Showing papers on "Quadrature amplitude modulation published in 1987"

Trellis-coded modulation with redundant signal sets Part I: Introduction

Abstract: rellis-Coded Modulation (TCM) has evolved over the past decade as a combined coding and modulation technique for digital transmission over band-limited channels. Its main attraction comes from the fact that it allows the achievement of significant coding gains over conventional uncoded multilevel modulation without compromising bandwidth efficiency. T h e first TCM schemes were proposed in 1976 [I]. Following a more detailed publication [2] in 1982, an explosion of research and actual implementations of TCM took place, to the point where today there is a good understanding of the theory and capabilities of TCM methods. In Part 1 of this two-part article, an introduction into TCM is given. T h e reasons for the development of TCM are reviewed, and examples of simple TCM schemes are discussed. Part I1 [I51 provides further insight into code design and performance, and addresses. recent advances in TCM. TCM schemes employ redundant nonbinary modulation in combination with a finite-state encoder which governs the selection of modulation signals to generate coded signal sequences. In the receiver, the noisy signals are decoded by a soft-decision maximum-likelihood sequence decoder. Simple four-state TCM schemes can improve. the robustness of digital transmission against additive noise by 3 dB, compared to conventional , uncoded modulation. With more complex TCM schemes, the coding gain can reach 6 dB or more. These gains are obtained without bandwidth expansion or reduction of the effective information rate as required by traditional error-correction schemes. Shannon's information theory predicted the existence of coded modulation schemes with these characteristics more than three decades ago. T h e development of effective TCM techniques and today's signal-processing technology now allow these ,gains to be obtained in practice. Signal waveforms representing information sequences ~ are most impervious to noise-induced detection errors if they are very different from each other. Mathematically, this translates into therequirement that signal sequences should have large distance in Euclidean signal space. ~ T h e essential new concept of TCM that led to the afore-1 mentioned gains was to use signal-set expansion to I provide redundancy for coding, and to design coding and ' signal-mapping functions jointly so as to maximize ~ directly the \" free distance \" (minimum Euclidean distance) between coded signal sequences. This allowed the construction of modulation codes whose free distance significantly exceeded the minimum distance between uncoded modulation signals, at the same information rate, bandwidth, and signal power. The term \" …

Spectral Correlation of Modulated Signals: Part II--Digital Modulation

Abstract: As a continuation of Part I, the spectral correlation function is presented for a variety of types of digitally modulated signals. These include digital pulse-amplitude, pulse-width, and pulse-position modulation, and various types of phase-shift keying and frequency-shift keying. The magnitudes of the spectral correlation functions are graphed as the heights of surfaces above a bifrequency plane, and these graphs are used as visual aids for comparison and contrast of the spectral correlation properties of different modulation types.

Spectral Correlation of Modulated Signals: Part I--Analog Modulation

Abstract: The importance of the concept of cyclostationarity in design and analysis of signal detectors, synchronizers, and extractors in communication systems is briefly discussed, and the central role of spectral correlation, in the characterization of random processes that are cyclostationary in the wide sense, is explained. A spectral correlation function that is a generalization of the power spectral density function is described, and a corresponding generalization of the Wiener-Khinchine relation and several other fundamental spectral correlation relations also are described. Explicit formulas for the spectral correlation function for various types of analog-modulated signals are derived. This includes pulse and carrier amplitude modulation, quadrature amplitude carrier modulation, and phase and frequency carrier modulation. To illustrate the differing spectral correlation characteristics of different modulation types, the magnitudes of the spectral correlation functions are graphed or described in graphical terms as the heights of surfaces above a bifrequency plane.

Performance Analysis of Digital Radio Links with Nonlinear Transmit Amplifiers

Abstract: This paper evaluates the effects of transmit amplifier nonlinearities on digital radio link performance. Special emphasis is given to links carrying 256-level modulations, for which the impact of even mild nonlinearities can be severe. Performance is measured in terms of the flat fade margin ( F ) normalized by its theoretical maximum (F max ). Curves of F / F_{max} versus amplifier input drive level are used to evaluate and compare numerous design strategies. A major contribution of this work is the development of a fast, accurate method of computer analysis, in contrast to the more cumbersome Monte Carlo simulations generally used for these assessments. Moreover, the new method is used to study a variety of techniques devised to combat the nonlinearity, particularly signal predistortion. It is also used to investigate various approaches to pulse shaping and filtering, to quantify the degradation in performance with increasing numbers of modulation levels, and to examine the possible benefits of linear equalization.

