Showing papers on "Demodulation published in 1988"

The phase of a vector perturbed by Gaussian noise and differentially coherent receivers

Abstract: Some results are presented regarding the asymptotic distribution of the phase of a vector perturbed by Gaussian noise. It is shown that for large signal-to-noise ratio, the asymptotic distribution of the phase is of the Tikhonov type. This framework is then used for the synthesis of differentially coherent receiver structures, one for M-ary phase-shift keying (MPSK) and the other for minimum-shift keying (MSK). The first structure bridges the performance gap between coherent and differentially coherent demodulation of MPSK. The MSK receiver uses matched filtering with differential demodulation. >

Single-user detectors for multiuser channels

Abstract: Optimum decentralized demodulation for asynchronous Gaussian multiaccess channels is considered. It is assumed that the receiver is the destination of the information transmitted by only one active user, and single-user detectors that take into account the existence of the other active users in the channel are obtained. The problem considered is one of signal detection in additive colored nonGaussian noise, and attention is focused on one-shot structures where detection of each symbol is based only on the received process during its corresponding interval. Particular emphasis is placed on asymptotically optimum detectors for weak interferers, for CDMA (code-division multiple-access) signature waveforms with long spreading codes, and for low background Gaussian noise level. >

Cellular data system

Abstract: An improved AMPS cellular system where non-interfering digital communication channels are added to the existing analog or digital voice communications channels in the system by utilizing frequency space between channels made possible by the AMPS co-channel and adjacent channel frequency coordination procedures. Interference is prevented by reduction of power, selection of frequencies, proper modulation and demodulation techniques, and unique allocation to the channels in frequency and location. The system is also applicable in general to the insertion of narrow frequency bandwidth channels in any existing communications system using co-channel and adjacent channel frequency allocation strategies.

Radio broadcast communication systems with multiple loop antennas

Abstract: The invention comprises a low power broadcast system that is applicable especially to the so-called "electronic shelf" for retail stores, wherein the shelf edge carries price displaying modules that can be addressed and controlled from a central computer operated station. The system also permits the modules to broadcast back to the central station to confirm safe receipt of data and to give information as to stock levels, etc. A broadcast system avoids the need for wiring so that location changes are facilitated. To overcome the extremely noisy environment and to conserve power consumption, and hence battery life, the system employs a low frequency (132 kHz) reference carrier transmitted by the base station in discrete segmented packages, each of which frames a base data word transmitted by the base station and a corresponding module data word transmitted by the module a fixed period after the end of the base word; the base receiver than has precise time information for receipt of the module word and can "look" for it among the noise. The carrier received by the module is divided and the lower frequency used to demodulate the information-carrying transmission from the base station of the same frequency, avoiding the need for a phase locked loop detector; this lower frequency is also used for the module transmission. The module employs an air-cored loop antenna coil for the lower frequency and a ferrite-cored loop antenna for the higher reference frequency, while the store antenna is segmented for selection of the group of modules to be addressed; the antenna contacts the metal shelving to provide electromagnetic coupling thereto. Each module contains a microprocessor which controls the operation. Each module has "concealed" buttons which can be enabled and used to insert data to be transmitted therefrom. A charging circuit can be used as the power source employing the received RF carrier energy.

Method and apparatus for combining encoding and modulation

Abstract: A method and apparatus for combining encoding and modulation creates signal sets from available amplitude and phase modulations by indexing ordered subspaces. The subspaces need not be limited to the class of subspaces known as binary subspaces. The resultant signal sets, for a preselected power and bandwidth, are widely separated and unlikely to be confused by the effects of channel noise. Such signals can be in either finite block or convolutional form, depending on the natural format of the desired transmission. Further according to the invention are basic apparatus for encoding and modulating as well as demodulating and decoding a signal in accordance with the invention. Specifically, a method is provided for decoding the incorporates a specific type of decoding/demodulation techniques which develops accurate estimates of the information from the received signal in a computationally efficient manner and which permits high speed operation using softdecision decoders.

