摘要:
The present disclosure provides for methods and systems for segmented spread-spectrum communication according to one embodiment of the invention. Segmented spread-spectrum communication may include replicating a signal, spreading each of the replicated signals with a code, and modulating each of the coded signals within a unique spectral segment. The spectral segments may be uniform or nonuniform in width and may or may not be contiguous within the spectrum. The receive processing may include interference detection within a spectral segment. In response to detected interference, spectral segments may be discarded, a signal gain of each segment may be adjusted according to the level of interference, and/or selected segments may be adjusted according to the level of interference. Moreover, at the receiver a number of transmitted spectral segments may be combined. As a further embodiment, a plurality of signals may spread among a plurality of spectral segments.
摘要:
A satellite clock system in which the frequency of the onboard satellite clock, which is implemented as a relatively high uncertainty voltage-controlled oscillator, is corrected in accordance with a high-stability, low-uncertainty terrestrial clock. Metering bursts are transmitted from the earth station to the satellite where portions of the metering bursts are truncated due to misalignment between the bursts and the synchronization windows timed by the onboard oscillator of the satellite. The patterns of the received bursts which are re-transmitted by the satellite are compared with a stored pattern and a phase shift value determined in accordance with the number of incorrect comparisons. The phase error measurement value is utilized to control a programmable divider connected between the high-stability, low-uncertainty oscillator and the burst transmitter to thus provide a short-term correction. The output values from the phase error measurement are accumulated over a sidereal day period to provide a sidereal day phase shift value. The accumulated value of the sidereal day phase shifts is summed with all previous daily values to compute a cumulative phase shift from the beginning of the system operation. The current and cumulative phase shift values are then summed and divided by a period of one sidereal day to produce an actual phase correction for the next sidereal day. The actual daily frequency correction is computed by summing all values of the sidereal day frequency correction and telemetering this value to the satellite. Alternately, the accumulation of the frequency corrections can be performed onboard the satellite.
摘要:
A communication system having a first station and a second station in communication over a wireless communications link. The first station is operative during a communication session to assemble signals from multiple data sources into a common data stream and to transmit the data stream as frame-based communication signals to the second station. The first station comprises a dynamically configurable multiplexer that is operative during a communication session (1) to generate the common data stream by multiplexing the signals in accordance with a plurality of control parameters and assemble said signals according to frames, (2) to dynamically modify the plurality of control parameters in accordance with changes in wireless link conditions and (3) to generate control signals identifying modifications to the control parameters. The first station is operative to transmit to said second station the signals assembled according to frames and the control signals
摘要:
A method for generating a Doppler-free local clock in a communications network having a master reference terminal (400) and a terminal (200) exchanging reference and management bursts, includes steps for determining a transmit timing correction value responsive to the management burst received by the master reference terminal (400), determining a receive timing correction value responsive to the reference burst received by the terminal (200), and adjusting the frequency of a clock responsive to both the transmit timing correction value and the receive timing correction value to thereby generate the Doppler-free local clock.
摘要:
In an on-board satellite clock correction system of the type wherein phase errors between the satellite clock and a ground-based clock are determined and a clock correction value sent to the satellite, the clock correction value is determined by curve-fitting the determined phase errors in accordance with a polynomial function, updating the polynomial function coefficients so as to minimize discrepancy between the determined phase errors and those according to the polynomial function, predicting a clock drift in accordance with the polynomial function and calculating an error correction value in accordance with the predicted clock drift.
摘要:
In a satellite network with on-board switching and bandwidth on demand, traffic monitoring is required to facilitate billing data collection and to avoid congestion at the satellite. In addition to traffic monitoring, performance monitoring is necessary to quickly respond to link degradation or possible equipment anomalies. Monitoring terminals specially equipped with traffic measuring and policing and link performance measuring capabilities are used to monitor traffic and performance. The monitoring terminal is located in each satellite beam to perform the monitoring functions for that beam. The monitoring terminals are low-cost terminals that receive down-link traffic in their respective beam, and record statistics on a per transmit-terminal or per virtual connection basis. Records are periodically transmitted to a central location where they are processed for billing, enforcing traffic contracts, and taking actions against link degradations.