Optimal reception of digital data over the Gaussian channel with unknown delay and phase jitter

Asymptotically optimum (in the sense of minimum per-symbol error rate) receiver structures for data communication over the white Gaussian channel with unknown time delay and carrier phase jitter are developed. The receiver structures apply to the following suppressed-carrier modulation systems: double sideband (DSB), quadrature amplitude modulation (QAM) with an arbitrary constellation, vestigial sideband (VSB) and single sideband. The resulting minimum error probability receivers are asymptotically equivalent to maximum-likelihood digital {em sequence}-estimating receivers. The optimum structures implicitly derive joint maximum-likelihood estimates of the unknown parameters and of the sequence of data symbols. It is shown that the parameter estimates can be obtained from two data-directed stochastic approximation algorithms. Unlike traditional theoretical treatments of this communication situation, which have separated the highly important carrier phase and timing recovery problem from the detection problem, a unified theory is presented from which the complete ideal receiver structure can be deduced.     

Modulation for terrestrial broadcasting of digital HDTV

The digital modulation methods used by the DigiCipher, DSC-HDTV, ADTV, and ATVA-P digital high-definition television (HDTV) systems are discussed. Three of the systems use a quadrature amplitude modulation method and the fourth uses a vestigial sideband modulation method. The channel equalization and spectrum sharing of the digital HDTV systems is discussed     

Turbo-Product-Coded QVSB

In this paper, a turbo-product-coded, quadrature-vestigial-sideband (QVSB), digital modulation and coding scheme are presented. This scheme is more complex than the VSB modulation and coding format employed for high-definition television; and it achieves spectral-efficiency performance within 4 to 5dB of the Shannon-Bound, with relatively conservative turbo-product-codes. Special QVSB bandlimiting, which is more restrictive than Nyquist filtering, is used to minimize crosstalk between its dual overlapping, quadrature data channels. To unravel the residual cross-channel interference for detection, a quadrature-crosstalk maximum-likelihood-sequence-estimator (QC-MLSE) is needed. The QC-MLSE output is 'hard- to soft-decision converted' to improve subsequent decoding performance. An external interleaver was also used to augment the turbo-product-code's internal helical interleaver, for improved performance     

A Computationally Efficient Multilevel Coding Scheme for ISI Channels

This paper proposes a multilevel coding scheme with linear mapping for intersymbol interference (ISI) channels and derives a low-complexity receiver structure that can achieve the ISI channel capacity. The transmitter superimposes many layers of independent binary antipodal streams to generate a quadrature amplitude modulation (QAM) or Gaussian-like channel input. The receiver performs multistage decoding with decision feedback and interference cancellation. Within each stage is a linear minimum mean-square-error (MMSE) equalizer followed by an error-correcting decoder. The complexity scales linearly with the channel length and the number of layers, and the process is shown to be asymptotically information lossless if a fixed input power is properly distributed over a sufficiently large number of layers. This framework is then extended to achieve the capacity of the ISI channel using a transmitter-side spectral shaping filter that converts a Gaussian input sequence with a white spectrum to one with a water-filling spectrum.      

Digital signal processing techniques in Nyquist-WDM transmission systems

In single-carrier wavelength-division multiplexing (WDM) systems, the spectral efficiency can be increased by reducing the channel spacing through digital signal processing (DSP). Two major issues with using tight filtering are cross talk between channels and inter-symbol interference (ISI) within a channel. By fulfilling the Nyquist criterion, Nyquist spectral-shaped WDM systems can achieve narrow channel spacings close to the symbol rate \((\hbox {R}_{\mathrm{S}})\) with negligible cross talk and ISI. In principle, DSP can generate any signals with arbitrary waveforms and spectrum shapes. However, the complexity of DSP is limited by its cost and power consumption. It is necessary to optimize the DSP to achieve the required performance at a minimum complexity. In this paper, we first introduced the background of digital signal processing for Nyquist spectral shaping in optical fiber WDM systems. Then, we investigated the use of digital finite impulse response (FIR) filters to generate Nyquist-WDM 16-ary quadrature amplitude modulation (16QAM) signals with the raised-cosine (RC) and root-raised-cosine (RRC) shape spectra. The system performance of both the RC and RRC spectra is also examined. Moreover, we explored the various methods to reduce digital-to-analog converter (DAC) sampling speed, such as using super-Gaussian electrical filters (E-filter) and spectral pre-emphasis. We also discussed receiver-side matched filter design for Nyquist-WDM receiver optimization.     

