采用新型峰均比降低技术的OFDM功放线性化方案

针对OFDM信号的高峰均比问题,提出了一种将新型峰均比降低技术与数字预失真技术相结合的功率放大器线性化方案.其中,峰均比降低技术由传统的削峰技术、新型的削谷技术和闲置载波技术组成,信号的峰值和谷值同时被削去,峰均比得到最大程度的压缩.传统削峰技术用于降低信号的峰值;新型的削谷技术采用基于切线原理的矢量孔调整法,同时改变信号的幅度和相位,使得信号谷值变大;闲置载波技术用于减少削峰削谷处理所产生的带内和带外失真.实测结果表明,基于记忆多项式模型的数字预失真技术可以将功放输出信号的ACPR值优化10.5 dB,而在结合了新型峰均比降低技术之后,本方案可以将ACPR值进一步优化18.5 dB.该方案适用于未来4G通信系统.     

基于脉冲成型的降低FBMC系统峰均比方法

针对滤波器组多载波(FBMC:Filter Bank MultiCarrier)系统峰均比(PAPR:Peak to Average Power Ration)较高的问题,基于FBMC系统中原型滤波器及其多项结构,借鉴正交频分复用(OFDM:Orthogonal Frequency Division Multiplexing)降低峰均比方法,提出一种基于脉冲成型(PS:Pulse Shaping)技术的降低FBMC系统峰均比的方法.该方法在综合滤波器S/P(Serial to Parallel)后添加频率加权,实现了时域的循环位移,从而达到降低峰均比的目的.仿真结果表明,在FBMC系统中引入PS技术后,峰均比有明显下降.     

高精度OFDM信道估计算法

为了降低OFDM系统经典最小均方误差(MMSE)信道估计算法的误码率(BER),提出了经带阻滤波的MMSE信道估计算法.该算法首先采用MMSE得到初始的信道估计值,再利用离散傅里叶变换的特性,将噪声和信道频率响应信息分离开来,最后通过带阻滤波器对估计算法进行滤波,进而提高系统的BER性能.仿真结果表明,在增加少量计算复杂度的情况下,在导频间隔保持不变或逐渐增加两种情况下,所提算法的估计性能始终优于经典MMSE信道估计算法.     

多径衰落信道下 OFDM系统定时同步优化

在多径环境下,正交频分复用(OFDM)系统对第1径的寻找是解决定时同步的关键,多数算法将最强径当作第1径,使得定时同步向后延迟,造成严重的ISI.本文在PN训练定时同步的基础上,通过寻找滑动求和值的第1个下降沿来确定第1径的位置.仿真结果证明了本算法的优越性,同时在第1径不为最强径的情况下算法也能得到较好效果.     

适用于快衰落环境的OFDM/TDM信道估计算法

针对正交频分复用/时分复用(OFDM/TDM)系统现有导频结构和信道估计算法缺乏对信道快衰落实时跟踪能力的问题,提出一种改进信道估计算法.该算法利用相邻2个时域复用导频序列对信道特性进行估计得到信道传递函数,通过内插处理获得数据符号的信道状态信息,并利用最小均方误差准则的频域均衡算法补偿信道衰落.仿真结果表明,与现有信道估计算法相比,在相同数据传输效率情况下,提出算法不仅能够适用于慢衰落信道,同时对快衰落信道的实时变化有良好的跟踪能力,改善系统性能.     

一种利用CORDIC算法降低WiMAX系统峰均值功率比方法的研究及实现

基于802．16标准的微波存取全球互通（WiMAX）技术能够提供较高数据速率传输和较高的频谱利用率,并且实现简单,是宽带无线接入系统中最富有竞争力的技术之一。针对WiMAX系统中峰均值功率比（PAPR）过高的问题,从硬件实现的角度出发,利用协调旋转数字计算（CORDIC）算法来求出信号的幅度,采用限幅加滤波的方法来达到降低队PR的目的。实验结果表明这种方法在降低PAPR．值方面具有结构简单,效果良好的特点。     

一种提高TD-LTE系统带宽效率的时域预编码研究

为了消除OFDM系统中的循环前缀(cyclic prefix,CP), 以实现更高的系统带宽效率,设计了一种新的时域预编码.给出了发送调制矩阵的构造方法,并在此基础上引入了记忆特性和符号反馈,设计了TDP预编码模块.通过在TD-LTE下行链路中增加TDP预编码模块,达到了与CP在OFDM系统中同样的性能.仿真结果表明,与具有CP的OFDM系统相比较,新系统的误码性能仅有很小的下降,并且由于不再需要发送CP信号,消除了冗余,带宽效率大大提高.     

相关天线下基于波束成型多用户MIMO-OFDM系统子载波分配研究

针对波束成型多用户MIMO-OFDM系统,以优化系统性能为目标,给出一种在天线具有相关性条件下基于部分信道状态信息的子载波分配算法.该算法采用克罗内克(Kronecker)模型作为相关天线的信道模型,并用信道状态统计信息来描述该模型的传递过程,从而得到相应的子载波分配原则.实验结果表明:系统性能不仅与收发两端的天线数量有关,也与天线相关矩阵中的相关系数以及延时反馈参数有关.     

