Abstract: A method, implementable on a computer, for filtering time-varying location solution coordinates P.sub.x,n, P.sub.y,n, and P.sub.z,n, determined by a Satellite Positioning System (SATPS, usually GPS or GLONASS), which operates in a static mode and a dynamic mode, to reduce large discontinuities and control the rate at which a changing sequence of measurement errors can induce a change in a sequence of location solutions. As an initial step, SATPS location solutions P.sub.x,n, P.sub.y,n, and P.sub.z,n, and SATPS velocity solutions V.sub.x,n, V.sub.y,n, and V.sub.z,n are generated for selected fix times t=t.sub.n with essentially no time lag in these solutions, when recent measurements are available from all satellites in the solution constellation. Sequences of filtered location coordinates {P.sup..LAMBDA..sub.x,n }, {P.sup..LAMBDA..sub.y,n }, and {P.sup..LAMBDA..sub.

Abstract: A method for compensating for temporary loss of differential GPS correction signals for a satellite, numbered j, during an IODE changeover interval. Differences .DELTA.e.sub.i (t;j;n+1,n)=e.sub.i (t;j;n+1)-e.sub.i (t;j;n) (i=1, . . . , I) are formed for I ephemeris parameters used to describe the ephemeris for the satellite (j) during IODE intervals number n+1 and n. These differences are approximated for a DGPS blank-out time interval, given by t(j;n+1).sub.IODE .DELTA.t.sub.rev,mob .ltoreq.t<t(j;n+1).sub.IODE +.DELTA.t.sub.ch +.DELTA.t.sub.rev,ref, during which a GPS reference station continues to broadcast DGPS correction information based on the old ephemeris data that was valid during the preceding IODE time interval, given by t(j;n).sub.IODE .ltoreq.t<t(j;n+1).sub.IODE. These ephemeris differences are used by a mobile station that receives DGPS correction information from the GPS reference station to produce corrected GPS information for a blank-out time interval.

Abstract: Methods for determining the present location coordinates of a user moving in a two-dimensional or three-dimensional space, with reference to an old map that may be inaccurate. Location coordinates (xi',yi') of two or three non-collinear landmarks in two dimensions), or coordinates (xi',yi',zi') of three or four non-coplanar landmarks (in three-dimensions), are indicated on the old map. Corresponding location coordinates (xi,yi) or (xi,yi,zi) are also determined or made available using a location determination system (LDS), such as GPS, GLONASS, Loran, Tacan, Decca, Omega, VOR, DME, JTIDS, PLRS or an FM subcarder system. Location coordinates (xi,yi) (or (xi,yi,zi)) for two or more physical landmarks can be combined into coordinates for a landmark representative. The user's location coordinates (xu,yu) (or (xu,yu,zu)) are also determined or provided using the LDS.

Abstract: Methods for secure communication of location and other information by two spaced apart receivers in a location determination (LD) system, such as GPS, GLONASS and LORAN-C, that use pseudorange corrections to enhance the accuracy of the computed present location of an LD receiver. A pseudorange correction signal PRC(t;i;j), presenting a correction of a pseudorange measurement made at time t at an LD receiver number i from an LD signal issued by an LD signal source number j, is transmitted at a consecutive sequence of times t=t.sub.0, t.sub.1, t.sub.2, . . . , t.sub.n. The pseudorange correction signal PRC(t.sub.n ;i;j), or a message sent in a time interval t.sub.n-1 <t.ltoreq.t.sub.n, is encrypted, using an encryption key that is a function of and depends non-trivially upon one or more of the preceding pseudorange correction values PRC(t.sub.k ;i;j) (k.ltoreq.n-1). This encryption key varies from one time interval t.sub.n-1 <t.ltoreq.t.sub.

Abstract: Method and apparatus for monitoring present location of a site arrestee confined to a permitted site of arbitrary size. Present location of the arrestee can be checked at selected time intervals of several hundred milliseconds to thousands of seconds, as desired. The arrestee wears a location-determining ("LD") unit that receives electromagnetic signals that contain information allowing determination of the present location of the LD unit and arrestee, from three or more non-collinear signal sources. These sources may be radiowave subcarrier transmitters, or may be a combination of radiowave subcarrier transmitters and (1) transmitters for a Loran, Omega, Decca, Tacan, JTIDS Relnav or PLRS or similar ground-based system, or (2) transmitters for a satellite-based positioning system, such as GPS or GLONASS. Present location or change in present location of the LD unit is determined and compared with the permitted site boundary at selected times to determine if the arrestee is present at the site.

