大功率多载波发射机的新设计

多载波通信系统中,发射机因为功率器件的非线性特性,会产生 多阶交调,影响发射信号频谱质量。介绍了一种大功率多载波发射机的新设计,该设计采用 运用快速初相搜索算法优化的信号产生、带AGC的上变频器和平衡式功率放大器。理论和实 践证明,该设计兼顾信号的线性度和整机效率,对交调分量、谐杂波等有较好抑制,能获得 较好的信号频谱和较高的效率。     

一种非线性元件实现线性放大的改进技术与仿真

提出了一种改进的非线性元件实现线性放大（LINC）理论,将幅度和相位均变化的输入射频信号分离成包络信 号和恒包络角调信号,再将包络信号正交调制到后者的相位中,然后对两路调制后的恒包络信号进行变频放大,最后通 过求和电路得到放大后的上变频输入射频信号。因为恒幅信号可以在放大器的非线性区放大而不失真,从而整体效率高。 本文推导出其电压增益为m KG E ,并对不同频率和幅度进行了仿真,得到的仿真结果表明实现了理论分析的预期的放大 效果。     

一种新的混合预失真器的设计

通信技术的发展对于功率放大器的要求越来越高,主要集中在高线性、高效率的功放.预失真是目前改善功放线性比较好的方法.新的自适应混合预失真系统充分利用模拟预失真,快速简单的和数字预失真算法的精确,输入信号先后经过模拟、数字两级预失真系统,并结合信号包络检测技术进行带外信号调节.通过对仿真结果的比较,IMD性能比单独使用数字预失真系统有了8 dB的改善,同时收敛时间也有所减少.     

一种用于APFC的模拟乘法器设计

在有源功率因数校正技术(APFC)中,通过对乘法器的输出与电感电流的峰值比较,控制功率开关管的开启与关断,使输入电流峰值包络跟随输入电压,功率因数理论上为单位值。而提高乘法器的线性度,减小非线性误差成为研究模拟乘法器的一个重要方向。本文提出的模拟乘法器采用有源衰减器显著的增大了输入信号电压范围,更重要的是在有源衰减电路中引入负反馈有效的减小了乘法器的非线性误差。基于CSMC 0.5um BCD工艺,采用Hspice进行仿真验证,在电源电压5V条件下,乘法器的一输入端的输入范围为0~2V,非线性误差小于0.6%,另一输入端的输入范围为1~4V,非线性误差小于0.3%。总谐波失真小于1.8%。     

调整初相提高多频点信号功率利用率的方法

通过分析信号初相与多频率合成信号包络的关系,提出利用初相调整的方法来优 化合成信号包络,从而提高功放的功率利用率。仿真分析结果和实际应用表明,该方法可以 很好地降低合成信号包络的最大电平,使合成信号包络尽可能在放大器的线性范围内,从而 有效抑制了交调和互调成分以及谐波成分,提高了功率利用率。     

一种基于LINC技术的信号分离算法

LINC（Linear Amplifier Using Nonlinear Components）技术是使用非线性的功放来实现信号的线性放大。LINC技术克服了传统线性化技术的效率低,带宽窄的问题,理想情况下能够达到100%的效率。信号分离是LINC的关键技术,信号分离的特性严重影响了LINC合成信号的性能。根据LINC技术信号分离原理,采用CORDIC算法来实现输入信号的幅相分离,将输入的调幅调相的变包络信号分离成两路恒包络调相信号。同时采用了一种优化的信号分离算法,把初步分离的两路数据进行角度比较,根据选择最小夹角原则重新分配两路数据,达到改进信号包络的目的。对信号分离过程进行仿真验证,表明信号的恒包络特点得到了显著改善,最后使用FPGA实现。     

毫米波功率放大器的预失真线性化改进研究

针对毫米波功率放大器的非线性失真问题,提出一种记忆多项式预失真优化算法,对功放的非线性失真进行补偿。预失真处理前后功放特性曲线表明该预失真算法的线性化效果明显;预失真处理后输出信号的相邻信道功率比原始输入信号高0.89 dB,比预失真前降低了7.8 dB,降低了相邻信道的干扰,符合理想功放线性化放大原则。     

