Abstract: Apparatus and method for paging a user terminal (UT) using a satellite communications system having a gateway and one or more satellites, wherein each satellite produces a plurality (n) of beams and each beam includes a plurality of channels. The method of the present invention includes the step of recalling a first location of the UT, wherein the first location corresponds to a location of the UT at a first time t1. In one embodiment, this is accomplished by performing a lookup in a table or database that includes location information for user terminals at different points in time. The method also includes the step of determining a first group (g1) of beams which covers the first location of the UT at a second time t2, where g1<n and time t2 is later in time than time t1. A page is then sent from the gateway to the UT on a channel, such as a paging channel, of at least one beam of the first group of beams. In one embodiment, the page is sent on the paging channel of each of the first group of beams.

Abstract: The information signals are transferred to end users, customers, or service subscribers using at least two signal sources, generally satellites, and polarized radiation. Two polarization modes are employed, with the preferred modes being left-hand and right-hand circularly polarized radiation, although other polarization modes may be employed. The total number of channels can be divided among the polarization modes and transferred to end users either through the use of polarization switching in the receivers to selectively switch between the satellites, or by switching elements in the satellites (sources) to switch between polarization modes used for transmission.

Abstract: A system and method for spatial multiplexing signals on the feeder links of a satellite communication system. A beamforming antenna forms a plurality of feeder beams from signals received from system gateways, each feeder beam illuminating one of the gateways and including a plurality of frequency division multiple access (FDMA) channels. A plurality demultiplexers separate each of the feeder beams into the FDMA channels, and signal combiners combine first and second ones of the channels, each comprising signals corresponding to user terminals illuminated by a specific user beam, to produce a user beam signal which is used by a beamforming user link antenna to form a specific user beam. In a further aspect, a user link beamforming antenna forms a plurality of user beams from signals received from user terminals, each including a plurality of FDMA channels, and a plurality of demultiplexers separate each of the user beams into the channels.

Abstract: A method and apparatus for controlling a signal transmission power. The method of the present invention includes the steps of demodulating a received signal to produce a demodulated signal and distorting the demodulated signal to produce a distorted demodulated signal. The demodulated signal can be distorted by, for example, adding noise. A signal quality measurement, such as signal-to-noise ratio, is then determined based on the distorted demodulated signal rather than the demodulated signal. An adjustment in the transmission power is then requested based on the signal quality measurement of the distorted demodulated signal.

Abstract: A handoff technique in which system users detect transitions in service between a current service area and an adjacent service area, and request a forward link channel in the new service area when a detected signal strength for the new service area exceeds predetermined threshold levels. The forward communications link in the current service area is maintained until the strength of the new service area signal reaches a certain level and appropriate channel quality is confirmed, as based on various known criteria. Typically, service area transitions are detected using the signal strength of pilot or paging signals associated with service areas, which are used to determine a relative signal strength of new service area signals. Pilot signal level adjustments used to counter roll-off effects are detected and compensated for in comparing signal levels.

Abstract: A handoff technique in which system users detect transitions in service between a current service area and an adjacent service area, and request a forward link channel in the new service area when a detected signal strength for the new service area exceeds predetermined threshold levels. The forward communications link in the current service area is maintained until the strength of the new service area signal reaches a certain level and appropriate channel quality is confirmed, as based on various known criteria. Typically, service area transitions are detected using the signal strength of pilot or paging signals associated with service areas, which are used to determine a relative signal strength of new service area signals. Pilot signal level adjustments used to counter roll-off effects are detected and compensated for in comparing signal levels.

Abstract: A method for reducing call dropping rates in a multi-beam communication system. The multi-beam communication system includes a user terminal, a gateway, and a plurality of beam sources, where each beam source projects a plurality of beams, and where a communication link between the user terminal and the gateway is established on one or more beams. The method according to the present invention relies on a messaging protocol between the gateway and the user terminal. Based on messages sent from the user terminal to the gateway, preferably on a preselected periodic basis, the gateway can determine the more desirable beam(s) for transmitting data or information to the user terminal. The messages sent from the user terminal to the gateway contain values representing beam strengths as measured at the user terminal. The gateway uses the user terminal measured beam strengths to select the beams that should be used for transmitting data or information to the user terminal.

