Showing papers on "Demodulation published in 2002"

Analysis and design of OFDM/OQAM systems based on filterbank theory

Abstract: A discrete-time analysis of the orthogonal frequency division multiplex/offset QAM (OFDM/OQAM) multicarrier modulation technique, leading to a modulated transmultiplexer, is presented. The conditions of discrete orthogonality are established with respect to the polyphase components of the OFDM/OQAM prototype filter, which is assumed to be symmetrical and with arbitrary length. Fast implementation schemes of the OFDM/OQAM modulator and demodulator are provided, which are based on the inverse fast Fourier transform. Non-orthogonal prototypes create intersymbol and interchannel interferences (ISI and ICI) that, in the case of a distortion-free transmission, are expressed by a closed-form expression. A large set of design examples is presented for OFDM/OQAM systems with the number of subcarriers going from four up to 2048, which also allows a comparison between different approaches to get well-localized prototypes.

OFDM signal communication system, OFDM signal transmitting device and OFDM signal receiving device

Abstract: An OFDM signal communication system used in broadband mobile communication, achieves stable operation under severe frequency selective fading environments, giving high quality. The OFDM signal communication system which transmits OFDM signals over the same radio frequency from N transmitting antennas, has an inverse matrix computer for computing an N×N inverse matrix constituted by propagation coefficients for respective propagation paths between each of N transmitting antennas and each of N receiving antennas, and a subcarrier demodulator which separates the signals of the respective propagation paths, based on the obtained inverse matrix.

Wireless systems and interference avoidance

Abstract: Motivated by the emergence of programmable radios, we seek to understand a new class of communication system where pairs of transmitters and receivers can adapt their modulation/demodulation method in the presence of interference to achieve better performance. Using signal to interference ratio as a metric and a general signal space approach, we present a class of iterative distributed algorithms for synchronous systems which results in an ensemble of optimal waveforms for multiple users connected to a common receiver (or colocated independent receivers). That is, the waveform ensemble meets the Welch (1974) bound with equality and, therefore, achieves minimum average interference over the ensemble of signature waveforms. We derive fixed points for a number of scenarios, provide examples, look at ensemble stability under user addition and deletion as well as provide a simplistic comparison to synchronous code-division multiple-access. We close with suggestions for future work.

Chaotic communications with correlator receivers: theory and performance limits

Abstract: This paper provides a review of the principles of chaotic digital communications using correlator receivers. Modulation schemes using one and two chaotic basis functions, as well as coherent and noncoherent correlation receivers, are discussed. The performance of differential chaos shift keying (DCSK) in multipath channels is characterized. Results are presented for DCSK with multiuser capability and multiple bits per symbol.

Coupling circuit arrangement for data communication over power lines

Abstract: A coupling circuit arrangement for data communication over a power line comprises a modulator/demodulator circuit (6) for modulating data signals for transmission over the power line (2,3), and for demodulating signals which have been transmitted over the power line into data signals, a power supply circuit (Vcc2), and isolation means (1) for providing galvanic isolation from the power line. The isolation means comprises light emitting elements and light detecting elements which are arranged between the modulator/demodulator circuit (6) and the power line (2,3). The isolation means may also be used to transmit a digital control signal which indicates the status of the power supply circuit or an over-temperature condition, or which is a transmit enable signal. The digital control signal may be encoded in the analog data signal by a digital shift in the DC bias level or by a complete removal of the DC biasing signal.

Multichannel, multimode docsis headend receiver

Abstract: A multichannel, mixed mode cable modem termination system receiver capable of receiving multiple channels of digital data transmitted on one or more hybrid fiber coaxial cable systems, each the channels being either single mode or mixed-mode. Mixed mode channels are time division multiplexed and have overlapping bandwidth and each sub-channel of a mixed mode channel can have a different center frequency, symbol rate and/or multiplexing type. The receiver is comprised of a plurality of analog front end circuits coupled to the various HFC systems, each selective coupled to any one of a plurality of digital front end receivers. Control circuitry controls these circuits to receive multiple mixed-mode or single mode channels, simultaneously if necessary. An arbiter decides which bursts get processed first in a back end shared demodulator which recovers the data from each burst. The preferred shared demodulator includes an equalizer, predictor and rotational amplifier which processes both TDMA and SCDMA data bursts post despreader to reduce reception data errors.

