Abstract: Methods and apparatus for scheduling mobile stations (MSs) to download data and/or to control the rate of downloading to an MS from a base station (BS) as a function of downlink channel condition information are described. Artificial channel variations, which can be measured at the MS, and feedback to a BS for scheduling purposes, are introduced through the use of two or more transmitter antennas at a BS. Each of the antennas transmits a signal at the same frequency having the same information content, e.g., modulated data. However the signals are made to differ with time in their phase and/or amplitude to introduce what appear to be channel variations to the MSs.

Abstract: A digital communications transmitter (100) includes a digital linear-and-nonlinear predistortion section (200) to compensate for linear and nonlinear distortion introduced by transmitter-analog components (120). A direct-digital-downconversion section (300) generates a complex digital return-data stream (254) from the analog components (120) without introducing quadrature imbalance. A relatively low resolution exhibited by the return-data stream (254) is effectively increased through arithmetic processing. Linear distortion is first compensated using adaptive techniques with an equalizer (246) positioned in the forward-data stream (112). Nonlinear distortion is then compensated using adaptive techniques with a plurality of equalizers (226) that filter a plurality of orthogonal, higher-ordered-basis functions (214) generated from the forward-data stream (112). The filtered-basis functions are combined together and subtracted from the forward-data stream (112).

Abstract: A mobile transceiver and a method of detecting movement of the mobile transceiver in a radio system. The radio system includes at least one base station and terminals. The movement of the mobile transceiver is measured by at least one acceleration sensor (114–116) to take the movement of the mobile transceiver onto account in the operation of the radio system.

Abstract: An improved multicarrier modulation system and method, which has the advantages of both isotropic orthogonal transfer algorithm orthogonal frequency division multiplexing (IOTA OFDM) and scalable advanced modulation (SAM), is introduced. The invention is root raised cosine (RRC) OFDM using the most spectrally efficient RRC filter without sacrificing the compact subchannel spacing of OFDM. The invention further provides an adjacent channel interference (ACI) suppression scheme and a modified RRC for better suppressing ACI of RRC OFDM. The ACI suppression scheme can also be applied to SAM with the modified RRC and to IOTA OFDM with a modified IOTA. The invention greatly improves a major problem of conventional OFDM namely ACI due to the use of a wide subchannel filter. Thus, the invention allows OFDM to meet even the strictest ACI requirements, which was not possible by using a conventional raised cosine windowing method.

Abstract: A remote control is operative to transmit a remote control signal composed of a first portion and a second portion. The first and second portions are typically a pulse and a space. The pulse has a pulse width of a given duration within a pulse width range, while the space has a space width of a given duration within a space width range. An interrupt signal provided to indicate the end of transmission of the remote control signal is disabled when a space portion requires a space width greater than the space width range. The interrupt signal signaling the end of the remote control transmission is then disabled for a predetermined period of time essentially equivalent to a length of time that the additional space exceeds the space width. During the predetermined period of time, the remote control thus transmits a space. The interrupt signal is then re-enabled after expiration of the predetermined period of time in order to allow for another remote control transmission.

Abstract: A sinusoidal RF carrier is modulated for the transmission of digital binary data streams through the amplitude suppression of carrier wavelets. These wavelets are defined between zero crossover positions representing zero energy locations. This modulation is accomplished when the carrier is slightly amplitude modulated with a modulation signal that is equal in frequency to the carrier itself and the modulation always begins or ends upon the exact zero voltage crossing point of the RF cycle phase. The modulation is applied as a slight shift of the amplitude of any single cycle, each cycle representing a single bit of data. A single cycle of RF will either represent a “1” or “0” depending upon the amplitude of the cycle, relative to other adjacent cycles in the same carrier.

Abstract: The invention relates to a system for electromagnetic processing of an input wave involving receiving a modified signal derived from two or more signals that represent the input wave when combined; and alternately regulating the modified signal using a digital signal containing at least one characteristic of said two or more signals. The invention may utilize in-phase and quadrature phase signals, where the magnitude portion of the signals may be used for regulating the modified signal. The modified signal may be created by modulating a characteristic of the I, Q signals, such as their sign, with an RF or other frequency carrier wave.