Electronic Communications Systems: Fundamentals through Advanced

Abstract: From the Publisher: All topics have been updated to present the latest information available in this fast-changing field, and completely new sections have been added to cover the following important topics: AM envelopes produced by complex nonsinusoidal signals Quadrature Amplitude Modulation Noise limiters and blankers Alternate signal-to-noise measurements Single-sideband suppressed carrier and frequency division multiplexing Double-sideband suppressed carrier and quadrature multiplexing Microstrip and stripline Light sources, optical power, optical sources, and link budget Trellis encoding CCIt modem recommendations PCM line speed Extended superframe format and wavelength division multiplexing Kepler's laws Clark orbits, and limits of visibility In addition, an entirely new chapter has been added with coverage of: Mobile telephone systems (including AMPS, PSC, and PCSS) This text is written for use in undergraduate level electronic communications courses in which students have prior knowledge of some of the basic electronic principles, as well as an understanding of mathematics through the fundamental concepts of calculus.

256 QAM Modem for Multicarrier 400 Mbit/s Digital Radio

Abstract: This paper describes the performance of a 256 QAM modem with 400 Mbit / s transmission capacity. A variety of novel techniques are introduced as ways to achieve good performance. Key techniques include 1) an accurate 256 QAM modulator employing a new monolithic multiplier IC, 2) a carrier recovery circuit which satisfies such requirements: good phase jitter performance and no false lock phenomenon, 3) a highly stable high-level decision circuit, and 4) a forward error correcting code. As an overall modem performance, BER characteristics and signatures are presented. The equivalent CNR degradations of 1 dB(at BER of 10-4) and 2 dB (at BER of 10-9)are obtained using a single Lee-error correcting code and a seven-tap baseband transversal equalizer. The residual bit errors are decreased below the order of 10-10. The performance of a 256 QAM multicarrier modem has given prospect for the development of 400 Mbit/s digital microwave radio system.

A comparison of data modulation techniques for land mobile satellite channels

Abstract: Several modulation schemes for transmitting data over land mobile satellite channels are compared using a Monte Carlo simulation. Schemes under consideration include differentially detected minimum shift keying (DMSK), differentially detected filtered offset quadrature phase shift keying (DOQPSK), and coherently detected binary phase shift keying with transparent tone-in-band processing (BPSK-TTIB). The transmission of data to and from a mobile radio, which is also capable of operating as an amplitude companded single sideband radio, is the application considered here. The nominal bit rate is 2400 bit/s, while the nominal channel spacing is 5 kHz. DOQPSK with nonredundant single-error correction (SEC) is shown to be a promising candidate. It is capable of outperforming DMSK with SEC by more than 1 dB. Techniques that send a reference signal along with a PSK signal and then perform coherent detection, such as BPSK-TTIB, are also shown to be inferior to DOQPSK with SEC for the class of channels considered here.

Performance of Quadrature Amplitude Modulation for Indoor Radio Communications

Abstract: The performance of M -QAM for indoor radio communications is evaluated via a realistic model for indoor multipath propagation [1]. It is found that the outage (BER < 10-4) is about 0.3 percent at 1 Mbit/s and 20 percent at 4 Mbits/s. Two-antenna predetection diversity reduces the outage from 1.2 to 0.04 percent at 2 Mbits/s. Increasing the signaling pulse rolloff factor from 0.5 to 1.0 reduces the outage by not more than 35 percent.