Abstract: Apparatus and method for accurately determining the location of an target or other designated object by an observer that is spaced apart from the object. The observer views the target through a viewer and rangefinder and determines the distance of the target from the observer. The observer determines its own location coordinates, and the angular orientation of the rangefinder relative to a selected line or plane, using Satellite Positioning System (SATPS) signals (such as GPS or GLONASS signals) received by three SATPS antennas and processed by a common SATPS receiver/processor. The SATPS receiver/processor then determines the displacement or offset coordinates of the target relative to the observer and displays the target coordinates on the target image seen in the viewer. The target location coordinates and/or the visual image of the target seen in the viewfinder are transmitted to a control station for subsequent use.

Abstract: Method and apparatus for monitoring the present location of an emergency or general serviceperson, such as a firefighter or a hazardous materials spill clean-up specialist, assigned to perform emergency services at a designated site. The site diameter can be as small as a few meters or as large as several kilometers. The serviceperson's present location can be checked at selected time intervals with time periods ranging from a few hundred milliseconds to thousands of seconds, as desired. The serviceperson wears or carries a location-determining ("LD") unit that receives electromagnetic signals that contain information allowing determination of the present location of the LD unit, and thus of the serviceperson, from three or more signal sources.

Abstract: A method for monitoring the movement of a vehicle along a selected route R to determine whether the vehicle is (i) adhering to that route and/or (ii) adhering to a selected time schedule along that route. Adherence to the route R requires that the vehicle travel within a corridor of selected positive width that surrounds a path defining the route R. Adherence to the time schedule requires that the vehicle move past one or more specified locations along or adjacent to the route R within a specified time interval. The method provides an electronic map with a visually perceptible display that indicates the present location of the vehicle and allows implementation of a snap-to-route command that displays the location on the route R that is closest to the present location of the vehicle.

Abstract: A method for compensating for the differences in time varying signals S(t;R;S) received and processed by two signal receiver/processors (R.sub.2 and R.sub.3), located at the same site, from two signal sources (S.sub.2 and S.sub.3) that are spaced apart from the receiver/processors. A receiver/processor (R.sub.1) is chosen as a baseline, and double difference signals DD(t;R.sub.1 ;R.sub.2 ;S.sub.2 ;S.sub.3)=S(t;R.sub.1 ;S.sub.2)-S(t;R.sub.1 ;S.sub.3)-S(t;R.sub.2 ;S.sub.2)+S(t;R.sub.2 ;S.sub.3) and DD(t;R.sub.1 ;R.sub.3 ;S.sub.2 ;S.sub.3)=S(t;R.sub.1 ;S.sub.2)-S(t;R.sub.1 ;S.sub.3)-S(t;R.sub.3 ;S.sub.2)+S(t;R.sub.3 ;S.sub.3) are formed. The respective time averages DD(R.sub.1 ;R.sub.2 ;S.sub.2 ;S.sub.3).sub.avg and DD(R.sub.1 ;R.sub.3 ;S.sub.2 ;S.sub.3).sub.avg of these two double difference signals are formed, using a time interval of length T lying in a preferred range given by 120 sec.ltoreq.T.ltoreq.1800 sec. First difference signals, DDC(t;R.sub.1 ;R.sub.2 ;S.sub.2 ;S.sub.3)=DD(t;R.sub.1 ;R.sub.2 ;S.sub.

Abstract: Integrated antenna apparatus for determination of the location of an observer and/or of the time of observation by use of a GPS or a GLONASS or other Satellite Positioning System that uses differential corrections of the pseudorange, the location and/or the observation time. The apparatus includes an antenna module and a display module, connected by a communication link. In one embodiment, the antenna module includes: a GPS antenna to receive the GPS signals; a signal frequency downconverter; a Differential GPS (DGPS) radiowave signal antenna and receiver to receive GPS correction information; a GPS/DGPS signal processor to receive the GPS antenna and DGPS antenna output signals and to determine at least one of (i) the present GPS antenna location, as corrected by the DGPS signals, and (ii) the observation time of such location; and a communication link to communicate GPS processor output signals to the display unit.

