低中频接收机I/Q不平衡的数字估计和补偿

相对于传统的超外差式接收机,低中频接收机由于不需要镜像抑制滤波器、中频滤波器等片外大体积昂贵器件,因而系统设计可以更加灵活,体积更小,成本更低,集成度更高。低中频接收机采用I/Q下变频进行镜像分离,但模拟前端I/Q不平衡导致的镜像抑制不足问题却是其一大缺点。本文提出了一种利用测试信号数字估计和补偿I/Q不平衡的方法来提高镜像抑制能力。仿真结果表明,在幅度不平衡不大于10%和相位不平衡不大于10°时,经补偿后的镜像抑制比能够达到50d B以上。     

正交通道中I/Q不平衡估计与补偿研究

I/Q通道普遍存在于信号处理的正交调制和解调过程中。严格的正交过程要求I/Q两个通道的增益和时延完全一致且I/Q两路中都不存在直流分量,同时还要求I路和Q路的本振信号的相位精确的相差90°。然而,在实际的信号处理过程中,难免会存在误差和不匹配的情况。基于I/Q通道不平衡的基础,研究各种不平衡因子对I/Q通道性能的影响。利用提出的补偿算法,在对存在不同幅度和相位不平衡的情况进行仿真,仿真结果表明在不同的不平衡条件下,该算法都能够有效地补偿不平衡,改善了系统性能。     

宽带信号I/Q采样不平衡校正方法研究

针对宽带信号模拟正交下变频时产生的I/Q信号不平衡问题,本文提出了一种在数字域对I/Q信号不平衡的校正方法,建立了 I/Q信号不平衡的数字模型,分析了 I/Q信号不平衡给系统带来的影响,推导了 I/Q信号不平衡的校正方法,并对校正结果进行了仿真验证,该方法已在某设备中成功应用.     

新一代数字卫星接收机中I／Q不平衡的数字补偿

为了克服零中频结构的卫星接收机产生的I／Q不平衡的影响,本文提出了基于I路信号和Q路信号互相关的数字补偿方法。通过仿真结构可知,该方法能够补偿较大的I／Q增益不平衡和I／Q相位不平衡。     

基于信道化架构的宽带I/Q不平衡校准技术

零中频接收机凭借其架构简单、易于集成等特点已被广泛应用于通信系统和雷达系统,为未来雷达通信一体化技术发展奠定了基础。然而,零中频接收机存在I/Q不平衡问题,这不仅会造成通信星座图的偏移,还会引入雷达虚假目标。现有宽带I/Q补偿方法的精度不高,且都集中于后处理,无法做到实时。因此,本文首先建立了宽带I/Q不平衡模型,并提出了一种融合信道化架构和盲估计补偿算法的宽带I/Q失衡校准技术。该技术利用信道化架构将宽带信号划分为窄带信号,并利用盲估计算法对带有镜像信号的子信道进行在线补偿。实验表明,该方法在获得高精度补偿参数的同时,完成了对宽带I/Q失衡的实时补偿。镜像抑制比达到55 dB。     

OFDM联合信道均衡与I/Q失衡补偿算法

分析多径衰落信道下零中频接收机的I/Q失衡对OFDM系统造成的影响,并在此基础上构造一个结合了信道频率响应与I/Q失衡因子的复合信道模型.通过设计OFDM双导频符号进行复合信道均衡,从而能同时补偿多径衰落信道和I/Q失衡对OFDM系统造成的影响.仿真结果表明:这种联合算法大大提高了OFDM系统的性能,而且具有较低的实现复杂度.     

存在I/Q不平衡的OFDM全双工双向译码转发中继系统及其性能分析

全双工技术可以使频谱利用率翻倍,是5 G系统的关键技术之一。采用直接变换结构的全双工系统中残余自干扰(Residual Self-Interference, RSI)和同相/正交(In-phase/Quadrature, I/Q)不平衡是限制系统性能的两大主要因素。该文针对存在I/Q不平衡的OFDM全双工双向中继系统,建立了译码转发中继模式下的全双工系统信号模型,分析了瑞利衰落信道下系统的中断性能,获得了系统中断概率的闭式表达式。仿真结果不仅验证了理论分析的正确性,还得到结论：随着I/Q不平衡程度和残余自干扰强度的降低,系统中断性能将得到改善;只有沿着最速下降路线降低I/Q不平衡或中继节点RSI,才能实现最优的性能提升;通过系统I/Q不平衡与RSI参数所在的坐标点和最速下降路线的相对位置关系,来确定改善全双工双向中继系统中断性能的最优措施。     

