Abstract: A method of baseband/passband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate. The method comprises the following steps: (1) generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; (2) selecting a passband or a baseband mode; and (3) generating an analog output signal in the passband or baseband mode. The step of selecting the passband or the baseband mode depends on the complexity of QAM constellation. If QAM constellation includes less than 64 QAM plant points, the passband mode is selected, and if QAM constellation includes more than 64 QAM plant points, the baseband mode is selected.

Abstract: A wireless packet communication system includes at least one radio terminal station, and a base station for multiplexing packets to be transmitted using a plurality of subcarriers and for sending the multiplexed packets to the at least one radio terminal station. The system has a unit provided in the base station for simultaneously sending reference signals on the subcarriers with the same level to the at least one radio terminal station, a report unit provided in the at least one radio terminal station for reporting to the base station received conditions of the reference signal of each subcarrier or of each subband corresponding to a frequency band occupied by a plurality of subcarriers, and a unit provided in the base station for allocating the subcarrier or the subband to each of the packets to be transmitted depending upon the reported received conditions of the subcarrier or the subband, the allocation being performed in a transmission order of the packets.

Abstract: A method for transmitting and receiving an uncompressed HDTV signal over a wireless RF link includes steps of: providing a clock signal synchronized to the uncompressed HDTV signal; and providing a stream of regenerated data from the uncompressed HDTV signal, with the clock signal synchronized to the stream of regenerated data. The clock signal is then used for demultiplexing the stream of regenerated data into an I data stream and a Q data stream. The method further includes steps of: modulating a carrier with the I data stream and the Q data stream; transmitting the carrier over the wireless RF link; demodulating the carrier so that the I data stream and the Q data stream are recovered; multiplexing the I data stream and the Q data stream into a single stream of HDTV data; and recovering the uncompressed HDTV signal from the single stream of HDTV data.

Abstract: A single, common correlation filter (CF) core is provided in a wireless system using CDMA. A plurality of channels with different data rates are provided in the wireless system. The channels provided in the wireless system include the access channel, the maintenance channel, and the traffic channel in which information (e.g., pilot or data symbols or both) is transmitted at the tier 1, tier 2 and tier 3 rates. The data rate for transmitting the information is programmable by digital signal processor (DSP). A user-unique code, such as a PN code, is applied to the information being transmitted in the channels of the wireless system. The information is QPSK modulated and transmitted in any one of the channels at any data rate. The transmitted information is correlated at the smallest data rate (i.e., the tier 1 rate) in the correlation filter (CF) of the wireless system by time multiplexing delayed versions of the PN code to the correlation filter core.

Abstract: Data pieces representative of in-phase components and quadrature components of a digital-modulation-resultant signal are assigned to frequencies for inverse fast Fourier transform. The inverse fast Fourier transform is executed at a predetermined sampling frequency Fs to convert the data pieces into a real-part signal and an imaginary-part signal. Phases of the real-part signal and the imaginary-part signal are shifted. Each of the phase-shifted real-part signal and the phase-shifted imaginary-part signal is divided into a sequence of even-numbered samples and a sequence of odd-numbered samples. A digital quadrature-modulation-resultant signal is generated from further manipulation of the even-numbered and odd-numbered samples.

Abstract: A method and offset removing apparatus for removing DC offset from a digital baseband signal value pair included in a set of digital baseband signal value pairs is described. The digital baseband signal value pairs, when plotted on a complex signal space I-Q diagram, lie on a predetermined figure. The I and Q coordinates of the central point of this predetermined figure are determined by a two-dimensional fitting of this figure through a subset of signal value pairs included within the set. These coordinates of this center point are subsequently subtracted from the I and Q coordinates of the digital baseband signal.

Abstract: The pulse-shaping look-up table with transient suppression (530) avoids hard turn-on and turn-off transients by modifying word segments of initial and final digital words during transmission of a digital data sequence. A controller (570) sends a mode signal and a digital data sequence to the pulse-shaping look-up table with transient suppression (530). A mode buffer and command block (560) uses the mode signal to control the creation of initial and final digital words created by a data buffer and control block (550) from the digital data sequence. The digital words are used by a look-up table (540) to create a sampled digital output waveform sequence. The pulse-shaping look-up table with transient suppression (530) provides an accurate output waveform sequence with reduced spectral emissions even during start-up and shut-down of digital data transmissions.

