Showing papers on "Quadrature amplitude modulation published in 1992"

Optimum diversity combining and equalization in digital data transmission with applications to cellular mobile radio. I. Theoretical considerations

Abstract: A comprehensive theory for Nth-order space diversity reception combined with various equalization techniques in digital data transmission over frequency-selective fading channels is developed. The channels are characterized by N arbitrary impulse responses possessing random parameters as well as N additive Gaussian noise sources. Various combiner-equalizers that minimize the mean-squared error are determined. Formulas are presented for the attainable least-mean-squared errors and upper bounds on average probabilities of error. The theory is applied to optimize system parameters and to predict performance for QAM data transmission operating over a model for the mobile radio channel. For this model, estimates of average attainable error rates and outage probabilities are provided as functions of system parameters. In the channel models the uncoded data rates as well as Shannon capacity are regarded as random variables. >

Analysis of the error performance of trellis-coded modulations in Rayleigh-fading channels

Abstract: This work presents an exact expression for the pairwise error event probability of trellis-coded modulation (TCM) transmitted over Rayleigh-fading channels. It includes phase shift keying (PSK) and multilevel quadrature amplitude modulation (QAM) codes, as well as coherent and partially coherent (e.g. differential, pilot tone, etc.) detection. Due to the form of the exact pairwise error event probabilities, this calculation technique cannot be used with the transfer function technique to obtain an upper (union) bound on the overall bit error probability. For this reason, the authors estimate the bit error probability by considering only a small number of short error events. Through simulations, they found that the estimation is usually very accurate at high signal-to-noise ratios but not as accurate at lower signal-to-noise ratios. They study several coded modulation schemes this way. Among the results are the fact that TCM provides significant improvement in the error floor when detected differentially, and an asymmetry in the pairwise error event probability for 16 QAM. >

Joint blind equalization, carrier recovery and timing recovery for high-order QAM signal constellations

Abstract: Two existing blind equalization tap update recursions for 64-point and greater QAM (quadrature amplitude modulation) signal constellations are studied, along with existing and novel carrier and timing recovery techniques. It is determined that the superior tap update recursion is the one known as the constant modulus algorithm. Carrier recovery requires a modified second-order decision-directed digital phase-locked loop. An all-digital implementation of band-edge timing recovery is used. With 14.4 kb/s outbound transmission using CCITT V.33 trellis-coded 128-QAM signals having 12.5% excess bandwidth, a prototype blind retrain procedure is developed to demonstrate the feasibility of the techniques for high-speed multipoint modems. A WE DSP32-based real-time digital signal processor was employed to test the retrain over a set of severely impaired channels. For each channel in the set, the retrain succeeded at least 90% of the time. >

Trellis precoding: combined coding, precoding and shaping for intersymbol interference channels

Abstract: On a linear Gaussian channel with intersymbol interference (ISI), trellis precoding is a method that achieves the equalization performance of Tomlinson-Harashima (TH) precoding, the coding gain of any known lattice-type coset code, and a considerable shaping gain. Trellis precoding may be viewed as a generalization of trellis shaping to Gaussian ISI channels, or, alternatively, as a generalization of TH precoding, with coded modulation that achieves shaping gain. With trellis precoding channel capacity can be approached essentially as closely on any strictly bandlimited, high signal-to-noise ratio Gaussian channel as on the ideal channel, using the same coding techniques. For first- and second-order FIR and IIR (finite and infinite impulse response) channels, it is shown that shaping gains close to 1 dB can be obtained with a two-dimensional four-state trellis code. Trellis precoding is quite practical whenever channel information is available at the transmitter. >

Mode selective quadrature amplitude modulation communication system

Abstract: A quadrature amplitude modulation (QAM) communication system is provided in which data can be communicated in any one of a plurality of QAM modes, such as 16-QAM, 32-QAM, and 64-QAM. A receiver detects the particular QAM mode transmitted on a trial and error basis, by attempting to decode the received data using different QAM modes until a synchronization condition is detected. The synchronization condition can require that a plurality of different synchronization tests be met. In a specific embodiment, a first synchronization test is met when a renormalization rate of a trellis decoder is below a threshold value. A second synchronization test is met when a first synchronization word is detected in the received data. A third and final synchronization test is met when a second synchronization word is detected in the received data. In order to reduce the cost of the receiver, most of the QAM mode dependent components are implemented using look-up tables stored in PROMs.

