Abstract:
A wireless device ( 104 ) selectively opreates near protected sites ( 110 ) including equipment at least intermittently using an operating frequency. The wireless device upon detecting a beacon signal from a beacon system ( 112 ) ascertains interference parameters. The interference parameters are used to control operation of the wireless device to prevent harmful interference with the equipment at the protected site. The operation is selectively altered depending upon the interference parameters ascertained. The wireless device can be intelligently controlled from a control system ( 105 ).

Description:
FIELD OF THE INVENTION 
     The present invention relates to preventing interference between wireless devices and protected sites. 
     BACKGROUND OF THE INVENTION 
     The advent of satellite communication systems has resulted in potential conflicts between emissions from the satellite telephones and other systems. A radio astronomy site (RAS) is one example of a site requiring protection. Equipment at radio astronomy sites take measurements of radio waves over an interval of time, known as the integration interval. During the integration intervals, signals emitted by nearby satellite telephones may be detected by the RAS equipment. This can result in errors in the measurements made at these sites. Other sensitive sites that satellite telephone transmissions might interfere with include airports where sensitive satellite navigation equipment may be used. 
     An approach has been developed to avoid such interference between satellite telephones and other systems. This approach includes transmission of a beacon signal from the site requiring protection. For example, the beacon signal is transmitted from the RAS during the integration interval of the RAS equipment. When a satellite telephone detects the beacon signal, it shuts down. This prevents emissions from the satellite telephone interfering with the protected site. The beacon signal is designed such that its transmit power, antenna pattern, shielding and frequency of operation produce beacon emissions that do not have a detrimental impact on the measurements. 
     Although this system prevents interference, it is desirable to provide a more intelligent beacon system. 
     SUMMARY OF THE INVENTION 
     A wireless device selectively operates near a protected site. The wireless device responds to a detected beacon signal. Interference parameters are used to control operation of the wireless device to avoid interference with equipment at the protected site. The operation is selectively altered depending upon the inference parameters ascertained whereby the wireless device does not necessarily have to be disabled. 
     A method of operating a control system to intelligently control a wireless device near a beacon system is also disclosed. 
     A wireless device selectively operating near a protected site is also set forth. A control system for wireless devices operating near a protected site is disclosed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a satellite communication system and a beacon system; 
     FIG. 2 is a circuit diagram in block diagram form illustrating a satellite terminal; 
     FIG. 3 is a circuit diagram in block diagram form illustrating a portion of a satellite control system; 
     FIG. 4 is a circuit diagram in block diagram form illustrating a beacon circuit; 
     FIG. 5 is a flow chart illustrating operation of a terminal; 
     FIG. 6 is signal diagram illustrating a spectrum mask, showing amplitude as a function of frequency, and 
     FIG. 7 is a flow chart illustrating operation of a satellite control system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A satellite communication system  100  (FIG. 1) includes a satellite  102 , satellite terminals  104  communicating with satellite  102 , and a satellite control system  105  communicating with satellite  102 . The satellite control system  105  communicates with a plurality of satellites as well as other satellite control systems. Although a single satellite  102  is shown, it will be recognised that a number of satellites  102  are provided in a satellite system. 
     Thus, the satellite  102  represents a network of satellites that communicate with the satellite terminals  104  and satellite control system  105 . 
     A protected site  110  includes a beacon system  112 . Equipment at the protected site uses an operating frequency that is subject to interference from satellite terminals  104 . The protected site can be an airport, a radio astronomy site, or any other location having equipment desiring protection against emissions from satellite terminals  104 . For brevity, the following description is based upon radio astronomy sites, but it will be recognised that it apples to any site requiring protection. 
     The satellite terminals  104  include a transceiver, having a transmitter  206  (FIG. 2) and a receiver  208 , connected to an antenna  210 . The transmitter  206  and receiver  208  communicate via antenna  210  under the control of a controller  212 . A memory  214  is connected to controller  212 . The controller  212  can be implemented using a digital signal processor (DSP), a microprocessor, a programmable logic unit (PLU), or the like. The transmitter  206  and the receiver  208  are implemented using any suitable transmitter and receiver circuitry for satellite communications. The memory  214  can be implemented by a random access memory (RAM), a read only memory (ROM), an electronically erasable programmable read only memory (EEPROM), or the like. The satellite terminals  104  can be a portable satellite telephone, a vehicle satellite telephone, a home or business satellite communication system, a mobile satellite multimedia terminal, a mobile satellite data terminal, or the like. 
     In addition to mobile satellite telephones, if land radio communications services interfere with sensitive sites, the beacon system can be employed. For protection from land mobile communicated services, communications between the mobile telephones and the control system take place via terrestrial base stations rather than satellites. For brevity, this description is based upon a satellite system, but it will be recognised that is applies to any mobile radio system. Accordingly, “wireless device” as used herein refers to satellite telephones, cellular radiotelephones, cordless radiotelephones, two-way radios, and any other wireless device emitting signals that may interfere with equipment at protected site, and the description of satellite terminals applies to each of these wireless devices and their equivalents. 
     The satellite  102  is of the type that orbits around the earth and acts as a repeater for signals communicated between the satellite control system  105  and the satellite terminals  104 . Such satellites are well known, and will not be described in greater detail herein for brevity. 
     The satellite control system  105  includes a transceiver, having a transmitter  302  (FIG. 3) and a receiver  304 , connected to a controller  306 . The transmitter  302  and the receiver  304  are implemented using any suitable circuitry for satellite communications, and are connected to an antenna, such as a satellite dish  312 . The controller  306  controls transmission of signals to the satellite  102 . The controller  306  can be implemented using a DSP, a PLU, a microprocessor, or a computer. A memory  308  is connected to the controller  306 . The memory  308  can be implemented using a RAM, a ROM, an EEPROM, or the like. The memory  308  stores operating programs for the controller  306 , satellite terminal status information, and beacon information. It will be recognized that the control system can be a satellite control system, land mobile controller such as a cellular base station, a dispatch center, or any other wireless device controller, and “control system” as used herein refers to each of these and their equivalents. 
     The beacon system  112  includes an antenna  404  (FIG. 4) positioned in close proximity to the protected site  110 . Beacon signals are input to the antenna  404  from a transmitter  406 . The transmitter  406  generates a signal having a predetermined frequency, and may for example have a frequency of 1.6264 Ghz. A controller  408  is connected to memory  410  and a control input  412 . Memory  410  stores the operating program for controller  408 . The control input  412  is used to activate the beacon system. The control input is implemented using a manually actuated switch, a personal computer, or any other suitable source of control signals. Activation of the beacon can thus be manual or automatic, such that the beacon signal is only generated when protection is required, and is thus generated at least intermittently. The controller  408  is implemented using a microprocessor, a DSP, a PLU, a computer, or the like. The controller  408  is responsive to the activation signal from the control input  412  to the control transmitter  406  to transmit the beacon signal via antenna  404 . 
     The satellite terminal  104  is responsive to a beacon signal from the beacon system  112  to selectively interrupt the operation of the satellite terminal  104 . In the absence of a beacon signal sufficiently strong for the satellite terminal to detect, the satellite terminal  104  operates freely according to ordinary processes. 
     Upon detection of a beacon signal, the satellite terminal controller  212  makes several measurements. The signal factor G is measured in block  502  (FIG.  5 ), as follows: 
     
