Abstract:
The instant disclosure concerns an antenna system and method for location-finding of a wireless communication device. A cellular multimode antenna is configured to analyze pilot signals from base station towers across a plurality of antenna modes. Information corresponding to the received signals and each antenna mode is analyzed to determine a location fix. In certain optional embodiments, the location fix determined by the cellular multimode antenna is used to determine an optimal mode for a second GPS modal antenna, such that the selected mode of the GPS modal antenna provides optimum signal quality with the global positioning system. In this regard, the cellular multimode antenna estimates the location of the device, and a mode for the GPS modal antenna is selected based on the location fix such that the GPS antenna is capable of quickly determining a precise position of the device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of priority with U.S. Provisional Ser. No. 61/511,109, filed Jul. 24, 2011; the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF INVENTION 
     This invention relates to location and positioning systems for mobile communication devices, and more particularly to an improved antenna system for location finding using cellular and global positioning system (GPS) signal reception. 
     BACKGROUND OF THE INVENTION 
     As mobile wireless devices and applications become increasingly prevalent, location and positioning services based on global positioning system (GPS) systems continue to flourish. Current GPS receiver technology allows for low cost, high performance GPS receivers to be installed in an increasing number of mobile devices. 
     In the United States the FCC 911 mandate addresses the requirement for location of cell phones during emergency situations available to dispatchers. Known as Assisted GPS, generally abbreviated as A-GPS, is a system which can, under certain conditions, improve the startup performance, or Time To First Fix (TTFF) of a GPS satellite-based positioning system. It is used extensively with GPS-capable cellular phones to address the 911 mandate. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to solve these and other problems in the art by providing a multimode antenna with multiple radiation pattern modes to improve the link budget for the GPS link as well as speed acquisition time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In accordance with various embodiments, the several figures can be understood in conjunction with a thorough review of the appended description, wherein: 
         FIG. 1  illustrates the compliment of GPS satellites orbiting the Earth, to form the GPS constellation. 
         FIG. 2  illustrates a mobile device with passive GPS antenna in the field of view of N GPS satellites. 
         FIG. 3  illustrates a mobile device with a multimode GPS antenna in the field of view of N GPS satellites. 
         FIG. 4  illustrates a mobile device with multimode GPS antenna in the field of view of N GPS satellites. 
         FIG. 5  illustrates a flowchart of a Modal Antenna Acquisition Process. 
         FIG. 6  illustrates a multimode cellular antenna in the field of view of three base stations. 
         FIG. 7  illustrates an example of a set of amplitude and phase patterns for a three Mode multimode antenna 
         FIG. 8  illustrates a multimode cellular antenna in the field of view of three base stations. 
         FIG. 9  illustrates a multimode antenna. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, for purposes of explanation and not limitation, details and descriptions are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these details and descriptions. 
     For purposes herein, the terms “multimode antenna” and “modal antenna” are each interchangeable and intended to be defined by its ordinary meaning as understood by those with skill in the art, that is, such a multimode antenna is defined as an antenna configurable about a plurality of modes, wherein the antenna is configured with a distinct radiation pattern exhibited from the antenna in each of the plurality of modes. An example of a multimode antenna can be further referenced in commonly owned U.S. Pat. No. 7,911,402, issued Mar. 22, 2011. 
     In one embodiment, a GPS modal antenna is connected to a low noise amplifier (LNA), a central processing unit (CPU) and memory bank. The memory bank stores information relating to configuration of the various antenna modes of the modal antenna. For example, a first mode might require a quantified current to be provided to a particular parasitic element positioned adjacent to a radiator portion of the GPS modal antenna. Various antenna modes will differ with regard to configuration and tuning. Several modes of the antenna are programmed and stored within the memory bank. The GPS modal antenna is configured to scan and ping various GPS satellites, and record a value for signal level of each of the GPS satellites queried. A satellite query is then performed across various antenna modes, and signal data is recorded for each mode. An optimal antenna mode is selected from the collected data based on maximum received signal, and number of satellites providing sufficient communication link quality. In this regard, an algorithm can be programmed into the CPU and memory of the antenna system, the algorithm being programmed to scan and determine an optimal antenna mode for maximizing GPS communications signal and establishing a position fix with the device. By scanning multiple antenna modes, the antenna can be configured for maximum signal efficiency, thus reducing GPS position acquisition time. 