A novel Haar wavelet-based precoded BPSK-OFDM system with reduced PAPR

The performance of OFDM systems may be degraded when intersymbol interference (ISI) chan- nels have spectral nulls. Recently, the precoded OFDM was proposed to combat this problem. How- ever, due to inserting (M-K) zeros between each two sets of K consecutive information symbols, the average transmitting power of the precoded OFDM system reduces by 10log10 (M/K) dB com- pared with the conventional OFDM system. Under the same points inverse fast Fourier transformation (IFFT), the precoded OFDM system has a higher peak-to-average power ratio (PAPR) compared with the conventional OFDM system. This paper proposes a novel precoded BPSK-OFDM system based on Haar wavelet transformation. The Haar wavelet transformation operating decomposition over the vector information symbols produced by a precoder shows that half of the information symbols are zeros and the rest are either √2 or -√2.Then ,we have the peak power and PAPR reduced by 10log102≈3dB at most compared with the precoded OFDM system. Finally, we compare PAPR of the proposed OFDM system with the precoded OFDM and the conventional OFDM system.     

Subcarrier and power allocation in OFDM-based cognitive radio networks

We formulate the subcarrier and power allocation problem in cognitive radio networks employing orthogonal frequency division multiplexing (OFDM) as a non-linear optimization problem with the objective of maximizing sum capacity under constraints of available subcarriers, interference temper- ature, power budget, etc. A close-to-optimal solution with much reduced complexity is proposed to separate the problem into two steps, which also considers fairness among secondary users. A fair al- gorithm for subcarrier allocation (FA_SA) is firstly presented. Secondly, a fast iterative water-filling algorithm for power allocation (FIWFA_PA) is also proposed to maximize the sum capacity. Exten- sive simulation results show that sum capacity performance of our low-complexity solution is very close to the optimal one, while significantly improving fairness and reducing computation complexity compared with the existing solutions.     

Enhanced EM-based channel estimation for MIMO-OFDM in highly mobile channels

An enhanced expectation-maximization (EM)-based iterative channel estimator for coping with channel time variation is proposed for mobile multiple-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems.In the proposed scheme,the recursive least squares (RLS) algorithm is applied to track the time-varying channel impulse response (CIR) within several symbols.By using the tracked time-varying CIR,the ICI are constructed and then cancelled from the received signal,thus reducing their impactions on the channel estimation.Moreover,based on an ovet-sampled complex exponential basis expansion model (OCE-BEM),an improved channel predictor is derived in order to improve the initial channel estimates accuracy of the iterative estimator.Simulation results show that the proposed scheme outperforms the classic counterpart in time-varying scenarios with a smaller cost of complexity.     

应用于无线传感网频率合成器的0.5V低电压鉴频鉴相器设计

基于0.13μm CMOS技术设计了一个应用于无线传感网频率合成器、电源电压为0.5 V的鉴频鉴相器.它的功能是比较输入信号的频率和相位差,并输出一个与该差值成比例的电压.因电源电压是0.5 V,所以该电路采用低阈值晶体管.为了增大相位误差的检测范围和提高最大工作频率,该电路采用了脉冲锁存的结构.当输入信号频率为2 MHz时,测得的相位误差检测范围为-358°～358°.与传统数字鉴频鉴相器相比,该电路具有较快的捕获速度.当输入信号的频率为2 MHz且相位误差为0°时,电路的功耗为1.8μW,并且最大工作频率为1.25 GHz.     

变频调速器在桥式抓斗吊车中的应用

论文主要介绍了电机的调速方法、变频器的工作原理以及日本FRNIC500G7型变频器在桥式抓斗吊车上的应用,并分析了使用绕线式电机调速与鼠笼式电机变频调速之间的优缺点。     

Optimization Evaluation Test of Strength and Toughness Parameters for Hot-Stamped High Strength Steels

Use of hot-stamped high strength steels (HSHSS) not only reduces the vehicle weight, but also improves the crash safety, therefore more and more mentioned steels are used to produce automobile parts. However, there are several problems especially the low ductility and toughness, which have restricted the application of HSHSS in automobile body. Suitable process parameters are very crucial to improve strength and toughness. In order to study the effect of austenization temperature, soaking time and start deformation temperature on strength and toughness of boron steel 22MnB5, an L9 (3⁴) orthogonal experiment which was analyzed by means of comprehensive evaluation was carried out based on Kahn tear method to obtain the value of fracture toughness. The results indicate that the excellent formability, high strength and toughness of boron steel 22MnB5 with 1.6 mm in thickness are obtained when the austenization temperature is in the range of 920 — 950 °C, the soaking time is 1 min and the start deformation temperature is in the range of 650 — 700 °C. The optimal parameters were used for typical hot stamping structural parts tests. Properties of samples such as tear strength, unit initiation energy and ratio of strength to toughness (RST) were improved by 10.91%, 20.32% and 22.17%, respectively. Toughness was increased substantially on the basis of a small decrease of strength.     

激光频率对激光诱导等离子体特性的影响

激光诱导击穿光谱(LIBS)技术是难熔、难溶物质成分分析的重要方法之一,而实验过程中激光的输出频率、能量、功率密度以及聚焦位置等都明显的影响等离子体的特性,从而影响定量分析的精确度。实验采用土壤标样为分析样品,以Fe、Ti、Sr、Al元素为分析元素,纳秒Nd:YAG激光器为激光光源,通过改变激光输出频率(1~20 Hz),研究了激光输出频率对等离子体的光谱信背比(SNR)、温度、谱线自吸以及信号稳定性的影响。研究结果表明,在其他实验条件不变的情况下,随着激光输出频率的增大等离子体的光谱信背比、等离子体温度都明显升高,自吸现象加重;激光输出频率为1、5、10、20 Hz时Fe I 363.360 nm谱线强度的相对标准偏差(RSD)分别为7.16%、7.89%、14.89%、11.85%,信号的稳定性随激光输出频率的增大呈下降趋势。结果表明重复频率能够影响等离子体的谱线质量,针对不同含量的元素分析,应选择合适的激光输出频率。