预失真技术在数字电视发射机中的应用研究

根据数字电视OFDM信号对电视发射机功率放大器线性的要求,介绍了一种可识别功放记忆效应的数字预失真器的结构和特点。经过计算机仿真表明,记忆效应预失真结构应用在数字电视发射机功放的线性化中可以取得令人满意的效果。     

高效Doherty功放在数字电视前端发射机中的应用

数字电视发射机是采用OFDM调制方式,因此对发射机中功率放大器的效率会提出非常高的要求。针对0FDM信号的高峰均比（PAPR）特性,将Doherty功放引入前端功率放大器,介绍了Doherty功放的原理和基本结构,通过计算机仿真验证了这种功放电路在数字电视发射系统中的应用效果,设计了具体的实际电路,并进行测试,取得实际的结果。结果表明所设计的Doherty功放很好地解决了目前数字电视前端发射机存在的效率低的问题,具有很大的实用性。     

电视发射机功率放大器线性化技术比较

本文结合数字电视发射对功率放大器线性性能的要求,提出4种常见的功率放大器的线性化技术,详细阐述了各种技术应用于高频大功率放大器的可行性和工程实现的局限性,为现用模拟电视发射机功率放大器用于数字电视发射进行了有益的探讨.     

数字电视发射机的原理与维修

当前,在广播电视发射领域当中,传统电视的发射机早已经逐步被数字化电视的发射机所替代。数字电视画面更为清晰,在实际应用中不仅能够满足用户日常电视节目收视需求,还能够控制用户,实行统一的收费。为保证数字电视信号传输的稳定性,加大力度对数字电视发射机原理与维修进行分析,具有一定现实意义。基于此,文章就数字电视发射机原理与维修进行简要的分析,希望可以提供一个借鉴。     

天塔机房电视系统信号传输链路数字化改造

随着人们对娱乐文化需求的不断提高以及通信技术的发展,模拟电视逐渐退出历史舞台,地面数字电视普及化加速。本文对天津广播电视塔机房地面数字电视播出系统整体改造中的前端信号传输链路部分的改造进行分析,对机房对从光端接收机接受信号到信号进入发射机激励器这一段传输链路的改造重点进行论述。     

关于电视发射机模数过渡中功率放大器的讨论

为适应数字电视地面广播的发展,实现电视发射技术由模拟到数字化的顺利过渡,并最大程度地节约成本投入,从数字电视发射机对功率放大器的特殊要求出发,讨论了为适应这些要求所采取的一些措施,以及电视发射机模数过渡过程中需要注意的问题。     

关于模拟电视发射机向数字电视发射机过渡的思考

电视发射机可以分为6部分:激励器、功率放大器、RF输出单元、电源、监控和冷却系统.当从模拟电视发射机过渡到数字电视发射机时,这6部分应分别考虑.     

地面无线数字电视发射系统

正一、引言地面无线数字电视传输是通过发射站、天线塔等设施,以无线电波的方式传输电视信号、电视用户采用天线接收信号来收看电视节目。广电总局2013年在漳州芝山转播台安装由新大陆生产的27频道地面无线数字电视发射机本人参加安装,调试工作。地面数字电视发射系统一个频道最多可同时播出8套数字电视节目。现对本台数字发射机及天馈系统及用户接收情况介绍如下:二、发射机的发展新趋势高效在国家节能环保政策提倡下,高效率已     

数字自适应预校正（DAP）——介绍数字电视发射机中的一种实用技术

现在我们清楚地认识到,数字地面电视标准为了将数字电视信号载入日益拥挤的频谱内以实现其应有特性及性能水平,不得不对发射机提出了一些苛刻的要求。高功率放大器（HPA）内失真的原因及影响已在许多论文和校正设计方案中提到过。本文首先将回顾一些数字电视的重要特性;然后将解释为什么对数字发射机来说DAP是最好的解决方法及带给发射系统什么优点;最终在介绍完DAP基本原理和发射机内具体实现以后将展示一些应用结果。     

数字电视传输概念

数字电视:数字电视继模拟电视之后的一种电视,它将要传输电平数值化,因而有抵抗杂波,信息量大等多项优点。 地面传输:就是通常所说的发射机发射信号。目前的电视节目传输有电缆,卫星以及地面传输多种方式。 调制:无线电波辐射要求天线尺寸与波长相近。用调制方法使电视信号相对带宽减小,实现信号传输。 编码:与模拟电视的编码器不同,是在数字平台上实现的。通过编码和解码完成压缩,抑制干扰各种处理手段。     

FPGA Implementation of a Power Amplifier Linearizer for an ETSI-SDR OFDM Transmitter

Most satellite digital radio （SDR） systems use orthogonal frequency-division multiplexing （OFDM） transmission, which means that variable envelope signals are distorted by the RF power amplifier （PA）. It is customary to back off the input power to the PA to avoid the PA nonlinear region of operation. In this way, linearity can be achieved at the cost of power efficiency. Another attractive option is to use a linearizer, which compensates for the nonlinear effects of the PA. In this paper, an OFDM transmitter conforming to European Telecommunications Standard Institute SDR Technical Specifications 2007-2008 was designed and implemented on a low-cost field-programmable gate array （FPGA） platform. A weakly nonlinear PA, operating in the L-band SDR frequency, was used for signal transmission. An adaptive linearizer was designed and implemented on the same FPGA device using digital predistortion to correct the undesired effects of the PA on the transmitted signal. Test results show that spectral distortion can be suppressed between 6-9 dB using the designed linearizer when the PA is driven close to its saturation region.     

