Showing papers on "Modulation published in 2002"

Frequency domain equalization for single-carrier broadband wireless systems

Abstract: Broadband wireless access systems deployed in residential and business environments are likely to face hostile radio propagation environments, with multipath delay spread extending over tens or hundreds of bit intervals. Orthogonal frequency-division multiplex (OFDM) is a recognized multicarrier solution to combat the effects of such multipath conditions. This article surveys frequency domain equalization (FDE) applied to single-carrier (SC) modulation solutions. SC radio modems with frequency domain equalization have similar performance, efficiency, and low signal processing complexity advantages as OFDM, and in addition are less sensitive than OFDM to RF impairments such as power amplifier nonlinearities. We discuss similarities and differences of SC and OFDM systems and coexistence possibilities, and present examples of SC-FDE performance capabilities.

Relationship between space-vector modulation and three-phase carrier-based PWM: a comprehensive analysis [three-phase inverters]

Abstract: This paper comprehensively analyzes the relationship between space-vector modulation and three-phase carrier-based pulse width modulation (PWM). The relationships involved, such as the relationship between modulation signals (including zero-sequence component and fundamental components) and space vectors, the relationship between the modulation signals and the space-vector sectors, the relationship between the switching pattern of space-vector modulation and the type of carrier, and the relationship between the distribution of zero vectors and different zero-sequence signal are systematically established. All the relationships provide a bidirectional bridge for the transformation between carrier-based PWM modulators and space-vector modulation modulators. It is shown that all the drawn conclusions are independent of the load type. Furthermore, the implementations of both space-vector modulation and carrier-based PWM in a closed-loop feedback converter are discussed.

Adaptive RF-photonic arbitrary waveform generator

Abstract: The system uses spectral shaping of a supercontinuum source followed by wavelength-to-time mapping to generate ultra wideband RF waveforms with arbitrary modulation. It employs adaptive computer control to mitigate the non-ideal features inherent in the optical source and in the spectrum modulation process. As proof of concept, ultra-wideband frequency hopped CDMA waveforms are demonstrated.

M-QAM-OFDM system performance in the presence of a nonlinear amplifier and phase noise

Abstract: The orthogonal frequency-division multiplexing (OFDM) modulation format has been proposed in Europe as the standard for broadcasting both audio and television digital signals and for wide-band wireless communication systems (e.g., HIPERLAN II). The performance of the OFDM scheme is severely affected by the nonlinearity of the high-power amplifier at the transmitter end and by the phase noise of the oscillators. In this paper, we investigate the joint effects induced on the OFDM signal by the amplifier nonlinearity and by the phase noise. An accurate statistical description of each contribution to the signal distortion is provided. Theoretical results show perfect agreement with those obtained by simulation and they can be used to derive the OFDM system performance, without the need to run extensive simulations.

Time division multiplexing over broadband modulation method and apparatus

Abstract: A packet switch router that processes downstream digital information to provide dedicated bandwidth to each subscriber destination in a hybrid fiber coax (HFC) network. The router includes a network module that terminates a network connection, a switch that forwards data from the network module, and a channel module. The channel module includes a switch interface, a cell processing engine, one or more modulators, and a radio frequency (RF) transmitter network. The switch interface forwards packetized data from the switch to the cell processing engine. The cell processing engine organizes the packetized data into multiple data streams, encapsulates data in each data stream into data cells, and multiplexes the data cells into a multiplexed cell stream. Each modulator is configured to modulate a multiplexed cell stream into an analog signal. The RF transmitter network up converts and combines a plurality of analog signals into a combined electrical signal for transmission.

Filtered multitone modulation for very high-speed digital subscriber lines

Abstract: A filter-bank modulation technique called filtered multitone (FMT) and its application to data transmission for very high-speed digital subscriber line technology are described. The proposed scheme leads to significantly lower spectral overlapping between adjacent subchannels than for known multicarrier techniques such as discrete multitone (DMT) or discrete wavelet multitone. FMT modulation mitigates interference due to echo and near-end crosstalk signals, and increases the system throughput and reach. Signal equalization in an FMT receiver is accomplished in the form of per-subchannel symbol-spaced or fractionally spaced linear or decision-feedback equalization. The problem of channel coding for this type of modulation is also addressed, and an approach that allows combined removal of intersymbol-interference via precoding and trellis coding is described. Furthermore, practical design aspects regarding filter-bank realization, initial transceiver training, adaptive equalization, and timing recovery are discussed. Finally, simulation results of the performance achieved by FMT modulation for very high-speed digital subscriber line systems, where upstream and downstream signals are separated by frequency-division duplexing, are presented and compared with DMT modulation.

