Abstract:
A system and method for implementing a wireless communications link between two equipment envelopes through inductive coupling include two “U” shaped inductors. Wireless communications is achieved via mutual inductance between the two inductors. Circuitry is provided, which enables the transmitter to determine if a receiver is within communications range. When the two envelopes are aligned, a dual-gap toroidal core is formed, in which the gaps have opposite polarity. The opposing polarity of the two gaps minimizes the far field signature of the transmitter/receiver pair, thus enhancing communication security.

Description:
BACKGROUND  
         [0001]    The present invention is generally related to short range wireless communication systems, and more specifically related to short range wireless communication systems utilizing inductive coupling.  
           [0002]    It is often desirable to conduct communications between two self contained portions of a system, such as a military man portable radio and associated equipment used to load information (e.g., configuration parameters) into the radio. Typically, many types of military equipment (e.g., man portable radios) require military hardening (e.g., enhanced vibration, shock, environmental, electrical specifications) and watertight integrity (e.g., submersible equipment), thus warranting self contained portions.  
           [0003]    Several disadvantages are associated with typical systems, which require that communications between the pieces of equipment be conducted via wired cables and electrical connectors, such as bayonet lock connectors and threaded connectors, for example. One disadvantage is that, in the field, carrying cables and/or connectors can place a burden on an operator. The cables/connectors are heavy and bulky, thus tiring the operator and slowing his reactions. Also, the size of the cables/connector can result in the operator becoming less covert.  
           [0004]    Another disadvantage is that in the field, or during an operation in which little time is available, connecting and disconnecting the portions of the system can take too long, thus possibly jeopardizing the mission.  
           [0005]    Another disadvantage is that these types of cables/connectors are subject to corrosion and interference with the operation of the connector (e.g., dirt in the threads) due to weather conditions and operational requirements, such as being submersed in water and/or mud, for example.  
           [0006]    Many military situations require covert operations, including secure communications between portions of the system. Due to the covert nature of many military operations, the cables connecting the portions of the system must be shielded to prevent unauthorized disclosure of the information being transferred. An associated disadvantage is that shielded cables/connectors tend to be heavy, bulky, stiff, and difficult to quickly connect and disconnect.  
           [0007]    Wireless systems have been explored. However, many wireless systems require that the structure (envelope) of the portions of the system be modified to facilitate communications. For example, a window may be put into a metallic envelope to support an infrared link. A associated disadvantage is that the envelope of the equipment is compromised.  
           [0008]    Many wireless systems do not adequately address the requirement for secure communications. For example, optical wireless systems may be subject to unauthorized monitoring/access simply by being visually observed. Furthermore, typical wireless systems utilizing electromagnetic communications means transmit signals which are also easily subjected to unauthorized access.  
           [0009]    An improved secure communications connection is desired.  
           [0010]    In one embodiment, a secure wireless communication system comprises a first portion and a second portion. The first portion comprises a first inductor and the second portion comprises a second inductor. The first inductor comprises a first end and a second end. The second inductor comprises a third end and a fourth end. The first portion and the second portion define a gap therebetween. Wireless communication is achieved across the gap through mutual inductance between the first inductor and the second inductor by aligning the first end with the third end, and the second end the said fourth end.  
           [0011]    In another embodiment, a method for providing secure wireless communications includes aligning the first portion of the communication system having the first inductor with the second portion of the communication system having the second inductor. When aligned, the first and second inductors form a dual-gap toroidal core. A wireless communication signal is conveyed across the gaps between the first and second portions via the first and second inductors.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    In the Figures:  
         [0013]    [0013]FIG. 1 is a cross sectional view of wireless secure connection illustrating a separation between the first and second inductors in accordance with an embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is a combination schematic diagram and cross-sectional view of a system comprising a wireless secure connection in accordance with an embodiment of the present invention;  
         [0015]    [0015]FIG. 3 is a plot comparing attenuation as a function of range for various range/attenuation relationships, in accordance with an embodiment of the present invention;  
         [0016]    [0016]FIG. 4 is a plot comparing attenuation as a function of range for differences of various range/attenuation relationships, in accordance with an embodiment of the present invention; and  
         [0017]    [0017]FIG. 5 is a flow diagram of a process for providing wireless secure communication in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    An embodiment of a secure wireless communication system in accordance with the present invention comprises two separate portions, wherein each portion includes a “U” shaped inductor. When the two separate portions are aligned, the two inductors form a transformer having a dual-gap toroidal core. Wireless communication is conducted between the two portions via mutual inductance across the two gaps of the dual-gap toroidal core. This embodiment allows each portion to be self contained, which is particularly advantageous in military applications requiring military hardening and/or a watertight integrity. Secure communications are facilitated by the low power level of the signal conveyed via mutual inductance and by signal loss due to eddy currents formed in the walls of each portion. Secure communications are also facilitated because radiation of electromagnetic energy from each gap of the dual-gap toroidal core has an opposing polarity, thus essentially canceling radiating electromagnetic energy in the far field. As described in more detail below, attenuation of radiated electromagnetic energy from the two gaps is proportional to 1/r 3 , wherein r is the distance from the gaps, thus providing more secure communications than existing systems having attenuation proportional to 1/r 2 .  
