Showing papers on "Demodulation published in 2009"

Multiple Access with Low-Density Signatures

Abstract: We present sets of spreading sequences that are specifically designed to suit a belief-propagation multiuser detection structure, recently presented for overloaded system scenarios. On one hand, our sequences are of the low-density type; on the other their distance spectrum properties ensure good performance in AWGN channels. Simulations results for raw and coded bit-error probability indicate that significant performance gain is achieved over random sequences and that the loss compared to the single-user bound can be kept small.

A demodulation method based on improved local mean decomposition and its application in rub-impact fault diagnosis

Abstract: Demodulation is an available method for mechanical diagnoses, and a demodulation technique based on improved local mean decomposition (LMD) is proposed in this paper. A method of boundary process and a strategy for determining the step size of moving average are presented to improve the LMD algorithm. Instantaneous amplitude (IA) and instantaneous frequency (IF) of the signal can be computed independently of Hilbert transform using the improved LMD method. A well-constructed description of the derived IA and IF is given in the form of instantaneous time–frequency spectrum (ITFS) which preserves both the time and frequency information simultaneously. Results of three synthetic signals indicate that this proposed method is the best demodulation approach to extracting the all-round carrier and modulated components as well as the accurate IF, compared with Hilbert–Huang transform and stationary wavelet transform. The validity of the technique is then demonstrated on a real rotor system of a gas turbine with rub-impact fault. Due to the opposite friction during operation, the transient fluctuations of the IF of the fundamental harmonic component are successfully identified in the ITFS. In addition, we find that the proposed technique is more effective and sensitive than other methods in detecting sub-harmonics and FM components contained in the rub-impact signals. Thus the present method is powerful in the analysis of modulated signals and is an effective tool for the detection of rub-impact faults.

Designing Time-Hopping Ultrawide Bandwidth Receivers for Multiuser Interference Environments

Abstract: The multiple-user interference (MUI) in time-hopped impulse-radio ultrawide bandwidth (UWB) systems is impulse-like and poorly approximated by a Gaussian distribution. Therefore, conventional matched filter receiver designs, which are optimal for Gaussian noise, are not fully efficient for UWB applications. Several alternative distributions for approximating the MUI process and the MUI-plus-noise process in UWB systems are motivated and compared. These distributions have in common that they are more impulsive than the Gaussian approximation, with a greater area in the tails of the probability density function (pdf) compared to a Gaussian pdf. The improved MUI and MUI-plus-noise models are utilized to derive new receiver designs for UWB applications, which are shown to be superior to the conventional matched filter receiver. Multipath propagation is abundant in UWB channels and is exploited by a Rake receiver. A Rake receiver uses multiple fingers to comb the multipath rays with a conventional matched filter implemented in each finger. Rake structures utilizing the new receiver designs that are suitable for reception of UWB signals in multipath fading channels are provided. An optimal performance benchmark, based on an accurate theoretical model for the interference that fully explains the features of the MUI pdf, is also presented. Analysis and simulation results are shown for the novel receivers, which demonstrate that the new designs have superior performance compared to the conventional linear receiver when MUI is significant. Several adaptive receivers are shown to always match or exceed the performance of the conventional linear receiver in all MUI-plus-noise environments. Parameter estimation for the new receivers also is discussed.

Phase compensation for multi-stimulus controller

Abstract: Determining a compensated phase matrix for a multi-stimulus demodulation process is provided. A first drive line of a multi-stimulus sensing system is selected, and a stimulation signal is transmitted on the selected drive line. A channel gain resulting from the stimulation signal is measured from a received sense signal resulting from the stimulation signal. The measured channel gain is compared with a known channel gain to obtain an individual phase compensation for the selected drive line. A compensated phase matrix is formed of the individual phase compensation values for multiple drive lines.

Communication network system, and transmission/reception apparatus, method and integrated circuit for use therein

Abstract: A communication network system sets communication parameters which enable an operation under a maximum possible communication rate in a situation where a transmission path has cyclic noise/impedance fluctuations. A transmission/reception apparatus 100 transmits training packets for checking the state of the power line at two distinct points in time. A transmission/reception apparatus analyzes SNR at each carrier frequency, and stores an SNR evaluation result. The transmission/reception apparatus compares two SNR evaluation results which are obtained through two instances of a channel estimation algorithm, selects an SNR evaluation result which dictates a faster PHY rate, and transmits it to the transmission/reception apparatus. The transmission/reception apparatus changes modulation/demodulation rules based on the received SNR analytical result.

Methods and systems for transmission of multiple modulated signals over wireless networks

Abstract: Receiver network for receiving a first filtered modulated transmitted signal in a first RF band and a second modulated transmitted signal in a second RF band and for providing received signals to one or more demodulators. A demodulator and baseband filter for demodulating and filtering the first filtered modulated received signal and for providing filtered demodulated baseband signal by a baseband filter mismatched to the filter of the first filtered modulated transmitted signal and demodulating the second modulated signal providing a demodulated baseband signal and a selector for selecting either the first or the second demodulated baseband signal. A receiver and demodulation system receiving a first TDMA modulated signal having a first bit rate and for receiving a second modulated signal having a second bit rate and for providing the received signals to a one or more demodulators and for providing cross-correlated demodulated in-phase and quadrature-phase baseband signals and demodulating the second bit rate modulated signal and providing a demodulated baseband signal.

Near field rf communicators

Abstract: A near field RF communicator has an inductive coupler (102) to couple inductively to an H field of an RF signal from another near field RF communicator in near field range to provide a received signal, a demodulator (300) coupled to extract any modulation from a source signal representing a received RF signal to provide an extracted modulation signal; and a controller (107) coupled to receive an extracted modulation signal from the demodulator. The demodulator (300) has a sampler (400) to sample the source signal in sampling periods and to compare signal samples with at least one of other signal samples and a clock or reference signal to remove or reject the carrier of the received RF signal and to extract the modulation.

Digital Coherent Receiver for Phase-Modulated Radio-Over-Fiber Optical Links

Abstract: A novel digital signal processing-based coherent receiver for phase-modulated radio-over-fiber (RoF) optical links is presented and demonstrated experimentally. Error-free demodulation of 50-Mbaud binary phase-shift keying (BPSK) and quadrature phase-shift keying data signal modulated on a 5-GHz radio-frequency (RF) carrier is experimentally demonstrated using the proposed digital coherent receiver. Additionally, a wavelength- division-multiplexing (WDM) phase-modulated RoF optical link is experimentally demonstrated. A 3times50 Mb/s WDM transmission of a BPSK modulated 5-GHz RF carrier is achieved over 25 km for the WDM channel spacing of 12.5 and 25 GHz, respectively.

Frequency guided methods for demodulation of a single fringe pattern

Abstract: Phase demodulation from a single fringe pattern is a challenging task but of interest. A frequency-guided regularized phase tracker and a frequency-guided sequential demodulation method with Levenberg-Marquardt optimization are proposed to demodulate a single fringe pattern. Demodulation path guided by the local frequency from the highest to the lowest is applied in both methods. Since critical points have low local frequency values, they are processed last so that the spurious sign problem caused by these points is avoided. These two methods can be considered as alternatives to the effective fringe follower regularized phase tracker. Demodulation results from one computer-simulated and two experimental fringe patterns using the proposed methods will be demonstrated.

Time-Frequency Coherent Modulation Filtering of Nonstationary Signals

Abstract: Modulation filtering is a class of techniques for filtering slowly-varying modulation envelopes of frequency subbands of a signal, ideally without affecting the subband signal's temporal fine-structure. Coherent modulation filtering is a potentially more effective type of such techniques where, via an explicit product model, subband envelopes are determined from demodulation of the subband signal with a coherently detected subband carrier. In this paper we propose a coherent modulation filtering technique based on detecting the instantaneous frequency of a subband from its time-frequency representation. We devise theory to show that coherent modulation filtering imposes a new bandlimiting constraint on the product of the modulator and carrier as well as the ability to recover arbitrarily chosen envelopes and carriers from their modulation product. We then formally show that a carrier estimate based on the time-varying spectral center-of-gravity satisfies the bandlimiting condition. This bandwidth constraint leads to effective and artifact-free modulation filters, offering new approaches for potential signal modification. However, the spectral center-of-gravity does not, in general, satisfy the condition of arbitrary carrier recovery. Finally, the results from modulation-filtering a speech signal are then used to validate the theory.

Cardiac stimulation control and communication system

Abstract: Cardiac stimulation control and communication system, including a pacemaker, having a processor for processing input signals to and/or from one or more electrodes located in a heart. A signal processing network for receiving input signals and for providing a Time Division Multiple Access (TDMA), a filtered signal, spread spectrum signal and/or Orthogonal Frequency Division Multiplex (OFDM) signal to a selector for selection and transmission. In-phase and quadrature-phase cross-correlated spread spectrum signals are provided to a modulator for modulation and transmission of signals received from one or more electrodes or probes or sensors used by a patient. An implantable cardiac stimulation device and a telemetry transmitter and telemetry wired or wireless receiver, for transmission and reception of wireless and or wired signals, wherein said telemetry signals are for monitoring and/or controlling the implantable cardiac stimulation device. A pacemaker, receiver and demodulator for receiving and demodulating a Global Positioning System (GPS) receiver for receiving location finder signals or a receiver and demodulator for receiving and demodulating other than GPS signals and for providing location finder signals and for connecting said location finder signals to a transmitter for transmitting said location finder signals. A Time Division Multiple Access (TDMA) signal is provided to a non-quadrature modulator for non-quadrature modulation of TDMA signal and a filtered signal is processed into a cross-correlated spread spectrum in-phase and quadrature-phase filtered signal and provided to a quadrature modulator for quadrature modulation of said cross-correlated spread spectrum filtered signal. The transmitted signals are received and used by a nurse or other health professionals.

Coded PPM and Multipulse PPM and Iterative Detection for Free-Space Optical Links

Abstract: Signal modulation has an important impact on the system performance in optical communication. Two attractive modulation schemes are pulse position modulation (PPM) and multipulse PPM (MPPM), which have the advantage of average energy efficiency and bandwidth efficiency, respectively. An important practical issue is to employ an efficient channel coding of reasonable (decoding) complexity adapted to these modulations. In this view, we consider the use of a classic binary convolutional code together with iterative soft demodulation and channel decoding at the receiver. In particular, we discuss the impact of bit-symbol mapping on the iterative receiver performance and provide design rules for optimal mapping in the case of MPPM.

Decomposition of Vibration Signals into Deterministic and Nondeterministic Components and its Capabilities of Fault Detection and Identification

Abstract: The paper investigates the possibility of decomposing vibration signals into deterministic and nondeterministic parts, based on the Wold theorem. A short description of the theory of adaptive filters is presented. When an adaptive filter uses the delayed version of the input signal as the reference signal, it is possible to divide the signal into a deterministic (gear and shaft related) part and a nondeterministic (noise and rolling bearings) part. The idea of the self-adaptive filter (in the literature referred to as SANC or ALE) is presented and its most important features are discussed. The flowchart of the Matlab-based SANC algorithm is also presented. In practice, bearing fault signals are in fact nondeterministic components, due to a little jitter in their fundamental period. This phenomenon is illustrated using a simple example. The paper proposes a simulation of a signal containing deterministic and nondeterministic components. The self-adaptive filter is then applied-first to the simulated data. Next, the filter is applied to a real vibration signal from a wind turbine with an outer race fault. The necessity of resampling the real signal is discussed. The signal from an actual source has a more complex structure and contains a significant noise component, which requires additional demodulation of the decomposed signal. For both types of signals the proposed SANC filter shows a very good ability to decompose the signal.

Method of estimating fading coefficients of channels and of receiving symbols and relative single or multi-antenna receiver and transmitter

Abstract: The method is for estimating the fading coefficients of a plurality of transmission channels on which signals to be sent, generated as a function of a sequence of symbols, are transmitted according to a particular modulation, e.g. AM-PSK modulation. The fading coefficients are estimated by using estimations of the transmitted symbols obtained in advance, thus obtaining DC components of the received signal by coherent demodulation locked to the phases of the transmitted AM-PSK signals, and processing these DC components. The method may not require the choice of a stochastic distribution model of the channel fading, thus it remains efficient even when the channel characteristics vary significantly. Moreover, the method works correctly even if the received stream is disturbed by inter-symbolic interference (ISI) and/or by multi-path fading.

Linearization of Phase-Modulated Analog Optical Links Employing Interferometric Demodulation

Abstract: We present a linearized phase-modulated analog photonic link that utilizes parallel interferometric demodulation to suppress the third-order intermodulation distortion present in the link. By utilizing two parallel interferometers with different differential delays, we are able to balance the third-order distortion in the output photocurrent and achieve a fifth-order limited link response. We demonstrate shot noise-limited spurious-free dynamic ranges of ~ 130 dB (1-Hz bandwidth) at ~ 1 GHz for a total DC photocurrent Idc~ 8 mA and ~ 131 dB (1-Hz bandwidth) at ~ 5 GHz for a total DC photocurrent Idc ~ 7 mA . These results represent a nearly two order-of-magnitude improvement in dynamic range over conventional intensity- or phase-modulated analog photonic links for a fixed received photocurrent.

Quantization for soft-output demodulators in bit-interleaved coded modulation systems

Abstract: We study quantization of log-likelihood ratios (LLR) in bit-interleaved coded modulation (BICM) systems in terms of an equivalent discrete channel. We propose to design the quantizer such that the quantizer outputs become equiprobable. We investigate semi-analytically and numerically the ergodic and outage capacity over single- and multiple-antenna channels for different quantizers. Finally, we show bit error rate simulations for BICM systems with LLR quantization using a rate 1/2 low-density parity-check code.

A Novel Method of Distance Measurement Based on Pulse Position Modulation and Synchronization of Chaotic Signals Using Ultrasonic Radar Systems

Abstract: This paper deals with a novel method of transmission and receipt of a signal based on both the property of two chaotic systems generating the same chaotic signal when they are synchronized and the property of pulse position modulation (PPM) to be insensitive to the distortions of the transmission channel. The method is discussed in the context of ultrasonic radar systems, in which the transmitter and receiver, which consist of ultrasonic sensors, are near each other, and the received signal consists of the transmitted signal reflected by an obstacle. A reference sinusoidal signal is superimposed to a chaotic signal generated by a master chaotic system, and the whole signal is modulated according to the PPM method and transmitted by the sensor. The received signal is demodulated, and the demodulated signal forces a slave chaotic system to generate the chaotic signal embedded in it, which allows recovery of the sinusoidal signal by subtracting this chaotic signal from the demodulated echo. The difference of the phases of the reference sinusoidal signal and the recovered sinusoidal signal allows computation of the time of flight of the signal and, consequently, the distance of the radar system from the obstacle. The novel method is illustrated and tested by both simulation and experiments. The interference problem between the considered radar system and other radar systems ( crosstalk) is also addressed, and a solution is proposed to avoid it.

A Novel Interface for Eddy Current Displacement Sensors

Abstract: In this paper, we propose a novel interface concept for eddy current displacement sensors. A measurement method and a new front-end circuit are also proposed. The front-end circuit demonstrates excellent thermal stability, high resolution, and low-power consumption. The proposed idea is analytically investigated. The demodulation principle, as well as the interface implementation, is also addressed. This interface is being introduced for measuring submicrometer displacements in medium- to high-resolution applications. The interface system consumes less than 12 mW and has an extremely low thermal drift. The interface circuit will be implemented as a system-in-a-package (SIP). The full-scale range of displacement is 1 mm with 50-kHz signal bandwidth and 11-bit resolution (less than 500 nm). The signal conditioning circuit utilizes a standard 0.35- mum complementary metal-oxide semiconductor (CMOS) technology. Simulation results, which were achieved on the basis of experimental results of testing a prototype coil, also confirm the high performance of the interface system, as expected from analytical results. Compared with previous reports, this low-power interface system demonstrates a much lower temperature drift.

Universal demodulation and modulation for data communication in wireless power transfer

Abstract: The present invention provides a universal demodulation circuit, a load modulation circuit and associated method, and an associated power transfer system, all suitable for use in wireless power transfer. A power receiver with signal strength detection is also provided. Modulation of the impedance of the demodulation circuit is determinable by detecting the amplitudes of a first and a second electrical parameter, thereby demodulating data communicated by modulation of the impedance of the demodulation circuit. The modulation circuit has a communication modulator to modulate the impedance of the modulation circuit, to a predetermined minimum modulation depth, thereby to communicate data.

Low-complexity linear frequency domain equalization for continuous phase modulation

Abstract: In this paper, we develop a new low-complexity linear frequency domain equalization (FDE) approach for continuous phase modulated (CPM) signals. As a CPM signal is highly correlated, calculating a linear minimum mean square error (MMSE) channel equalizer requires the inversion of a nondiagonal matrix, even in the frequency domain. In order to regain the FDE advantage of reduced computational complexity, we show that this matrix can be approximated by a block-diagonal matrix without performance loss. Moreover, our MMSE equalizer can be simplified to a low-complexity zero-forcing equalizer. The proposed techniques can be applied to any CPM scheme. To support this theory we present a new polyphase matrix model, valid for any block-based CPM system. Simulation results in a 60 GHz environment show that our reduced-complexity MMSE equalizer significantly outperforms the state of the art linear MMSE receiver for large modulation indices, while it performs only slightly worse for small ones.

Optical Differential-Phase-Shift-Keying Demodulation Using a Silicon Microring Resonator

Abstract: We have for the first time experimentally demonstrated an ultrasmall, low power penalty, and robust 10 - Gb/s differential-phase-shift-keying demodulator using a silicon-based microring resonator. The microring resonator is compatible with a wide range of signal bit rates. In optical transmission measurements with 11.6-km nonzero dispersion-shifted fiber, the microring resonator demodulator had comparative power penalty compared with a Mach-Zehnder delay interferometer both in single ended detection. Error-free detection was achieved.

A Two-Stage Capacity-Achieving Demodulation/Decoding Method for Random Matrix Channels

Abstract: Iterative processing for linear matrix channels, aka turbo equalization, turbo demodulation, or turbo code-division multiple access (CDMA), has traditionally been addressed as the concatenation of conventional error control codes with the linear (matrix) channel. However, in several situations, such as CDMA, multiple-input-multiple-output (MIMO) channels, orthogonal frequency-division multiplexing (OFDM), and intersymbol-interference (ISI) channels, the channel itself either contains inherent signal redundancy or such redundancy can readily be introduced at the transmitter. For such systems, iterative demodulation of the linear channel exploiting this redundancy using simple iterative cancellation demodulators, followed by conventional feedforward error control decoding, provides a low-complexity, but extremely efficient decoding alternative. This two-stage demodulator/decoder outperforms more complex turbo CDMA methods for equal power modes (users). Furthermore, it is shown that arbitrary numbers of modes can be supported if an unequal power distribution is adopted. These power distributions are nested, which means that additional modes can be added without disturbing an existing mode population. The main result shows that these nested power distributions enable the two-stage receiver to approach the Shannon capacity of the channel to within less than one bit for any signal-to-noise ratio (SNR).

