Abstract: An asymmetrical (inbound only) high frequency communication system for asset tracking is made up of a message preparation and transmitter subsystem, a receiving subsystem, and a system monitoring subsystem. A transmission channel is selected randomly or pseudorandomly. Prior to each transmission, the transmitter performs a radiometric measurement of a selected channel. If the measurement exceeds a predetermined threshold, transmission in the selected channel is canceled and another channel is selected. The transmission protocol achieves frequency diversity by sequentially transmitting a message on a plurality of different channels. The receiving subsystem has a plurality of spatially separated receiver sites at various geographical points, thereby providing spatial diversity. The receiver sites are linked to a common processing center. Onboard the asset and collocated with the transmitter, a system monitoring subsystem records and stores parameters related to the message preparation and transmitter subsystem.

Abstract: A method and apparatus for implementing a spread spectrum communication system of the "transmitted reference" type provides both multipath and interference protection with little complexity. Need for a local reference is avoided by transmitting a reference that the receiver can use to perform despreading. In general, the transmitted reference system sends both a message signal and a reference signal to the receiver. The message signal contains the information to be communicated, which has been spread through multiplication with a wide band "spreading waveform". The reference signal consists of the spreading waveform itself which the receiver call use to despread the message signal and recover the information.

Abstract: Turbo-coding in a communications system involves coding/decoding information in stages in order to avoid retransmission of a full L-bit packet upon occurrence of a packet error. In addition to a set of code bits generated by an encoder using a turbo-coding scheme, a punctured set of code bits is generated and stored in transmitter memory. The original set of code bits is transmitted as an L-bit data packet to a receiver which stores received data samples corresponding to the original set of code bits. The receiver decodes the data packet using a turbo-decoder and determines whether the data packet has been received in error. If so, the received data samples are maintained in memory, and a request for more information is made. Some or all of the punctured information is then forwarded from the transmitter to the receiver.

Abstract: A direct conversion receiver for a delay-and-correlate transmitted reference spread spectrum signaling method and apparatus is based on minimal component digital circuitry instead of analog delay and multiplier circuits. The method allows direct RF to baseband conversion and eliminates the need for an IF stage. The receiver includes an RF converter for converting a received direct sequence spread spectrum signal to baseband. An analog-to-digital converter samples the baseband signal at a rate greater than the chipping rate of the direct sequence spread spectrum signal. A delay stage coupled to the output of the analog-to-digital converter generates a delayed signal. Multiplier logic receives output signals from the analog-to-digital converter and the delay stage and, in response, generates control output signals. A counter responsive to the control output signals increments or decrements a count or recycles, depending on the decoded control output signals.

Abstract: A direct conversion receiver for delay-and-correlate transmitted reference spread spectrum signaling apparatus improves the performance of a delay-and-correlate transmitted reference spread spectrum communication system with essentially no added complexity over prior designs. The message signal contains the information to be communicated, which has been spread through multiplication with a wide band spreading waveform. The reference signal consists of the spreading waveform itself which the receiver can use to despread the message signal and recover the information. Operation of the invention hinges on generation of a class of reference signals at the transmitter which produce more reliable data output signals at the receiver.

Abstract: A low complexity and low cost transmitted reference spread spectrum communications system provides several methods of generating a suitable wideband carrier, a method for combining the wideband carrier with a narrowband modulated wideband carrier, and a number of implementations of a simple, inexpensive receiver for the transmitted reference communications system. The transmitter includes a balanced modulator for modulating a wideband spreading signal with a narrowband message signal to generate a wideband carrier. A signal combiner combines the wideband carrier with a narrowband modulated wideband carrier to generate a transmitted reference spread spectrum signal. The receiver includes a selectable time delay device having a plurality of taps for receiving a detected received signal from the transmitter. A tap selector selects a delayed signal from the selectable time delay device.