         [0019]    Referring now to FIG. 1, there is shown a cross-sectional view of a wireless secure connection  100  comprising a first inductor  16  and second inductor  18  separated by a gap distance  27 , illustrating wirelessly conveyed signal  25 . The first inductor  16  comprises a first end  20  and a second end  22 . The second inductor  18  comprises a third end  24  and a fourth end  26 . Inductors  16 ,  18  are shown as “U” shaped. The first end  20  and the third end  24  define a first gap  23  therebetween and the second end  22  and the fourth end  26  define a second gap  29  therebetween. However, each inductor  16 ,  18  may vary in shape and size, while maintaining a configuration having ends  20 ,  22 ,  24 , and  26 , respectively. For example, each inductor  16 ,  18  may be rectilinear, arcuate (“U” shaped being a subset of arcuate), or a combination thereof. The signal  25  is indicative of information communicated via mutual inductance between the inductors  16 ,  18 .  
         [0020]    Also shown in FIG. 1 is first portion  12  comprising the first inductor  16  and second portion  14  comprising the second inductor  18 . Each portion,  12  and  14 , is a separate self contained unit. Each portion,  12  and  14 , may comprise, for example, a transmitter, a receiver, or a combination thereof. In one embodiment, the portion  12  is a military radio, such as a man portable military radio, for example, and the portion  14  is a faceplate and/or headset configured to provide information to the military radio  12  such as configuration/operational parameters (e.g., modulation type, transmit frequency, receive frequency), cryptographic keys, or a combination thereof. To aid in ensuring that the signal  25  is conveyed via mutual inductance between the first and second inductors  16 ,  18 , the first and second portions  12 ,  14 , are aligned.  
         [0021]    Aligning the first portion  12  with the second portion  14  comprises aligning the first end  20  with the third end  24  and aligning the second end  22  with the fourth end  26 . The first portion  12  and the second portion  14  are aligned to facilitate the conveyance of signal  25  between the respective ends,  20 ,  22 ,  24 ,  26 , of inductors  16 ,  18 . The first portion  12  and the second portion  14  may be aligned by any appropriate means. For example, one of the walls (wall  1  or wall  2 ) may comprise a protrusion, or a plurality of protrusions. The other wall may comprise a conformably shaped corresponding indentation, or plurality of indentations, (e.g., pimple and dimple) configured to receive each respective protrusion, such that when the protrusion(s) are inserted into the indentation(s), the first and second portions  12 ,  14 , are aligned. Examples of other types of alignment means include slots, fasteners, visually aligning characteristics of the first and second portions  12 ,  14 , (e.g., aligning edges of portions  12 ,  14 , to be flush), or a combination thereof.  
         [0022]    Wall  1  and wall  2  represent sides of portion  14  and portion  12 , respectively. Each wall may comprise any appropriate material allowing electromagnetic energy to traverse therethrough. For example, each wall ( 1 ,  2 ) may comprise steel, iron, aluminum, plastic, ceramic, or combination thereof (including alloys). In situations where secure communications are desired, such as military scenarios wherein classified data is being communicated, it is advantageous for the signal  25  to be conveyed between the first portion  12  and the second portion  14  with as little error as practicable. However, it is also advantageous if the wireless signal  25  is attenuated as the distance from the source of the electromagnetic energy (e.g., the gaps  23 ,  29 ) increases. Thus, allowing the signal  25  to wirelessly convey information across the gaps  23 ,  29 , but also preventing unauthorized access/monitoring of the signal  25  from a monitoring point a distance away from the gaps  23 ,  29 .  