改进的动态记忆多项式功放模型及预失真应用

针对无线通信系统中射频功放的强非线性、强记忆效应特征,提出一种改进的多支路组合模型——改进的动态记忆多项式(G-DMP)模型。该模型以动态记忆多项式模型为基础,引入记忆时刻输入信号包络对当前输入信号的影响项和当前输入信号包络对记忆时刻输入信号的影响项,更灵活地对功放强记忆效应建模。同时采用改进的RLS_LMS联合算法对G-DMP模型进行自适应预失真系统仿真。结果表明:G-DMP模型比DMP模型精度优于0.5dB时,系数减少14.29%,邻信道功率比(ACPR)改善了4dB,由此可知,G-DMP模型能获得更好的建模精度和线性化效果。     

基于多项式与查找表的预失真技术研究

为补偿功率放大器固有的非线性,提出了一种新型的预失真器。该预失真器结合查找表和多项式两种常用的预失真方法实现,在查找表中存储分段低阶多项式系数,根据输入信号的幅度查表得到相应的多项式系数对输入信号进行预失真处理。仿真结果表明,该预失真器对互调失真（IMD）的改善优于多项式预失真器,能有效改善信号因功放非线性失真而导致的信号星座图扭曲及频谱再生,提高通信系统的性能。     

集成运放的非线性失真分析及电路应用

集成运放差分放大电路的非线性失真分析,可以用来对集成运放电路特性进行优化设计,抑制带内各次谐波的产生。对双集成运放AD8062的非线性参数分析,优化其外围电路的连接方式,减小共模输入电压,实现了集成运放的线性输出。AD8062的电路优化设计提高了ISM频段定位系统接收前端射频电路增益,有效抑制了各次谐波的产生,输出信号幅度满足后端A/D采样器的门限要求。     

Two fast nearest neighbor searching algorithms for image vectorquantization

In this paper, two efficient codebook searching algorithms for vector quantization (VQ) are presented. The first fast search algorithm utilizes the compactness property of signal energy on transform domain and the geometrical relations between the input vector and every codevector to eliminate those codevectors that have no chance to be the closest codeword of the input vector. It achieves a full search equivalent performance. As compared with other fast methods of the same kind, this algorithm requires the fewest multiplications and the least total times of distortion measurements. Then, a suboptimal searching method, which sacrifices the reconstructed signal quality to speed up the search of nearest neighbor, is presented. This algorithm performs the search process on predefined small subcodebooks instead of the whole codebook for the closest codevector. Experimental results show that this method not only needs less CPU time to encode an image but also encounters less loss of reconstructed signal quality than tree-structured VQ does     

短波高速QAM信号解调算法的研究

文中针对短波高速QAM信号,提出并实现了一种全数字的解调方案。采用了最大平均功率定时同步算法和最大似然载波相位估计算法。利用同步导频使信号的眼图张开,进而对数据段进行信道均衡与相位补偿。采用判决反馈模式的非线性均衡器,更好地补偿了信道畸变。这种前向式解调结构减小了算法的复杂性,易于DSP实现。Matlab仿真结果表明该方案有效可行。     

基于瞬时相位拟合的LFM信号参数估计算法

针对传统线性调频（LFM）信号参数估计算法中复杂的搜索和计算问题,提出了一种不需要参数搜索的快速LFM信号参数估计算法。该算法先用希尔伯特变换估计LFM信号瞬时相位,再用二次相位函数拟合LFM信号瞬时相位从而得到初始频率和调频斜率的估计。仿真验证了本文算法的有效性,说明该算法能够给出满意的参数估计结果。     

长线电缆数字基带传输中自适应均衡器的设计

长线电缆受实际工作环境的影响非常大.各种因素都会引起传输信号的幅度和相位失真,采用自适应均衡技术可解决信道失真的问题.采用RLS算法求解均衡器的系数.最后通过仿真和测试结果,分析了均衡性能.     

