Showing papers on "Quadrature amplitude modulation published in 1995"
TL;DR: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered and the degradation of the bit error rate is evaluated.
Abstract: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered. The degradation of the bit error rate (BER), caused by the presence of carrier frequency offset and carrier phase noise is analytically evaluated. It is shown that for a given BER degradation, the values of the frequency offset and the linewidth of the carrier generator that are allowed for OFDM are orders of magnitude smaller than for single carrier systems carrying the same bit rate. >
1,816 citations
TL;DR: The minimum mean-squared-error decision-feedback equalizer (MMSE-DFE) has properties that suggest that it is a canonical equalization structure for systems that combine equalization with coded modulation, and the structure and performance are succinctly derived using linear-estimation-theoretic principles.
Abstract: The minimum mean-squared-error decision-feedback equalizer (MMSE-DFE) has properties that suggest that it is a canonical equalization structure for systems that combine equalization with coded modulation. The structure and performance of the MMSE-DFE are succinctly derived using linear-estimation-theoretic principles in this first part of this two-part paper. The front-end of the MMSE-DFE, called the "mean-square whitened matched filter" (MS-WMF), is preferable in some ways to a matched filter or a whitened matched filter as a canonical receiver front end. In a coded system, the feedback filter of the MMSE-DFE may be implemented in the transmitter using precoding. The MMSE-DFE can perform significantly better than a zero-forcing decision-feedback equalizer, particularly at moderate-to-low SNR's and on severe-ISI channels. The MMSE-DFE is biased. The optimum unbiased MMSE-DFE is the MMSE-DFE with the bias removed. Removing bias improves error probability, but reduces the SNR to SNR/sub MMSE-DFE,U/=SNR/sub MMSE-DFE/-1. It is shown that this SNR relationship is a particular case of a very general result and that SNR/sub MMSE-DFE,U/ gives a more realistic estimate of SNR. The results are extended to partial response equalization and to equalization with correlated inputs in an appendix. >
608 citations
TL;DR: How the adaptive QAM modems can be employed and their use in a DECT-like TDD packet structure is considered and it is shown that the variable rate system has about 5 dB improvement in channel SNR over a fixed 16-level QAM system.
Abstract: Quadrature amplitude modulation (QAM) schemes which vary the number of modulation levels in accordance with the mobile radio fading channel variations are investigated. Important parameters considered are the fading rate and the block size used. We describe how the adaptive QAM modems can be employed and consider their use in a DECT-like TDD packet structure. System performance in the presence of cochannel interference is also considered. Simulations show that the variable rate system has about 5 dB improvement in channel SNR over a fixed 16-level QAM system for BER's between 10/sup -2/ and 10/sup -5/ and channel SNR's between 25 and 40 dB. >
496 citations
01 Aug 1995
TL;DR: This paper presents a multi-carrier digital modulation technique-orthogonal frequency division multiplexing and the ideas of using a guard interval to accommodate long delay ghosts and of creating spectrum notches to combat co-channel interferences are discussed.
Abstract: This paper presents a multi-carrier digital modulation technique-orthogonal frequency division multiplexing. A review of the technique and its development and implementation are provided. The advantages and disadvantages in comparison to other modulation techniques are also discussed. The ideas of using a guard interval to accommodate long delay ghosts and of creating spectrum notches to combat co-channel interferences, as well as of assigning different order of modulations or power levels to different sub-carriers for layered services are discussed. The effects of phase noise and the peak-to-average power ratio of the OFDM signal are also analysed. >
399 citations
18 Jun 1995
TL;DR: A simple feed-forward correction technique based on pilot cells is proposed, that dramatically reduces the degradation due to phase-noise and allows the design of low-cost tuners through specifying the required phase- noise characteristics.
