Patent Publication Number: US-2007111722-A1

Title: Filtered wireless communications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a Divisional of U.S. patent application Ser. No. 11/095,867 titled, “Filtered Wireless Communications,” filed 31 Mar. 2005. 
    
    
     FIELD OF THE INVENTION  
      The invention relates generally to the field of telecommunications, and more specifically to the field of wireless communication, for example, cellular telephones.  
     BACKGROUND OF THE INVENTION  
      The present invention pertains in general to the planning and deployment of cells in a cellular telephone network, and more particularly, to filtering the operation of cellular telephones in well delineated geographical areas. While the embodiment described herein is directed to cellular phones, the principles of the present invention apply to all types of wireless communication devices such as cellular phones, personal digital assistants, beepers, pagers, portable computers, and other wireless communication devices.  
      Today mobile telephones are becoming more and more frequent. The use of mobile telephones has in many regards facilitated the daily life for many people. For instance, cellular phones offer convenience in personal relationships and business dealings, by allowing users to stay in communication with the world in practically any public location. However, one person&#39;s convenience can be another person&#39;s annoyance.  
      For example, in some places the use of mobile telephones is not appreciated and in some places even prohibited. Often, cellular phones ring and phone conversations occur, in some of the most inappropriate locations. For example, the peaceful enjoyment of a movie, play or musical performance can be destroyed by the “ringing” of cellular phones in the audience. The concentration of students taking an exam or listening to a lecture can be broken by a cellular phone&#39;s ringing, or by another student&#39;s engagement in a conversation on a cellular phone. Also, a cellular phone can be disturbing to the public, and embarrassing to the cellular phone&#39;s owner, during church services, dining at a restaurant or during quiet times observed in public, such as opening prayers, the Pledge of Allegiance, and the National Anthem. The same applies to other locations such as for example, courtrooms, libraries, theaters, meeting rooms, conference rooms or any other location that radio frequency transmissions might be disruptive to persons or equipment in the vicinity.  
      Often certain locations have restrictions, rules or laws forbidding the operation of cellular phones. For example, hospitals attempt to prohibit use of cellular telephones because of the risk that the transmissions from the cellular telephone could interfere with electronic medical equipment. Also, the use of cellular telephones is currently prohibited in an airplane while the airplane is preparing for take-off since transmissions from the cellular telephone could interfere with the operation of the airplane. Although cellular telephone network providers can attempt to locate cell sites away from prohibited locations such as airport runways, it is unlikely that cellular telephone service can be excluded from the geographical location of the airport runway while at the same time providing service to geographical areas adjacent to the runway. Also, some schools forbid students to use cellular phones or beepers on school grounds, in order to reduce the likelihood of drug trafficking and gang activity.  
      Therefore, there is a perceived need for a mobile telephone system that minimizes or completely removes the possibility to use a mobile telephone in certain restricted areas.  
      In order to solve this problem a number of different solutions have been proposed. In one approach, the goal is to eliminate the disturbance caused by a mobile station located in a certain area. One type of such approach simply eliminates or “blocks” signals in a given area by, for example, generating and radiating a magnetic field pattern, which includes a command signal, which commands a transmission interruption to a radio communication terminal. Another type of such system provides the mobile station with a control, which mutes the mobile station upon receiving a particular message transmitted from a transmitting station provided in the certain area.  
      In another approach, the goal is to notify the user of the restricted area. Thus, in one type of such approach a base station  151  in a mobile telecommunication network is provided with a message transmission function that is installed near the place where use of a mobile telephone is restricted. When a mobile unit enters the area managed by the base station  151  having the message transmission function, a message is transmitted from the base station  151  to the mobile unit instructing the mobile unit to turn off a power supply for the mobile unit.  
