Abstract:
A communication system that intercepts incoming radio signals and transmits a second signal notifying the user that a radio signal has been intercepted. The communication does so by using an interference generator that is passive, such as a shield, or active, such as destructive interference generators to create a zone in which the radio device does not receive the original incoming radio signal. Using an antenna located outside that zone, a registrar then intercepts incoming signals and notifies the user of the communication using a user-defined method. For example, the incoming signal can be rerouted to a landline or a paper message can be generated and delivered to the user.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to an apparatus and method for radio frequency communication. More particularly, the invention relates to methods and apparatus for isolating radio frequency communication devices and diverting the communication to more acceptable locations. 
   Since the advent of radio, people have been disturbed by other people&#39;s use of such devices. The use of early AM radios were no doubt restricted to low volumes in certain settings. As portability increased, so did the settings in which these devices were viewed with disdain. Boom boxes are not allowed, or at least discouraged, from use in various venues. 
   In recent years, a new form of communication device has taken center stage—the cellular telephone (“cell phone”). By this time, millions of people in the United States and around the world use cellular phones. One of the most interesting things about a cell phone is that it is actually a radio—an extremely sophisticated radio, but a radio nonetheless. 
   With the popularity of cell phones increasing, their use in public areas is also increasing. Use in restaurants and elevators, for example, is looked at with contempt by some, but usually not restricted. 
   Pagers are another wireless device that has seen a surge in popularity recently. Unlike cell phones, their ability to disturb is generally restricted to the audible alert that can accompany a page. However, like cell phones their alerts in the wrong environment can be disconcerting. For example, when they ring in a courtroom, a theater, or a library, the disturbance is substantial. 
   Likewise, other personal communicators such as personal digital assistants (PDAs), portable email devices and the like are performing more and more wireless communications, most also including an audible alert capability. 
   Requiring that these devices be disabled in certain environments is currently the best method of stopping these problems. However, in the case of an emergency, this is potentially dangerous where the user is now no longer easily reachable. For example, a doctor would no longer be available to receive a page from a hospital. Further, it requires that the users comply with the request. 
   There are still other forms of communication devices which have had their use questioned. Various consumer information devices are incorporating a communication standard known as Bluetooth. This, inter alia, allow the devices to communicate with other surrounding Bluetooth devices. Airlines have raise safety concerns over the inability to stop these devices from communicating and their potential for interference with aircraft electronics. 
   In order to best understand the invention with respect to the common example used herein, some basics of a cellular telephone system must be understood. For that purpose, a prior art cellular system  10  is described in  FIG. 1 . The cellular system  10  divides a city into small cells. This allows extensive frequency reuse across a city. Because cell phones  12  and base stations  18  use low-power transmitters, the same frequencies can be reused in non-adjacent cells. 
   Each cell has a base station  18  that consists of a tower  14  and a small building  17  containing the radio equipment  17 . 
   Each cell phone uses two frequencies per call—a duplex channel—so in an analog system, each carrier typically has 395 voice channels and another 42 frequencies for control channels. With digital transmission methods, the number of available channels increases. An analog system will be described, for the purpose of simplicity, though one skilled in the art will realize that the invention works equally with a digital system. 
   The cellular approach requires a large number of base stations  18  in a city of any size. Each carrier in each city also runs one central office called the Mobile Telephone Switching Office (MTSO)  20 . This office  20  handles all of the phone connections to the normal land-based phone system  22 , and controls all of the base stations  18  in the region. 
   All cell phones  12  have special codes associated with them. These codes are used to identify the phone, the phone&#39;s owner and the service provider. The cell phone codes are the following:
         Electronic Serial Number (ESN)—a unique 32-bit number programmed into the phone when it is manufactured   Mobile Identification Number (MIN)—a 10-digit number derived from the user&#39;s phone&#39;s number   System Identification Code (SID)—a unique 5-digit number that is assigned to each carrier by the FCC       

   While the ESN is considered a permanent part of the phone  12 , both the MIN and SID codes are programmed into the phone  12  when a user purchases a service plan and have the phone activated. 
