Showing papers on "Quadrature amplitude modulation published in 2000"

Maximum-likelihood classification for digital amplitude-phase modulations

Abstract: We apply the maximum-likelihood (ML) method to the classification of digital quadrature modulations. We show that under an ideal situation, the I-Q domain data are sufficient statistics for modulation classification and obtain a generic formula for the error probability of a ML classifier. Our study of asymptotic performance shows that the ML classifier is capable of classifying any finite set of distinctive constellations with zero error rate when the number of available data symbols goes to infinity.

Digital Modulation Techniques

Abstract: Baseband modulation frequency shift keying phase shift keying minimum shift keying continuous phase modulation multi-H phase shift keying quadrature amplitude modulation other nonconstant envelope modulations multicarrier modulation spread spectrum modulation coded modulation applications in baseband data communications applications in wired telephony applications in wireless mobile communications applications in fixed terrestrial microwave links applications in satellite links.

Single- and Multi-carrier Quadrature Amplitude Modulation : Principles and Applications for Personal Communications, WLANs and Broadcasting

Abstract: Single- and Multi-carrier Quadrature Amplitude Modulation Principles and Applications for Personal Communications, WLANs and Broadcasting L. Hanzo Department of Electronics and Computer Science, University of Southampton, UK W. Webb Motorola, Arlington Heights, USA formerly at Multiple Access Communications Ltd, Southampton, UK T. Keller Ubinetics, Cambridge Technology Centre, Melbourn, UK formerly at Department of Electronics and Computer Science, University of Southampton, UK Motivated by the rapid evolution of wireless communication systems, this expanded second edition provides an overview of most major single- and multi-carrier Quadrature Amplitude Modulation (QAM) techniques commencing with simple QAM schemes for the uninitiated through to complex, rapidly-evolving areas, such as arrangements for wide-band mobile channels. Targeted at the more advanced reader, the multi-carrier modulation based second half of the book presents a research-orientated outlook using a variety of novel QAM-based arrangements. * Features six new chapters dealing with the complexities of multi-carrier modulation which has found applications ranging from Wireless Local Area Networks (WLAN) to Digital Video Broadcasting (DVB) * Provides a rudimentary introduction for readers requiring a background in the field of modulation and radio wave propagation * Discusses classic QAM transmission issues relevant to Gaussian channels * Examines QAM-based transmissions over mobile radio channels * Incorporates QAM-related orthogonal techniques, considers the spectral efficiency of QAM in cellular frequency re-use structures and presents a QAM-based speech communications system design study * Introduces Orthogonal Frequency Division Multiplexing (OFDM) over both Gaussian and wideband fading channels By providing an all-encompassing self-contained treatment of single- and multi- carrier QAM based communications, a wide range of readers including senior undergraduate and postgraduate students, practising engineers and researchers alike will all find the coverage of this book attractive.

On the computation and reduction of the peak-to-average power ratio in multicarrier communications

Abstract: For any code C defined over an equal energy constellation, it is first shown that at any time instance, the problem of determining codewords of C with high peak-to-average power ratios (PAPR) in a multicarrier communication system is intimately related to the problem of minimum-distance decoding of C. Subsequently, a method is proposed for computing the PAPR by minimum-distance decoding of C at many points of time. Moreover an upper bound on the error between this computed value and the true one is derived. Analogous results are established for codes defined over arbitrary signal constellations. As an application of this computational method, an approach for reducing the PAPR of C proposed by Jones and Wilkinson (1996) is revisited. This approach is based on introducing a specific phase shift to each coordinate of all the codewords where phase shifts are independent of the codewords and known both to the transmitter and the receiver. We optimize the phase shifts offline by applying our method for computing the PAPR for the coding scenario proposed by the ETSI BRAN Standardization Committee. Reductions of order 4.5 dB can be freely obtained using the computed phase shifts. Examples are provided showing that most of the gain is preserved when the computed optimal phase shifts are rounded to quantenary phase-shift keying (PSK), 8-PSK, and 16-PSK type phase shifts.

Classical and modern receiver architectures

Abstract: This article is a review of several classical and modern wireless receiver architectures used in wideband wireless communication systems. The emphasis is on configurations suitable for integration on a single silicon chip. A full understanding of the design trade-offs discussed in this article is necessary for the proper introduction of a new modulation scheme presented in the article by Mirabbasi and Martin (2000) entitled, "Hierarchical QAM: a spectrally efficient DC-free modulation scheme".