      While the use of these “blocking” systems has gained support in certain jurisdictions, such blocking systems cannot be utilized in the United States. This is because cell-phone jamming runs afoul of the Federal Communications Commission, whose approval is required for devices that send signals over the air. In particular, the operation of transmitters designed to jam or block wireless communications is a violation of the Communications Act of 1934 (“Act”). See 47 U.S.C. § 301, 302a, 333. The Act prohibits any person from willfully or maliciously interfering with the radio communications of any station licensed or authorized under the Act or operated by the U.S. government. 47 U.S.C. § 333. The manufacture, importation, sale or offer for sale, including advertising, of devices designed to block or jam wireless transmissions is prohibited. 47 U.S.C. § 302a(b). Parties in violation of these provisions may be subject to the penalties set out in 47 U.S.C. § 501-510. Fines for a first offense can range as high as $11,000 for each violation or imprisonment for up to one year, and the device used may also be seized and forfeited to the U.S. government. Likewise, certain jurisdictions outside the United State prohibit use of jamming systems.  
     SUMMARY OF THE INVENTION  
      A virtual wireless phone booth is provided within a filtered wireless zone. A filtered wireless zone is provided. A geographically limited signal is contained within the filtered wireless zone. When a handset in the filtered wireless zone attempts to place a call, the call attempt is blocked. In addition, a handset in the geographically limited signal contained within the filtered wireless zone is allowed to place calls. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram of an example cellular telephone network.  
       FIG. 2  is a radio channel assignment matrix.  
       FIG. 3  shows a filtered wireless zone in accordance with the principles of the present invention.  
       FIG. 4  shows an alternative method of capturing control of handsets in the filtered wireless zone of  FIG. 3 .  
       FIG. 5  shows a “virtual phone booth” with in the filtered wireless zone. 
    
    
     DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION  
      In the planning and deployment of a cellular telephone network, the geographical service area to be covered by the cellular telephone network is partitioned into a plurality of cells. While in operation, a cellular telephone continually compares received signal strengths from base stations in cells adjacent to the cellular telephone. Typically, the cellular telephone establishes communication with the base station having the strongest signal. As the cellular telephone moves about the service area. Signal strengths from the base stations vary and eventually the cellular telephone reselects a new base station or, if on call, is handed-off from the current base station servicing the cellular telephone to a base station now having a stronger signal.  
      Conventionally, when a power ON operation is carried out for the portable telephone set within a service area, a position registration process of the telephone is performed for a database used for position management and located in the network. In other words, a position registration request is made from the portable telephone set to a position management server via a public base station, and the position registration server informs, after its registration, the portable telephone set of its position registration reception.  
      Cellular units are directed or “listen” automatically to predetermined control frequencies, while they are in the standby mode. The control is two-way full duplex, such that there are a plurality of forward control channels (FCC) from the cell to the portable unit (uplink), and a plurality of reverse control channels (RCC) from the telephone to the cell (downlink). The cellular units automatically adjust to the best of these channels available in the cell or sector.  
      In one of two possibilities in establishing a cellular conversation, the subscriber initiates a conversation from the cellular unit to any telephone subscriber. In this case, the destination subscriber number is dialed and the send button is pressed, and this begins a handshake routine opposite the local cellular cell, which provides service in a given area. The call handling is then passed to an area cellular mobile telephone switch office (MTSO), which checks the information, performs a verification that the subscriber is operating properly, and is entitled to receive service and then connects to the destination subscriber. This process is known as “call setup”.  
      In the second possibility, the cellular system receives a request to establish a conversation with a cellular subscriber, and the area cellular MTSO performs a subscriber locate/search activity by sending a “search call” to all the cellular cells (connected to it) and then broadcast it on their control frequencies. The destination subscribers (when in a standby mode) which are tuned to the local control frequency, respond to the search call and this begins a handshake routine with the area cellular MTSO. When finished, the system assigns a pair of specific frequencies, a forward control channel (FCC) from the cell to the portable unit, and a reverse control channel (RCC) from the telephone to the cell, in full duplex mode, to which the telephone and cell are tuned. Only after this, a ring command is broadcast to the telephone, activating the cellular subscriber&#39;s ringing unit, and this clears the way for a full conversation.  
      More particularly, referring to  FIG. 1  an example cellular telephone network is diagramed. As previously described, a typical cellular telephone network consists of a MTSO  110  connected on one side to the Public Switched Telephone Network (PSTN)  101  via trunk lines  105 , and on the other side to a series of cell sites  141  via backhaul trunks  131 . Associated with the MTSO  110  is a Subscriber Data Base  114 , which stores information relating to subscribers normally associated with that particular MTSO  110 . While multiple elements are described herein, for ease of description like reference numerals are utilized.  