Abstract: In OFDM transmission schemes, phase-noise from oscillator instabilities in the receiver is a potentially serious problem, especially when bandwidth efficient, high order signal constellations are employed. The paper analyses the two effects of phase-noise: inter-carrier interference (ICI) and a phase error common to all OFDM sub-carriers. Through numerical integration, the ICI power can be evaluated and is shown as a function of the number of OFDM sub-carriers and various parameters of the phase-noise model. Increasing the number of sub-carriers causes an increase in the ICI power, which our analysis indeed shows to become a potential problem, since it can lead to a BER floor. The analysis allows the design of low-cost tuners through specifying the required phase-noise characteristics. A similar technique is applied to calculate the variance of the common phase error. After showing that the common phase error is essentially uncorrelated from symbol to symbol, we propose a simple feed-forward correction technique based on pilot cells, that dramatically reduces the degradation due to phase-noise. This is confirmed by BER simulations of a coded OFDM scheme (proposed for terrestrial transmission of digital television) with 64 QAM.
252 citations
TL;DR: It is shown that any binary continuous phase-modulated signal may be exactly decomposed into the sum of a few PAM waveforms, and that this property extends to multilevel CPM signaling.
Abstract: It is widely known that minimum shift keying (MSK) may be seen as a PAM signaling scheme and that the same is true, albeit approximately, with MSK-like modulations. It is also known (perhaps not so widely) that any binary continuous phase-modulated (CPM) signal may be exactly decomposed into the sum of a few PAM waveforms. In this paper we show that this property extends to multilevel CPM signaling. Features of a PAM decomposition are discussed as a function of the alphabet size, the modulation index, and the frequency response of the system. It is found that, especially with signaling schemes with a long memory, the decomposition has so many terms that it becomes unmanageable. For these cases an approximation is proposed with a limited number of terms. >
228 citations
TL;DR: In this article, a six-port phase/frequency discriminator (SPD) was used in conjunction with a digital signal processor (DSP) to perform various PSK and QAM demodulations directly at microwave and millimeter-wave frequencies.
Abstract: A novel digital millimetric receiver (DMR) scheme is introduced. Using a six-port phase/frequency discriminator (SPD) in conjunction with a digital signal processor (DSP), the receiver performs various PSK and QAM demodulations directly at microwave and millimeter-wave frequencies. An important feature of the new DMR is that hardware imperfections such as phase/amplitude imbalance are readily eliminated by a simple calibration procedure. The concept is proved through computer simulation and measurements at 26.5 GHz. This receiver scheme is proposed for small/medium capacity digital terminals typically found in various wireless communication networks.
167 citations
01 Aug 1995
TL;DR: In this paper, an approach for easy calculation of SNR, independent of carrier numbers, is given, using a plot of the phase noise power density for the calculation, which leads to an improved synthesizer concept.
Abstract: This paper explains the mechanisms that lead to a degradation of an OFDM signal because of the phase noise of the RF oscillators. An approach for easy calculation of SNR, independent of carrier numbers, will be given. This SNR approach uses a plot of the phase noise power density for the calculation. The theoretical results lead to an improved synthesizer concept. Values of SNR and BER will be given for the new synthesizer concept. >
140 citations
TL;DR: A 200 MHz quadrature direct digital frequency synthesizer/complex mixer (QDDFSM) chip is presented in this article with a spectral purity of -84.3 dBc and frequency resolution is 0.047 Hz with a corresponding switching speed of 5 ns and a tuning latency of 14 clock cycles.
Abstract: A 200 MHz quadrature direct digital frequency synthesizer/complex mixer (QDDFSM) chip is presented. The chip synthesizes 12 b sine and cosine waveforms with a spectral purity of -84.3 dBc. The frequency resolution is 0.047 Hz with a corresponding switching speed of 5 ns and a tuning latency of 14 clock cycles. The chip is also capable of frequency, phase, and quadrature amplitude modulation. These modulation capabilities operate up to the maximum clocking frequency. The chip provides the capability of parallel operation of multiple chips with throughputs up to 800 MHz. The 0.8 /spl mu/m triple level metal N-well CMOS chip has a complexity of 52000 transistors with a core area of 2.6/spl times/6.1 mm/sup 2/. Power dissipation is 2 W at 200 MHz and 5 V. >
121 citations
14 Nov 1995
TL;DR: Simulation results show that all the block turbo coded QAM modulations tested are at 2.9/spl plusmn/0.2 dB of their Shannon's limit, and convolutional turbo coded and TCM schemes exhibit slightly better performance for spectral efficiencies greater than 4 bits/s/Hz.
Abstract: We present the results of our investigation concerning the performance of block turbo codes associated with high spectral efficiency QAM modulations. By using a pragmatic approach, simulation results show that all the block turbo coded QAM modulations we have tested are at 2.9/spl plusmn/0.2 dB of their Shannon's limit. The block turbo coded QAM modulations also outperform TCM schemes by at least 1 dB at a BER (bit error rate) of 10/sup -5/. Concerning convolutional turbo coded QAM modulations, the block turbo coded QAM modulations exhibit slightly better performance for spectral efficiencies greater than 4 bits/s/Hz.
120 citations
TL;DR: The performance of QAM systems with the conventional receiver designed for Gaussian noise is analyzed and the numerical results show that the performance is much worse than that achieved underGaussian noise.
Abstract: This paper describes the performance of QAM (quadrature amplitude modulation) systems under impulsive noise environment. In the analysis, we employ, as a model of the impulsive noise, Middleton's (1977) model labeled class A. First, the statistical characteristics of the in-phase and quadrature components of the impulsive noise are investigated, and it is proved that, in contrast to Gaussian noise, these components are dependent especially for the impulsive noise with small impulsive indices. Next, with consideration of the dependence between the in-phase and quadrature components of the noise, the performance of QAM systems with the conventional receiver designed for Gaussian noise is analyzed. The numerical results show that the performance is much worse than that achieved under Gaussian noise. Moreover, we show the design of the maximum likelihood receiver for class A impulsive noise and the great performance improvement by this receiver is confirmed. >
14 Sep 1995
TL;DR: CD3-OFDM allows to achieve C/N performance similar to coherent demodulation with pilot tones, when the same channel coding and modulation scheme is adopted, and can be suitable for digital television broadcasting services over selective radio channels.
Abstract: The paper describes a novel channel estimation scheme (identified as CD3, coded decision directed demodulation) for coherent demodulation of OFDM (orthogonal frequency division multiplex) signals making use of any constellation format (e.g. QPSK, 16 QAM, 64 QAM). The structure of the CD3-OFDM demodulator is described, based on a new channel estimation loop exploiting the error correction capability of a forward error correction (FEC) decoder and frequency and time domain filtering to mitigate the effects of noise and residual errors. In contrast to the conventional coherent OFDM demodulation schemes, CD3-OFDM does not require the transmission of a comb of pilot tones for channel estimation and equalisation, therefore yielding a significant improvement in spectrum efficiency (typically between 5% and 15%). The performance of the system with QPSK and 64 QAM modulations is analysed by computer simulations, on AWGN and frequency selective channels. The results indicate that CD3-OFDM allows to achieve C/N performance similar to coherent demodulation with pilot tones, when the same channel coding and modulation scheme is adopted. Otherwise, when the additional capacity is exploited to increase the FEC redundancy instead of the useful bit-rate, CD3 can offer significant C/N advantages (typically from 2 to 5 dB depending on the channel characteristics). Therefore CD3-OFDM can be suitable for digital television broadcasting services over selective radio channels.
TL;DR: The authors propose a solution to the parallel concatenation of trellis codes with multilevel amplitude/phase modulations and a suitable iterative decoding structure that outperforms all codes reported in the past for the same throughput.
Abstract: We propose a new solution to parallel concatenation of trellis codes with multilevel amplitude/phase modulations and a suitable iterative decoding structure. Examples are given for throughputs 2 bits/sec/Hz with 8PSK and 16QAM signal constellations.
14 Sep 1995
TL;DR: A multilevel differential modulation technique, the so-called differential amplitude and phase shift keying (64-DAPSK) is proposed, in which the phase and the amplitude are used simultaneously for differential modulation.
