Showing papers on "Modulation published in 1996"

Signal design for transmitter diversity wireless communication systems over Rayleigh fading channels

Abstract: Transmitter diversity wireless communication systems over Rayleigh fading channels using pilot symbol assisted modulation (PSAM) are studied. Unlike conventional transmitter diversity systems with PSAM that estimate the superimposed fading process, we are able to estimate each individual fading process corresponding to the multiple transmitters by using appropriately designed pilot symbol sequences. With such sequences, special coded modulation schemes can then be designed to access the diversity provided by the multiple transmitters without having to use an interleaver or expand the signal bandwidth. The code matrix notion is introduced for the coded modulation scheme, and its design criteria are also established. In addition to the reduction in receiver complexity, simulation results are compared to, and shown to be superior to, that of an intentional frequency offset system over a wide range of system parameters.

Digitally programmable multifunction radio system architecture

Abstract: A system that partitions or divides the functions of a radio into channels and divides the functions of each channel into two major functions: 1) antenna interfce and power amplification; and 2) hardwired mixing, modulation/demodulation and signal processing and further partitions the mixing through signal processing functions into the functions of a) programmable analog mixing and b) programmable digital modulation/demodulation and signal processing. Control and user interface functions, if needed for a particular application can also be functionally partitioned. A typical received signal pathway will encounter an antenna module, an antenna interface and power amplification module, a receiver module partitioned into an analog submodule that performs mixing and down conversion to produce a common intermediate frequency signal and a digital submodule that further down converts the intermediate frequency signal, demodulates the signal and performs the other signal processing necessary to provide a useful information signal. A typical transmitter pathway includes a transmitter module partitioned into a digital submodule that performs signal processing and modulation and an analog submodule that performs upconversion and mixing, followed by a power amplification and interface module and an antenna module. Control and user interface modules can also be provided along with modules that perform additional processing and information security functions.

Differential chaos shift keying : A robust coding for chaotic communication

Abstract: The statistical attributes of the received chaotic signal are evaluated in the noncoherent chaos shift keying (CSK) modulation scheme in order to perform the demodulation. This approach offers a very simple circuit configuration, but like the other solutions proposed before, it is sensitive to the channel noise and imperfections. In the differential chaos shift keying (DCSK) approach every incoming information bit is encoded into two bits. The first signal serves as a reference, while the second one carries the information. If the binary information to be transmitted is ”1” then first the reference signal is transmitted and after it that signal is repeated. For a ”0”, the inverted version of the reference signal is transmitted. The receiver has a storage capability and the demodulation is performed by evaluating the cross-correlation of the two signals. The effect of noise is reduced by averaging and proper design of the channel filter. The effect of channel imperfections is also reduced, because both the signal and its reference are sent via the same channel. The DCSK approach offers a very robust solution for the chaos communication and it can be implemented with very simple circuitry even in the microwave frequency region.

Adaptive OFDM for wideband radio channels

Abstract: An OFDM (orthogonal frequency division multiplexing) transmission system is simulated with time-variant transfer functions measured with a wideband channel sounder. The individual subcarriers are modulated with fixed and adaptive signal alphabets. Furthermore, a frequency-independent as well as the optimum power distribution are used. The simulations show that with adaptive OFDM, the required signal power for an error probability of 10/sup -3/ can be reduced by 5...15 dB compared with fixed OFDM. The fraction of channel capacity which can be achieved with adaptive OFDM depends on the average signal-to-noise ratio and the propagation scenario.

