Showing papers on "Modulation published in 1998"

Effects of clipping and filtering on the performance of OFDM

Abstract: Orthogonal frequency division multiplexing (OFDM) is an attractive technique for wireless communication applications. However, an OFDM signal has a large peak-to-mean envelope power ratio, which can result in significant distortion when passed through a nonlinear device, such as a transmitter power amplifier. We investigate, through extensive computer simulations, the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the crest factor, and the bit-error rate. Our results show that clipping and filtering is a promising technique for the transmission of OFDM signals using realistic linear amplifiers.

Modulation and coding for linear Gaussian channels

Abstract: Shannon's determination of the capacity of the linear Gaussian channel has posed a magnificent challenge to succeeding generations of researchers. This paper surveys how this challenge has been met during the past half century. Orthogonal minimum-bandwidth modulation techniques and channel capacity are discussed. Binary coding techniques for low-signal-to-noise ratio (SNR) channels and nonbinary coding techniques for high-SNR channels are reviewed. Recent developments, which now allow capacity to be approached on any linear Gaussian channel, are surveyed. These new capacity-approaching techniques include turbo coding and decoding, multilevel coding, and combined coding/precoding for intersymbol-interference channels.

Robust channel estimation for OFDM systems with rapid dispersive fading channels

Abstract: Orthogonal frequency division multiplexing (OFDM) modulation is a promising technique for achieving the high-bit-rates required for a wireless multimedia service. Without channel estimation and tracking, OFDM systems have to use differential phase-shift keying (DPSK), which has a 3 dB signal-to-noise ratio (SNR) loss compared with coherent phase-shift keying (PSK). To improve the performance of OFDM systems by using coherent PSK, we investigate robust channel estimation for OFDM systems. We derive a minimum mean-square-error (MSE) channel estimator, which makes full use of the time- and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. Since the channel statistics are usually unknown, we also analyze the mismatch of the estimator to channel statistics and propose a robust channel estimator that is insensitive to the channel statistics. The robust channel estimator can significantly improve the performance of OFDM systems in a rapid dispersive fading channel.

Space-time coded OFDM for high data-rate wireless communication over wideband channels

Abstract: There has been an increasing interest in providing high data-rate services such as video-conferencing, multimedia Internet access and wide area network over wideband wireless channels. Wideband wireless channels available in the PCS band (2 GHz) have been envisioned to be used by mobile (high Doppler) and stationary (low Doppler) units in a variety of delay spread profiles. This is a challenging task, given the limited link budget and severity of wireless environment, and calls for the development of novel robust bandwidth efficient techniques which work reliably at low SNRs. To this end, we design a space-time coded orthogonal frequency division multiplexing (OFDM) modulated physical layer. This combines coding and modulation. Space-time codes were previously proposed for narrowband wireless channels. These codes have high spectral efficiency and operate at very low SNR (within 2-3 dB of the capacity). On the other hand, OFDM has matured as a modulation scheme for wideband channels. We combine these two in a natural manner and propose a system achieving data rates of 1.5-3 Mbps over a 1 MHz bandwidth channel. This system requires 18-23 dB (resp. 9-14 dB) receive SNR at a frame error probability of 10/sup -2/ with two transmit and one receive antennas (resp. two transmit and two receive antennas). As space-time coding does not require any form of interleaving, the proposed system is attractive for delay-sensitive applications.

Full-field optical coherence microscopy.

Abstract: We present a new microscopy system for imaging in turbid media that is based on the spatial coherence gate principle and generates in parallel a complete two-dimensional head-on image without scanning. This system has been implemented in a commercial microscope and preserves the lateral resolution of the optics used. With a spatially incoherent source, speckle-free images with diffraction-limited resolution are recorded at successive depths with shot-noise-limited detection. The setup comprises a photoelastic modulator for path difference modulation and a two-dimensional CCD array and uses a multiplexed lock-in detection scheme.

On the effect of Wiener phase noise in OFDM systems

Abstract: Multicarrier modulation exhibits a significant sensitivity to the phase noise of the oscillator used for frequency down-conversion at the portable receiver. For this reason, it is important to evaluate the impact of the phase noise on the system performance. We present an accurate method to determine the error probability of an orthogonal frequency-division multiplexing (OFDM) system in the presence of phase noise. In particular, four modulation schemes are analyzed and their performances are compared.