     In certain embodiments, a modal GPS antenna includes an antenna radiator disposed above a ground plane and forming an antenna volume there between; a tuning conductor positioned within the antenna volume, the tuning conductor attached to a first active element for varying a reactance of the antenna; a steering conductor outside of said antenna volume and adjacent to the antenna radiator, wherein the steering conductor is attached to a second active element for varying a current mode thereon. The antenna radiator is configured and the steering conductor is adjusted in length and positioned in relation to the antenna radiator to tune the frequency response of the antenna radiator to provide for reception of signals in the GPS frequency band, and provide multiple radiation modes within the GPS frequency band. 
     In other embodiments, an algorithm is programmed within the memory of the device to switch antenna modes in an efficient method to reduce acquisition time for determination of a location fix. The algorithm commands the modal antenna to dwell on Mode 0 and acquire signals from various satellites within the field of view. If a time metric for signal acquisition is exceeded for one or multiple satellite signals, then the algorithm commands the modal antenna to switch to the next antenna mode and signals are acquired. The satellite signals acquired per antenna mode are stored in a data base for future reference. 
     In another embodiment, an algorithm is programmed within the memory of the device to reduce “Cold” and “Hot” start times for a 2D (two dimensional) fix for a GPS system by conducting a survey of all modes on a modal antenna to determine the mode with the strongest signal strength from three satellites. During the initial survey of modes, the algorithm commands the mode to be used just long enough for a measure of signal strength from the three satellites with the strongest signals. The algorithm then commands the modal antenna to switch to and sample signal strength on the next mode. When all modes have been sampled the mode with the strongest three signals is selected and used to acquire a 2D location fix. All antenna modes sampled during the signal acquisition process are stored in a data base for use to determine antenna mode with highest probability of acquisition for future system usage. 
     In yet another embodiment, an algorithm is programmed within memory of the device and adapted to reduce “Cold” and “Hot” start times for a 2D (two dimensional) fix for a GPS system by switching to Mode 0 and sampling receive signal strength. If the received signal strength from three satellites is above a specific metric, the algorithm commands that this mode be used for location fix. If the signal strength from three satellites on this mode falls below a signal level metric, the algorithm commands the modal antenna to switch to the next mode and repeat the sampling process. All antenna modes sampled during the signal acquisition process are stored in a data base for use to determine antenna mode with highest probability of acquisition for future system usage. 
     In certain embodiments, the algorithm includes wherein a 3D (three-dimensional) location fix is required and the algorithm samples all antenna modes to determine the mode with the four strongest signals. 
     In certain other embodiments, the algorithm includes wherein a 3D (three-dimensional) location fix is required and the algorithm samples the first Mode and dwells on this Mode if the received signal strength from three satellites is above a specific metric. If the signal strength from four satellites on this mode falls below a signal level metric, the algorithm commands the modal antenna to switch to the next mode and repeat the sampling process. All antenna modes sampled during the signal acquisition process are stored in a data base for use to determine antenna mode with highest probability of acquisition for future system usage. 
     The first and second active elements are individually selected from the group consisting of: switches, voltage controlled tunable capacitors, voltage controlled tunable phase shifters, varactor diodes, PIN diodes, MEMS switches, MEMS tunable capacitors, BST tunable capacitors, and FET&#39;s. 
     In another embodiment, an algorithm is configured to acquire a location fix wherein all modes on a GPS modal antenna are surveyed and one or a combination of modes are used to determine a location fix. If two or less satellites can be acquired during a specific timeframe, a base station is accessed using the A-GPS system to determine a unique location. 
     In another embodiment as illustrated in  FIG. 9 , a multimode antenna  100  comprises: an antenna radiator  104  disposed above a ground plane  108  and forming an antenna volume there between; a tuning conductor  116  positioned within the antenna volume, the tuning conductor attached to a first active element  117  for varying a reactance of the antenna; a steering conductor  112  positioned outside of said antenna volume and adjacent to said antenna radiator, the steering conductor attached to a second active element  113  for varying a current mode thereon. The antenna radiator is configured and the steering conductor is adjusted in length and positioned in relation to the antenna radiator to tune the frequency response of the antenna radiator to provide for reception of signals in one or multiple cellular or communication frequency bands, and provide multiple radiation modes within the one or multiple frequency bands. Wherein pilot signals from two or more base stations are received with the multimode antenna; multiple radiation modes are used to measure the pilot signals and the received power level of the pilot signals for multiple modes are measured and stored in memory in a microprocessor or other memory located on the mobile device that the multimode antenna is connected to. The receive signal levels are compared to a data base of stored radiation patterns for the multiple modes, and a measure of angle of arrival of the pilot signals are performed. An intersection of rays or lines parallel to the angle of arrival of two or more pilot signals are used to determine a location fix. 