Abstract: Apparatus for providing accurate local time for one or more timed devices that depend on such time for operation. In one embodiment, a Satellite Positioning System (SATPS), such as GPS or GLONASS, provides the time signal information. In another embodiment, the time signal information is provided by telecommunication means, such as a telephone, cellular telephone or similar apparatus. The local time signal is distributed by a time signal distribution module to one or more timed devices by a wire or transmission line, by radio waves, or by direct contact with an input terminal of a timed device. The time signal distribution module may be a single station, a master station for a system of timed devices, or a portable module that can be moved from one timed device to the next.

Abstract: Methods for provision of a sequence of timing signals for one or a plurality of microprocessors, microprocessor peripheral devices or other timing-controlled instruments ("users"), using timing signals determined from a Satellite Positioning System (SPS), such as GPS or GLONASS. In a first embodiment, one or a plurality of users is individually provided with SPS signal antennas and receiver/processors, and timing signals are optionally individually for each user. The timing signals can be periodic, for example, a One-Pulse-Per-Second signal for fine corrections of high frequency timing signals issued by an internal or external clock. The timing signals can also be substantially non-periodic. The timing signals may also be used to determine the time at which selected events occur, such as issuance of interrupt commands in, or directed to, a microprocessor.

Abstract: A method for enhancing the accuracy of location coordinates and/or clock bias computed for a mobile user station that is part of a Satellite Positioning System (SATPS), such as GPS or GLONASS. A reference SATPS station is provided with known location coordinates, and pseudoranges PR(t) and pseudorange corrections .DELTA.PR(t) for the reference station are computed as in a conventional differential GPS approach. A matrix equation H(t) .DELTA.W(t)=.DELTA.PR(t) relates the corrections for the spatial location coordinates and clock bias at the mobile station (or at the reference station) to the pseudorange correction values at that station, where H is an M.times.N matrix (M.ltoreq.N; N=3 or 4) with known entries. Each of the N rows of the matrix H has M entries and forms a row vector, and these row vectors are linearly independent in an M-dimensional vector space. These row vectors span an N-dimensional vector space.

Abstract: Methods for synchronizing to a reference signal the timing of a received composite, code phase SATPS signal, which consists of a preferred, interference-free signal distorted by at least one interfering signal, to determine an undistorted timing point of the preferred signal. An idealized correlation function A.sub.I (t), formed from the product of a digital reference signal with a time-shifted reference signal, and a measured correlation signal A.sub.M (t), formed from the product of a received signal and a time-shifted reference signal, are computed. Peak amplitudes A.sub.M (p.sub.M) and A.sub.I (p.sub.I) are found for the respective measurable and idealized punctual code phase shifts p.sub.M and p.sub.I. In a first embodiment of the invention, the correlation measurements formed on the early side (or on the late side) of the peak for the correlation function A(t) are combined to form an estimate of the time delay associated with a multipath signal.

Abstract: A method for directing a vehicle from a fleet of N vehicles, numbered n=1, 2, . . . , N(N.gtoreq.2), to respond to a call for assistance received at a central processing station that communicates with a communications unit on each of these vehicles. The central station receives information by radio wave signals on the present location and present status of each vehicle on patrol at a sequence of times. Optionally, the vehicles may be divided into mutually exclusive groups, with each group reporting its location and status at separate times with different frequencies of reporting. An information response interval for a group includes a number of time slots, with each time slot allocated to a vehicle in the group so that no slot is empty. When the central station receives a call for assistance, an assistance message is transmitted to the fleet, specifying the site at which assistance is needed and any available information on the nature of the assistance required.

