Analyzing the FCC's DTV spectral emission mask and potentialdegradation to adjacent channels due to antenna pattern differences

The FCC DTV spectral emission mask is analyzed with an NTSC subjective noise weighting function to determine the desired NTSC to undesired adjacent channel DTV signal ratio at the threshold of visibility of interference. Factors which alter the NTSC/DTV adjacent channel signal ratio at various receiving locations within the NTSC service are examined: (1) the azimuth patterns of the NTSC and DTV broadcast antennas; (2) the elevation patterns of the NTSC and DTV broadcast antennas; and (3) the centers of radiation of the NTSC and DTV broadcast antennas. These factors together with the NTSC/DTV authorized power ratio may make the DTV spillover spectrum exceed acceptable picture (and sound) interference levels even though compliance with the FCC DTV spectral emission mask is met. Spectral shaping solutions are examined by use of the NTSC subjective noise weighting     

ATSC中NTSC抑制滤波器的设计

讨论了NTSC信号与数字电视ATSC信号在相邻信道中的相互影响以及NTSC抑制滤波器的设计与应用。     

Advanced digital HDTV transmission system for terrestrial videosimulcasting

Transmission aspects of the advanced digital high definition television (AD-HDTV) system, for terrestrial simulcast delivery of HDTV are described. In AD-HDTV, two quadrature-amplitude-modulated (QAM) carriers, with different power spectral densities, are employed in a frequency division multiplex (FDM) mode within the standard 6-MHz channel. The resulting spectral shaping allows a larger power to be transmitted, compared to that for a single QAM carrier, for the same level of perceptual interference into cochannel NTSC. The coded video data are split into high-priority (HP) data and standard-priority (SP) data, and the vital information is sent on the appropriate QAM carrier, resulting in a robust audio and video transmission system. The availability is higher in scenarios where the carrier-to-noise ratio (CNR) is above the threshold for HP reception but below the threshold for SP reception; this is important in fringe areas. The NTSC planning factors, suitably modified for HDTV delivery, are used to estimate the coverage area for AD-HDTV. The calculated AD-HDTV coverage area of 54.5 miles is comparable to that for NTSC transmission     

Precoding technique for partial-response channels with applicationsto HDTV transmission

An equivalent partial-response (PR) channel 1-Z^-k arises in the envisioned terrestrial over-the-air broadcasting of digital high-definition television (HDTV) signals when a comb filter is used by an HDTV receiver to reduce the NTSC cochannel interference. The design of signal constellations and their associated precoders for this PR channel is considered. Besides PAM and square QAM, it is shown that generalized square and hexagonal constellations can also be used. Coded modulation and graceful degradation in the received signal quality are discussed. The results extended to a more general PR channel     

Baseband pulse shaping for π/4 FQPSK in nonlinearly amplifiedmobile channels

We apply baseband pulse shaping techniques for π/4 QPSK in order to reduce the spectral regeneration of the bandlimited carrier after nonlinear amplification. These Feher's patented techniques, namely, π/4 FQPSK (superposed QPSK) and π/4 CTPSK (controlled transition PSK), may also be noncoherently demodulated. Application of these techniques is in fast fading, power efficient channels, typical of the mobile radio environment. Computer simulation and experimental studies demonstrate that with these baseband waveshaping techniques, carrier envelope fluctuations are significantly reduced, and the out-of-band power after nonlinear amplification is suppressed by up to 20 dB compared to π/4 QPSK. In frequency noninterleaved land or satellite mobile radio systems operating in a nonlinear, fading and ACI (adjacent channel interference) environment, these techniques may achieve 20%-50% higher spectral efficiency compared to π/4 QPSK. In mobile cellular systems using π/4 QPSK, such as the new North American and the Japanese digital cellular systems, the application of these baseband pulse shapes may allow more convenient and less costly amplifier linearization     

DTV repeater emission mask analysis

Terrestrial digital television (DTV) requires careful planning in the allocation of RF channels, especially during the transition period when intermixing both analog and digital signals in the same coverage area. One important issue to consider is adjacent channel interference, which limits the number of RF channels utilized in any given area. This issue is important in the deployment of not only full service stations, but also of secondary stations such as translators, on-channel repeaters, and low power television stations. Full service stations have FCC rules that limit the amount of adjacent channel splatter by requiring the splatter energy to remain below a rigid emission mask. Currently there are no FCC rules for translators and low power television stations. The paper discusses typical DTV transmitter splatter sidebands and their causes, as well as specific methods for interference analysis from adjacent channel DTV splatter into adjacent NTSC or DTV signals. Two rigid emission masks ("simple" and "stringent") are proposed and evaluated. Several filter designs are computer simulated and analyzed for minimizing adjacent channel splatter interference as well as in-band DTV signal degradation. Linear pre-correction techniques are analyzed for various length (15-tap and 31-tap) transversal filter equalizers. The simulation is verified by measuring and evaluating DTV system performance for two hardware band-pass filters individually placed at the output of a low power (30 W average) transmitter.     

Anti-blocker design techniques for MOSFET-C filters for directconversion receivers

A linearized MOSFET-C low-pass filter suitable for a baseband channel selection filter for a direct conversion receiver is presented. Using polysilicon resistors instead of MOSFET resistors in the input and output part, the filter achieves very high out-of-band linearity but maintains the original transfer function under the control of a continuous on-chip cutoff tuning scheme. In order to enhance the linearity of the triode-mode MOSFET variable resistors, the gates of the MOSFETs are driven by a charge pump in the cutoff control loop. Also, an appropriate gain scaling is implemented to lower the input referred noise, thus making the out-of-band dynamic range wider. This fifth-order elliptic filter achieves -2 dBV in-band IIP3, +28 dBV out-of-band IIP3, +94 dBV out-of-band IIP2 and -87 dBV input-referred noise, and dissipates 6.2 mW from a 2.7-V supply; the on-chip continuous automatic tuning system dissipates 4.1 mW     

Methods for accommodation of HDTV terrestrial broadcasting

In the United States, consideration is underway to provide for the terrestrial emission of high-definition television (HDTV) signals in the existing VHF/UHF allocations. Analyses show that it may be necessary to reduce cochannel spacings to a minimum of 160 km if the vast majority of existing terrestrial broadcasters are to be accommodated with an HDTV service in addition to their NTSC capability. HDTV coverage and acceptable cochannel interference levels of these spacings are under investigation. Techniques that determine if there is sufficient spectrum to provide for the additional services are described. The techniques include assessments of the need to maintain UHF taboo restrictions currently applied to NTSC, analysis of effective coverage areas, and development of allotment/assignment methodologies     

Spectral sensitivity of power amplifiers to quadrature modulatormisalignment

Misalignments in the quadrature modulator feeding a nonlinear high power amplifier can produce distortion products that lead to spectrum leakage into adjacent channels. Expressions are derived relating the out-of-band spectra to these misalignments and to the complex coefficients of the power series describing the amplifier. For most applications the adjacent channel leakage is proportional to the square of the misalignment error (carrier leak, differential gain, differential phase and level error) except in the case of some higher order products of continuous phase modulations (CPM). A technique for estimating the spectrum for the above situations is described. It involves summing the weighted spectrum of each distortion product. The weighting coefficients can be varied to account for amplifier characteristics, backoff, and misalignment error. The analysis is applicable to linear or continuous phase modulations with or without predistortion. The spectrum estimate is particularly good for continuous phase modulated signals where the error is normally much less than 1 dB     

Experimental Results Supporting the Determination of Service Quality Objectives for DBS Systems

A summary of the results of a joint United States and Canadian program on subjective measurements of the picture degradation caused by noise and interference on an NTSC encoded color television signal is given in this paper. The effects of system noise, cochannel and adjacent channel interference, and both single entry and aggregate as well as a combination of these types of interference were subjectively evaluated by expert and nonexpert viewers under reference conditions. These results were used to develop the rationale used at RARC '83 to establish the service quality objective for planning the DBS service for the American continents.     