Abstract: In digital terrestrial video broadcasting (DTVB) applications the objective is to transmit a high data rate of 34.368 Mbit/s in a single radio channel (bandwidth of 7 or 8 MHz). In this paper the performance of a multicarrier transmission technique, the well-known orthogonal frequency division multiplexing (OFDM) method, is analysed and the system parameters for the DTVB application are considered. A multilevel differential modulation technique, the so-called differential amplitude and phase shift keying (64-DAPSK) is proposed, in which the phase and the amplitude are used simultaneously for differential modulation. A differential modulation technique does not require any explicit knowledge about the radio channel properties in the differential channel equalization process. In an OFDM/64-DAPSK receiver it is therefore not necessary to implement a channel estimation and a frequency-domain equalizer, which reduces the computation complexity. The performance of both modulation techniques has been analysed in the uncoded case referring to Gaussian and frequency-selective Rayleigh fading channels. The results are described.
Patent•
26 Sep 1995TL;DR: In this article, the authors proposed a modulation filter such as a finite impulse response (FIR) filter to add only a nominal, controlled amount of amplitude modulation, high efficiency, nonlinear power amplifiers may be employed to transmit the filtered continuous phase modulated (CPM) signals.
Abstract: Continuous phase modulated (CPM) signals, such as quaternary CPFSK signals, are filtered to limit their bandwidth while simultaneously minimizing the amount of amplitude modulation and intersymbol interference introduced by this filtering process. By designing a modulation filter such as a finite impulse response (FIR) filter to add only a nominal, controlled amount of amplitude modulation, high efficiency, nonlinear power amplifiers may be employed to transmit the filtered CPFSK signals. Although the filter adds a small amount of amplitude modulation and intersymbol interference, digital signal processor-based receivers satisfactorily demodulate this type of signal using sequence estimation algorithms such as the Viterbi algorithm. Thus, the filtering of CPM signals permits narrowing of the transmitted signal spectrum while managing the intersymbol interference resulting from the controlled amount of amplitude modulation added by filtering. Narrowed bandwidth along with high efficiency, nonlinear power amplifiers make the present invention particularly well suited to narrowband mobile radio communications.
06 Nov 1995
TL;DR: Numerical analysis shows that the proposed system is an effective high-quality and high-speed image transmission technique in a fading channel.
Abstract: This paper proposes a new mobile image transmission system based on the hierarchical modulation scheme for achieving a high quality and high speed digital image transmission in a band-limited fading channel. The proposed system uses a hierarchical QAM (quadrature amplitude modulation) scheme to give unequal transmission reliability depending on the importance of DCT (discrete cosine transform)-based compressed images. Numerical analysis shows that the proposed system is an effective high-quality and high-speed image transmission technique in a fading channel.
25 Jul 1995
TL;DR: The results show that the proposed method improves the BER performance and delay spread immunity of a system transmitting data at a constant rate under multipath fading conditions and the performance is better than that of TCM-32QAM in Rayleigh fading conditions with small Doppler frequency.
Abstract: The performance of an adaptive-modulation/time division duplex (TDD) scheme to support constant-bit-rate services under transmission delay time constraint conditions is evaluated in this paper. According to the received signal conditions, the modulation levels or transmission modes are selected from transmission-off, QPSK, 16QAM, or 64QAM by using the reciprocity of the propagation path characteristics in the TDD systems. Moreover, the transmission delay time is limited to keep data transmission rate constant by the memory buffer. The received signal condition is estimated by using extrapolation of pilot symbol or estimated received signal distortion at the decision stage. The performance is evaluated by computer simulation in case of 32 ksymbol/s transmission and is compared with the performance of conventional trellis-coded (TCM) 32QAM. The results show that the proposed method improves the BER performance and delay spread immunity of a system transmitting data at a constant rate under multipath fading conditions and the performance is better than that of TCM-32QAM in Rayleigh fading conditions with small Doppler frequency.
TL;DR: A multi-stage blind clustering algorithm is proposed for equalisation of multi-level quadrature amplitude modulation (M-QAM) channels that achieves much faster convergence and is very robust when input symbols are not sufficiently white.