Universal carrier recovery and data detection for digital communication systems

Abstract: A universal demodulator programmable for any digitally modulated carrier signal having a known constellation format which can be characterized by a unique constellation pattern of phase-amplitude states. The demodulator also generates phase and gain-error signals for locking onto the phase and amplitude of the digitally modulated carrier. The demodulator splits the received digitally modulated carrier signal into an inphase component, Dx, and a quadrature-phase component, Dy. Using a preprogrammed memory device keyed to the identified modulation format, each Dx signal is mapped into one of a plurality of one-dimensional zones each having Rx center values. Using a second preprogrammed memory device also keyed to the identified modulation format, each Dy signal is similarly mapped into a plurality of orthogonal one-dimensional zones having Ry centers. Each pair of Rx and Ry values represents a point in a two-dimensional signal space corresponding to one of the transmitted phase amplitude states. The data assignment signals, Ax and Ay, are generated and outputted by selecting a predetermined portion of the Rx and Ry center values. Using the digital signals Rx, Ry, Dx and Dy and signal vector relationships, a logic circuit generates for each periodic signal pair a phase-error signal Φe corresponding to the phase difference between the phase angle associated with (Dx and Dy) and the phase angle associated with (Rx and Ry). Also generated is a gain-error signal Ge corresponding to the amplitude differential between the amplitude associated with (Dx and Dy) and the amplitude associated with the signal pair (Rx and Ry). The phase and amplitude of the modulated carrier signal is adjusted in accordance with the phase-error signal Φe and the gain-error signal Ge respectively.

Hydrophone demodulator circuit and method

Abstract: The optical signal in a fiber optic interferometer is phase modulated to provide a carrier signal for phase changes caused by changes in a physical parameter being sensed. The signal is then demodulated to measure changes in the parameter. A crystal oscillator frequency reference and passive filtering cause the circuit to have low phase noise. Digital phase shifters provide mixer references that have low phase noise and stable gain. The signal processing techniques of the present invention are applicable to sensor arrays using a single carrier excitation source, time demultiplexing of individual carrier signals and demodulation of each sensor carrier signal. This demodulator circuit is also applicable to frequency-multiplexed approaches, which utilize direct frequency modulation of the source, slightly unbalanced interferometers, and electronic frequency-division multiplexing. The passive homodyne technique allows large linear dynamic range of about 100 dB so that both small and large amplitude signals commonly encountered in acoustic sensing applications may be observed with excellent fidelity.

Digital fm demodulator with a reduced sampling rate

Abstract: A method of recovering a frequency modulated signal wherein the frequency modulated information signal is sampled at a rate less than the Nyquist sampling rate, following which the under sampled signal can be demodulated to extract the original information signal.

Selective calling receiver

Abstract: PURPOSE: To reduce the current consumption of the title receiver so that the battery of the receiver can be extended in service life by operating the receiver with high-speed clocks only when it is detected that the receiver itself is called during the receiving period of the group to which the receiver itself belongs, with the receiver being operated with low-speed clocks while the receiver itself is not called. CONSTITUTION: A control circuit 40 outputs ON/OFF control signals to a battery saving circuit 10 after acquisition of synchronism is completed to set a radio circuit 2 and demodulator circuit 3 to reception operating states during the receiving period of its own group 2 only. The control circuit 40 leads in and uses low-speed clocks generated from the 2nd clock oscillator 29 as operating clocks through the full period of one frame unless a call to its own receiver is detected. Upon detecting a call to its own receiver as a result of collation to individual number coding, the circuit 40 switches the operating clocks from the low-speed clocks to high-speed clocks generated by a 1st clock oscillator 91. Thereafter, message codes are decoded synchronously to the high-speed clocks and, upon completing the decoding, the operating clocks are returned to the low-speed clocks. COPYRIGHT: (C)1990,JPO&Japio

