Abstract:
A smart signal jammer is disclosed that receives a description of an unwanted signal or signals to be jammed, and transmits one or more jamming signals in one or more temporal transmission patterns of pulses that jam the unwanted signal or signals. This is in contrast to basic jammers in the prior art, which typically receive a description of a signal or signals to be transmitted. A smart jammer according to the present invention can improve the efficiency with which available transmitters are used to transmit jamming pulses, thus reducing the number of needed transmitters, compared to a prior-art jammer. A smart jammer according to the present invention comprises a jamming signal calculator that calculates the parameters of the jamming signals to be transmitted. The calculations are based on inequalities that are satisfied by an efficient jamming signal.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to communication disruption in general, and, more particularly, to jamming unwanted communication. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the American Heritage Dictionary, third edition, one of the meanings reported for the verb “to jam” is: “to interfere with or prevent the clear reception of . . . signals . . . by electronic means.” In this disclosure, the verb “jam” and its conjugated forms (e.g., “jammed,” “jamming,” “jammer,” etc.) are used, in a somewhat broader sense, to mean: disrupting an unwanted signal of any kind (e.g., radio, optical, acoustic, electrical, etc.) by transmitting an interfering signal of a similar or related kind into the medium (e.g., radio channel or band, optical fiber, waveguide, audio channel or environment, cable or wire or transmission line, etc.) occupied by the unwanted signal, in such a way that the reception of the unwanted signal is disrupted, or prevented or, at least, impaired. Jamming unwanted, unauthorized or threatening communication signals is a technique that is commonly used by military personnel. For example, a jammer that overwhelms a radio channel with interference can be an effective defense against enemy communications in the battlefield. Indeed, disruption of unwanted radio signals is a common application of jamming techniques. Hereinafter this disclosure will use language frequently associated with radio communications and radio signals; however, such language should be understood to have a broader applicability to any kind of signal, as indicated above. 
         [0003]      FIG. 1  is a schematic diagram of the salient components of an illustrative signal jammer in the prior art. It is labeled a “basic” signal jammer to highlight the simple architecture of signal jammers that is common in the prior art. Basic signal jammer  100  comprises: receiver  110 , transmitter  111 - 1 , transmitter  111 - 2 , and transmitter  111 - 3 , interconnected as shown. 
         [0004]    Receiver  110  is a device that receives a description  101  of signals to be transmitted, and converts that description into parameters of jamming signals to be transmitted (hereinafter, “jamming-signal parameters”). Receiver  110  conveys the values of the jamming-signal parameters to transmitters  111 - 1 ,  111 - 2 , and  111 - 3 . 
         [0005]    Transmitters  111 - 1 ,  111 - 2 , and  111 - 3  transmit jamming signals  102 - 1 ,  102 - 2 , and  102 - 3 , respectively. Each signal can be transmitted in a different band, and different signals can be transmitted in different bands at different points in time. In particular, each transmitter can transmit a short burst (hereinafter “pulse”) of interfering signal in one band and, immediately afterwards, transmit another pulse in another band, and so on, in a pattern that is usually repeated periodically in time (hereinafter “temporal transmission pattern”). The specific parameters of the temporal transmission patterns to be transmitted by the three transmitters are provided by description  101  and are incorporated into the jamming-signal parameters by receiver  110 . 
         [0006]    In typical prior-art jammers, the selection of parameters for the temporal transmission patterns is performed by a human operator of basic signal jammer  100 . The human operator usually knows one or more characteristics of the signal, or signals to be jammed, and, based on his or her experience and skill, can generate parameters for the temporal transmission patterns so as to achieve an effective jamming of the unwanted signals. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention enables a signal jammer that avoids some of the costs and disadvantages of signal jammers in the prior art. For example, an embodiment of the present invention is a “smart” signal jammer that receives a description of an unwanted signal or signals to be jammed, (in contrast to basic jammer  100  in the prior art, which receives a description of signals to be transmitted) and transmits one or more jamming signals in one or more temporal transmission patterns of pulses that jam the unwanted signal or signals. 
         [0008]    Furthermore, a smart jammer according to the present invention can improve the efficiency with which available transmitters are used to transmit jamming pulses, thus reducing the number of transmitters needed by the smart jammer, compared to a prior-art jammer. 
         [0009]    A smart jammer according to the present invention comprises a jamming signal calculator that calculates the parameters of the jamming signals to be transmitted. The calculations are based on inequalities that are satisfied by an efficient jamming signal. An embodiment of the present invention comprises a method of generating jamming-signal parameters that satisfy the inequalities. Therefore, the jamming signals transmitted by a smart jammer according to the present invention can efficiently and effectively jam the signals whose description is provided to the smart jammer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic diagram of the salient components of an illustrative signal jammer in the prior art. 
           [0011]      FIG. 2  is a schematic diagram of the salient components of smart signal jammer  200  in accordance with an illustrative embodiment of the present invention. 
           [0012]      FIG. 3  depicts a method for using jamming signal  202 - 1  to jam an unwanted signal  304  that is transmitted at the maximum symbol rate, R max , specified by description  201 . 
           [0013]      FIG. 4  depicts a method for using jamming signal  202 - 1  to jam an unwanted signal  404  that is transmitted at the minimum symbol rate, R min , specified by description  201 . 
           [0014]      FIG. 5  is a flowchart of the salient tasks for generating jamming-signal parameters according the illustrative embodiment. 
           [0015]      FIG. 6  is a diagram that illustrates how method  500  works on an example signal description  201 . 
           [0016]      FIG. 7  is a diagram of an example of temporal transmission patterns transmitted by smart signal jammer  200 . 
       
