Showing papers on "Quadrature amplitude modulation published in 1981"

GMSK Modulation for Digital Mobile Radio Telephony

Abstract: This paper is concerned with digital modulation for future mobile radio telephone services. First, the specific requirements on the digital modulation for mobile radio use are described. Then, premodulation Gaussian filtered minimum shift keying (GMSK) with coherent detection is proposed as an effective digital modulation for the present purpose, and its fundamental properties are clarified with the aid of machine computation. The constitution of modulator and demodulator is then discussed from the viewpoints of mobile radio applications. The superiority of this modulation is supported by some experimental test results.

The Structure of Quantization Noise from Sigma-Delta Modulation

Abstract: When the sampling rate of a sigma-delta modulator far exceeds the frequencies of the input signal, its modulation noise is highly correlated with the amplitude of the input. We derive simple algebraic expressions for this noise and its spectrum in terms of the input amplitude. The results agree with measurements taken on a breadboard circuit. This work can be useful for designing oversampled analog to digital converters that use sigma-delta modulation for the primary conversion.

Effects of Multipath Propagation on Digital Radio

Abstract: This paper summarizes experimental work at Bell Laboratories in the field of multipath propagation as it affects digital radio. Field and laboratory measurements are presented on commercial-quality high-speed digital radio systems working in the 4, 6, and 11 GHz common carrier bands. Circuits and equipment used in these systems are all state of the art, but no attempt has been made to describe them in any detail. Modulation types are offset-4 PSK, conventional 8 PSK, and 16 QAM. Outages (BER > 10^{-3}) vastly exceeding accepted objectives are measured on unprotected radio hops. A very effective method for reducing outages has been the use of a space diversity combiner followed by an amplitude slope equalizer. Results from single, as well as dual-polarized digital radio relay systems, are presented. The paper also describes the laboratory measurement of an equipment "signature" as a means to compare different digital radio designs in their sensitivity to multipath fading.

Correlative Phase Shift Keying--A Class of Constant Envelope Modulation Techniques

Abstract: Correlative phase shift keying (CORPSK) is described. CORPSK is a constant envelope modulation technique with smooth transitions between fixed phase positions with successive transitions correlated. A number of CORPSK members for 2 and 4 input levels are analyzed, including tamed frequency modulation (TFM). Main lobe bandwidth is the same or less than in other constant envelope modulation techniques such as MSK, QPSK, and CPFSK, but the out-of-band radiation is much lower. Carrier extraction can be realized with simple techniques, so that coherent detection with optimum receiver performance is practically feasible. Simulation results are presented for coherent as well as noncoherent detection. A power efficiency 2 dB better than four MSK and DQPSK can be obtained for CORPSK with no more than for phase positions. A wide variety of modulations exists within the CORPSK class, with ample opportunity for tradeoffs between power, bandwidth, and complexity. Practical results for TFM are reported.

Demodulation and Carrier Synchronization of Multi-h Phase Codes

Abstract: Multi- h phase coding is a bandwidth-efficient modulation which offers substantial performance improvement over conventional digital modulations with little or no bandwidth expansion. This paper examines the demodulation of the multi- h signals, and in particular examines the behavior of a decision-directed carrier loop which utilizes the Viterbi algorithm decoder in the calculation of the loop error signal. Both analytic and simulation results are presented and the agreement between the two is shown to be very close.

Performance of Frequency-Hopping Multiple-Access Multilevel FSK Systems with Hard-Limited and Linear Combining

Abstract: In comparing two proposed frequency-hopping mobile radio systems for digitized speech, Goodman et al. have observed that the system employing multiple-frequency-shift-keying (MFSK) can accommodate many more users than the ones with differential-phaseshift-keying (DPSK). Besides the difference in modulation methods, the MFSK system uses hard-limited combining while the DPSK one uses linear combining. In this paper, we show that using linear combining in the MFSK system causes the performance to degrade considerably.