Serial concatenated trellis coded modulation with rate-1 inner code

Abstract: We develop new, low complexity turbo codes suitable for bandwidth and power limited systems, for very low bit and word error rate requirements. Motivated by the structure of previously discovered low complexity codes such as repeat-accumulate (RA) codes with low density parity check matrix, we extend the structure to high-level modulation such as 8PSK, and 16QAM. The structure consists of a simple 4-state convolutional or short block code as an outer code, and a rate-1, 2 or 4-state inner code. Two design criteria are proposed: the maximum likelihood design criterion, for short to moderate block sizes, and an iterative decoding design criterion for very long block sizes.

A recursive algorithm for the error probability evaluation of M-QAM

Abstract: A general recursive algorithm for the efficient and accurate computation of the bit error rate (BER) of square-shaped M-QAM constellations over additive white Gaussian noise (AWGN) channels is derived. We take advantage of the relationship amongst different square-shaped M-QAM constellations using Gray coded bit mapping.

Channel estimation and equalization for M-QAM transmission with a hidden pilot sequence

Abstract: Blind equalization techniques are useful to counteract multipath effects in radio local loop (RLL) and in general for wireless point to multipoint transmissions. One of the main drawbacks of blind equalization is the slow convergence time of the equalizer. Another major problem of blind equalization is the possible convergence toward wrong solutions. When these two main disadvantages cannot be tolerated it is necessary to adopt trained channel estimation and/or equalization techniques to counteract multipath. The training sequence is usually time division multiplexed with the informative sequence. This solution reduces the bandwidth efficiency and can be unusable when too frequent updating of the communications parameters need to be performed in the receiver. It is shown that bandwidth efficiency can be preserved at the expense of an increase in the transmitted power. The additional transmitted power is used to send a known pilot sequence hidden into the informative sequence. The hidden sequence is superimposed onto the symbols to be transmitted before waveform modulation. Thus each pilot symbol has the same period of the informative symbol so that no bandwidth spreading is necessary. High spectral efficiency M-QAM modulation is considered but the technique can be easily extended to any type of digital modulation format. We analyze the problems of channel estimation and of equalization based on the hidden pilot sequence. To prove the effectiveness of the proposed technique simulation results are provided. It is observed that in the case of equalization a pilot recovery subsystem should be used before using the pilot to train the equalizer.

Multilevel coded modulation for unequal error protection and multistage decoding. II. Asymmetric constellations

Abstract: In this paper, theoretical upper bounds and computer simulation results on the error performance of multilevel block coded modulations for unequal error protection (UEP) and multistage decoding are presented. It is shown that nonstandard signal set partitionings and multistage decoding provide excellent UEP capabilities beyond those achievable with conventional coded modulation. The coding scheme is designed in such a way that the most important information bits have a lower error rate than other information bits. The large effective error coefficients, normally associated with standard mapping by set partitioning, are reduced by considering nonstandard partitionings of the underlying signal set. The bits-to-signal mappings induced by these partitionings allow the use of soft-decision decoding of binary block codes. Moreover, parallel operation of some of the staged decoders is possible, to achieve high data rate transmission, so that there is no error propagation between these decoders. Hybrid partitionings are also considered that trade off increased intraset distances in the last partition levels with larger effective error coefficients in the middle partition levels. The error performance of specific examples of multilevel codes over 8-PSK and 64-QAM signal sets are simulated and compared with theoretical upper bounds on the error performance.

A study of a loop interference canceller for the relay stations in an SFN for digital terrestrial broadcasting

Abstract: In each relay station in an SFN (single frequency network) for DTB (digital terrestrial broadcasting), the loop interference is caused by the coupling from the transmitting antenna to receiving antenna. The interference must be reduced to an allowable level in order to avoid problems with distortion and oscillation. We propose a frequency-domain adaptive cancellation algorithm using reference signals carried in the OFDM signal. The principle of the proposed algorithm is outlined and the usefulness of the algorithm is verified by the results of computer simulations.

Bit error probability of M-ary quadrature amplitude modulation

Abstract: So far the general expression of bit error rate (BER) has not been derived for M-ary square quadrature amplitude modulation (QAM). In this paper, a generalized closed-form BER expression of M-ary square QAM with Gray code bit mapping is derived and analyzed in the presence of additive white Gaussian noise (AWGN) channel.

A frequency and symbol synchronization system for OFDM signals: architecture and simulation results

Abstract: A data-aided frequency and symbol synchronization scheme for M-QAM OFDM signals is suggested. At first, the phase discriminator (PD) and frequency discriminator (FD) for, respectively, the symbol and frequency synchronization loop are described. Second, the transfer function and design parameters of the loop filters are provided. The acquisition and tracking performance of the synchronization system are evaluated using simulation for a 4-PSK signal constellation. The cases of additive white Gaussian noise (AWGN) and frequency and time selective multipath Rayleigh channels are separately tested.