    
    
     DETAILED DESCRIPTION  
       [0017]      FIG. 2  is a schematic diagram of the salient components of smart signal jammer  200  in accordance with an illustrative embodiment of the present invention. Smart signal jammer  200  comprises: receiver  210 , jamming signal calculator  212 , transmitter  111 - 1  through transmitter  111 - 3 , interconnected as shown. 
         [0018]    Although the illustrative embodiment comprises three transmitters, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention that comprise one, two, or more than three transmitters. 
         [0019]    Receiver  210  is a device that receives a description  201  of a signal to be jammed, (in contrast to receiver  110 , which receives description  101  of signals to be transmitted) and converts that description into a format that can be used by jamming signal calculator  212 . Although receiver  210  receives one description of a signal, it will clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention which receive:
       i. a description of a plurality of signals, or   ii. a plurality of descriptions, each of which is of one or more signals, or   iii. a combination of i and ii.       
 
         [0023]    Description  201  can be provided in a variety of ways. For example, and without limitation, description  201  can be provided through:
       i. knobs, switches and pushbuttons set by a human operator, or   ii. a graphical user interface implemented through one or more digital or analog displays, or   iii. a graphical user interface implemented through a general-purpose computer, or   iv. a mouse, or a trackball, or a stylus, or any other graphical input device, or   v. a text-entry device, or a numerical-entry device such as a keyboard or a keypad, or   vi. a voice-entry system, or   vii. a data cartridge, disk, module, memory, or other storage device containing the description, or   viii. a radio signal modulated with data that convey the description, or   ix. any kind of signal that can be used to convey data (e.g., sound, infrared, electrical, etc.), or   x. any combination of i, ii, iii, iv, v, vi, vii, viii, and ix.
 
It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the description is provided through one of the methods listed above, or through other methods for conveying data.
       