Abstract: The base band signal processing circuit of the present invention intends to improve both the noise characteristic and the distortion characteristic, and moreover set both the characteristics in a desirable balance. The base band signal processing circuit is configured as follows: the first active low-pass filter and the second active low-pass filter are each formed in the balanced type, the first D/A converter differentially outputs the first base band signals and differentially inputs them to the first active low-pass filter, the second D/A converter differentially outputs the second base band signals and differentially inputs them to the second active low-pass filter, the first active low-pass filter differentially outputs the first base band signals, and the second active low-pass filter differentially outputs the second base band signals.

Abstract: The present invention is an apparatus and method for performing a &pgr;/4-DQPSK baseband modulation based on a signal mapping to be simplified. The apparatus mainly comprises a memory unit and as processing unit. The memory unit stores a plurality of parameters and their corresponding tabular data of a low pass filter, and the parameters and their corresponding tabular data are simplified in advance. The low pass filter is used for reducing the bandwidth of the apparatus and increasing the utilization of the bandwidth. The processing, unit bases on the input digital data and the tabular data in the memory unit to generate a digital in-phase signal In and a digital quadrature-phase signal Qn.

Abstract: A modulated signal (10) is sinusoidal wave signal wherein each half wave cycle carries a digital data value associated with an amount of its amplitude. A positive half wave cycle with an amplitude of M encodes a binary level zero digital data value while a positive half wave cycle with an amplitude of M+x encodes a binary level one digital data value. Similarly, a negative half wave cycle with an amplitude of −M encodes a binary level zero digital data value while a negative half wave cycle with an amplitude of −M−x encodes a binary level one digital data value. The positive and negative half wave cycles may transport dual portions of a channel at the same frequency as a modulated signal (20) for either a dual transmission capability or as a full duplex bidirectional transmit/receive channel.

Abstract: A QPSK modulation scheme uses a data spreading mechanism to rob a relatively limited portion of available transmitter power, and inject into the QPSK waveform a prescribed amount of carrier signal power, through which detection and non-regenerative extraction of the carrier at the receiver may be achieved without incurring a signal-to-noise degradation penalty. In addition, the injected carrier-based modulation scheme of the invention may employ high performance forward error correction coding, to significantly reduce the signal power required for achieving a very low energy per bit-to-noise density ratio (Eb/N0)—on the order of one to zero dB.

Abstract: In all wireless systems, the first operation that must take place at the receiver is the acquisition of the carrier and timing. OFDM systems are particularly sensitive to carrier offsets since these can introduce inter-carrier interference and loss of signal power. An algorithm, termed modulo-sub-carrier (ModSC), which can estimate the local oscillator offset in a fast and efficient manner has been devised. The carrier offset can be brought to within one half the carrier spacing within 1 to 10 OFDM symbols. By inserting a null in the center carrier, carrier acquisition can be easily accomplished by locating this null in the FFT bins at the receiver. The offset of this null from the designed position indicates the local oscillator offset in units of number of sub-carriers. An additional carrier tracking algorithm is used to estimate the offset within one half the inter-carrier spacing. Together, the ModSC and carrier tracking algorithms completely estimate the local oscillator offset.

Abstract: A simplified method for frequency offset estimation in a TDMA cellular PCS environment using &pgr;/4-shifted DQPSK comprises the steps of multiplying a complex conjugate of a received complex-valued symbol and a succeeding symbol to produce a comparison vector having an angle equal to the phase angle between the received complex-valued symbol and the succeeding symbol, rotating the comparison vector so that the angle thereof is between 0° and 90°, and estimating the frequency offset by determining a constant deviation of the phase angle from an ideal phase angle value of 45° by calculating an average phase angle for a plurality of successive comparison vectors or correlating the rotated comparision vector against a bank of unit vectors to determine a maximum correlation.