Optical transmission apparatus

Abstract: In a transmission apparatus 8, modulation sections 201 convert digital data signals into DSL modulated signals, which are thereafter subjected to frequency conversion so as to span respectively different frequency bands. A combination section 207 frequency-division-multiplexes output signals from the modulation sections 201. An optical modulation section 102 converts the frequency-division-multiplexed signal into an optical signal. An optical detection section 104 reconverts the optical signal which has been transmitted over the optical transmission section 103 into an electrical signal. A splitter section 408 demultiplexes the electrical signal. Each of second frequency conversion sections 811 subjects either one of the demultiplexed signals to frequency conversion, and sends a resultant DSL modulated signal onto an electrical transmission section 105. The DSL demodulation section 106 reconverts the DSL modulated signal which has been transmitted over the electrical transmission section 105 into the original digital data signal.

Biosensor apparatus and method with sample type and volume detection

Abstract: A biosensor apparatus and method with sample type and cell volume detection. The apparatus includes a sine wave generator to apply an AC signal to a biosensor cell containing a sample, a current-to-voltage converter, a phase shifter, a square wave generator, a synchronous demodulator, and a low pass filter which yields a signal proportional to the effective capacitance across the biosensor cell, which is proportional to the volume of the sample. In addition, the current-to-voltage converter yields a signal indicative of the type of sample contained within the biosensor cell. The method includes applying a sine wave to the biosensor cell, shifting the phase of the resultant signal, generating a square wave synchronous with the sine wave, demodulating the resultant signal with the square wave, and filtering the demodulated signal to produce a signal proportional to the effective capacitance across the biosensor cell. The biosensor apparatus and method are capable of determining sample type and measuring glucose levels over a wide range of sample volumes.

Bandwidth-efficient wireless network modem

Abstract: Wireless communication network dynamically assigning communicators to allocated channels by considering the interference and noise environment to maximize the number of communicators and effective bandwidth of the channel. The present invention provides a digital wireless modem capable of measuring interference and noise in a channel, signaling the information on a control channel, accepting dynamic channel assignments from a controlling element and demodulating signals in the presence of interference and noise. The modem uses a demodulator (92 and 94) capable of recovering information from data signals in the presence of noise and interference stronger than the primary signal, and there is a controlling element (102) for transmitting noise and interference measurements to a central network controller and a controlling element (105) for determining channel assignments with the central network controller and setting the modem to the correct transmission and reception channel.

Turbo-equalization for multilevel modulation: an efficient low-complexity scheme

Abstract: This paper addresses the problem of iterative equalization and decoding (turbo-equalization) when bit-interleaved multilevel modulations are considered. The goal is to propose an efficient low-complexity solution in this context, where optimal turbo-equalization is totally untractable. Therefore, we generalize reduced-complexity soft-in/soft-out (SISO) equalizers based on the minimum mean square error (MMSE) criterion (originally proposed in a BPSK context) to this particular scheme. Performances are illustrated through simulations. We show the influence of the mapping on the signal-to-noise ratio (SNR) threshold and on asymptotic performances, and link the obtained results to iterative demodulation and decoding on an additive white Gaussian noise (AWGN) channel.

Spectrally efficient noncoherent communication

Abstract: This paper considers noncoherent communication over a frequency-nonselective channel in which the time-varying channel gain is unknown a priori, but is approximately constant over a coherence interval. Unless the coherence interval is large, coherent communication, which requires explicit channel estimation and tracking prior to detection, incurs training overhead which may be excessive, especially for multiple-antenna communication. In contrast, noncoherent detection may be viewed as a generalized likelihood ratio test (GLRT) which jointly estimates the channel and the data, and hence does not require separate training. The main results in this paper are as follows. (1) We develop a "signal space" criterion for signal and code design for noncoherent communication, in terms of the distances of signal points from the decision boundaries. (2) The noncoherent metric thus obtained is used to guide the design of signals for noncoherent communication that are based on amplitude/phase constellations. These are significantly more efficient than conventional differential phase-shift keying (PSK), especially at high signal-to-noise ratio (SNR). Also, known results on the high-SNR performance of multiple-symbol demodulation of differential PSK are easily inferred from the noncoherent metric. (3) The GLRT interpretation is used to obtain near-optimal low-complexity implementations of noncoherent block demodulation. In particular, this gives an implementation of multiple symbol demodulation of differential PSK, which is of linear complexity (in the block length) and whose degradation from the exact, exponential complexity, implementation can be made as small as desired.

Digital, phase-sensitive detection for in situ diode-laser spectroscopy under rapidly changing transmission conditions

Abstract: A new harmonic detection scheme for fully digital, fast-scanning wavelength-modulation spectroscopy (DFS-WMS) is presented. DFS-WMS is specially suited for in situ absorption measurements in combustion environments under fast fluctuating transmission conditions and is demonstrated for the first time by open-path monitoring of ambient oxygen using a distributed-feedback diode laser, which is doubly modulated with a fast linear 1 kHz-scan and a sinusoidal 300 kHz-modulation. After an analog high-pass filter, the detector signal is digitized with a 5 megasample/s 12-bit AD-converter card plugged into a PC and subsequently – unlike standard lock-ins – filtered further by co-adding 100 scans, to generate a narrowband comb filter. All further filtering and the demodulation are performed completely digitally on a PC with the help of discrete Fourier transforms (DFT). Both 1f- and 2f-signals, are simultaneously extracted from the detector signal using one ADC input channel. For the 2f-signal, a linearity of 2% and a minimum detectable absorption of 10-4 could be verified experimentally, with the sensitivity to date being limited only by insufficient gain on the 2f-frequency channel. Using the offset in the 1f signal as a transmission ‘probe’, we could show that the 2f-signal can be transmission-corrected by a simple division by the 1f-background, proving that DFS-WMS provides the possibility of compensating for transmission fluctuations. With the inherent suppression of additive noise, DFS-WMS seems well suited for quantitative in situ absorption spectroscopy in large combustion systems. This assumption is supported by the first measurements of oxygen in a high-pressure combustor at 12 bar.

Receiver window design for multicarrier communication systems

Abstract: Multicarrier modulation formats have been chosen for some wireline and wireless communication systems. These systems use the Fourier transform to convert a convolutive channel into multiple memoryless subchannels, which allows for simple equalization at the receiver. However, because the received signal is windowed in time, noise is spread between subchannels. As a result, narrowband interference sources can degrade the performance over a large number of subchannels. Receiver windowing has been proposed as a computationally efficient technique for reducing noise spreading in multicarrier communication systems. We propose a receiver window design algorithm which minimizes the noise power of the demodulated multicarrier signal. Simulations demonstrate the effectiveness of the windows on a variety of different channels and noise sources.

Integrated beamformer/modem architecture

Abstract: A transceiver employing a steerable phased-array antenna includes a modem architecture in which signals from each antenna element in the array are independently processed down to the individual baseband channel level, and digital beamforming is performed at baseband. The data rate reduction from IF to baseband permits parallel signal data from multiple antenna elements to be time multiplexed and serially processed at acceptable data rates at baseband with minimal modem hardware requirements. Both for transmit signal modulation and received signal demodulation, the computation of carrier tracking, automatic gain control (AGC)/power-control, and beamforming are shared by the same processing circuitry for all channels when performed at baseband. The resulting baseband circuitry is only incrementally larger than that required for carrier tracking and AGC alone, yet accomplishes independent beamforming for each antenna element on each user channel.

Adaptive coding and modulation

Abstract: The present invention provides a unique feedback system in a wireless communication system wherein the transmission channel is always overloaded with data, which is configured and modulated at a select order of modulation. Based on the channel conditions, only a portion of the data can be successfully received. As such, the receiver will attempt to receive the data using demodulation techniques corresponding to the different levels of modulation used to encode the data transmitted. The receiver will determine the data that is recovered, or the highest order of modulation at which the data is recovered, and provide feedback to the transmitter. The transmitter will then retransmit the data that was not properly received. By overloading the channel at all times, the maximum amount of data capable of being transmitted over the channel is optimized without requiring or heavily relying on the receiver feeding back channel condition information to the transmitter.

Wireless communications with an adaptive antenna array

Abstract: Systems and techniques for parallel demodulation and searchning using an adaptive antenna array with a processor configured to co ntrol the adaptive antenna to search for a first signal with the first beam and to receive a second signal for demodulation with a second beam.

Digital broadcast channel reception system and method and portable terminal for use in such system

Abstract: A digital broadcast channel reception system and a portable terminal allow watching a digital broadcast on the terminal. In the examples, a receiver unit for receiving digital broadcasts transmits video data to a display unit, using its TX data manipulator, modulator, TX circuit, and antenna. The TX data manipulator manipulates the output from an OFDM demodulator into data to transmit from the TX circuit and appends error correction codes to the data. The modulator modulates the output from the TX data manipulator. A display unit for digital broadcast display receives video data transmitted from the receiver unit, using its antenna, TX/RX section, and modulator/demodulator. After error correction codes in the received signals are decoded by a TX/RX data manipulator, video data is extracted. After the video data is decoded by a MPEG4 decoder, a picture is output on the display.

Method of and apparatus for detecting impulsive noise, method of operating a demodulator, demodulator and radio receiver

Abstract: In a digital receiver for receiving COFDM modulated television signals or the like, consecutive samples are compared with a detection threshold and the number of samples having amplitudes greater than the threshold is determined. This is compared with a further threshold and, if the number of such samples exceeds the further threshold, affected samples are blanked to zero. Similarly, an automatic gain control loop is disabled when the samples are blanked. A demodulator forms the difference in phase of pilot carriers from symbol to symbol. If the variance of the phase differences exceeds an averaged value, this indicates the presence of impulsive noise and is used to inhibit signal correction techniques within the demodulator. Noise energy is thus reduced and propagation of effects resulting from impulsive noise from symbol to symbol is substantially reduced.

Ka-band direct digital receiver

Abstract: A new direct-conversion wideband (26-28.5 GHz) six-port receiver is proposed for mass-market wireless communications. This six-port receiver is designed to operate without the need for precise power reading and the use of a digital signal processor that is usually required in other receivers. The proposed receiver architecture is chosen to satisfy requirements of hardware receivers used in high-speed QPSK communications. The receiver contains a receiver front-end, QPSK demodulator, and carrier recovery module. A reverse modulation loop was used to provide a rapid carrier recovery. The maximum bit rate is determined solely by the limiting speed of the baseband module. This new hardware receiver is proposed as a robust, rugged, low-cost receiver for use in wide Ka-band wireless mass-market QPSK communications such as local multipoint distribution system services, which is a prime example of communication equipment requiring such receivers. Bit-error-rate results are presented versus the noise and reference signal phase shift.

A sequential Monte Carlo blind receiver for OFDM systems in frequency-selective fading channels

Abstract: We consider the application of the sequential Monte Carlo (SMC) methodology to the problem of blind symbol detection in a wireless orthogonal frequency-division multiplexing (OFDM) system over a frequency-selective fading channel. Bayesian inference of the unknown data symbols in the presence of an unknown multipath fading channel is made only from the observations over one OFDM symbol duration. A novel blind SMC detector built on the techniques of importance sampling and resampling is developed for differentially encoded OFDM systems. The performance of different schemes of delayed-weight estimation methods is studied. Furthermore, being soft-input and soft-output in nature, the proposed SMC detector is employed as the first-stage demodulator in a turbo receiver for a coded OFDM system. Such a turbo receiver successively improves the receiver performance by iteratively exchanging the so-called extrinsic information with the maximum a posteriori (MAP) outer channel decoder. Finally, the performance of the proposed sequential Monte Carlo receiver is demonstrated through computer simulations.

Improved, operationally-passive interferometric demodulation method using 3×3 coupler

Abstract: An improved algorithm for demodulating the phase output of a Mach-Zehnder interferometer that uses a 3×3 coupler is presented Error analysis and experimental data show how a generalised 3×3 coupler description eliminates signal distortion and frequency mixing

Vector network analyzer applique for adaptive communications in wireless networks

Abstract: A test signal generator at a transmitter station and a facsimile generator at a receiver station go through an acquisition and tracking process which aligns the two signals so that a logical processor can compute the frequency transfer function of the entire propagation path for use in an adaptive, concurrently sent communication signal. The frequency transfer function is conveyed back to the transmit end via a control channel permitting an adaptivity function at the transmit end to influence subsequent selection of communication parameters, among which are typically transmitted data rate, selection of modulation, selection of forward error correcting coding, and selection of frequency band for transmission. The same measurement is conveyed to an adaptivity function at the receive end for use in the communications receiver to select demodulator variables such as gain control, and equalization of amplitude and phase, versus frequency. The adaptivity function also permits interspersing of reverse-direction communications over the same frequency bands in a time-share mode between forward-direction and reverse-direction communication with the measurement signals having to be transmitted in only one direction. An alternate embodiment invention of this type is described which is additionally useful for mobile communications channels. Another variation embodiment is described for pure propagation measurements only, absent conveyance of end-user information.

QPSK and 16 QAM self-generating synchronous direct downconversion demodulator

Abstract: A system for recovering and demodulating a carrier includes a carrier recovery loop and a data detector. The carrier recovery loop receives the carrier as an input and produces a recovered carrier at a frequency approximately equal to that of the carrier. The carrier recovery loop includes a downconverting mixer, a ×5 multiplier, a ×4 multiplier, and a phase locked loop. The downconverting mixer receives the carrier input, and the phase locked loop provides a VCO reference frequency through the ×5 multiplier to the downconverting mixer, which provides a frequency shifted signal. The frequency shifted signal is passed through the ×4 multiplier as input to the phase locked loop. The data detector receives the carrier and the recovered carrier as inputs and uses the recovered carrier to demodulate the carrier and detect I channel data and Q channel data.

Design of bi-directional and multi-channel miniaturized telemetry module for wireless endoscopy

Abstract: A bi-directional and multi-channel wireless telemetry capsule, 11 mm in diameter, is presented that can transmit video images from inside the human body and receive a control signal from an external control unit. The proposed telemetry capsule includes transmitting and receiving antennas, a demodulator, decoder, four LEDs, and CMOS image sensor, along with their driving circuits. The receiver demodulates the received signal radiated from the external control unit. Next, the decoder receives the stream of control signals and interprets five of the binary digits as an address code. Thereafter, the remaining signal is interpreted as four bits of binary data. Consequently, the proposed telemetry module can demodulate external signals so as to control the behavior of the camera and four LEDs during the transmission of video images. The proposed telemetry capsule can simultaneously transmit a video signal and receive a control signal determining the behavior of the capsule itself. As a result, the total power consumption of the telemetry capsule can be reduced by turning off the camera power during dead time and separately controlling the LEDs for proper illumination of the intestine.

Cellular radio transmission apparatus and cellular radio transmission method

Abstract: Signals from distributed radio sections (102-1-102-N) are sent to a demodulator (1031) of BTS (103). In the demodulator (1031), maximum ratio combining is performed with respect to each signal after radio reception processing. That is to say, since, in conventional DHO, demodulation processing is performed individually in,each BTS and demodulated data after the demodulation processing is sent to RNC, where selection diversity is performed with the demodulated data, maximum ratio combining cannot be performed during the demodulation processing in BTS. However, the present invention is configured such that a single BTS processes signals received in distributed antennas, so that the demodulator (1031) can perform maximum ratio combining with respect to every signal after radio reception processing, thereby improving the reliability of the demodulated data.