 
         [0034]    Description  201  can comprise elements that specify various characteristics (hereinafter “parameters”) of the signal or signals to be jammed. Such parameters can be specified as unique values, or they can be specified as sets or ranges. For example, and without limitation, they can be exact numerical values or ranges of numerical values. In an illustrative embodiment of the present invention, description  201  comprises a range of baud values and a specification of frequency bands in which the signal to be jammed can exist. A range of baud values can be specified as an uninterrupted range extending from a minimum baud value, R min , to a maximum baud value, R max . The specification of frequency bands can comprise the number of frequency bands, B, and also comprise identifiers to uniquely identify the frequency bands. Hereinafter, the frequency bands will be denoted by integers from 1 to B. It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention which utilize other methods of, or formats for specifying baud ranges and frequency bands, or other parameters of the signal, or signals to be jammed. 
         [0035]    The use of baud values to characterize the signal to be jammed implies that the signal is digital. In particular, it is well known in the art that baud is a unit of measure of symbol rate in digital communication systems, with 1 baud corresponding to 1 symbol/second. Therefore, the range of baud values from R min  to R max  specifies that the symbol rate of the signal to be jammed can be anywhere within that range. 
         [0036]    Jamming signal calculator  212  accepts, from receiver  210 , a converted version of description  201 . In an illustrative embodiment of the present invention, receiver  210  converts description  201  into electronic data, and jamming signal calculator  212  is implemented as an electronic computer; however, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention which use other implementations of jamming signal calculator  212 . 
         [0037]    Jamming signal calculator  212  generates jamming-signal parameters and conveys them to transmitters  111 - 1 ,  111 - 2 , and  111 - 3 , which transmit jamming signals  202 - 1 ,  202 - 2 , and  202 - 3 , respectively, based on the jamming-signal parameters. These transmitters are the same as transmitters  111 - 1 ,  111 - 2 , and  111 - 3  used in prior-art jammer  100 ; however, jamming signals  202 - 1 ,  202 - 2 , and  202 - 3  are different from jamming signals  102 - 1 ,  102 - 2 , and  102 - 3  because they are based on the jamming-signal parameters calculated by jamming signal calculator  212 . 
         [0038]    Jamming signal calculator  212  calculates the jamming-signal parameters based on several constraints that can be expressed as inequalities that involve the jamming-signal parameters in combination with elements of description  201 . These inequalities are devised such that, when satisfied, jamming signal  202  is an effective jamming signal.  FIG. 3  and  FIG. 4  illustrate how such inequalities are derived. 
         [0039]      FIG. 3  depicts a method for using jamming signal  202 - 1  to jam an unwanted signal  304  that is transmitted at the maximum symbol rate, R max , specified by description  201 . Signal  304  is structured as a sequence of digital messages  310 , wherein each message  310  is a sequence of digital symbols. Accordingly, description  201  can further comprise, in addition to the three elements R min , R max , and B already mentioned, also a minimum number of symbols, N b , that each message is known to contain (also referred to as the minimum length of a message). 
         [0040]      FIG. 3  shows that jamming signal  202 - 1  comprises a short pulse  311  of jamming energy transmitted in the band where signal  304  exists. The short pulse  311  is represented by a shaded rectangle in  FIG. 3 , and is repeated at periodic intervals; the time duration of pulse  311  is denoted the parameter L w  (which is an abbreviation of “window length”). In between repetitions of pulse  311 , jamming signal  202 - 1  comprises other pulses  312 , represented by white rectangles in  FIG. 3 , that are transmitted in other frequency bands in order to jam unwanted signals that might exist in those bands. All pulses have the same duration, L w , and to jam all the bands specified by description  201 , the total number of transmitted pulses is B. Accordingly, the repetition period of pulse  311  is L w B. 
         [0041]    In modern digital communications, error-correction techniques enable a signal to tolerate errors, up to a certain extent. Accordingly, description  201  can further comprise an indication of the extent to which message  310  can tolerate errors. In particular, description  201  can comprise an element, N o , that is the minimum number of symbols of message  310  that must be overlapped by pulse  311  (also referred to as the minimum size of a portion of the message, the portion to be overlapped by the second signal). For example, a value of N o  can be computed from the probability, P o , that the presence of pulse  311  will cause a symbol error, and from the maximum number, N e , of symbol errors that message  310  can tolerate, as N o =┌(N e +1)/P o ┐. 
         [0042]    To insure that the required number of symbols, N o , is overlapped by pulse  311 , the inequality L w ≧N o /R max  must be satisfied. To insure that at least one pulse  311  occurs during each message  310 , the repetition period of pulse  311  must be no greater than the duration of message  310 ; i.e., the inequality L w B≦N b /R max  must be satisfied. 
         [0043]      FIG. 4  depicts a method for using jamming signal  202 - 1  to jam an unwanted signal  404  that is transmitted at the minimum symbol rate, R min , specified by description  201 . As in  FIG. 3 , signal  202 - 1  comprises a sequence of pulses  311  transmitted in the band where signal  404  exists.  FIG. 4  shows a sequence of individual digital symbols  410  from signal  404 . Each pulse  311  overlaps only a fraction of a symbol  410 ; if that fraction is too small, the pulse will not succeed in jamming the symbol. How small is too small depends on the details of the modulation scheme used by signal  404 ; accordingly, description  201  can further comprise a minimum fraction, f, of a symbol, the minimum fraction to be overlapped by pulse  311 . For pulse  311  to overlap the minimum fraction, f, of symbol  410 , the inequality L w ≧f/R min  must be satisfied. 
         [0044]    As was true for signal  304 , it is necessary that N o  symbols be jammed in a message; i.e., there must occur at least N o  repetitions of pulse  311  within the time interval occupied by a message. This requirement means that the inequality L w B≦N b /(R min  N o ) must be satisfied. Table I lists the four inequalities that must be satisfied. Table II summarizes the definitions of the variables appearing in the inequalities. 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 inequalities 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 L w B ≦ N b /R max   
               