         [0023]    For example, the first portion  12  may comprise a man portable military radio for communicating secure information with other radios. In the field, this radio may have to be reconfigured (e.g., change frequencies, provide cryptographic keys, change modulation type). Accordingly, the second portion  14  may be configured as a faceplate which fits on the front panel of the radio  12 . When the faceplate  14  is aligned with the front panel of the radio  12 , reconfiguration parameters may be wirelessly conveyed (e.g., via signal  25 ) to the radio  12  in a secure manner via mutual inductance. Furthermore, the configuration parameters may be predetermined, such that the radio operator need only activate a switch to select the set of configuration parameters to be conveyed to the radio  12  from the faceplate  14 . This exemplary configuration of secure wireless connection  100  is particularly advantageous in situations where the radio operator is in a hostile environment and desires to keep his hands on his weapon.  
         [0024]    [0024]FIG. 2 is a diagram of a communication system  200  comprising the secure wireless connection  100  and amplification and detection circuitry, in accordance with an embodiment of the present invention. System  200  comprises input signal  44 , input amplifier  38 , exclusive or gate  30 , comparator  40 , sense resistance  32 , a voltage divider circuit comprising resistance  34  and resistance  36 , termination resistance  28 , output amplifier  42 , and output signal  46 . The herein description of system  200  is in terms of the first portion  12  being a receiving portion and the second portion  14  being a transmitting portion, however, it is to be understood that the system  200  is not limited to this configuration. In one embodiment, the first portion  12  is a receiving portion (receiver) of the communication system  200  and the second portion  14  is a transmitting portion (transmitter) of the communication system  200 . In this embodiment, input signal  44  is provided to the transmitting portion  14  and is conveyed, via wireless signal  25 , to the receiving portion  12 . The input signal  44  is indicative of information to be conveyed to the receiving portion  12 , such as the configuration parameters described above, for example. The input amplifier  38  amplifies the input signal  44  and provides amplified signal  45  to the second inductor  18  via sense resistance  32 . The input amplifier  38  may also filter the input signal  44 . The amplified input signal  45  is provided to the second inductor  18  and transferred, via mutual inductance via the wireless signal  25  across the gaps  23 ,  29 , to the first inductor  16 . The conveyed signal  47  is provided to the output amplifier  42 . The output amplifier  42  amplifies, and optionally filters, the conveyed signal  47  to provide output signal  46 . It is envisioned that other embodiments of the system  200  may comprise various types of circuitry for performing signal processing, such as filtering, error detection, error correction, noise reduction, gain control, or a combination thereof, for example.  
         [0025]    Another embodiment of the system  200  comprises detection circuitry for determining if the first portion  12  and the second portion  14  are within communication range of each other. Detection circuitry is advantageous in scenarios including secure communications. For example, if a radio operator wants to transmit configuration parameters to a radio via the wireless communication system  200 , if the receiving portion  12  is not within communication range of the transmitting portion  12 , secure information may be transmitted into the air, and possible intercepted by an unauthorized user. Detection circuitry, for determining if the first portion  12  and the second portion  14  are in communication range of each other, and for providing an indication of same, helps prevent this type of unauthorized access.  