Abstract: Disclosed is a digital communication system for mobile communication, which has: a transmitter for mixing and outputting outputs from two independent and equivalently synchronized transmitting circuits in a &pgr;/4 shift QPSK modulation system; and a receiver for receiving a mixed wave transmitted from the transmitting circuits and demodulating the received signal by using information as to its phase and amplitude.

Abstract: Methods and systems for iterative demodulation of a message are provided. A first copy of the message is received to provide a first set of symbols associated with the message. A second copy of the message is received to provide a second set of symbols. The first copy is associated with a first interleaving pattern and the second copy is associated with a second interleaving pattern different from the first interleaving pattern. The first set of symbols and the second set of symbols are iteratively demodulated using extrinsic information associated with the first set of symbols for demodulation of the second set of symbols and extrinsic information associated with the second set of symbols for demodulation of the first set of symbols to provide a set of symbol estimates for the message. Transmit methods and systems for selective interleaving to generate the copies of the message in a retransmission based communication system are also provided.

Abstract: A method and apparatus for transporting signals from a high speed serial bus along a coaxial cable without using the physical layer (PHY). The wires from the high speed serial bus are used as analog inputs to a quadrature modulator. The quadrature modulator has a single radio frequency (RF) signal output that is connected to a coaxial cable for transmission along a distance of up to 100 meters. Furthermore, the RF signal is converted by a direct conversion tuner into signal outputs. The signal outputs are coupled to a second high speed serial bus connection. The high speed serial bus may be IEEE1394, Ethernet, or USB cable.

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: The offset QPSK modulation analytic system capable of estimating the initial phase of an offset QPSK modulated signal is disclosed. For each of a plurality of candidate values for the initial phase, the correlation coefficient between a signal whose clock delay has been estimated and compensated and an ideal signal generated based on the signal is computed, and the candidate value having the maximum value of the computed correlation coefficient is estimated as the optimum initial phase.

Abstract: A modulated signal (10) is sinusoidal wave signal wherein each half wave cycle carries a digital data value associated with an amount of its amplitude. A positive half wave cycle with an amplitude of M encodes a binary level zero digital data value while a positive half wave cycle with an amplitude of M+x encodes a binary level one digital data value. Similarly, a negative half wave cycle with an amplitude of −M encodes a binary level zero digital data value while a negative half wave cycle with an amplitude of −M−x encodes a binary level one digital data value. The positive and negative half wave cycles may transport dual portions of a channel at the same frequency as a modulated signal (20) for either a dual transmission capability or as a full duplex bidirectional transmit/receive channel.

Abstract: A system and method for demodulating slots having a mixed slot formation including differential and coherently encoded slots is disclosed. The method includes pre-phase encoding data and a predetermined sequence in a slot at a transmitter such that the encoded data and the predetermined sequence have equal reference phases from a reference symbol of a previous slot having a reference phase. Another method includes pre-phase encoding the predetermined sequence with a phase determined from a reference symbol from the previous slot at the transmitter. Yet another method includes differentially phase encoding the predetermined sequence according to IS-136A standards using a reference phase of π 4 . In another method pre-phase encoding data includes phase shifting data using one of a group of different phase angles, each of the different phase angles an integer multiple of π 2 .

Abstract: A method for phase encoding DPSK and N-PSK which maintains phase continuity and which does not require any reference symbols when using N-PSK. A sequence of known DPSK phases are encoded with respect to an initial phase. The N-PSK phases are then all offset by this same initial phase. The known DPSK phases can be used at a receiver to determine a sum consisting of the initial phase and any further phase shift introduced by the channel, and this sum is used to decode the unknown N-PSK phases. The method is more generally applicable to any case where a switch between a phase encoding method which requires an absolute phase reference and a phase encoding method which does not have an absolute phase reference is to be implemented on a single carrier or channel.