Radio broadcast communication systems

Abstract: The invention comprises a low power broadcast system that is applicable especially to the so-called "electronic shelf" for retail stores, wherein the shelf edge carries price displaying modules that can be addressed and controlled from a central computer operated station. The system also permits the modules to broadcast back to the central station to confirm safe receipt of data and to give information as to stock levels, etc. A broadcast system avoids the need for wiring so that location changes are facilitated. To overcome the extremely noisy environment and to conserve power consumption, and hence battery life, the system employs a low frequency (132 kHz) reference carrier transmitted by the base station in discrete segmented packages, each of which frames a base data word transmitted by the base station and a corresponding module data word transmitted by the module a fixed period after the end of the base word; the base receiver then has precise time information for receipt of the module word and can "look" for it among the noise. The carrier received by the module is divided and the lower frequency used to demodulate the information-carrying transmission from the base station of the same frequency, avoiding the need for a phase locked loop detector; this lower frequency is also used for the module transmission. The module employs an air-cored loop antenna coil for the lower frequency and a ferrite-cored loop antenna for the higher reference frequency, while the store antenna is segmented for selection of the group of modules to be addressed; the antenna contacts the metal shelving to provide electromagnetic coupling thereto. Each module contains a microprocessor which controls the operation. Each module has "concealed" buttons which can be enabled and used to insert data to be transmitted therefrom. A charging circuit can be used as the power source employing the received RF carrier energy.

Method of demodulating digitally modulated signals, and apparatus implementing such a method

Abstract: A signal may be demodulated without using any analog components by using a digital processor. A digitizer delivers the amplitude of the signal to be demodulated at a sampling rate. The signal is acquired from the digitizer and stored in a common memory. The amplitude samples are converted to phase samples. Symbol rate phase hypotheses are generated for splitting the time signal into slices. The carrier phase for one symbol is then calculated for each symbol rate phase hypothesis so that the carrier phase can be estimated over a plurality of (S) symbols. The symbol phase is compared to the carrier phase so that the demodulated signal may be extracted and so that the quality of the demodulation may be estimated.

Carrier-to-noise detector for digital transmission systems

Abstract: A carrier-to-noise detector comprises an A/D converter (1) which samples an output of the demodulator of a digital transmission system at a symbol clock rate and converting it to a digital signal having positive and negative values. An absolute value converting circuit (2) converts the output of A/D converter into an absolute value which is averaged by a first averaging circuit (3) over a period sufficient to suppress short term variations and then squared by a first squaring circuit (4) to give an output representing the carrier component. The output of A/D converter is, on the other hand, squared by a second squaring circuit (5) and averaged by a second averaging circuit (6) to suppress short term variations to give an output representing a total of the carrier and noise components. The carrier component in the output of the second averaging circuit 6 is subtracted by a subtractor (7). A ratio between the outputs of the first squaring circuit (4) and subtracting circuit (7) is derived by a divider (8) as a representation of a carrier-to-noise ratio.

FSK demodulation circuit

Abstract: An FSK demodulation circuit which receives as input an FSK modulated reception signal, obtains two quadrature pulse trains, i.e., a first pulse train and a second pulse train, from a phase detection circuit, is provided with at least two sampling means which use the edge of one of the pulse trains and sample the logic of the other pulse train, produces two or more sample outputs at different timings, and determines the logic of the reproduced data from a combination of the logics "1" and "0" of the sample outputs.

Apparatus for adapting computer for satellite communications

Abstract: Computer controllable apparatus for receiving and demodulating a satellite broadcast signal. A programmable radio frequency tuner/demodulator demodulates the broadcast signal to produce a baseband output signal. A video demodulator then demodulates the baseband output signal to produce a video output signal. First and second programmable audio frequency tuner/demodulators further demodulate the baseband output signal to produce first and second audio output signals. A data demodulator further demodulates the second audio output signal to produce a data output signal.

Line-sequential pyramid processing of a plurality of raster-scanned image variables

Abstract: A plurality of raster-scanned image variables are time-compressed and time-division multiplexed on a line-sequential basis for pyramid analysis. The resulting differential pulse code modulation is statistically encoded and assembled together with digital audio code and synchronizing code. The assembler supplies a serial stream of bits to a transmitter. Receiving apparatus for a video teleconferencing station includes a receiver complementary to the transmitter and a parser for separating digital codewords. Those codewords that are statistical codes descriptive of differential pulse code modulation of video are demodulated. The demodulation results are formatted for a pyramid synthesizer. The stream of samples provided as output signal from the pyramid synthesizer is time-division demultiplexed and time expanded to recover the plurality of raster-scanned image variables.