               
                   
                 L w  ≧ N o /R max   
               
               
                   
                 L w  ≧ f/R min   
               
               
                   
                 L w B ≦ N b /(R min  N o ) 
               
               
                   
                   
               
             
          
         
       
     
         [0045]    If a value for L w  exists that satisfies all four inequalities, signal  202 - 1  is sufficient, by itself, to jam any signal that fits description  201 . In this case, jamming signal calculator  212  can set the jamming-signal parameters such that transmitters  111 - 2  and  111 - 3  are turned off, while transmitter  111 - 1  is configured to transmit a periodic temporal transmission pattern of pulses of duration L w  in the B bands specified by description  201 . 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE II 
               
               
                   
               
               
                 variables 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 R min   
                 minimum baud value of signal to be jammed 
               
               
                   
                 R max   
                 maximum baud value of signal to be jammed 
               
               
                   
                 B 
                 number of frequency bands to be jammed 
               
               
                   
                 N b   
                 minimum number of symbols in a message to be jammed 
               
               
                   
                 L w   
                 time duration of jamming pulse 
               
               
                   
                 N o   
                 minimum number of symbols to be overlapped 
               
               
                   
                 f 
                 minimum fraction of a symbol to be overlapped 
               
               
                   
                   
               
             
          
         
       
     
         [0046]      FIG. 5  is a flowchart of the salient tasks for generating jamming-signal parameters according the illustrative embodiment. In method  500 , a value for L w  that satisfies all four inequalities is found. If necessary, method  500  finds modified values B 1  for B, and R max1  for R max , that allow it to find such a value, wherein B 1 ≦B and R max1 ≦R max . Jamming signal calculator can use method  500  to generate jamming-signal parameters to configure transmitter  111 - 1  such that jamming signal  202 - 1  jams signals that can exist in B 1  bands with a symbol rate between R min  and R max1 . If B 1 =B and R max1 =R max , this is the case mentioned in paragraph [0032] wherein signal  202 - 1  is sufficient, by itself, to jam any signal that fits description  201 . Otherwise, method  500  calls itself recursively, to generate additional jamming-signal parameters to configure transmitters  111 - 2  and  111 - 3 , such that signals  202 - 1 ,  202 - 2  and  202 - 3 , in combination, jam any signal that fits description  201 . Although this example illustrates how to generate jamming-signal parameters for three transmitters, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention wherein method  500  calls itself recursively additional times in order to generate jamming-signal parameters for additional transmitters. 
         [0047]      FIG. 6  is a diagram that illustrates how method  500  works on an example signal description  201 . Region  601  represents the signals that are jammed by signal  202 - 1  when B 1 &lt;B and R max1 &lt;R max  (i.e., the first use of method  500  “covers” region  601 ). Regions  602  and  603 , together, represent all the signals that fit description  201  but that are not jammed by signal  202 - 1 . Because regions  602  and  603  are rectangular in shape—the same shape as the region defined by description  201 —jamming signal calculator  212  can use method  500  again to cover each of these two regions. In particular, method  500  is used again twice, once for region  602  and once for region  603 , to generate jamming-signal parameters for signals  202 - 2  and  202 - 3 , respectively. It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention that comprise more than three transmitters and in which method  500  is used again, recursively, to generate additional jamming-signal parameters for the additional transmitters. 