On the UWB system coexistence with GSM900, UMTS/WCDMA, and GPS

Abstract: This paper evaluates the level of interference caused by different ultra-wideband (UWB) signals to other various radio systems, as well as the performance degradation of UWB systems in the presence of narrowband interference and pulsed jamming. The in-band interference caused by a selection of UWB signals is calculated at GSM900, UMTS/wideband code-division multiple-access (WCDMA), and Global Position System (GPS) frequency bands as a function of the UWB pulsewidth. Several short-pulse waveforms, based on the Gaussian pulse, can be used to generate UWB transmission. The two UWB system concepts studied here are time hopping and direct sequence spread spectrum. Baseband binary pulse amplitude modulation is used as the data modulation scheme. Proper selection of pulse waveform and pulsewidth allows one to avoid some rejected frequency bands up to a certain limit. However, the pulse shape is also intertwined with the data rate demands. If short-pulses are used in UWB communication the high-pass filtered waveforms are preferred according to the results. The use of long pulses, however, favors the generic Gaussian waveform instead. An UWB system suffers most from narrowband systems if the narrowband interference and the nominal center frequency of the UWB signal overlap. This is proved by bit-error rate simulations in an additive white Gaussian noise (AWGN) channel with interference at global system for mobile communication (GSM) and UMTS/WCDMA frequencies.

Optimum harmonic reduction with a wide range of modulation indexes for multilevel converters

Abstract: This paper proposes a novel modulation technique to be applied to multilevel voltage-source converters suitable for high-voltage power supplies and flexible AC transmission system devices. The proposed technique can generate output stepped waveforms with a wide range of modulation indexes and minimized total voltage harmonic distortion. The main power devices switch only once per cycle, as is suitable for high-power applications. In addition to meeting the minimum turn-on and turn-off time requirements for high-power semiconductor switches, the proposed technique excludes from the synthesized waveform any pulses that are either too narrow or too wide. By using a systematic method, only the polarities and the number of levels need to be determined for different modulation levels. To verify the theory and the simulation results, a cascaded converter-based hardware prototype, including an 8-b microcontroller as well as modularized power stage and gate driver circuits, is implemented. Experimental results indicate that the proposed technique is effective for the reduction of harmonics in multilevel converters, and both the theoretical and simulation results are well validated.

Low-density parity-check codes for digital subscriber lines

Abstract: The paper investigates the application of low-density parity-check (LDPC) codes to digital subscriber-line (DSL) transmission systems that employ discrete multitone modulation. A family of linear-time encodable binary LDPC codes that are well-suited for DSL transmission is introduced. Encoding and symbol mapping for multilevel modulation are described. Simulation results show that even under tight latency constraints good net coding gains can be achieved. Implementation complexity is analyzed and compared with that of trellis-coded modulation as employed in current asymmetric DSL transceivers. The incorporation of powerful LDPC coding techniques into next-generation DSL modems appears to be possible with reasonable increase in transceiver complexity.

Mitigating multiple access interference and intersymbol interference in uncoded CDMA systems with chip-level interleaving

Abstract: The presence of intersymbol interference (ISI), in addition to multiple access interference, severely hampers the performance of a code-division multiple-access (CDMA) communication system. In such a situation, channel coding can be used to obtain better performance, but at the cost of a reduction in rate of flow of information. In this paper, it is shown with the help of simulation results that the chip-interleaved CDMA system effectively combats ISI without requiring additional channel coding. The system differs from the conventional CDMA system in the sense that, the chip sequence resulting from the pseudo noise (PN) sequence modulation is interleaved before transmission. Two receivers are proposed, one based on the turbo equalization method which employs a maximum a posteriori equalizer of exponential complexity and the other based on minimum-mean square error-optimized iterative interference cancellation principles which is of linear complexity. Simulation results are provided which show that error rates close to the no-ISI single-user case can be obtained. The shortcomings of the coded CDMA with turbo detection system in the presence of ISI are also discussed.

