Showing papers on "Demodulation published in 1993"

Chaos shift keying: modulation and demodulation of a chaotic carrier using self-synchronizing Chua's circuits

Abstract: Describes a technique for transmitting digital information using a chaotic carrier. Each symbol to be transmitted is coded as an attractor in Chua's circuit. The symbols are detected at the receiver by cascaded self-synchronizing Chua's circuit subsystems. A proof of the synchronization effect is demonstrated using weak assumptions on the statistical behavior of the chaotic carrier to be transmitted. Furthermore a bound for the average time of synchronization is given. Results of both practical experimentation and simulations are presented which verify the approach. >

On amplitude and frequency demodulation using energy operators

Abstract: It is shown that the nonlinear energy-tracking signal operator Psi (x)=(dx/dt)/sup 2/-xd/sup 2/x/dt/sup 2/ and its discrete-time counterpart can estimate the AM and FM modulating signals. Specifically, Psi can approximately estimate the amplitude envelope of AM signals and the instantaneous frequency of FM signals. Bounds are derived for the approximation errors, which are negligible under general realistic conditions. These results, coupled with the simplicity of Psi , establish the usefulness of the energy operator for AM and FM signal demodulation. These ideas are then extended to a more general class of signals that are sine waves with a time-varying amplitude and frequency and thus contain both an AM and an FM component; for such signals it is shown that Psi can approximately track the product of their amplitude envelope and their instantaneous frequency. The theoretical analysis is done for both continuous- and discrete-time signals. >

Adaptive data rate modem

Abstract: An adaptive data rate modulator/demodulator (modem) (102), particularly useful for transmitting data over fading communications channels, uses an adaptive data rate technique which supports multiple data rates in the same device. The modem incorporates an adaptive data rate encoder (104) and an adaptive data rate decoder (105) using adaptive, parallel-branch decoding to translate received symbols into corresponding data bits. Significantly, the soft decision metrics of the decoder are also used to provide an estimate W of the signal-to-noise ratio. An optional predictor (232) receives W from the adaptive data rate decoder (105) and predicts the future signal-to-noise ratio to determine the desired data rate for the modem. The data rate is changed automatically and dynamically without interrupting the decoding process. A constant channel symbol rate and a single signal set simplify signal acquisition and synchronization. Incoming and outgoing data are buffered, and the transmission rate is changed dynamically by a memory controller (109) to avert buffer overflows and underflows. An optional adaptive phase-lock loop system (116) maintains synchronization of the decoder at all data rates.

Adaptive compensation for imbalance and offset losses in direct conversion transceivers

Abstract: The current interest in linear modulation and multilevel signals has resulted in an emphasis on DSP implementations to achieve precision signal manipulation. However, most transceivers, and direct conversion designs in particular, rely on analog implementations of the quadrature modulator and demodulator, thereby sacrificing much of the precision gained through DSP. The present paper focuses on the three principal impairments of analog quadrature modulators and demodulators: gain imbalance, phase imbalance, and DC offset. The paper contains three main contributions. First is an analysis and quantitative assessment of the losses-primarily a degraded BER and out-of-band power in the transmitted signal-due to imbalances and offsets. The second contribution is an adaptive compensation technique for the quadrature modulator at the transmitter, and the third is a compensation technique for the quadrature demodulator at the receiver. Both compensation methods converge quickly and present only a modest computational load. >

Carrier recovery system using acquisition and tracking modes and automatic carrier-to-noise estimation

Abstract: A carrier recovery system for use in illustratively a passband QAM (quadrature amplitude modulation) demodulator (10) and specifically such a system, including apparatus and accompanying methods, that employs separate acquisition and tracking modes and automatic carrier-to-noise estimation. In particular, a carrier recovery system (200) is operated in two modes: an acquisition mode to first attain an initial carrier lock, during which simplified reduced constellation slicing is used to determine a quadrant of each incoming symbol; and a tracking (or lock) mode, during which full slicing is used, to accurately track variations in frequency and phase that may occur to a carrier while the system remains locked. The mode changes based upon whether, e.g., the average error energy associated with fully sliced symbols is greater than or less than a pre-defined switching threshold value. The value of the switching threshold changes in a pre-determined manner with changes in noise content, particularly a carrier-to-noise ratio (CNR), of the received symbols. Two appropriately spaced switching threshold values, one for use in each mode, can be used to provide enhanced operational stability. An implementation of a QAM CNR estimator circuit (800) is also provided.