Design and Field Test of a 256-QAM DIV Modem

Abstract: The increasing demand for digital transmission facilities has led to the development of modems which allow the transmission of T1 (1.544 Mbit/s) data streams over the existing analog FM and AM/SSB links. The DTS model 2001 data in voice (DIV) modem uses 256-QAM modulation to transmit a T1 data stream in a single supergroup. This paper describes the technical requirements and design of the modem. A number of particularly interesting aspects of the design are discussed in more detail. These items are 1) the extensive use of digital signal processing in the implementation; 2) the techniques used in the demodulator control loops; 3) the use of a low-rate error correction codec and interleaver for random and burst error correction; and 4) the use of signaling constellation customization as a design tool.

Using Times-Four Carrier Recovery in M-QAM Digital Radio Receivers

Abstract: We have investigated the performance of the times-four method of carrier recovery in a digital radio link transmitting M -level quadrature amplitude modulation ( M -QAM), where M can be 16, 64, 256, etc.. With the help of a recently built multipath fade simulator, we measured rms phase jitter for various combinations of fade notch frequency and fade depth. This paper reports on the experiment and the associated analysis. The times-four method has the virtues that it does not depend upon accurate data decisions, and it does not interact with the receiver's adaptive equalizer. Our results show that the rms phase jitter using this method, for all but the most severe and improbable fades, could be held to a few degrees. Although the measurements were done only for 16 QAM, the analysis predicts only modest increases for higher numbers of levels. The analysis also predicts, and the measurements verify, that the recovered carrier amplitude shrinks to zero for four distinct combinations of fade notch frequency and fade depth. To our knowledge, this phenomenon has not been reported in the literature heretofore. We show that, from a statistical viewpoint, the damage associated with it (measured in terms of outage time) should be quite small.

An ARQ Scheme with Memory and Integrated Modulation

Abstract: In this paper, the integration of the modulation operation in an automatic-repeat-request scheme, using error-detecting codes, is analyzed. A new protocol is described, in which the modulation operation facilitates the recovery of the transmitted code word. The results show a net improvement in the throughput of the automatic-repeat-request scheme, particularly for mean and high error-rate conditions. Continuous-phase-frequency shift keying modulations, which present a low bandwidth occupancy, are particularly considered.

Carrier Phase and Clock Recovery for Continuous Phase Modulated Signals

Abstract: This paper presents an analysis of a synchronization circuit to be used for carrier-phase and symbol-timing recovery in continuous phase modulation systems. M -ary modulation formats with arbitrary pulse shaping and rational modulation indexes are assumed. Circuit performance is expressed in terms of variances of phase and timing errors. Numerical results are provided for some important cases, including minimum shift keying and tamed frequency modulation. Theoretical results are found in good agreement with computer simulations.

Method and apparatus for carrier synchronization and data detection

Abstract: The present invention is directed to circuitry for achieving an improved carrier synchronization (i.e. estimation of carrier's phase) and data detection for digital data, suppressed carrier transmission systems. A new method--and corresponding apparatus--for pattern jitter cancellation and quadrant ambiguity removal, when incorporated within known or new carrier recovery scheme, results in an improved carrier synchronization and data detection. The resultant carrier recovery and data detection circuitry might be employed for phase estimation and the detection of balanced and unbalanced, coded or uncoded, quadrature amplitude modulation signals. Global positioning system receivers, cable, satellite and radio systems are some examples of where these circuitry might find an application.

An Efficient DFE a ML Suboptimum Receiver for Data Transmission Over Dispersive Channels Using Two-Dimensional Signal Constellations

Abstract: The DFE & ML receiver is presented for data transmission systems using QAM modulation. A substantial improvement in performance results as compared to other one- or two-stage receiver structures at relatively low computational complexity.

Full Digital Adaptive Equalization in 64-QAM Radio Systems

Abstract: In view of a digital implementation of most of the signal processing required in a QAM demodulation-equalization Structure, a performance analysis as a function of equalizer complexity, A/D conversion resolution, and precision of internal arithmetic is presented. The analysis is focused on a 140 Mbit/s 64-QAM modulation scheme (corresponding to CEPT-4 or 3 \times DS3 systems), but extension to other QAM constellations is straightforward. Considerations of currently available technology, overall computational complexity, and related optimal quantization formats are presented. For high-speed 64 QAM, it is shown that satisfactory performance may be expected from a full digital implementation of reasonable complexity, using current technology.