Multiplexed address control in a tdm communication system

Abstract: A message communication system employing one or more centralized communication stations (22) transmitting messages through Earth orbit relay satellites (20) to mobile receivers (10) utilizing Time Division Multiplexed (TDM) communication signals having signal time frames divided into a series of transmission channels. A predetermined number of the channels are designated as address channels with the remainder being used for data transfer. Information transmitted on the address channels is used by receivers to determine both the presence of a message and its corresponding data transmission channel. Each system receiver (70) scans, and tracks only the communication signal address channels until a message addressed to that receiver is detected, at which time the selected receiver changes channels to the designated data channel for reception of the message. Thus, demodulation of the entire communication signal is not required and processing time and power is reduced for the typical waiting condition when messages are not being received. While a message is being received only a portion of the communication signal need be received, demodulated and decoded. The decoded message is then displayed on a display screen (88) or similar device for the recipient.

Method and apparatus for high speed digital phased array coherent imaging system

Abstract: A method for generating an output stream of digital data words, with each data word representing the amplitude of an analog signal at one of a multiplicity F samples each second and with substantially equally spaced time intervals T therebetween, is obtained from a digital baseband demodulation system used for array beam forming. A data stream, formed of interleaved ADC output digital data words acquired from a set of converters, is at a rate of F total samples/second. Subsequent digital demodulation, filtration, and decimation provides digital output signals which need less delay resolution prior to the formation of coherent sum signals, thereby reducing overall channel memory requirements. The output baseband data stream has enhanced dynamic range, thereby reducing the ADC bit density requirements.

Differential phase-shift keying demodulator

Abstract: A digital modem is provided for demodulation of differential phase-shift keyed (DPSK) signals in a land mobile satellite receiver. The DPSK demodulator comprises a coarse frequency and lock detect module for identifying and estimating the frequency of the input signal, a numerically controlled oscillator (NCO) for generating in-phase and quadrature signals from the input signal, one pair each of delayed and non-delayed integrate and dump (I&D) modules, a symbol timing module for achieving symbol synchronization by determining the dump time of the I&D modules, a dot product detector for receiving the output of the non-delayed I&D modules and providing a detected data output, and an AFC loop comprising a cross product detector and an AFC loop filter that provides feedback to the NCO and lock detect module. The DPSK demodulator achieves symbol synchronization independent of carrier phase or frequency and at low signal-to-noise ratios. Overall, the modem achieves the theoretical bit error rate capability of DPSK on a narrow band, white Gaussian noise channel with minimal implementation loss.

Method and system of background noise suppression in an audio circuit particularly for car radios

Abstract: To improve the fidelity of reproduction of automobile radios during conditions of extraneous in the passenger compartment, noise signals are derived, for example from a microphone installed in the engine compartment of the vehicle The audio program signals are conducted through a multichannel equalizer; the program audio signals and the noise signals are separated into a plurality of frequency bands, for example three bands, the envelope of which are demodulated and the derived demodulation signals are instantaneously compared to then control the transfer characteristics of the respective bands of the equalizer in accordance with the derived comparison between the respective bands of the noise and program signals Preferably, amplitude, change of transfer amplitude and rate of change is controlled by weighting the comparison signals and the rate of change thereof in relation to the frequency bands and the extent of change of the signals

Theory for optical heterodyne narrow-deviation FSK receivers with delay demodulation

Abstract: A theoretical model is presented that includes the effects of laser phase noise, receiver noise, imperfect modulation, IF bandwidth, and postdetection filtering. Detailed numerical results for 140-Mb/s and 400-Mb/s systems are presented, showing excellent agreement with independent published experimental results and strongly supporting the theoretical analysis. It is found that an IF linewidth of less than 0.25% of bit rate is required to avoid degrading the receiver sensitivity by more than 1 dB in a system with a strong local oscillator and modulation index of 0.7. A larger modulation index allows a larger linewidth to be accommodated. If the demodulation is not optimal, a narrower linewidth is necessary. >