         [0048]    The recursive feature of method  500  is accomplished by tasks  515  and  516 . Task  515  covers region  602 , and task  516  covers region  603 ; however, in task  515 , the recursive call to method  500  uses the value B- 1  for the number of bands, instead of the value B, even though, according to  FIG. 6 , B is the number of bands that region  602  comprises. This is because, at any instant in time, signal  202 - 1 , which covers region  601 , is transmitting a pulse in some band and, therefore, there are only B- 1  bands remaining that do not already contain a jamming signal. There is no need for transmitter  111 - 2  to transmit a jamming pulse in a band where another transmitter (in this case, transmitter  111 - 1 ) is already transmitting a jamming pulse. The temporal transmission pattern of pulses comprised by signal  202 - 2  is repeated periodically only over the B- 1  bands available at any given time. In particular, at the instant in time when a new transmission pulse is to begin, the new transmission pulse is placed in the next available transmission band; i.e., it is placed in the next band that is unoccupied at that instant in time.  FIG. 7  illustrates the resulting pattern. 
         [0049]      FIG. 7  is a diagram of an example of temporal transmission patterns transmitted by smart signal jammer  200 . In particular, temporal transmission patterns  700 , as depicted in  FIG. 7 , are for an illustrative embodiment of the present invention wherein B=5, and the first use of method  500  yields B 1 =B and R max1 &lt;R max . In this case, only signals  202 - 1  and  202 - 2  are required for jamming. The top half of the diagram in  FIG. 7  shows the temporal transmission pattern of signal  202 - 1 ; the bottom half of the diagram shows the temporal transmission pattern of signal  202 - 2 . Individual pulses are shown as shaded rectangles such as pulse  711 - 1 , which is for signal  202 - 1 , and pulse  711 - 2 , which is for signal  202 - 2 . The pulses of signal  202 - 1  are transmitted sequentially in each of the five bands specified by description  201 , and then repeat periodically. The pulses of signal  202 - 2  are transmitted sequentially in each of the four remaining band, and then repeat periodically among the four bands that remain unoccupied by signal  202 - 1  at any given time. It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention wherein method  500  is used to generate temporal transmission patterns for a different number of signals, or a different number of bands, or a combination of both. 
         [0050]    The flowchart provided in  FIG. 5  is intended for illustrative purposes. It will be clear to those skilled in the art, after reading this disclosure, how to make and use embodiments of the present invention wherein method  500  is implemented through other tasks, or is implemented through software, firmware or hardware, including all the details necessary to insure its proper execution and termination. For example, and without limitation, an embodiment of method  500  can include a termination test wherein the method terminates if it is called with B=0, or with R min =R max . It will also be clear to those skilled in the art, after reading this disclosure, how to make and use embodiments of the present invention wherein other methods are used to achieve jamming-signal parameters for one or more transmitted signals that satisfy all or some of the inequalities. 
         [0051]    It is to be understood that this disclosure teaches just one or more examples of one or more illustrative embodiments, and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure, and that the scope of the present invention is to be determined by the following claims.