Adaptive depolarization-interference-compensator

Abstract: An adaptive depolarization-interference-compensator for a digital radio relay system using multi-level quadrature amplitude modulation (QAM) with co-channel operation of the orthogonally polarized signals which is not necessarily synchronous with the clock frequency and/or carrier frequency and produces good compensation of depolarization effects. The receiving branch of the two receivers (3, 4), which use the same RF-local oscillator (5) or separate RF-local oscillators are synchronized for the differently polarized signals and each contain a quadrature demodulator (8, 14) for two signal components (I- and Q-channel). A canceller is provided which consists of two quadrature demodulators (20, 23) for the two polarization directions, which are each supplied at with an IF-received signal of one polarization and the IF-carrier (9, 15) of the respective other polarization, and which consist of complex transversal filters (21, 22, 24, 25) (I- and Q-channel) in the signal paths to the two quadrature demodulators (20, 23). The transversal filters (21, 22, 24, 25) have their outputs coupled into the receiving branch of the respective other polarization. The delay time τ0 between the tappings of the transversal filters corresponds at the maximum to half the reciprocal value of the frequency of the highest spectral component of the base-band signal with a rational ratio m/n which preferably supplies a delay time which is shorter than or equal to τ0 (m/n=ratio of the symbol period of the interference signal to the transit time between the tappings of the transversal filter; m, n whole numbers).

Optimization of Linearly Equalized QAM

Abstract: A QAM signal transmitted over a channel with linear distortion and additive white Gaussian noise can be linearly equalized at the receiver to eliminate intersymbol interference. If the QAM signal is power constrained and a given symbol error rate is required, we show that it is possible to maximize the bit rate of this system by optimizing the symbol rate and the number of bits/symbol. Ideal linear equalization is assumed at the receiver to overcome the distortion introduced by the channel. As an example, a Gaussian channel is chosen, and the bit rate is maximized for this channel. The QAM maximization is especially useful for channels with slowly decaying channel attenuation characteristics, e.g., the twisted-pair channel.

An approach to Ungerboeck coding for rectangular signal sets (Corresp.)

Abstract: A method of finding good Ungerboeck codes for large rectangular [quadrature amplitude modulation (QAM)] signal sets is described. Using the concept of Euclidean weights due to Ungerboeck, we prove that a 2^{n} point basic constellation may be employed to determine exactly the free distance for an Ungerboeck-coded rectangular 2^{m} point set, when m-n-1 bits are uncoded and the remaining bits pass through a rate (n-1)/n convolutionai encoder. It is shown that rate 2/3 encoders may be used to achieve most of the theoretically possible coding gain in the proposed scheme where the effect of the error coefficient on the coding gain has been considered.

Constant amplitude PSK modulator

Abstract: A phase modulating system for providing PSK modulation with minimum side lobe generation. Phase changes, during the phase transition period, are accomplished with a minimum of carrier amplitude variation. I and Q components of the carrier system are multiplied (39,43) by functions derived from the data and then combined (47) to form a constant amplitude signal during all phases of the data signal.

Digitalized Cross-Polarization Interference Canceller for Multilevel Digital Radio

Abstract: This paper proposes a newly developed, highly precise cross-polarization interference canceller (XPIC), utilizing digitalized transversal filters. Performance of the digitalized XPIC is solely determined by quantization and tap numbers and is not affected by any circuit imperfection. Moreover, it can be universally applied to different bit rates and various modulation schemes. Performance of the XPIC is analytically estimated for various modulation schemes and various interference conditions. Then, the digitalized XPIC is realized and applied to a 12.5 MB 256 QAM digital radio system. Experimental results have closely conformed with theoretical estimations and it is confirmed that the XPIC is a powerful countermeasure against multipath fading for a future digital radio.