Abstract: A radio, and related methods of radio communication, consisting of a multi-modulation modem, wherein the multi-modulation modem that modulates and demodulates signals using a plurality of modulations. The radio also comprises a frequency converter coupled to the multi-modulation modem for converting the signals to a radio frequency and a transceiver unit including an antenna coupled to the frequency converter for transmitting the signals over a radio communications link. The multi-modulation modem includes a modulator that includes a modulation selector unit that selects respective ones of the plurality of modulations to modulate the signals. The multi-modulation modem also includes a demodulator for demodulating the signals having been modulated using the plurality of modulations.

Abstract: A FSK demodulation system of the present invention has a means for comparing two preset values across 0, a positive side level shift amount and a negative side level shift amount, with an inputted amplitude level; and a demodulation means for performing demodulation based on the comparison result.

Abstract: Sample acquisition apparatus for sampling first and second signals within a signal processing arrangement, said apparatus comprising a sampler for capturing sections of the waveforms of both the first and second signals, a switch for alternating correction of the sampler to a point in the arrangement where said first signal can be sampled and a point in said arrangement where said second signal can be sampled and a timer for timing the operation of the switch to cause the sampler to capture a first waveform section of said first signal and a second waveform section of said second signal, wherein said second signal is responsive to said first signal and the timing of said switch is such that said second section comprises a portion that has been generated in response to said first section.

Abstract: A adaptive deciding method and apparatus for frequency shift key signals are provided to sample the demodulated FSK signal, input the values of the sample points in sequence to a sample group, and compare at least a pair of the sample points, thereby finding out the central point of the FSK signal to improve decoding due to signal attenuation.

Abstract: A system and method of amplitude modulation is described in which first and second 180 degrees out-of-phase signals are produced and are each amplified by one of two (different amplification factor) non-linear amplifiers. One of the signals is amplified using constant amplification by a first non-linear amplifier to generate a relatively small amplified signal. The other of the signals is modulated using variable amplification by a second non-linear amplifier to generate a relatively larger amplitude modulated signal. The two resulting 180 degree out-of-phase signals are combined, such that the smaller signal effectively cancels out lower level distortion exhibited by the larger amplitude modulated signal. Alternatively, a symmetrical structure can be used for generating AM signals which include phase reversals of the carrier.

Abstract: Systems and methods are disclosed for applying layered modulation to an 8-VSB signal as used in the Advanced Television Systems Committee (ATSC) digital television signal. A system for transmitting the layered signal includes a first antenna for transmitting an upper layer signal comprising an 8-VSB signal and a second antenna for transmitting a lower layer signal. A layered modulation signal comprises the upper layer signal and the lower layer signal both interfering in a common frequency band. At least one receiver demodulates the upper layer signal directly from the layered modulation signal and demodulates the lower layer signal after subtracting the upper layer signal from the layered modulation signal. The second antenna can have a selectively limited range so that the lower layer signal does not interfere with the upper layer signal in a range where the lower layer signal could not be demodulated.

Abstract: The invention provides a &pgr;/4 shift QPSK modulator, as well as a communication device, which is capable of reducing the storage capacity of ROM for previously storing impulse response data, and which allows the power consumption to be lowered and the circuit scale to be downsized. In an impulse response storage section within an impulse response computing circuit, storage capacity for impulse response data is halved by using, in common, impulse response data of a one-side waveform of an impulse response waveform bilaterally symmetrical with respect to a peak value. Also, a read address signal is switched over by an address inversion section of a simple constitution so that blocks of two kinds of magnitudes, “1” and “1/{square root over (2)}”, of the impulse response storage section are not accessed simultaneously.