Alternatives for on-board digital multicarrier demodulation

Abstract: In this paper alternatives for digital multicarrier demodulators (MCD) suitable for advanced digital satellite communications systems are presented. The MCD permits the direct on-board interfacing of FDMA and TDM communication links by digital signal processing techniques. Two main functions are implemented by a MCD: demultiplexing (DEMUX) and demodulation (DEMOD). We focus here only on a digital implementation of the MCD, looking at its advantages, flexibility, better performance and VLSI integrability. The DEMUX may be implemented in a number of ways: the analytic signal method, fast Fourier transform with polyphase network technique, or multistage methods. For all the implementation methods considered it is shown that a certain degree of integration of DEMUX and DEMOD functions is possible. To this end, in the proposed MCD schemes the receiver pulse-shaping filter has been integrated in the DEMUX structure, reducing the overall implementation complexity. It is shown that, for the per-channel structure based on the analytic signal method, a highly modular and flexible implementation can also be achieved. Coherent demodulation is used to reduce the signal-to-noise ratio required to achieve a specified bit error rate. The coherent demodulation is carried out by using the maximum likelihood (ML) estimation method. Two different approaches to receiver synchronization have been studied. For the first, the carrier phase and symbol timing estimates are independently derived by suitable techniques. The second approach makes use of the maximum a posteriori probability method to estimate both the carrier phase and symbol timing of the receivied signal. In particular, for this technique it is shown that, by a suitable choice of the architecture of the digital coherent receiver, the ML demodulator can be integrated in the joint carrier and clock recovery circuit, with no increase in the overall system complexity. The digital architecture of the proposed MCD can be adapted to different digital modulation techniques. However, here we consider only the application for QPSK signals, as this modulation scheme is the most promising for digital satellite communications. A theoretical analysis and computer simulation have been used to evaluate the performance degradation of the proposed MCD, including finite-arithmetic implementation effects.

Aspects of instrumentation design for impedance imaging.

Abstract: This paper takes the circuit for a general purpose impedance imaging data measurement system and analyses the importance of several components. For high accuracy it is shown that stray capacitances in the input circuitry are the major problem although the use of a phase sensitive demodulator can minimise this problem. It is shown that harmonic distortion in the constant current generator can cause errors which are, however, reduced if a linear multiplying demodulator is used rather than a switching demodulator.

Complex digital sampling converter for demodulator

Abstract: A complex digital sampling converter, for use with an IF demodulator, includes: an analog-to-digital converter (ADC) receiving the IF analog signal for conversion to a digital data stream by sampling at a sampling rate frequency substantially equal to four times the IF signal frequency; a digital mixer for converting the sampled data to baseband; a sorter for separating the interleaved sequential in-phase I data words and quadrature-phase Q data words into a pair of concurrent I and Q data word streams; and at least one of a circuit for removing the effects of any DC offset in the analog IF signal applied to the ADC, and a circuit for correcting misalignment errors in the concurrent I and Q streams. Preferably, both correction circuits are utilized, with the DC offset removal circuit using averaging of all of the baseband samples, and the misalignment correction circuit averaging each pair of quadrature-phased Q data words while compensating the in-phase I data streams for the extra delay in the averaged Q data.

Dual port fm demodulation in phase locked receivers

Abstract: A problem arises in attempting to recover low frequency FM components in receivers using wide bandwidth tracking loops. Wide loop bandwidths are desirable for rapid signal acquisition but interfere with demodulation of low frequency FM components, such as those produced by digital signalling data. This invention permits recovery of the full modulation spectrum with flat frequency response. A conventional FM demodulator (15) recovers the high frequency modulation components; the frequency control signal for the local oscillator (3) provides the low frequency components. Combining (35) the components with proper weighting (31, 33) produces recovered modulation (37) with bandwidth limited only by the IF bandpass filter (7) or demodulator. The invention would find application in an FM receiver of the superheterodyne or direct conversion type that requires precise frequency control, such as one used for communications in a narrow channel spacing environment at ultra-high frequencies.