Binary phase shift keying modulation system or frequency multiplier

Abstract: A low cost spread spectrum modulator for BPSK, or Binary Phase Shift Keying capable of outputting the high modulation rate and suppressed carrier output needed in spread spectrum systems. The present invention provides high quality BPSK modulation without the double balance mixers as required in the prior art, thereby dispensing with the necessity of complex transistor/potentiometer or diode/transformer arrangements. The present invention provides BPSK modulation utilizing only one transformer (A), which can be adjusted for carrier suppression and two transistors (C, D), FET's, or digital logic gates or the like, allowing the present system to be driven from low power CMOS logic levels, yet producing eight db of gain. The present invention may also be utilized as a frequency multiplier, with the utilization of the appropriately high frequency transistor, FET, digital logic gate, or the like.

QAM: the modulation scheme for future mobile radio communications?

Abstract: With spectral congestion increasing, and plans announced to dramatically increase the number of mobile telephone users over the coming decade, many approaches are being considered to reduce the bandwidth requirements of each user. One approach is the use of quadrature amplitude modulation (QAM), a particular form of multilevel modulation where each symbol contains several bits of information. The use of QAM for mobile radio applications is considered and it is shown that this form of multilevel modulation can offer an attractive solution to current bandwidth restrictions in microcellular networks. An advanced variable-rate system is also considered and hardware development of a QAM modem discussed.

Communication signal having a time domain pilot component

Abstract: A quad 16 QAM transmission (132-136) and reception (600) methodology wherein a time domain pilot reference is advantageously associated therewith. There may be one or more such pilot references for each packet of multiple 16 QAM pulses (200). Depending upon the embodiment, each 16 QAM pulse can include a time domain pilot reference, or an estimated pilot reference (402 and 301) for that pulse can be determined either by reference to pilot references in other pulses sharing the same packet, or by reference to pilot references for other previously received 16 QAM pulses corresponding to that same pulse.

Quadrature amplitude modulation synchronization method

Abstract: In a QAM communication system, a novel synchronizing sequence of symbols added to the information channel simplifies acquisition of timing and synchronization by a receiver. Such synchronization vector provide signals for improved AFC control control signal generation.

MMSE diversity combining for wide-band digital cellular radio

Abstract: A study of minimum mean-square error (MMSE) diversity combining for wide-band digital cellular radio, designed to combat intersymbol interference (ISI) caused by frequency selective fading is outlined. The systems analyzed use binary phase-shift keying (BPSK), quarternary phase-shift keying (QPSK) or 16-level quadrature amplitude modulation (16-QAM) with cosine rolloff spectral shaping, and space diversity with selection, maximal ratio or MMSE combining. A set of performance curves is presented for selected combining schemes showing the influence of the following system parameters: the diversity order (1 to 4); the cosine rolloff factor; the power delay spectrum (with its associated delay spread); the signal-to-interference ratio; and the number of modulation levels (2, 4 and 16). >

Quadrature amplitude modulation system with compensation for transmission system characteristics

Abstract: Digital signals are converted to phase and amplitude altered, periodic, analog signals and emplaced on an output link. The system is adaptive and includes a plurality of simple quadrature phase shift keying modulators, each modulator having a plurality of controlling digital inputs, the states of which determine which of a plurality of phase displaced signals will be outputted. A local oscillator provides a periodic sinusoidal signal to each QPSK modulator. Summing circuits combine the outputs of the modulators so as to produce a constellation of phase and amplitude-displaced output sinusoidal signals. A processor/mapper combination enables conversion of a first set of digital inputs to a different set of digital outputs in accordance with a control input. Thus, the processor enables the alteration of the constellation of outputs in accordance with a control input, which may be indicative of the condition of a transmission facility.