Digital signal transmission system based on partitioning of a coded modulation with concatenated codings

Abstract: Digital signal transmission system which operates by coded modulation of a constellation, the system comprising an encoder (5) which includes a modulator (13) installed at a transmitting station, and a decoder (105) which includes a demodulator (113) installed at a receiving station. A multistage channel encoder (12) carries out a concatenation of internal and external codes to blocks and divides the coding over various partitioning levels of the constellation. The coded symbol blocks are subjected to the work of a frequency-division interleaver (37), the modulator (13) operating according to an orthogonal carrier frequency-division multiplexing technique. The decoder (105) includes circuitry to carry out reverse operations to those carried out for the coding.

Differential detection of pi /4-shifted-DQPSK for digital cellular radio

Abstract: The detection of pi /4-shifted-DQPSK modulation using a tangent-type differential detector with an integrated symbol timing and carrier frequency offset correction algorithm is discussed. pi /4-shifted-DQPSK modulation has been proposed for use in a high-capacity, TDMA-based digital cellular system being developed in the US; differential detection could potentially allow the production of low-complexity mobile units. Results obtained using the proposed IS-54 TDMA frame structure for base to mobile transmissions are presented. Theoretical and simulation bit-error-rate (BER) results are presented for static and Rayleigh fading channels. BER results are provided as a function of E/sub b//N/sub 0 /and C/I, where the interferer is a second pi /4-shifted-DQPSK signal. Additional results are provided which show the BER sensitivity to Doppler frequency shifts, time delay spread, and carrier frequency offsets. >

AM/FM multi-channel implantable/ingestible biomedical monitoring telemetry system

Abstract: A multi-channel circuit for telemetering signals representing physiological values from a point in a human body to a receiver (24) outside of the body. The two signals (S 1 , S 2 ) other than the temperature signal (27') are used to provide two frequency modulated signals (14, 16) summed by an amplifier (18) with the summed FM signal then being applied to amplitude modulate (21) a carrier (8) whose frequency varies as a function of temperature. The resulting FM/AM signal (22) is telemetered inductively outside of the body to an external receiver (24). Appropriate demodulation, filter, and shaping circuits within the external circuit detect the FM signals (14, 16) and thus produce three independent frequencies two of which are the original physiological variables and the third a function of local temperature. Real time plot of the two physiological variables can be obtained using FM discriminators while the temperature dependent frequency is best monitored by a counter.

A fully digital feedforward MSK demodulator with joint frequency offset and symbol timing estimation for burst mode mobile radio

Abstract: A strictly feedforward demodulator structure for minimum shift keying (MSK) modulation with joint nondata-aided symbol clock and frequency offset estimation is presented. Due to its feedforward operation, clock synchronization and frequency offset compensation are hang-up free, and the demodulator is well suited for a digital implementation. The sampled baseband signal is passed through a nonlinearity and smoothed by a digital filter. The magnitude of the filter output directly drives the clock recovery process. The phase of the smoothed signal is an estimate of the carrier frequency offset and is used for offset compensation. Following synchronization, the signal is demodulated by differentially coherent detection. The performance of the demodulator is assessed for the AWGN and the Rayleigh flat and frequency-selective fading channel by computer simulations. >

Frequency synchronized bidirectional radio system

Abstract: A bidirectional radio system for low cost high throughput accumulation of data from a large number of sites units (50). Frequency synchronisation is achieved at low cost by transmitting a hig accuracy carrier and clock signal at a base station (44), and using receiving circuitry at remote stations (46) to extract the base clock signal and base carrier frequency and a phase lock loop (242, 248, 254, 258) to stabilize the remote station carriers. A burst demodulator (156) at a base station receiver can decode a short remote station response by scaling the response with the phase and amplitude of an initial segment of the response. The burst demodulator (156) may continuously update the decoding threshold based on a comparison of the signal amplitude and the current value of the decoding threshold.

Receiver adaptively operable for multiple signal transmission systems

Abstract: A receiver for selectively receiving high frequency signals from analog modulated signals and digital modulated signals. The receiver has an intermediate frequency signal circuit for selecting a desired channel of the high frequency signals and for frequency-converting the high frequency signal of the selected channel into an intermediate frequency signal, a demodulator for demodulating the intermediate frequency signal, which is adapted to be capable of demodulating modulated signals in a variety of modulation systems, the demodulator including at least a digital section, and a controller for controlling the demodulator to be able to discriminate between the analog modulated signals and the digital modulated signals, based on a demodulated signal output from the digital section of the demodulator and to be switched into a demodulation mode suited for modulation system of the selected channel of the high frequency signals.