Bandwidth efficient transmultiplexers. II. Subband complements andperformance aspects

For pt.I see ibid., vol.40, no.1, p.70-84 (1992). The performance issues related to the quadrature amplitude modulation (QAM) and vestigial sideband (VSB) transmultiplexers synthesized previously are examined. An analysis of the limitations of the configured systems regarding intersymbol interference and crosstalk suppression arising from the use of practical filters is made. A new design technique for an finite impulse response (FIR) low-pass prototype that takes the practical degradations into account is formulated. The procedure involves the unconstrained optimization of an error function. A performance evaluation reveals that for four of the five systems, the new method is superior to a minimax approach in that lower intersymbol interference and crosstalk distortions are achieved with a fewer number of filter taps. For the other transmultiplexer, the advantage of the optimized design over the minimax design is in the added flexibility of taking crosstalk into account, thereby diminishing the crosstalk distortion. The five transmultiplexers can be converted into new subband systems. The authors show how the optimized design approach formulated for the transmultiplexers over to the new subband systems     

Dual-Band Adjustable and Reactive I/Q Generator With Constant Resistance for Down- and Up-Converters

Adjustable and reactive in-phase/quadrature (I/Q) generators with constant resistance are proposed for the first time in this paper with the properties of low loss, dual-band implementation, and high quadrature accuracy. The quadrature phase property and input matching of the I/Q generator can be achieved at all frequencies simultaneously by the constant-resistance I/Q generator. However, the magnitude balance of the dual-band I/Q generator is achieved at two designed frequencies. A 2.4/5.2-GHz I/Q down-converter and a 2.4/5.7-GHz single-sideband up-converter are fabricated using 0.35- $mu{hbox{m}}$ SiGe BiCMOS technology. The dual-band I/Q generator along with two single-to-differential amplifiers is integrated to provide differential quadrature local oscillator signals for dual-band mixers. The magnitude imbalance and phase error between the I and Q channels of the down-converter are $≪$1% and $≪{hbox{1}}^{circ}$, respectively, while the maximum sideband rejection ratio of the up-converter is up to 50 dB. Additionally, the operation bandwidth (sideband rejection ratio $> $30 dB) is 200 MHz at 2.4 GHz and 720 MHz at 5.7 GHz.      

The Performance of Staggered Quadrature Amplitude Modulation in the Presence of Phase Jitter

We report on the performance of band-limited staggered quadrature amplitude modulation (SQAM) in the presence of phase jitter and additive Gaussion noise. It is demonstrated that offsetting, or staggering, the in-phase and quadrature data streams by a fraction of a symbol interval improves the phase-jitter immunity of a conventional QAM data transmission system. For example, with a raised cosine pulse having unity rolloff, staggering can reduce the effective jitter variance by a factor of two. Under the constraint of no intersymbol interference, the optimum staggering epoch is shown to be half a symbol interval, and since the resulting system is equivalent to a form of vestigial sideband modulation (VSB)VSB is superior to QAM with respect to phase-jitter immunity. Using both optimum pulse design and data staggering, it is shown that the improvement over conventional QAM is proportional to the excess bandwidth. Consequently, SQAM may be warranted whenever a high-quality phase-locked loop is not used to track phase jitter. While the SQAM technique is not new, it has heretofore not been recognized as possessing the above-mentioned advantages.     

A New Carrier Recovery Technique for Vestigial-Sideband (VSB) Data Systems

In this concise paper we have developed a new carrier recovery system for vestigial sideband amplitude modulation (VSB-AM) data sets. Neither dc restoration nor extra bandwidth is required for the proposed system. A pilot tone is transmitted at the carrier frequency and the phase jitter is derived from the quadrature chnnnel. "Artificial" phase jitter which is introduced by the data signal can be eliminated by properly shaping the transmitted signal. We have also shown that even in the presence of channel distortion and white Gaussian noise, the proposed system can faithfully track up to 60-Hz phase jitter.     

Electrical Dispersion Compensation for 40-Gb/s DQPSK Signal Utilizing MIMO DFEs

We investigate electrical dispersion compensation for 40-Gb/s differential quadrature phase-shift keying modulation signals utilizing multi-input–multi-output (MIMO) decision-feedback equalizers (DFEs). In our scheme, all branch signals after balanced-photodiode detection or single-photodiode detection are analogous to antennae in a MIMO wireless transmission systems. Chromatic dispersion and polarization-mode dispersion tolerances for various MIMO DFE configurations are compared. The flexible scheme can be easily extended to ${m}$ -ary PSK modulation formats.      

