the use of not identical signal power on all channels.
Moreover complementary transmitting devices, for example the security card reader devices, adapted for transmitting signals with equal power may be provided. However, it is preferable that complementary transmitting devices transmit signals with different power levels, which allows greater versatility in the sizing of the transceiver assembly and corresponding radiating elements.
In addition, a preferred embodiment provides that the devices establish a communication only if they receive equal SNIR on all channels; in this case, it is possible to compensate any differences of SNIR on the different reception channels with different transmitted signal powers.
To satisfy the preferred condition of reception of signals with equal SNIR by the transceiver apparatus 1110 and 1120, it is, therefore, possible to especially dimension the transceiver 1100 set in reception if the transceivers apparatus 2110 and 2120 transmit signals with equal power; however, it is preferable to adjust different transmission powers of the transceiver apparatus 2110,2120 to a preferred sizing of transceiver apparatus 1110,1120 of the first device.
Further advantageous aspect of the present invention is that the use of beams with different value of OAM allows a strong simplification of the post-processing of the signals needed by secure communication devices, such as security cards 1000,3000. The post-processing can be of the static kind and needs not be dynamically re-calibrated depending on the position of the receiver. An advantageously simple post-processing, for example static, can be implemented with properly dimensioned transmission lines (e.g., microstrips) connected to the antennas of the transceiver assembly.
According to a further preferred embodiment, a secure communication device according to the invention can be implemented in the form of a portable multimedia device, such as a smartphone, tablet or similar.
The multimedia device will incorporate a transceiver assembly, for example implemented by means of antenna arrays, capable of transmitting/receiving at least two beams with different value of OAM topological charge, and associate corresponding secure transmission channels Ci thereto.
Advantageously, this embodiment allows having portable multimedia devices able to carry out financial transactions or exchange of secure data with great versatility.
In addition, such a device may be arranged to carry out in a very simple way the alignment to a reader device or to a corresponding second multimedia device with which to securely exchange data at short-range: for example, an application can be programmed in order to detect, for example through the transceiver apparatus of the device, a minimum of intensity of the signal received on one or more channels carried by beams with non-zero OAM and indicate the correct alignment position with the complementary reader/multimedia device. The alignment based on a minimum of power as reference is advantageously simpler than that using a maximum. This renders unnecessary the presence of alignment means on the reader device. A graphical interface of the application can easily help the user to achieve the proper alignment.
The size of smartphones or similar devices implies less stringent limits on the size of the transceiver assembly, and allows insertion of a greater number of radiating elements, which allows to more easily generate/receive EM beams with high values (for example, l=10) of OAM topological charge; it is, in fact, known that the minimum number of antennas needed to form an array of antennas able to generate a beam with OAM of value l is equal to 2l+1 (antennas). Higher values of OAM are more difficult to intercept because the divergence/opening of an OAM beam is proportional to the square root of the value of the OAM of the beam, which diverges more quickly with the increasing value of OAM, decreasing the area where it is possible to intercept the radio communication.
A high number of channels (for example, greater than two or three) associated to carriers with different OAM synergically enables both an increase of capacity and an increase of security, obtained thanks to the subdivision of the useful signal on multiple channels, as well as the greater difficulty of interception.
The best compromise between the various parameters and requirements may be selected by the designer.
With a dynamic post-processing, for example with phase-shift lines connected to configurable phase shifters, it is possible to vary the configuration of the antenna array to transmit/receive beams with different values of topological charge of OAM, subject to the minimum number of antennas given by 2l+1.
The devices of the present invention can, therefore, implement a short-range radio communication method in which security of the communication is obtained using at least two co-polar data channels with same frequency, whose respective carriers comprise (or consist of) a first EM beam with non-zero orbital angular momentum (OAM) and at least one second EM beam with OAM different—even zero—from the OAM of the first beam.
The radio communication, for example, can be a transmission, a reception or a mono or bi-directional point-to-point radio communication.
In fact it is clear that, although the invention has been described with reference to preferred transceiver apparatus capable of transmitting and receiving the beams with different OAM transmission channels carrying the Ci, it is not necessary that the radio communication is bi-directional (or full-duplex) and that for certain protocols and applications it may be advantageous that the transmitter apparatus are not adapted for reception and/or vice versa.
In addition, it is meant that the said beams are preferably substantially coaxial.