         [0026]    Detection circuitry, as depicted in FIG. 2, comprises the sense resistance  32 , the voltage divider circuit comprising resistances  34  and  36 , comparator  40 , exclusive or gate  30 , and termination resistance  28 . It is to be understood that this configuration of detection circuitry is exemplary and that other configurations of detection circuitry are envisioned, such as via optical means, acoustic means, other electronic circuits, or a combination thereof, for example, wherein the goal is to determine if the first portion  12  and the second portion  14  are within communication range of each other. In operation, a detection signal is provided to the second inductor  18 . This detection signal may be a signal specifically designated for determining if the first and second portions  12 ,  14 , are within communication range of each other, may be a component of the information being conveyed from the first portion  14  to the second portion  12  (e.g., signals  44 ,  45 ), may be a specifically designed detection interspersed with the information, or a combination thereof. The detection signal is provided to the second inductor  18  via sense resistance  32 . The voltage divider circuitry (resistances  34  and  36 ) provides a predetermined portion of the detection signal to input terminal  40   b  of the comparator  40 . The detection signal is conveyed from the second inductor  24  to the first inductor  16  via mutual inductance across the gaps  23 ,  29  (e.g., signal  25 ). The termination resistance  28  provides termination impedance to the first inductor  16  which is reflected back to the second inductor  18  via transformer action. This reflected termination impedance develops a reflected signal, referred to as a reflected impedance signal. The reflected impedance signal is provided to the input terminal  40   a .. For example, if the first inductor  16  is not within communication range of the second inductor  18 , no reflected impedance signal is generated, and the value of voltage provided to the input terminal  40   a  is indicative of this configuration. If the first inductor  16  is within communication range of the second inductor  18 , a reflected impedance signal is created and the value of the voltage provided to input terminal  40   a  is indicative of this configuration and differs from the value of the voltage provided to the input terminal  40   a  when the inductors  16 ,  18 , are within communication range of each other. The comparator  40  provides a comparison signal  41 , which is indicative of the status of the determination if the first portion  12  is within communication range of the second portion  14 . If the signal at terminal  40   a  is greater than the signal at terminal  40   b , the comparison signal will provide one indication, and if the signal at terminal  40   a  is less than the signal at terminal  40   b , than the comparison signal will provide another indication. Thus, the detection circuitry may be configured to indicate that the first and second portions  12 ,  14 , are within communication range of each other by selecting specific (predetermined) values of resistance  34  and  36 . Selecting predetermined values of resistances  34  and  36  provides a predetermined portion of the detection signal being provided to the input terminal  40   b  of the comparator  40 . The values of the resistances  34  and  36  may be determined analytically, empirically, or a combination thereof. The comparison signal  41  is provided to the exclusive or gate  30 , which also receives the detection signal. An indicator signal  43  is provided by the exclusive or gate  30 . The indicator signal  43  is indicative of the determination if the first portion  12  and the second portion  14  are within communication range of each other. Response to the indicator signal  43  may be by the operator and/or may occur automatically. For example, upon receipt of the indicator signal  43 , the radio operator (or the system) may choose to ignore the indicator signal  43 , terminate transmission, not commence transmission, or a combination thereof.  
         [0027]    As mentioned above, secure communications are facilitated if the attenuation of a wireless signal increases as the distance increases from the source of radiation of the wireless signal. Thus, the more rapidly the attenuation increases, as a function of distance, the more secure the system. Existing systems attenuate the radiated signal as a function of the distance from the source of radiation, r, raised to the second power (1/r 2 ). It has been shown, analytically, that a secure wireless connection in accordance with the present invention provides attenuation of the radiated wireless signal increases as a function of the distance from the source of radiation raised to the third power (1/r 3 ). A system providing attenuation as a function of 1/r 3  is more secure than a system providing attenuation as a function of 1/r 2 .  
         [0028]    [0028]FIG. 3 is a graphical plot of attenuation versus range for attenuation in accordance with a secure wireless connection in accordance the present invention (curve  50 ), as a function of r 4  (curve  52 ), as a function of r 3  (curve  54 ), and as a function of r 2  (curve  56 ). It can be shown that the attenuation of a radiated electromagnetic signal (e.g., signal  25 ) is attenuated as a function of range, F(r), in accordance with the following equation.  
                 F        (   r   )       =       1     r   2       -     1       (     r   +   a     )     2           ,           (   1   )                               
 
         [0029]    wherein:  
         [0030]    F(r) is a function of r, r is the average distance from the two gaps (see FIG. 1), and “a” is a constant value equal to the distance between the two ends of an inductor (see FIG. 1).  
         [0031]    Curve  50  is a plot of F(r), curve  52  is a plot of 1/r 4 , curve  54  is a plot of 1/r 3 , and curve  56  is a plot of 1/r 2 . As shown in FIG. 3, the curve  50  is closer to curve  54  than the other curves ( 50 ,  56 ). Thus the function F(r) is closest to attenuation as a function of 1/r 3 . Also, only curves  52  and  54  appear to have the same shape. If curves  52  and  54  have the same shape than the two curves are proportional.  