Performance enhancement of spectral-amplitude-coding optical CDMA using pulse-position modulation

Abstract: Spectral-amplitude-coding optical code-division multiple-access (OCDMA) systems are limited by interference between incoherent sources. A detailed analysis of this limit for a system with a balanced receiver is presented. Additional pulse-position modulation (PPM) coding is proposed as a method to improve the system performance beyond this limit. A simple and robust PPM decoding structure is proposed, and the performance analysis of the whole PPM-OCDMA system is presented. The interference-limited performance of the PPM-OCDMA system is found to be superior to that of the original system when the number of simultaneous users is of the order of the PPM word length or larger. In particular, for a PPM word length of two, an increase in spectral efficiency of up to 100% is possible with no change in the signaling rate, data rate, or bit-error rate (BER).

Highly bandwidth efficient communications

Abstract: A discrete multitone stacked-carrier spread spectrum communication method is based on frequency domain spreading including multiplication of a baseband signal by a set of superimposed, or stacked, complex sinusoid carrier waves. In a preferred embodiment, the spreading involves energizing the bins of a large Fast Fourier transform (FFT). This provides a considerable savings in computational complexity for moderate output FFT sizes. Point-to-multipoint and multipoint-to-multipoint (nodeless) network topologies are possible. A code-nulling method is included for interference cancellation and enhanced signal separation by exploiting the spectral diversity of the various sources. The basic method may be extended to include multielement antenna array nulling methods for interference cancellation and enhanced signal separation using spatial separation. Such methods permit directive and retrodirective transmission systems that adapt or can be adapted to the radio environment. Such systems are compatible with bandwidth-on-demand and higher-order modulation formats and use advanced adaptation algorithms. In a specific embodiment the spectral and spatial components of the adaptive weights are calculated in a unified operation based on the mathematical analogy between the spectral and spatial descriptions of the airlink.

High efficiency channel drop filter with absorption induced on/off switching and modulation

Abstract: A highly efficient channel drop filter. The filter employs a coupling element including a resonator-system between two waveguides, which contains at least two resonant modes. The resonator-system includes one or more interacting resonant cavities which in addition to being coupled to the waveguides, can also be coupled directly among themselves and indirectly among themselves via the waveguides. Each component of the coupling element can be configured or adjusted individually. The geometry and/or dielectric constant/refractive index of the resonator-system are configured so that the frequencies and decay rates of the resonant modes are made to be substantially the same. The filter can achieve 100% signal transfer between the waveguides at certain frequencies, while completely prohibiting signal transfer at other frequencies. In exemplary embodiments, the filter is configured with photonic crystals. In accordance with alternative embodiments of the invention, the filter is configured as an absorption induced on/off switch and modulator. The switching action is achieved with either electrical or optical absorption.

Error statistics in data transmission over fading channels

Abstract: We investigate the behavior of block errors which arise in data transmission on fading channels. Our approach takes into account the details of the specific coding/modulation scheme and tracks the fading process symbol by symbol. It is shown that a Markov approximation for the block error process (possibly degenerating into an identically distributed (i.i.d.) process for sufficiently fast fading) is a good model for a broad range of parameters. Also, it is observed that the relationship between the marginal error rate and the transition probability is largely insensitive to parameters such as block length, degree of forward error correction and modulation format, and depends essentially on an appropriately normalized version of the Doppler frequency. This relationship can therefore be computed in the simple case of a threshold model and then used more generally as an accurate approximation. This observation leads to a unified approach for the channel modeling, and to a simplified performance analysis of upper layer protocols.

An IC for linearizing RF power amplifiers using envelope elimination and restoration

Abstract: Efficient power amplifiers (PAs) are desirable because power amplifiers typically dominate the power consumed in portable radio devices. Cellular systems such as the advanced mobile phone system (AMPS) employ modulation schemes that generate constant amplitude RF outputs to use efficient but nonlinear PAs. Modern digital communication standards such as the North American dual-mode cellular (NADC) system require nonconstant amplitude RF outputs to maximize frequency spectral usage, and therefore require linear PAs. The traditional approach to linear RF power amplification is to back-off the output power of a PA until its distortion is reduced to an acceptable level. Power back-off can lead to significant reduction in output power and efficiency. The envelope elimination and restoration (EER) system is an alternative to power back-off, to simultaneously achieve efficiency and linearity in RF PAs.

A method for selecting a combination of modulation and channel coding schemes in a digital communication system

Abstract: A communication system that supports multiple modulation and channel coding schemes selects an optimum RF link by measuring link quality parameters, such as C/I ratio. All of the available RF links are characterized based on the measured link quality parameters by calculating mean values and variances of the parameters. Based on the characterization of the RF link, user quality values, such as user data throughput and speech quality values, are estimated. The communication system selects the RF link that provides the best user quality value.

Simulation of carrier transport and nonlinearities in quantum-well laser diodes

Abstract: The two-dimensional (2-D) quantum-well (QW) laser diode simulator Minilase-II is presented in detail. This simulator contains a complete treatment of carrier dynamics including bulk transport, quantum carrier capture, spectral hole burning, and quantum carrier heating. The models used in the simulator and their connectivity are first presented. Then the simulator is used to demonstrate the effects of various nonlinear processes occurring in QW lasers. Finally, modulation responses produced by Minilase-II are compared directly with experimental data, showing good quantitative agreement.

Multilevel Power Conversion - An Overview Of Topologies And Modulation Strategies

Abstract: Multilevel power converters represent a potential breakthrou,qh in employing swirching converters to medium voltage applications (2-13 k w . This pciper summarizes the stat e of the art in this rapidly a'eveloping Jeld ofpower electronics.

Image-forming method and image-forming apparatus

Abstract: A microscopy and apparatus capable of obtaining superresolution, and a fringe projection light-cut microscopy and apparatus capable of obtaining a natural light-cut image and enabling real-time observation. At the component separating step, a plurality of modulated images of an observation object (O) are formed by subjecting the observation object (O) to spatial modulation including a plurality of modulation components while varying the component ratios of the modulation components by moving a diffraction grating (21), which modulates the observation object (O), to a plurality of different positions. The modulated images are detected with an image pickup device (22). Modulated image components corresponding to the modulation components are separated from the number of modulated images that is not less than the number of the modulation components by using linear computation. At the component demodulating step, at least one of the separated modulated image components is demodulated.

Maximum-likelihood synchronization of a single user for code-division multiple-access communication systems

Abstract: Code-division multiple access (CDMA) has emerged as an access protocol well-suited for voice and data transmission. One significant limitation of the conventional CDMA system is the near-far problem where strong signals interfere with the detection of a weak signal. Multiuser detectors assume knowledge of all of the modulation waveforms and channel parameters, and exploit this information to eliminate multiple-access interference (MAI) and to achieve near-far resistance. A major problem in practical application of multiuser detection is the estimation of the signal and channel parameters in a near-far limited system. We consider maximum-likelihood estimation of users delay, amplitude, and phase in a CDMA communication system. We present an approach for decomposing this multiuser estimation problem into a series of single-user problems. In this method the interfering users are treated as colored non-Gaussian noise. The observation vectors are preprocessed to be able to apply a Gaussian model for the MAI. The maximum-likelihood estimate (MLE) of each user's parameters based on the processed observation vectors becomes tractable. The estimator includes a whitening filter derived from the sample covariance matrix which is used to suppress the MAI, thus yielding a near-far resistant estimator.