1024-QAM and 256-QAM Coded Modems for Microwave and Cable System Applications

Abstract: Low redundancy FEC coded 1024-QAM modems, staggered 1024-QAM, and 256-QAM modems for spectrally efficient (up to 8.84 bits/s/Hz) microwave and cable systems applications are described. Such a high spectral efficiency is required for CEPT-1 (2.048 Mbit/s) rate digital transmission in a single analog supergroup (SG` band as well as for other emerging systems applications. Practical constraints of operational analog FDM systems are presented and taken into account in the choice of the low redundancy FEC codec and the coded 1024-QAM modem. Theoretical, computer simulation and experimental results of 256QAM modems have been extended to the feasibility study of 512-QAM, 961-QPRS, and 1024-QAM modems. Our experience with 256-QAM modems which have a T-1 (1.544 Mbit/s) rate in a 240 kHz analog supergroup (SG) band, i.e., an efficiency of 6.66 bits/s/Hz, demonstrates that a regenerative span over 1000 km is feasible over FDM radio systems. A significantly increased spectral efficiency of 8.84 bits/s/Hz is required for CEPT-1/SG system applications. Our R&D results, presented in this paper, demonstrate the feasibility of FEC coded 1024QAM modems, equipped with powerful digital adaptive equalizers, carrier phase noise, and symbol clock jitter cancellation subsystems, for the transmission of CEPT-1 rate signals in a single SG band.

Advanced Time- and Frequency-Domain Adaptive Equalization in Multilevel QAM Digital Radio Systems

Abstract: Digital radio systems employing multilevel QAM are at least optionally equipped with adaptive time- and/or frequency-domain equalizers. Their purpose is to reduce the vulnerability of these systems to linear distortion caused by multipath propagation. Linear transversal filters are prominent candidates for the realization of time-domain equalizers, especially for high-capacity applications. They are well known for their good performance and their relatively easy implementation at a high data rate. On the other hand, decision feedback equalizers are known to be very capable of eliminating linear distortion, especially of the so-called minimum-phase type. But realization problems are likely to occur in a high-speed application. A solution is proposed which merges the relative advantages of both the linear transversal and the decision feedback approaches. The goal of a frequency-domain equalizer, which is the restoration of the shape of the power density spectrum of the received signal without any recovered carrier and timing signals, can also be achieved with the aid of a transversal filter. The performance obtained with the joint utilization of the novel timeand frequency-domain equalizers is described.

Trellis-Coded Modulation for Fading Channels

Abstract: In proposed communication system, digital signals transmitted efficiently over fading channel by combination of trellis coding and multiple-phase-shift keying with addition of asymmetry to signal set. Coding and modulation schemes not designed separately as in previous systems but integrated to yield bandwidth-efficient modulation and forward-error-correction coding. Helps to satisfy need for reliable high-quality transmission of voice and data between land-mobile units via satellites, where limitations of power and bandwidth imposed simultaneously. Also applicable to ionospheric communications between fixed or mobile units.

Performance of Coherent Phase and Amplitude Digital Modulations with Carrier Recovery Noise

Abstract: A model of decision feedback carrier recovery noise is presented as a function of the number of symbols over which the carrier is derived. For this model, quantitative results for performance degradation in BPSK, QPSK, 8-phase, 16-QAM, 32-QAM, and 64-QAM coherent demodulators are presented. When the carrier is derived from only the last symbol, these results reduce to the performance for differential detection. Carrier integration over 100 symbols is shown to be adequate to provide performance quite close to ideal for all the modulations considered.

A power-efficient linear digital modulator and its application to an anti-multipath modulation PSK-RZ scheme

Abstract: This paper describes a new concept in modulation methods for high speed digital mobile communications. Linear modulation is introduced to allow amplitude variation in the modulated signal. This primarily brings the advantage that sharp cut-off band restriction can be performed to enhance the transmission efficiency. Also, we can adopt as a multipath strategy an amplitude-shift anti-multipath modulation technique, which is found to be more effective than its phase-shift counterpart. A linear modulation method is presented to meet the mobile radio requirement on power efficiency. We finally derive a narrow-band anti-multipath modulation scheme, with required bandwidth compatible with other narrow-band modulation techniques and with superior anti-multipath effect.