Digital baseband transmission and recording

Abstract: From the Publisher: Digital Baseband Transmission and Recording provides an integral, in-depth and up-to-date overview of the signal processing techniques that are at the heart of digital baseband transmission and recording systems. The coverage ranges from fundamentals to applications in such areas as digital subscriber loops and magnetic and optical storage. Much of the material presented here has never before appeared in book form. The main features of Digital Baseband Transmission and Recording include: -- a survey of digital subscriber lines and digital magnetic and optical storage; -- a review of fundamental transmission and reception limits; -- an encyclopedic introduction to baseband modulation codes; -- development of a rich palette of equalization techniques; -- a coherent treatment of Viterbi detection and many near-optimum detection schemes; -- an overview of adaptive reception techniques that encompasses adaptive gain and slope control, adaptive detection, and novel forms of zero-forcing adaptation; -- an in-depth review of timing recovery and PLLs, with an extensive catalog of timing-recovery schemes. Featuring around 450 figures, 200 examples, 350 problems and exercises, and 750 references, Digital Baseband Transmission and Recording is an essential reference source to engineers and researchers active in telecommunications and digital recording. It will also be useful for advanced courses in digital communications.

Orthogonal frequency division multiplexing

Abstract: In an orthogonal frequency division modulation (OFDM) apparatus and method, a transmitter produces a clock and a reference signal to provide an accurate phase in modulation of a carrier. A receiver is thus able to reproduce the reference signal, even if the signal-to-noise (S/N) ratio of the carrier is poor. The OFDM method includes the steps of AM-modulating a group of digital signals with a plurality of carriers, in which a reference signal is frequency-modulated at a symbol period, combining the AM-modulated carrier and modulating the combined carrier into a main carrier, detecting the main carrier by phase-locking the frequency-modulated reproduced reference signal with the transmitted reference signal and fast-Fourier-transforming the combined carrier to demodulate the digital signal.

Multistage linear receivers for DS-CDMA systems

Abstract: A new family of multistage low-complexity linear receivers for direct sequence code division multiple access (DS-CDMA) communications is introduced. The objective of the proposed design is to mitigate the effect of multiple access interference (MAI), the most significant limiting factor of user capacity in the conventional DS-CDMA channel. The receivers presented here employ joint detection of multiple users and therefore require knowledge of all the signature codes and their timing. In addition, for a multipath environment, reliable estimates of the received powers and phases are assumed available for maximal ratio RAKE combining. Each stage of the underlying design recreates the overall modulation, noiseless channel, and demodulation process. The outputs of these stages are then linearly combined. The combining weights can be chosen to implement different linear detectors, including the decorrelating and minimum mean square error (MMSE) detectors. In this paper, we focus on implementing the MMSE detector. Simulation results illustrate that significant performance gains can be achieved in both synchronous and asynchronous systems.

Transcutaneous energy and information transmission apparatus

Abstract: An apparatus for transcutaneously transmitting power and communication signals to an implantable device. The apparatus can include generators for power and information signals; receivers; and a coupler for independently coupling the power signal and a first information signal. An internal unit can have receivers for power and information signals; a second signal generator; and an independent coupler. The first and second information signal can be transmitted at a frequency greater than the power frequency. The external unit can also include a signal conditioner for symmetrically transceiving the first and second information signals; and an external data controller for symmetrically controlling the information signals. The internal unit can also include a voltage regulator converter; an internal signal conditioner for symmetrically transceiving the information signals; and a data controller. Symmetrically controlling can include ASK modulation of a data signal upon an RF carrier signal.

Dual mode modulated backscatter system

Abstract: A radio communication system includes an Interrogator for generating and transmitting a first modulated signal by modulating a first information signal onto a radio carrier signal, the first information signal indicating in which of multiple response modes a receiving Tag should respond. One or more Tags of the system receive the first modulated signal and decode it to obtain the first information signal. A Backscatter Modulator modulates the reflection of the first modulated signal using a second information signal whose content, data rate, or modulation is determined by said first information signal, thereby forming a second modulated signal. The Interrogator receives and demodulates the second modulated signal to obtain the indicated second information signal.