         [0032]    [0032]FIG. 4 is a graph of the difference between curves  56  and  50  (curve  58 ), curves  54  and  50  (curve  60 ), and curves  52  and  50  (curve  62 ). Curve  58  is a plot of the difference between 10 log 1/r 2  (curve  56 )−10 log F(r) (curve  50 ). As shown in FIG. 4, curve  58  is not a straight line, thus indicating that curves  50  and  56  are not the same shape. Curve  62  is a plot of the difference between 10 log 1/r 4  (curve  52 )−10 log F(r) (curve  50 ). As shown in FIG. 4, curve  62  is not a straight line, thus indicating that curves  50  and  52  are not the same shape. Curve  60  is a plot of the difference between  10  log 1/r 3  (curve  54 )−10 log F(r) (curve  50 ). As shown in FIG. 4, curve  60  is a straight line, thus indicating that curves  50  and  54  are the same shape, and thus proportional. Therefore, a secure wireless connection in accordance with the present invention provides attenuation of a radiated electromagnetic signal (e.g., signal  25 ) that is inversely proportional to the distance from the gaps raised to the third power (i.e., proportional to 1/r 3 ).  
         [0033]    [0033]FIG. 5 is a flow diagram of a process for providing wireless secure communication in accordance with an embodiment of the present invention. The first portion  12  and the second portion  14  are aligned at step  70 . Aligning the first and second portion  12 ,  14 , includes aligning the first end  20  of the first inductor  16  with the third end  24  of the second inductor  18 , and aligning the second end  22  of the first inductor  16  with the fourth end  26  of the second inductor  18 . When aligned, the inductors,  16 ,  18 , are configured to form a dual-gap toroidal core. As described above, the polarities of the electromagnetic field created at each gap  23 ,  29 , have opposite polarities. Thus, the opposite polarity fields cancel each other when combined (e.g., far field). Also, as described above, the attenuation of radiated electromagnetic energy from the gaps  23 ,  29 , is attenuated in accordance with an equation proportional to 1/r 3 .  
         [0034]    At steps  72  through  82 , it is determined if the first portion  12  and the second portion  14  are within communications range of each other. At step  72 , the detection signal (which may be amplifier and/or filtered) is provided to the second inductor  18 . At step  74 , the detection signal is conveyed from the second inductor  18  to the first inductor  16  via wireless mutual inductance. An impedance signal is created at step  76  (e.g., via termination resistance  28 ). The impedance signal is reflected back to the second inductor  18  via transformer action (mutual inductance) generating a reflected impedance signal at step  78 . At step  80 , a predetermined portion (e.g., via voltage divider circuitry) of the detection signal is provided to the comparator (e.g., comparator  40 ). The predetermined portion of the detection signal and the reflected impedance signal are compared with each other at step  82 . If the first and second portions  12 ,  14 , are within communication range, as determined at step  78 , the secure wireless communications via mutual inductance via the gaps,  23 ,  29 , of the dual-gap toroidal core may be conducted. If it is determined, at step  78 , that the first and second portion  12 ,  14 , are not within communication range of each other, an out of range indication is provided ate step  86 . As described above, various courses of action may be pursued as a result of this out of range indication, such as manually and/or automatically ignoring the out of range indication, terminating communications, not initiating communications, or a combination thereof.  
         [0035]    A secure wireless connection in accordance with the present invention facilitates secure communications by attenuating a radiated signal proportional to 1/r 3 , where r is the average distance from the two gaps of the dual-gap toroidal core. This secure wireless connection also provides a communications link between two self contained portions of a system through low frequency (e.g., voice or base band, low data rate signal) magnetic fields that can penetrate the envelope of the equipment when aligned with each other. Secure communications are also facilitated by the low power level of the transmitted signal, by eddy currents formed in the walls of the first and second portions  12 ,  14 , and by aligning the first and second portions  12 ,  14 . The secure wireless connection in accordance with the present invention does not require mechanical connectors, such as threaded connectors and/or bayonet connectors, thus reducing the weight and set up time. A system comprising the secure wireless connection in accordance with the present invention, such as a radio communication system, is capable of being configured to allow water tight integrity, military hardening, and does not require modification of the structure (envelope) of the first and second portions,  12 ,  14 , to facilitate communications. Because no change in material is required, such as occurs when a window is put into a metallic envelope to support an infrared link, the envelope of the equipment is not compromised.  
         [0036]    Although illustrated and described herein with reference to certain specific embodiments, the wireless secure connection as described herein is nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention.