Showing papers on "Demodulation published in 1995"

Blind adaptive multiuser detection

Abstract: The decorrelating detector and the linear minimum mean-square error (MMSE) detector are known to be effective strategies to counter the presence of multiuser interference in code-division multiple-access channels; in particular, those multiuser detectors provide optimum near-far resistance. When training data sequences are available, the MMSE multiuser detector can be implemented adaptively without knowledge of signature waveforms or received amplitudes. This paper introduces an adaptive multiuser detector which converges (for any initialization) to the MMSE detector without requiring training sequences. This blind multiuser detector requires no more knowledge than does the conventional single-user receiver: the desired user's signature waveform and its timing. The proposed blind multiuser detector is made robust with respect to imprecise knowledge of the received signature waveform of the user of interest. >

Digital communication techniques : signal design and detection

Abstract: 1. Introduction to Telecommunications. 2. Power Spectral Density of Digital Modulations. 3. Scalar and Vector Communications Over the Discrete Memoryless Channel. 4. Coherent Communication with Waveforms. 5. Noncoherent Communication with Waveforms. 6. Partially Coherent Communication with Waveforms. 7. Differentially Coherent Communication with Waveforms. 8. Double Differentially Coherent Communication with Waveforms. 9. Communication over Bandlimited Channels. 10. Demodulation and Detection of Other Digital Modulations. 11. Coded Digital Communications. 12. Block-Coded Digital Communications. 13. Convolutional-Coded Digital Communications. Index.

Cell site demodulation architecture for a spread spectrum multiple access communication systems

Abstract: An integrated demodulation processor used in a modem for a spread spectrum communications system despreads multipath receive signals then uses a time sliced transform processor to process the multiple signals in to a single series of soft decision results. The demodulation processor uses a single transform engine which operates on a time slice basis. The output of the processor engine cascade through a pipeline processor which, on a time slice basis, operates on signals corresponding to each multipath receive signal. The processed results are dual maxima decoded to provide soft decision data.

Optical fiber modulation and demodulation system

Abstract: This invention is directed toward a fiber optic modulation and demodulation system, and more particularly directed toward a telemetry system for relaying signals from sensors in remote, harsh environments. Light is modulated using one or more optical reflective grating and piezoelectric crystal combinations, and demodulated using an interferometer system. The one or more modulators are driven by the responses of one or more sensors thereby modulating one or more carrier wavelengths of a carrier light source. The modulated light signal is transmitted from the sensor or sensors, over an optical fiber, to an interferometer which is used to demodulate the reflected signals and thereby determine the responses of one or more sensors. One embodiment of the invention set forth is that of a telemetry system linking sensors within a borehole to detection and processing equipment at the surface of the earth.

Computer and measurement simulation of a new digital receiver operating directly at millimeter-wave frequencies

Abstract: A novel digital millimetric receiver (DMR) scheme is introduced. Using a six-port phase/frequency discriminator (SPD) in conjunction with a digital signal processor (DSP), the receiver performs various PSK and QAM demodulations directly at microwave and millimeter-wave frequencies. An important feature of the new DMR is that hardware imperfections such as phase/amplitude imbalance are readily eliminated by a simple calibration procedure. The concept is proved through computer simulation and measurements at 26.5 GHz. This receiver scheme is proposed for small/medium capacity digital terminals typically found in various wireless communication networks.

The lock-in CCD-two-dimensional synchronous detection of light

Abstract: A new type of CCD image sensor for two-dimensional synchronous detection ("lock-in imager") is presented. The measurement principle allows each pixel to measure the size of the amplitude modulation, the relative phase and the mean brightness level (background) of an oscillating optical wave field. Design, operation and measurement results are presented. A typical application for this sensor would be in 3-D imaging (range measurement) using heterodyne interferometry. >

Influence of RF oscillators on an OFDM signal

Abstract: This paper explains the mechanisms that lead to a degradation of an OFDM signal because of the phase noise of the RF oscillators. An approach for easy calculation of SNR, independent of carrier numbers, will be given. This SNR approach uses a plot of the phase noise power density for the calculation. The theoretical results lead to an improved synthesizer concept. Values of SNR and BER will be given for the new synthesizer concept. >

Method and apparatus for AM compatible digital broadcasting

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 modulated by an analog program signal; and simultaneously braodcasting a plurality of digitally modulated carrier signals within a bandwidth which encompasses said first frequency spectrum, each of the digitally modulated carrier signals being modulated by a portion of a digital program signal, wherein a first group of the digitally modulated carrier signals lying within the first frequency spectrum are modulated in-quadrature with the first carrier signal, and wherein second and third groups of the digitally modulated carrier signals lie outside of the first frequency spectrum and are modulated both in-phase and in-quadrature with the first carrier signal. Transmitters and receivers which operate in accordance with the above method are also provided.

