2.4G直接下变频接收机射频前端的设计与研究

射频前端模块性能关系到整个接收机的性能,直接下变频接收机有体积小,价格低和高集成度的优点而受到了广泛的重视。本文对直接下变频接收机进行了研究,分析了该接收机特点,提出了一种直接下变频接收机的射频前端实现方案,并用软硬件平台对其实现,实测的2.4G本地振荡信号和接收机解调信号表明达到系统要求指标。     

中频数字正交解调接收机的研究及实现

数字接收机在现代雷达、电子战、通信等领域的应用越来越广泛,数字接收机的性能是由正交解调信号的幅相一致性决定的。这里描述了数字正交解调的核心部分—数字滤波器的设计,通过运用均方误差最小化准则设计法和切比雪夫等波纹逼近设计法设计FIR数字滤波器,并利用MATLAB平台进行仿真,比较分析表明了用均方误差最小化准则设计法设计具有严格线性相位特性的FIR数字滤波器的最优性,即:可以获得较好的幅度误差和相位误差,从而保证了数字接收机的性能。     

一种数字接收机开发平台的设计与实现

针对实际信号接收系统的开发受硬件限制和可扩展性差等问题，基于软件无线电的思想，通过VC与Matlab混合编程，设计并实现了一套虚拟数字接收机系统，主要完成了对接收信号的正交分解、下变频、信号特征提取、信号解调。实际应用表明，其结果对实际数字化接收系统的底层开发和扩展研究具有理论指导作用。     

一种基于DFT的AM信号数字化解调算法

该文提出一种在软件无线电中基于离散傅立叶变换（DFT）算法的幅度调制信号（AM）数字化解调算法,方法是对采样后的数字化AM信号进行带通滤波后,按照每一个（或数个）载波周期内的采样值进行离散傅立叶变换（DFT）,求出载波的幅值,再去掉直流量。与数字化正交解调结构相比,省去了本地载波恢复,两路低通滤波,简单而易于实现。该解调方案的仿真结果表明抗干扰性能也有所明显改善,可望在采用AM信号方式的数字化接收机的设计中得到应用。     

直接序列扩频的分层级联随机共振接收算法

为提高现有直接序列扩频通信的接收信号的解调增益,提出分层级联随机共振接收算法。通过在接收信号的载波下变频和基带信号解扩过程中分别设计级联双稳态随机共振系统,一方面实现了正弦载波信号的宽带化解调接收,另一方面实现了信道噪声的能量向信号能量的逐步转化。理论分析和仿真实验结果表明,所提算法可以通过改变采样频率扩大接收机的频谱适用范围,同时通过增加两层级联随机共振系统的级联数量提高接收机性能。     

基于希尔伯特解调的LFM信号调频斜率的识别

脉冲调制信号调制参数的识别与计算是很多领域的研究重点,文中以希尔波特解调为基础,依据LFM信号相位信息的特点和最小二乘法的拟合,研究了一种全新的线性调频信号的识别算法,并分析了识别算法对载频不敏感的特点,并通过迭代算法以及自身的收敛特性,可快速解调出LFM信号的调制参数;通过各类仿真信号的解调分析,算法的正确性和有效性得到了验证;结合虚拟仪器技术,本算法在某雷达接收机线性调频信号的测试得到了工程应用,进一步验证了算法的有效性。     

带频偏校准的GMSK解调器设计与实现

提出了一种在零中频低功耗蓝牙接收机中使用的GMSK解调器。GMSK是一种恒包络调制方式,针对其解调最重要的判决依据是相位变化,而接收机的本振频率与发射机的载波频率误差会对相位产生干扰。因此提出了一种频偏校准算法来解决频偏对解调性能的影响。该算法由改进的一比特差分解调与CORDIC(COordinate Rotation Digital Computer)算法结合实现,与传统的频偏校准算法相比复杂度大大降低。在150kHz以内的频偏条件下,要达到10~(-3)误码率要求,需要的信噪比与无频偏时相比差距在1 dB以内。该解调器通过Verilog实现,并用FPGA进行验证。     