Self-Orthogonal Convolutional Coding for the DPCM-AQB Speech Encoder

A fixed-tap differential pulse code modulation (DPCM) system with a robust backward-adaptive Jayant quantizer is investigated for speech encoding at 16-40 kbits/s using binary phase shift keying over an additive white Gaussian noise channel. The performance of this system becomes unacceptable as the channel bit error rate(P_{b})approaches 10^-2. Using high-rate, long constraint length, self-orthogonal convolutional codes, the DPCM system performance is much-improved for10^{-4} < P_{b} < 10^{-2}depending on the transmitted data rate. The use of high-rate(n - 1)/n, n = 2,3,4,, and 5 codes minimizes the number of bits allocated to channel coding, and decoding complexity is reduced by employing self-orthogonal codes which admit threshold decoding. Subjectively, while there is additional quantization noise with channel coding, the irritating popping and squeaking sounds due to channel errors are eliminated.     

A Single Sideband RF-Modulator for Digital-IF Transmitter

The limitation of the single-sideband rejection ratio (SSRR) performance of transmitters based on I/Q mismatching due to high frequency signals has been investigated. The proposed single-sideband radio frequency-modulator (SSM) is capable of generating a single sideband frequency without implementing a quadrature local oscillator which displaces a phase of a local oscillating signal by 90$^{circ}$ at a high frequency. This technique is promising for radio transmission with a SSRR of more than 60 dBc. Also, the architecture of digital-intermediate frequency transmitter using the proposed SSM can be applied for a future software-defined radio solution supporting multiband and multimode wireless communications.      

Multichannel coherent optical communications systems

Balanced coherent receivers perform substantially better than single-detector receivers in multichannel optical fiber FDM communications systems since the balanced approach eliminates the direct-detection and signal-cross-signal interference. The permissible channel spacingDdepends on the intermediate frequency fIF, on the bit rate Rb, and on the modulation/demodulation format. In particular,Dincreases by 2 Hz for every 1-Hz increase of the fIF. The signal-to-interference ratio SIR, as defined in the text, provides a simple measure of the amount of the interference generated by undesired channels. The criterion SIR = 30 dB is selected in this paper and leads to the following minimum channel spacings: for heterodyne systems,3.8R_{b}for FSK,9.5R_{b}for ASK, and12.4R_{b}for PSK; for homodyne systems,7.5R_{b}for ASK and10.5R_{b}for PSK. Simultaneous transmission of several channels generates an excess shot noise studied here for the first time. If the local oscillator power is 40 dB above the received signal power and 2000 channels are transmitted without optical prefiltering, the excess shot noise power penalty is less than 1 dB.     

Evaluation of channel coding, modulation and interference ofdigital ATV terrestrial transmission systems

This paper presents results of computer simulations and laboratory tests to investigate various digital techniques (i.e., trellis coded QAM, vestigial sideband (VSB) modulation, orthogonal frequency division multiplexing (OFDM), and adaptive equalization) proposed for Advanced Television (ATV) terrestrial broadcasting. The performance of these channel coding and modulation techniques, in the presence of various interferences (i.e., Gaussian noise, ATV and NTSC co-channel interference) and in a multipath distortion environment, is evaluated and compared. The effects of ATV interference into NTSC systems are also investigated     

A 200-Mbps 0.02-nJ/b Dual-Mode Inductive Coupling Transceiver for cm-Range Multimedia Application

A 200-Mbps 0.02-nJ/b dual-mode inductive coupling transceiver is proposed for cm-range multimedia application. The inductive link geometry and the advantage of the pulse-based inductive coupling are explained. In this paper, the parallel capacitor connected with the TX inductor, the intersymbol interference (ISI) reduction scheme, and the pulse generation scheme are newly proposed. The parallel capacitor connected with the TX inductor increases the transmitter impedance so that it enhances the transmission distance by twofold, and the ISI reduction scheme pushes data rate up to 200 Mbps. Moreover, the pulse generation scheme reduces the energy consumption as low as 0.02 nJ/b. Maximum data rate and energy consumption are achieved in simulation. The transceiver occupies $0.012~{hbox {mm}}^{2}$ in 0.25-$mu{hbox {m}}$ CMOS process.      

