Patent Publication Number: US-6906684-B2

Title: Controlling a telescopic antenna mast

Description:
FIELD OF THE INVENTION 
   This invention relates to a method and system of controlling a telescopic antenna mast. 
   BACKGROUND OF THE INVENTION 
   An antenna mast may be mounted on a vehicle to support the mounting of antenna. The antenna may be used for reception, transmission or both reception and transmission of an electromagnetic signal. The mast may be limited in height because of obstructions in the environment. Obstructions may include vegetation, vine canopies, tree canopies, bridges, traffic signals, buildings or otherwise. The limitation in height of the antenna may limit the maximum range of effective communications between the vehicle and a communications device located remotely apart from the vehicle. For example, electromagnetic radiation that is in the microwave frequency range may be limited to propagation in line-of-sight paths or may be severely attenuated by ground clutter where antenna height is insufficient for a requisite level of clearance. Accordingly, a need exists for maximizing the available antenna height of an antenna mast mounted on a vehicle to improve the range and reliability of communications. 
   SUMMARY OF THE INVENTION 
   A receiver receives an electromagnetic signal via an antenna mounted on an antenna mast. A signal evaluator measures or determines a signal quality level associated with the received electromagnetic signal. The signal evaluator compares the measured signal quality level to a threshold minimum signal quality level. A current elevational position of the antenna mast is detected or tracked. The antenna mast is raised to a greater height than the current elevational position if the measured signal quality level is less than the threshold minimum signal quality level and if the current elevational position is less than a maximum height of the antenna mast. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of one embodiment of a system for controlling a telescopic antenna mast in accordance with the invention. 
       FIG. 2  is a flow chart of a first example of a method for controlling a telescopic antenna mast in accordance with the invention. 
       FIG. 3  is a flow chart of a second example of a method for controlling a telescopic antenna mast in accordance with the invention. 
       FIG. 4  is a block diagram of another embodiment of a system for controlling a telescopic antenna mast in accordance with the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates an antenna mast assembly and a system for controlling an elevation of the antenna mast  46  to enhance communications between an antenna  10  mounted on the antenna mast  46  and another communications device spatially separated from the antenna  10 . 
   The antenna mast assembly comprises an antenna mast  46 , an antenna  10  mounted thereon, transmission line  14  coupled to the antenna  10 , and one or more transmission line guides ( 12 ,  24 ) for supporting the transmission line  14 . The antenna mast  46  includes multiple sections. For example, the antenna mast  46  includes at least a first section (e.g., upper section  16 ) and a second section (e.g., lower section  18 ). Each section may have a generally circular, elliptical, triangular, rectangular cross section or a cross section of another shape that interlocks or slidably engages at least one adjacent section. Although the antenna mast  46  may be of virtually any height that can be carried by a vehicle and supported stably thereby when completely erected, in one embodiment the antenna mast  46  adjusts from a height of approximately 1 meter to approximately 10 meters. The height or current elevational position, minimum height, and maximum height of the antenna mast  46  may be defined with reference to the vehicle or a fixed point on the vehicle, for example. 
   The transmission line guides may include an upper guide  12  and a lower guide  24 . The upper guide  12  and the lower guide  24  are fastened to the antenna mast  46 . The upper guide  12  retains or secures at least a portion of the transmission line  14 . The lower guide  24  may include rollers, rotatable spherical members, a recess, a hole or another interface that allows for retention and generally vertical movement of the transmission line  14  relative to the lower guide  24 . The transmission line  14  or other transmission lines may support, carry or multiplex signals (e.g., direct current, radio frequency or otherwise) associated with the receiver  32 , a transmitter, a transceiver, a tower-top amplifier, a tower-top power transmitting amplifier, an obstacle detector  42 , and a position sensor  44 . 
   The system for controlling an antenna mast  46  comprises a receiver  32  coupled to the transmission line  14  associated with the antenna  10 . The receiver  32  is coupled to a signal evaluator  34  (e.g., a signal quality module). In turn, the signal evaluator  34  provides a signal quality indicator to the controller  36 . The controller  36  is coupled to an elevational system  38 . The controller  36  outputs control data or a control signal responsive to the signal quality indicator. 