Blind channel and carrier frequency offset estimation using periodic modulation precoders

Abstract: Previous results have shown that blind channel estimators, which are resilient to the location of channel zeros, color of additive stationary noise, and channel order overestimation errors, can be developed for communication systems equipped with transmitter-induced cyclostationarity precoders. The present paper extends these blind estimation approaches to the more general problem of estimating the unknown intersymbol interference (ISI) and carrier frequency offset/Doppler effects using such precoders. An all-digital open-loop carrier frequency offset estimator is developed, and its asymptotic (large sample) performance is analyzed and compared to the Cramer-Rao bound (CRB). A subspace-based channel identification approach is proposed for estimating, in closed-form, the unknown channel, regardless of the channel spectral nulls. It is shown that compensating for the carrier frequency offset introduces no penalty in the asymptotic performance of the subspace channel estimator. Simulations are presented to corroborate the performance of the proposed algorithms.

Tight error bounds for nonuniform signaling over AWGN channels

Abstract: We consider a Bonferroni-type lower bound due to Kounias (1968) on the probability of a finite union. The bound is expressed in terms of only the individual and pairwise event probabilities; however, it suffers from requiring an exponentially complex search for its direct implementation. We address this problem by presenting a practical algorithm for its evaluation. This bound is applied together with two other bounds, a recent lower bound (the KAT bound) and a greedy algorithm implementation of an upper bound due to Hunter (1976), to examine the symbol error (P/sub a/) and bit error (P/sub b/) probabilities of an uncoded communication system used in conjunction with M-ary phase-shift keying (PSK)/quadrature amplitude (QAM) (PSK/QAM) modulations and maximum a posteriori (MAP) decoding over additive white Gaussian noise (AWGN) channels. It is shown that the bounds-which can be efficiently computed-provide an excellent estimate of the error probabilities over the entire range of the signal-to-noise ratio (SNR) E/sub b//N/sub 0/. The new algorithmic bound and the greedy bound are particularly impressive as they agree with the simulation results even during very severe channel conditions.

Adaptive subcarrier loading

Abstract: A wireless multicarrier transmission method in which a multicarrier transmission uses n modulated frequency subcarriers (n is an integer number), and a fading condition of each subcarrier is detected to generate fading channel profile information. The modulation of each subcarrier includes selecting a standard modulation scheme, a lower modulation scheme, and a higher modulation scheme; selecting three integer numbers x, y, and z representing the number of subcarriers for modulation with the lower modulation scheme, with the standard modulation scheme, and with the higher modulation scheme respectively, the sum of x, y, and z is n and a resulting number of coded bits of a multicarrier symbol is constant; and modulating the x subcarriers having low fading channel profile information with the lower modulation scheme, modulating the y subcarriers having medium fading channel profile information with the standard modulation scheme, and modulating the z subcarriers having high fading channel profile information with the higher modulation scheme.

New equalization approach for OFDM over dispersive and rapidly time varying channel

Abstract: The paper proposes and analyses a new receiver structure to mitigate the effect of Doppler on the reception of OFDM signals. A discrete-frequency channel representation is developed for the link between the input of the transmit I-FFT and the output of the receive FFT. It is based on a Taylor expansion of the time variations of the received subcarrier amplitudes. The model realistically addresses the correlation of fading at neighboring subcarriers. We study a new type of receiver which estimates not only amplitudes but also derivatives of subcarriers amplitudes. An adaptive MMSE filter is proposed to cancel the intercarrier interference (ICI) resulting from Doppler. This results in a substantial improvement of the link performance.

Method and system for detecting and classifying the modulation of unknown analog and digital telecommunications signals

Abstract: Disclosed is a unique system and method for recognizing the type of modulation embedded in an unknown complex baseband signal, comprising a receiver section for extracting the complex baseband signal from a modulated signal having a carrier frequency, and comprising an orderly series of signal processing functions for (a) estimating the bandwidth of the unknown signal, (b) removing the out-of-band noise and correcting gross carrier frequency errors, (c) discriminating between constant envelope and irregular envelope signals, (d) estimating and correcting residual carrier frequency errors, (e) classifying a constant envelope signal into one of the following modulation formats: {Continuous Wave (CW), Frequency Modulation (FM), Frequency Shift Keying (FSK)}, and (f) classifying an irregular envelope signal into one of the following modulation formats: {Amplitude Modulation (AM), Double Sideband Suppressed Carrier (DSB-SC), Binary Shift Keying (BPSK), Quaternary Phase Shift Keying (QPSK), π/4-shifted QPSK, M-ary PSK (MPSK), and OTHER classes}.