Combined angle demodulator and digitizer

Abstract: A new technology for simultaneously performing the previously separate functions of analog phase-tracking and A/D conversion, represented by a family of systems referred to as delta-sigma frequency-to-digital converters (ΔΣFDCs). Each system uses coarse analog phase measurements, quantization noise shaping, and decimation filtering to perform instantaneous frequency-to-digital conversion. Because they operate on instantaneous frequency in the manner that ΔΣ modulators operate on amplitude, they share many of the benefits enjoyed by ΔΣ modulator-based A/D converters such as reduced analog circuit requirements and amenability to VLSI implementation.

Bioelectric impedance measurements using synchronous sampling

Abstract: Synchronous sampling has been applied to the demodulation of bioelectric impedence signals This overcomes the need for analog demodulators in bioimpedance measurements The sampling rate is determined by signal bandwidth, rather than by the highest frequency component before demodulation >

FM quadrature demodulator

Abstract: of EP0574083FM quadrature demodulator having in-phase and quadrature terminals for applying a pair of FM-modulated signals in a mutual phase quadrature thereto, comprising a modulation signal which is frequency-modulated on a carrier, one of the two terminals (Q) being coupled to a first input (I11) of a first phase comparison circuit (M1) and the other terminal (I) being coupled to a second input (I12) of the first phase comparison circuit (M1) via a first phase-shifting circuit (RA) which realises a phase shift varying with said modulation signal, said first phase comparison circuit (M1) being connected to an output of the FM quadrature demodulator via a low-pass filter (LF). In order to enhance, inter alia, the signal processing and the field of use of the FM quadrature demodulator, this demodulator according to the invention comprises a second phase comparison circuit (M2) having first (I21) and second (I22) inputs, in which one of the two in-phase and quadrature terminals (I) is coupled to the first input (I21) of the second phase comparison circuit (M2) and the other terminal (Q) is coupled to the second input (I22) of the second phase comparison circuit (M2) via a second phase-shifting circuit (RA) which realises a phase shift varying with said modulation signal, said FM quadrature demodulator also comprising a differential stage (S1) which is coupled between outputs of the two phase comparison circuits (M1,M2) and an input of the low-pass filter (LF).

Optically readable record carrier for recording information, method and apparatus for manufacturing such, apparatus for recording and reading information on a such a record carrier

Abstract: A record carrier on which information may be optically recorded and/or read, having a disc-shaped substrate with a spiral or concentric pattern of preformed tracks thereon and a radiation-sensitive layer extending over such track pattern. The tracks are in the form of ridges of substantially constant width and having a periodic radial wobble of a substantially constant mean frequency, which frequency is modulated by a position-information signal identifying the relative positions of the tracks in the track pattern. Apparatus for forming such a track pattern includes means for modulating the radial track wobble in accordance with the position-information signal. Apparatus for reading an information signal recorded on such a record carrier includes an FM demodulator for recovering the position-information signal from variations in the reflected scanning beam produced by the track modulation, and which also recovers from such variations a clock signal corresponding to the mean frequency of such modulation and which is used to control the scanning velocity. Apparatus for recording an information signal on such a record carrier includes an FM demodulator for recovering the position-information signal from variations in the radiation reflected from the tracks during recording.

Spread spectrum communication system

Abstract: A spread spectrum communication system includes a receiving section which receives a signal produced by modulating a carrier of a predetermined frequency with a spread spectrum signal which has been modulated with a spread code of a clock frequency fC and mixes the received signal with a local oscillation signal to provide a spread spectrum signal component wherein a local oscillation frequency fL of said local oscillation signal is set at fL≈fC+fo or fL>fC+fo or fL≈fo-fC or fL

Offset correction circuit

Abstract: The direct conversion receiver DCR receives analog modulating signals with a reference average value and modulated within assigned time slots of a TDMA-structure on a carrier with a carrier frequency FC which changes from time slot to time slot. DCR includes a demodulator circuit DC-coupled to a baseband circuit, the demodulator circuit including a local oscillator LO and a mixer MIX and the baseband circuit including an offset correction circuit OCC/OCC' for updating different variable parameter offset correction values for different FC stored in a memory MEM and compensating offset introduced in DCR. OCC/OCC' determines, upon occurrence of an assigned time slot, an updated offset correction value as a function of an old offset correction value in a corresponding storage location of MEM and the difference between an average value of the analog signal and the reference average value, and thereupon stores the result in the corresponding storage place.

