Showing papers on "Demodulation published in 2000"

Unitary space-time modulation for multiple-antenna communications in Rayleigh flat fading

Abstract: Motivated by information-theoretic considerations, we propose a signaling scheme, unitary space-time modulation, for multiple-antenna communication links. This modulation is ideally suited for Rayleigh fast-fading environments, since it does not require the receiver to know or learn the propagation coefficients. Unitary space-time modulation uses constellations of T/spl times/M space-time signals (/spl Phi//sub i/, l=1, ..., L), where T represents the coherence interval during which the fading is approximately constant, and M

Differential space-time modulation

Abstract: Space-time coding and modulation exploit the presence of multiple transmit antennas to improve the performance on multipath radio channels Thus far, most work on space-time coding has assumed that perfect channel estimates are available at the receiver In certain situations, however, it may be difficult or costly to estimate the channel accurately, in which case it is natural to consider the design of modulation techniques that do not require channel estimates at the transmitter or receiver We propose a general approach to differential modulation for multiple transmit antennas based on group codes This approach ran be applied to any number of transmit and receive antennas, and any signal constellation We also derive low-complexity differential receivers, error bounds, and modulator design criteria, which we use to construct optimal differential modulation schemes for two transmit antennas These schemes can be demodulated with or without channel estimates This permits the receiver to exploit channel estimates when they are available The performance degrades by approximately 3 dB when estimates are not available

OFDM blind carrier offset estimation: ESPRIT

Abstract: In orthogonal frequency-division multiplex (OFDM) communications, the loss of orthogonality due to the carrier-frequency offset must be compensated before discrete Fourier transform-based demodulation can be performed. This paper proposes a new carrier offset estimation technique for OFDM communications over a frequency-selective fading channel. We exploit the intrinsic structure information of OFDM signals to derive a carrier offset estimator that offers the accuracy of a super resolution subspace method, ESPRIT.

Variable gain amplifier for low voltage applications

Abstract: An integrated communications system. Comprising a substrate having a receiver disposed on the substrate for converting a received signal to an IF signal. Coupled to a VGA for low voltage applications and coupled to the receiver for processing the IF signal. The VGA includes a bank pair having a first bank of differential pairs of transistors and a second bank of differential pairs of transistors. The bank pair is cross-coupled in parallel, the IF signal is applied to the bank pair decoupled from a control signal used to control transconductance output gain of the bank pair over a range of input voltages. A digital IF demodulator is disposed on the substrate and coupled to the VGA for low voltage applications, for converting the IF signal to a demodulated baseband signal. And a transmitter is disposed on the substrate operating in cooperation with the receiver to establish a two way communications path.

Implanted medical device telemetry using integrated microelectromechanical filtering

Abstract: A telemetry receiver for an implantable medical device such as a cardiac pacemaker has an RF antenna coupled to a telemetry circuit that includes an out-of-band rejection filter comprising a microelectromechanical filter. The telemetry circuit further includes an amplifier coupled to the microelectromechanical filter and a demodulator coupled to the amplifier. The filter, amplifier and demodulator are all fabricated on a common integrated circuit die. A multichannel telemetry receiver for an implantable medical device has a plurality of microelectromechanical bandpass filters defining individual channels. A multiplexing circuit selects the signal of an individual bandpass filter channel for application to a demodulator circuit that recovers programming data from a modulated RF transmission from a programming unit. Identification of a preferred data transmission channel for communication of programming data to the implanted medical device is determined by obtaining samples of the signals being passed by each of a plurality of microelectromechanical bandpass filters that define individual channels and evaluating the samples to determine the noise level for each channel. The implantable medical device may be programmed to receive downlink telemetry communications from a programming unit on the channel identified as being the preferred data transmission channel having the lowest noise level.