Fully Digital BPSK Demodulator and Multilevel LSK Back Telemetry for Biomedical Implant Transceivers

Abstract: A novel fully digital binary-phase-shift-keying (BPSK) transceiver for forward data telemetry and a multilevel load-shift-keying (LSK) transceiver for passive back telemetry are implemented. The digital architecture for the BPSK demodulator allows for much less power consumption compared with prior art. The basic premise of the demodulation is to regenerate the incoming BPSK signal using a digital phase-locked loop. We demonstrate the silicon realization of the BPSK demodulator operating at 13.56 MHz in a 0.5-mum complementary metal-oxide-semiconductor process with power consumption of 2.3 mW. The silicon area is 536 times 546 mum2. A novel multilevel LSK for passive back telemetry is implemented, and it works by modulating the load impedance at the implant to create distinct reflections at the primary coil of the reader. The reflections at the reader are decoded for data information using a discrete realization of highly sensitive LSK receiver. The simulation and measurement results indicate 2times improvement in data rate compared with conventional bilevel back telemetry. This brief also shows the implementation of a forward BPSK modulator based on a class-E power amplifier to complete a full biomedical implant transceiver implementation.

Block-Wise Estimation of and Compensation for I/Q Imbalance in Direct-Conversion Transmitters

Abstract: This correspondence proposes a new technique for accurate estimation and compensation for I/Q imbalance in modulators and demodulators used in direct-conversion radio transmitters. This technique uses the actual in-phase (I) and quadrature (Q) components of the modulated signals at the input and output of the transmitter-under-test for adaptive determination of the modulator and demodulator complex gain imbalances. The accuracy of the new algorithm is carefully assessed and compared to earlier works. The robustness of the algorithm to a number of common practical implementation issues (group delay, DC offset, propagation delay) are also discussed and demonstrated.

A method and apparatus for symbol detection via reduced complexity sequence estimation processing

Abstract: Teachings presented herein offer the performance advantages of sequence estimation for received signal symbol detection, while simultaneously providing potentially significant reductions in computational overhead. Initial demodulation of a received signal (12) identifies a reduced number of candidate symbol values (24) for all or a subset of a sequence (14) of symbols (16) represented in the received signal (12). A sequence estimation process, e.g., an MLSE process, constrains its state spaces (62-1, 62-2, 62-3) to the reduced number of candidate symbols values (24), rather than considering all possible symbol values.

Extraction of tacho information from a vibration signal for improved synchronous averaging

Abstract: Time synchronous averaging (TSA) is a procedure that allows the extraction of a deterministic component from a vibration signal. TSA requires a constant frequency deterministic component. Practically, a vibration signal from rotating machinery contains small frequency variations, even when operating at nominally constant speed. To remove these variations, the signal is order-tracked with respect to the deterministic component. This is normally accomplished using a reference signal from a tachometer directly coupled to the rotating shaft of interest. When the tachometer cannot be directly coupled to the shaft of interest, alternative methods are required to generate a reference signal. A case presented here is for the high pressure shaft (HPS) of a gas turbine engine, where the tachometer is coupled to an auxiliary shaft via a gearbox, with unknown exact gear ratio. This paper proposes two approaches to generate the reference signal for order-tracking. The first is to accurately estimate the gear ratio between the auxiliary shaft and the HPS, which will then be combined with the tachometer to produce a suitable reference signal. The second approach extracts a reference signal directly from the vibration signal using phase demodulation. TSA results derived using both methods are compared to evaluate their effectiveness.

A Blind $I/Q$ Imbalance Compensation Technique for Direct-Conversion Digital Radio Transceivers

Abstract: Although the quadrature mixing radio front-end offers an attractive way to perform frequency translation, its image-rejection capability is severely affected by the gain and phase imbalances (I/Q imbalances) between its two analog signal paths. Digital signal processing techniques have widely been proposed to compensate for these mixer imperfections. Of these techniques, the class of blind compensation techniques seems very attractive since no test signals are required. This paper presents a novel I/Q imbalance extraction technique that uses a Cholesky decomposition of the received signal's covariance matrix to extract the exact imbalances of the front-end. An analysis is also presented on extracting and separating the imbalances of a cascaded imbalanced modulator and demodulator. Both a block-based and an adaptive variant of the technique are proposed, and a performance evaluation over multipath channels is presented.