Digital precompensation of imperfections in quadrature modulators

Abstract: Residual carrier, balance, and quadrature error imperfections that are normally present in phase/quadrature modulators limit the use of direct modulation techniques in some applications. The classical precompensation techniques are revised and an adaptive solution proposed that improves performance by some order of magnitude.

On power adaptation in adaptive signaling systems

Abstract: The Shannon capacity of a fading channel under an average-power constraint with channel side information at the transmitter and receiver is only negligibly larger than the capacity of the same channel when constant-power transmission is employed. However, power adaptation has been shown to be quite useful in practical systems, where it has been conjectured that it allows for compensation of the effect of rate quantization. Here, an average bit-error probability constraint is employed instead of the conventional instantaneous bit-error probability constraint. When the set of rates available to the transmitter is unrestricted in practical systems, necessary conditions for jointly optimal power and rate allocation are derived and used to demonstrate that power adaptation is of limited utility. However, when the rates available to the transmitter are restricted to the nonnegative integers for the example of uncoded quadrature amplitude modulation over frequency-nonselective Rayleigh fading channels, a 0.5-0.75 dB loss in power efficiency is incurred when employing only a single power level for each constellation, and a 0.5-bits/symbol loss in rate is incurred when constant power transmission is employed.

Very efficient frequency usage system using convolutional spread time signals based on complete complementary code

Abstract: We have proposed a method for increasing the information transmission rate and the frequency usage rate based on a new method for estimating multipath channels and spread time signals convolution. We used a pilot signal and data-transmission signals in the same frequency and in the same time. For this purpose, we used the complete complementary code on approximately synchronized systems. The information transmission rate came to (1.3/k) chip/bit, where k was the QAM factor. In this paper, a new usage method for a complementary code is proposed. The new method is far simpler than the old method. By applying the proposed usage method for a complete complementary code on the above high rate information transmission method, the high rate information transmission can be realized easier.

Quasi-differential modulation/demodulation method for multi-amplitude digital modulated signals and OFDM system

Abstract: The invention proposes the separate processing of the phase and amplitude of multi-amplitude digital modulation techniques, such as a QAM. The phases are differentially modulated and the amplitudes coherently processed. Also proposed is a method to correct the amplitude distortion of the symbols on each subcarrier, either from the QAM signal itself or from any PSK signal, if available. The invention shows that differential modulation/demodulation of multi-amplitude signals with no equidistant phases such as QAM is possible. Complex equalizer means to perform a channel estimation is no more needed as for coherent systems. Further, no pilot sucarriers are needed, thus the bandwidth efficiency is much higher. Furthermore, the frequency snychronization of differential demodulated signals is less complex. An implementation proposal of the new modulation/demodulation technique is described.

Dynamic adaptive modulation negotiation for point-to-point terrestrial links

Abstract: A transmission device that transmits a signal along a link (50) and method therefor that includes a forward error correction encoder unit (44) to insert error correction information into the signal transmitted along a link and output a corresponding encoded signal. A modulation unit (46) variably modulates the encoded signal and outputs a modulated signal, having a corresponding quadrature modulation index, to the receiving device. A control unit (34, 40) variably controls the inserted forward error correction information and the quadrature amplitude modulation index based on link quality information with respect to substantially the entire link to increase throughput during periods of reduced environmental degradation.

Some simple bounds on the symmetric capacity and outage probability for QAM wireless channels with Rice and Nakagami fadings

Abstract: In this article, quickly computable upper and lower bounds are presented on the symmetric capacity of flat-faded Rice and Nakagami channels with side information (SI) for data-transmissions via finite-size quadrature amplitude modulation (QAM) constellations. The proposed bounds exhibit the appealing feature to be tight and asymptotically exact both for high and low signal-to-noise ratios (SNRs). Furthermore, exponentially tight Chernoff-like formulas are also presented for an analytical evaluation of the resulting system outage probabilities when interleaved packet transmissions are carried out.

A fast linear programming algorithm for blind equalization

Abstract: A fast implementation of a special non-MSE cost function for blind equalization is presented here. This baud-rate equalization algorithm is based on a convex cost function coupled with a simple linear constraint on the equalizer parameters. For a generic class of channels with persistently exciting quadrature amplitude modulation input signals, this new algorithm allows the convergence of equalizer parameters to a unique global minimum achieving intersymbol interference suppression and carrier phase recovery.