      There is also a Remote Data Link  118  to a Roaming Data Base  117 , which is usually a distributed data base residing in a number of other MTSOs. In this way, as will be described, handsets registering to the MTSO  110  may be defined as either home, that is, normally located within the area controlled by the particular MTSO  110 , or roaming, that is, normally located within the area controlled by another MTSO  110 . Handsets not found in either database are normally denied any service.  
      Each cell site consists of a series of Cellular Base Stations  151 . The Cellular Base Stations  151  in turn communicate via radio channels  161  to a number of handsets  171  (or mobile installations). The radio channels  161  may be defined not only by specific radio frequencies and bandwidths, but in the case of modem systems by particular time slot assignments in a Time Division Multiplex (TDM) scheme, and/or by differing spreading codes in a Code Division Multiple Access (CDMA) plan, as is understood by one skilled in the art.  
      Referring now to  FIG. 2 , a Radio Channel Assignment matrix is shown. In  FIG. 2 , the various radio frequencies available in a single cell are shown along the top of the chart, numbered  1 ,  2 ,  3 , . . .  8 ; the various TDM time-slot assignments are shown along the left side, designated A, B, . . . G. Therefore, for example, the channel corresponding to the upper left box in the chart consists of TDM slot A within frequency  1 , and might be designated as “ 1 A”. Likewise, for example, the channel corresponding to the box to the right of the upper left box in the chart consists of TDM slot A within frequency  2 , and might be designated as “ 2 A”. Similarly, for example, the channel corresponding to the box under the upper left box in the chart consists of TDM slot B within frequency  1 , and might be designated as “ 1 B”. The other channels available would be similarly labeled with their corresponding frequency and TDM slot identifiers, as shown in the chart. Also, each such radio channel consists of two distinct parts: a downlink part for communications from the base station  151  to the handset  171 , and an uplink part for communications from the handset  171  to the base station  151 .  
      In order to allow land-to-mobile calls to be sent to any of the handsets  171 , the MTSO  110  designates a channel in each cell site as a “signaling channel”. That channel repeatedly transmits on the downlink part a specific data sequence called the signaling channel marker, and all handsets  171  search for that sequence. In the case where a handset  171  may be able to receive signaling channels from more than one cell site, the handset  171  scans all available signaling channels and chooses the strongest signaling channel for the next step in the protocol process.  
      After a given handset  171  has selected a signaling channel, the handset  171  notifies the MTSO  110  that the handset  171  is available for receiving calls. The handset  171  does this by transmitting on the uplink part of the signaling channel a registration request message. The MTSO  110  searches for the subscriber data first in its own Subscriber Data Base  114 , and if found returns a home registration acceptance message to the handset  171 . If the handset  171  is not found in the local Subscriber Data Base  114 , the MTSO  110  initiates a search of the Roaming Data Base  117 . If the handset  171  is found in the Roaming Data Base  117  the MTSO  110  both sends a roaming registration acceptance message to the handset  171  and notifies the handset&#39;s home MTSO  110  of the handsets  171  location so that calls to the handset  171  may be forwarded to the proper MTSO  110 .  
      When a call for a particular handset  171  arrives at the MTSO  110 , the call sends a ring message to handset  171  via the cell site and signaling channel to which the handset  171  registered, as described above. Then handset  171  replies with a call acknowledgement message on the signaling channel, and then the MTSO  110  sends a voice channel assignment message to the handset  171 . The handset  171  then switches to the assigned channel, and the voice connection is completed.  
      When a handset  171  places a call, the handset sends a call placement request message (usually including the called telephone number) to the MTSO  110 . The MTSO  110  places the call to the PSTN  101 , and at the same time sends a voice channel assignment message to the handset  171 , which switches to the assigned channel to complete the voice connection.  