System and method for performing accurate demodulation of turbo-encoded signals via pilot assisted coherent demodulation

Abstract: An efficient telecommunications receiver system for accurately decoding a received composite signal having a data signal component and a pilot signal component includes a first circuit for receiving the composite signal and extracting a pilot signal and a data signal from received composite signal. A second circuit calculates a log-likelihood ratio as a function of a channel estimate based on the pilot signal. A third circuit scales the log-likelihood ratio by a predetermined log-likelihood ratio scaling factor and provides an accurate log-likelihood value in response thereto. A fourth circuit decodes the received composite signal based on the accurate log-likelihood value and the data signal. The third circuit includes a carrier signal-to-interference ratio circuit for computing a first signal-to-interference ratio and a second signal-to-interference ratio based partly on the pilot signal.

Multiuser detection in flat fading non-Gaussian channels

Abstract: This paper deals with the problem of multiuser detection in direct-sequence code-division multiple-access (CDMA) fading channels with impulsive noise. This issue arises in practical situations because in many realistic wireless channels, the ambient channel noise is impulsive, resulting from various natural and man-made impulsive sources. An M-estimator-based structure for noncoherent demodulation of differentially phase-shift keyed (DPSK) signals transmitted simultaneously via a CDMA flat-fading channel and embedded in impulsive noise, is proposed and analyzed. Analytical and numerical results show that, in highly impulsive noise, the performance gain afforded by the proposed multiuser detector can be substantial when compared to the linear decorrelating detector for DPSK, with little attendant increase in algorithmic complexity.

Dual mode phone line networking modem utilizing conventional telephone wiring

Abstract: A networking modem capable of full duplex communication over a telephone line is adapted for use as a component of a computer system. The modem comprises a digital signal processor (DSP) capable of implementing a plurality of digital modulation and demodulation techniques, including pulse position modulation (PPM), quadrature phase shift keying (QPSK), and quadrature amplitude modulation (QAM). The DSP implements a digital phase locked loop (DPLL), including a carrier NCO and a carrier detector to synchronize local demodulation timing to an incoming carrier signal. Available processing options include spectral agility for optimizing channel capacity, symbol shaping to compensate for evolving channel conditions, and echo cancellation. The digital processing provides a flexible, adaptive, programmable, and backward compatible solution to eliminate various problems with prior art systems, including timing inaccuracies, incompatibility with standard modulation techniques, the half duplex limitation, and the susceptibility to noise that increases intersymbol interference and limits throughput.

High-precision laser vibrometers based on digital Doppler-signal processing

Abstract: Recent developments in the field of digital signal processing (DSP) hardware and affordable powerful PC platforms enable the realisation of a new generation of laser-Doppler vibrometers, providing outstanding measurement accuracy and resolution. The paper presents both PC based and DSP based solutions for digital Doppler signal processing, utilized within the latest vibrometer models introduced by Polytec GmbH, Waldbroim. It is shown, that heterodyne interferometer technology in combination with high-speed AID conversion and numerical demodulation methods provides superior accuracy and resolution in a wide amplitude and frequency range. Depending on the particular application, either PC based systems or plug-in DSP decoder modules are the preferred solution. Advantages and tradeoffs of both ways are analysed. In addition to digital decoding technology, the presented systems make use of digital signal transmission via a standard S/P-DIF interface, commonly known from digital-audio equipment. This interface allows distortion-free signal recording on digital media and signal acquisition without expensive A/D boards. Based on the described technology, a primary calibration system for accelerometers has been developed in a cooperation project. The aim of this paper is the demonstration of digital signal processing as a powerful alternative to analog technology, that will advance measurement accuracy of future laser-Doppler vibrometers.