       
           G =(signal power)/sensitivity. 
       
     
     The signal power is the measurement of the received beacon signal level. The sensitivity is the minimum signal level that the satellite terminal  104  is able to detect. The sensitivity is predetermined, being established when the satellite terminal is manufactured. It will be recognized that the sensitivity level can be a predetermined signal level for all satellite terminals of a particular model, based upon a typical sensitivity of the receiver of the satellite terminal model. Alternatively, the sensitivity can be individually set for each satellite terminal based upon actual measurements taken at the factory. 
     The satellite terminal controller  112  also calculates a ratio α in block  504 : 
     
       
         α=(worst case interference)/(estimated actual interference). 
       
     
     The ratio α depends on the frequency separation between the satellite terminal  104  and the frequency used at the protected site  110 . The worst case interference is the maximum interference that is possible from the satellite terminal  104 . The worst case interference occurs when the satellite terminal transmit channel and the frequency spectrum of interest to the equipment at the protected site  110  are the closest that they can be in their respective allocated spectrums, the power level of the transmit signal is at its highest possible level, and the transmitter is emitting channel signals at the spectrum mask of the satellite terminal transmit channel. The spectrum proximity between the frequency of operation of the protected site  110  and the operating frequency of the satellite terminal  104  is Δf. Thus for example, the frequency protected in a RAS system is 1.6106 to 1.6138 GHz, and a satellite telephone has transmit channels in the range of 1.6215 GHz-1.6263 GHz. 
     The satellite terminal  204  transmit channels have a spectrum mask shown in FIG.  6 . The mask is the maximum energy that the signals emitted by the transmitter  106  can have as a function of frequency. As can be seen from FIG. 6, the mask amplitude is lower for frequencies farther from the allocated spectrum. Accordingly, the proximity Δf and the spectrum mask at the maximum power output of the satellite terminal  104  determines the worst case interference. The actual interference is the amount of interference that is expected given the actual spectrum proximity, the spectrum mask, and the actual transmission power of the satellite terminal  104 . It will be recognised that the power level of the satellite terminal will change as the path between the satellite  102  and the satellite terminal  104  changes. 
     The controller  212  periodically calculates an interference margin  13  in block  506 , where: 
     