Modulation methods for PCNs

Abstract: The interference levels that may be expected for a range of conventional cellular and microcellular clusters used in personal communication networks (PCNs) and personal communication systems (PCSs) are discussed. Simulation results show that for conventional size cells, 32- and 64-level quadrature amplitude modulation (QAM) schemes are preferred for bit error rates (BER) above 1*10/sup -2/, while 4PSK or variable-rate QAM schemes are better for lower BER. For microcells with communications at both 900 MHz and 1.8 GHz, four- or six-cell clusters are advocated, depending on the SNR expected. Based on the expected signal-to-noise ratio (SNR) and interference levels, it is argued that variable-rate QAM schemes are superior to the other modulation schemes considered. For low BERs 4PSK may often provide the best performance, whereas for high BERs, particularly when the SNR is high, 32- and 64-level star QAM are the most suitable. >

Implementation and test of a digital quasi-random modulated SFAVM PWM in a high performance drive system

Abstract: The authors propose a modulation scheme for reducing the acoustic noise effect from an AC machine which can be implemented digitally. The scheme is based on a stator flux asynchronous vector modulation (SFAVM) imposed by a digital bandlimited white noise generator. The modulation strategy is tested in a 1 kVA high-performance 16 b microprocessor controlled AC drive system. Fast Fourier transform spectra on the line-line voltage and the acoustic noise are presented, and it is shown that the new modulation strategy can decrease the noise effect. The stator flux polygon and the line current are measured, and the random modulation strategy is demonstrated. The total sound pressure level from the AC machine is investigated with fixed switching frequencies and with different random modulated frequency spans. It is concluded that a properly chosen fixed switching frequency has the lowest total sound pressure level. However, the random modulation strategy distributes the noise frequencies, and the noise is much more comfortable and less annoying. >

TCM scheme with fractional bit rates, framing signals and constellation shaping

Abstract: Data are transmitted using quadrature amplitude modulation to select for transmission symbols from two (or more) different signal point constellations; constellation switching being used to facilitate transmission of a non-integral average number of bits per symbol and/or frame synchronisation. Trellis shaping (where redundancy is introduced and selection of constellation "regions" performed (206) over a number of symbols so as to minimise transmitted power) is employed; switching (205,209) is provided so that power information (from stores (207, 208)) is available appropriate to the constellation in use for each respective symbol. Synchronisation may alternatively be provided by substitution outside the power control loop, of a symbol from an outer region for one selected from an inner region of a constellation. In another aspect of the invention, constellation-switching is employed within frames of A symbols, where A is not a power of two.

Blind adaptive equalizers for quadrature amplitude modulated communication systems based on convex cost functions

Abstract: Blind adaptive channel equalizers are important devices to remove channel distortion in high data-rate, bandlimited digital communication systems when the transmission of a training sequence is impractical or very costly. Traditional blind equalization algorithms adapt the equalizer parameters to minimize some specially designed non-MSE cost functions. These algorithms can experience local convergence problems and can thereby result in insufficient or no removal of channel distortion. We present a new quadrature amplitude modulated blind equalization scheme that is globally convergent in the equalizer parameter space to a compact set containing the desired ideal equalizer parameter setting. Our new algorithm is based on a convex cost function and a linear constraint on the equalizer parameters. For a generic class of channels, this new algorithm results in the equalizer parameter convergence to a unique global minimum achieving intersymbol interference suppression and carrier phase error removal. Different implementation approaches are assessed and simulation results are shown to confirm the theoretical global convergence of the new algorithm.

On the Computation of 16-QAM and 64-QAM Performance in Rayleigh-Fading Channels

Abstract: SUMMARY Quadrature Amplitude Modulation (QAM)schemes are attractive in terms of bandwidth efficiency and offer a numbcr of subchannels with dil'erent integrities via both Gaussian and Rayleigh-fading channels, Specifically, the 16-QAM phasor constellation has two, while the 64-QAM possesses three such subchannels, which become dramatically different via Rayleigh-fading channels. The analytically derived bit error rate (BER) formulae yield virtually identical curves with simulation results, exhibiting adequate BERs for the highest integrity subchannels of both 16-QAM and 64-QAM to be further reduced by forward error correction coding (FEC). However, the BERs of the lower integrity subchannels require fading compensation to reduce their values for FEC techniques to become effective. This property creates ground for a variety of carefully matched, embedded mobile transmission schemes of diRerent complexities. The practical implementation of such an embedded scheme is demonstrated by a low-cost, low-complexity and lowconsumption 50 KBd mobile video telephone scheme offering adequatc spccch and image quality Tor channel SNRs in excess of about 20 dB via Rayleigh-fading channels. key words: QAM theorq; modularion for microcellular fading channels

Quadrature modulation circuit

Abstract: A quadrature modulation circuit includes a low pass filter (20) which operates by a time division process for the in-phase channel (I) and the quadrature-phase channel (Q), and reduces address requirements data using the amplitude symmetry of the wave form and/or using the symmetry wave form on the time axis. The capacity of the ROM (201) is reduced by one half or more and the configuration of the quadrature modulation circuit is simplified.