Performance of a satellite modem transmitting convolutionally and differentially encoded 8PSK signals

The paper studies a digital satellite modem for mobile systems. The modem transmits a convolutionally and differentially encoded eight-phase-shift-keyed (CDE8PSK) signal over a satellite link and employs a near-maximum-likelihood decoder at the receiver. The signal can tolerate phase ambiguities that are multiples of 4 radians, which normally result from the carrier recovery loop at the receiver. However, the carrier recovery loop is not considered here. The high-power amplifier (HPA) at the earth-station transmitter may introduce non-linear distortion to the CDE8PSK signal, and predistortion may or may not be used. Several different earth-stations are assumed to have simultaneous access to a given transponder on the satellite, in an arrangement of frequency division multiple access, but the satellite transponder is assumed to be linear. Thus the CDE8PSK signals that occupy the immediately adjacent frequency bands can introduce adjacent-channel interference (ACI) to the desired CDE8PSK signal. Extensive computer-simulation tests have been carried out to evaluate the effects of non-linear distortion with predistortion, in the presence of ACI, on the tolerance of the modem to additive white Gaussian noise. Four different bandwidths of the transmitted signal are considered, together with three different arrangements of the demodulator. The predistorter operates on the baseband signal at the input to the modulator and assumes a prior knowledge of the HPA characteristics. In all simulation tests, an equivalent baseband model of the transmission system is used, and the results are used to determine the preferred modem design.     

放大器非线性失真研究装置

本文设计并制作了一种基于晶体管放大器的非线性失真研究装置。本装置以频率为1kHz、峰峰值为20mV的正弦波作为晶体管放大器输入信号,输出峰峰值不低于2V的无明显失真波形及其余四种失真波形,并对输出波形进行AD采集后,通过FFT方式计算输出信号的总谐波失真值(Total Harmonic Distortion)。本装置由STM32F407核心控制板、晶体管及偏置电路组成。通过改变五个通道的放大器偏置电路调节静态工作点,同时采用4051模拟开关进行五种波形通道的切换,实现“无明显失真”、“顶部失真”、“底部失真”、“双向失真”、“交越失真”五种波形输出,并在TFT LCD屏上显示波形以及THD值。     

一种OFDM系统峰均比的改良PTS算法

部分传输序列（PTS）方法通过选择合适的相位序列以降低信号峰值出现的概率，该方法不会使信号发生畸变。但是传统的PTS技术计算复杂度非常大，需遍历所有可选的相位因子，其计算量随分割子序列数按指数增长。本文提出了一种正倒二叉树多层相位序列方法，该方法通过对称的树形搜索，搜索出最优的相位序列。仿真结果表明，该方法大大降低系统的复杂度．同时PAPR得到更好地抑制。     

Blind DOA and polarization estimation for polarization-sensitive array using dimension reduction MUSIC

A novel blind direction-of-arrival (DOA) and polarization estimation algorithm for polarization-sensitive uniform linear array using dimension reduction multiple signal classification (MUSIC) is proposed in this paper. The proposed algorithm utilizes the signal subspace to obtain an initial estimation of DOA, then estimates more accurate DOA through a one-dimensional (1-D) local searching according to the initial estimation of DOA, and finally obtains polarization parameter estimation via the estimated polarization steering vectors. The proposed algorithm, which only requires a one-dimension local searching, can avoid the high computational cost within multi-dimensional MUSIC algorithm. The simulation results reveal that the proposed algorithm has better DOA and polarization estimation performance than both estimation of signal parameters via rotational invariance technique algorithm and trilinear decomposition algorithm. Furthermore, the proposed algorithm can be suitable for irregular array geometry, obtain automatically paired multi-dimensional parameter estimation, and avoid multi-dimensional searching. Simulation results verify the effectiveness of the proposed algorithm.     

Amplifier linearization using simultaneous harmonic and basebandinjection

A novel linearization scheme utilizing injection of distortion signal at the input of amplifier is described. Harmonic and baseband signal generated by predistortion circuits is fed to the input of the main amplifier and by controlling the power level of the harmonic and baseband signal properly, mixing products can be made to cancel out with the FET inherent distortion signals. Unlike many other techniques, no precise phase adjustment is required for the RF signal path. For verification, the two-tone performance of a constructed linearized amplifier is measured and a reduction of the third-order IMD power level of about 27 dB is observed     

拉曼放大器的基本原理及其在有线电视光纤网长距离传输中的应用

当前在残留边带调幅（AM-VSB）调制的外调制光纤有线电视系统中,为实现长距离传输普遍采用大功率掺铒光纤放大器（EDFA）,而大的入纤光功率在光纤的色散作用下存在严重的非线性失真,根据受激拉曼散射原理,提出分布式光纤拉曼放大器（DFRA）在长距离信号传输中的应用对改善组合二阶失真（CSO）起到明显的效果,并与EDFA对比实验验证了其结果。