Showing papers on "Quadrature amplitude modulation published in 1999"

Simplified processing for high spectral efficiency wireless communication employing multi-element arrays

Abstract: We investigate robust wireless communication in high-scattering propagation environments using multi-element antenna arrays (MEAs) at both transmit and receive sites. A simplified, but highly spectrally efficient space-time communication processing method is presented. The user's bit stream is mapped to a vector of independently modulated equal bit-rate signal components that are simultaneously transmitted in the same band. A detection algorithm similar to multiuser detection is employed to detect the signal components in white Gaussian noise (WGN). For a large number of antennas, a more efficient architecture can offer no more than about 40% more capacity than the simple architecture presented. A testbed that is now being completed operates at 1.9 GHz with up to 16 quadrature amplitude modulation (QAM) transmitters and 16 receive antennas. Under ideal operation at 18 dB signal-to-noise ratio (SNR), using 12 transmit antennas and 16 receive antennas (even with uncoded communication), the theoretical spectral efficiency is 36 bit/s/Hz, whereas the Shannon capacity is 71.1 bit/s/Hz. The 36 bits per vector symbol, which corresponds to over 200 billion constellation points, assumes a 5% block error rate (BLER) for 100 vector symbol bursts.

Analysis of new and existing methods of reducing intercarrier interference due to carrier frequency offset in OFDM

Abstract: Orthogonal frequency division multiplexing (OFDM) is very sensitive to frequency errors caused by frequency differences between transmitter and receiver local oscillators. This sensitivity is analyzed in terms of the complex weighting coefficients which give the contribution of each transmitter subcarrier to each demodulated subcarrier. Previously described windowing and self intercarrier interference (ICI) cancellation methods are analyzed in terms of these weighting coefficients. New ICI cancellation schemes with very much improved performance are described. A condition for orthogonality of windowing schemes is derived in terms of the discrete Fourier transform (DFT) of the windowing function.

M-PSK and M-QAM BER computation using signal-space concepts

Abstract: In this paper, we introduce a simple geometric approach that is based on signal-space concepts to efficiently evaluate the performance of M-ary phase-shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM) schemes over an additive white Gaussian noise channel. In particular, new bit error rate approximations are derived and shown to be in excellent agreement with Monte Carlo simulation results.

Adaptive coding for time-varying channels using outdated fading estimates

Abstract: The idea of using knowledge of the current channel fading values to optimize the transmitted signal in wireless communication systems has attracted substantial research attention. However, the practicality of this adaptive signaling has been questioned due to the variation of the wireless channel over time, which results in a different channel at the time of data transmission than at the time of channel estimation. By characterizing the effects of fading channel variation on the adaptive signaling paradigm, it is demonstrated here that these misgivings are well founded, as the channel variation greatly alters the nature of the problem. The main goal of this paper is to employ this characterization of the effects of the channel variation to design adaptive signaling schemes that are effective for the time-varying channel. The design of uncoded adaptive quadrature amplitude modulation (QAM) systems is considered first, and it demonstrates the need to consider the channel variation in system design. This is followed by the main contribution of this paper; using only a single outdated fading estimate when neither the Doppler frequency nor the exact shape of the autocorrelation function of the channel fading process is known, adaptive trellis-coded modulation schemes are designed that can provide a significant increase in bandwidth efficiency over their nonadaptive counterparts on time-varying channels.

Effect of channel estimation error on M-QAM BER performance in Rayleigh fading

Abstract: We determine the bit-error rate (BER) of multilevel quadrature amplitude modulation (M-QAM) in flat Rayleigh fading with imperfect channel estimates, Despite its high spectral efficiency, M-QAM is not commonly used over fading channels because of the channel amplitude and phase variation. Since the decision regions of the demodulator depend on the channel fading, estimation error of the channel variation can severely degrade the demodulator performance. Among the various fading estimation techniques, pilot symbol assisted modulation (PSAM) proves to be an effective choice. We first characterize the distribution of the amplitude and phase estimates using PSAM. We then use this distribution to obtain the BER of M-QAM as a function of the PSAM and channel parameters. By using a change of variables, our exact BER expression has a particularly simple form that involves just a few finite-range integrals. This approach can be used to compute the BER for any value of M. We compute the BER for 16-QAM and 64-QAM numerically and verify our analytical results by computer simulation. We show that for these modulations, amplitude estimation error leads to a 1-dB degradation in average signal-to-noise ratio and combined amplitude-phase estimation error leads to 2.5-dB degradation for the parameters we consider.