Abstract: A multi-stage blind clustering algorithm is proposed for equalisation of multi-level quadrature amplitude modulation (M-QAM) channels. A hierarchical decomposition divides the task of equalising a high-order QAM channel into much simpler sub-tasks. Each sub-task can be accomplished fast and reliably using a blind clustering algorithm derived originally for 4-QAM signals. The constant modulus algorithm (CMA) is used as a benchmark to assess this multi-stage blind equaliser. It is demonstrated that the new blind algorithm achieves much faster convergence and is very robust when input symbols are not sufficiently white. This multi-stage clustering equaliser only requires slightly more computations than the CMA and, like the latter, its computational complexity does not increase as the levels of digital symbols increase. >
12 Mar 1995
TL;DR: A multirate wavelet based modulation format is presented which can utilize existing channels designed for conventional QAM and has advantages including dimensionality in both time and frequency for flexible channel exploitation and an efficient all digital filter bank implementation.
Abstract: Building on recently introduced multidimensional signalling techniques, a multirate wavelet based modulation format is presented which can utilize existing channels designed for conventional QAM. Customizable wavelet packet basis functions are employed as novel pulse shapes upon which independent QAM data at lower rates are placed. The advantages include dimensionality in both time and frequency for flexible channel exploitation and an efficient all digital filter bank implementation. >
Book•
31 Aug 1995
TL;DR: This textbook explores the theoretical concepts of digital signal processing and communication systems by presenting laboratory experiments using real-time DSP hardware and recommends methods for adaptive equalization, carrier recovery, and symbol clock tracking.
Abstract: Designed for senior electrical engineering students, this textbook explores the theoretical concepts of digital signal processing and communication systems by presenting laboratory experiments using real-time DSP hardware. Originally designed for the Texas Instruments TMS320C6701 Evaluation Module or TMS320C6711 DSK, this new editionupdates the experiments based on the TMS320C6713 (but can easily be adapted to other DSP boards). Each chapter begins with a presentation of the required theory and concludes with instructions for performing experiments to implement the theory. In the process of performing the experiments, students gain experience in working with software tools and equipment commonly used in industry. The primary focus of this book is on communication systems. Algorithms that are particularly suited to DSP implementations are presented. Chapters 1 and 2 introduce the software and hardware tools. Chapter 3 presents FIR and IIR digital filters and Chapter 4 investigates the FFT. Chapters 4 through 8 discuss modulators and demodulators for classical analog modulation methods such as amplitude modulation (AM), double-sideband suppressed-carrier amplitude modulation (DSBSC-AM), single sideband modulation (SSB), and frequency modulation (FM). Chapters 9 through 16 explore digital communication methods leading to the implementation of a complete telephone-line modem. These chapters include shift register pseudo-random binary sequence generators, the RS-232 protocol, pulse amplitude modulation (PAM), quadrature amplitude modulation (QAM) transmitters and receivers, and echo cancellation. Methods for adaptive equalization, carrier recovery, and symbol clock tracking are presented. Chapter 17 gives suggestions for additional experiments.
TL;DR: Novel 2-D TCM schemes that attain diversity of order two even for a trellis structure that includes parallel paths with one symbol per edge are developed and assessed via computer simulation for some representative TCM-QAM schemes.
Abstract: The design of trellis coded modulation (TCM) schemes for QAM constellations to counteract simultaneous flat fading and additive white Gaussian noise (AWGN) is considered. Motivated by the results of Divsalar and Simon (see IEEE Trans. Commun., vol.36, p.1004, 1988), and incorporating some recent ideas from Boulle and Belfiore (1992), we develop novel 2-D TCM schemes that attain diversity of order two even for a trellis structure that includes parallel paths with one symbol per edge. An algorithm is described that transforms codes designed for the AWGN channel into codes that achieve significant gains over flat fading channel, while preserving their coding gain over AWGN channel. Their performance is assessed via computer simulation for some representative TCM-QAM schemes under the assumption of uncorrelated fading and perfect channel state information (CSI). Finally, the effects of finite interleaving as well as imperfect CSI on code performance are investigated. >
25 Jul 1995
TL;DR: The authors show that the successive IC scheme for higher modulation together with mixed modulation or parallel channels give a considerable increase in performance and flexibility compared to single modulation systems employing a conventional detector.
