Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Patent
1990-02-07
1991-09-03
Issing, Gregory C.
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
342463, G01S 302
Patent
active
050458612
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a navigation and tracking system using radio or other broadcast transmissions.
A navigation system is a means by which the position of a navigator can be determined, either by the navigator himself, or at another location from which the information is relayed to the navigator or is used to direct his progress. A tracking system is a means by which the position of a remote roving point may be tracked at one or more base stations, the coordinates defining the position of the rover being continuously available at each base station. There are many different systems.
For example, conventional radio navigation systems are known which use the signals from two or more pairs of special radio transmitters, and fall into two distinct categories (1) time referencing, and (2) phase referencing.
Systems in the first category include the Long Range Navigation System (LORAN-C) set up by the U.S. Coastguard. The radio transmissions take the form of radio pulses whose times of arrival at the roving point can be accurately measured. The navigator uses a special receiver to determine the time difference between the reception of pulses from each of a pair of such transmitters. This information defines a curve on which he must lie, along which all points have the same difference in distance from the two transmitters. The navigator then measures the time difference between the reception of pulses from a second similar pair of transmitters. The information defines a second curve and the point of intersection of the two curves is the position of the navigator. In general, there is more than one point of intersection, but the navigator usually knows roughly where he is and can select the correct one, or he can use signals from a third pair of transmitters to determine his position uniquely.
Systems in the second category include the Decca Navigation System. In such systems the radio transmissions from a pair of transmitters are coherent with each other, that is, they maintain a predictable phase relationship at all times. In the simplest case, they may be continuous sinusoidal transmissions of exactly the same frequency. The transmissions then form an interference, or `fringe`, pattern in which curves of minimum and maximum intensity may be identified. The navigator measures the fluctuations in intensity as he moves around. He also measures the fluctuations in intensity of signals from another pair of coherent signal transmitters. If he knows his position at the start, he can determine his position at any subsequent time by counting the numbers of fringes of each pair that he has crossed, thereby establishing a point of intersection of the fringes and hence his location within the intersecting fringe patterns. A similar system is described in U.S. Pat. No. 3,889,264 which shows the use of pairs of transmitters to create plural grids of isophase hyperbolic lines, two or more pairs being required for tracking purposes.
Other systems rely on signals transmitted by a roving object whose position is to be measured. U.S. Pat. No. 4,651,156 discloses a system in which the position of a roving object is measured by comparing the phase of a range tone transmitted by the rover with that transmitted by a fixed transmitter. U.S. Pat. No. 4,169,245 discloses a system for tracking a roving transmitter by estimating the differences in times of arrival of signals at two pairs of spaced receivers, using the spread of frequences associated with modulation of the carrier transmission wave.
In U.S. Pat. No. 3,774,215 the system shown uses OMEGA (very low frequency) transmitters transmitting to a roving object, the roving object receiver detecting differences in phase between a reference signal and the received transmissions. Phase difference data is transmitted to a communication station where it is analysed in a computer and positional data determined therein is transmitted back to the roving receiver.
U.S. Pat. No. 4,054,880 discloses the use of three transmitters, the phases of which are compared with a local oscillator re
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Issing Gregory C.
The Lynxvale - Cril Partnership
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