      For any of several reasons, the handset  171  may decide that the received signal strength of the current signaling channel is insufficient. This may be due for example to the handset  171  location changing to a less advantageous location for the particular cell site chosen earlier, or a number of other factors. When the received signal strength of the current signaling channel is insufficient, the handset  171  searches for a new signaling channel, sampling the signal strength of all available signaling channels as described above before making a new choice. There may also be situations where the MTSO  110  decides to assign a different signaling channel within a particular cell site. In this case, there is the facility for the MTSO  110  to send a new signaling channel assignment message to all handsets  171  registered to the existing signaling channel. This message contains the identity of the new signaling channel, and all the registered handsets  171  immediately switch to the new channel.  
      A given MTSO  110 , usually belonging in one metropolitan area to a given cellular service provider, will, as described above, control several cell sites  141 , and more than one of these cell sites  141  may be received by a given handset  171 . In this case, the handset  171  chooses which site to register with by the strongest-signal method described above. There may also be multiple MTSOs in a metropolitan or geographic vicinity, belonging to various cellular service providers, within range of a given handset  171 . In this case, the handset  171  normally searches first for cell sites  141  belonging to the MTSO  110  (and therefore the cellular service provider) with which the handset  171  is registered; failing to find one such ‘home’ site, the handset  171  searches by signal strength, and attempts to register with the strongest ‘non-home’ MTSO  110 . In some instances, the MTSO  110  associated with the cell site so selected may decline to offer service to the handset  171 ; in that instance, the handset  171  normally attempts to register with another ‘non-home’ MTSO  110 .  
      As an alternative to the requirement that the local signaling channel be substantially stronger than that utilized by the MTSO, in one embodiment it is possible to implement a “signaling channel priority” structure. In this method, the data stream emitted by each signaling channel would include a priority flag; that from the MTSO would be assigned a low priority, say ‘2’, while that from the local filtered system would be assigned a higher priority, say ‘1’. The handset would search first for the strongest signaling channel of the highest priority, and would only go on to search for lower-priority channels in the event that a high-priority one was not available. In this manner, it can be assured that the handset will lock onto the signaling channel in the filtered zone, and not that from the MTSO, even in the case where the signal from the former is not substantially stronger than that from the latter.  
      Referring to  FIG. 3 , a block diagram is shown that describes an embodiment of a filtered wireless zone in accordance with the principles of the present invention. A system in accordance with the present invention can comprises a system control  301 , connected to a signaling channel receiver  310  and a system signaling channel transmitter-receiver  320 . The signaling channel receiver  310  is located outside the filtered wireless zone while the system signaling channel transmitter-receiver  320  is located within the filtered wireless zone. External signaling channel receiver  310  is arranged so that signaling channel receiver  310  may receive the previously described signaling channel of cell sites  141  (from any MTSO  110 ) in the geographic vicinity. Internal system signaling channel transmitter-receiver  320  is arranged so that system signaling channel transmitter-receiver  320  covers the filtered wireless zone. The system signaling channel transmitter-receiver  320  provides a radio-frequency (RF) signal strength substantially higher than any RF signal strength that may be possibly received from any cell site belonging to the MTSOs normally serving that locality in the filtered wireless zone. Achieving a higher RF signal strength higher may be accomplished by known RF propagation techniques, and may be extended if necessary by using several Tunable Internal System Signaling Channel Transmitter-Receivers, as will be familiar to one skilled in the art of cellular system design.  
      In operation, system control  301  commands external signaling channel receiver  310  to scan all possible signaling channels belonging to any and all MTSOs normally serving the geographic vicinity, recording the channel identity and the system identity of each signaling channel. System control  301  then commands internal system signaling channel transmitter-receiver  320  to the first such channel, causing the internal system signaling channel transmitter-receiver  320  to radiate a signaling channel marker. In most cases internal system signaling channel transmitter-receiver  320  will include in that marker a new system identity that corresponds to a unique identity; in other cases, internal system signaling channel transmitter-receiver  320  may radiate (while it is on that specific channel) the identity of the ordinary system the system signaling channel transmitter-receiver  320  is supplanting.  
      When the internal system signaling channel transmitter-receiver  320  radiates the identity of the ordinary system that it is supplanting, the internal system signaling channel transmitter-receiver  320  will give the handsets  171  that have registered to that channel time for their internal decoders to stabilize on the new signal. The internal system signaling channel transmitter-receiver  320  will then transmit a “new signaling channel assignment” message, sending the handsets  171  to a new capture channel, where the internal system signaling channel transmitter-receiver  320  will already be radiating the appropriate signal to keep the handsets  171  locked to the new capture channel.  