Abstract: An apparatus for receiving signals includes a low noise amplifier (LNA) configured to receive a radio frequency (RF) signal. An I/Q direct down converter is coupled to the LNA. The I/Q direct down converter is configured to split the RF signal into real and imaginary components and to down convert the real and imaginary components directly to baseband signals. A local oscillator (LO) is coupled to the I/Q direct down converter and is configured to drive the I/Q direct down converter. First and second filters are coupled to the I/Q direct down converter. The first and second filters are configured to filter the down converted real and imaginary components, respectively. First and second analog-to-digital converters (ADCs) are coupled to the first and second filters, respectively. The first and second ADCs are configured to convert the real and imaginary components into digital signals.

Abstract: The invention relates to a threshold extension block phase estimator (TEBPE) which estimates phase in the presence of noise. Threshold and sector slips are controlled by an iterative calculation. This can be of crucial advantage in coded systems. Another attribute of the TEBPE is it can be configured as a hybrid feedback loop incorporating characteristics of both the BPE and the PLL. This gives a high degree of flexibility with very fast acquisition times at high signal-to-noise ratio (SNR), and improved threshold performance at low SNR.

Abstract: On a transmitter side, a known bit inserting section 101 inserts a known bit having a predetermined length at a predetermined position of transmitting data, and a tail bit inserting section 102 inserts a tail bit thereto so as to generate frame data. Then, a frame length detecting section 103 detects a length of frame data, a convolutional coding section 104 convolutional codes the frame data, and a dummy bit inserting section 105 inserts a dummy bit to the frame data so as to obtain a transmitting signal. On a receiver side, a decoding section 205 divides a receiving signal into a convolutional coded portion, including a head portion to a tail of a known bit, and a subsequent portion so as to perform decoding on a receiver side. Then, an unnecessary bit removing section 206 removes the known bit, the tail bit, and the dummy bit from the decoded data.

Abstract: A transmitter which includes a quadrature phase shift keying (QPSK) modulator, and a receiver which includes a pilot correlation filter (PCF), a data matching filter (DMF), a timing recovery mechanism, a sampler, and a QPSK demodulator are provided in a wireless communication system. The transmitter transmits a frame of data symbols and pilot symbols to a receiver in a wireless system. The pilot symbols are inserted in the frame at known time intervals. The QPSK modulator modulates the frame of data and pilot symbols. As the receiver receives the frame of data and pilot symbols from the transmitter, the PCF recovers the pilot symbols sent by the transmitter, whereas the timing recovery mechanism tracks the timing of the pilot symbols in the frame. The DMF enhances the multipath response of the frame of data and pilot symbols at the known time intervals of the pilot symbols, and outputs a plurality of enhanced peaks.

Abstract: A method for simple synchronization of a receiving device to a transmitting device for a transmission of a dispersed-energy QPSK signal. The signal is composed at the transmitting end of two mixed products, the mixed product of an I signal and a transmitted carrier and the mixed product of a Q signal and the transmitted carrier shifted through 90°. In order to synchronize the received carrier to the transmitted carrier without any problems, it is proposed that an amplitude of an SQ signal be measured at the time of the zero crossing of the rising flank of an SI signal, and that an amplitude of the SI signal be measured at the time of the zero crossing of the falling flank of the SQ signal. The measured values are a measure of a discrepancy from synchronicity between the received carrier and the transmitted carrier, and that the frequency of the received carrier be varied until the amplitude of an error signal obtained from this measurement is zero.

Abstract: A one-way and two-way multichannel radio frequency transmission system and method employing a sectorized broadcasting technique is described. The system and method reduces the effective bandwidth of the broadcast signal by multiplexing available channels of signals into a set of formatted independent digital bitstreams—where each of the bitstreams includes all or a portion of the available channels provided by the system program provider. The independent bitstreams are transmitted to transmitting towers using point-to-point transmission methods. The transmitting towers phase modulate and amplify the bitstreams to generate a set of independent modulated signals. Each transmitter tower includes an antenna for broadcasting the modulated signals to a sectorized service area each sector in the service area receiving a different one of the set of independent modulated signals. The antenna includes a set of individual antenna panels each panel for broadcasting one of the set of modulated signals.