A preferred aspect of the method according to the invention provides for realizing a point-to-point short-range radio communication between two secure communication devices, in which each EM beam with different value of OAM transmittable/receivable by one of the secure communication devices is associated with a corresponding secure channel data of the radio communication.
In more detail, an exemplary method of realization of a point-to-point short-range radio communication according to the invention preferably comprises the steps of:
For substantial alignment, it is meant an alignment sufficient to discriminate reception channels. For example, according to a non-limiting criterion assumed in this description, an alignment such as to allow a concatenation of the beams with non-zero OAM which allows to receive the channels with a variation of SNIR with respect to the optimal position at the given distance not lower than −3 dB.
For appropriate distance, it is meant a distance between a minimum distance and a maximum distance appropriately defined, for example as a function of the transceiver apparatus used and of the OAM beams used as carrier for the channels (array dimensions, type of antennas used, transmitted power, value of the OAM of the beams, etc), and preferably an optimal distance in which the receiving apparatus are substantially disposed within or around the corona of maximum intensity of the intensity distribution of the corresponding transmitted OAM beam, preferably arranged along the circumference of radius rmax=w√{square root over (l/2)}.
According to one embodiment, the step of arrangement of the first and second secure communication devices includes:
The appropriate distance and/or the region of substantial alignment can be defined as a function of the dimensions, the operating frequency, the power of the transceiver apparatus and the values of generated/received OAM. In other embodiments, the dimensions of the transceiver apparatus can be defined in terms of preferred values of proper distance and/or proper alignment and/or transmitted power. These choices will be made by the designer on the basis of more or less stringent limits imposed by international standards and of the practical needs related to the different situations of application.
For communication on at least two said channels it is meant that at least one useful signal S1, S2, S3 is transmitted at least partially on the channel associated with the carrier comprising said first beam with non-zero OAM value, while simultaneously on said at least one further channel at least one signal is transmitted with a non-null power (not necessarily a signal carrying useful data).
Preferably, the at least one useful signal S1, S2, S3 is divided on two or more communication channels associated with carriers comprising or consisting of EM beams with different values of OAM, for example according to a composite plot of subdivision of the useful signal.
According to a further preferred aspect, it is possible to use the method of the invention to securely exchange a cryptographic key. In more detail, the at least one useful signal S1 transmitted in a secure way comprises said cryptographic key. After the exchange of the encryption key, the devices can communicate with each other in a secure way even on one or more other radio channels not necessarily carried by beams with non-zero OAM, transmitting only signals appropriately encrypted using the above encryption key transmitted/received by the method of the present invention. Preferably, the encryption key is updated after a short time such as to prevent fraudulent eavesdropper to decipher the key within that time.
It is, therefore, clear how the device and the system according to the invention make it possible to establish a short-range radio communication with a high security feature based on a physical substrate which uses at least two EM beams (or fields) as carriers for communication channels, at least one of which has a non-zero topological charge of OAM, and at least one of which with topological charge different from the topological charge of the first. A high security physical substrate for wireless communication is thereby established.
On this substrate, more existing technologies for secure communications can be applied; one can use techniques such as encryption (also quantum) or mechanisms for detecting and correcting errors as FEC (Forward Error Correction) on each channel.
In addition, with devices, systems and methods according to the invention it is possible to use a high number (even more than three, four or five, and only limited by the technology) of communication channels associated with EM beams or fields characterized by different values of OAM topological charge (therefore, intrinsically orthogonal), obtaining a synergic enhancement of transmission capacity and of security of the communication.
Being able to take full advantage of such channels by splitting thereon useful signals to be transmitted, one can take full advantage of the increase in capacity obtained through the use of channels associated with beams with different OAM.
In addition, the device can be formed with different types of antenna, for example dipoles or planar antennas, both active and passive and with different arrangements: coaxial or concentric circumferential arrays, which are preferred because they second the rotational symmetry of the OAM beams, or even arrays of different shape, provided that they include antennas arranged on a closed line around the singularity of the OAM beam to be transmitted/received.
The described devices and method are also viable for applications operating at millimeter wavelengths (working frequencies around 60 GHz), or infrared (Terahertz).
Although described in the context of certain embodiments and of some preferred examples of embodiment of the invention, it is intended that the scope of protection of the present patent is determined only by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| MI2015A000401 | Mar 2015 | IT | national |
| MI2015A000404 | Mar 2015 | IT | national |