   In one embodiment, the elevational system  38  comprises an air compressor  28  for feeding and pressurizing a chamber  22  within the mast  16  with air or an inert gas. An inlet valve  26 , an outlet valve  20 , and seals  40  are associated with the chamber  22  within the antenna mast  46 . The chamber  22  receives compressed air or an inert compressed gas via the inlet valve  26  from the air compressor to raise or maintain a peak height of the antenna mast  46 , while the outlet valve  20  and the seals  40  cooperate to make the chamber  22  generally air-tight or substantially hermetically sealed. Once the chamber  22  is pressurized to a target pressure to maintain a desired height of the antenna mast  46 , the inlet valve may be closed  26 . To lower the height of the antenna mast  46  that is not fully lowered, compressed air or inert compressed gas may be released or bled from the chamber  22  via an outlet valve  20 . 
   To support raising and lowering of the antenna mast  46 , the elevational system  38  further comprises a retractable tensioner  30  for receiving or releasing the transmission line  14 . In one configuration, the retractable tensioner  30  comprises a reel or spool  32  upon which the transmission line  14  is wound to a great extent when the antenna mast is fully lowered and to a lesser extent (or not at all) when the antenna mast is fully raised. The spool  32  may be spring-loaded to retract the transmission line  14  and a releasable ratchet mechanism (e.g., a generally circular gear with teeth, the gear mounted coaxially to the spool, where the teeth engage a movable pawl) may prevent the spool from moving when the tower is elevated above its lowest height. 
   The receiver  32  receives an electromagnetic signal via an antenna  10  mounted on an antenna mast  46 . The received signal is carried by the transmission line  14  to the receiver  32 . 
   A signal evaluator  34  measures or determines a signal quality level associated with the received electromagnetic signal. The signal evaluator  34  is arranged to compare the measured signal quality level to a threshold minimum signal quality level. The user or a technician may establish the threshold minimum signal quality based on one or more of the following: (1) target reliability (e.g., 99.9% reliability) or target availability of communications (e.g. reception, transmission or both) for the antenna and associated communications equipment, (2) a maximum bit-error rate for digitally modulated signals, (3) a minimum signal-to-noise ratio, and (4) a minimum signal strength. The threshold minimum signal quality may vary with the environment or location of the vehicle and may vary over time, such that time-averaged readings of the measured signal are used for signal quality determinations. In one embodiment, the signal quality comprises the measured signal-to-noise ratio of the received signal and the minimum signal quality level comprises a minimum signal-to-noise ratio defined by a user or technician. In another embodiment,the signal quality comprises signal strength of the received signal, and the minimum signal quality level comprises a minimum signal strength defined by a user or technician. 
   A position sensor  44  detects a current elevational position or current peak height of the antenna mast  46 . The positional sensor  44  may represent a tower-mounted optical ranging device that measures a distance at or near its tower position to a fixed point at the base of the antenna mast  46 . Alternately, the positional sensor  44  may be associated with monitoring the forward and reverse rotations (e.g., and including fractional rotations) of the spool  32  to estimate the height of the antenna mast  46 . 
   In one example, an obstacle detector  42  detects an obstacle (e.g., an object) in a clearance zone above and about the antenna mast  46 . In one embodiment, the obstacle detector  42  comprises an ultrasonic transmitter that emits a directional ultrasonic transmission or pulse and an ultrasonic receiver that is arranged to receive any reflected pulse from an obstacle within a certain range of the obstacle detector  42 . In another embodiment, the obstacle detector  42  may comprise one or more of the following: an ultrasonic detector, an optical sensor, a tactile sensor, and/or a metal detection circuit. The metal detection circuit might be used to detect the presence of over-head wires, cables or telephone lines that might interfere with the operation of the antenna mast  46 . 
