Quadrature Amplitude Modulation Modulation Research Articles

QAM Resource Allocation in Mixed-Format VoD Systems

A Quadrature Amplitude Modulation (QAM) resource allocation algorithm for Video on Demand (VoD)traffic is presented. Based on stream encoding rates and available system capacity, the proposed on-line non-mixing algorithm will select the QAM modulator that maximizes system efficiency in a VoD service group. A discrete event simulator has been developed to compare the performance of the proposed algorithm against two commonly deployed algorithms known as the least-loaded and most-loaded algorithms. Our analysis suggests that the non-mixing algorithm performs better than the two algorithms under a range of assumptions that take into account peak concurrent usage rate and traffic mixture composition. We show that the non-mixing algorithm leads to an average of 4.39% higher allowed peak usage rate than the least-loaded and most-loaded algorithms.

Novel architecture for QAM modulator–demodulator and its generalization to multicarrier modulation

This paper presents an architecture for quadrature amplitude modulation (QAM) modulator and demodulator with hardware economic structure. While the modulator part requires simple logic circuits for its implementation, the more complex demodulator utilizes Running Fourier transform based on CORDIC (Co-Ordinate Rotation DIgital Computer) processor, for demodulation as well as synchronization. The basic design philosophy has been extended to multicarrier modulation and demodulation technique by using pipelined CORDIC structure for computing Running Fourier transform. The architectures have been implemented with 16 bit wordlength in Xilinx Spartan series field programmable gate arrays (FPGA).

A multicarrier QAM modulator for WCDMA base-station with on-chip D/A converter

In this paper, design and implementation of a multicarrier quadrature amplitude modulation (QAM) modulator for a wideband code division multiple access (WCDMA) base-station with a 14-bit on-chip D/A converter is described. The modulator is capable of modulating four carriers with four independent in phase (I) and quadrature (Q) data streams. The proposed modulator structure consists of an interpolation chain for data streams and four digital frequency synthesizer/modulators, which are based on a coordinate rotation digital computer (CORDIC) vector rotation algorithm. The interpolation chain consists of a root-raised cosine pulse shaping filter and three half-band filters for image filtering. The modulated carriers are combined to form a multicarrier WCDMA signal. The SINC-attenuation effect of a digital/analog (D/A) converter is canceled by an inverse-SINC predistortion filter. The multicarrier signal is converted to the analog domain with a 14-bit current steering D/A converter, which is integrated on the same silicon chip. The modulator is implemented with a 0.35-mum BiCMOS process with CMOS transistors only

A frequency-agile single-chip QAM modulator with beamforming diversity

Architecture and circuit design techniques for VLSI implementation of a single-chip quadrature amplitude modulation (QAM) modulator with frequency agility and antenna beamforming characteristics are presented. In order to achieve reliable wireless communication modem function, the single chip all-digital QAM modulator implements various features, including high data rates with bandwidth efficiency, flexibility, meeting a wide variety of user throughput requirements with variable and width and data rates in a multi-user system, and robustness, incorporating diversity and redundancy techniques to guarantee robust communication for various operating environments. The modulator components consist of several digital processing building blocks, including various finite-impulse-response (FIR) filters, an innovative variable interpolation filter, a four-channel frequency translator with quadrature mixer for antenna beamforming diversity, a quadrature direct digital frequency synthesizer (QDDFS), a numerically controlled oscillator (NCO), a QAM formatter, a pseudorandom noise (PN) generator, an x/sinx filter, and a microcontroller interface. An optimized architecture and chip implementation for the variable modulator is derived and evaluated which will support symbol rates from 6 kBaud to 8.75 MBaud continuously and digitally flexible IF frequencies up to 70 MHz with four-channel antenna beamforming function.

A multicarrier QAM modulator

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.

A single-chip universal cable set-top box/modem transceiver

A mixed-signal digital cable-TV transceiver IC containing two distinctly separate quadrature amplitude modulation (QAM) receivers and a single QAM modulator has been designed. An integrated 10-b analog-to-digital converter (AID) interfaces the first receiver directly to an analog signal. This receiver demodulates 4/16/32/64/128/256-QAM signals carrying the television programs or cable modem data with a variable symbol rate from 1 to 7 MBaud. A 6-b A/D is integrated to interface the second receiver to an analog signal. This receiver, used by cable operators for access control, demodulates quadrature phase shift keying (QPSK) signals with a variable symbol rate from 0.75 to 1.6 MBaud. The upstream modulator provides two-way communication required for interactive television or cable modem services. Capable of QPSK/16-QAM modulation with a variable transmission rate up to 25 Mb/s, the modulator also includes an integrated 10-b digital-to-analog converter to provide radio-frequency analog output from 0 to 65 MHz. Both receivers and the transmitter incorporate on-chip forward error correction compliant with multiple worldwide standards allowing global deployment. The carrier, phase, and timing recovery for each receiver is achieved with on-chip tracking loops. Adaptive decision feedback equalizers are incorporated to eliminate intersymbol interference. The transmitter incorporates preamble prepending and preequalization to facilitate reception. The device further integrates access control message separation, set-top box control circuitry, and a parallel microprocessor bus interface to boost system performance. The design employs a combination of semicustom and custom circuit design techniques for speed, mixed-signal performance, and layout density. Fabricated in a single poly, four-layer metal, 0.35-/spl mu/m standard CMOS process, the chip area is 64 mm/sup 2/. The device is packaged in a 256 tape ball grid array (TBGA), and dissipates 3 W at 3.3 V.

SER Analysis of QAM with Space Diversity in Rayleigh Fading Channels

This paper derives the symbol error probability for quadrature amplitude modulation(QAM) with L-fold space diversity in Rayleigh fading channels. Two combining techniques, maximal ratio combining(MRC) and selection combining(SC), are considered. The formula for MRC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an additive white Gaussian noise(AWGN) channel over a chi-square distribution with 2L degrees of freedom. The obtained formula overcomes the limitations of the earlier work, which has been limited only to deriving the symbol error rate(SER) of QAM with two branch MRC space diversity. The formula for SC space diversity is obtained by averaging the symbol error probability of M-ary QAM in an AWGN channel over the distribution of the maximum signal-to-noise ratio among all of the diversity channels for SC space diversity. No analysis for QAM with SC space diversity has been reported yet. Analytical results show that the probability of error decreases with the order of diversity. We can also see that the incremental diversity gain per additional branch decreases as the number of branches becomes larger. On the other hand, the performance of 16 QAM with MRC becomes much better than that of SC as the number of branches becomes larger. By giving the order of diversity, L, and the number of signal points, M, we have been able to obtain the SER performance of QAM with general space diversity. These results can be used to determine the order of diversity to achieve the desired SER in land mobile communication system employing QAM modulation.