Abstract:
A modal antenna is implemented to provide a variable radiation pattern for improved GPS (Global Positioning System) signal reception. A multitude of antenna radiation patterns generated from a modal antenna provide the capability to optimally acquire GPS signals across a wide range of angles of arrival. Minimum radiation pattern roll-off is observed from the composite pattern generated from the multiple patterns. An algorithm is described that reduces the acquisition time for a location fix for cold and hot start conditions.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to location and positioning systems for mobile communication devices, and more particularly to an improved antenna system for GPS signal reception. 
       BACKGROUND OF THE INVENTION 
       [0002]    As mobile wireless devices and applications become increasingly prevalent, location and positioning services based on 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. 
         [0003]    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 TTFF (Time To First Fix) 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 
       [0004]    Accordingly, it is an object of the present 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 
         [0005]    In accordance with various embodiments, the several figures can be understood in conjunction with a thorough review of the appended description, wherein: 
           [0006]      FIG. 1  illustrates the compliment of GPS satellites orbiting the Earth, to form the GPS constellation. A variable number of satellites are in the field of view of the receiving antenna at any point in time. 
           [0007]      FIG. 2  illustrates an a mobile device with passive GPS antenna in the field of view of N GPS satellites. The radiation pattern of the passive antenna is shown. 
           [0008]      FIG. 3  illustrates an a mobile device with a multimode GPS antenna in the field of view of N GPS satellites. The radiation patterns generated by the multiple modes are shown. 
           [0009]      FIG. 4  illustrates a mobile device with multimode GPS antenna in the field of view of N GPS satellites. The radiation patterns generated by the multiple modes are shown. The number of satellite signals 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. 
           [0010]      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. 
           [0011]      FIG. 6  illustrates a multimode cellular antenna in the field of view of three base stations. Three antenna modes are shown. 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 from the base stations. 
           [0012]      FIG. 7  illustrates an example of a set of amplitude and 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. 
           [0013]      FIG. 8  illustrates a multimode cellular antenna in the field of view of three base stations. A variable antenna radiation pattern is shown. The null in the radiation pattern is steered to scan the pilot signals from the base stations. The angle of arrival is determined by null position for lowest received signal for the pilot signal under test. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    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. 
         [0015]    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. 
         [0016]    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. 
         [0017]    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. 
         [0018]    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. 
         [0019]    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. 
         [0020]    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. 
         [0021]    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. 
         [0022]    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. 
         [0023]    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. 
         [0024]    In another embodiment, a multimode antenna comprises: 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 positioned outside of said antenna volume and adjacent to said antenna radiator, the steering conductor 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 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. 
         [0025]    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. 
         [0026]    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.