Acoustic sensing system for downhole seismic applications utilizing an array of fiber optic sensors

Abstract: A system for sensing subterranean acoustic waves emitted from an acoustic source includes a plurality of laser sources, each emitting light at different frequencies; a plurality of subterranean optical sensors, receiving and altering the light in response to acoustic waves; at least one optical detector, receiving the altered light and outputting an electrical signal; and electronics, receiving the electrical signal and converting it into seismic data format. Light from the optical sources is modulated at a plurality of modulation frequencies. The electronics can demodulate the signal by mixing the signal with periodic waveforms having frequencies corresponding to one and two times the modulation frequencies. The modulation frequencies are selected such that at least one of the second harmonic frequencies associated with the modulation frequencies is interleaved in a non-interfering manner within the corresponding set of first harmonic frequencies, and preferably such that at least one of the first harmonic frequencies is interleaved in a non-interfering manner within the corresponding set of modulation frequencies. The hydrophone for sensing the acoustic signals is able to operate at pressures and temperatures of at least 5,000 psi and 130° C., respectively. The hydrophone may be housed in a cable having a diameter less than about 1.5 inches. The hydrophone's sensor preferably includes a reference mandrel, two sensing mandrels, and a telemetry cam, which are aligned in a coaxial, end-to-end configuration to reduce the profile of the hydrophone. The mandrels have hemispherically-shaped endcaps and are joined by flexible interlinks having grooves for receiving optical fiber.

Analysis of the uplink of an asynchronous multi-user DMT OFDMA system impaired by time offsets, frequency offsets, and multi-path fading

Abstract: We study through analysis the joint effect of time offsets, frequency offsets, and multi-path fading in the uplink of an asynchronous multi-user system for wireless communications deploying discrete multi-tone modulation and demodulation. We derive analytical expressions for the multiple access interference, and we quantify its detrimental effects through the evaluation of both the average SINR, and the symbol-error-rate performance. As a result it is shown that the MAI strongly depends not only on the aforementioned impairments but also on the tone assignment algorithm used to multiplex the users. Based on our analysis, the insertion of appropriate time and frequency guard intervals and the accurate selection of the tone assignment algorithm effectively reduce the MAI, so that a proper trade off with spectral efficiency can be met to optimize system performance.

Radio communication equipment and radio communication method

Abstract: PROBLEM TO BE SOLVED: To provide a radio communication equipment that conducts communication with a communication system corresponding to a change in channel. SOLUTION: A separate section 109 separates an output signal from a demodulation section 108 into received data and an OK signal or an NG signal, provides an output of the received data and an output of the OK signal or the NG signal to a transmission system changeover decision section 110. The transmission system changeover decision section 110 stores the number of times of receiving the OK signal or the NG signal, decides whether or not revising a transmission system depending on the frequency of reception of the OK signal or the NG signal and outputs an instruction as to whether or not the transmission system is to be revised to a transmission system changeover control section 111. The transmission system changeover control section 111 controls a transmission frame generating section 102, a modulation section 103, a transmission wireless section 104 and an antenna multicoupler section 105 to instruct a buffer 101 to output transmission data for re-transmission when the revision of the transmission system is required according to the instruction from the transmission system changeover discrimination section 110. COPYRIGHT: (C)2001,JPO

Blind estimation of the pseudo-random sequence of a direct sequence spread spectrum signal

Abstract: Direct sequence spread spectrum transmissions (DS-SS) are now widely used for secure communications, as well as for multiple access. They have many interesting properties, including low probability of interception. Indeed, DS-SS transmitters use a periodical pseudo-random sequence to modulate the baseband signal before transmission. A receiver which does not know the sequence cannot demodulate the signal. In this paper, we propose a method which can estimate the spreading sequence in a noncooperative context. The method is based on eigenanalysis techniques. The received signal is divided into windows, from which a covariance matrix is computed. We show that the sequence can be reconstructed from the two first eigenvectors of this matrix, and that useful information, such as the desynchronization time, can be extracted from the eigenvalues. Experimental results show that the method can provide a good estimation, even when the received signal is far below the noise level.

Digital IF demodulator for video applications

Abstract: An integrated communications system. A substrate having a receiver disposed on the substrate for converting a received signal to an IF signal, a digital IF demodulator disposed on the substrate and coupled to the receiver for converting the IF signal to a demodulated baseband signal, and a transmitter disposed on the substrate operating in cooperation with the receiver to establish a two way communications path.