基于正交解调的超宽带接收机数据采集系统设计

根据超宽带接收机信号处理的需要,设计并实现了一套基于正交解调的超宽带脉冲体制接收机数据采集系统。介绍了系统的硬件部分和软件部分,特别是提出了I／Q正交解调及脉冲体制超宽带信号幅相误差校正方案。实际应用表明,该系统达到了实时高速稳定数据采集的要求。     

OFDM系统中频数字接收机的工程实现

对带通采样理论进行了简单介绍,并对带通欠采样数字正交解调进行了详细的数学推理,并介绍了一种数字中频接收机的工程实现办法。该数字接收机具有较大的动态范围,较高的I,Q输出精度,采用带通欠采样进行中频采样,数字滤波法进行数字正交相干解调。介绍了传统模拟中频接收机的不足和数字中频接收机的优点,根据本课题的技术指标要求进行了中频数字接收机的设计,包括中频放大电路和数字控制VGA、数字中频A/D采样和数字相干解调。结果表明,两路信号幅度的误差〈0.4%,相位的正交误差〈0.4%,满足了设计指标要求,技术指标明显优于传统的模拟接收机。     

中频数字正交解调参数的优化设计

微波遥感数据处理中往往要对接收的回波信号在中频直接进行正交解调,以采样定理为基础,通过对遥感器接收到的回波线性调频信号的数字频谱分析和对数字滤波器的性能分析,得出正交解调运算量与回波信号采样率以及低通滤波器阶数的关系。针对某一带宽的信号,设计出对应于不同采样率的解调滤波器,对其性能和运算量作了分析对比并得出最佳设计。     

New estimation and compensation method for quadrature modulator and demodulator errors in digital predistortion system

This article proposes a new method to estimate and compensate for the in‐phase and quadrature (IQ) imbalance errors of the quadrature modulator (QM) and demodulator (QDM) without interrupting the transmission. It uses two groups of captured signals, which transmit through two feedback loops with different propagation delays, to separate and estimate the IQ imbalance errors. In comparison with the previous methods, the greatest advantage of the proposed method is that both compensators of the QM and QDM can be obtained without additional feedback loop, and then the digital predistorter can be designed without the disturbance of IQ imbalance errors. This method can improve the compensation performance of digital predistortion with lower costs and less complexity. Experimental results show the correctness and effectiveness of the proposed method. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

SAW 无线传感器的高精度信息提取及硬件实现

在无线声表面波传感器系统中,由于模拟正交解调电路调整等方面I、Q两通道间幅度一致性和两路本振信号不完全正交,或双路A／D特性不一致,而使在传感器信息提取时相位检测误差较高,为高精度提取SAW传感器信息,提高传感器的测量精度和灵敏度,本文利用中频采样,使得A／D变换的采样通道数由传统模拟式I、Q检波时的双通道变为中频直接采样的单通道,并在数字域中利用Hilbert法对信号进行正交检波,从而提高了相位检测精度,此外,给出了系统的硬件实现。     

基于FPGA的正交I/Q解调实现

介绍了一种基于Stratix-Ⅲ高端系列FPGA的数字I/Q正交解调实现,并利用SignalTapⅡ工具对FPGA实时处理的数据进行了离线分析。该I/Q解调方式实现简单、实时性好,具有平滑功能,且占用FPGA资源少。该方法为用于软件无线电前端数字I/Q解调提供了一种实现方案。     

I/Q幅度和相位不平衡对脉冲压缩的影响及其矫正方法

就脉冲压缩雷达中接收机I/Q输出相位不平衡对脉冲压缩的影响以及矫正方法进行了研究,并提出了进行矫正的方法。研究表明,I/Q相位不平衡将引起旁瓣电平升高,主瓣宽度增加。当I/Q幅度相对误差在±15%以内,相位相对误差在±3°以内时,对脉冲压缩的影响可以忽略。但如果幅度相对误差达到±25%以上,相位相对误差在±10°时,对脉冲压缩的影响不能忽略,必须进行相位矫正处理。矫正方法的核心思想就是将经过幅度和相位不平衡矫正后的I/Q信号考虑进参考函数中。模拟表明,经过矫正处理后,对脉冲压缩的改善非常显著,从而可以对I/Q解调的硬件设 计降低要求。     

UHF RFID读写器零中频解调方式的研究与实现

在对UHF RFID读写器工作原理进行分析的基础上,介绍一种工作在UHF频段下的读写器的射频接口电路,并确定读写器的解调方式,重点对正交零中频解调方式进行研究,并给出读写器的实现方案.     