       
         β=μ* G *( Pt/Pm )/α. 
       
     
     The beacon power is calculated to protect against a single continuous maximum power, Pm, transmission assuming the worse case unwanted emissions. At a particular instant, the required uplink transmission power of a particular satellite terminal  104  is Pt. The duty cycle μ is the expected proportion of time a terminal is transmitting, which will depend on voice activity, video transmissions or data activity (that is the proportion of time a user is speaking or has data to send), and the access scheme such as time division multiple access (TDMA), code division multiple access (CDMA), or frequency division multiple access (FDMA). 
     The satellite terminal controller  212  determines if the interference margin β is met (i.e., β&lt;1), such that the transmission interference with the protected site equipment is below a level, in decision block  508 . If it is met, the call is continued, as indicated in block  509 . If the interference margin β is not met (i.e., β&gt;1), then the call is suspended. The controller then determines if the transmit power, or the transmit bit rate, can be reduced such that Pt is reduced and the interference margin β&lt;1 is met, in decision block  510 . If it is, then the satellite terminal controller  212  will control the transmitter  206  to transmit a signal to the satellite control system  105  requesting this change in block  512 , and the call will continue. If not, then the controller will determined if a different channel can be selected such that α can be reduced and the interference margin β&lt;1 is met, in decision block  512 . If a channel can be selected such that the interference margin can be met, as determined in decision block  514 , then the satellite terminal controller  212  will control the transmitter  206  to transmit a signal to the satellite control system  105  requesting the change, in block  516 , and the call will continue. If a suitable channel can not be selected, then the transmitter  206  is disabled in block  518 . By disabling only the transmitter  206 , the satellite terminal can still receive signals. 
     The satellite terminal controller  212  reactivates the transmitter at the end of the beacon transmission period. The end is determined when the beacon is no longer detected. Alternatively, the end is detected using time remaining information contained in the beacon signal. The time remaining information can be used by a timer. For example, the controller  212  can act as a timer to count down the time remaining, at the end of which the transmitter  206  is enabled. 
     Thus, if the interference margin β is less than or equal to one, it will be met, and the call will continue. If the interference margin is not met, such that  13  is greater than one, some action is taken by the controller  212 . The actions that can be taken can include changing to a different channel, such that the spectrum of the satellite terminal  104  is further from the spectrum of the potentially interfered with protected equipment. Alternatives include lowering the power level of the satellite terminal  104 . If the power can not be lowered, the satellite terminal controller  212  can wait for the transmission path to improve such that communication at a lower power level is possible. The controller  212  will inform the user that they will have to wait until the satellite terminal can successfully communicate with the satellite  102  at a lower power level, such as when the satellite  102  is positioned above the satellite terminal  104 . The power level required to transmit signals to the satellite  102  changes as the signal path from the satellite terminal  104  to the satellite  102  changes. 
     Either the transmitter  206  alone, or the transmitter  206  and the receiver  208  together, can be turned off. The power measurement is preferably repeated periodically. For example, every 1 second while the beacon is detected, a measurement is made. This allows the satellite terminal  104  to accommodate power changes of the transmitter  206  emissions, as well as location changes relative to the protected site  110 . 
     Another possible action is to limit the length of satellite terminal transmitter  206  usage while it is within the range of beacon system  112 . This allows the satellite terminal  104  transmitter to be used for brief periods of time, so long as it does not interfere with the protected site  110 . More particularly, in the case of RAS integration times for example, the RAS will make a measurement over an integration interval. The integration interval will vary, and may for example be a 30 minute time period. During the 30 minute integration interval, a short transmission by the satellite terminal  104  will not substantially harm the measurement by the RAS equipment. In the case of a 3 minute transmission by transmitter  206 , the margin β can be relaxed to 10% of its former value, since only {fraction (1/10)} of the energy would be put into the RAS band during the integration period. Thus, the satellite control system can allow the satellite terminal to make a short 3 minute call during a 30 minute integration period. However, if the RAS Integration time is short, such as 3 minutes long, the margin β can be reduced by a certain amount, such as 1/10 for 5 dB, as sensitivity is assumed to be proportional to the square root of the observation internal for a RAS device. Therefore, the margin β for the satellite terminal can be lowered 5 dB for a 3 minute integration time relative to the corresponding threshold for a 30 minute integration time. Thus, the margin β can be adjusted depending on duration of the satellite terminal transmission and the RAS integration time. By reducing β, the threshold margin β&lt;1 is more easily met. 