Apparatus and method for digital data transmission over video cable using orthogonal cyclic codes

Abstract: A method and apparatus for carrying out synchronous co-division multiple access (SCDMA,) communication of multiple channels of digital data over a shared transmission media such as a cable television system coaxial cable, a fiber optic or copper conductor telephone link, terrestial microwave, satellite link, local or wide area network, wireless including cellur network or some combination of these media using suitable interface circuitry. The system includes modems at remote units and a central unit to receive time division multiplexed digital data arranged into timeslots or channels and uses orthogonal codes to encode each channel of multiple data and spread the energy of each channel data over a frame of data transmitted in the code domain. Spreading the data this way makes the system less susceptible to impulse noise. Frames are synchronized as between remote and central units using a ranging scheme which is also useful in any other system transmitting data by frames in a distributed system where synchronizing the frames as between all units regardless of differences in propagation delays is necessary. Each frame in the SCDMA modulation scheme includes a gap or guardband containing no other data. The ranging process involves training each remote unit to impose enough delay prior to re-transmission of a barker code received from the CU such that a barker code sent by the RU arrives at the CU during the gap. The process of setting the delay in each RU is a trial and error process, and each RU starts the ranging process asynchronously. Contention resolution protocols such that only one RU is aligning to the gap at any particular time are taught.

Single-mode waveguide microcavity for fast optical switching.

Abstract: We investigate the properties of a tunable single-mode waveguide microcavity that is well suited for frequency modulation and switching. The cavity mode has a volume of less than one cubic half-wavelength, and the resonant frequency is tuned by refractive-index modulation. We suggest using a photorefractive effect to drive the device, based on the photoionization of deep donor levels known as DX centers in compound semiconductors. Picosecond on–off switching times are achievable when two of these cavities are placed in series. The resulting switch has the advantages of being compact and requiring as little as 10 pJ of energy of operate.

Optimisation of switching levels for adaptive modulation in slow Rayleigh fading

Abstract: Multi-dimensional minimisation techniques are used to optimise, for specific applications, the upper bound bit error rate (BER) and bits per symbol (BPS) performances of adaptive modulation schemes over Rayleigh channels. This is achieved by modifying the switching criteria for selecting the appropriate modulation scheme.

Adaptive modulation system with variable coding rate concatenated code for high quality multi-media communication systems

Abstract: This paper proposes an adaptive modulation system with a concatenated code (AMS-CC) for land mobile communications to achieve high quality, high bit rate transmission in Rayleigh fading environments. The proposed system adaptively controls the coding rate of the inner convolutional code, symbol rate, and modulation level according to the instantaneous fading channel conditions. The performances in Rayleigh fading environments are evaluated theoretically and by computer simulation. The results show that the proposed system can realize higher quality transmission without the degradation in average bit rate compared to conventional adaptive modulation systems.

Femtosecond self- and cross-phase modulation in semiconductor laser amplifiers

Abstract: We present detailed derivation of our new model for femtosecond pulse amplification in semiconductor laser amplifiers. The various dynamic nonlinear terms of gain compression and associated self-phase modulation are derived semiphenomenologically, and are discussed physically. Included are the effects of carrier depletion, carrier heating and spectral hole-burning, as well as linear and two photon absorption and the instantaneous nonlinear index. Additionally, we account for dynamically changing gain curvature and slope. We apply the theory to strong signal cross-phase-cross-gain modulation experiments with /spl sim/500 fs pulses in a broad area GaAs amplifier and show that the model accurately describes the observed complex phenomena. We also present experimental results on single beam strong signal amplification in two different quantum-well amplifiers using 150-200 fs duration pulses. For such pulse lengths, carrier heating becomes an integrating nonlinearity and its self-phase modulation is similar to that due to carrier depletion. Additionally, since the pulse spectrum is broad, the gain slope and curvature shift and narrow it. The resultant spectral distortions are very different than observed (and modeled) earlier for the /spl sim/500 fs pulses. The model is again able to correctly describe the evolution of these ultrashort pulses, indicating that it remains valid, even though pulse durations approach the intraband relaxation time.