Two-dimensional Phase Locked Loop Demodulation of Interferograms

Abstract: A new technique for continuous phase determination of an interferogram based on a digital phase locked loop is presented. The main advantage of this method, with respect to well established techniques such as Fourier or phase stepping demodulation, is that the traditional approach to phase unwrapping processes by removal of discontinuities is not required. The phase is determined continuously as the phase locked loop scans the two-dimensional interferogram. Because of the sequential nature of the algorithm proposed, this can be implemented using a special purpose video processor for phase determination at video rates. The above mentioned properties makes the presented technique a fast algorithm for phase determination of carrier frequency interferograms modulated by a two-dimensional smooth phase function.

System and method for joint demodulation of CDMA signals

Abstract: Methods and systems for jointly demodulating CDMA signals are presented The disclosed methods and systems provide, among other advantages, for accurate demodulation of such signals in multipath, time-dispersion environments Single signal or multiple signal demodulation, with or without taking intersymbol interference into account can be accomplished according to the present invention

Adaptive equalizer and receiver

Abstract: A receiver capable of effecting frame synchronization control even at the time of initial acquisition and hand off in the presence of frequency selective fading. The receiver is provided in a demodulator part thereof with a quasi-coherent detector (140), a memory (144) for temporarily storing the output of the quasi-coherent detector, a write address counter (145) for the memory, an incoherent correlator (146) that determines correlation between a received data pattern and a known UW data pattern, a UW tentative detection circuit (147) that is supplied with the output of the address counter and the output of the incoherent correlator, an adaptive equalizer (148) that equalizes the received data stored in the memory by using the output of the UW tentative detection circuit, a UW detector (103) that effects UW position detection on the basis of the equalized data, and a frame synchronization control circuit (150) that effects frame synchronization control on the basis of the output of the UW tentative detection circuit and the output of the UW detector.

Method and apparatus for amplifying, modulating and demodulating.

Abstract: A highly efficient linear amplifier and/or modulator and demodulator comprising first and second feedback loops is provided. Each loop processes a component of the input signal and the component signals are recombined at, for example, a summing junction (18). The feedback signals for each loop are dependent upon the output signal and are in phase quadrature. The input signal is separated into I and Q signals, which are also in phase quadrature, by a component separator (10).

Multi-processor demodulator for digital cellular base station employing partitioned demodulation procedure with pipelined execution

Abstract: Demodulation is provided for a base station receiver in a cellular communication system by a demodulator having four data linked digital signal processors. An MLSE equalizer and maximal ratio combiner for diversity paths includes multiple components that are partitioned among the processors for pipelined execution with predetermined time ordering.

Quadrature local oscillator network

Abstract: A compact local oscillator network for use in a quadrature modulator and/or demodulator is presented. Single side band circuitry is configured to produce quadrature signals with a high degree of accuracy such that two equal amplitude signals are generated having a precise 90° phase difference. The network accuracy is substantially not affected by phase or amplitude imbalances within or introduced into the network. For example, the network may include: a first quadrature circuit for dividing a first input signal into a first in-phase signal and a first quadrature signal 90° out of phase; a second quadrature circuit for dividing a second input signal into a second in-phase signal and a second quadrature signal 90° out of phase; a first mixer for mixing said first in-phase signal and said second in-phase signal; a second mixer for mixing said first quadrature signal and said second quadrature signal; a third mixer for mixing said first quadrature signal and said second in-phase signal; a fourth mixer for mixing said first in-phase signal and said second quadrature signal; a first combiner for combining the outputs of said first and second mixers into a first combiner for combining the outputs of said first and second mixers into a first local oscillator output signal; and a second combiner for combining the outputs of said third and fourth mixers into a second local oscillator output signal.

Spectrum spread receiver and spectrum spread transmitter-receiver including same

Abstract: A spectrum spreading receiver including a super-regenerative demodulator which is capable of receiving a spectrum spread signal and which is resistant to noise and has a wide band, resulting in being simplified in structure and decreased in manufacturing cost. A signal of which a spectrum is spread by a PN code is received by a receiving antenna and then demodulated by the super-regenerative demodulator. Then the same PN code as the PN code having carried out the spectrum spreading is generated and the correlation between the signal and the PN code is made by a correlation unit, resulting in the decoding of the spread signal into the original base band signal.