   When a user turns on the cell phone  12  and someone tries to call the user, the following occurs:
         a. When the user first powers up the phone  12 , the phone  12  listens for an SID on the control channel. The control channel is a special frequency that the phone  12  and base station  18  use to talk to one another about things like call set-up and channel changing. If the phone  12  cannot find any control channels to listen to, it knows it is out of range and displays a “no service” message.   b. When the phone  12  receives the SID, the phone  12  compares it to the SID programmed into the phone  12 . If the SIDs match, the phone  12  knows that the cell it is communicating with is part of its home system.   c. Along with the SID, the phone  12  also transmits a registration request, and the MTSO  20  keeps track of the user&#39;s phone&#39;s location in a database. This way, the MTSO  20  knows which cell the user is in when it wants to ring the user&#39;s phone  12 .   d. The MTSO  20  gets the call, and it tries to find the user. It  20  looks in its database to see which cell the phone  12  is in.   e. The MTSO  20  picks a frequency pair that the user&#39;s phone  12  will use in that cell to take the call.   f. The MTSO  20  communicates with the user&#39;s phone  12  over the control channel to tell it which frequencies to use, and once the user&#39;s phone  12  and the base station  18  switch on those frequencies, the call is connected. The user is talking by two-way radio to a friend.       

   As the user travels, the signal is passed from cell to cell. 
   SUMMARY 
   Accordingly, it is an object of this invention to provide a communication system that ceases communication to personal electronics in a predefined environment. 
   It is another object of this invention to provide a communication system that that continues to allow users to be reached in the case of an emergency, or otherwise. 
   It is still another object of this invention to provide communication system that does not require a user to disable their radio communication device. 
   The aforementioned and other objects are achieved by the invention which provides a communication system for isolating consumer and other electronics and a method associated therewith. 
   A communication system is disclosed for use with a radio communication device where an incoming signal alerts a user to a communication on the radio communication device. The communication system comprises a signal interference device, an antenna and a receiver. 
   The signal interference apparatus is adapted to interfere with the incoming signal and has a predetermined border outside of which the signal interference device&#39;s effects are nominal. In essence, the signal interference device creates a zone in which the radio communication device does not receive the original signal or, if received, the original signal is unintelligible. The signal interference apparatus, therefore, selectively interferes with predetermined radio frequencies or a spectrum of frequencies. 
   The antenna is disposed beyond the predetermined border of the signal interference device. Thus, the antenna is not materially affected by the interference of the signal interference apparatus. 
   The receiver is electrically connected to the antenna so that it receives the incoming signal. The receiver, in essence, intercepts the incoming signal. A Registrar then selectively tracks devices within the zone of the signal interference apparatus and parses out communications intended for those devices that have been registered. 
   Once intercepted, the signal intended for the registered devices are processed to create a message or redirect the message elsewhere. For example, if the incoming signal is a cellular phone call, the signal may be redirected to a landline. If the incoming signal is from a pager, it may be redirected to an email message. If the signal is not intended for a registered device, the registrar of this embodiment of the invention discards the signal. 
   In further aspects, the invention provides methods in accord with the apparatus described above. The aforementioned and other aspects of the invention are evident in the drawings and in the description that follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects of this invention, the various features thereof, as well as the invention itself, may be more fully understood from the following description, when read together with the accompanying drawings in which: 
       FIG. 1  shows a diagram of a prior art cellular telephone system. 
       FIG. 2  shows a diagram of a structure isolated from radio communication in accordance with the invention. 
       FIG. 3  shows a diagram of an alternative embodiment of a radio communication in accordance with the invention. 
       FIG. 4  shows a block diagram of a registrar in accordance with the invention of  FIGS. 2 and 3 . 
   

   DETAILED DESCRIPTION 
   While the present invention retains utility within a wide variety of communication devices and may be embodied in several different forms, it is advantageously employed in connection with radio-frequency communication devices such as cellular telephones. Though this is the form of the exemplary embodiment and will be described as such, this embodiment should be considered illustrative and not restrictive. One skilled in the art will recognize that cellular telephones are simply one of many devices with which this invention may be used. Other devices in the non-exhaustive list comprise pagers, citizens band (CB) radios, AM/FM radios, wireless PDAs, wireless linked game units, and blue tooth devices. In addition, the invention is not frequency dependant, if the application so required, the invention is also useful with microwave radios, inter alia. 
     FIG. 2  is a diagram of structure  30  isolated from radio communication. The structure  30  shown is an entire building, though it can be a room within a building or other defined area. Moreover, the structure need not be fixed. One skilled in the art will recognize that a mobile structure such as the housing of aircraft, an elevator, or an automobile, inter alia, can be similarly used. Thus, the structure  30  shown as a building should be considered illustrative and not restrictive. 
