Abstract: An integrity monitoring system (IMS) monitors data upload errors, internal data processing errors, clock faults, and transmit signal distortions in a transmitter system. The IMS includes a receiver with an A/D converter that under-samples a multi-band RF signal to produce a composite, aliased IF digital signal. Individual signals are extracted from the composite signal via correlation with the appropriate spreading code. The resulting signals are evaluated to determine whether any signal distortion is present in the RF signals being transmitted, and data is extracted from the signals to perform checks of data uploaded to the transmitter system and data present in the transmitted RF signals that was generated within the transmitter system. The IMS also checks for clock faults in the transmitter system without requiring an independent timing reference by using clock phase information provided by the transmitter system's time keeping system.

Abstract: A communication system generates a constant-envelope composite signal containing at least two signals whose power levels, bandwidths, and/or data rates are independently controllable. Binary offset carrier (BOC) modulation is applied to the signals to be combined in the composite signal. The BOC modulated signals are then combined via interplex modulation to form a constant-envelope composite signal in which the constituent signals modulate different offset carriers. For example, real BOC modulation can be used to generate a ranging signal in edge portions of the transmission band of the composite signal, while complex BOC modulation can be used to generate a frequency agile data signal in a center portion of the transmission band. Such a signal can be used for full duplex communications in satellite crosslinks. The interplex modulation allows independent control of the power levels of the two signals while maintaining a constant envelope, permitting use of saturated RF amplifiers.

Abstract: A quadrature multi-frequency ranging system applied to DSSS multipath mitigation problems is described. The QMFR techniques include taking the time-of-arrival measurements on the received signal at a time when the multipath component is at a 90 degree angle to the direct path. Further, the preferred embodiment of the present invention recognizes that when a signal is transmitted at a series of frequencies, and the spread of these frequencies is sufficient, a quadrature or near quadrature condition can be forced to occur, at which the TOA estimation gives the highest certainty of measurement.

Abstract: A communication device according to the present invention detects a frequency-hopped signal in an environment including sinusoidal interference. The frequency-hopped signal includes a frequency shift keying (FSK) sequence, where the sequence alternates between frequencies shifted from the carrier signal or hop frequency by positive and negative frequency offsets. The communication device of the present invention uses independent detection paths for each of the shifted frequencies. In the detection path for the upper frequency (e.g., positive frequency shift), a series of filters suppresses signals in the lower frequency band (e.g., negative frequency shift), while the detection path for the lower frequency employs a separate series of filters to suppress signals in the upper frequency band. The filter outputs from each detection path are separately examined to detect the presence of an expected signal.

Abstract: A quadrature multi-frequency ranging system applied to DSSS multipath mitigation problems is described. The QMFR techniques include taking the time-of-arrival measurements on the received signal at a time when the multipath component is at a 90 degree angle to the direct path. Further, the preferred embodiment of the present invention recognizes that when a signal is transmitted at a series of frequencies, and the spread of these frequencies is sufficient, a quadrature or near quadrature condition can be forced to occur, at which the TOA estimation gives the highest certainty of measurement.

Abstract: A quadrature multi-frequency ranging system applied to DSSS multipath mitigation problems is described. The QMFR techniques include taking the time-of-arrival measurements on the received signal at a time when the multipath component is at a 90 degree angle to the direct path. Further, the preferred embodiment of the present invention recognizes that when a signal is transmitted at a series of frequencies, and the spread of these frequencies is sufficient, a quadrature or near quadrature condition can be forced to occur, at which the TOA estimation gives the highest certainty of measurement.

Abstract: A communication device according to the present invention detects a frequency-hopped signal in an environment including sinusoidal interference. The frequency-hopped signal includes a frequency shift keying (FSK) sequence, where the sequence alternates between frequencies shifted from the carrier signal or hop frequency by positive and negative frequency offsets. The communication device of the present invention uses independent detection paths for each of the shifted frequencies. In the detection path for the upper frequency (e.g., positive frequency shift), a series of filters suppresses signals in the lower frequency band (e.g., negative frequency shift), while the detection path for the lower frequency employs a separate series of filters to suppress signals in the upper frequency band. The filter outputs from each detection path are separately examined to detect the presence of an expected signal.

Abstract: A quadrature multi-frequency ranging system applied to DSSS multipath mitigation problems is described. The QMFR techniques include taking the time-of-arrival measurements on the received signal at a time when the multipath component is at a 90 degree angle to the direct path. Further, the preferred embodiment of the present invention recognizes that when a signal is transmitted at a series of frequencies, and the spread of these frequencies is sufficient, a quadrature or near quadrature condition can be forced to occur, at which the TOA estimation gives the highest certainty of measurement.

Abstract: A quadrature multi-frequency ranging system applied to DSSS multipath mitigation problems is described. The QMFR techniques include taking the time-of-arrival measurements on the received signal at a time when the multipath component is at a 90 degree angle to the direct path. Further, the preferred embodiment of the present invention recognizes that when a signal is transmitted at a series of frequencies, and the spread of these frequencies is sufficient, a quadrature or near quadrature condition can be forced to occur, at which the TOA estimation gives the highest certainty of measurement.

Abstract: Personal communications in a code division multiple access system operated without a base is provided with simultaneous transmission of a communications channel and a control channel, each spread by different PN codes. The PN code facilitates restricting communications on the network to a particular conversation mode and between identified radios. Transmissions are performed in a time division duplex manner in 62.5 milliseconds slots. One of the radios initiates transmission and maintains power control and time synchronization normally done by a base station. A network control station can voluntarily or by command transfer control of the network to any of the other radios on the network. Colliding transmissions from more than one radio require the radios to retry transmitting until one of the radios transmits in an earlier time slot.

Abstract: Multirate wire line modem apparatus operable at either of two rates in either transmission or reception modes is provided according to the teachings of the instant invention. Full duplex operation and echo cancellation are utilized for both voice and data. Structurally an IOP processor acts as a system controller in controlling transmission and reception digital signal processors which provide the independent transmission and reception functions of the resulting multirate modem apparatus.

Abstract: An improved modem system for HF data transmission over a varying communication channel transmits data in packets formatted into successive frames, each having two identical training sequences following a sequence of data. Each training sequence has a time length longer than the expected time length of the multipath dispersion in the communication channel, in order to isolate one training sequence in each frame from multipath interference from the preceding data sequence. The "clean" training sequence allows the receiving modem system to derive very accurate channel estimates for each frame by autocorrelation to the known symbol sequence stored at the receiver. By interpolating across the channel estimates for the current and previous frames, the modem system can track the communication channel by interpolated estimates for any part or any point in time of the data sequence.

Abstract: Multirate wire line modem apparatus operable at either of two rates in either transmission or reception modes is provided according to the teachings of the instant invention. Full duplex operation and echo cancellation are utilized for both voice and data. Structurally an IOP processor acts as a system controller in controlling transmission and reception digital signal processors which provide the independent transmission and reception functions of the resulting multirate modem apparatus.