Abstract: Based on changing reception conditions, a wireless receiver adapts its demodulation method during active communications. Phase errors detected in the received signal indicate current reception conditions, and, optionally, received signal strength serves as an additional indicator. The receiver supports operation with fully coherent, fully non-coherent, and partially coherent demodulation. The receiver determines a demodulation quality indicator based on the phase error signal. The value of the demodulation quality indicator increases with increasing phase error. When the demodulation quality indicator is below a first defined threshold, the receiver operates with fully coherent demodulation. When the demodulation quality indicator is above a second defined threshold, the receiver operates with fully non-coherent demodulation. For demodulation quality indicator values between the first and second defined thresholds, the receiver operates with partially coherent demodulation.

Abstract: An equalizer providing a filtered signal to a data decision unit calculates an amplitude error signal by comparing the filtered signal with the data signal output from the data decision unit, and calculates a squared envelope error signal from the filtered signal. These two error signals are separately weighted according to the absolute value of the amplitude error, the weight of the amplitude error signal decreasing and the weight of the squared envelope error signal increasing as the absolute value of the amplitude error increases. The weighted amplitude error signal and weighted squared envelope error signal are added to obtain an error signal used in updating filter coefficients in the equalizer. Rapid convergence of the filter coefficients is obtained, with small residual error.

Abstract: The modulator has an input (30) which receives data to be modulated. A plurality of memory regions acting as look-up tables (38-44) are arranged to contain information relating to the modulation method to be carried out by the modulator. At least one of the memory regions provides time independent modulation values and at least one of the memory regions provides time dependent modulation values. Values provided by the memory region is dependent on the data received via the input. Processing means provide a modulating signal based on the values provided by the memory regions.

Abstract: A method and apparatus for telemetering data on a channel having a maximum data rate by utilizing a power efficient communication protocol is provided. The data to be telemetered comprises a number of source symbols where each source symbol is characterized by a probability of occurrence. A sequence of signals forming codewords having an energy and a length is produced. The length for the codewords is based at least on the number of symbols to be coded. Each codeword signifies a specified source symbol on the basis of a mapping between source symbols and codewords. The mapping is such that each source symbol of lower probability of occurrence is associated with a codeword of at least equal energy.

Abstract: A digital communication system and method is provided for increasing bit-rates while maintaining the reliability of transmitted digital information and avoiding increased power demands. The communication system includes a transmitter that modulates one or more bits onto a carrier signal to generate and transmit a first transmission signal during the first part of a pulse time TB, receives an additional bit, and based on the value of the additional bit, either transmits the first transmission signal again during the second part of the pulse time TB or transmits a second transmission signal during the second part of the pulse time TB.

Abstract: A receiver architecture includes a selectivity filter (206) for selectively passing a wanted channel and rejecting unwanted channels. The selectivity filter has a filter BT of about one-half the BT of the transmitter filter. A discriminator (208) is coupled to the selectivity filter for converting received symbols from the frequency domain to the time domain symbols. A symbol recovery processor (210) is coupled to the discriminator for recovering the symbols through a two-state maximum likelihood sequence estimation (MLSE) technique in which templates are optimized with a BT substantially less than the BT of the transmitter filter.

Abstract: A communication satellite system (100) is established using one or more satellite constellations (110, 120). The two or more satellite groups (110, 120) are connected via long range crosslinks (145) which provide a communication path between the long range satellites (150, 170) in the two satellite groups (110, 120). Each satellite group (110, 120) comprises long range satellites (150, 170) and short range satellites (160, 180) which are interconnected using short range crosslinks (155, 175). A single antenna on each satellite provides both crosslinks. The long range crosslink (145) is established using the antenna's main beam and the short range crosslinks (155, 175) are established using the antenna's sidelobes.

Abstract: Spectral efficient transmitters-receivers (transceivers), modulation-demodulation (Modem) methods, architectures, structures and implementation technologies for enhanced performance and increased capacity CDMA, TDMA, GSM,OFDM, CMA, FDM and other wireless and wired communications, broadcasting and telemetry systems and integrated Modems/Transceivers suitable for operation over Non-Linearly Amplified (NLA) power efficient RF systems are described. Cross-correlated cascaded Time Constrained Signal (TCS) response processors and Long Response (LR) filtered Bit Rate Agile (BRA) in phase (I) and quadrature phase (Q) baseband signals are disclosed. These spectral efficient high performance processing, transmitting and receiving methods are designated as Feher's Quadrature Phase Shift Keying (FQPSK) Transceivers.