   The structure  30  is isolated from radio communication by a shield  32 . The shield  32  insulates the structure  30  using any of various highly attenuating materials. Shielding can work both to prevent radio waves from radiating out or to prevent radio waves from getting in. The effectiveness of a shield is a function of the material, the frequency, the angle of incidence, coverage, and the thickness of the material. Metal is commonly used to shield radio waves. Plastic materials used as shields are coated or impregnated with reflective and adsorptive materials or have embedded screens. 
   The cell phone  12  is shown within the structure  30  and the structure is shown as a restaurant. As stated previously, the cell phone  12  can be any of various other radio device and the restaurant can be any of various other structures. 
   With the cell phone  12  disposed within the shield, communication waves  16  are attenuated prior to reaching the cell phone  12 . As such, the phone does not ring when the base station  18  attempts to establish communication. 
   Instead, when a user wishes to be available for a call while in the structure  30 , that user registers the phone with the registrar  38 . The registrar  38  reads from the cell phone  12  its SID either directly from the phone  12  or as a result of user input from a console (not shown). The user input may be the cellular phone number and/or the cellular service used by the service, for example. Since cellular phone services are assigned blocks of phone numbers, the SID can be a database lookup using the cellular phone&#39;s number. This information then allows the registrar to look up in its database the control channel frequencies used by the cellular service. 
   Likewise, the phone  12  is queried or sufficient data is input for the registrar to determine the MIN and any other information needed to establish communication between the registrar  38  and the base station  18  such that the registrar can act as if it were the phone  12 . 
   Once the registrar  38  knows the control channel(s), the registrar  38  receives radio  16  communication from an antenna  34  located outside of the shield  32 . The antenna  34  is in electrical communication with the registrar  38  via a cable  36 . One skilled in the art will recognize that the cable  36  can be replaced by wireless communication as long as both the transmitting antenna attached to the antenna  34  is located within the shield  32  as well as a receiving antenna attached to the registrar  38 . 
   The registrar  38  then listens on the control frequency associated with that phone  12  for an incoming call, similarly to what the cell phone  12  itself would do if the phone  12  were outside the shield  32 . Note that the registrar  38  of the invention is enabled to register multiple radio devices simultaneously and thus monitor multiple control channels. 
   If an incoming call is detected, the registrar  38  establishes contact over the control channel using the protocol expected by the base station  18 . The MTSO  20  communicates with the registrar  38  over the control channel to tell the registrar  38  which frequencies to use. The registrar then switches to those frequencies to communicate with the base station  18  on those frequencies. This is performed transparently to the base station  18  since the registrar is performing as if the registrar  38  were the phone  12 . 
   A telephone  42  connected to the registrar is then signaled and the call is connected. In the restaurant example, the host would be able to answer the phone  42  and take a message. In the registration process, the user can put table location information or receive a structure-dependant pager to receive messages. The host then delivers the message. The user steps to the lobby to use the phone  42  or to exit the structure to use his/her cell phone  12  to return the call, inter alai. 
   The registrar is enabled to communicate within private branch exchanges (PBX) or to simply forward calls to other phones. For example, if the structure  30  is a meeting room within a firm, the registrar  38  can be set up to send the call to the user&#39;s internal voice mail. The registrar can also be enabled to allow a caller to indicate that the call is urgent in which case the call is directed to a landline within the meeting room. Therefore, the actions performed upon the call upon receipt are programmable and selectable. The operator of the registrar  38  thus selects how the registrar will respond to calls of differing priority levels or to different registered users. 
   The registrar  38  is also enabled to accept voice messages. The user is then informed that a voice message is awaiting him/her, which can be collected at the cell phone user&#39;s convenience. The caller, upon being connected to voice mail, is presented the option of leaving the voice mail message and designating that the message is urgent or electing low priority, inter alia. If the message is urgent, the preprogrammed action sequence is executed. In the case of a restaurant, the host is usually notified and the host retrieves the user to take the call. In the case of a low priority call, the call is redirected to the voice mailbox associated with the user&#39;s cellular telephone account. 
     FIG. 3  shows a structure  30  equipped with destructive interference (DI) transmitters  40 . The DI transmitters  40  are low-power radio-frequency transmitters designed to interfere with the radio devices within the structure, in this case the cell phone  12 . DI transmitters  40  can be used instead of or in addition to the shield  32 , depending upon the required system design characteristics. 