I/Q不平衡对卫星高速数据中继系统的影响

卫星高速数传中继系统中采用QPSK调制传输高达300 Mbit/s的数据,在调制过程 中由于调制系统的不理想造成I/Q支路增益不平衡和相位不平衡,由此对传输系统的误比特 率带来影响。着重分析了卫星高速数据中继传输业务中,I/Q支路增益不平衡和相位不平衡 对误比特率带来的影响,随后对失真情况进行计算机仿真,得出可信的结果,即在高速数传业 务中,增益不平衡在±0．5 dB之内和相位不平衡在土5°之内所带来的对误比特率的影响非 常小。     

基于LS的OFDM零中频接收机IQ不平衡数字补偿技术

零中频接收机已成为未来无线终端发展潮流,但是零中频的结构会引入较大的射频损伤;本文首先介绍了射频I/Q不平衡时对高斯以及频率选择性信道下OFDM接收机性能的影响;通过特殊导频设计,解耦合I、Q路的相互影响;如此可以方便地估计和补偿射频I/Q不平衡对高斯以及频率选择性信道的影响。仿真表明本文所示方法大大提高了OFDM零中频接收机的性能。     

不理想的信道互易性对波束成形技术的影响…

在无线通信系统中,基站可以根据信道互易性使用波束成形(Beam Forming)技术提升系统性能。信道互易性的准确程度对性能是有影响的,因此需要对其分析以指导系统设计。对长期演进(LTE)系统的互易性进行建模,指出了终端发送天线和接收天线数目的不对称性,以及基站信道估计的误差对信道互易性的影响。通过数值仿真验证了不理想的信道互易性使波束成形性能受到损失,并为系统改进提出思路。其结论容易推广到其他应用波束成形的无线通信系统。     

GLCP OFDM systems with I/Q imbalance

In this work, a grouped linear constellation precoded orthogonal frequency-division multiplexing (GLCP OFDM) system, with the transceiver in-phase/quadrature (I/Q) imbalance operating over frequency-selective fading channels are studied. A new subcarrier grouping scheme in such a system is proposed. Through analysis and simulations, we demonstrate that with the proposed scheme, low-complexity solutions can be developed to mitigate I/Q imbalance, and provide a performance comparable to (or better than) the optimal subcarrier grouping scheme with no I/Q imbalance.     

Joint estimation of the channel and I/Q imbalance for two-way relay networks

In modern day communication systems, the massive MIMO architecture plays a pivotal role in enhancing the spatial multiplexing gain, but vice versa the system energy efficiency is compromised. Consequently, resource allocation in-terms of antenna selection becomes inevitable to increase energy efficiency without having any obvious effect or compromising the system spectral efficiency. Optimal antenna selection can be performed using exhaustive search. However, for a massive MIMO architecture, exhaustive search is not a feasible option due to the exponential growth in computational complexity with an increase in the number of antennas. We have proposed a computationally efficient and optimum algorithm based on the probability distribution learning for transmit antenna selection. An estimation of the distribution algorithm is a learning algorithm which learns from the probability distribution of best possible solutions. The proposed solution is computationally efficient and can obtain an optimum solution for the real time antenna selection problem. Since precoding and beamforming are also considered essential techniques to combat path loss incurred due to high frequency communications, so after antenna selection, successive interference cancellation algorithm is adopted for precoding with selected antennas. Simulation results verify that the proposed joint antenna selection and precoding solution is computationally efficient and near optimal in terms of spectral efficiency with respect to exhaustive search scheme. Furthermore, the energy efficiency of the system is also optimized by the proposed algorithm, resulting in performance enhancement of massive MIMO systems.

     

Advanced methods for I/Q imbalance compensation in communicationreceivers

I/Q signal processing is widely utilized in today's communication receivers. However, all I/Q processing receiver structures, such as the low-IF receiver, face a common problem of matching the amplitudes and phases of the I and Q branches. In practice, imbalances are unavoidable in the analog front-end, which results in finite and usually insufficient rejection of the image frequency band. This causes the image signal to appear as interference on top of the desired signal. We carry out general signal analysis of an imbalanced I/Q processing receiver and propose novel methods for I/Q imbalance compensation using baseband digital signal processing. A simple structure for compensation is derived, based on a traditional adaptive interference canceller. Improved image rejection can also be obtained by using more advanced blind source separation techniques. Theoretical analysis of the performance of the proposed imbalance compensation structures is presented. In addition, some simulation results are provided in order to further evaluate the performance of the proposed methods. The results indicate that the I/Q imbalance can be effectively compensated during the normal operation of the receiver even in the rapidly changing case, as long as a linear system model for the imbalance is valid     