Continuous Phase Chirp (CPC) Signals for Binary Data Communication--Part II: Noncoherent Detection

Abstract: Chirp (linear FM) signals provide an attractive wideband digital modulation scheme in applications where interference rejection is important. This paper evaluates the error rate (performance) of coherent binary continuous phase chirp (CPC) receivers operating on the additive white Gaussian noise (AWGN) channel and determines the improvement in performance made possible by multiple bit observation. In particular, it is shown that a receiver with two bit observation, giving up to 1.75 dB signal-to-noise ratio (SNR) improvement over the optimum single bit chirp receiver, provides a good compromise between SNR gain and system complexity. Furthermore, a simple, suboptimum, average matched filter (AMF) receiver is analyzed, and it is shown that a two-bit observation is optimum, giving a performance equivalent to that of antipodal phaseshift keying (PSK). An implementation of this receiver in the form of in-phase and quadrature demodulators is also derived.

Full duplex communication system for voice grade channels

Abstract: A pair of full duplex modems (12,14), each at one end of a two-wire voice grade telephone channel (16), simultaneously transmit synchronous data at high speeds in both directions. In each modem, the simultaneous transmission and reception are accomplished by frequency division. The high speed operation is obtained by odd/even bit stream division and full response binary to ternary level coding coupled with nine level quadrature amplitude modulation and correction framing techniques.

Analysis of maximum-likelihood sequence estimation performance for quadrature amplitude modulation

Abstract: This paper considers maximum-likelihood sequence estimation (MLSE) for quadrature amplitude modulation (QAM) signaling at rates approaching several baud/Hz. In this regime, intersymbol interference and possibly cross channel coupling are the dominant transmission impairments. We derive the structure of a detector that optimally accommodates both impairments. A bit error rate performance bound is found, and the concept of an error state transition matrix is introduced to facilitate the analysis. We explore a modulation scheme wherein cross-channel coupling is intentionally introduced, and find that it improves detection efficiency. The use of MLSE may be an important consideration for power and spectrally efficient digital radio systems, either terrestrial or satellite, since rates approaching the Shannon limit may be attainable without channel coding, and frequency selective fading is handled in an optimum manner.

Optimum Pulse Shaping in Digital Angle Modulation

Abstract: This paper presents a technique for optimizing the baseband pulse shapes in digital angle modulated signals to minimize the fraction of out-of-band power for a given channel bandwidth. As examples of practical interest, the optimization is carried out for channel bandwidths up to three times the bit rate and for the range of modulation indices usually encountered in digital transmission. Results for MSK-type signals appear as a special case.

Digital Modulation in Rayleigh Fading in the Presence of Cochannel Interference and Noise

Abstract: The error rate performance of several digital modulation methods in a fading environment and in the presence of one cochannel interference and AWG noise is analyzed. A unique formula emerges for different PSK systems. It is shown how this information can be used in determining acceptable degradation caused by cochannel interference in the case of a digital mobile communication system.

Adaptive equalization and phase tracking for simultaneous analog/digital data transmission

Abstract: The general problem of equalization for data transmission where one of the two data sources produces continuous amplitude data samples is studied. There are various ways to configure a modem for such a transmission scheme, and we describe how a standard quadrature amplitude modulation structure can be modified to operate in this mode. This solution can be specialized to include various linear modulation schemes, such as single sideband and vestigial sideband. Theoretical analysis shows that adaptive equalization and adaptive phase tracking can be achieved with similar quality as in the familiar digital-only modem. We provide extensive computer simulation results which confirm the validity of our theory.

Comments on Transmission System Using Pseudonoise Modulation of Linear Chirps

Abstract: The combination of phase shift keying (PSK) with different chirp waveforms is investigated in respect to its signal form and spectrum shape. A reasonable compromise for low probability of exploitation and jam sensitivity is found for a system where the chirp bandwidth is in the vicinity of the bitrate of the pseudonoise code.