     The beacon system  112  provides integration time and time remaining information in the beacon signal. The beacon signal can also provide information identifying the location of the protected site  110 . The satellite terminal  104  uses this information in determining when the beacon system  112  will be done transmitting (i.e. when the protected site will no longer require protection) and for adjusting the margin level β according to the transmission time, as described above. Operation of the satellite control system  105  for an intelligent beacon management system will now be described with reference to FIG.  7 . The satellite control system receives control information originated in the beacon system  112  and communicated through the satellite terminal  104  and the satellite  102 , in block  702 . This information includes broadcast information on the protection requirements of the protected site, the total time duration of the protection period, and the remaining time duration for the protection period. The satellite terminals  104  measure the beacon power and input the beacon information transmitted therewith. This information is passed from the satellite terminal  104  to the satellite  102  and on to the satellite control system  105 . This burst is preferably short to avoid interfering substantially with the beacon measurement. 
     The controller  306  of the satellite control system  105  is responsive to information received from the satellite terminals  104  to control signal transmissions by satellite terminals  104  within the zone of the beacon system  112 . The beacon zone is the transmission range of the beacon system  112 . The satellite control system  105  determines the number of satellite terminals  104  within the beacon zone by counting the number of terminals detecting the beacon, in block  704 . The satellite control system  105  also monitors the estimated interference to the protected site form each user active in a call, in block  704 . The controller  306  determines whether capacity is available when one or more of the terminals has requested permission to transmit, in decision block  706 . If one of the satellite terminals  104  has requested permission to transmit, the controller  306  determines whether limited or full transmission capacity is available, in block  708 . This will depend upon the relative distance between the requesting satellite terminal  104  and the protected site  110 , the predicted power of transmissions from the satellite terminal  104 , the spectrum masks for the requesting satellite terminal  104 , the estimated interference from other active terminals and an activity factor (integration time and time remaining) for the protected site  110 . The distance can be determined from the signal strength of the beacon signal detected by the requesting satellite terminal  104 . Alternatively, it can be measured from the position of the satellite terminal  104 , measured by Doppler measurements from the satellite  102  or a global positioning information, and the position of the protected site  110 , as included in the beacon signal. 
     Responsive to this information, the control system  105  transmits control parameters, which may be constraints on transmissions for example, to the requesting satellite terminal  104 , in block  710 . These parameters include maximum length of call indications, channels that can be used by the satellite terminal  104 , a maximum power and the bit rates permissible for the call. The control system  105  can deny access until one or more of the other terminals  104  ceases being active. In some cases the satellite control system  105  can determine that the activity level is so high that it transmits a signal telling all of the satellite terminals  104  within the beacon zone to turn off. 
     Following the transmission of the parameters, or a determination that no request for transmission has occurred, as detected in block  706 , the controller  306  determines whether the protected site  110  no longer requires protection, in decision block  712 . This can be detected by the lack of a beacon signal or the lapse of the protected time interval indicated by the beacon signal, if included. If protection is no longer needed, the controller  306  returns to block  706 . If the protection interval is over, the controller  306  controls transmitter  302  to broadcast a signal informing the satellite terminals  104  that they can operate freely. In this way, the satellite terminals  104  are intelligently monitored and controlled to avoid interference with the protected site. 
     Thus, the satellite terminals  104  operate in a manner to reduce the emissions that would potentially interfere with equipment at a protected site. This is done by operating only at low power levels and/or by changing to a signal which has further separation from the operating frequency of the protected site  110 , and if necessary, by disabling transmission by the satellite terminals  104 . The satellite terminals  104  can operate in the presence of the beacon signal in such situations that the satellite terminal  104  will not cause substantial interference with the system of the protected device.