Modulation characteristics of quantum-dot lasers: the influence of p-type doping and the electronic density of states on obtaining high speed

Abstract: The influence of p-type modulation doping on self-organized quantum-dot lasers is studied using a quasiequilibrium model that includes the multi-discrete energy levels and the energy levels of the wetting layer. Calculations are presented showing that laser performance can be greatly enhanced through p-doping and that, in contrast to planar quantum-well lasers, the p-doping requirements are moderate. Optimized cavity lengths are found, and the threshold temperature and modulation characteristics are determined for these cavity lengths. The model shows that close energy spacing of the discrete hole levels can severely limit the modulation response, as suggested previously, and that this effect is countered through creation of an excess hole concentration using p-type doping. Good agreement is obtained with the modulation response reported in recent experiments for undoped quantum-dot active regions. The calculations suggest that bandwidths greater than 30 GHz can be obtained with sufficient p-doping. A reduction in the inhomogeneous broadening might increase the laser speed to over 60 GHz.

Optical transmission apparatus

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

Electrosurgical generator apparatus

Abstract: An electrosurgical generator apparatus controls a variable output signal to electrodes. The generator apparatus operates in a cut mode, a coagulation mode or a stimulate mode. The generator apparatus comprises a DC power supply that provides regulated low voltage and high voltage outputs and a radio frequency (RF) waveform generator circuit that provides pulse duration modulation (PDM) of a carrier signal. The carrier signal directly affects the variable output signal to the electrodes. A control circuit controls a variable output signal to electrodes used in electrosurgical procedures. The control circuit comprises a DC power supply circuit that provides regulated low voltage and high voltage outputs and an RF waveform generator circuit that provides pulse duration modulation of a carrier signal. The carrier signal directly affects the variable output signal to the electrodes.

An approach to reduce common mode voltage in matrix converter

Abstract: In this paper, an approach to reduce common-mode voltage at the output of a matrix converter is discussed. A new modulation strategy which reduces the common-mode voltage at the output is presented. The proposed method maintains the active voltage vector and distributes zero vector equally within a sampling period and reduces square RMS of ripple components of input current. Advantages of the scheme include: 34% reduction in the common-mode voltage (peak value); improved harmonic spectrum; reduced switching losses and no more additional switching instants over one sampling period; and simplified implementation via software. Further, the voltage transfer ratio is unaffected by the proposed scheme. Simulation results are shown to demonstrate the advantages of the new pulsewidth modulation approach. Experimental results on a 230-V 3-kVA matrix converter-fed adjustable-speed drive based on a digital signal processor controller are presented.

A Novel UWB Pulse Shape Modulation System

Abstract: In this paper novel modified Hermite polynomial functions for use in impulse radio (ultra-wideband) communications are proposed. With these functions pulse shapes which are orthogonal and have nearly constant pulse width regardless of the pulse order are generated. These properties hold under the effects of differentiation. An M-ary communication system is constructed using these pulse shapes. A Matlab model for generating the pulses is designed and the effect of timing jitter on the performance of the system is investigated by computer simulation.

Rate selection for an ofdm system

Abstract: Techniques to determine the rate for a data transmission in an OFDM system. The maximum data rate that may be reliably transmitted over a given multipath (non-flat) channel by the OFDM system is determined based on a metric for an equivalent (flat) channel. For the given multipath channel and a particular rate (which may be indicative of a particular data rate, modulation scheme, and coding rate), the metric is initially derived from an equivalent data rate and the particular modulation scheme. A threshold SNR needed to reliably transmit the particular data rate using the particular modulation scheme and coding rate is then determined. The particular rate is deemed as being supported by the multipath channel if the metric is greater than or equal to the threshold SNR. Incremental transmission is used to account for errors in the determined data rate.

Low-complexity blind carrier frequency recovery for OFDM signals over frequency-selective radio channels

Abstract: This paper introduces a blind (ie, data independent) algorithm for carrier frequency offset recovery in an orthogonal frequency-division multiplexing (OFDM) receiver operating over frequency-selective fading channels The main idea behind this algorithm is to exploit the time-frequency-domain exchange inherent to the modulation scheme Due to this feature, a carrier frequency offset has a similar impact on OFDM as a clock timing offset has in a quadrature amplitude modulation (QAM) system The scheme we propose is a variant of Oerder-Meyr's (1988) feedforward clock recovery Its performance is assessed by simulation, and the results are compared to those obtained from Van de Beek-Sandell-Borjesson's (1997) frequency synchronizer, which bears comparable complexity The new scheme is shown to outperform the latter over frequency-selective fading channels, notably at medium to high signal-to-noise ratios We also evaluated the efficiency of two different (time domain and frequency domain) offset correction strategies embedded in a particular OFDM receiver