Nonlinear channel equalization for QAM signal constellation using artificial neural networks

Abstract: Application of artificial neural networks (ANN's) to adaptive channel equalization in a digital communication system with 4-QAM signal constellation is reported in this paper. A novel computationally efficient single layer functional link ANN (FLANN) is proposed for this purpose. This network has a simple structure in which the nonlinearity is introduced by functional expansion of the input pattern by trigonometric polynomials. Because of input pattern enhancement, the FLANN is capable of forming arbitrarily nonlinear decision boundaries and can perform complex pattern classification tasks. Considering channel equalization as a nonlinear classification problem, the FLANN has been utilized for nonlinear channel equalization. The performance of the FLANN is compared with two other ANN structures [a multilayer perceptron (MLP) and a polynomial perceptron network (PPN)] along with a conventional linear LMS-based equalizer for different linear and nonlinear channel models. The effect of eigenvalue ratio (EVR) of input correlation matrix on the equalizer performance has been studied. The comparison of computational complexity involved for the three ANN structures is also provided.

Characterization of spectral regrowth in microwave amplifiers based on the nonlinear transformation of a complex Gaussian process

Abstract: A statistical technique is presented for the characterization of spectral regrowth at the output of a nonlinear amplifier driven by a digitally modulated carrier in a digital radio system. The technique yields an analytical expression for the autocorrelation function of the output signal as a function of the statistics of the quadrature input signal transformed by a behavioral model of the amplifier. The amplifier model, a baseband equivalent representation, is derived from a complex radio-frequency envelope model, which itself is developed from readily available measured or simulated amplitude modulation-amplitude modulation and amplitude modulation-phase modulation data. The technique is used in evaluating the spectral regrowth for a CDMA signal.

Maximum-likelihood modulation classification for PSK/QAM

Abstract: This paper addresses automatic modulation classification for PSK and QAM signals under coherent and noncoherent conditions. In particular, the paper extends previous results by treating the classification of higher-state QAM signals. A maximum-likelihood algorithm is presented for coherent classification of PSK and QAM signals. We evaluate the algorithms performance for various PSK and QAM modulation types including 64-state QAM and then compare it with a psuedo maximum-likelihood noncoherent classification technique in terms of the error rate, false alarm rate, and computational complexity. The application of these results to the design and performance of an automatic signal recognizer is discussed throughout the paper.

Characterization of Spectral Regrowth in Microwave Amplifiers Based on the Nonlinear Transformation of a

Abstract: A statistical technique is presented for the character- ization of spectral regrowth at the output of a nonlinear amplifier driven by a digitally modulated carrier in a digital radio system. The technique yields an analytical expression for the autocorrela- tion function of the output signal as a function of the statistics of the quadrature input signal transformed by a behavioral model of the amplifier. The amplifier model, a baseband equivalent rep- resentation, is derived from a complex radio-frequency envelope model, which itself is developed from readily available measured or simulated amplitude modulation-amplitude modulation and amplitude modulation-phase modulation data. The technique is used in evaluating the spectral regrowth for a CDMA signal.

Effect of channel estimation error on M-QAM BER performance in Rayleigh fading

Abstract: We determine the bit error rate (BER) of multi-level quadrature amplitude modulation (M-QAM) in flat Rayleigh fading with imperfect channel estimates. Despite its high spectral efficiency, M-QAM is not commonly used over fading channels because of the channel amplitude and phase variation. Since the decision regions of the demodulator depend on the channel fading, the estimation error of the channel variation can severely degrade the demodulator performance. Among the various fading estimation techniques, pilot symbol assisted modulation (PSAM) proves to be an effective choice. We first characterize the distribution of the amplitude and phase estimates using PSAM. We then use this distribution to obtain the BER of M-QAM as a function of the PSAM and channel parameters. By using a change of variables our exact BER expression has a particularly simple form that involves just a few finite range integrals. This approach can be used to compute BER for any value of M. We compute the BER for 16-QAM and 64-QAM numerically and verify our analytical results by computer simulation. We show that for these modulations, amplitude estimation error leads to a 1 dB degradation in E/sub b//N/sub o/ and combined amplitude-phase estimation error leads to 2.5 dB degradation for the parameters we consider.

Performance analysis of a coded OFDM system in time-varying multipath Rayleigh fading channels

Abstract: We analyze the combined influence of the interchannel and intersymbol interferences, which result from the time variation and delay spread of mobile channels, on the performance of an orthogonal frequency-division multiplexing (OFDM) system. Both analysis and simulation results are presented for uncoded 16-QAM. We also investigate the performance of a Reed-Solomon (RS) coded 16-QAM OFDM system when the number of subcarriers varies: it is observed that there is an optimum number of subcarriers that minimizes the post decoding symbol error probability of the RS code for each channel state.