Abstract: Method and apparatus for providing GPS pseudorange correction information over a selected geographic region S with a diameter of up to 3000 km with an associated inaccuracy no greater than 5 cm. N spaced apart GPS fiducial stations (N.gtoreq.3), whose location coordinates (u.sub.n, v.sub.n, v.sub.n) are fixed and are known with high accuracy, are provided within or adjacent to the region R. Each fiducial station n (n=1, 2, . . . , N) receives GPS signals from at least four common-view GPS satellites, numbered m=1, 2, . . . , M (M.gtoreq.3), computes its own GPS-determined location coordinates, compares these coordinates with its known location coordinates determines the pseudorange corrections PRC(t;t0;m;n) for its GPS-determined location, and transmits these correction signals to a central station located within or adjacent to the region S. The central station retransmits the pseudorange correction signals throughout the region S.

Abstract: Apparatus for measuring surveying parameters, such as distances and angular displacements between survey stations, with improved accuracy. The invention combines a differential satellite positioning system (SATPS), available with positioning systems such as GPS and GLONASS, with electromagnetic measurements of distances and optically encoded angles by a conventional electro-optical survey instrument to provide survey measurements that can be accurate to within a few millimeters in favorable situations. The differential satellite positioning system relies upon carrier phase measurements, after removal of certain phase integer ambiguities associated with carrier phase SATPS signals. The SATPS may be retrofitted within the housing of the conventional electro-optical instrument.

Abstract: Method and apparatus for reducing or cancelling impulse noise from a signal containing noise. The desired noise-free signal is assumed to have a representative frequency .omega..sub.3, but may have a range of frequencies adjacent to this frequency, and is assumed to have substantially zero amplitude for all frequencies .omega.<.omega..sub.1 and/or for all frequencies .omega.>.omega..sub.2, where .omega..sub.1 <.omega..sub.3 <.omega..sub.2 or .omega..sub.1 <.omega..sub.2. An input (noisy) signal is filtered and analyzed in a narrow frequency region surrounding .omega.=.omega..sub.1 and/or a narrow frequency region surrounding .omega.=.omega..sub.2 to obtain one or two output signal components n.sub.1 (t) and/or n.sub.2 (t), respectively, that, ideally, contain no contribution from the desired signal. The input signal is also filtered and analyzed in a narrow frequency region surrounding .omega.=.omega..sub.3 to obtain an output signal s(t)+n.sub.3 (t) component including the desired signal s(t).

Abstract: Method and apparatus for reducing the contributions of receiver noise signal error and multipath signal error from signals received in a Satellite Positioning System (SATPS) from one or more SATPS satellites by formation and appropriate filtering of differences of signals DD that are differences of SATPS signals received by the SATPS receiver/processor. A difference signal DD of code-phase-derived delta range signals and carder-phase-derived delta range signals is formed, and this difference signal is passed through a first statistical processing filter with an associated time constant .tau.1 in the approximate range 50-500 sec, to produce smoothed or filtered signal with the estimated receiver noise error reduced or removed. The difference signal DD is passed through second and third statistical processing filters having associated time constants .tau.2=5-20 sec and .tau.

Abstract: Methods for determining the integrity of pseudorange and pseudorange rate signals received from a plurality of M Satellite Positioning System satellites (SATPS, including GPS and GLONASS), numbered j=j1, j2, . . . , jM, at a reference SATPS station (RS), using pseudorange and pseudorange rate signals received from the same satellites at a signal integrity monitoring (SIM) station located near the reference station. Pseudorange correction values PRC(t;i;j).sub.RS and PRC(t;i;j).sub.SIM and pseudorange rate correction values PRRC(t;i;j).sub.RS and PRRC(t;i;j).sub.SIM for the signals received at the reference station (RS, number i) and at the SIM station are computed, and difference values DPRE(t;i;j)=PRC(t;i;j).sub.RS -PRC(t;i;j).sub.SIM and DRRE(t;i;j)=PRRC(t;i;j).sub.RS -PRRC(t;i;j).sub.SIM are computed from these correction values. If .vertline.DPRE(t;i;j).vertline..ltoreq.DPRE(i;j).sub.thr and .vertline.DPRRE(i;j).vertline..ltoreq.DPRRE(i;j).sub.thr, where DPRE(i;j).sub.thr and DPRRE(i;j).sub.