Abstract: A system and method of providing featureless covert communication is described. After synchronization is achieved between a covert transmitter and a covert receiver using two channels, one of which is a transmitted reference signal, a single channel is used to transmit the bulk of the communication message. The featureless covert communication system uses a digitally controlled noise source (capable of reproducing a pre-selected pseudo-random signal indistinguishable from ambient noise) at both transmitter and receiver. The digitally controlled noise source produces an uncorrupted reference signal at both locations. Since only once channel is used to transmit the message, 3 dB in power is saved. And, since the same reference signal is being generated locally at the receiver, corruption of the reference signal is eliminated, which improves the efficiency of the system by at least another 10 dB.

Abstract: A spread spectrum processing system that employs wide bandwidth spread spectrum radio transmissions overlaid over the existing cellular voice signals to simultaneously provide additional cellular services without causing objectionable interference to current users of the cellular voice channel. The spread spectrum radio transmissions also support a large number of low rate digital messages. Both vehicle location and messaging functions are obtained without sacrificing any of the existing voice channel capacity. The cell site processor is designed to share the existing cellular frequencies, real estate, antenna towers, antennas, and low noise amplifiers used in the cell site radio frequency receiver chain. The only additional cell site equipment is the spread spectrum signal processor. The processing system provides a means for achieving vehicle location accuracies that are improved by greater than two orders of magnitude over that which is possible by the current transmissions in that band.

Abstract: A vehicle location system incorporating a plurality of ground enhancement stations and at least one satellite to receive encoded transmissions from a radio transmitter aboard a user vehicle. The satellite transmits the signals received directly from the user and those relayed by the ground enhancement station to a base station where a computer calculates the position of the user on the basis of the time difference between the time of arrival of the signals. The use of the ground enhancement stations, located throughout the area in which the user is to be located provides lower geometric dilution of precision than purely satellite or purely ground base systems, and in combination with the relatively simple transmitter aboard the vehicle and transponders at the ground enhancement stations and satellite, substantially reduces the cost of deployment of such a system.

Abstract: A vehicle locating system (VLS) comprises a large number, for example, several million, vehicle-mounted transmitters and several benchmark transmitters; first, second and third signal relay stations and a central processing station at which the transmitter locations are determined, the central station being connected by conventional links to subscriber stations. One hundred microsecond-long RF signals are transmitted by each transmitter in a non-synchronized, mutually random manner. Each signal comprises a 20 microsecond synchronization symbol followed by six, four bit transmitter indentification symbols, each of ten microseconds length. Following the indentification symbols are 10 microsecond message and processing symbols. The control station includes correlation means for correlating the synchronization symbols on each relayed signal against stored data to identify the beginnings of the signals.