Abstract: Analyses a successive interference cancellation (IC) scheme for M-ary QAM modulation in direct sequence code division multiple access (DS/CDMA) systems. The performance under Rayleigh fading is analysed for single modulation systems and systems employing either of two different methods, mixed modulation or parallel channels, for handling multiple data rates. The authors show that the successive IC scheme for higher modulation together with mixed modulation or parallel channels give a considerable increase in performance and flexibility compared to single modulation systems employing a conventional detector.
26 Sep 1995
TL;DR: In this paper, the performance of a range of 1, 2 and 4 bit/symbol pilot symbol assisted modulation (PSAM) arrangements employing first-order linear, low pass, polynomial and optimum higher-order Linear interpolation schemes is analysed in contrast to that of the equivalent non-coherent modems.
Abstract: The performance of a range of 1, 2 and 4 bit/symbol pilot symbol assisted modulation (PSAM) [1, 3] arrangements employing first-order linear, low pass, polynomial and optimum higher-order linear interpolation schemes is analysed in contrast to that of the equivalent non-coherent modems. Both the non-coherent modems as well as the coherent PSAM schemes exhibited a residual bit error rate (BER), but the best compromise in terms of performance, system delay and complexity was attributable to the first-order linear interpolator. In case of short interpolation buffers the polynomial interpolator slightly outperformed the low-pass and the higher-order linear optimum interpolators, but this advantage erodd in case of longer buffers. The higher complexity of the minimum mean squared error interpolator is not justifiable in terms of performance improvements. The low-complexity linearly interpolated PSAM schemes have a n improved performance in comparison to the differential schemes in case of higher order constellations, such as 4- and 16-level quadrature amplitude modulation.
Patent•
21 Dec 1995
TL;DR: In this paper, a modulation and demodulation scheme for video signals may be used for HDTV signals using VSB-PAM, analog NTSC signals using SBS-AM and digital video signals using QAM.
Abstract: A modulation and demodulation scheme for video signals may be used for HDTV signals using VSB-PAM, analog NTSC signals using VSB-AM and digital video signals using QAM. VSB-PAM modulation and demodulation may be performed using in-phase and quadrature baseband filters. By adjusting the filter taps, a single modulator structure may be used for QAM and VSB-PAM modulation. Similarly, a single demodulator structure may be used for QAM and VSB-PAM demodulation. This demodulator may also be used for VSB-AM modulation.
25 Jul 1995
TL;DR: In this paper, a semi-analytical performance evaluation for M-QAM-orthogonal frequency division multiplexing (OFDM) digital radio systems in the presence of an additive white gaussian noise (AWGN) transmission channel and nonlinear distortions due to a high power amplifier (HPA) is presented.
Abstract: The paper presents a model for a semi-analytic performance evaluation in M-QAM-orthogonal frequency division multiplexing (OFDM) digital radio systems in the presence of an additive white gaussian noise (AWGN) transmission channel and nonlinear distortions due to a high power amplifier (HPA). It is shown that, in the case of an OFDM system with a large number of sub-carriers, the distortion on the received symbol caused by the amplifier can be modelled, with negligible error, as a "Gaussian nonlinear noise" added to the received symbol. Considering this important remark the semi-analytical approach is only used to estimate means and variances of the "nonlinear noise" while these estimated parameters are subsequently used to evaluate the system bit error rate (BER) in a closed form. The advantage of this proposed method is that it strongly reduces the computational time. The proposed procedure is applied to evaluate M-QAM-OFDM performance in presence of nonlinear distortions due to high power amplifiers.
TL;DR: A technique for the compensation of nonlinear distortions in the received signal constellation in an all-digital demodulator for rate-3/4 16-state trellis coded (TC) 16-QAM, and shows that, by simple modifications to the metric computer in the Viterbi decoder, the optimum operating point of the amplifier can be moved much closer to saturation than in the conventional case, without any need for on-board amplifier linearization.