Identification of digital modulation types using the wavelet transform

Abstract: Automatic identification of the digital modulation type of a signal has found applications in many areas, including electronic warfare, surveillance and threat analysis. This paper studies the use of wavelet transform to distinguish QAM signal, PSK signal and FSK signal. The approach is to use the wavelet transform to extract the transient characteristics in a digital modulation signal, and apply the distinct pattern in wavelet transform domain for simple identification. The relevant statistics for optimum threshold selection are derived under the condition that the input noise is additive white Gaussian. The performance of the identification scheme is investigated through simulations. When the CNR is greater than 5 dB, the percentage of correct identification is about 97% with 50 observation symbols.

Design of pulse shaping OFDM/OQAM systems for high data-rate transmission over wireless channels

Abstract: Orthogonal frequency division multiplexing (OFDM) is a promising technique for high data-rate transmission over wireless channels. In general, wireless channels are time-frequency dispersive. The performance of wireless OFDM therefore depends critically on the time-frequency localization of the pulse shaping filter used. It has been pointed out in Haas (1996) that OFDM systems based on offset QAM (OFDM/OQAM) bypass a major disadvantage of OFDM schemes based on ordinary QAM, namely the fact that well-localized pulse shaping filters are prohibited in the case of a critical time-frequency grid where spectral efficiency is maximal. In this paper, we derive general orthogonality conditions for OFDM/OQAM systems and we propose efficient (FFT-based) design procedures for time-frequency well-localized OFDM/OQAM pulse shaping filters with arbitrary length and arbitrary overlapping factors. Finally, we present design examples.

Exact evaluation of maximal-ratio and equal-gain diversity receivers for M-ary QAM on Nakagami fading channels

Abstract: Exact integral expressions are derived for calculating the symbol-error rate (SER) of multilevel quadrature amplitude modulation (MQAM) in conjunction with L-fold antenna diversity on arbitrary Nakagami fading channel. Both maximal-ratio combining (MRC) (in independent and correlated fading) and equal-gain combining (EGC) predetection (in independent fading) diversity techniques have been considered. Exact closed-form SER expressions for two restricted Nakagami fading cases (MRC reception) are also derived. An exact analysis of EGC for MQAM has not been reported previously, despite its practical interest. Remarkably, the exact SER integrals can also be replaced by a finite-series approximation formula. A useful procedure for computing the confluent hypergeometric series is also presented.

Demonstration of return-to-zero signaling in both OOK and DPSK formats to improve receiver sensitivity in an optically preamplified receiver

Abstract: Summary form only given. We demonstrate record receiver sensitivities at 1O Gb/s using RZ signaling and optimization of the optical filter bandwidths (for a Fabry-Perot optical filter and fixed 10 GHz electrical filter bandwidth). Two different modulation formats are considered: on-off keying (OOK) and differential phase shift keying (DPSK). To the best of our knowledge, this is the first demonstration of encoding phase information on RZ optical pulses to be subsequently decoded in a DPSK demodulator, and as such we christen the term RZDPSK to describe this format. Direct comparison with NRZ signaling and constant intensity DPSK reveals an improvement of about 1 dB in receiver sensitivity.

Adaptive trellis coded MQAM and power optimization for OFDM transmission

Abstract: We propose an adaptive trellis coded modulation orthogonal frequency division multiplexing (ATCM-OFDM) scheme to provide high rate transmission with high spectral efficiency for an indoor environment Our objective is to minimize the overall transmit power in each OFDM transmission by optimizing the power distribution, the code rate and modulation scheme in each OFDM subchannel so as to maintain a constant data transmission rate and a fixed bit error rate (BER) In the simulation, the ATCM-OFDM scheme can achieve more than 7 dB power reduction compared with the OFDM scheme using fixed TCM

Spectrally efficient FQPSK, FGMSK, and FQAM for enhanced performance CDMA, TDMA, GSM, OFDN, and other systems