Step-scanning interferometer with digital signal processing

Abstract: A novel step-scan FT-IR spectrometer incorporating a digital signal processor for demodulation of the detector signal is described. The potential advantages of this method of signal processing are discussed and illustrated. The instrument is based on a commercial cube-corner interferometer which has been modified by replacement of the drive motor with a stepper motor-micrometer and piezoelectric transducer combination. The interferometer retardation is feedback controlled by a 48650 personal computer, which also controls the digital signal processor and collects spectral data. More than one phase modulation frequency can be imposed simultaneously, allowing for a multiplex advantage in photoacoustic depth profiling. Digital signal processing allows for simultaneous demodulation of multiple frequencies which would normally require several lock-in amplifiers. Data that illustrate the feasibility of these concepts are presented. The suitability of this instrument for double-modulation step-scan FT-IR measurements such as polymer stretching and electrochemically modulated step-scan FT-IR is also discussed.

Joint demodulation of cochannel signals using MLSE and MAPSD algorithms

Abstract: Sequence estimation and symbol detection algorithms for the demodulation of cochannel narrowband signals in additive noise are proposed. These algorithms are based on the maximum likelihood (ML) and maximum a posteriori (MAP) criteria for the joint recovery of both cochannel signals. The error rate performance characteristics of these nonlinear algorithms were investigated through computer simulations. The results are presented. >

CCD demodulator/correlator

Abstract: A charge-coupled device (CCD) used as a demodulator and a correlator in the receiver of a spread spectrum radio system The device implements both functions in the charge domain, thereby avoiding unnecessary conversions between voltage and charge that would normally be required if the functions were separately implemented In its preferred form, the demodulator and correlator include an in-phase filter (170), a quadrature filter (172), delay circuits (174, 176), decimation circuits (181-184), correlators (191-194), and signal combiners (200, 202) The delay circuits are used in the preferred embodiment to compensate a time shift between the in-phase and quadrature channels that result from the minimum shift keying modulation used, but would not necessarily be required for other types of modulation The decimation circuits match the data rate of the in-phase and quadrature filters to the data rate used by the correlators, which is determined as a function of chip rate used to spread the data Each of the in-phase and quadrature channels are implemented in a CCD, which includes a "pipe organ" filter structure to implement the respective filters that process the analog input signal for each channel Storage sites are configured as delay lines in the device

Joint estimation algorithms for cochannel signal demodulation

Abstract: Nonlinear algorithms for the joint recovery of cochannel narrowband signals are proposed. For finite impulse response channel characteristics, maximum likelihood and maximum a posteriori criteria are employed to derive cochannel demodulators of varying complexities and degrees of performance. The error rate performance of these joint estimation algorithms is examined through computer simulations. >

Composite spread spectrum signal including modulator demodulator

Abstract: A composite spread spectrum signal including modulator and demodulator therefor is disclosed. The composite signal having a multi-dimensional signal space, comprising a pulse position modulation dimension generated by varying starting positions of cyclically repeated chipping sequences, a frequency shift key dimension generated by varying a carrier frequency between a plurality of frequencies, code shift keyed dimensions generated by selecting the chipping sequences from among a plurality of orthogonal sequences, and amplitude shift key dimensions generated by selecting amplitudes of each subcarrier for each message bundle. This signal may further comprise a phase shift key dimension generated by assigning a phase relationship of the orthogonal subcarriers.

An adaptive digital technique for compensating for analog quadrature modulator/demodulator impairments

Abstract: Analog quadrature modulators and demodulators have three major impairments: gain imbalance, phase imbalance, and dc-offset. A digital technique is presented for compensation of these modulator and demodulator impairments. Part of the RF signal is fed to an envelope detector. The detector output, along with the baseband quadrature components, is used to estimate the impairment values. The estimated impairment values are then used to compensate for the impairments. Simulation results show that spurious signals can be suppressed by more than 30 dB using this technique. The effect of modulator/demodulator impairments on RF power amplifier linearization techniques is also discussed. The quadrature modulator and demodulator impairment compensator can decrease intermodulation distortion products by 12 dB for the complex gain predistorter and by about 5 dB for the Cartesian coordinate negative feedback method of RF power amplifier linearization. >