Abstract: A communication system (10) includes a transmitter (20) having programmable signals (46, 58, 60, 80) which can be used to adjust transmitter-caused quadrature-phase signal imbalances. A receiver (18) of the system (10) is remotely located from the transmitter (20) and generates a signal quality statistic (102, 112) that is monitored in a slow-tracking feedback loop to formulate commands which indicate how to program the programmable signals (46, 58, 60, 80). This receiver (18) performs its signal quality statistic monitoring while a data stream (36) is being extracted from a received communication signal.

Abstract: A method is provided of adding an encryption element to the QAM modulation/demodulation process. This is achieved by first forming a sequence of transmit QAM constellation symbols on the basis of the information signal to be modulated/demodulated, which signal is comprised by a corresponding sequence of transmit information values. Each QAM transmit constellation symbol is based on a fixed transmit constellation in a complex plane and is characterized by a real part and an imaginary part, each part including a sign, the sign consisting of plus or minus. On the basis of a fixed algorithm, during signal modulation, one or more of the transmit constellation symbols are altered by, for example, conjugating the sign value of either the real or imaginary parts thereof to form a disguised or encrypted set of symbols.

Abstract: A method of demodulating voice or data and control information in systems that support multiple modulation schemes modulates voice or data using a first linear modulation scheme, such as 16QAM modulation scheme, and modulates control information using a second linear modulation scheme, for example, QPSK modulation scheme, that has the same symbol rate as that of the first modulation scheme. The first linear modulation scheme has a higher modulation level than the second linear modulation scheme. Information modulated using the second linear modulation scheme, which uses a reduced signal set of the first linear modulation scheme, are demodulated using the same demodulator that is used for demodulating information modulated using the first linear modulation scheme. Also, in-band signalling information within a traffic channel, such as stealing flags, are modulated using the second modulation scheme.

Abstract: The transmitter QPSK-modulates the audio data, generates a transmission channel clock having a frequency 5/4 times the data clock based on the audio data, and outputs the modulated signal resulted from QPSK-modulation at the timing of the transmission channel clock. The infrared emitter emits infrared-rays based on the modulated signal. Digital data is thus efficiently transmitted by way of infrared-rays with suppressed complexity of data processing for modulation and demodulation.

Abstract: In a radio communication system (100), enhanced communication capability is provided while maintaining standard channel modulation compatibility. At a transmitter (110, 200, 600), a first information signal is generated from data according to a predefined standard modulation scheme (212, 613). A second information signal is generated from data that provides supplemental information to the standard modulated data (213, 616). For transmission, the first and second information signals are combined into a composite signal (214, 619) that represents the first information signal when interpreted according to the predefined standard modulation scheme.

Abstract: An apparatus and process for improving the performance of a cellular communication system using direct sequence spread spectrum techniques. The apparatus and process enable dynamic modification of communication system parameters including PN code length, chipping rate and modulation technique for transmission of a data packet. Modification is based on proximity of the transmitter and receiver, transmitter and receiver capabilities and other factors. The system evaluates tradeoffs between data transmission speed and communication range to improve system performance.

Abstract: Amplitude and phase errors between branches I and Q of a transceiver utilizing phase quadrature modulation are corrected by preventing propagation of a nominal-frequency signal from a digital part through a loop part and a reception branch to an RSSI indicator by changing the frequency response of a component on the path of the signal. The same indicator that normally measures the payload signal, here measures only undesired signal components. After this, such amplitude and/or phase correction signals are determined with which the measuring result obtained from the indicator reaches the minimum. The resultant correction signals are stored in the memory, and the frequency response of the system is then restored to normal.

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: A quadrature phase shift keying (QPSK) modulating apparatus includes a bit splitter for dividing a bipolar input bit stream into first and second data streams, first and second binary phase shift keying (BPSK) modulators, and a combiner for combining output signals of the first and second BPSK modulators to obtain a QPSK modulated output. The first BPSK modulator includes a voltage-controlled first electrical source which receives the first data stream, and a first oscillator which includes a first resonator that has a first resonant frequency and that is excited by the first electrical source in response to the first data stream so as to generate a first sine wave output.