Adaptive equalizer for quadrature amplitude modulation

Abstract: An adaptive equalizer includes first means (20-22) (31) (32) for equalizing a quadrature amplitude-modulated wave in response to a first control signal; second means (80-82) (91) (92) for generating said first control signal from the output of said first means; third means (45) for detecting asynchronism in the control loop of the adaptive equalizer, thereby providing a second control loop, and fourth means (51-60) cooperating with said second means arranged in a self-feedback loop and operative in response to said second control signal to set said first control signal at a fixed level.

Switched-capacitor modulator for quadrature modulation

Abstract: A switched-capacitor modulator for quadrature modulation is disclosed. The modulator of the present invention provides a means for simultaneous modulation of two carrier signals in quadrature by two input signals in such a way that the gains of the two modulations are exactly the same. In accordance with the invention a switched-capacitor modulator is provided having a plurality of input signal sources for quadrature amplitude modulation. The invention provides for a single common switched-capacitor network with multiple switches or multiple switched-capacitor networks for each incoming modulating signal. A switched-capacitor network utilized to form and modulate a carrier signal for shaping the carrier to reduce sidebands of the third and fifth harmonics in the modulated signal is also disclosed.

Hard-limited versus linear combining for frequency-hopping multiple-access systems in a Rayleigh fading environment

Abstract: In comparing two proposed frequency-hopping mobile radio systems for digitized speech, Goodman et al. have observed that the system employing multiple frequency-shift keying (MFSK) can accommodate many more users than the one with differential phase-shift keying (DPSK). Besides the difference in modulation methods, the MFSK system uses hard-limited combining while the DPSK one uses linear combining. Upper bounds are obtained on the probability of error for DPSK systems with hard-limited combining and linear combining. These bounds suggest that the DPSK system with hard limiters can support about twice as many users as the original one.

Adaptive equalizer system for quadrature amplitude modulation

Abstract: An adaptive equalizer system for quadrature amplitude modulated waves is disclosed herein. The equalizer system comprises a circuit for equalizing the received signal as a function of a composite control signal; a circuit for generating a first control signal as a function of the deviation of the equalized signal from a zero-forced waveform; a circuit for generating a second control signal as a function of the asynchronization of the equalizer system; and an output circuit for processing both of said first control signal and said second control signal, producing the composite control signal which controls the equalizing means of the equalizer system.

Cochannel interference immunity of high capacity QAM

Abstract: To achieve very high bandwidth efficiencies in digital-radio large-level quadrature amplitude modulation (QAM) is an attractive modulation scheme In the letter, the cochannel interference immunity of such high capacity QAM is determined

Direct Generation of MSK Modulation at Microwave Frequencies

Abstract: Direct generation of a modulated signal at microwave frequencies offers considerable simplicity and economy in the transmitter of a microwave communication system. Minimum-shift-keying (MSK) is a digital modulation which yields the same bit-error-rate performance as coherent PSK even though this modulation may be generated as a continuous phase frequency-shift- keying. Utilizing this feature of MSK, this paper describes novel circuits for generation of MSK modulation at microwave frequencies.

High-speed digital transmission experiments in 920 MHz urban and suburban mobile radio channels

Abstract: Field experiments have been conducted to clarify the feasibility introducing a newly developed GMSK (Gaussian filtered minimum shift keying) modulation method into 920 MHz mobile radio systems, and have been performed in the Tokyo urban, and the Yokosuka suburban areas.

A general modulation theory for single-phase Thyristor systems

Abstract: Amplitude Modulation (AM) and Phase Modulation (PM) processes of discrete form have been discussed in a previous associated paper. This present paper discusses discrete Frequency Modulation (FM) in power frequency circuits, highlighting their advantages compared with amplitude and phase modulations. Mixed modulation systems of both PM and FM nature are introduced to solve the disadvantages and undesirable features associated with pure FM modulation. A generalised equation of modulation is introduced to represent the various forms of power frequency modulation.

Circuit for demodulating amplitude and angle modulated broadcast signals

Abstract: A superheterodyne receiver is described for demodulating signals containing both amplitude and angle modulation components. An intermediate frequency signal is produced which is simultaneously amplitude detected as well as angle demodulated. Detector means are provided for detecting the occurrence of high negative amplitude modulation peaks of the broadcast signal. During high negative amplitude modulation peaks, the angle demodulator output is held at a fixed level until the amplitude of an input signal is restored to a predetermined minimum level.