Abstract: Although providing high spectral efficiency, sixteen-level quadrature amplitude modulation (16-QAM) is customarily considered a power-inefficient transmission technique for satellite communication systems, due to the considerable output back-off (OBO) of the optimum operating point of the nonlinear amplifier. The authors present a technique for the compensation of nonlinear distortions in the received signal constellation in an all-digital demodulator for rate-3/4 16-state trellis coded (TC) 16-QAM. They show that, by simple modifications to the metric computer in the Viterbi decoder, the optimum operating point of the amplifier can be moved much closer to saturation than in the conventional case, without any need for on-board amplifier linearization. The simulation results demonstrate a BER of 10/sup -5/ with a power saving of roughly 3.5 dB in a typical nonlinear channel, when compared to conventional uncoded 8-PSK. This figure includes all of the impairments produced by increased satellite amplifier OBO and by the presence of the subsystems for symbol timing recovery, carrier phase estimation and automatic gain control. >
25 Jul 1995
TL;DR: The author introduces two additional degrees of freedom by allowing both the transmit power and the data rate to vary, subject to an average power constraint, and proposes an adaptive joint source/channel coded modulation technique.
Abstract: Shannon's (1948) fundamental theorem showing that source coding and channel coding can be separated without any loss of optimality does not apply to general time-varying channels. Since the distortion by the source encoder decreases with the data rate, while the channel errors increase with the data rate, the joint source/channel coding problem reduces to allocating bits in an optimal way between the source and channel encoders as the source and channel vary. The author introduces two additional degrees of freedom by allowing both the transmit power and the data rate to vary, subject to an average power constraint. Under these varying power and rate conditions, he first obtains an expression to minimize the end-to-end distortion of general joint source/channel codes for fading channels. He then proposes an adaptive joint source/channel coded modulation technique. The channel code adapts both the transmission rate and power using variable-rate coded MQAM (on a Rayleigh fading channel). He analytically derives the minimum end-to-end distortion of our joint coding scheme. The solution cannot be obtained in closed form, and therefore requires computer search methods. He also obtains a simple upper bound on the distortion by holding the channel error rate constant. Numerical results for this distortion upper bound as a function of the channel coding gain and error rate are obtained. The optimal power control which achieve this bound is also determined.
30 Oct 1995
TL;DR: In this paper, a new maximum-likelihood method for modulation classification of digital amplitude-phase modulations, applicable to any constellation-based modulation types in an AWGN environment, is presented.
Abstract: We develop or new maximum-likelihood method for modulation classification of digital amplitude-phase modulations, applicable to any constellation-based modulation types in an AWGN environment. Under reasonable assumptions, the method is tractable to theoretical performance analysis, something lacking by many existing modulation classification methods. The classifier performance for a variety of modulations is analyzed and the theoretical results are compared with simulations.
TL;DR: When applied to HDSL-like systems with a single (or dominant) interferer, this work confirms that wider-than-Nyquist transmitters provide a large performance advantage over Nyquist-limited transmitters, and explains why PAM and QAM systems operating at the same spectral efficiency do not perform identically over the crosstalk channel.
Abstract: In many digital communications systems, crosstalk, rather than additive noise, is the primary channel impairment. For such systems, it is known that the spectral support of the optimum transmitter is not, in general, restricted to a Nyquist set, in contrast to the case for the additive-noise channel. Nevertheless, the problem of determining the optimum transmitter shaping function for the crosstalk channel without the Nyquist restriction is a difficult one, and has so far remained unsolved. Motivated by current interest in the high-speed digital subscriber line (HDSL) and related crosstalk-dominated applications, we explore a subcase of this problem in which only a single interferer is present. When applied to HDSL-like systems with a single (or dominant) interferer, our analysis and numerical results confirm that wider-than-Nyquist transmitters provide a large performance advantage over Nyquist-limited transmitters. Several interesting and counter-intuitive results also arise. For example, PAM and QAM systems operating at the same spectral efficiency do not, in general, perform identically over the crosstalk channel, despite their essential equivalence in additive noise. We explain why this is so, and show that for channels qualitatively similar to the HDSL wire-pair, QAM has a significant advantage over PAM at high data rates. Finally, we show how the characteristics of HDSL-like channels can be exploited by optimizing the symbol rate. >
TL;DR: In this paper, the maximum signal levels that are possible with modulation transfer spectroscopy using both amplitude modulated and frequency modulated pump fields are theoretically investigated, and the results indicate that amplitude modulation produces signals that are larger than those obtained with frequency modulation for modulation frequencies that are suitable for frequency locking applications.