   In one example, an elevational system  38  raises the antenna mast  46  to a greater height than the current elevational position if the measured signal quality level is less than the threshold minimum signal quality level and if the current elevational position is less than a maximum height of the antenna mast  46 . In another example, the elevational system  38  lowers the antenna mast  46  at a proper height that avoids physical contact or interference with an obstacle upon detection of an obstacle within the clearance zone. In yet another example, a controller  36  prohibits the raising of the antenna mast  46  until the obstacle is no longer present in the clearance zone. 
   Although the elevational system  38  of  FIG. 1  comprises a pneumatic device or an air compressor  28 , the elevation system  38  may be associated with one or more of the following components: a pressurized tank of air, a pressurized tank of inert gas, a hydraulic pump, a hydraulic device, and a mechanical device. 
     FIG. 2  is a flow chart of a first example of a method for controlling a telescopic antenna mast  46  that is associated with or mounted on a vehicle. The method of  FIG. 2  begins with step S 100 . 
   In step S 100 , a receiver  32  receives an electromagnetic signal via an antenna  10  mounted on an antenna mast  46 . For example, the receiver  32  receives a radio frequency or microwave signal via the antenna  10  and the transmission line  14 . 
   In step S 102 , a signal evaluator  34  measures or determines a signal quality level associated with the received electromagnetic signal. The measured signal quality may be defined in terms of a bit-error rate, a maximum bit-error-rate, percentage of reliability, an availability, a signal-to-noise ratio, and a signal strength. 
   In step S 104 , the signal evaluator  34  compares the signal quality level to a threshold minimum signal quality level. Step S 104  may be carried out in accordance with various definitions of the minimum signal quality level. In accordance with one definition, the minimum signal quality level comprises a minimum signal-to-noise ratio. In accordance with another definition, the minimum signal quality level comprises a minimum signal strength. In accordance with another definition, the minimum signal quality means a maximum bit-error-rate of a digitally modulated signal. The signal evaluator  34  may provide a status datum and a corresponding time-stamp indicated whether or not the measured signal quality data is compliant with the threshold minimum signal quality level during a certain window of time. 
   In step S 106 , a position detector or tracking device detects a current elevational position of the antenna mast  46 . For example, the position detector may record or tabulate the latest or most up-to-date mast height of the antenna mast  46  at regular intervals and/or after each generally vertical movement of the antenna mast  46 . 
   In step S 108 , an elevational system  38  or controller  36  raises the antenna mast  46  to a greater height than the current elevational position if the compared signal quality level is less than the threshold minimum signal quality level and if the current elevational position is less than a maximum height of the antenna mast  46 . The received signal is noncompliant if the measured signal quality is less than the threshold minimum signal quality or target signal quality. The raising, lowering or maintenance of an elevation or height of the antenna mast  46  is accomplished by pneumatically, hydraulically or mechanically applying force to one or more slidably movable sections of the antenna mast  46 . 
   Following step S 108  or during step S 108 , the method of  FIG. 2  may be supplemented by additional procedures related to the detection of an obstacle with respect to the antenna mast  46 . In accordance with a first procedure, an obstacle detector  42  detects or attempts to detect an obstacle in a clearance zone above and around the antenna mast  46 . Further, the controller or the elevational system lowers or maintains the antenna mast  46  upon detection of an obstacle within the clearance zone. 
   In accordance with a second procedure, an obstacle detector  42  detects an obstacle in a clearance zone above or around the antenna mast  46 . The controller or the elevational system prohibits the raising of the antenna mast  46  until the obstacle is no longer present in the clearance zone. The clearance zone may be defined as a generally cylindrical zone extending about a vertical longitudinal axis of the mast  46 . Further, the clearance zone may extend above the highest point of the antenna mast  46  by a fixed amount based on the tolerance and accuracy of the obstacle detector  42 . 
   The method of  FIG. 2  has wide application to mobile antenna masts  46  associated with vehicles. For example, the antenna mast  46  may be used to remote control operation of a vehicle on which the antenna mast  46  is mounted from a greater range or with greater reliability than otherwise possible. Environmental obstructions and physical effects on propagation may detract from reliability. 