A 60-mbaud, 480-mbit/s, 256-qam Decision-feedback equalizer in 1.2amu;m CMOS

Abstract: Using a combination of architecture optimization techniques and unconventional circuit designs, a 60 MHz decision-feedback equalizer (DFE) chip is presented for high-bit-rate digital modem applications. The equalizer can accommodate quaternary phase-shift keying (QPSK), and 16, 64, and 256 quadrature amplitude modulation (QAM) and achieves a peak throughput rate of 480 MB/s. The chip contains four complex-valued programmable filter taps and incorporates coefficient updating circuitry for implementing the LMS adaptive algorithm with user-selectable adaptation step sizes. Cut-set retiming architecture techniques were used so that the chips could be cascaded to implement longer equalizer lengths without any speed degradation, and a circuit design technique called adaptively biased pseudo-NMOS logic (APNL) was adopted to reduce on-chip critical-path delays. The fully parallel chip architecture achieves a computational throughput of 1.44 billion operations per second (GOPS). >

A new method for the integration of modulation and channel coding in an ARQ protocol

Abstract: A method for the integration of the modulation operation in an automatic-repeat-request (ARQ) scheme is described. This method uses a memory for the successive transmissions of a codeword and, through a suitable encoding operation, the Euclidean distances among the codewords are significantly increased with the number of transmissions. The application of the described method to some different modulation schemes, such as M-ary PSK with M>2 and continuous-phase frequency shift keying modulation, is described. The optimum combination of the modulation and channel coding operations for some short block codes is also presented. The results of the theoretical analysis show that the method described permits improving both the error probability and the throughput of an ARQ protocol with respect to similar schemes. >

Blind equalization and estimation of digital communication FIR channels using cumulant matching

Abstract: The problem of blind estimation and equalization of digital communication FIR (finite impulse response) channel is considered. The channel parameters are estimated by nonlinear batch optimization of a quadratic cumulant matching criterion involving second- and fourth-order cumulants of the received data. A new algorithm is proposed for (asymptotically) globally convergent, linear estimation of the FIR channel parameters where the FIR model order is not necessarily known. The nonlinear cumulant matching algorithm is initialized by the linear parameter estimator. The estimated channel impulse response is then used to construct a linear equalizer. An illustrative simulation example using QAM (quadrature amplitude modulation) signals is presented. >

Bandwidth efficient transmultiplexers. I. Synthesis

Abstract: Develops a set of conditions which allow bandwidth efficient transmultiplexers to be synthesized. The synthesis procedure is based upon a generalized impulse response for the combining (modulating) and separation (demodulating) filters. In particular, the combining and separation filters are bandpass versions of one of two low-pass prototypes and are configured to cancel crosstalk by exploiting relationships between the center frequencies, delays, and phases in their impulse response. Based on the derived conditions, five different transmultiplexers are synthesized. Three of them implement multicarrier quadrature amplitude modulation (QAM). The other two accomplish multicarrier vestigial sideband modulation (VSB). Intersymbol interference is eliminated by appropriately designing the prototypes. The two band case is treated as a special case. For this case, the extra flexibility in choosing the center frequencies leads to the synthesis of additional transmultiplexers. >

Digital carrier combining apparatus in a multiple QAM digital television signal receiver

Abstract: In a high definition television signal encoder, high priority and standard priority digital data are each separated into quadrature I and Q components, spectrally shaped by digital filtering, and time division multiplexed to produce respective quadrature amplitude modulated signals of the 32-QAM type. The high priority QAM signal and the standard priority QAM signal exhibit different bandwidths and carrier frequencies. The high priority and standard priority QAM signals are combined in digital form to produce a prioritized dual 32-QAM digital signal before being conveyed to a single analog-to-digital converter and analog RF transmission networks.