Adaptive receiver algorithms for near-far resistant CDMA

Abstract: Adaptive receiver algorithms are considered for the demodulation of code-division multiple-access (CDMA) signals. These algorithms include neural-network based algorithms and algorithms adapted from linear channel equalization techniques. Convergence issues are treated, and the performance of various algorithms is compared via computer simulations. >

Data transmitter and receiver of a spread spectrum communication system using a pilot channel

Abstract: An improved spread spectrum communication system includes a transmitter and a receiver utilizing a pilot channel for the transmission of pure rather than modulated PN codes for code acquisition or tracking purposes with a lower bit error rate. The pilot signal is used to obtain initial system synchronization and phase tracking of the transmitted spread spectrum signal. At the transmitter side, Walsh an orthogonal code generator, a Walsh modulator, a first PN code generator, a first band spreader, a second band spreader, finite impulse response filters, digital-to-analog converter, low-pass filters, an intermediate frequency mixer, a carrier mixer, a band-pass filter are used to transmit a spread spectrum signal. At the receiver side, a corresponding band-pass filter, a carrier mixer, an intermediate-frequency mixer, low-pass filters, analog-digital converters, a second PN code generator, an I channel despreader, a Q channel despreader, a PN code synchronization controller, a Walsh an orthogonalcode generator, a first Walsh demodulator, a second Walsh demodulator, accumulator & dump circuits, a combiner, and a data decider are used to demodulate a received spread spectrum signal.

Wireless radio modem with minimal interdevice RF interference

Abstract: A wireless radio modem for incorporation into a host system includes radio frequency modulation/demodulation circuitry employing electronic device elements that operate in a frequency range that minimize the RF interference between the radio modem and the host system. Radio modem power conservation is further maximized by 1) simplifying signal modulation processing by use of a single sideband suppressed carrier waveform transition table, thereby reducing processing requirements; and 2) incorporating a "sleep mode" feature in which all non-timer circuitry is powered-down when not in use.

Dual mode code division multiple access communication system and method

Abstract: A CDMA communication system capable of operating at higher data rates with less bit errors and reduced cochannel interference facilitates coherent detection without the use of a pilot tracking signal. A transmitter in the communication system includes a coherence interval channel encoder, an orthogonal function encoder, such as a Walsh encoder, as well as a pseudo noise (PN) channel modulator. The channel encoder processes data sequences into sufficiently short encoded data blocks to minimize any phase shifts at a receiver in a high mobility environment due to a Doppler frequency shift. Depending on the application, several transmitters may be synchronized such that the corresponding transmitted information signals are orthogonal to one another. A receiver of the communication system includes a channel demodulator, matched filters and coherent decoder that generates weighted decoded signals, one of which is determined to be a proper coherent synchronous reading of the received information signals without the use of a pilot tracking signal. The communication system may be used as a forward and/or reverse communications link in a cellular telephone system.

CDMA system having time-distributed transmission paths for multipath reception

Abstract: An arrangement (apparatus and method) for providing a code division multiple access (CDMA) transmission system in an urban environment using spatially-diverse antennas and time-diversity devices and techniques to provide improved cell coverage without the detrimental effects of multipath (Rayleigh) fading. The spatially-diverse antennas output identical CDMA-modulated signals to a serving area at different times, whereby each CDMA-modulated signal output from a corresponding antenna has a sufficent delay to avoid mutual interference with the identical CDMA-modulated signals output from other antennas. The delay assigned to each antenna is within a range greater than a chip interval, and less than or equal to a base station sequence offset between base stations. As a result, a subscriber station is able to separately demodulate the received CDMA-modulated signals from the different antennas as CDMA signals having adequate multipath delay for demodulation using a rake receiver. The delays may be implemented as delay devices supplying delayed system clock signals from a GPS receiver to corresponding base stations having identical spreading sequences. Alternatively, the delays may be implemented as successively delaying a CDMA-modulated signal output by a single base station before transmission to the antennas along corresponding transmission paths.