Optical Communication with Chaotic Waveforms

Abstract: A chaotic carrier of information can be considered a generalization of the more traditional sinusoidal carrier. In communication systems which use chaotic waveforms, as in many more conventional methods, information can be recovered from the carrier using a receiver which is “tuned,” or synchronized, to the dynamics of the transmitter. Communication methods using chaotic carriers have been studied for the past few years, and several methods have been experimentally demonstrated in electronic circuits [1]. While chaotic electronic circuits typically have bandwidths of 100 kHz or less [2], the optical system presented here has a bandwidth of at least several GHz. In those electronic chaotic communication methods that have been demonstrated, the chaos usually has been low dimensional. For certain low-dimensional chaotic communication methods, it has been shown previously that the message can be extracted from the transmitted signal by reconstructing the system’s chaotic attractor [3]. A communication method utilizing higher dimensional chaos is likely to provide enhanced privacy. Numerical analysis of our experimental data indicates that the dynamics of our system are indeed high dimensional, of order 10 or greater. Previously, Goedgebuer and colleagues have demonstrated chaotic communication of a 2 kHz sine wave using a hybrid electro-optic system to generate highdimensional chaotic fluctuations in wavelength [4]. Also in earlier work, we injected a small 10 MHz square wave optical message into a ring laser producing highdimensional chaotic light. The square wave message was masked by the chaotic intensity fluctuations of the light from the ring laser as it propagated to a receiver, where the message was recovered [5]. Here we describe several qualitatively new developments, in both concept and technique, over previous work. Rather than using the chaotic light to mask a message, an intracavity intensity modulator is used to directly encode the message onto an optical chaotic carrier. Unlike our previous work, the message signal does not have to be small compared to the carrier or slow compared to the bandwidth of the laser fluctuations; they can have comparable bandwidths. The message modulation drives the chaotic dynamics of the laser. The laser dynamics, in turn, incorporate the digital message into the chaotic waveform. Both transmitter and receiver have configurations that involve two separate time delays, thereby enhancing the privacy of the transmission —successful recovery of the message depends on multiple parameter settings and a matched geometric configuration in the receiver. Finally, the receiver utilizes the polarization properties of the light to recover the digital information by dividing two signals, rather than taking a difference. These innovations enable us to demonstrate recovery of a pseudorandom sequence of bits at 126 Mbitsysec, limited by the bandwidth of our photodiodes. Placing a 1.5 km communication channel between the transmitter and receiver did not cause any obvious degradation of performance. The experimental setup of the fiber-optic system is shown in Fig. 1. The inner ring of the transmitter includes EDFA 1 (erbium-doped fiber amplifier) and a polarizing lithium niobate sLiNBO3d intensity modulator which encodes the message onto the chaotic light. The inner ring is approximately 40 m in length. The outer loop contains EDFA 2, to adjust the amplitude of the light field, and a polarization controller. The polarization controller consists of three wave plates (ly4, ly2, and ly4, respectively) which allow control over the relative phase and polarization of the light fields in the inner ring and outer loop. The outer loop itself is approximately 36 m long and provides a time delay between these light fields. Light coupled out of the transmitter propagates through a fiber-optic communication channel to the receiver. Ten percent of the transmitted light is sent through an attenuator to photodiode A (3-dB roll-off at 125 MHz). The length of the fiber in the outer loop of the receiver has been matched to the length of the transmitter’s outer loop. The time delay between reception of a signal at photodiode A and reception at photodiode B (also 3-dB roll-off at 125 MHz) has been matched to the round-trip time in the inner ring of the transmitter. The signals detected by the photodiodes are recorded by a digital sampling oscilloscope at a rate of 1 3 10 9 samplesysec.

Symbol rate and modulation level-controlled adaptive modulation/TDMA/TDD system for high-bit-rate wireless data transmission

Abstract: This paper proposes a time-division multiple-access/time-division duplex (TDMA/TDD)-based symbol rate and modulation level-controlled adaptive modulation system for high-bit-rate data transmission. The proposed system controls both the symbol rate and modulation level for the next transmission time slot according to the estimated carrier power to noise spectral density ratio (C/N/sub 0/) and delay spread for the time slot to achieve higher bit rate and higher transmission quality as well as higher delay-spread immunity. It is demonstrated by computer simulation and laboratory experiments that the proposed system can achieve a higher average bit rate with higher transmission quality in comparison with the fixed-rate quaternary phase-shift keying (QPSK) system and modulation level-controlled adaptive modulation system in both flat Rayleigh and frequency-selective fading environments. The simulated and experimental results also show that the proposed adaptive modulation techniques can be applied to 1-2-Mb/s indoor and outdoor microcellular systems with its delay spread of up to 250 ns and its terminal mobility of up to pedestrian speed without employing any special antifrequency-selective fading techniques, such as the adaptive equalizer and space diversity.

Error free 100 Gbit/s wavelength conversion using grating assisted cross-gain modulation in 2 mm long semiconductor amplifier

Abstract: The authors demonstrate the first error free operation of 100 Gbit/s wavelength conversion employing cross-gain modulation in a semiconductor optical amplifier. A near transform limited non-return-to-zero data stream is generated at the device output.

Modular home-networking communication system and method using disparate communication channels

Abstract: A modular home-networking communications system which uses a physical layer modulation scheme suitable for transmission in both RF and powerline communication channels. The modulation system is based on direct-sequence spread-spectrum (DS-SS) using Barker codes to spread the information symbols, which provides both operation at low signal to noise ratio and very good resistance to time dispersion distortion due to the excellent autocorrelation properties of the Barker codes. This type of modulation system is ideal for the powerline communications channel since it spreads the transmission power over a wide range of frequency, lowering the power spectral density enough that it will provide long distance coverage without violating FCC radiated emission and conducted power regulations.