Six-dimensional trellis-coding with QAM signal sets

Abstract: A family of 6-D trellis-coded modulation (TCM) schemes which involve a 2-step partitioning of the constituent QAM signal alphabet is presented. With infinite constellations without shaping, the asymptotic coding gain is 3 dB for the 2-state code, 4 dB for the 4- and 8-state codes, and 5 dB for the 16- and 32-state codes which involve a smaller alphabet expansion. The authors also describe a rotationally invariant 16-state code that achieves the same asymptotic gain as its linear counterpart. Practical signal constellations are described for 6-D TCM with the spectral efficiency of uncoded 64-QAM, and the performance of these schemes is studied by means of computer simulations. It was found that they achieve an additional coding gain of 0.2-0.3 dB over infinite hypercube-type constellations. The performance of the presented schemes at practical signal-to-noise ratio values is evaluated using transfer function techniques. >

Equalizer for linear modulated signal on radio channel

Abstract: The linear modulated signal is received in blocks or frames and the impulse response of the channel is estimated during training sequences before and after a frame. Interpolation is used to estimate the impulse response at each point in the frame. From this, the coefficients of an equalizer 24, 26 are calculated for equalising the signal. The technique is particularly applicable to land mobile radio systems using 16QAM or other linear modulation schemes. It can compensate for Rayleigh fading and multipath spread.

Method and circuit arrangement to generate a phase modulated or frequency modulated signal

Abstract: The invention relates to a method, in which a phase modulated or frequency modulated signal can be directly generated with a PLL frequency synthesizer. With an interpolating synthesizer it is possible to create a very dense output frequency (f x ) raster, so that the pulses received in the phase comparator (63) both from the reference signal (f o ) branch and from the voltage controlled oscillator VCO (65) are lengthened in lengthening means (62, 69; 67, 68; k 1 , L+ΔL; k 2 , L) by a desired amount. The numbers k 1 and k 2 are proportional to the amount of lengthening. When these integers now further are changed proportionally to the modulating signal, the change of the integers causes a change of the time difference of the pulses received by the phase comparator (63). This change of the time difference further causes a change in the output signal (f x ) of the voltage controlled oscillator. The method is particularly well suited to provide digital quadrature phase modulation QPSK or quadrature amplitude modulation QAM, in which the shift from one carrier phase to another has a predetermined size and waveform as a function of time.

A 64 kbps digital land mobile radio system employing M-16QAM

Abstract: The authors describe a 64 kbps digital mobile radio system which has been tailored for trunked radio system applications. Using a combination of digital speech coding, time division multiple access (TDMA), and spectrally efficient linear modulation technologies, up to 6 voice links are supported per 25 kHz RF channel. A key feature of the system is a new modulation method, M-16QAM, which makes possible high speed signaling in land mobile radio channels without the use of an equalizer. After a brief description of the overall system, including the TDMA frame/slot structure and speech coder, focus is shifted to the modulation technique. The motivation behind M-16QAM, as well as its design and simulated performance, are discussed in more detail. Results of field trials of an experimental modem are also discussed. >

A preliminary performance evaluation of a linear frequency hopped modem

Abstract: The benefits of using linear modulation methods for a frequency hopping (FH) transmission system in narrowband, i.e., voice cellular networks, are considered. In particular, the use of a 16-level modulation scheme derived from 16 QAM combined with FH is evaluated operating in a channel subject to noise and multipath fading, characteristic of the mobile environment. >

Frame Synchronisation for QAM

Abstract: Frames synchronisation for data transmitted using quadrature amplitude modulation is achieved by providing that one symbol per frame is chosen from a larger signal point constellation than the remaining symbols. Thus, bits are assembled (2) into groups of unequal size to control the mapping (7) between the data and the signal points. Where constellations having a number of points not equal to a power of two, these may be coded in groups: or the data may be converted into a mixed-base number the bases of which correspond to the numbers of points in the respective constellations.

Fractionally spaced decision feedback multilayer perceptron for adaptive MQAM digital mobile radio reception

Abstract: The authors describe a fractionally spaced decision feedback multilayer perceptron (FSDFMLP) for adaptive multilevel quadrature amplitude modulation digital mobile radio reception that can overcome the performance degradations due to multipath fading of channels and reject cochannel interference and additive white Gaussian noise simultaneously. The two-ray model is used for the frequency selective fading channel. A fast adaptive learning algorithm called the mixed gradient based fast learning algorithm with variable learning gain and selective updates was used to train the FSDFMLP. The preliminary experimental results obtained are satisfactory, which shows that the FSDFMLP can perform more efficiently than the conventional least mean square based decision feedback filter in the presence of multipath fading of channels with non-Gaussian interferences. >