A space-time model for frequency nonselective Rayleigh fading channels with applications to space-time modems

Abstract: This paper extends the traditional Clarke/Jakes (1968, 1974) model for a frequency flat fading process in a land mobile radio system to facilitate the examination of coherent space-time demodulation systems. The work develops a space-time correlation function using a ring of scatterers model around the mobile unit. The resulting correlation function permits the investigation of a variety of issues concerning base station configurations in space-time systems. The interrelationship of the fading process between the space and the time domain is explored. A detailed example regarding the effects of antenna separation in a receiver diversity system is considered. A set of design rules for interleaving depth and antenna separation in a space-time modem is presented and quantified.

Wide audio bandwidth transduction method and device

Abstract: The present invention is directed to a communication system wherein bone conducted ultrasonic signals are used as carriers to efficiently produce high fidelity, wide audio bandwidth sound. Exemplary embodiments rely on the use of modulation techniques which can achieve high fidelity audible sound, such as carrier plus single sideband (SSB) modulation. Known non-linearities within the ear itself can be exploited to demodulate the modulated ultrasonic carrier without producing audible sounds at the input to the user's ear. The non-linearities of the ear itself, in conjunction with the human brain's perception of audible frequencies generated in response to modulated ultrasonic stimulation, are relied upon to detect audio information.

Multicomponent AM-FM demodulation via periodicity-based algebraic separation and energy-based demodulation

Abstract: Previously investigated multicomponent AM-FM demodulation techniques either assume that the individual component signals are spectrally isolated from each other or that the components can be isolated by linear time-invariant filtering techniques and, consequently, break down in the case where the components overlap spectrally or when one of the components is stronger than the other. In this paper, we present a nonlinear algorithm for the separation and demodulation of discrete-time multicomponent AM-FM signals. Our approach divides the demodulation problem into two independent tasks: algebraic separation of the components based on periodicity assumptions and then monocomponent demodulation of each component by instantaneously tracking and separating its source energy into its amplitude and frequency parts. The proposed new algorithm avoids the shortcomings of previous approaches and works well for extremely small spectral separations of the components and for a wide range of relative amplitude/power ratios. We present its theoretical analysis and experimental results and outline its application to demodulation of cochannel FM voice signals.

Method and apparatus for complex phase equalization for use in a communication system

Abstract: Method and apparatus for complex phase equalization in a communication system. The method includes receiving and downconverting a two-dimensional communication signal to generate in-phase (I) and quadrature (Q) components that have been phase-rotated by an unknown amount during propagation from a transmitter, and then processing the I and Q signals in a cumulant recovery processing system to obtain phase correction of the I and Q signals prior to demodulation. The final step is demodulating the two-dimensional communication signal. Phase correction is effected without regard to modulation type and independently of the demodulating step.

Demodulation pixels in CCD and CMOS technologies for time-of-flight ranging

Abstract: A new generation of smart pixels, so-called demodulation or lock-in pixels is introduced in this paper. These devices are capable of measuring phase, amplitude and offset of modulated light up to some tens of MHz, making them ideally suited to be used as receivers in 3D time-of-flight (TOF) distance measurement systems. Different architectures of such devices are presented and their specific advantages and disadvantages are discussed. Furthermore, a simple model is introduced giving the shot noise limited range resolution of a range camera working with these demodulation pixels. Finally, a complete TOF range camera based on an array of one of the new lock-in pixels will be described. This TOF- camera uses only standard components and does not need any mechanically scanning parts. With this camera non- cooperative targets can be measured with a few centimeters resolution over a distance of up to 20 meters.

Time-variant distortions in OFDM

Abstract: We analyze the degradation of orthogonal frequency division multiplexing (OFDM) signals from time-variant distortions like carrier and sampling frequency offset, Doppler spread and oscillator phase noise. We propose a novel analytical framework in the discrete-time domain based on the FFT demodulation of a single OFDM symbol and unify previous methods with some new results. Exact definitions of the signal-to-subcarrier-interference ratio (SIR) and the effective signal-to-noise ratio (SNR) are given and evaluated for a HIPERLAN/2 system.