Efficient integrated RF telemetry transmitter for use with implantable device

Abstract: An efficient RF telemetry transmitter system includes a first stage and a second stage. The transmitter system sends power and data to an implant device using pulse-width modulation of a high fixed frequency clock signal, e.g., a 49 MHz clock signal, within the first stage in order to provide efficient generation of an RF output signal in the second stage. Digital logic gates and related circuitry, e.g., implemented in an application specific integrated circuit (ASIC), are used in the first stage to provide pulse-width modulation of the fixed frequency clock signal in order to optimally set the drive level of the output signal of the first stage, or inter-stage signal. ON/OFF keying, or other modulation scheme, further modulates the clock signal with data in the first stage. The second stage includes a Class-E amplifier circuit implemented with a single RF transistor, biased with a temperature-compensated offset voltage set just below the cut-off voltage of the transistor. An LC filter placed in the front end of the second stage filters out all but the fundamental frequency component of the inter-stage signal. The drive level of the inter-stage signal is selected to prevent both overdriving and underdriving of the Class-E amplifier. An adjustable or selectable collector voltage coupled to the single RF transistor allows the amplitude of the output signal to be set to an optimum power level for transmission to the implant device.

A general analytical method for determining the theoretical harmonic components of carrier based PWM strategies

Abstract: The analysis of pulse width modulation schemes for switched power converters has been a major research area for several decades, and considerable effort has gone into attempting to develop analysis techniques which allow one scheme to be evaluated against another for various fundamental and carrier frequencies and at different modulation depths. Except for a limited number of analytical solutions developed for specific modulation strategies, this analysis is generally done by digital simulation of the switched waveform and subsequent FFT or performance index calculation. This approach can require substantial computing capacity, and also has a significant potential for inaccuracies caused by subtle programming errors, which may cause erroneous comparisons to be made between different PWM schemes under particular operating conditions when the performance differences are slight. This paper presents a general method for determining the theoretical harmonic components of all major known variations of PWM. The method identifies appropriate inner and outer integral limits of the double Fourier integral solution of the switched waveform to suit each modulation strategy, and then solves this double integral using Jacobi-Anger expansions to establish closed form solutions. The method is applicable irrespective of the pulse ratio between the carrier and the fundamental, and the computational requirements are essentially constant irrespective of the absolute value of the carrier frequency.

Improved universal lan power line carrier repeater system and method

Abstract: An improved local area network (LAN) to power line carrier (PLC) interface and protocol using FSK is described. This system provides improved data symmetry, higher data rates, lower bit error rates, improved synchronization and alignment of data, as well as improved carrier detection. The system provides high speed frequency shift key (FSK) modulation over the power line to achieve high data rates. Performance may be further improved by using a novel combination of FSK modulation and differential shift key (DFSK) modulation to provide an improved local area network (LAN) to power line carrier (PLC) interface and protocol using FSK and DFSK. DFSK is described and shown to provide improvements in the modulation and demodulation of data transferred over digital networks.

Broad-band millimeter-wave (38 GHz) fiber-wireless transmission system using electrical and optical SSB modulation to overcome dispersion effects

Abstract: A spectrally efficient millimeter-wave (mm-wave) fiber-wireless transmission system is presented demonstrating downstream transportation of 155-Mb/s BPSK data at 38 GHz over 50 km of standard single-mode fiber and a 5-m wireless link. The effect of fiber chromatic dispersion on the transmission of the mm-wave optical carrier was overcome by using a single dual-electrode Mach-Zehnder modulator to generate optical single-sideband (SSB) modulation with carrier. We also demonstrate a simple technique for obtaining electrical SSB that will allow the effect of fiber dispersion across the bandwidth of the information to be overcome with simple electrical delay equalization. We predict that this fiber-wireless system could permit the transportation of mm-wave signals with large bit rates over long optical fiber distances.