DPSK 32 x 10 Gb/s transmission modeling on 5 x 90 km terrestrial system

Abstract: Reduction of DWDM nonlinear fiber penalties by the use of DPSK modulation and an optically preamplified self-homodyning receiver is discussed. Maintaining a constant instantaneous channel power by phase shift keying, we can anticipate reduction of cross-phase modulation penalties. Our modeling results show 0.9-dB benefit in Q performance for 50-GHz spaced, 32/spl times/10 Gb/s transmissions with nonzero dispersion shifted fiber.

A fast adaptive predistorter for nonlinearly amplified M-QAM signals

Abstract: M-QAM has been considered to achieve high bandwidth efficiency for broadband wireless communications. However, due to its envelope fluctuation, it exhibits large spectral re-growth and performance degradation when the transmit power amplifier operates in a nonlinear region close to saturation. In this paper, an adaptive predistortion technique suitable for DSP implementation at the baseband signals is introduced to counter-balance the AM/AM and AM/PM nonlinear effects of the transmit power amplifier. Based on nonlinear adaptive Volterra filtering, the proposed pre-distortion technique shows that M-QAM can be used with a transmit power amplifier operating near saturation to a highest power efficiency, while its transmitted spectrum and performance are kept close to those in a linear channel. The convergence behavior of the adaptive predistortion technique is analyzed. The spectral re-growth and performance of a 16 QAM system using a predistorter/SSPA are evaluated using simulation. The adaptive predistortion technique has a low complexity and fast convergence.

A multicarrier QAM modulator

Abstract: A multicarrier quadrature amplitude modulation (QAM) modulator has been developed and implemented with programmable logic devices. The multicarrier QAM modulator contains four CORDIC-based QAM modulators. A conventional QAM modulator needs two multipliers, one adder, and sine/cosine ROM's. The designed CORDIC-based QAM modulator has about the same logic complexity as the two multipliers and the adder with the same word sizes. Each QAM modulator accepts 13-bit in-phase and quadrature data streams, interpolates them by 16, and upconverts the baseband signal to a selected center frequency. The frequencies of the four carriers can be independently adjusted. The proposed multicarrier QAM modulator does not use an analog I/Q modulator, and therefore, the difficulties of adjusting the dc offset, phasing, and the amplitude levels between the in-phase and quadrature-phase signal paths are avoided. The multicarrier QAM modulator is designed to fulfil the spectrum and error vector magnitude (EVM) specifications of the wideband code-division multiple-access (WCDMA) system. The simulated EVM is 1.06% root mean square (rms), well below the specified 12.5% rms for WCDMA. The measured ratio of the integrated first/second/third adjacent channel power (4.096-MHz bandwidth) to the integrated channel power (4.096-MHz bandwidth) is -68.16/-68.24/-66.17 dB versus the specified -45/-55/-55 dB.

Upper-bound performance of a wide-band adaptive modem

Abstract: Adaptive modulation is applied in conjunction with a decision-feedback equalizer (DFE) in order to mitigate the effects of the slowly varying wide-band multipath Rayleigh fading channel in a noise-limited environment. An upper-bound mean bit-error rate and bits per symbol performance is introduced for this scheme by utilizing the pseudo signal-to-noise ratio at the output of the DFE in order to switch the modulation schemes on a burst-by-burst basis.

Adaptive spatial-subcarrier trellis coded MQAM and power optimization for OFDM transmissions

Abstract: Space-time coding or coded modulation has demonstrated that significant increases in system capacity and performance can be achieved by incorporating multiple antennas at the transmitter and (optional) multiple antennas at the receiver. In this paper, we propose an adaptive spatial-subcarrier trellis coded modulation using MQAM for orthogonal frequency division multiplexing (OFDM) transmission by using instantaneous channel state information and employing multiple antennas at both the transmitter and the receiver. In particular, our objective is to minimize the total transmit power required for each OFDM transmission, by optimizing the power allocation, code rate and modulation scheme in each spatial-subcarrier channel, while maintaining a given data rate and bit error probability. To illustrate the potential of our proposed system, Monte Carlo simulation results are provided.

On random rotations diversity and minimum MSE decoding of lattices

Abstract: We establish a simple relation between high-diversity multidimensional rotations obtained from totally complex cyclotomic fields and the discrete Fourier transform. The diversity distribution of an Hadamard-like random rotation is derived analytically. It is shown that a random multidimensional rotation exhibits an excellent diversity distribution and can be combined to quadrature amplitude modulation (QAM) constellations to combat channel fading. We also describe a mean-square error (MSE) universal lattice decoder suitable for large dimensions up to 1024. The MSE criterion treats the lattice structure as intersymbol interference. The universal decoder is applied to both Gaussian and Rayleigh fading channels to decode dense lattice sphere packings and rotated cubic constellations, respectively.