Synchronized modulation/demodulation method and apparatus for frequency division multiplexed spectrophotometric system

Abstract: An improved method and apparatus is disclosed for use in frequency division multiplexed spectrophotometric systems. The invention provides for the modulation of a plurality of light sources at different frequencies and in accordance with a predetermined phase relationship. Light from the sources (12a, 12b) that is transmitted through a tissue under test is detected at a detector (20). A composite signal indicative of the intensity of light received at the detector (20) is demodulated based on the different modulation frequencies and predetermined phase relationship to obtain signal portions corresponding with each of the light sources (12a, 12b). The modulation waveforms used to modulate the light sources (12a, 12b) and corresponding demodulation waveforms used to demultiplex the composite signal are symmetrically timed about a center point for each of the measurement periods. The invention reduces artifacts associated with rising/falling light source amplitude levels, thereby reducing system noise sentivity.

Nonlinear pre-distortion modulator and long loop control

Abstract: Method for predistortion compensation for nonlinear distortion produced by the non-linear power amplifier of the QAM signal at the transmitter side of the direct digital communication channel. The out-of-band signal power is monitored by the existent receiver at the receive side of the direct propagation channel. The nonlinear distortion compensation signal is generated at the receiver/demodulator side of the direct propagation channel and transmitted across the direct propagation channel to an input of a pre-distortion block at the transmitter/modulator side of the direct propagation channel. The nonlinear distortion compensation signal is used to adjust the set of parameters of the pre-distortion block in order to minimize the out-of-band power produced by the non-linear amplifier (NLA).

Single chip cmos transmitter/receiver and method of using same

Abstract: A single chip RF communication system and method is provided including a transmitter and a receiver The RF communication system in accordance with the present invention can include an antenna that receives/transmits RF signals, a PLL that generates multi-phase clock signals having a frequency different from a carrier frequency and a reference signal having the carrier frequency, a demodulation-mixer that mixes the received RF signals with the multi-phase clock signals having the frequency different from the carrier frequency to output signals having a frequency reduced relative to the carrier frequency, two stage amplification that amplifies a selected channel signal to a required dynamic level, and an A/D converting unit for converting the RF signals from the mixing unit into digital signals The two stage amplification can provide the selected channel signal with sufficient gain, even when an adjacent channel signal is output by the demodulation mixer with greater amplitude or power

A 10.7 MHz IF-to-baseband /spl Sigma//spl Delta/ A/D conversion system for AM/FM radio receivers

Abstract: This analog-to-digital converter digitizes a radio signal at a 10.7 MHz intermediate frequency (IF) using integrated quadrature mixing and /spl Sigma//spl Delta/ modulation. The paper shows a block diagram of a highly-integrated AM/FM radio receiver. The IF A/D conversion and digital filtering, demodulation and further signal processing can be integrated on a single CMOS IC. The radio front-end mixes both AM and FM signals to 10.7 MHz IF, so that the A/D conversion is shared. A single channel filter is used, selecting one 200 kHz FM channel. For AM, over 20 channels pass through this filter, resulting in high dynamic range of the IF signal. When the radio is tuned to a weak AM radio station, strong neighboring channels should not introduce disturbance of the weak signal. This multi-channel aspect for AM puts severe requirements on the automatic gain control (AGC) amplifier and A/D converter in terms of noise, intermodulation and crossmodulation distortion.

Optimum Semicodeless Carrier-Phase Tracking of L2

Abstract: reconstruction of the L2 carrier phase. Most receivers utilize a hybrid technique. The L1 carrier is recovered after C/A code correlation, and the L2 carrier is reconstructed without knowledge of the Y or W codes. There are four known techniques that have been published in the past: squaring, cross-correlation, P-code aided L2 squaring, and Z-tracking. Because of the lack of knowledge of the W code, these techniques perform significantly worse (14 to 31 dB at a typical L2 C/N o) than an ideal phase lock loop. This paper presents five additional techniques that can be used to reconstruct the L2 carrier without knowledge of the W-code. These five techniques are: 1) Code-aided L2 Costas loop with W-Bit integrate and dump arm filtering; 2) P-code aided L1, L2 Cross Correlation; 3) Soft decision Z-tracking; 4) Optimum L2 demodulation motivated by maximum a posteriori (MAP) estimation theory; and 5) Linear approximation of the MAP approach. The first three techniques are modification of existing techniques, with improved performance. Techniques 4 and 5 are optimum and near optimum techniques based on statistical estimation theory. A detailed derivation of the MAP approach is given. Also presented is a detailed comparison of the squaring losses of the various L2 recovery techniques as functions of received L2 C/No's. The performance of the MAP technique and its linear approximation is shown to be at least 3 dB better than all techniques published previously. In addition, it is analytically shown that the MAP approach provides the minimum squaring loss that is possible, and represents an upper bound of achievable performance for L2 carrier recovery without knowledge of the W-code. Computer simulation results agree with theory.