Abstract: The present invention provides a bandwidth-efficient fading-resistant transmission scheme where a base station implements transmitter diversity using L antennas or L carrier frequencies or L time slots, regardless of the use of frame oriented power control. When the antennas or carriers are spaced sufficiently far apart, or when a different power is used for each power control frame, the transmission from each antenna or carrier or time frame undergoes independent fading. These transmissions are coordinated to mitigate the effects of Rayleigh fading and the mobile receiver can recover the entire L-dimensional transmitted vector as long as the signal energy of at least one coordinate is large enough. L-dimensional fading-resistant signal constellations are generated by maximizing a figure of merit for the Rayleigh fading channel. This scheme offers a significant performance improvement over a conventional single-antenna or single-carrier narrowband BPSK scheme when coding is ineffective due to slow fading.

Abstract: Systems and methods according to the present invention provide a combination of demodulation and decoding, termed decodulation herein. By using knowledge of known symbols, decoding known symbols first, and then using the information obtained by decoding known symbols to decode unknown symbols, improved performance can be achieved. This technique can also be used to alleviate the conventional 3dB loss suffered systems using differentially coding and modulation as compared to coherent detection systems.

Abstract: To receive a response signal from a radio card, a card reader transmits a carrier (not modulated) to the radio card. In the radio card, a phase modulator phase-modulates the a sub-carrier with a response signal, thereby generating a PSK signal, and a phase modulator phase-modulates the carrier with the PSK signal, producing a PSK-PSK signal. The PSK-PSK signal is supplied to an antenna via a signal-extracting device. The antenna sends the PSK-PSK signal toward the card reader. In the card reader, a distributor distributes the PSK-PSK signal to a synchronous detector and an orthogonal detector. The detectors performs synchronous detection by using carriers which differ in phase by 90.degree.. Low-pass filters extract sub-carrier components from the outputs of the detectors. The sub-carrier components are delayed and detected by delay detectors and added together by an adder.

Abstract: A process for transmitting digital signals, in which the digital data are coded differentially in symbols of a symbol period T.sub.s (2.1, 2.2), the symbols transmitted with the Q component being delayed by T.sub.s /2, relative to those of the I component, to achieve a time-staggering. A cross interference of the I and Q components, occurring on the receiver end and caused by the differential coding nd the time staggering, is resolved with a trellis decoder (10), for example. As a result, a differential offset QPSK process achieved on this basis combines the advantages of DQPSK and OQPSK procedures.

Abstract: The amount of memory needed for a ROM-based .pi./4 DQPSK filter is reduced by using a mapper in an IQ modulator (inverse mapper in a demodulator) that incorporates a 90.degree. phase shift for every other symbol. During the intervening symbols no additional phase shift is incorporated by the mapper. This produces a coarse precession of 90.degree. for every other symbol. The 90.degree. of coarse precession may be produced by using alternate DQPSK mappers for alternate symbols. Both mappers share a common repertoire, so no new modulation state symbols are required. During the alternate 0.degree. symbols the filter inserts a 45.degree. phase shift, but does not insert such a 45.degree. phase shift during those intervening times when the mapper (or inverse mapper) is inserting a 90.degree. phase shift. This produces a fine precession. The result is to produce a uniform precession of 45.degree. between each modulation state symbol.

Abstract: A digital signal transmitting apparatus, a digital signal transmitting method, and a digital signal transmitter-receiver, for transmitting a digital signal within a specified frequency band by using an infrared transmission method. An infrared signal within a specified frequency band can be obtained by using a QPSK modulation circuit 13 having roll-off filters 132 and 133 and applying roll-off filtering and QPSK modulation to an inputted digital audio signal, and thereby generating a digital modulated signal S2 whose bandwidth is narrowed and driving an infrared emitter based on the modulated digital audio signal S2.