Abstract: In a communication system using the time diversity transmission scheme, the communication system provided with the stable automatic frequency control circuit with the wide frequency pull-in range and under low CN ratio transmission is achieved by removing the modulation phase from the received data through the application of the data correlation of the time diversity.

Abstract: A broadcasting method for simultaneously broadcasting analog and digital signals in a standard AM broadcasting channel is provided by: broadcasting an amplitude modulated radio frequency signal having a first frequency spectrum, wherein the amplitude modulated radio frequency signal includes a first carrier at a frequency of f0 modulated by an analog program signal representative of program material; and simultaneously broadcasting a plurality of digitally modulated orthogonal frequency division multiplexed carrier signals within a frequency range of about f0±15 kHz, which encompasses the first frequency spectrum, each of the digitally modulated carrier signals being modulated by a portion of a digital program signal, wherein the digital signal includes a digital representation of the program material, additional data, or a combination of the program material and the additional data.

Abstract: A stream of complex numbers is converted into polar form, including an amplitude-representative part and a phase-representative part. The amplitude-representative part of each of the converted complex numbers is represented as a plurality of digits of decreasing numerical significance. The phase-representative part of each of the converted complex numbers is phase-modulated at the radio carrier frequency to produce a phase-modulated drive signal. The phase-modulated drive signal is amplified in a plurality of power amplifiers. A respective one of the power amplifiers provides a maximum output power level at a respective amplifier output that is related to a respective one of the decreasing numerical significance. The output amplitude of a respective one of the plurality of power amplifiers is controlled by applying a respective one of the plurality of digits of decreasing numerical significance to a respective one of the plurality of power amplifiers.

Abstract: A method for detecting and quantifying impairments of a received communication signal of a QAM data communication system represented by a plurality of ideal values. The method includes storing a statistically significant number of a plurality of received points of the signal for each ideal value corresponding to a plurality of groups of said plurality of ideal values. The received points are defined by an in-phase and a quadrature components in a coordinate system in which a first axis is the in-phase axis and a second axis is a quadrature axis. The components have corresponding ideal components from their respective ideal value. Each group corresponds to respective impairments and is specific to the same. The method also comprises analyzing the components of the points of respective group in relation with their respective ideal components to quantify the impairments of said signal and provide calculated values of the same.

Abstract: Communication architectures and methods that implement random phase shift keying. A transmitter and a receiver are coupled by way of a communications channel. The transmitter uses a data source and a mapper that produces an amplitude phase keyed (APK) waveform having a plurality of symbol phases. A transmitter multiplier multiplies random phase signals with the APK waveform to produce a random phase keyed output signal. A vector modulator modulates the random phase keyed output signal. A transmitter mixer mixes the random phase keyed output signal with a local oscillator signal from a transmit local oscillator to produce a modulated carrier signal that is transmitted over the communication channel. The receiver has a demodulator including a receiver mixer that receives and mixes the received modulated carrier signal with a local oscillator signal derived from a receive local oscillator to produce an estimate of the random phase keyed signal. The estimated random phase keyed signal is synchronously sampled.

Abstract: A method 1100 and apparatus 1200 utilizing unbalanced modulation for providing users in a communication system with different amounts of effective communication energy according to their individual communication environments. A user's communication energy needs are determined based on conditions such as weather, signal-to-noise ratio, and cell location. Signals destined for a user are modulated according to the determined needs of the user. A signal destined for a user operating in a relatively friendly communication environment is modulated with less effective energy than a signal destined for a user operating in a relatively hostile communication environment.

Abstract: A digital signal processing circuit for field programmable radio frequency communications system including a digital controlled numerical controlled oscillator (NCO), dual digital signal conditioning circuits, and dual mixer circuits. The various circuits are responsive to digital commands for configuring the digital signal processing circuit to function with a variety of signaling schemes or waveforms. When configuring for angle modulation, a single conditioning and mixer is used and the modulating digital input signal is up converted to the center frequency of the NCO by the conditioning circuit and applied to an offset input of the NCO.