     In another embodiment, a multimode antenna includes a tunable component with two or more tuning states being connected to the steering conductor to alter the reactance of the steering conductor. The tunable component is adjusted to steer the null, or low signal region, and pilot signals are monitored as the null of the radiation pattern of the multimode antenna is steered. A measure of the receive signal strength of multiple pilot signals is performed and the angle of arrival of two or more pilot signals is determined. An intersection of rays or lines parallel to the angle of arrival of two or more pilot signals are used to determine a location fix. 
     In another embodiment, the location information derived from the antenna system is sent to the GPS receiver and used to update location information in the GPS system. 
     Now turning to the drawings,  FIG. 1  illustrates the compliment of GPS satellites  201  orbiting the Earth  200 , to form the GPS constellation. Each respective GPS satellite is shown having a respective orbit  202  associated therewith. A variable number of satellites  205  are in the field of view of the receiving antenna  206  at any point in time. 
       FIG. 2  illustrates a mobile device  301  with a passive GPS antenna in the field of view of “N” GPS satellites  303   a ;  303   b ;  303   c . The radiation pattern  302  of the passive antenna is shown. The satellites communicate with the mobile device via signals  304   a ;  304   b ;  304   c . Depending on a variety of factors, such as the antenna pattern, reactive loading of the device, and orientation of the device during operation, the passive antenna may have a gain maxima or minima in the direction of the satellite and corresponding signals. 
       FIG. 3  illustrates a mobile device  301  with a multimode GPS antenna, also referred to as a “modal antenna”, the device and antenna being in the field of view of N GPS satellites  303   a ;  303   b ;  303   c . Each satellite communicates with the device via a signal  304   a ;  304   b ;  304   c , respectively. The plurality of radiation patterns  311 ;  312 ;  313 ;  314  generated by the antenna when configured in each of the multiple modes are shown. The antenna will produce a distinct radiation pattern in each antenna mode. Because the antenna can be configured about various antenna modes, an optimal mode having gain maxima in the direction of the intended satellites can be selected for optimum signal quality. 
       FIG. 4  illustrates a mobile device  320  coupled to a low noise amplifier (LNA)  330  and further coupled with a multimode GPS antenna  340  in the field of view of N GPS satellites  303   a ;  303   b ;  303   c ;  303   d ;  303   e . The radiation patterns generated by the multiple modes (Mode 0 to Mode N) are shown. The number of satellite signals  304   a ;  304   b ;  304   c ;  304   d ;  304   e  per mode is stored in a look-up table in the processor for use in a more rapid acquisition of multiple signals for a location fix. 
       FIG. 5  illustrates a flowchart of a Modal Antenna Acquisition Process. The process leads to a more rapid location fix of a GPS system for both “cold” and “hot” starts, and takes into account the desire or requirement for a 2D or 3D location fix. 
       FIG. 6  illustrates a wireless device  701  including a cellular multimode antenna  704  coupled to a low noise amplifier (LNA)  703  and further coupled to a processor and memory  702  with the device in the field of view of three cellular base stations  706   a ;  706   b ;  706   c . Three radiation patterns  705   a ;  705   b ;  705   n  each corresponding to one of three antenna modes are shown about the device. A processor in the mobile device accesses pre-stored radiation pattern data for the modes to use a reference for comparison with real-time measurements to estimate angle of arrival of received signals  707   a ;  707   b ;  707   c  from the base stations. 
       FIG. 7A  illustrates amplitude patterns for a three mode multimode antenna. 
       FIG. 7B  further illustrates phase patterns for a three mode multimode antenna The unique properties of either or both amplitude and phase can be used to discern angle of arrival. 
       FIG. 8  illustrates a wireless device  901  having a multimode cellular antenna  904  coupled to an LNA  903  and further coupled to a processor and memory  902 , the device being in the field of view of three base stations  906   a ;  906   b ;  906   c . A variable antenna radiation pattern is shown  905   a ;  905   n . The null in the radiation pattern is steered to scan the pilot signals  907   a ;  907   b ;  907   c  from the base stations. The angle of arrival is determined by null position for lowest received signal for the pilot signal under test.