   The DI transmitters  40  can interfere with the cell phone reception in any of numerous ways. Those methods are more technology dependent and thus will again be described by way of example. The overall goal of the DI transmitters  40  is to create confusion within a received radio signal due to the presence of noise (as atmospherics) or signals from two or more transmitters on a single frequency. 
   The DI transmitters  40  of the instant invention utilize inter-modulation to interfere with the reception. Inter-modulation noise is caused by the blending of two or more signals. This is the “classic” form of noise in radio-frequency devices. Communication systems are ever evolving and, thus, the DI transmitters  40  must simply use a type of noise that is sufficient to interfere with the devices in question. The usual variables in creation of the noise are phase, frequency and amplitude, though other methods known in the art may be employed. 
   That is, there is no standard level of interference or a single formula that can be used to compute it. What constitutes interference in one system may be totally invisible or inconsequential in another. Thus the DI transmitters  40  designed for use with pagers may be different than that used with cellular telephones or walkie-talkies. 
   To understand interference within its unique environment, it can be defined in terms of its amplitude relationship to the amplitude of the desired or “carrier” signal. This relationship is known as a “carrier-to-interference ratio” (C/I). 
   Every communications receiver has a minimum carrier-to-interference ratio that must be maintained in order to recover 100% of the information from a desired signal. If this minimum ratio of signal over interference is not met, communications will be disrupted, and the system becomes unusable. The specific receiver C/I characteristics depend on the usable dynamic range of the receiver front-end, as well as the type of demodulator and modulation being employed. 
   One method that can be employed by the DI transmitters  40  is to create dynamic range problems. The DI transmitters  40  would do so by subjecting the cell phone  12  to RF overload. The RF overload occurs by placing a strong RF signal on the control frequencies known to the registrar  38 . This requires the registrar&#39;s database to contain all control frequencies used by each carrier in the geographic area in which the registrar is used. The strong signal on the carrier channel causes inter-modulation distortion or degradation of the receiver&#39;s threshold sensitivity. In cases of inter-modulation distortion, inter-modulation products confuse the receiver&#39;s demodulator. In other words it is unable to discriminate between the “real” signal information and the “phantom” inter-modulation signal components, which results in garbage output. 
   In another embodiment, the DI transmitters  40  employ strong localized signals on the carrier channel to achieve receiver desensitization. The signals transmitted by the DI transmitters  40  are rectified by the receiver mixer diode junction(s), and the rectified DC voltage “pushes” the mixer&#39;s bias point away from the optimal operating point for signal mixing functionality. As a result, the mixer&#39;s weak signal performance is degraded, which decreases the receiver&#39;s sensitivity, or ability to “hear” signals of low amplitude. 
   In the alternative, the registrar can coordinate the destructive interference generated by the DI transmitters  40 . Since the antenna  34  is receiving the control frequency, it can determine the control signal&#39;s phase and signal strength. The registrar  38  informs the DI transmitters  40  of the frequency and phase information. The DI transmitters  40  then transmits a signal within the structure  30  in the same or substantially similar frequency which adaptively matches amplitude proportionally to that of the signal strength, but 180 degrees out of phase from the control signal. This then negates the control signal to a point below the C/I threshold for the cell phone  12 . This method is preferably used in conjunction with a shield  32  to avoid interference outside of the structure  30 . 
   Another example among the many possible means of interference generation is to not shield the structure at all and let the control signal through. However, using the same method as described above, the DI transmitters  40  transmits a signal within the structure  30  in the same frequency and phase as the control signal. This then becomes an additive signal relationship where the amplitude is then used to overload the receivers input. This would exceed the receiver&#39;s ability to read the signal again creating a form of destructive interference within the cell phone  12 . 
   The primary examples used above describe fixed-frequency interference. The DI transmitters  40  can also follow a control signal that is frequency hopping to create the interference described above simply by mimicking the hops as seen by the registrar  38 . Each carrier&#39;s frequency hopping schemes are generally known in the industry and can be preprogrammed too. 
   Alternatively, the DI transmitters  40  can generate interference across a frequency spectrum. This method of interference generation addresses carriers that employ spread spectrum and also those utilizing multiple control channels in a given frequency band. One method of accomplishing this is for the DI transmitters  40  to generate their interference, or noise, with a wider bandwidth about a center frequency. 
   The foregoing describes a system where the user does not have control over the structure  30 . There are instances however, where the user controls the structure and still elects to use the invention. In this case the invention is used to augment the radio signal  16 . An example of such an environment if an automobile. 