Abstract: A communication system (100) provides selecting a first modulation-coding scheme (111) based on a quality indicator of a communication between a source user and a first destination user, determining a first possible number of data bits (201) that can be modulated and encoded according to selected modulation-coding scheme (111) and spread according to one spreading code of a plurality of spreading codes (108-1 through 108-k) which results in fitting in a predetermined time frame, determining a first number of data bits (102) to be transmitted from the source user to the first destination user, determining a first load level based on comparing first number of data bits (102) and first possible number of data bits (201), and, if the first load level is unequal to a whole number, rounding to a next first whole number, selecting a first number of plurality of spreading codes (108-1 through 108-k) based on the first whole number of load level for spread coding of first number of data bits (102) after being modulate

Abstract: An analogue to digital or digital to analogue data converter 1 for converting between a first digital signal 101,102 at a first sampling rate fo and a first analogue signal 171,172, comprises a first conversion stage 11,12,21,22,31,32 for converting an input signal 101,102 into an intermediate digital signal 131,132 at a second sampling rate fsm which is greater than the first over-sampling rate fo; a processing stage 30,41,42,43,44,51,52 for performing digital signal processing on the intermediate digital signal to generate a processed intermediate digital signal 151,152; and a second conversion stage 61,62,71,72 for converting the processed intermediate digital signal into an output signal 171,172, wherein the input and output signals comprise the first analogue signal and the first digital signal or vice versa depending on whether the data converter is performing analogue to digital or digital to analogue conversion.

Abstract: A method and apparatus are provided for modulating an intermediate frequency of a radio frequency transmitter with a digital sample stream. The method includes the steps of interpolating the digital sample stream by an over sampling factor and modulating the interpolated digital sample stream to a single bit sample stream, while spreading and shaping quantization noise created by the modulation outside a bandwidth of the intermediate frequency. The method further includes the steps of converting the single bit sample stream to an analog signal and bandpass filtering the analog signal around the intermediate frequency.

Abstract: A system and method for the transmission of additional special marker symbols in a circular signal space constellation allows the communication of additional control information without requiring any additional power to transmit the additional symbol. Additional symbols can include "Start of Message", "End of File", "End of Transmission", "Increase Data Rate", "Decrease Data Rate", "Save State" or "Clear", or any additional command signal desired to be transmitted.

Abstract: In a digital modulator with compensation, a digital bit stream from a microphone (705), a speech coder (706), and a channel encoder (707) is sent to an encoder (720) which translates the bits into I/Q digital pulses with phase shift keying. A symbol correlater (730) notes when predetermined target phase symbol sequences, which contribute to a high peak-to-average power ratio, enter the encoder. If a target symbol sequence is encountered, the correlater directs compensation amplifiers or compensation filters (734, 737) of the I/Q signals. Next, I/Q pulse shaping filters (764, 765) filter the I/Q pulses according to communication system specifications. The filtered I/Q signals are then sent to a quadrature modulator (790) for RF modulation. Compensation of target symbol sequences reduces the negative impact they have on peak-to-average power ratio and increases the efficiency of the power amplifier (795) which extends the battery life of a communication device (700).

Abstract: An automatic meter reading system utilizes repeater technology to access hard to read meters within a fixed network structure. The components of the radio system that are needed for two-way communications are employed without adding significant cost to the meter. Using this approach, each meter in the network has the ability to repeat messages as required.

Abstract: A digital sound broadcasting receiver and method receives a radio wave from a digital sound broadcasting station, demodulates the radio wave into baseband signals at a tuner, subjects the signals to demodulation, performs error detection and error correction at signal processors to obtain digital data, and inputs the digital data into an audio circuit to obtain audio or data output. A CRC error rate detector 13 for a fast information channel (FIC) for APC pseudo lock releasing action on demodulating the signals is arranged to determine, based on the possibility of an error rate of an error-detecting code (CRC) of the FIC, whether an APC pseudo lock state occurs, and to control releasing action for the APC pseudo lock state.