RF power and I/Q imbalance calibration in B3G/4G MIMO-OFDM systems

Radio frequency (RF) front-end nonidealities in multi-input and multi-output (MIMO) systems are more serious than in single-input and single-output systems and must be calibrated. According to the effects of RF power and in-phase/quadrature-phase (I/Q) imbalance, calibration methods for multi-input and multi-output-orthogonal frequency division multiplexing (MIMC-OFDM) systems in transmitter and interference in receiver are improved, respectively, in this article. Furthermore, a calibration scheme including I/Q imbalance errors and amplitude variations is proposed and implemented in the B3G/4G time division duplex communication system. Simulation results show that the calibration algorithms are feasible, and the bit error rate (BER) performances for MIMO-OFDM systems are improved after calibrations.     

Joint estimation of carrier frequency offset, dc offset and I/Q imbalance for OFDM systems

Orthogonal frequency division multiplexing (OFDM) systems with direct-conversion receiver (DCR) are vulnerable to carrier frequency offset (CFO), dc offset (DCO) and in-phase/quadrature (I/Q) imbalance. In this paper, we propose blind estimator for joint estimation of CFO, DCO and I/Q imbalance in OFDM systems with DCR. Simulation results show that performance of proposed estimator approaches Cramér-Rao lower bound (CRLB) asymptotically, which demonstrates its effectiveness.     

Low-complexity pilot-aided compensation for carrier frequency offset and I/Q imbalance

We propose a novel pilot-aided compensation scheme for carrier frequency offset (CFO) and I/Q imbalance. The proposed scheme comprises a generalized periodic pilot and a low-complexity acquisition algorithm, where the CFO and the coefficients for I/Q imbalance compensation can be obtained in explicit closed-form.     

OFDM零中频接收机I/Q不平衡的数字估计与补偿

由于零中频接收机的优点,其已经成为未来无线终端发展的方向.但它也有固有缺陷,即引入较大的射频损伤.首先分析了I/Q不平衡的系统模型,接着推导出其在OFDM系统中对接收机的影响.提出了一种硬件容易实现的简便时域估计和补偿I/Q不平衡的算法.最后通过仿真给出了该算法的性能,仿真表明在AWGN和频率选择性衰落信道下能够明显提高接收机的误码率性能.     

Parallel Correction and Adaptation Engines for I/Q Mismatch Compensation

We present a low-area implementation of an I/Q mismatch compensation (IQMC) circuit that comprises a correction engine and an adaptation engine. The correction engine performs I/Q mismatch compensation in the data path using a filter whose coefficients are updated after a programmable amount of time by a parallel adaptation engine that performs sample-by-sample off-line adaptation. This scheme allows very fast online adaptation while protecting the receiver data path from the degradations caused by a fast converging algorithm. The proposed scheme has been successfully implemented in 90-nm digital CMOS process for a low-IF quad-band GSM transceiver SoC. A single multiplier is used to perform complex multiplications for both correction and adaptation engines, resulting in a 0.025 ${hbox {mm}}^{2}$ circuit. Image Rejection Ratio in excess of 50 dB is measured that is sufficient for IF frequencies as high as 200 kHz for GSM application.      

Circularity-Based I/Q Imbalance Compensation in Wideband Direct-Conversion Receivers

Communication receivers that utilize I/Q downconversion are troubled by amplitude and phase mismatches between the analog I and Q branches. These mismatches are unavoidable in practice and reduce the obtainable image frequency attenuation to the 20-40-dB range in practical receivers. In wideband multichannel receivers, where the overall bandwidths are in the range of several megahertz and the incoming carriers located at each other's mirror frequencies have a high dynamic range, the image attenuation of the analog front-end (FE) alone is clearly insufficient. In this paper, two novel blind low-complexity I/Q imbalance compensation techniques are proposed and analyzed to digitally enhance the analog FE image attenuation in wideband direct-conversion receivers. The proposed algorithms are grounded on the concept of circular or proper complex random signals, and they are, by design, able to handle the often overlooked yet increasingly important case of frequency-dependent I/Q mismatches. The first technique is an iterative one, stemming from adaptive filtering principles, whereas the second one is a moment-estimation-based block method. The performance of the algorithms is evaluated through computer simulations, as well as real-world laboratory signal measurement examples in practical multicarrier receiver cases. Based on the obtained results, the proposed compensation techniques can provide very good compensation performance with low computational resources and are robust in the face of different imbalance levels and dynamics of the received signals, as well as many other crucial practical aspects such as the effects of the communications channel and carrier synchronization.