摘要:
A ranging system for a communications spacecraft (14) overlays a Gaussian noise signal over a broadband channel which also carries information or traffic signals. The noise is used to establish the range between a ground station (12) and the spacecraft (14). The range is determined by delaying the Gaussian noise in a controllable delay (32), and autocorrelating the delayed noise with the noise returned over the communications channel from the spacecraft. The ranging system (FIG. 4) reduces the bandwidth of the noise in a filter (18) during initial acquisition, to color the noise and broaden the autocorrelation peak (FIG. 3a). The broad peak shortens the initial search time. Once the peak is initially found, the noise bandwidth is progressively broadened to narrow the autocorrelation peak (FIG. 3c) and to give a more accurate indication of range.
摘要:
In a time division multiple access spacecraft communication system, each ground station determines when to send its information packets to arrive at the spacecraft at the beginning of a time slot. The calculation is based upon knowledge of the location of the spacecraft. A master ground station determines the location of the spacecraft by the use of the propagation delays between the various ground stations (including itself) and the spacecraft, together with knowledge of the locations of the ground stations. The spacecraft location is then transmitted back to the various ground stations. The determination of propagation delay by each ground station is performed in two major steps. The first step determines coarse time delay to within one bit interval by repeatedly transmitting a multibit unique word to the spacecraft, and counting bits until the next unique word is received from the spacecraft. To determine fine propagation delay, a high-frequency clock signal is counted from the time of transmission of each bit edge until the reception of the next bit edge. The sum of the coarse and fine delays, together with a plurality of frame intervals, establishes the range to the spacecraft.
摘要:
In a time division multiple access spacecraft communication system, each ground station determines when to send its information packets to arrive at the spacecraft at the beginning of a time slot. The calculation is based upon knowledge of the locations of the spacecraft and the transmitting ground station. A master ground station determines the location of the spacecraft by the use of the propagation delays between the various ground stations (including itself) and the spacecraft, together with knowledge of the locations of the ground stations. The spacecraft location is then transmitted back to the various ground stations. The determination of propagation delay by each ground station is performed by repeatedly transmitting a ranging signal containing a multiple-bit unique word to the spacecraft, and counting spreading code chips until the next unique word is received from the spacecraft.
摘要:
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. A mixer combines output signals of the selectable time delay device and the tap selector, and a leaky integrator receives the mixer output signal and controls the tap selector. The leaky detector generates the narrowband message signal.
摘要:
A control system for the uplink transmitter of a ground station communicating with a spacecraft includes an antenna located at the ground station, pointed toward the spacecraft for receiving downlink signals transmitted therefrom. The received signals are accompanied by noise attributable to ambient, sky and ground temperatures. A low-noise receiver is coupled to the output port of the antenna, for establishing the receiver noise temperature. A processor is coupled to the low-noise receiver apparatus and to the power control input port of the uplink transmitter, for responding to changes in the received noise power attributable to the presence or absence of precipitation in the downlink. The processor does this by producing an estimate of the attenuation attributable to the rain in the downlink, and generates the control signal in response to the estimate of the attenuation. The control signal increases the signal power of the uplink transmitter in response to increases in the estimate of the rain attenuation, and decreases the signal power of the uplink transmitter in response to decreases in the estimate of the rain attenuation. The processor determines the downlink rain attenuation L.sub.a,D by L.sub.a,D f(.DELTA.N.sub.R)=T.sub.eff /(1+T.sub.eff -.DELTA.N.sub.R) where T.sub.eff =(T.sub.amb -T.sub.sky)/(T.sub.LNA +T.sub.g +T.sub.sky)
摘要:
A receiver for a unique word sequence or a spreading code sequence includes a memory which is preloaded with all possible phases of the code. The sequence in the received signal is correlated, in parallel, with sums of various ones of the different phases of the code. Thus, the received code is correlated with all possible phases of a replica of its own code. Consequently, one of the sums will exhibit a correlation peak, which indicates that the desired phase of the code is included in that particular sum. The other sums will not exhibit a correlation peak, and are is discarded. The different phases in the one sum which displayed correlation are divided into new sums, each having fewer phases, and the correlation is again performed. Again, those sums exhibiting no correlation are discarded, and the sum exhibiting correlation is divided into sums of fewer codes.
摘要:
A communications system includes first and second ground stations and a spacecraft repeater. Data signals are transmitted between ground stations by way of the repeater, together with spread-spectrum ranging signals. Uplink rain attenuation is compensated for changing the transmitted power at the ground stations. The amount of downlink attenuation is determined by measuring the total carrier-to-noise ratio in three paths, station 1 to station 2, station 2 to station 1, and station 1 to station 1. With these three values of total attenuation, the two downlink attenuations and the number of active signals traversing the repeater can be determined. The downlink attenuations are converted to uplink attenuations, and used to control the transmitters.
摘要:
A communication system includes a transmitter configured to pulse shape a GHM signal to confine the frequency spectrum of the GHM signal within a predefined frequency range. A receiver is also included that receives the transmitted GHM signal. The receiver includes a processor for maximizing the GHM signal to noise ratio and minimizing the bit error rate. The GHM signals are also synchronized to establish a relative time for correct interpretation of bit positions.
摘要:
A system for spread spectrum power line communications employs a harmonic modulation (HM) transmitter coupled to the power line for transmitting message bits to an HM receiver. The spread spectrum accommodates a plurality of HM transmitters simultaneously occupying the same bandwidth. The spectrum of HM, in a frequency range above 60 Hz but below the maximum frequency that will carry through a distribution transformer, is ideal in combating carrier synchronous noise since it can be interleaved with the noise harmonics and therefore be effectively spectrally disjoint with the synchronous noise process spectrum.
摘要:
The invention provides an aggregator for use in connection with a power distribution network including a power line. The aggregator comprises a receiver, a controller, and a data outbound link. The receiver is coupled to the power line and is configured to receive signals comprising messages, for example geometric harmonic modulation (GHM) signals, from the power line. The controller is coupled to the receiver and to the data outbound link. The controller is configured to provide messages received by the receiver to the data outbound link for transmission by radio frequency energy to a destination, for example a power control station.