Abstract: Spectral efficient transmitters-receivers (transceivers), modulation-demodulation (Modem) methods, architectures, structures and implementation technologies for enhanced performance and increased capacity CDMA, TDMA, GSM,OFDM, CMA, FDM and other wireless and wired communications, broadcasting and telemetry systems and integrated Modems/Transceivers suitable for operation over Non-Linearly Amplified (NLA) power efficient RF systems are described. Cross-correlated cascaded Time Constrained Signal (TCS) response processors and Long Response (LR) filtered Bit Rate Agile (BRA) in phase (I) and quadrature phase (Q) baseband signals are disclosed. These spectral efficient high performance processing, transmitting and receiving methods are designated as Feher's Quadrature Phase Shift Keying (FQPSK) Transceivers. Integrated Modem and transceiver technologies also disclosed herein and designated as Feher's Quadrature Amplitude Modulation (FQAM), Feher's Gaussian Minimum Shift Keying (FGMSK) and Feher's Minimum Shift Keying (FMSK) are subsets of 2nd generation FQPSK systems. Bit rate and RF agile embodiments are described. The 2nd generation of FQPSK systems with Adaptive Antenna Arrays (AAA) and adaptive Feher Equalizers (FE) and smart diversity systems has additional enhanced spectral/RF power efficiency and end-to-end performance advantages.

Analysis of hybrid selection/maximal-ratio combining of diversity branches with unequal SNR in Rayleigh fading

Abstract: The performance of a hybrid selection/maximal-ratio combining (H-S/MRC) diversity system in multipath fading environment is analyzed. With H-S/MRC, L out of N diversity branches are selected and combined using maximal-ratio combining (MRC). This technique provides improved performance over L branch MRC when additional diversity is available, without requiring additional resources (i.e., power consumption, RF electronics). In particular, we consider independent Rayleigh fading on each diversity branch without assuming equal signal-to-noise ratio (SNR) averaged over the fading. We analyze this system using a "virtual branch" technique which results in a simple derivation and formula for the mean of the combiner output SNR for any L and N. We further obtain the symbol error probability (SEP) for coherent reception of M-ary phase-shift keying (MPSK) and quadrature amplitude modulation (MQAM).

Performance bounds for turbo-coded modulation systems

Abstract: We apply the standard union bound to turbo-coded modulation systems with maximum-likelihood decoding. To illustrate the methodology, we explicitly derive the bounds for the 2-bits/s/Hz 16 QAM system. Generalization of this bound to other turbo-coded modulation systems is straightforward. As in the case of the standard union bound for turbo codes, we expect these bounds to be useful for rather large values of signal-to-noise ratios, i.e., signal-to-noise ratios for which the code rate is smaller than the corresponding cutoff rate. The bound is based on "uniform interleaving" just as its counterpart for standard turbo coding. The derived bound provides a tool for comparing coded modulation schemes having different component codes, interleaver lengths, mappings, etc., using maximum-likelihood decoding. It is also useful in studying the effectiveness of various suboptimal decoding algorithms. The bounding technique is also applicable to other coded-modulation schemes such as serially concatenated coded modulation.

Amplitude modulation to phase modulation cancellation method in an rf amplifier

Abstract: An RF amplifier for a transmitter develops a phase modulation command representing a desired phase modulation of an RF signal, and an amplitude modulation command representing a desired amplitude modulation of the RF signal. An oscillator develops an RF input signal phase modulated based on the phase modulation command. A power amplifier receives the RF input signal and amplifies the RF input signal based on the amplitude modulation command to develop an RF output signal. A modulation control is operatively associated with the oscillator. The modulation control includes a phase memory for storing phase correction information correlating the amplitude modulation commands to a phase modulation error and a phase control for varying the phase modulation command based on the phase modulation error to correct for unintended phase errors created by amplitude modulation of the power amplifier.

Interference detection and avoidance technique

Abstract: The present invention of interfering continuous-wave signals are automically detected in the demodulated output of a quadrature amplitude modulation data communications receiver. The transmitter (16) is re-tuned in order to avoid the detected interferer. Statistical information concerning the received signal is accumulated at a receiver (18) and is analyzed to determine whether a reduction in the received bit-error-rate is due to the presence of an interferer. If an inteferer is determined to be present within the signal transmission bandwidth, then the potentially available transmission band is spectrum analyzed to find a new portion of that band in which the signal can be transmitted free of the interferer. The results of the statistical analysis and the spectral analysis are conveyed back to the transmitter (16) which then readjusts the transmission parameters and forwards the new parameters to the receiver (18). The system resumes operation in the new transmission band with no interference and with the bit-error-rate restored to its required level.

Error probabilities of two-dimensional M-ary signaling in fading

Abstract: A new exact method for computing the average symbol error probability of two-dimensional M-ary signaling in slow fading is presented. The method is generally applicable to polygonal decision regions. The exact average symbol error rate of coherent 16-star-QAM is obtained and compared to that of 16-rectangular-QAM. New results for optimum ring ratios of 16-star-QAM in additive white Gaussian noise (AWGN) and in slow fading are also given.

