COMMUNICATIONS AND POSITION
LOCATION SYSTEM AND METHOD
BACKGROUND OF THE INVENTION
The present invention relates to communications and position location systems and specifically to a communications and position location system that may utilize laser light strings or normal laser light propagation.
Global positioning system (GPS) navigational and position 10 location systems are often used by military and civilian naval, ground, and airborne vehicles for navigation. GPS systems can experience blackout areas or regions when line-of-site (LOS) is broken with the satellites due to signal blockage. For example GPS systems often experience loss of signal when 15 they are operated in dense urban environments next to large buildings (e.g., urban canyon). Additionally recent attempts at augmenting GPS for this coverage deficiency has had mixed success and has not resulted in a low-cost widespread solution. 20
Communications systems operating in the VHF/UHF and higher frequency bands have LOS problems similar to GPS. Vehicles operating in a city or in rugged or mountainous terrain have difficulty communicating due to signal link-loss and blockage. Furthermore, there are few technical options 25 for delivering high-speed data, video, and position location Information from a mobile unit or a large number of mobile units. For example, mobile units may include emergency response vehicles requiring broadband transmission of video from an emergency scene back to an emergency operations 30 center. Rough terrain, line-of sight, ground network infrastructure and antenna technical challenges generally force or limit options having lower or unsatisfactory bit rate solutions. There are many solutions for providing high-speed data to a mobile unit. However most high data rate (broadcast) data 35 channels options for mobile units with antenna height disadvantages do not work well for transmissions from the mobile units.
Laser diode technology has advanced in recent years with the development of low cost direct emission devices. These direct emission devices offer high-speed modulation capabilities for laser data communications systems. These state of the art laser diodes are available in several power levels and wavelengths including green, blue, and blue violet.
Laser communications systems known in the art provide end-to-end or point-to-point systems where a laser transmitter must be pointed directly at a laser receiver to establish communications. As with some radio communications systems, these laser communications systems are not useable in 5Q rough terrain or urban canyon situations.
There is a need for a position location and communications system that not only is less susceptible to blackout prone and high loss areas, but has wide bandwidth for high-speed data communications and is inherently low cost. 55
SUMMARY OF THE INVENTION
A laser communications and position location system using laser light beam concentration and atmospheric scatter- 60 ing is disclosed. The laser communications and position location system has a laser transmitter for radiating laser beams upward at convergence angles. The laser beams converge at a free space junction that provides a concentration of the laser beams. The laser beams are scattered at the free space junc- 65 tion and a laser receiver receives scattered laser beam light. The convergence angles determine an altitude of the free
space junction. The laser beams are modulated by data at the laser transmitter to provide a data signal received by the laser receiver.
The laser transmitter further comprises a laser array. The laser array comprises a plurality of laser diodes arranged in a circular array. A modulator modulates the array of laser diodes with the data from a data source. The laser diodes may operate at a wavelength optimized for free-space transmission using continuous wave (CW) or ultra-short pulses. The laser transmitter may transmit a unique identification code. The laser transmitter may include a data link for transmitting a position of the free space junction to the laser receiver to assist in locating the free space junction.
The laser receiver upon finding the free space junction rejects an unnecessary field of view to enhance signal-tonoise ratio. The laser receiver may also include a filter to reject unwanted light to enhance laser detection. The laser receiver determines a precise location of the laser transmitter upon finding the free space junction. The laser receiver comprises an optical detector with an adjustable optical field of view and gain to minimize background light noise and to demodulate the received scattered laser beam light.
It is an object of the present invention to provide a laser communications and position location system using atmospheric scattering from laser light under a wide range of atmospheric conditions and weather.
It is an object of the present invention to provide a communications and position location system to provide communications and position location in rugged terrain or urban canyons.
It is an advantage of the present invention to provide covert high data rate data from a mobile user.
It is an advantage of the present invention to provide precision position location of a vehicle in rugged terrain or city locations.
It is a feature of the present invention to provide high data rate low-cost communications using low-cost semiconductor lasers.
It is a feature of the present invention to provide communications and position location using a laser system with ultra-short low-power laser pulses.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be more fully understood by reading the following description of the preferred embodiments of the invention in conjunction with the appended drawings wherein:
FIG. 1 shows the communications and position location system of the present invention that utilizes a laser light and atmospheric scatter phenomena for communications and position location;
FIG. 2 shows details of a laser transmitter portion of the communications and position location system of FIG. 1;
FIG. 2a illustrates driving laser diodes as a phased array in the laser transmitter of FIG. 2;
FIG. 3 shows the communications and position location system of the present invention in a rugged terrain application example;
FIG. 4 shows the communications and position location system of the present invention in a city application example; and
FIG. 5 shows the communications and position location system of the present invention in a fixed application.