Abstract: A method and apparatus for accurately determining the operating characteristics or impact of nonlinear effects on devices or communication systems transferring orthogonally coded spread-spectrum communication signals. A Walsh Power Ratio, is used to more accurately determine system response. This information can be used by power control loops in controlling or adjusting the operation of nonlinear elements or stages such as high power amplifiers in orthogonal CDMA communication systems to provide improved system response. The information can also be employed in assigning channels to systems users, and to proceed with physical changes to system hardware. The measurements used to formulate the WPR can be made to individual components or to entire systems by injecting communication signals in multiple channels containing data, and leaving at least one empty channel. The received power per channel on the output side of the system or device is then measured.

Abstract: A variable rate transmission system wherein a packet of variable rate data generated by a variable rate data source is modulated on traffic channel by traffic channel modulator if the capacity of the traffic channel is capable of transmitting the packet. And where the packet of variable rate data is modulated onto traffic channel by traffic channel modulator and at least one overflow channel by traffic channel modulator, if the capacity of the traffic channel is less than required to transmit the packet. A receiving system for receiving variable rate data transmitted in accordance with the above.

Abstract: A television system for generating video signals for reception by a receiver having adaptive processing circuitry susceptible of errors includes circuitry for emulating portions of the receiver and detecting the occurrences of such errors. A signal representing the occurrences of the errors is generated and combined with the transmitted video signal. At the receiver the error signal is separated from the video signal and utilized by the adaptive processing circuitry to ameliorate the effects of such errors.

Abstract: A transmitted signal includes a pilot signal, a plurality of information signals and a carrier signal modulated by a modulating signal related in frequency to the pilot signal frequency. At a receiving station, the carrier signal is demodulated and the demodulated signal is used to generate a reference signal to translate the frequencies of the recovered pilot signal and the plurality of information signals by an amount sufficient to correct for undesirable frequency shifts which have occurred in the transmitted signal.

Abstract: A digital television transmitter has a buffer that receives a low resolution low pass filtered signal. A high resolution high pass filtered signal is applied to the buffer only when the buffer can accept it without overflowing. A digital television receiver receives a digital television picture signal and preferably a transmitter buffer occupancy state signal. A low resolution low pass filtered signal is applied to an adder. A high resolution high pass filtered signal is applied to the adder when the buffer state is low and also when it is intermediate and no substantial motion is present. The transmitter and receiver are useful in video teleconferencing.

Abstract: A transmitter and receiver for direct sequence spread-spectrum (SS) communications is described. The audio or other analog information to be communicated controls the clock rate of a pseudorandom sequence (PRS) to produce clock rate encoded direct sequence spread spectrum signals. The signals are decoded by a feedback loop including a voltage controlled oscillator which clocks a local PRS generator. A phase detector responds to the clock rate encoded received PRS signal and to the local PRS signal to produce a control signal. The control signal is filtered and applied to the VCO to control the local PRS clock rate. The decoder loop forces the VCO rate to track the clock rate of the encoded signal, and the decoder loop VCO control signal reproduces the analog information. A demodulator for a clock rate encoded SS signal upconverted by a carrier includes a pair of mixers, a first of which receives the signal to be demodulated and the local PRS sequence from the decoder.

Abstract: An arrangement for generating an electrical audio signal in response to a sound signal applied to a microphone in a reverberating room removes the reverberations with an adaptive filter. The filter learns or adapts so as to cancel the room echoes by receiving both the audio signal affected by reverberation and a clean audio signal from a highly directional local-acting microphone placed near the source of the sound. The signal to be filtered is applied to a transversal filter including a tapped delay line having variable taps or multipliers to produce incrementally delayed multiplied samples. The multiplied samples are summed, and the sum signal is subtracted from the clean signal to produce a difference signal. A .mu.P is programmed to iteratively calculate the effects of changes to the tap values and to select tap values which tend to reduce the magnitude of the difference signal. When the filter is converged, the difference signal is near zero.