Coding approaches for multiple antenna transmission in fast fading and OFDM

Abstract: Multiple-antenna channel coding for orthogonal frequency-division multiplexing (OFDM) transmission over dispersive channels is reconsidered because with frequency interleaving, the effective channel characteristic across subcarriers is rather fast fading. The channel does not comply with the quasistatic model widely assumed for space-time trellis codes (STCs). For that reason, we first study the ideal fast-fading multiple transmit and receive antenna channel and then compare the performance of STCs with that of bit-interleaved coded modulation in fast fading. Mutual information of the ergodic channel is evaluated for numerous modulation scenarios, and capacity comparisons generate guidelines on how to jointly adjust coding rate and modulation cardinality. Bit-based coding offers large flexibility in rate adaptation, and simulation results show that it outperforms STCs in ideal fast fading and, finally, in a realistic OFDM application as well.

All-digital impulse radio with multiuser detection for wireless cellular systems

Abstract: Impulse radio is an ultrawideband system with attractive features for baseband asynchronous multiple-access, multimedia services, and tactical wireless communications. Implemented with analog components, the continuous-time impulse radio multiple-access model utilizes pulse-position modulation and random time-hopping codes to alleviate multipath effects and suppress multiuser interference. We introduce a novel continuous-time impulse radio transmitter model and deduce from it an approximate one with lower complexity. We also develop a time-division duplex access protocol along with orthogonal user codes to enable impulse radio as a radio link for wireless cellular systems. Relying on this protocol, we then derive a multiple-input/multiple-output equivalent model for full continuous-time model and a single-input/single-output model, for the approximate one. Based on these models, we finally develop design composite linear/nonlinear receivers for the downlink. The linear step eliminates multiuser interference deterministically and accounts for frequency-selective multipath while a maximum-likelihood receiver performs symbol detection. Simulations are provided to compare performance of the different receivers.

The role of p-type doping and the density of states on the modulation response of quantum dot lasers

Abstract: The modulation response of quantum dot (QD) lasers is analyzed using a quasi-equilibrium approach. The model suggests that present QD lasers are limited due to hole levels that are closely spaced in energy, as well as inhomogeneous broadening. Significant improvements are predicted through p-type modulation doping. The results are consistent with present QD lasers being limited in their modulation response by their differential gain as opposed to carrier capture.

Multiple modulation wireless transmitter

Abstract: A dual modulation transmitter apparatus ( 100 ) includes first ( 134 ), second ( 136 ), and third ( 132 ) signal paths. The first signal path includes a polar modulator ( 120 ) coupled to a data input ( 115 ). The second signal path includes a quadrature modulator ( 122 ) coupled to the data input. The third signal path is coupled to an antenna ( 142 ) and includes a switch ( 128 ) configured to couple the third signal path to the first signal path under a first condition and to couple the third signal path to the second signal path under a second condition. Thus, the transmitter apparatus enjoys the best of both worlds, since it utilizes quadrature or polar modulation in the most appropriate circumstances.

Pseudo-Linear Transmission of High-Speed TDM Signals: 40 and 160 Gb/s

Abstract: Publisher Summary The pseudo–linear transmission is a method for the transmission of high-speed time-division multiplexed (TDM) signals where fast variations of each channel waveform with cumulative dispersion allows important averaging of the intrachannel effects of fiber nonlinearity. The pseudo–linear transmission involves complex optimization of modulation format, dispersion mapping, and nonlinearity. These transmissions occupy a space somewhere between dispersion-mapped linear transmission and nonlinear soliton transmission. The pseudo-linear regime of transmission is characterized by a rapid pulse broadening, which results in a dramatic reduction of the solitonic effect on each pulse. As a result, full dispersion compensation can be used in this regime. Extensive analysis of pseudo-linear transmission and reviews of the TDM transmission experiments at 40 and 160 Gb/s have been provided in the chapter. Two new forms of nonlinear interactions between rapidly dispersing pulses namely intrachannel cross–phase modulation (IXPM) and intrachannel four–wave mixing (IFWM) are also presented. These two intrachannel effects are the most important nonlinear interactions in pseudo-linear transmission and determine the dispersion mapping even for the wavelength–division multiplexed (WDM) systems. Further, the chapter describes the semiconductor–based technologies that enable the development of stable and reliable high–speed transmitters and receivers.