Book Review: Information Transmission, Modulation and Noise 3rd Ed.Information Transmission, Modulation and Noise 3rd Ed.: SchwartzMischa (McGraw-Hill, 1980, 646 pp., £16.75)

Abstract: mation problem. The author makes considerable use of the concept of the nullor element in the analysis of RC active circuits and whilst this concept is used most effectively in this text, it may not appeal to some teachers. Professor Bruton has considerable experience of the design and construction of practical active filters and this is reflected in the text, but there is no concise discussion of some of the problems arising from the non-ideal nature of practical devices. However, two chapters are devoted to the very practical subjects of sensitivity and tolerancing analysis. In his preface the author suggests that these chapters be omitted from an undergraduate teaching program, but I would strongly recommend the inclusion of Chapter 6, unless the undergraduates are taught tolerance analysis elsewhere in their course. The coverage of the various approaches to active filter design is well-balanced, and many circuits are analysed in detail, although the author has been selective in his choice of circuits. This book could be a useful teaching text and it certainly deserves a place in any reading list on RC active circuits. M. R. LEE, School ofElectronic Engineering, Newcastle Upon Tyne Polytechnic

Carrier wave reproducing circuit for multi-value qam

Abstract: PURPOSE:To obtain a high-quality reproduced carrier wave without increasing the jitter nor causing any step-out although the noise or disturbance, by controlling a voltage controlling oscillator with the output that is obtained by giving a sample holding to the control signal with the frame signal CONSTITUTION:The 16QAM signal supplied from the input terminal 1 receives a synchronous wave detection by the phase detectors 2 and 3 and based on the output of the voltage controlling oscillator 18 plus the output obtained by giving a 90 deg-phase shift to the above-mentioned output Thus the base band signal is obtained An arithmetic process is given to the base band signal plus the 1st path signals 20 and 21 that are discriminated by the 4-value discriminators 10 and 11 to obtain the voltage proportional to sin4thetae (thetae: phase error) This voltage is fed back to the oscillator 18 via a sample holding circuit 16 On the other hand, the frame signal is extracted out of the signals 20 and 21 through the frame synchronous circuit 13, and the circuit 16 is controlled by the frame signal or one output in the asynchronous state and sent from the synchronous/asynchronous deciding circuit 14

Introduction to digital integrated communications systems

Abstract: introduces the reader to the DARE P simulation system. The DARE P system is an equation-oriented continuous system simulation language developed by the authors at the University of ArizonaIt is designed for batch-mode processing, and the system programs are coded in ASNI Fortran IV. Several examples from the disciplines of electrical circuits, control systems, and aerospace engineering are given to illustrate the versatility of the DARE P system. In Chapter 5 the design and application of minicomputer interactive stimulation systems is described with particular reference to the DARE/ELEVEN system. Chapter 6 describes methods for increasing the computing speed of the simulation language. A comparison of the performance of different simulation-language systems is also given. Appendix A contains a discussion of integration routines. Appendix B contains Fortran subroutines while Appendix C discusses numerical techniques. Since the general purpose digital computer is replacing the analog computer as the primary tool of engineers and scientists for the simulation of continuous time systems, a book on this subject is important to the scientific community. This book is valuable in that it gives a simple overview and a logical development of the subject, and together with the DARE package enables the user to obtain a digital simulation of a continuous system without becoming overly involved in the intracacies of the simulation language itself. In our opinion this book provides a good introduction to the subject of digital simulation of continuous systems. It is not suitable as a classroom textbook. However, to those who avail themselves of the DARE system (the programs are available from the authors at a nominal cost) it would serve as a valuable companion to the users’ manual. Unfortunately the book is difficult to read. The authors use specific terms and phrases without adequately defining them. In many instances the narration is too brief and confusing. The technique of providing explanations under the figures themselves rather than in the main body of the text makes for disjointed reading.