Abstract: The invention relates to a wireless local area network system having data terminals and transceivers which communicate with the data terminals and transmit and receive data, for forming a wireless link between at least two data terminals, the system transmitting data as outputs in a certain frequency range. The output has a signal (B) which is visible as a narrow-band signal in the frequency range of the output. The signal (B) can be detected from farther away than a conventional output by arranging circuits (7, 8, 9) in the local area network system for filtering and detecting the narrow-band signal of a certain frequency from the received signal.

Abstract: A system and method is provided for using underused or unused local telephone company local loops to subscriber premises for providing to such premises a connection to an alternate service provider having a common channel signaling controlled switched network. The use of the local loop is leased to the service provider at a rate dependent upon the usage of the circuit. Information and data to permit efficient and convenient billing for leased usage of the loops is implemented by linking the common channel signaling control network of the telephone network and the common channel signaling control network of the service provider network. Common channel signaling control signals indicating call set-up and call tear-down are transmitted by the service provider's common channel signaling network to and stored in the telephone common channel signaling network in the storage of the controller therein to permit billing therefrom.

Abstract: A frequency-domain CAP receiver is provided that reduces the number of operations required to demodulate a CAP signal. The frequency-domain CAP receiver provides computational advantages over an equivalent time-domain version as the filter length required in the receiver increases.

Abstract: A data transmission system in which an on/off keyed (OOK) AM/DPSK modulated data signal with an on/off ratio exceeding about 80 dB which has been modulated on a carrier is received at a compact, easily fabricated and battery powered data receiver which operates without automatic gain control and which includes a double loop antenna (diameter of about two inches) with a trimmer capacitor center tapped to the antenna for providing a conjugate impedance match between the antenna and a low noise amplifier. In the receiver, a square-law detection AM demodulator for demodulating the amplified signal is in a bipolar silicon IC, and a DPSK data detector for decoding the demodulated signal is in a separate digital CMOS IC.

Abstract: A transmission system is disclosed which permits the receiving end to demodulate multi-valued modulated symbols successfully under fading conditions and reduces the amount of transmitted reference data to improve data transmission efficiency. At the transmitting end, a multiplexing section, a modulating section, and a transmitting section are provided. In transmitting an OFDM transmission frame, null symbols and reference symbols are placed in the beginning portion of the frame and QPSK symbols are placed in an information symbol data region in the frame with equal spacings in time and frequency. At the receiving end, a receiving section, a demodulation section, an equalizing section, and a demultiplexing section are provided. An error detector detects amplitude and phase errors of each carrier from the reference symbols, and a variation detector detects variations in the amplitude and phase of a received signal from the QPSK symbols.

Abstract: A communication system having a carrier oscillator for generating a carrier of predetermined frequency, a quadrature modulator for orthogonally modulating the carrier by input baseband I and Q signals and outputting a quadrature modulation wave, and a quadrature demodulator for orthogonally demodulating the quadrature modulation wave using the carrier and outputting demodulation baseband I and Q signals. The phase of the carrier input to the quadrature demodulator is shifted by a predetermined amount in accordance with a phase shift signal. The amplitude of the demodulation baseband I and Q signals output from the quadrature demodulator is corrected on the basis of a control signal, and demodulation baseband I and Q signals thus corrected are output. The amplitude of the input baseband I and Q signals is corrected on the basis of the control signal, and the baseband I and Q signals thus corrected are input to the quadrature modulator.

Abstract: A system for combining AM and FM transmissions. In-band, On-channel, FM Digital Audio Broadcast (IBOC FM-DAB) allows simultaneous transmission of DAB and FM over existing FM allocations without interfering with conventional analog FM signals. The utility of existing FM spectrum allocations is therefore enhanced.