Abstract: A high frequency code division multiple access spread spectrum (CDMA SS) communications system includes multiple transmitters and their associated receivers, and a pilot carrier source. In order to reduce errors in the receiver IF frequency due to unavoidable differences between the desired transmitted carrier and receiver local oscillator (LO), the transmitted carrier ferquency is related to the pilot frequency. The receiver phase-locks the pilot carrier to the local oscillator, thereby providing an IF data signal with reduced frequency error. The IF data signal is multiplied by sine and cosine demodulating signals related to the local oscillator frequency to produce inphase (I) and quadrature (Q) components of the received data signal. The I and Q signals are applied to code matched filters, which produce filtered or decoded signals the amplitudes of which are related to the phase error between the demodulating signals and the IF carrier.

Abstract: A communication system comprising a satellite, a master earth station (MES), and a plurality of small earth stations (SESs) provides signal transmissions addressed and transmittable to a selectable other SES via the satellite, the MES, and then the satellite again. The signal transmissions consist of bit representing pseudo random sequence (PRS) signals PRS.sub.SES which in turn consist of chips arranged in predetermined and identifiable patterns and with the bit and chip occurrence rates C.sub.SES and B.sub.SES of each SES being synchronized with each other as they arrive at the MES. The satellite responds to the signal transmissions from the SESs to retransmit the signal transmissions to the MES, which in turn responds to the signal transmissions from the satellite to amplify and retransmit such signal transmissions back to the satellite again. The satellite again responds to the signal transmissions from the MES to retransmit them to the SESs.

Abstract: A system for determining the bit error rate in a communication system comprising logic for generating a stream of data bits, bit extracting logic for periodically extracting N consecutive bits after the occurrence of every Mth bit, where the N consecutive bits are divided into a group of A bits and a group of C bits, where A and C are equal integers, and a single B bit is positioned between the group of A and C bits, where M>>A, where the N bits can be any combination of binary 1's and 0's. Logic extracts and stores a finely quantized sample of the B bit of each group of N bits. An adder adds an auxiliary group of X bits to the N bits to form a memory address consisting of A, B, C, and X bits. A plurality of memories each has storage locations for a single finely quantized B bit sample. Each memory further is selectable by a unique combination of the binary bits A+B+C with any given storage location in each memory being accessible by various combinations of the X bits.

Abstract: A system is described in which the audio subcarrier components are attenuated relative to the other components of composite television signals by an inexpensive IF filter. This filter incidentally produces quadrature distortion between the two color difference signal components of the composite television signals. The disclosed invention includes a differentiator, responsive to at least one of the color difference signals, that derives signals proportional to the quadrature distortion components present in the other color difference signal. These distortion components are then subtracted from the other color difference signal to produce a signal that is substantially free of quadrature distortion. The differentiator and subtracter are advantageously realized in the form of a simple FIR filter.

Abstract: Output weighted FIR filters usually consist of a tapped delay line, weighting circuits coupled to the taps for weighting delayed samples and adder circuitry for combining the weighted samples. In designing such circuitry, tradeoffs are made between device complexity and the desired filter transfer function. FIR filters employing shift-and-add weighting circuits may have the resolution of their weighting circuits significantly enhanced with slight added circuit complexity by providing a parallel tapped delay line to which scaled input samples are applied. The scaled and non-scaled signal samples from the parallel tapped delay lines are both made available to the weighting circuits. The availability of both such samples for shifting and adding, nominally increases the number of possible weighting coefficients realizable from the weighting circuits more than two fold and thus, improves the design flexibility of the filter significantly.

Abstract: Apparatus is disclosed for demodulating sampled data chrominance signals that include a first component that modulates a carrier to produce asymmetrical sidebands, and a second component modulated in quadrature to produce double sidebands. Samples representing the second component are derived and subtracted from the chrominance samples. The samples produced represent the asymmetrical sideband component. These samples are passed through a Nyquist filter to produce samples representing the first component signal but having the frequency spectrum of a vestigial sideband modulated signal. Demodulation of these samples by conventional means produces samples of the first component signal having a uniform range of amplitude values over the frequency band of the first signal.