A compound structure and a single‐step identification procedure for I/Q and DC offset impairments and nonlinear distortion modeling and compensation in wireless transmitters

The nonlinear behavior of power amplifiers (PAs) and the in‐phase/quadrature (I/Q) imbalance in I/Q modulators are considered as the main sources of distortions and impairments in radio frequency transmitters. In this article, a compound structure and a single‐step identification procedure are proposed for the modulator's I/Q imbalance and DC offset and the PAs nonlinearity modeling and compensation of wireless transmitters. In fact, the performance of the digital predistortion technique used for PA linearization is adversely affected by the I/Q modulator's impairments that result mainly from gain/phase imbalance and DC offset. The measurement results reveal the robustness of the proposed model in modeling and linearization of the PA in the presence of I/Q modulator imperfections and show its superiority as compared to the generalized memory polynomial model and the dual‐input polynomial model. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

一种高性能QAM解调器的设计与实现

提出了一种适用于DVB-C标准的高性能QAM解调器。通过采用改进的解调算法并优化其VLSI实现结构,该设计在现场测试中不仅取得良好的性能并且节约了硬件资源。该解调器支持4/16/32/64/128/256QAM六种调制模式,符号率1～7 MSps范围内连续可调,具有高灵敏度以及可捕获最大达±700 kHz的载波频偏。实现结果表明该文设计的解调器非常适合于低成本的有线电缆系统。     

A simplified adaptive sparse digital pre‐distorter for joint mitigation of frequency‐dependent transmitter impairments

The interplay between the unavoidable various nonlinearities of the direct conversion transmitter, such as local oscillator leakage, power amplifier (PA) nonlinearities, and in‐phase and quadrature (I/Q) branch imbalance, and so forth will degrade the communication system performance seriously. To overcome these nonlinear interactive effects, an accurate adaptive sparse behavioral model is proposed for the joint compensation of the transmitter impairments in this article. First, a three‐input nonlinear joint compensation model, which is composed of the nonlinear frequency‐dependent cross terms between the I and Q branches as well as the magnitudes of the input signal, is developed. Second, to prune the redundant terms and reduce the computational complexity of the full three‐input model, an efficient robust quasi‐newton–based adaptive greedy algorithm is developed. To verify the performance of the proposed method, the different imperfect transmitters based on single‐device GaN Class‐F PA and GaN Doherty PA are used for experimental verification and analysis. Experiment results show that the proposed method can efficiently construct a sparse joint compensation model with improved modeling and distortion mitigation capability than the reported I/Q imbalance model, where nonlinear distortion and I/Q imbalance characteristics in the transmitter can be almost completely removed.     

Standard-independent I/Q imbalance estimation and compensation scheme inOFDM

Direct-conversion transceivers are gaining increasing attention due to their low power consumption. However, they suffer from a serious in- and quadrature-phase (I/Q) imbalance problem. The I/Q imbalance can severely limit the achievable operating signal-to-noise ratio (SNR) at the receiver and, consequently, the supported constellation sizes and data rates. In this paper, we first investigate the effects of I/Q imbalance on orthogonal frequency division multiplexing (OFDM) receivers, and then propose a new I/Q imbalance compensation scheme. In the proposed method, a new statistic, which is robust against channel distortion, is used to estimate the I/Q imbalance parameters, and then the I/Q imbalance is corrected in the frequency domain. Simulations are performed to verify the effectiveness of the proposed method for I/Q imbalance compensation. The results show that the proposed I/Q imbalance compensation method can achieve bit error rate (BER) performance close to that in the ideal case without I/Q imbalance in additive white Gaussian noise (AWGN) or multipath environments. Furthermore, because no pilot information is required, this method can be applied in various standard communication systems.