A Data And Voice System For The General Service Telephone Network

Abstract: This paper describes a low cost system that simul-taneously provides a data and a voice channel over a standard general service telephone network (GSTN) 2-wire connection. Time domain harmonic scaling (TDHS) [1] is used to frequency compress the voice signal. Data rates up to 1200 bits/s full-duplex have been achieved using a low complexity quadrature amplitude modulation (QAM) algorithm. A real-time implementation has been built using three TMS32010 DSP chips for full-duplex operation.

Outage Performance of QAM Digital Radio Using Adaptive Equalization and Switched Space Diversity Reception

Abstract: Recently, the ability of anti-fading measures to reduce the outage which occurs on digital microwave radio links has been the subject of considerable study. Ideal and nonideal adaptive equalization in both the time and frequency domain have been evaluated for nondiversity reception using various performance criteria. Ideal adaptive equalization and space diversity reception have been considered using a recently published model of multipath fading on space diversity radio channels. In this paper, we determine the outage of 16-QAM and 64-QAM digital radio systems using adaptive slope equalization, finite-tap decision feedback equalization, and switched space diversity reception. The outage is evaluated by computing the probability of occurrence of those channel realizations which cause the bit error rate to exceed a critical value. The dependence of the outage prediction on the equalization method and the outage defining criterion is investigated by also considering ideal adaptive equalization and a signal-to-distortion ratio, respectively.

Performance of Reduced-Bandwidth 16 QAM with Decision-Feedback Equalization

Abstract: This paper presents and investigates the performance of a reduced-bandwidth 16 QAM (RB-16 QAM) signaling technique which employs severe narrow-band filtering and decision-feedback equalization in the receiver to compensate for the resulting intersymbol interference The overall filtering is designed so as to provide the spectral efficiency of 64 QAM RB-16 QAM is compared to 64 QAM in terms of its performance on additive white Gaussian noise channels, in multipath fading environment, as well as in terms of its sensitivity to modem imperfections including carrier and timing phase errors, filter imperfections, nonlinear distortion and sinusoidal interference The results show that depending on the spectral shaping filters and the equalizer used, RB16 QAM can be significantly more advantageous than 64 QAM A most interesting finding is that while RB-16 QAM is comparable to 64 QAM in terms of its spectral efficiency, its robustness against system imperfections is very much like that of conventional 16 QAM

A CMOS 5-V analog front end for 9600-bit/s facsimile modems

Abstract: A CMOS 9600-b/s facsimile-modem analog front end was designed with the consideration that it be capable of being fabricated on the same chip with digital signal processing circuits. To achieve the dynamic range required in the high-speed QAM (quadrature amplitude modulation) modem environment with a single 5-V power supply, a fully differential architecture is used. The die area is 23 kmil/SUP 2/ and the power consumption is only 35 mW. The experimental results show that 76-dB dynamic range is achieved from the fully differential bandpass filter. The zero crossing detector in the MF-1 detection block can normally operate with -50-dBm input signal.

On the Computational Cutoff Rate, R 0 for the Peak-Power-Limited Gaussian Channel

Abstract: The "computational cutoff rate," R 0 , represents a practical measure of the maximum reliable data rate that can be achieved by coding over a given communication channel using a given modulation format, in contrast with the "channel capacity," C , which represents an idealized theoretical limit on the achievable data rate. Moreover, designing signal sets with good error probabilities using the R 0 criterion results in a mathematical problem that is much more tractable than that obtained by using the probability of error itself as a criterion. Both of the above reasons establish the importance of R 0 in communications theory. This paper starts with a brief tutorial background, which reveals the origin and the significance of R 0 . Next, the problem of achieving R 0 over the additive white Gaussian noise (AWGN) dispersive or nondispersive channel, using quadrature-amplitude modulation (QAM) with a peakpower constraint, is addressed. The major result is that, for both cases, the optimum transmission signal set is chosen from a discrete distribution. The solution is derived in detail for the peak-power-limited nondispersive channel, where it is shown that the optimum QAM symbols are selected independently from a probability distribution that is uniform in the phase and discrete in the radius. The solution for the corresponding peak-power-limited dispersive channel is obtained only asymptotically, for large signal-to-noise ratio (SNR), where it is shown that the QAM symbols are selected independently from a uniform distribution within a disk in the complex signal space.