Performance analysis of Viterbi decoding for 64-DAPSK and 64-QAM modulated OFDM signals

Abstract: The multilevel modulation techniques of 64-quadrature amplitude modulation (QAM) and 64-differential amplitude and phase-shift keying (DAPSK) have been proposed in combination with the orthogonal frequency-division multiplexing (OFDM) scheme for digital terrestrial video broadcasting (DTVB). With this system a data rate of 34 Mb/s can be transmitted over an 8-MHz radio channel. A comparison of these modulation methods in the uncoded case has been presented by Engels and Rohling (see European Trans. Telecommun., vol.6, p.633-40, 1995). The channel coding scheme proposed for DTVB by Schafer (see Proc. Int. Broadcasting Convention, Amsterdam, The Netherlands, p.79-84, 1995) consists of an inner convolutional code concatenated with an outer Reed-Solomon (RS) code. In this paper the performance of the convolutional codes is analyzed for the two modulation techniques. This analysis includes soft decision Viterbi (1971) decoding of the convolutional code. For soft decision decoding of DAPSK modulated signals a new metric is developed.

Performance analysis of wavelength converters based on cross-gain modulation in semiconductor-optical amplifiers

Abstract: An analytical theory describing all-optical wavelength converters based on cross-gain modulation (XGM) in semiconductor-optical amplifiers is derived. Our theory consists of two parts: a large-signal analysis yielding the transmission function for the signal, and a small-signal analysis in order to describe the transformation of the signal and probe intensity noise. Both the large-signal as well as the small-signal theory reveal similar performance for the co- and the counterpropagating injection scheme for bit rates up to 2.5 Gb/s. This is confirmed by computer simulations. Consequently, the counterpropagating configuration is preferable because the implementation is simpler and conversion to the same wavelength is possible. In order to increase the conversion efficiency it is better to reduce the average signal power than to increase the probe power, which additionally reduces the output power range. However, there is a tradeoff between conversion efficiency and output extinction ratio. According to the small-signal analysis, the relative-intensity noise (RIN) due to the probe and due to the amplified spontaneous emission is negligible. Moreover, the converted signal has a lower RIN than the input signal.

30-THz span optical frequency comb generation by self-phase modulation in an optical fiber

Abstract: The width of an optical frequency comb (OFC) was increased to 30 THz by using self-phase modulation (SPM) in an optical fiber. This value is 2.7 times larger than the maximum OFC span obtained by the OFC generator alone. We compare the resulting spectrum to numerical simulations to confirm that the SPM and the higher order dispersion of the fiber contribute to broaden the spectral profile.

A general constant-frequency pulsewidth modulator and its applications

Abstract: Constant-frequency pulsewidth modulation (PWM) is the most frequently used method in the control of switching converters. This paper proposes a general PWM modulator that realizes various control schemes with either trailing-edge or leading-edge modulation. Based on that a general double-edge modulator ran be constructed. The proposed modulator is applied to feedforward control of a family of converters, current-mode control with linear or nonlinear compensating slope, and a family of unity-power-factor rectifiers at continuous or discontinuous conduction mode to demonstrate its generality. Experimental and PSPICE verifications are provided.

Direct multilevel carrier modulation using millimeter-wave balanced vector modulators

Abstract: The importance of being able to design affordable, high-performance, millimeter-wave transmitters for digital communications and radar applications is increasing. To this end, two monolithic millimeter-wave vector modulators have been realized at 38 and 60 GHz for use in direct multilevel carrier modulation. It is shown that, by employing balanced biphase amplitude modulator elements, accurate constellations are achieved with broad-band operation from 20 to 40 GHz and 55 to 65 GHz. Modulations of 16- and 256-QAM have been demonstrated, both at 38 and 60 GHz, using this technique. Each balanced biphase amplitude modulator uses a pair of reflection-type attenuators operated in push-pull mode. This study investigates the suitability of this topology for use as a full biphase amplitude modulator for multilevel digital modulation schemes. It is found that the technique is very robust and the resulting analog vector modulator can be a very important component for many future millimeter-wave applications.

An agile ISM band frequency synthesizer with built-in GMSK data modulation

Abstract: In this paper, a high-resolution fractional-N RF frequency synthesizer is presented which is controlled by a fourth-order digital sigma-delta modulator. The high resolution allows the synthesizer to be digitally modulated directly at RF. A simplified digital filter which makes use of sigma-delta quantized tap coefficients is included which provides built-in GMSK pulse shaping for data transmission. Quantization of the tap coefficients to single-bit values not only simplifies the filter architecture, but the fourth-order digital sigma-delta modulator as well. The synthesizer makes extensive use of custom VLSI, with only a simple off-chip loop filter and VCO required. The synthesizer operates from a single 3-V supply, and has low power consumption. Phase noise levels are less than -90 dBc/Hz at frequency offsets within the loop bandwidth. Spurious components are less than -90 dBc/Hz over a 19.6-MHz tuning range.