A Super-Tripling Technology Used in Radio-Over-Fiber Systems for Multiservice Wireless Signals Within a Millimeter-Wave Band

A super-tripling technology used in radio-over-fiber systems is presented in this letter for the optical generation and multiplexing of multiservice wireless signals within a millimeter-wave band. To realize the technology, optical carrier suppression is followed by optical single sideband with suppressed carrier modulation in the central station and optical stopband filtering in the base station is utilized. With the technology, 38.5-GHz amplitude shift keying and 41-GHz differential phase-shift keying signals both with 1.25-Gb/s data bit rate were demonstrated experimentally, and power penalties of about 1 dB at a bit-error rate of $10^{-8}$ were obtained after both signals transmitted over 10 km fiber. The spurious-free dynamic range of the link was measured to be 65 $hbox{dB}cdothbox{Hz}^{2/3}$ for the 38.5-GHz channel and 70 $hbox{dB}cdothbox{Hz}^{2/3}$ for the 41-GHz channel, both with the phase-noise at about ${-}$70 dBc/Hz.      

Comparison of High-Level Modulation Schemes for High-Capacity Digital Radio Systems

This paper presents a comparative study of four 2ⁿ-state quadrature amplitude modulation techniques, namely, 16, 32, 64, and 128 QAM, in a digital radio system environment. The effects of filtering, interference, amplifier nonlinearities, and selective fading are investigated using computational and simulation methods. Increase of the carrier-to-noise ratio (CNR) at a fixed symbol error probability(10^{-3}) is taken as a robustness criterion.     

XPSK: A New Cross-Correlated Phase-Shift Keying Modulation Technique

A new modulation technique, cross-correlated phase-shift keying (XPSK), is introduced. XPSK is a band-limited offset QPSK modulation technique which has an almost constant envelope. In XPSK modulators, a controlled amount of cross correlation between the in-phase (I) and quadrature (Q) channels is introduced.IandQcross correlation reduce the envelope fluctuation Of the intersymbol-interference and jitter-free OQPSK (IJF-OQPSK) modulation scheme, introduced by Feher et al. [1], [2], from 3 dB to approximately 0 dB, thus further improving the performance of IJF-OQPSK systems in nonlinear radio systems [7], [14]. It is shown that the baseband signal of the modulator, theP_{e} = f(E_{b}/N_{0})performance, and the spectral characteristics of nonlinearly amplified (hard-limited or saturated) radio systems of XPSK and tamed frequency modems (TFM) are practically the same. The XPSK demodulator is a conventional OQPSK demodulator, the TFM demodulator requires a somewhat more complex signal processor. For this reason, the XPSK approach may lead to significant demodulator hardware cost savings, particularly in point-to-multipoint distribution systems such as broadcast systems. Simulation results for linear and nonlinear (saturated amplifier) systems operated in an adjacent-channel interference environment (in addition to thermal noise) are presented. Measurement results performed on a 128 kbit/s rate hardware-prototype modem are also reported. Experimental eye diagram and power spectrum density measurement results are in close agreement with the computer simulation results.     

A list-type reduced-constraint generalization of the Viterbi algorithm

The Viterbi algorithm (VA), an optimum decoding rule for aQ-ary trellis code of constraint lengthK, operates by taking the best survivor from each ofQ^{K-1}lists of candidates at each decoding step. A generalized VA (GVA) is proposed that makes comparisons on the basis of a label of lengthL(Lleq K). It selects, incorporating the notion of list decoding, theSbest survivors from each ofQ^{L-1}lists of candidates at each decoding step. Coding theorems for a discrete memoryless channel are proved for GVA decoding and shown to be natural generalizations of those for VA decoding. An example of intersymbol interference removal is given to illustrate the practical benefits that the GVA can provide.     

A Low-Power and High-Precision Spread Spectrum Clock Generator for Serial Advanced Technology Attachment Applications Using Two-Point Modulation

A new technique utilizing two-point (TP) modulation for a spread spectrum clock generator (SSCG) for serial advanced technology attachment is presented in which the divider ratio is varied by a digital ${Sigma}{Delta}$ modulator, and the voltage-controlled oscillator is modulated analogically. With this technique, the modulation bandwidth is enhanced in order that the modulation profile accuracy and jitter performance caused by the ${Sigma}{Delta}$ modulator can be improved at the same time. The order of the ${Sigma}{Delta}$ modulator and the loop filter can be reduced to save power and area, while the electromagnetic interference (EMI) suppression still satisfies specifications. The dual-path loop filter (DL) reduces the size of the loop capacitor and enables full integration. The proposed TPDL-SSCG has been fabricated in a 0.18- $mu$m CMOS process. The size of the chip area is $hbox{0.44} times hbox{0.48 mm}^{2}$. The circuit produces a clock of 1.5 GHz with a down-modulation ratio of 0.5%, 10.14 dB EMI of reduction, 5.485 ps rms jitter, and 35 ps peak-to-peak jitter. The power consumption, excluding an output buffer, is only 15.3 mW.