High-speed data services using multiple transmit antennas

Abstract: High-speed wireless data systems and methods are described for simultaneously supporting multiple data users, including flexible mixed-traffic services, using an illustrative CDMA architecture. Embodiments are compatible with current and third generation CDMA systems, while achieving spectral efficiencies that are in some cases an order of magnitude or more higher. Embodiments advantageously employ multiple antennas at the transmitter and receiver and code spreading to realize multiple access systems. Some illustrative receiver embodiments advantageously employ a decorrelating detector, while other features a decorrelating decision-feedback detector. In typical operation, each of a plurality of high-speed data streams directed to respective data users is demultiplexed into multiple (G⊃1) lower rate substreams, which are modulated by a CDMA spreading code and transmitted from M antennas at a base station. A receiver employs P antennas and multi-user detection to demodulate the G data substreams of its associated user. Performance measures for a variety of illustrative transmission and receiver configurations are derived using novel techniques for calculating system level capacities and spectral efficiencies (measured in bits per second per Hertz per sector). System design and configuration tradeoffs are readily made based on such performance determinations.

Method and apparatus for a CDMA cellular radio transmission system

Abstract: A method of transmitting/receiving signals in a CDMA cellular radio transmission system comprising modulating a signal source with a channelization code having a length corresponding to a spreading factor to form a signal intended for transmission over a radio link According to the invention, the spreading factor is adapted for use in said modulation step When receiving the modulated signals, the spreading factor used in an adaptive manner during modulation is determined and employed during demodulation Further, the invention relates to a corresponding transmitter and receiver embodied preferably as a base station and a mobile station, respectively

Closed-loop magnetoresistive current sensor system having active offset nulling

Abstract: A magnetoresistive sensor system having resistive elements changing in ohmic value in the presence of a magnetic field of a current being measured. The variant values of the elements are amplified by some electronics that inherently add offset to the resultant values. The elements themselves also add an offset. The output of the electronics is modulated and then buffered as an output. This output is demodulated and integrated. The resultant signal is fed back to the input of the electronics to null out the offsets. The output of the buffer also goes to an inductive coil that is magnetically coupled to the resistive elements to null out the magnetic field from the current being measured. The buffer output indicates the magnitude of the current being measured. An oscillator outputs a signal to actuate the modulator and the demodulator. The oscillator signal also goes to a set/reset circuit for setting and resetting the resistive elements of the magnetoresistive sensor.

Synchronization in software radios. Carrier and timing recovery using FPGAs

Abstract: Software defined radios (SDR) are highly configurable hardware platforms that provide the technology for realizing the rapidly expanding third (and future) generation digital wireless communication infrastructure. Many sophisticated signal processing tasks are performed in a SDR, including advanced compression algorithms, power control, channel estimation, equalization, forward error control and protocol management. While there is a plethora of silicon alternatives available for implementing the various functions in a SDR, field programmable gate arrays (FPGAs) are an attractive option for many of these tasks for reasons of performance, power consumption and configurability. Amongst the more complex tasks performed in a high data rate wireless system is synchronization. This paper is about carrier and timing synchronization in SDRs using FPGA based signal processors. We describe and examine a QPSK Costas loop for performing coherent demodulation, and report on the implications of an FPGA mechanization. Symbol timing recovery is addressed using a differential matched filter control system. A tutorial style approach is adopted to describe the operation of the timing recovery loop and considerations for FPGA implementation are outlined.