Generalized minimum shift-keying modulation techniques

Abstract: The simultaneous data demodulation and phase tracking of an MSK signal using the Viterbi algorithm is described, and two variations of MSK modulation are studied. The MSK with overlay is a dual-rate modulation techniques in which low-rate and high-rate data are superimposed on an MSK signal. Here the demodulator uses the Viterbi algorithm to estimate both the low-rate and high-rate data simultaneously. The MSK with pseudorandom sequence spreading combats intentional or unintentional jamming. A simplified receiver for these spread-spectrum MSK signals is found that takes into consideration the effect of random phase perturbations. The performance of these demodulators is evaluated using transfer-function bounds for the bit error probability. For demodulation of the spread spectrum MSK signal, a simplified receiver is derived, and its performance in the presence of continuous jamming is evaluated. >

Demodulation technique for coherence multiplexed optical data transmission system

Abstract: An improved demodulator and demodulation method usable in a coherence multiplexed, optical data transmission system. The demodulator comprises an interferometer and a signal processor. The interferometer has first and second arms having first ends coupled to receive radiation from an optical bus, and second ends connected to the signal processor. The path length difference between the arms is selected to approximately match that of a corresponding modulator, to within the coherence length of the optical carrier. The signal processor processes the optical signals emerging from the arms in combination, to produce a pair of electrical ouput signals. Linearly independent pairs of electrical ouput signals are produced for any two modulation signals that do not produce modulator optical path length differences that differ from one another by an integral multiple of a half wavelength of the optical carrier. In a preferred embodiment, the electrical output signals correspond to the cosine and sine of the phase modulation angle produced in the associated modulator.

Multi‐carrier demodulators for on‐board processing satellites

Abstract: A study of the digital transmultiplexor element of an on-board multi-carrier demodulator (MCD) results in design data for various architectures (FFT, tree etc.) which can be applied to a wide range of applications. A detailed design based on the latter for a 4 × 16 kb/s MCD for the U.K. T-SAT mobile OBP payload is presented. Implementation of the MCD using TMS320C25 signal processor technology has been performed and early test results are presented.

Method of demodulation in digital communication systems with multipath propagation

Abstract: Method of demodulation in digital communication systems with multipath propagation in a channel between transmitter and receiver, based on the use of algorithms of the Viterbi, Fano, Stack and similar types, with decoding of the soft decision type, where there is included a calculation of reference values in the receiver. On account of the complexity, possibly current consumption, the receiver is adapted to process only sequences each having a limited number (nu) of consecutive data symbols, here denoted ''known'' data symbols, the channel and the transmitter together containing more than the ''known'' data symbols, and these other symbols being denoted ''unknown'' data symbols. The method is based on the concept that the receiver by means of a channel estimator (23) forms an estimate of the instantaneous impulse response (h(t)) of the multipath propagation channel (possibly convolved with the ambiguity function ($(1,1)$(t)) of the channel estimated). The calculation of reference values comprises utilization of the impulse response (h(t)) of the channel and knowledge of the signal transmitted by the transmitter for a given sequence with known and unknown data symbols, and this transmitted signal is averaged over at least a part of the unknown data symbols.

Method and arrangement for synchronizing a receiver in digital transmission systems

Abstract: A method and circuit arrangement for synchronizing a receiver in a digital transmission system with transmission of a special preamble selected in such a manner that, with correct demodulation, the received signal has a cosine shape with a pattern frequency fp from which the clock pulse frequency results, and wherein frequency and/or phase of the carrier and clock pulse signal, respectively, are estimated, and, after demodulation with an assumed carrier frequency ft0, the individual spectral lines (gp, gn) of the received signal (rd) are obtained by filtering, and from these signals, their frequency (fgp, fgn) and phase ( gp, gn) are determined by linear regression, with these frequency and phase values being used, by means of subsequent difference and sum formation, to obtain the following estimated values: ##EQU1##

Remote control repeater

Abstract: A repeater for receiving data transmitted thereto via a first transmission medium, transmitting that data over AC power lines to a remote location and re-transmitting that data from the remote location via a second transmission medium. The data is applied to the AC power lines by frequency modulating an FM carrier and supplying that modulated carrier to the power lines by way of a bandwidth limiting circuit. At the remote location, a resonant circuit in combination with a reject circuit receives the modulated FM carrier from the AC power lines and passes only an extremely limited band of FM signals to a tuned amplifier which, in turn, supplies the band-limited FM signals to a demodulator.