      The internal system signaling channel transmitter-receiver  320  then ceases radiating on the first channel, and proceeds to the second external signaling channel previously recorded. The internal system signaling channel transmitter-receiver  320  repeats the above process, sending the handset  171  registered there to its capture channel, joining those already captured. The internal system signaling channel transmitter-receiver  320  repeats this process for all the external signaling channels previously located. In order to capture new handsets  171  entering the filtered wireless zone, and to compensate for the external MTSOs changing signaling channels, the internal system signaling channel transmitter-receiver  320  continues to repeat the scanning and sequential capturing processes.  
      When a handset  171  that has been so captured attempts to place a call to the PSTN  101 , system control  301  replies to the request for call signal with an all trunks busy message, thereby blocking the call attempt; however, if the call is an emergency call (911 in the US), the call is routed to an emergency call line  305 , so that emergency calls may be properly handled. This is in accordance with the processing of unregistered ‘foreign’ handsets  171  by any ordinary MTSO  110 .  
      When a handset  171  is captured in accordance with the present invention, the normally associated MTSO  110  will realize that the handset  171  is not available, just as though the phone had entered a dead zone or had its power switch turned off. Therefore, when a call for that handset  171  is received from the PSTN  101 , the call will be routed to the voice-mail or other processing, as previously configured for that handset  171 .  
      Referring now to  FIG. 4 , an alternative method of capturing control of handsets is described. This alternative method is applicable to situations where handset  171  users always enter a filtered wireless zone  405  through one or a few specific entryways or portals  410 . Such entryway  410  is constructed with wall material that attenuates the received RF energy from the outside cellular system or systems. An internal antenna  441  for the system in accordance with the present invention  440  (which is as described above) is placed within the shielded portal area. Therefore, when entering filtered wireless zone  405 , the handsets  171  lose contact with the outside network on which the handsets  171  were formerly registered, and search for and find the signaling channel of the present invention  440 , and so are captured as described previously.  
      In another embodiment, the attenuation within the entryway portal may be obtained by active cancellation rather then by shielding. This is also shown in  FIG. 4 . RF energy from the outside cellular network or networks is received by sense antenna  431 , amplified and phase-controlled by amplifier  430 , and radiated by canceling antenna  432 . The gain and phase shift of amplifier  430  are adjusted so as to cancel the ambient signal from the outside cellular system within the entry portal, thereby providing the necessary attenuation to cause entering handsets  171  to lose communication with the system to which the handsets  171  were previously registered, to search for a new signaling channel.  
      It is also possible to create a “virtual phone booth” with in the controlled area. In one embodiment, a set of transmitter-receivers as shown in  FIG. 5  can be configured so that they cover a very limited geographic area. This limited geographic area could be for example a “phone booth” within the controlled area where cellular calls are permitted. The signaling-channeling transmitter receiver function (under control of the control unit or a nearby MTSO) to register any handset that may be carried into the virtual phone booth. These handsets, once identified as being within the allowed area, are then allowed to place normal calls via the associated voice channel transmitter-receiver sets. Note that these calls may—in the case of control by the local control unit—be placed over an ordinary telephone line or—in the case of control by a MTSO—over a line to that MTSO. In addition, in one embodiment—most usually in the case of control by a MTSO—handsets identified as being within the allowed area can be allowed to receive normal calls.  
      Limiting of the covered area can be done by careful control of the power level of the transmitters concerned, along with techniques of radio propagation design that are know to one skilled in the art.  
      Thus, a filtered wireless zone is provided in accordance with the principles of the present invention. Because a filtered wireless zone in accordance with the present invention does not jam, it should not be in violation of the Communications Act of 1934 (“Act”). See 47 U.S.C. § 301, 302a, 333. Likewise, in jurisdictions outside the United State that prohibit use of jamming systems, a filtered wireless zone in accordance with the present invention should be permitted.  
      While the invention has been described with specific embodiments, other alternatives, modifications and variations will be apparent to those skilled in the art. All such alternatives, modifications and variations are intended to be included within the spirit and scope of the appended claims.