Ultra-high-speed multiple-quantum-well electro-absorption optical modulators with integrated waveguides

Abstract: Integrating the input and output waveguides with a multiple-quantum-well (MQW) electro-absorption (EA) optical modulator is shown to achieve ultra-high-speed modulation while keeping the total device length long enough for easy fabrication and packaging. Testing with fabricated modulators showed that a shorter modulation region results in a larger modulation bandwidth. The additional loss due to the waveguide integration was less than 1 dB. An optimized modulator showed a large modulation bandwidth of 50 GHz, a low driving voltage of less than 3 V, and a low insertion loss of 8 dB. A prototype module of this modulator had a bandwidth of greater than 40 GHz. Optimizing the MQW structure makes the modulator insensitive to polarization. These results demonstrate that MQW-EA modulators with integrated waveguides are advantageous in terms of fabrication, packaging, and ultra-high-speed modulation.

Apparatus and method for medical monitoring, in particular pulse oximeter

Abstract: A method for measuring medical parameters of a patient by radiation of electromagnetic waves into a sample and for measurement and subsequent analysis of the electromagnetic waves which have passed through the sample, the following steps are carried out. First and second modulation signals are generated having equal frequencies and a first phase difference of substantially 90°. Irradiating a first electromagnetic wave of a first wavelength into the sample, under control of the first modulation signal. Irradiating the sample with a second electromagnetic wave of a second wavelength, under control of the second modulation signal. Receiving electromagnetic waves of both wavelengths which have passed through the sample and demodulating the received signals by multiplying the same with a first sinusoidal demodulation signal and with a second sinusoidal demodulation signal having the first phase difference with respect to the first sinusoidal signal, the first and second sinusoidal demodulation signals having the same frequency as the first and second modulation signals, such as to generate a first and a second demodulated signal. The first and the second sinusoidal demodulated signals are set so as to have a phase difference relative to the first and second modulation signals corresponding to a system phase shift.

Method and system for transporting ancillary network data

Abstract: A method and system for transporting ancillary network data is provided. A sub-carrier modulation signal containing ancillary network data is superimposed on a high bit-rate data signal prior to transport over an optical link. The monitoring subcarrier signal is significantly lower in both frequency and amplitude than the main data signal so as to not impact reliable reception of the main data signal. A low-pass filter filters the sub-carrier modulation signal from the data signal. By demodulating the sub-carrier signal, the ancillary network data is recovered. The ancillary network data includes any combination of data type information related to different network elements. The recovered ancillary network data is useful for any network management purpose. Especially important applications include restoration, wavelength re-use and routing, and any other general network management operation.

Automatic modulation mode selecting unit and method for modems

Abstract: An automatic modulation mode selecting unit (208) and a method (100) provide for selection from a plurality of modulation modes having an optimized transmission time for a data file. This is particularly useful where a small data file is to be transmitted, such as for a hand-held message pad. The present invention may select a modulation mode having a slow data rate but a short training time to achieve a shorter transmission time a small data file in comparison with using another modulation mode having a fast data rate but a longer training time, and thus a longer transmission time. The automatic modulation mode selecting unit includes a mode select controller (202), a mode computer (204), and a mode select switch (206) for selecting a modulation mode based on a calculated optimized transmission time.

Transmitter for encoded data bits

Abstract: Quadrature Amplitude Modulated signals are generated from data bits by using a first Quadrature Phase Shift Keying (QPSK) modulator for encoding a first pair of the data bits into one of four carrier signal phases, thereby producing a first QPSK signal. A second QPSK modulator encodes a second pair of the data bits into one of four carrier signal phases, thereby producing a second QPSK signal. The first QPSK signal is amplified to a first power level, and the second QPSK signal is amplified to a second power level. The first and second amplified signals are then combined to produce a signal in which four data bits are encoded. In another aspect of the invention, a new type of modulation, called Offset Quadrature Phase Shift Keying (OQPSK), is used in place of the first and second QPSK modulators, so that an Offset Quadrature Amplitude Modulation (OQAM) transmitter is formed. An OQPSK modulator encodes data bits by encoding a first sub-group of the data bits into a real part of a complex signal at an odd instant of a clock, and by encoding a second sub-group of the data bits into an imaginary part of the complex signal at an even instant of the clock. OQPSK modulation provides the benefit of having all signal transitions being constrained to trajectories around constant radius circles, thereby producing spectral efficiency.