Modulation identification by the wavelet transform

Abstract: There is a need, for example in surveillance of the radio spectrum, to determine the modulation type of a received signal. By knowing the modulation type, one can demodulate the incoming signal for useful information. This paper proposes the use of wavelet transform for the identification problem. Application of wavelet transform on a digital modulation signal results in distinctive patterns for different types, which enables simple processing for identification. Three identifiers for classifying PSK and FSK, M-ary PSK, and M-ary FSK are considered and the relevant statistics for optimum decision making are included. Simulations are included for performance evaluation.

A novel technique for double sideband suppressed carrier modulation of optical fields

Abstract: We present a simple and efficient technique to produce double sideband suppressed carrier (DSBSC) modulation for coherent analog optical communications. When operating a Mach-Zehnder electro-optic modulator at the appropriate bias point the carrier exits one of the output ports while the information carrying sidebands exit the other output port. The absence of a strong carrier component in the DSBSC output allows the use of an optical amplifier immediately following the modulator where the light signals are still relatively strong hence preserving the high S/N. In our experiments using heterodyne detection at 1319 nm, we show a -28-dB carrier suppression using a commercial M-Z modulator. >

Signal processing apparatus and method

Abstract: An integrated digital communication system utilizing multilevel vestigial sideband transmission is provided. The communication system receives a multi-level pulse-amplitude modulated digital signal from a limited bandwidth channel. The system includes processing stages which demodulate, sample and filter the incoming signal prior to recovery of the digital data. Other stages recover the timing and lock on to the frequency and phase of the transmitted signal, as well as provide for automatic gain control. An adaptive equalizer, error correction circuitry, and an output interface recover the digital data and provide for transfer to other devices.

Method and apparatus for system determination in a multi-mode subscriber station

Abstract: A method and apparatus for selecting a communication system in a multi-mode subscriber station (1). In the exemplary embodiment, the subscriber station (1) capable of operating in CDMA mode and analog mode comprises an analog modulation and demodulation and processing element (4) and a CDMA modulation and demodulation and processing element (6) and a system determination element (8). System determination element (8) examines exit parameters provided by the communication element excited and determines the next system upon which to attempt acquisition in accordance with a system preferences table (12), a CDMA channel table (10) and a non-volatile memory element (14).

Apparatus for demodulating and decoding video signals encoded in different formats

Abstract: An adaptive receiver includes an adaptive demodulator and an adaptive decoder for providing demodulated and decoded output data from a video signal encoded for satellite, terrestrial or cable transmission. The demodulator recovers demodulated output data by using an adaptive timing recovery network and an adaptive carrier recovery network that incorporates a selectable slicer network. In addition, an Automatic Gain Control network within the demodulator provides a gain control output as a function of a difference between signals produced both prior to and following the slicer. The demodulator may also incorporate a signal quality detector that uses carrier recovery network signals to provide an estimate of the error in the demodulated output data. The decoder produces a Viterbi decoded output from the demodulated output data by using a selectable code rate Viterbi decoder.

Direct downconverter circuit for demodulator in digital data transmission system

Abstract: A digital downconverter circuit for a digital data transmission system is provided, comprising (i) a bandpass filter circuit for filtering a received analog intermediate frequency (IF) carrier signal onto which baseband information has been modulated, and outputting a bandpass analog IF signal; (ii) an analog-to-digital converter for converting the bandpass analog IF signal into a bandpass digital IF signal; (iii) a phase shifter device for outputting a complex pair of phase shifted baseband signals operating at a local baseband frequency; (iv) a mixer device for mixing the bandpass digital IF signal separately with each of the complex pair of phase shifted baseband signals and outputting a complex combined baseband/bandpass signal comprising inphase and quadrature components; (v) filtering circuitry for recovering the baseband information onto the phase shifted baseband signals; and (vi) sampling circuitry for sampling the information-bearing recovered baseband signals and outputting a sampled complex baseband output signal. The phase shifter device, the mixer device, the filtering circuitry, and the sampling circuitry are all implemented on a gallium arsenide (GaAs) application specific integrated circuit (ASIC). The filtering circuitry includes a single half-band pre-filter and a multi-pole low pass filter. The analog-to-digital converter operates at the sampling clock frequency, which is about 512 megahertz (MHz), and the IF carrier signal operates at about 52-176 MHz. An automatic gain control circuit controls the amplitude of the bandpass analog IF signal prior to its being converted into the bandpass digital IF signal.