Integrated beamformer/modem architecture

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

Multi-channel communications transceiver

Abstract: A transceiver system according to the present invention transmits data utilizing the baseband and one or more frequency separated transmission bands. A baseband transmitter is combined with one or more transmitters that transmit data into one of the frequency separated transmission bands. A baseband receiver is combined with one or more receivers that receive data from the frequency separated transmission bands. Any combination of modulation systems can be utilized (e.g. PAM for the baseband and QAM for the frequency separated bands). A transceiver circuit or chip according to the present invention includes a transmitter and a receiver and communicates with a corresponding transceiver chip. In some embodiments, one baseband PAM transmitter is combined with one frequency separated QAM transmitter.

Optimal pilot waveform assisted modulation for ultra-wideband communications

Abstract: Performance of ultra-wideband (UWB) communication systems can be enhanced by collecting multipath diversity gains, once the channels are acquired at the receiver. In this paper, we develop a novel pilot waveform assisted modulation (PWAM) scheme that is tailored for power-limited UWB communications, and can be implemented in analog form. The PWAM parameters are designed to jointly optimize performance and information rate. The resulting transmitter design also minimizes the mean square error (MSE) of channel estimation and thereby achieves the Cramer-Rao lower bound (CRLB).

Adaptive coding and modulation

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

Record carrier and apparatus for scanning the record carrier

Abstract: A record carrier (1) is described which has a servo track (4) indicating an information track (9) intended for recording information blocks. The servo track (4) has a periodic variation of a physical parameter at a predetermined frequency, usually called wobble. the servo track has modulated parts for encoding position information according to a predetermined type of modulation. The record carrier comprises a management area in which the servo track comprises permanent data. The permanent data is encoded using a different type of modulation, but using the variations of the same physical parameter. Direct digital modulation (41) is proposed for the different type of modulation. Further a device for reading and/or writing the record carrier is described.

A holey fiber-based nonlinear thresholding device for optical CDMA receiver performance enhancement

Abstract: We demonstrate the use of an optical thresholder based on a short length of holey fiber to achieve enhanced code recognition quality in a 255-chip 320-Gchip/s superstructured fiber Bragg grating-based optical code-division multiple access code:decode system. The nonlinear thresholder is based on bandpass filtering of spectrally broadened components generated by self-phase modulation and assisted by the Raman effect in an 8.7 m length of highly nonlinear holey fiber. Error free penalty free system performance is obtained with complete recovery of the original input pulse shape.

Wavelength switching components for future photonic networks

Abstract: This article provides a review of integrated laser and semiconductor optical amplifier components that have been configured to provide a variety of all-optical functions such as wavelength conversion, routing, signal regeneration, and add-drop multiplexing. The components have been devised so that they can be reliably and simply used within a multiwavelength network. The article introduces the components by outlining the current leading techniques for wavelength conversion using SOAs, namely by way of cross-gain modulation, cross-phase modulation, and four-wave mixing. The integrated SOA distributed feedback laser is then shown to provide excellent regeneration properties, not only overcoming fiber dispersion limitations but also polarization mode dispersion. Finally, the devices are shown to make possible a regenerative wavelength switching node where routing is achieved using a tunable laser to provide regenerative wavelength conversion followed by an arrayed waveguide router. This switch shows promise for use in future photonic packet switching architectures.

Efficient pulse amplitude modulation transmit modulation

Abstract: Efficient PAM transmit modulation is provided by a PAM modulator that includes an oscillator ( 404 ) that provides a clock signal, CKV, ( 408 ). The clock signal 408 and a delayed version (CKV_DLY) 420 of the clock signal are provided to a logic gate ( 414 ). The output of logic gate ( 414 ) is used as a power amplifier input signal (PA_IN) for radio frequency power amplifier ( 416 ). Depending on the relative time delay of the CKV clock signal ( 408 ) and the CKV_DLY delayed clock signal ( 420 ), the timing and duty cycle of the logic gate ( 414 ) duty cycle can be controlled. The duty cycle or pulse-width variation affects the turn-on time of the power amplifier ( 416 ); thereby establishing the RF output amplitude.