Methods for crosstalk measurement and reduction in dense WDMsystems

We propose a scheme for the monitoring and reduction of crosstalk arising from the limited stop-band rejection of optical bandpass filters in dense WDM systems. The optical carrier at each wavelength is modulated with a subcarrier tone unique to that wavelength. The level of crosstalk from a given channel can be determined by measuring the power of the corresponding tone. Crosstalk from other channels can be cancelled in a linear fashion by weighting and summing the photocurrents of the desired channel and several adjacent interfering channels. Alternatively, in nonlinear crosstalk cancellation, decisions are made on the interfering signals, and these decision are weighted and summed with the photocurrent of the desired channel. For example, assuming an optical filter having a Gaussian passband, the channel density can be increased from 20 to 30%, depending on the number of adjacent channels detected. The signal-to-interference ratio can be increased by 10-20 dB and the system can achieve a BER<10^-9 under conditions where, without interference cancellation, the signal-to-interference ratio would be less then 10 dB     

Analysis of ATV transmission subsystem field test data

This paper examines the data from the field test of the Grand Alliance HDTV transmission subsystem conducted in Charlotte, NC in 1994. The field test data provides HDTV system designers and researchers with first-hand information on the performance of digital HDTV terrestrial broadcasting as well as on NTSC performance in the real-world environment. Analyses of the field test data are performed with respect to the system performance of an 8-VSB digital transmission subsystem, the performance of NTSC as reference and the television channel characteristics. Observations and conclusions derived from the analyses are provided     

Cross-correlated correlative encoding: an efficient modulationmethod

A new cross-correlated correlative baseband encoding scheme is presented as a means of doubling the capacity of a mobile communication systems without the cost of complex baseband filtering. System performance is studied in a non-linear amplified channel for 6 to 9 dB improved power efficiency. The system is analyzed for spectrum efficiency, adjacent channel interference (ACI), co-channel interference (CCI) and bit error rate (BER) performance in a Rayleigh faded cellular network. Computer simulated results and hardware experimentation show that modified correlative encoding achieves up to a 70% improvement in spectrum efficiency and double network capacity when compared to constant envelope GMSK modulation used in GSM, DCS1800, PCS1900 and DECT systems     

Hardware nonlinearities in digital TV broadcasting using OFDMmodulation

FFT-based coded orthogonal frequency division multiplexing (COFDM) is one of the techniques for digital TV broadcasting over multipath fading channels. A FFT-based OFDM signal is subject to various hardware nonlinearities in both the transmitter and receiver. Hardware nonlinearities not only affect the in-band performance of an FFT-based OFDM system but also may affect the system performance of an adjacent channel signal because of regenerated sidelobes of the transmitted signal. The paper investigates the in-band and out-of-band behaviour of a 64QAM-OFDM system under various nonlinear devices. It is shown that the inherent signal clipping in the IFFT processors with a limited word length reduces the required RF amplifier output backoff (OBO) where adjacent channel interference is the limiting factor. For a 0.25% clipping rate, an additional 2 dB OBO is required for the COFDM signal to achieve the same level of adjacent channel interference as for the single carrier system. The loss in SNR due to signal clipping is negligible in a coded OFDM system     

Spectral Energy Distribution of Radio Link FM

The series expansion for the energy distribution of quasi-niose-modulated and arbitrarily preemphasized FM signals is being derived. Computer evaluations for the CCIR multichannel preemphasis in the range applicable to systems between 12- and 1800-channel loading show that not the total phase deviation but the deviation ηtopof the upper baseband portion is the quantity governing the energy density beyond 1.5 times base bandwidth off the carrier frequency. The interference into the adjacent channel is computed and a channel spacing formula is deducted based on an interference level equivalent to 3 pW. The formula isB_{n} = 3M + 1KD, whereMis the highest baseband frequency,Ka factor between 0 and 1, andDthe peak frequency deviation obtained with peak factor of 9 dB.     