Dual-mode radiotelephone apparatus for digital or analog modulation

Abstract: A dual-mode radiotelephone capable of operation in analog or digital modes. According to exemplary embodiments, a digital signal processor receives a speech signal to be transmitted in the digital or analog mode and generates In-phase (I) and Quadrature (Q) modulating signals. The I and Q signals are supplied to a quadrature modulator for generating a digitally modulated signal and are supplied to an analog modulator for generating an analog modulated signal.

Modulation format adaptive messaging receiver and method thereof

Abstract: A messaging receiver (400) and corresponding system (100b) and method adaptable to a plurality of modulation formats including; a processor (401) having flexible resources (404), preferably software based, for receiving a signal to provide a modulation identifier, and a controller (403), coupled to the processor, for deploying the flexible resources responsive to the modulation identifier. Alternatively the messaging receiver includes a buffer (412) for storing a signal having a modulation format, and the processor processes the signal in accordance with the plurality of modulation formats so as to differentiate the modulation format, and the controller deploys the flexible resources responsive to the modulation format.

Principles and Applications of Optical Communications

Abstract: I Overview 1 Introduction to Optical Communications 2 From Point-to-Point Links to Networking II Basic Point-to-Point Communication Blocks 3 Light Sources 4 Optical Fibers 5 Photo Detectors 6 Noise in Optical Communications 7 Incoherent Detection III Networking 8 Time Domain Multiple Access (SONET, FDDI, B-ISDN, etc.) 9 Frequency Domain Multiple Access 10 Subcarrier Multiplexing 11 Photonic Switching IV Signal Processing 12 Direct Modulation 13 External Modulation 14 DFB Modulation 15 Coherent Detection 16 Line Coding and Timing Recovery 17 Optical Amplification 18 Soliton Transmission

Top surface-emitting vertical-cavity laser diodes for 10-Gb/s data transmission

Abstract: Intensity modulated proton-implanted top surface-emitting vertical-cavity InGaAs QW lasers (VCSELs) with a small-signal modulation bandwidth of 12 GHz butt-coupled to multimode fibers are investigated as light source for optical interconnection. At 10-Gb/s pseudorandom data rates the bit-error rate (BER) remains under 10/sup -11/ after transmission over 500 m of graded index multimode fiber. Optimum transmission behavior is achieved for linearly polarized nearly single-mode laser operation with a side-mode suppression of better than 25 dB under modulation. Spectral characterization indicates that linearly polarized single-mode light output is essential for good BER performance.

A low-power CMOS chipset for spread spectrum communications

Abstract: In future personal communication services, high-bandwidth multimedia data will be delivered over wireless pico-cellular networks to high densities of users. The system described here is designed to simultaneously supply 1 Mb/s to up to 50 users in a single cell, requiring a system bandwidth in excess of 50 Mb/s. The use of spread-spectrum techniques, in particular direct sequence code-division multiple access (CDMA), provides a multiple-access strategy to maintain parallel, separate streams of real-time data to all users, and to reduce sensitivity to multipath, narrow band fades, and interference present in the radio environment. Three chips in standard digital 0.8 /spl mu/m CMOS technology implement the critical parts of a spread spectrum transceiver: the digital modulator; the analog receiver front-end and ADC; and the digital receiver baseband processor. The transmit system transmitter is based loosely on the US IS-95 digital cellular CDMA standard, but at more than an order of magnitude higher date rate.