Amplitude and phase estimation method in a wireless communication system

Abstract: Apparatuses for a transmitter and a receiver (202) which enhance the performance of a system coherent demodulation by utilizing non-pilot sub-channels to enhance the accuracy of estimates of amplitude and phase noise inherent in the transmission channel. This enhancement is accomplished by utilizing the corrected received data on a fundamental channel to enhance a pilot channel estimate, which is subsequently utilized by a dot product module in demodulating a supplementary data channel.

OFDM packet communication receiver system

Abstract: A preamble for synchronization, or a reference timing for operation of an OFDM packet communication receiver system is detected finely even under environment of large waveform distortion due to thermal noise and/or multi-path propagation, and/or large carrier frequency offset between a transmit side and a receiver side. A correlator (1) detects a pattern of a short preamble (t1 - t10) in a preamble for synchronization. An output of the correlator (1) is applied to a complex filter (7) which separates a short preamble having a predetermined repetition period from uniformly distributed noise. A scalar filter (9) integrates some period of short preambles which have distributed-delay by multi-path propagation as if a single short preamble with no delay were received for determining a reference timing. When a correlator output exceeds a predetermined threshold level a plurality of times far every repetition periods (T) of a short preamble, and an output of the correlator after time (T) from the last short preamble is decreased a predetermined ratio as compared with that of the last short preamble, it is determined that a preamble for synchronization is detected. Carrier frequency offset compensation is carried out either for each short preamble during reception of a short preamble, or based upon the last received short preamble during reception of an OFDM symbol after the last short preamble. As a preamble for synchronization is detected accurately, a guard interval of each OFDM symbol is removed accurately, or an FFT window is defined accurately, so that a demodulation is possible in spite of noise and/or interference.

Performance Comparison of FH/MC DS-CDMA with Single- and Multi-Carrier DS-CDMA

Abstract: In this contribution we review the slow frequency hopping multicarrier direct-sequence code-division multiple-access (SFH/MC DS-CDMA). Then, the system's performance is ecalated and compared to that of the conventional single-carrier (SC) DS-CDMA and MC DS-CDMA under the assumptions of constant system bandwidth and of constant transmitted signal power. Both random and 'uni$ormlFH are considered and their advantages as well as disadvantages are investigated. We assume that the system operates in a multipath Nakagami-m fading environment and a maximum ratio combining (URC) assisted RAKE receiver is used for demodulation.

On the performance of iterative noncoherent detection of coded M-PSK signals

Abstract: Differential encoding is often used in conjunction with noncoherent demodulation to overcome carrier phase synchronization problems in communication systems employing M-ary phase-shift keying (M-PSK) It is generally acknowledged that differential encoding leads to a degradation in performance over absolutely encoded M-PSK systems with perfect carrier synchronization In this paper, we show that when differential encoding is combined with convolutional encoding and interleaving, this degradation does not necessarily occur We propose a novel noncoherent receiver for differentially encoded M-PSK signals that is capable of significantly outperforming optimal coherent receivers for absolutely encoded M-PSK using the same convolutional code This receiver uses an iterative decoding technique and is based on a multiple differential detector structure to overcome the effect of the carrier phase error In addition, to better illustrate the benefits of the powerful combination of convolutional encoding, interleaving, and differential encoding, we also present an iterative coherent receiver for differentially encoded M-PSK

Device for sending and receiving data through power distribution transformers

Abstract: A powerline communication system including a transmitter having a pair of terminals for connection to the power lines. The transmitter comprises a carrier frequency generator for generating a carrier frequency modulated by the data signal and a switching circuit connected to the carrier frequency generator for being switched by the carrier frequency generator for generating a carrier signal having the carrier frequency. The switching circuit is connected to the terminals for providing the generated carrier signal thereto. The switching circuit comprises at least one storage means for storing energy when generating a portion of a cycle of the carrier signal and providing the stored energy when generating another portion of the cycle of the carrier signal. The system also comprises a receiver coupled to the power lines. The receiver includes a filter means for filtering the carrier signal from the power line signal and a demodulator connected to the filter means for extracting the data signal from the carrier signal. Both the transmitter and receiver may utilize a digital algorithm in a computing device to synchronize the carrier signal to the power line frequency to adaptively track changes in the power line frequency to minimize interference with power line harmonics and provide accurate frequency alignment between the transmitter and receiver.