     FIG. 3  is a flow chart of a second example of a method for controlling a telescopic antenna mast  46  that is associated with or mounted on a vehicle. The method of  FIG. 3  begins with step S 100 . The method of  FIG. 3  is similar to the method of  FIG. 2 , except the method of  FIG. 3  includes new step S 207 , new step S 209 , and replaces step S 108  with step S 208 . Like reference numbers in FIG.  2  and  FIG. 3  indicate like procedures or steps. 
   Before, during or after step S 106 , step S 207  is executed. In step S 207 , the obstacle detector  42  detects whether an obstacle is present about clearance zone of the antenna mast  46  in the current elevation position. The clearance zone may be defined as including a vertical clearance zone above the current highest point of the antenna mast  46 , a cylindrical clearance zone about a vertical longitudinal axis of the antenna mast  46 , and a direction-of-travel zone that extends in the direction of travel of the vehicle. For example, the direction-of-travel zone may extend as a generally planar or generally rectangular shape with a height equal or greater than the peak antenna mast height from the cylindrical zone in the direction of the heading of the vehicle. The distance that the direction of travel zone extends away from the vehicle is proportional to the speed and acceleration of the vehicle. If the vehicle adheres to a path plan, the present and future speed, heading, and acceleration may be known. The obstacle detector  42  may be mounted on the antenna mast  46 , but need not be mounted on the antenna mast  46 . If the obstacle detector  42  does not detect an obstacle in the clearance zone in step S 207 , the method continues with step S 208 . S 106 , However, if the obstacle detector  42  detects an obstacle in the clearance zone, the method continues in step S 209 . 
   In step S 208 , the elevational system or the controller raises the antenna mast  46  to a greater height than the current elevational position if the following three conditions are satisfied: (1) the compared signal quality level is less than the threshold minimum signal quality level, (2) the current elevational position is less than a maximum height of the antenna mast  46 , and (3) the detected obstacle is not within a clearance zone about the antenna mast  46 . 
   In step S 209 , the controller  36  or the elevational system  38  maintains or lowers the antenna mast  46  such that the peak height of the antenna mast does not contact, strike, collide, intercept or mechanically interfere with the obstacle upon detection of an obstacle within the clearance zone. Further, the controller  36  may prohibit the raising of the antenna mast  46  until the obstacle is no longer present in the clearance zone, regardless of the measured or determined signal quality level of step S 102 . The method of  FIG. 3  may be applied to using the antenna mast  46  to remote control operation of a vehicle on which the antenna mast  46  is mounted. The raising, lowering or maintenance of the height or elevation of the antenna mast  46  is accomplished by pneumatically, hydraulically or mechanically applying force to one or more sections of the antenna mast  46 . 
   The configuration of  FIG. 4  is similar to the configuration of  FIG. 1 , except the elevational system  38  of  FIG. 1  differs from the elevational system  138  of FIG.  4 . In particular,  FIG. 1  represents a pneumatic configuration of the elevational system  38 , whereas  FIG. 4  represents a hydraulic configuration of the elevational system  138 . The pneumatic configuration may be better suited for lower, lighter antenna masts or antenna masts with lighter wind-loading than the hydraulic configuration. The pneumatic configuration may support, but does not necessarily support, quicker movement of mast sections to their desired positions than the hydraulic counterpart. Like reference numbers in FIG.  1  and  FIG. 4  indicate like elements. 
   The elevational system  138  of  FIG. 4  comprises a fluid pump  29  (e.g., oil pump or hydraulic pump) coupled to an inlet valve  26 . The fluid pump  29  is configured to pump or pressurize hydraulic fluid with sufficient pressure to raise or maintain a position of an upper section  16  of the antenna mast  46  with respect to a lower section  18 . If or when the antenna mast  46  is lowered, hydraulic fluid may be bled via the output valve  20  into a tank  31 . The tank  31  provides hydraulic fluid to the fluid pump  29 . Accordingly, hydraulic fluid is circulated and recovered in a closed-loop containment system. The seals  40  between the exterior surface of the upper section  16  and the interior surface of the lower section  18  are configured to seal  40  a maximum design pressure of the hydraulic fluid. 
   Having described the preferred embodiment, it will become apparent that various modification can be made without departing from the scope of the invention as defined in the accompanying claims.