A 200 MHz Quadrature Digital Synthesizer/Mixer in 0.8 m CMOS

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 ?>m triple level metal N-well CMOS chip has a complexity of 52 000 transistors with a core area of 2.6 x 6.1 mm2. Power dissipation is 2 W at 200 MHz and 5 V.

Quantum detection and mutual information for QAM and PSK signals

Abstract: We analyze the performance of the error probability and the mutual information for quadrature amplitude modulation (QAM) and phase-shift keying systems based on quantum detection theory. It is shown that the quantum receiver called square root measurement gives about 5.7 dB improvement in power in comparison with the classical one. Furthermore, we show that the quantum QAM system can achieve the same reliability as the conventional intensity modulation-direct detection (IM-DD) system with almost equal power, compressing the required bandwidth, while the reliability is degraded in general.

Detection of multicarrier modulations using 4th-order cumulants

Abstract: This paper deals with modulation classification. Our goal is to discriminate single-carrier (SC) modulations from multicarrier (MC) modulations of OFDM type. Because MC modulations are asymptotically Gaussian, we propose here a detector using the statistical test of Giannakis and Tsatsanis (1990) based on fourth-order cumulants. This test is here adapted to the specific case of digital modulations which allows one to reduce the algorithm complexity. Simulations are provided and show that in the worst case (filtered 256-QAM versus 32-OFDM) the detector achieves a probability of detection Pd=0.99 for a probability of false alarm Pfa=10/sup -2/.

LINC imbalance correction using baseband preconditioning

Abstract: An open loop means of correcting the imbalances in a linear amplification using nonlinear components (LINC) transmitter is presented it is shown that all amplitude, phase and quadrature errors can be compensated for by preconditioning the baseband modulation signals and making one DC adjustment in the transmitter the six necessary compensation coefficients can be determined by a simple set of relative RF power measurements. Using an automatic tuning procedure, a one watt VHF LINC transmitter was able to meet the FCC emissions mask with 6.25 kHz /spl pi//4 QPSK modulation.

Constellation shape as a robust signature for digital modulation recognition

Abstract: This work reports on a new digital modulation recognition algorithm in an AWGN channel and in the presence of carrier recovery errors. The proposed classification technique uses the signal constellation shape as a stable modulation signature. The recovered constellations are modeled by binomial nonhomogenous spatial random fields and are used in an ML classifier. We experimentally show that shape as a global signature exhibits considerable stability in high noise, weakly synchronous environments. Experimental results are shown for various modulation standards including V.29, V.29 fallback, 8-PSK and 16-QAM.

A multilevel modulation scheme for high-speed wireless infrared communications

Abstract: To investigate short-distance, point-to-point, infrared channels, a test-bench and circuits were constructed to determine the limitations of existing optoelectronics. The results of these measurements are used to formulate a channel model which is employed for the subsequent analysis of candidate bandwidth efficient modulation schemes. A new multilevel modulation scheme, Adaptively Biased QAM (AB-QAM), is proposed which has an asymptotic 3 dB SNR improvement over PAM and a 4.5 dB improvement over QAM for large constellations while maintaining the same bandwidth efficiency. Expressions are derived for the performance of each modulation scheme and are verified in simulation.

Bit rate agile third-generation wireless CDMA, GSM, TDMA and OFDM system

Abstract: Systems, apparatus, and methods for new generations of wireless systems, including multiple standard, interoperable Third-Generation (3G) and Second-Generation (2G), Spread Spectrum CDMA, WCDMA, GSM, Enhanced GSM systems and CSMA, TDMA and OFDM. Bit Rate Agile (BRA), Modulation and Code Selectable processing techniques of Gaussian Minimum Shiftl Keying (GMSK), Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (QAM), and of Mis-Matched demodulator filters in which the demodulator filter set is mis-matched to the filter set of the signal modulator.

Methods and circuits using frequency shift keying modulation to transfer data over transmission lines simultaneous with television signals

Abstract: Data is transferred using frequency shift keying modulation in a frequency range that is not within a television signal frequency range used to conduct the television signal over the transmission line. Consequently, the present invention may allow the television signal and the data to be conducted on the same cabling. The frequency shift keying modulation is provided by generating a modulated data signal based on information included in the data. For example, the frequency shift keying modulation generates a modulated data signal at a first frequency when the data is equal to a logical 0 and at a second frequency when the data is equal to a logical 1.