Effects of clipping and filtering on the performance of OFDM

Orthogonal frequency division multiplexing (OFDM) is an attractive technique for wireless communication applications. However, an OFDM signal has a large peak-to-mean envelope power ratio, which can result in significant distortion when passed through a nonlinear device, such as a transmitter power amplifier. We investigate, through extensive computer simulations, the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the crest factor, and the bit-error rate. Our results show that clipping and filtering is a promising technique for the transmission of OFDM signals using realistic linear amplifiers     

A Digital Envelope Modulator for a WLAN OFDM Polar Transmitter in 90 nm CMOS

A digital envelope modulator as part of a polar transmitter architecture for the 802.11a/g WLAN OFDM standards is investigated. The digital envelope modulator is quite similar to a state-of-the-art DAC design, but now it has been optimized to deal with envelope signals. A thermometer-coded envelope DAC has been implemented in a 90 nm digital CMOS process. Measurements of a test chip show the digital envelope modulator to reach an OFDM output power of 5 dBm for 54 Mb/s using 64 QAM at 2.45 GHz and fulfilling EVM specifications and in-band spectral mask requirements using just 12.7 mW from a 1.2 V supply. Combining the digital envelope modulator with an off-chip power amplifier gives an output power of 20.4 dBm, while fulfilling EVM specifications and in-band spectral mask requirements. The output power of the presented envelope DAC can be increased in a re-design by scaling device sizes. The envelope DAC is a key component in a software-defined-radio transmitter.     

Simultaneous broadcasting of analog FM and digital audio signals bymeans of adaptive precanceling techniques

A method for broadcasting digital audio simultaneously with existing analog frequency modulation (FM) radio is presented. The method is based on precomputing the response of the host analog FM signal at the digital receiver and precanceling it at the transmitter. As a result, the digital transmission is free from interference from analog FM. We select the rate and power level of the digital transmission in a manner that the interference the digital data incur on the analog FM signal remains at acceptably low levels. The digital transmission is based on adaptive orthogonal frequency-division multiplexing (OFDM) (adaptive multicarrier). The frequencies and number of carriers of the digital multicarrier modem are judiciously selected in a time-varying fashion so as to cause a negligible distortion in a standard receiver for analog FM. Simulations based on conservative nonoptimized signal design indicate that data rates up to about 130 kb/s inside the 200-kHz FM channel are achievable for acoustic test signals. We present a number of numerical examples where the average digital data use up to 50% of the 200-kHz power spectrum with digital signal power levels 25-35 dB below the analog signal. Due to the resulting variable-rate digital transmission, a control channel is required. A method of precanceling with multiple orthogonal direct-sequence spread-spectrum schemes is also presented     

Minimization of the Intermodulation Distortion of a Nonlinearly Amplified OFDM Signal

In the course of development of the HIPERLAN-Standard OFDM (Orthogonal Frequency Division Multiplexing) was a possible candidate for the modulation scheme.An advantage of OFDM is that it can be implemented simply and that it is suitable for the transmission of high data rates in the mobile radio channel. Furthermore, it is insensitive against disturbances caused by multipath propagation. However, the OFDM signal shows a nonconstant envelope that leads to unwanted out-of-band radiation, in case the transmitter amplifier has a nonlinear characteristic.In this paper a method for the reduction of the fluctuation of the envelope of an OFDM signal is presented. Combined with a predistortion to linearize the characteristic of the transmitter amplifier an efficient method for the reduction of the out-of-band radiation results so that OFDM could prove to be a suitable modulation scheme for future mobile telecommunication applications.     

A data broadcasting system expanding the information capacity of existing analog communication systems

This paper presents the physical layer functions powering a new wireless data broadcasting system over analog television signals, referred to as dNTSC system (for data over National Television System Committee (NTSC) standard). Novel data insertion techniques at the transmitter and data extraction techniques at the receiver allow data rates of 1-4 Mbps that coexist with existing analog transmission but do not adversely affect normal television reception. Novel digital signal processing (DSP) techniques include a video abatement system that reduces data-to-video crosstalk for unimpaired analog television reception, adaptive nonlinear amplifier compensation, and advanced video cancellation and adaptive data equalization methods in the receiver. An analysis of the dNTSC system through noisy, multipath channels reveals the subtleties of the dNTSC system, compared to a conventional, dedicated digital communication link.