Method and system for demodulation of downlink CDMA signals

Abstract: Demodulation of a CDMA downlink signal is performed by filtering correlations of the received signal with a known signature sequence. Unlike the conventional Rake receiver, the filtering is not necessarily a FIR filter (102) with coefficients equal to the conjugates of channel tap estimates (105). Instead, the present invention filters in such a way as to maximize the output signal-to-noise ratio, accounting for the fact that part of the noise comes from the same base station as the signal, so that it is colored by the same channel as the signal. This is accomplished by replacing the RAKE FIR (102) combining filter with a more general filter such as IIR filter (202) or FIR filter (402).

Diversity reception device

Abstract: A diversity reception device which weights in proportion to the reception level and combines a plurality of reception signals, includes a phase demodulator for demodulating the phase of the reception signal, a converter to output the sine and cosine elements of the reception signal, a sine element adder to add up sine element of each reception signal, and a cosine element adder to add up cosine element of each reception signal. The converter fetches and outputs predetermined values on sine and cosine elements of the reception signal upon input of the reception signal's reception level and phase data that is sent from phase demodulator. Therefore, the present device does not require expensive electronic circuits and can be made of small digital circuits suitable for IC including a memory.

CD3-OFDM: a new channel estimation method to improve the spectrum efficiency in digital terrestrial television systems

Abstract: The paper describes a novel channel estimation scheme (identified as CD3, coded decision directed demodulation) for coherent demodulation of OFDM (orthogonal frequency division multiplex) signals making use of any constellation format (e.g. QPSK, 16 QAM, 64 QAM). The structure of the CD3-OFDM demodulator is described, based on a new channel estimation loop exploiting the error correction capability of a forward error correction (FEC) decoder and frequency and time domain filtering to mitigate the effects of noise and residual errors. In contrast to the conventional coherent OFDM demodulation schemes, CD3-OFDM does not require the transmission of a comb of pilot tones for channel estimation and equalisation, therefore yielding a significant improvement in spectrum efficiency (typically between 5% and 15%). The performance of the system with QPSK and 64 QAM modulations is analysed by computer simulations, on AWGN and frequency selective channels. The results indicate that CD3-OFDM allows to achieve C/N performance similar to coherent demodulation with pilot tones, when the same channel coding and modulation scheme is adopted. Otherwise, when the additional capacity is exploited to increase the FEC redundancy instead of the useful bit-rate, CD3 can offer significant C/N advantages (typically from 2 to 5 dB depending on the channel characteristics). Therefore CD3-OFDM can be suitable for digital television broadcasting services over selective radio channels.

Method and apparatus for adjustable frequency scanning in ultrasound imaging

Abstract: Method for scanning a field of view using a scan format, wherein the carrier frequency of the imaging pulse is higher in the center of the field of view than at the edges. The frequency variation can be accomplished on transmit by modulating appropriately delayed programmable initial waveform information samples with a programmable carrier frequency (T-102). This results in a pulse transmitted into the body whose frequency is highest in the center portion of the scan, and is reduced in a controlled fashion as the steering angle is increased in order to mitigate grating lobe artifacts. The technique preserves signal energy because modulation merely translates the signal in frequency substantially without modification of the pulse shape itself. The technique is also useful on receive, wherein demodulation to or near baseband followed by post-beamformation predetection remodulation (R-100) can correct for systematic scan-line-to-scan-line phase variations to ensure scan-line-to-scan-line phase coherency for subsequent coherent processing across scan lines or for coherent image formation (R-26) using the phase and amplitude information from multiple beams.

Extended time tracking and peak energy in-window demodulation for use in a direct sequence spread spectrum system

Abstract: A direct sequence spread spectrum communication system in a digital cordless telephone having a basestation and a handset that each implement an extended .linevert split.EE.linevert split.+.linevert split.E.linevert split.-.linevert split.L.linevert split.-.linevert split.LL.linevert split. time tracking system and peak matched filter demodulation within a related window to permit one sample per chip analog-to-digital conversion and demodulation for longer code sequences (providing savings in hardware and complexity) and to permit enhanced two sample per chip analog-to-digital conversion and demodulation for shorter code sequences (providing more robust fading immunity).