Method for automatically searching a frequency range for signal channels in a receiver for digitally modulated signals, and receiver for applying such a method

Abstract: A method for automatically searching a frequency range for signal channels in a receiver for digitally modulated signals is described, each channel having a center frequency, a symbol rate, and a modulation type. The method comprises the steps of scanning the frequency range in first frequency steps corresponding with just less than half the minimum expected symbol rate of the channels, measuring the RF level at each frequency step and comparing the measured RF value with a threshold value, and, if the measured RF value is below the threshold value, continuing said scanning and measuring steps until the frequency range is fully scanned, and, if the measured RF value is above the threshold value, assuming the corresponding frequency as an indication of a digitally modulated signal channel and scanning a frequency area in second frequency steps to determine the edge frequencies of the channel, said second frequency steps being much smaller than said first frequency steps, determining the center frequency of the channel from said edge frequencies, and continuing said scanning and measuring steps for further signal channels until the frequency range is fully scanned.

Am compatible digital waveform frame timing recovery and frame synchronous power measurement

Abstract: In a broadcast system having a complex waveform of digital and analog segments, frame timing is recovered (290) and the frame synchronous power (284) of the digital portion of the composite AM compatible Digital Audio Broadcast (DAB) waveform is measured by examining a portion of the signal (284) The frame timing necessary for proper demodulation is recovered from the received signal (200), and a signal power measurement for scaling (242) is provided (294) The composite AM compatible DAB waveform is produced by a modulation method in which a digital representation of an audio signal is encoded together with an analog amplitude modulated (AM) signal and transmitted simultaneously in the same frequency channel

Performance of an OFDM-TDMA mobile communication system

Abstract: The multicarrier transmission technique (OFDM) is considered in combination with a TDMA/TDD multiple access scheme for a cellular mobile communication system. Performance analysis is presented for the uncoded and coded (TCM) case. It is shown that OFDM systems have a large potential concerning the flexible allocation of the total given bandwidth to different users. This flexibility can be exploited to adapt to the impairments of the radio channel, thus increasing the overall performance. Two methods, namely (1) a simple principle to leave out weak subcarriers, and (2) the individual modulation of each subcarrier (adaptive modulation) are studied (for the up-/downlink case in a frequency selective and time-variant radio channel), and results with respect to throughput and BER performance are discussed.

The effect of quantization in a digital signal component separator for LINC transmitters

Abstract: Spectrally efficient modulation schemes have been chosen for the second generation of cellular systems in the United States and Japan, as well as for private mobile radio (PMR) systems This paper analyzes the effect of quantization in a digital signal component separator (SCS) for linear amplification with nonlinear components (LINC) transmitters The analysis relies on the fact that the two signal components can be obtained as the source signal plus/minus a signal in quadrature to the source signal The equations derived are vital because they allow the designer to optimize digital signal processor (DSP) power consumption and bandwidth The word lengths that are required for the source signal and the quadrature signal can be calculated from the amplifier gain characteristic, the probability density function for the modulation scheme, and the specified adjacent channel interference (ACI) The validity of the analysis has been verified by means of simulations

Method of error protected transmission, method of error protected reception of data and transmission system for transmission of data

Abstract: Data is transmitted via a signal containing a number of simultaneously active modulated frequency channels. The data is encoded in an error protecting code. Successive data items are mapped pseudo-randomly to different frequency channels. This protects against fading which affects frequency channels that are located at periodic distances from each other. The pseudo random mapping is realized by writing the data-items into memory in one order and reading them from memory in another order. Successive signals are each modulated in this way. The memory locations vacated upon reading data items for the modulation of one signal are filled by data-items for modulating the next successive signal. This is kept up by permuting the order of the memory locations in which the data-items are written for each successive signal.

Theoretical analysis of modulation response and second-order harmonic distortion in vertical-cavity surface-emitting lasers

Abstract: A rate-equation model is developed, with the consideration of size effects, to analyze the steady state and dynamic behavior of index-guided vertical-cavity surface-emitting lasers. The size dependence of spatial hole burning, cavity loss, as well as thermal resistance of device cavity are taken into account. Using this model, the influence of size effects on the amplitude modulation response and second-order harmonic distortion are studied. It is found that a laser with a small core radius exhibits better modulation response and less harmonic distortion than that of a large waveguide device, however, there is a tradeoff between the output power and modulation efficiency of the lasers.