Abstract: A radio-frequency broadcasting system and method for simultaneously broadcasting analog and digital signals in a standard AM broadcasting channel wherein the system includes: a transmitter for providing, and broadcasting, a composite signal containing an adaptively-modulated phase-shift-keyed digital signal with analog programming material modulated thereon; and a receiver for detecting the composite signal, extracting the analog audio signal and digital audio, or data, therefrom, and playing back the received audio programming. The adaptively-modulated phase-shift-keyed digital signal is responsive to the transmitted signal, dynamically increasing the digital data transmission rate as the transmitted signal power increases. Symbol states are generally arranged around concentric arcs, and adjacent symbol states are generally equidistant.

Abstract: A method and apparatus for encoding and convolutionally decoding a data word of a data word sequence. Each data word has k bits. An encoder selects, using a trellis encoding algorithm and a previous data word, a 2.sup.k subset of signal points from a square set of M by M signal points having X coordinates and Y coordinates. The square set of M by M signal points includes a constellation of 2.sup.k+1 signal points. The encoder selects, using the n.sup.th data word, a signal point from the selected subset of signal points. A modulator generates a first channel symbol and a second channel symbol from the selected signal point. A demodulator demodulates the first channel symbol as a received X coordinate and the second channel symbol as a received Y coordinate. A decoder estimates, using a second processor, a 2.sup.k received subset of signal points using the convolutionally decoding algorithm and a previously received data word. The decoder estimates, an n.sup.

Abstract: A radio communication apparatus comprises a first/second modulator for modulating a first/second signal according to a first/second frequency, a first demodulator for detecting the received first modulation signal and regenerating the carrier, a clock regenerator for regenerating a clock from the detection output from the first demodulator, an amplitude sampler for sampling the amplitude of the received first modulation signal according to the regenerated clock, a second demodulator for controlling the frequency of the received second modulation signal and executing demodulation for the signal, and a gain controller for executing gain control for the output from the second demodulator according to the output from the amplitude sampler.

Abstract: A multiple-modulation communication system includes a transmitter that modulates and transmits communication signals modulated by a first modulation technique and communication signals modulated by a second modulation technique. The first modulation technique and the second modulation technique are different. The communication system also includes a receiver capable of receiving the communication signals modulated by the first modulation technique and the communication signals modulated by the second modulation technique and demodulating the communication signals.

Abstract: Data are transmitted using multiple carriers modulated by quadrature amplitude modulation. In general, the carriers carry different numbers of bits, to exploit the fact that the properties of a transmission path are more favorable to carriers at some frequencies than to those at others. The bit allocation process is made closer to optimum by permitting allocation of a non-integer number of bits to a carrier. Input bits are grouped for several carriers and this binary representation is converted to a number representation in which the base of each digit corresponds to the number of points in the QAM constellation for a respective carrier (or to this number divided by a power of two).

Abstract: A digital receiver includes a tuner and a demodulator that obtains the baseband signal carried in a received analog signal. A first sampler operates at a preselected fixed sampling rate asynchronous with the baseband component to produce a first sampler output. A controllable digital filter resamples the first sampler output to produce a filter output with a selectable resampling rate. The resampled output is time-position locked to the baseband signal epochs. The second sampling is processed to ascertain the symbol bit stream of the baseband signal. The controllable filter sampling rate is automatically varied to correspond to the symbol rate of the baseband signal, so that the sampling rate of the first sampler need not change. Initial signal acquisition is achieved by operating the receiver as a frequency spectrum analyzer. A single signal-carrying band is identified and demodulated, and a menu carried on a transport layer is read.

Abstract: A signal transmitter-receiver system comprising first and second transmitter-receiver units interconnected by a signal transmission line, a first transmitter-receiver unit including a first transmission circuit for delivering a selected one of a plurality of a.c. signals each having a distinct phase difference with respect to a reference a.c. signal to the signal transmission line at each of successive predetermined communication time interval, the second transmitter-receiver unit including a second receiving circuit for identifying the phase difference of the a.c. signal or the signal transmission line with respect to the reference a.c. signal at each communication time interval, the second transmitter-receiver unit including a second transmission circuit for changing the combination of positive and negative amplitudes of the a.c.