Broadcast receiver adapted for analog and digital signals

Abstract: Background: Digital satellite TV broadcasting systems use an analog IF input followed by an analog QPSK-demodulator and analog lowpass filters prior to A/D conversion. Normally, two A/D converters would be required for digital demodulation of the in phase and of the quadrature component. Gist of the Invention A first IF frequency of about 2 GHZ and a second IF of about 140 MHz allows to demodulate FM signals of 27 MHz bandwidth. A subsequent local 70 MHz local oscillator is followed by a lowered resolution A/D converter operating at about 100 MHz sampling frequency in a subsampling mode. A single A/D converter (7) is required only and allows high quality FM demodulation. Advantages Allows multi-standard front-end architecture, architecture is suited for digital and analogue input signals, the possible net data rate around 40MBit/s is even higher than required for DirecTV.

A Well Data Telemetry System

Abstract: A well data telemetry system for transmitting data along at least a part of a well bore 2 containing tubing of magnetically permeable material comprises a transmitting coil 9 located to transmit a magnetic flux signal along the modulation circuitry connected to the coil 9 for modulating tubing and/or the surrounding geological formations, the magnetic flux signal in response to a data signal, and an ac magnetometer 10 located to detect and respond to the magnetic flux signal at a position spaced from the transmitting coil 3 By using an ac magnetometer instead of a conventional receiver coil to detect and respond to the magnetic flux signal, the system is capable of responding to the low levels of signal which are likely to be received in practice Furthermore, the response of the ac magnetometer is independent of frequency so that the system may be used at low frequencies as well as high frequencies and demodulation of the transmitted signal can be effected without difficulty

Multiple carrier transmission in common wave broadcasting networks

Abstract: In order to prevent wanted signal capacity from being reduced during OFDM modulation of digital coded data, control symbol protecting intervals in the frame head of each OFDM transmission frame are larger than data symbol protecting intervals in wanted data areas of each OFDM transmission frame. The length of data symbol protecting intervals is determined during demodulation and data symbol scanning times are then determined depending on the thus determined length of the protecting intervals.

Optical micro cell transmission system

Abstract: An optical micro cell transmission system comprising a radio base station, at least one optical interface section connected to the radio base station, and an optical forward base station connected to the optical interface section via optical fibers for transmitting and receiving signals through an antenna, and being flexible for the variation of an amplifier due to a change in temperature or a change in the length of an optical segment, and also being available for detecting faults in the optical forward base station is provided. Pilot signal generators 30, 51 are provided for generating pilot signals. For a transmitted signal 11, a coupler 21 in the optical interface section convolutes a pilot signal P D , and a demodulator 48 in an optical forward base station detects the level of the pilot signal P D and controls a downward signal amplifier 42 according to the result of detection. For a received signal received by an antenna 6, a coupler 45 in the optical forward base station convolutes a pilot signal P U , a demodulator 27 in the optical interface section detects the level of the pilot signal P U and controls an upward signal amplifier 25 according to the result of detection. Furthermore, control signals and fault information signals are transmitted in a modulated signal for the pilot signals P D , P U .

Direct conversion receiver

Abstract: In a first direct conversion receiver for demodulating I and Q signals, having a quadrature relation therebetween, obtained from a received FSK signal through a direct conversion, a first D FF latches a level of the I signal when a sign condition of I and Q signals moves from the same to different sign conditions, a second D FF latches a level of the Q signal when the sign condition of the I and Q signals moves from the different to same sign condition and EXCLUSIVE OR operations are made among the I and Q signals and the outputs of the first and second D FFs to provide a frequent data judgement to improve a receiving sensitivity of an FSK signal having a relative low modulation index. In a second direct conversion receiver, a sign change in the Q signal is detected by a first edge detection circuit 17, a first D FF holds the level of the I signal, and an EXCLUSIVE OR circuit provides a first demodulation result. A sign change in the I signal is detected by a second edge detection circuit 17, a second D FF holds the level of the Q signal, an EXCLUSIVE OR circuit provides a second demodulation result and a subtracting circuit combines the first and second demodulation results. An earlier change detection circuit also combines the first and second demodulation results with a delay in the first and second demodulation results reduced.

Data-aided noncoherent demodulation of DPSK

Abstract: Considers noncoherent demodulation of DPSK when the receiver has partial knowledge of the information being transmitted. This partial knowledge represents preamble symbols, pilot symbols, or past decisions when operating in a decision-feedback mode. The maximum likelihood (ML) noncoherent receiver for this case is derived. It is shown that known demodulation schemes such as multi-symbol differentially coherent receivers and decision-feedback differential receivers can be considered as special cases of this data-aided noncoherent DPSK demodulator. A simple recursive structure for this receiver is introduced and its performance analyzed. >