基于FPGA的平方根升余弦滤波器设计

为了满足陆上集群无线电(TETRA)数字集群系统对基带信号成形处理的要求,提出了一种用于TETRA数字集群系统的平方根升余弦(SRRC)滤波器设计,论述了基带成形滤波和SRRC滤波器的基本原理,分析了窄带调制带宽限制、TETRA邻道干扰限制和滤波器阶数等需解决的问题,论述了滤波器参数设计和FIR滤波器FPGA实现等关键技术,完成了对基于FPGA的SRRC滤波器设计的仿真分析。     

全数字高清晰度电视中8—VSB传输系统

分析了全数字高清晰度电视（ＨＤＴＶ）中地面广播信道的干扰及抑制措施，给出了抑制同频干扰的梳状滤波器的设计方法和ＨＤＴＶ中８－ＶＳＢ基本原理及传输方案，并基于传信率１／Ｔ＝２３．５４８Ｍｂｐｓ的８－ＶＳＢ作了计算机模拟。     

基于图像特征相关度的激光干扰卫星效果评估

针对激光干扰光学成像卫星效果难以评估的问题,借鉴图像处理相关理论,将干扰前后卫星图像特征相关度作为评估指标,并采用HVS(人眼视觉系统)对指标进行修正,利用基于一致相邻度熵权的综合赋权方法,建立激光干扰效果综合评估模型。运用模型对受激光干扰条件下的卫星图像进行评估,得到的结论既能客观地反映激光干扰的实际效果,又能与人的主观感受保持较好的一致性,验证了模型在激光干扰光学成像卫星效果评估方面的适用性和科学性。     

Digitally Phase Modulated (DPM) Signals

Some properties of digitally phase modulated (DPM) signals are presented. Phase modulation with (overlapping) pulses generated by a digital FIR filter belong to this class, which may be considered to be a practical approximation to continuous phase modulated (CPM) signals. The power spectra of DPM signals are derived analytically. The ability of these signals to operate through an additive white Gaussian noise channel is assessed by calculating their minimum Euclidean distance. Their noise and spectral properties are found to be similar to those of CPM signals. Assuming that a Viterbi decoder is used to resolve symbol interference, the out-of-band power tends to decrease as the pulse duration increases, and the noise immunity is enhanced. At the same time the receiver complexity grows exponentially. Hence, noise immunity and spectrum compactness are achieved at the cost of higher received complexity. Modems for DPM signals are believed to be easier to implement than those for CPM signals. This is because filter design is simple and a residual carrier component can be retained to facilitate carrier regeneration. Furthermore, the accumulated carrier phase does not need to be continuously evaluated in order to perform matched filtering. The analytic results derived are supported by measurements and simulations.     

Performance analysis of coded multicarrier spread-spectrum systemsin the presence of multipath fading and nonlinearities

In this paper, we analyze the effects of a nonlinear amplifier on the performance of convolutionally coded multicarrier spread-spectrum systems in the presence of multipath fading. Two performance measures, bit-error rate (BER) and adjacent channel power ratio (ACPR) are considered to assess the effects of in-band interference and out-of-band interference (spectral regrowth) from the nonlinear amplifier, respectively. A memoryless polynomial model is used to represent the bandpass amplifier amplitude nonlinearities (AM/AM) and a slow frequency-nonselective Rayleigh fading channel is assumed for each modulated carrier. Analytical results for the BER for uncoded systems and upper bounds on the BER for coded systems are presented. The optimum amplifier output power backoffs for both systems, which yield the smallest system power consumption, are also determined. The obtained ACPR shows its slow (inverse linear) falloff with the amplifier output backoff