   In a controlled environment, the cell phone  12  is registered with the registrar and then purposely disabled. This can occur through shielding and DI transmitters as previously described, or simply by the user turning off the power to the cell phone. If the registrar has a mating console on which the phone can rest, the console can operate with the phone to disable it. 
   Once off, the registrar  38  acts as the cell phone&#39;s surrogate. A call is received through a fixed antenna  34  on the outside of the car and transmitted internally. The registrar  38  is then connected to a speakerphone mounted within the car or through the car&#39;s audio system. 
   In the alternative, the registrar  38  interferes with the control signal until it  38  needs to make use of it. Once a call is received, the registrar  38  informs the cell phone  12  of an incoming call over the control channel as is typical, but chooses a frequency pair that differs from that which was chosen by the MTSO  20 . The call is then retransmitted at an extremely low power within the structure  30  of the car and the cell phone  12  is used as designed. The retransmission method minimizes any possibility of outside noise while the low power transmission ensures that the registrar does not interfere with any user outside of the car on the same frequency pair. 
   The registrar  38  in either case has the advantage of using a stronger receiver wired directly to the car&#39;s electrical system and/or an external fixed antenna. 
     FIG. 4  shows the elemental components of one embodiment of the registrar  38  and will be described with continuing reference to  FIGS. 2 and 3 . As before, the radio signal is taken from the antenna  34  through the cable  36  or other such signal transmission method. 
   The signal is then brought in to the registrar  38  through a receiver  50 . The receiver is tuned to one or more frequency bands depending upon the application. In the foregoing implementation, the receiver is tuned to receive the control frequencies of the major cellular telephone carriers in the region where the registrar is located. Since there is generally one such channel per carrier, the receiver  50  is capable of receiving up to the number of licensed carriers in a region. However, in practice, the number of channels that the receiver  50  monitors is small since it will only try to monitor the control channels for those devices that have been registered. That is, even though the shield  32  and DI transmitter  40  interferes with many radio signals across a broad spectrum of radio frequencies, if the user does not register the radio device, i.e. the phone  12 , then the registrar does not monitor that control channel. One skilled in the art will recognize that even if multiple users register radio devices that use the same commercial service provider, only one control channel associated with that commercial service provider need be monitored. However, in the event that a commercial service provider utilizes multiple control channels, the receiver  50  would simply monitor the multiple channels associated with that commercial service provider. In this embodiment, the maximum number of channels is sixty-four, though this is a design choice and can be varied. 
   For each control channel being monitored, the receiver  50  decodes the signal and passes the data to a processor  52 . The processor  52  compares the data to the registration information stored in memory  54 . 
   The memory  54  can be any of various volatile or non-volatile data storage devices including hard disks or solid state memory. 
   The processor  52  also stores in the memory  54  user-specific data for later retrieval. In this way, when the user returns to the structure  30  at a later date, the registration process is as easy as accessing the database entry for that user. The data can also be used for marketing activities. 
   The registration data, user-specific information and notification rules are all input through the console  56 . The console  56  has a keyboard for alphanumeric input. In this embodiment, the console  56  has multiple data ports to mate with a wide variety of models of radio devices. For the radio devices that allow radio-frequency queries, the console  56  has a low-power transmitter/receiver to communicate directly with the radio device to interrogate it for registration information. 
   The processor  54  of this embodiment has a display  58  associated with it. The display provides real-time feedback to the operator and provides alerts as part of the notification system  60 . 
   The notification system  60  is provided with notification option selections from the console  56  and/or the processor  54 . Once an incoming signal is received in the receiver  50  and the processor  52  determines that the incoming signal is intended for a registered user, the processor signals the notification system  60 . 
   The notification system  60  then alerts the user, the operator or both, depending upon which selections were made during registration. As previously described, the notification system  60  can simply actuate a dedicated telephone  42 . Another option would be to send notification through an external network  62 , such as the telephone network (POTS), a PBX, or the Internet for example. The message can be audio, video, text or a combination of those, again depending purely upon design and implementation. 
   In other implementations, the notification system  60  can operate with dedicated wireless pagers  64  that vibrate and/or flash a light upon notification. 
   Finally, the notification system  60  can send a radio frequency signal through its own transmitter/antenna  66 . One use of this feature would be to further boost and clarify a signal within a structure  30 . One example of this would be in an office where use of cellular telephones and pagers is encouraged, a sales office for example. Many buildings already attenuate radio signals without any additional shielding simply due to their metal framework. Re-transmitting the incoming signal internally would enhance call quality. 
   The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.