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 transmitting equipment includes a holding circuit for dividing a time-series digital signal into I and Q digital signals, holding the I and Q digital signals, and outputting them in parallel, a waveform forming circuit, having a memory for storing a plurality of oversampling codes corresponding to the I and Q digital signals, for reading the oversampling codes out of the memory and outputting them as I and Q waveform forming signals, a modulation circuit for orthogonally modulating the I and Q waveform forming signals output from the waveform forming circuit and outputting I and Q modulated signals, an addition circuit for adding the I and Q modulated signals output from the modulation circuit and outputting I and Q sum signals, a filter for removing high-frequency components from the I and Q sum signals output from the addition circuit, and a transmitting signal generation circuit for adding the I and Q sum signals from which the high-frequency components are removed by the filter and generating a transmit

Abstract: A method is disclosed of demodulating a signal (20) modulated by differential quadrature phase shift keying so that two bits of information are coded into each symbol period. The method comprises using a high frequency clock to determine the time taken (t.sub.1, t.sub.2, t.sub.3, t.sub.4), for the modulated signal to execute a predetermined number of cycles, such as 21, in the symbol period (T) and comparing the time thereby determined with the time (t.sub.o) of execution of the predetermined number of cycles for an unmodulated signal.

Abstract: A communication system for transmitting variable rate data is disclosed wherein redundancy is added to the variable rate data to provide repetition symbols. The repetition symbol data is transmitted with symbol energy scaled in accordance to the rate of the variable rate data when the variable rate data is greater than or equal to a nominal data rate. When the variable rate data is less than the nominal data rate, the symbol data is transmitted at nominal symbol energy and redundancy is removed by transmission gating of a proportion of the transmission symbol data determined in accordance with the rate of the variable rate data. Furthermore, a receiver for receiving the variable rate data is disclosed which uses the redundancy in the transmitted data symbol stream to make a corrected estimate of the transmitted symbol data.

Abstract: A transmitting section performs error-correcting coding of signal streams, converts the signal streams into a 2.sup.m -value quadrature amplitude-modulated radio signal, and transmits the radio signal to a channel. A receiving section receives the radio signal and generates signal streams having the same signal format as that of the above signal streams. An encoder codes a signal stream according to even and odd parity rules respectively set for the first and second half portions of a frame pulse. A decoder decodes a signal stream on the assumption that different parity rules are applied for the first and second half periods of the signal stream, and at the same time reproduces a frame pulse. This coded modulation scheme can eliminate uncertainty in the arrangement of signal streams in a rate converter.

Abstract: In a convolutional coding and Viterbi decoding system transparent to phase skips of .pi. and .pi./2 with applications in TDMA transmission, the transmitter 3 includes a demultiplexer receiving a digital bit stream and operating at the bit timing rate, a QPSK differential coder receiving the demultiplexed bit streams and supplying two coded bit streams, two convolutional coders each supplying one code word, and two multiplexers each receiving one code word from a respective convolutional coder and supplying one component of a symbol to be transmitted. The receiver generates two received symbol components which are applied to two demultiplexers each supplying one code word. Each bit of a code word is applied to a single Viterbi decoder. A QPSK type differential decoder supplies two decoded bit streams which are then multiplexed.

Abstract: Information often modulates an underlying carrier signal, thereby producing a modulated information signal 70. This same carrier signal is required, with a few modifications, to demodulate the modulated information signal. This required signal is called the demodulator reference signal. It must be complex, that is, it must contain separate in-phase and quadrature outputs. A degraded version 10 of this signal is often available with the correct frequency, but with the wrong phase and amplitude, and with a direct current (dc) offset. The present invention 68 produces a digital demodulator reference signal 38, 46 from the degraded signal 10. It eliminates dc offset with a dc blocker 18, adjusts amplitude with a scaler 14, adjusts phase with a first Hilbert transformer 20, multipliers 26 and 28 and summer 34, and produces in-phase and quadrature outputs with a second Hilbert transformer 36 cascaded with the first.

Abstract: A rotationally invariant, multilevel coded modulation scheme is provided by partitioning a constellation, such as an M-PSK or QAM constellation, into several trellis-subsets, each of which is further partitioned into block subsets. The input bits are then encoded to select a signal point from the constellation. A first portion of the input bits are differentially encoded. A second portion of the input bits, together with at least one of the differentially encoded bits, are trellis encoded to select a trellis subset of the constellation. A third portion of the input bits--excluding any differentially encoded bits --are block encoded to select a block subset from the selected trellis subset. A fourth portion of the input bits, together with the remaining differentially encoded bits, are used to select a signal point from the selected block subset.