I/Q mismatch compensation using adaptive decorrelation in a low-IF receiver in 90-nm CMOS process

We present a single multiplier based adaptive I/Q mismatch compensation circuit for narrowband quadrature receivers. Adaptive decorrelation between I and Q channel data is used for correcting gain and phase mismatches. Adaptation step size is computed from L/sub 1/-norm inverse power measurement and a gear-shifting mechanism is used that allows fast initial convergence and slow adaptation on actual burst data. Image rejection ratio in excess of 50 dB is reported for GSM receiver after compensation allowing the receiver to use IF frequencies higher than half of the channel bandwidth. The presented mismatch compensation circuit is implemented as part of a single-chip GSM wireless transceiver fabricated in a 90-nm digital CMOS process. The presented techniques are, however, equally applicable to other narrowband packet-based applications.     

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.     

Data-aided approach to I/Q mismatch and DC offset compensation in communication receivers

A digital signal processing technique for compensating both the I/Q mismatch and the DC offset in communication receivers is derived with an emphasis on direct-conversion architectures. The I/Q mismatch and DC offset are estimated in a least-squares sense using a training sequence. Also, a group of training sequences that minimizes the mean square error of the estimate is determined. The advantages of the proposed technique are demonstrated through computer simulation.     

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。     

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.     

An adaptive matched filter that compensates for I,Q mismatch errors

An approach to adaptively match filter the I and Q components of complex-valued inputs consisting of a desired signal embedded in correlated external noise is presented. This approach is tolerant of I,Q mismatch errors, i.e., the external noise is effectively rejected and the desired signal enhanced in the presence of significant receiver I,Q errors. I,Q adaptive weighting removes many of the deleterious effects of I,Q quadrature detection imbalance, which can severely limit the adaptive matched filter (AMF) performance. However, for the I,Q AMF, the unknown desired signal's initial phase complicates the design procedure and even for a reasonable design criterion, the AMF performance can fluctuate significantly as a function of this phase. An I,Q AMF technique whose performance is almost phase invariant is developed, and example of its utility is shown     

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     

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.     

Adaptive calibration of I and Q mismatch in quadrature receiver

The mismatch of in-phase and quadrature channels in quadrature receiver affects and constrains radar detection performance in coherent radar.It is necessary to keep the in-phase and quadrature branches symmetrical.In this letter,an adaptive method to detect imbalance parameters is derived by means of evaluating channel errors from the received signal sequences.No matter how the bias degree of the gain and phase errors in I/Q channels are ,the proposed adaptive scheme can obtain good calibration results.And the required calculations are only a few multiplications and additions.No need of a special test signal,the introduced method is simple to implement and easy to operate.     

Estimation and compensation for transmitter and receiver I/Q imbalance of full-duplex terminals

In order to reduce I/Q imbalance of the full-duplex terminal with direct-conversion transceiver,an algorithm based on self-interference signal was proposed for the estimation and compensation of I/Q imbalance in both transmitter (Tx) and receiver (Rx).Without the perfect transmitter or receiver for I/Q imbalance estimation,the self-interference signal from Tx chain to Rx chain was used for parameter estimation and separation,and the Tx and Rx I/Q imbalance parameters were obtained,respectively.Then the pre-compensation before transmission and the correction after receiving was processed,so that there was nearly no I/Q imbalance in this full-duplex terminal from the view of the other terminals,and the complexity of the signal processing will be reduced as a result of the absent of the I/Q imbalance estimation.The simulation results show that the proposed algorithm can effectively estimate and compensate the I/Q imbalance of the full-duplex Tx ＆ Rx terminal,and improve the overall signal quality and the system performance.     

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.

     

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。     

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.     

Phase error resilience to I/Q mismatch of a simplified CPM receiver

A low complexity receiver which was devised in previous papers proved there to be quasioptimum over additive gaussian noise and also showed low power penalty with flat Rayleigh fading, i.e., with random phase, and despite the fact that one of three reduced complexity blocks of that receiver relies on symmetries on signal's phase transitions. This letter analyzes the origin of that error resilience during the derivation of the metrics.     

An I/Q mismatch-free switched-capacitor complex sigma-delta Modulator

This paper presents a technique to suppress the mismatch between the in-phase (I) and quadrature-phase (Q) channels of a switched-capacitor complex sigma-delta modulator that is used for the analog-to-digital conversion of a real intermediate-frequency radio signal. The mismatch is suppressed through time sharing of the critical capacitors, i.e., the input sampling capacitor and the capacitor of the feedback digital-to-analog converter, between the I and Q channels. Circuit simulations verifying the proposed technique are presented.     

基于STBC的MIMO OFDM系统中的I/Q不平衡及CFO的联合均衡策略

基于STBC方案,针对MIMO OFDM通信系统中同时存在发射机和接收机I/Q不平衡、前端滤波器失配、CFO和频率选择性信道失真的组合影响进行了深入研究,并提出了一种适用的联合均衡策略;具体实现是首先通过对MIMO OFDM系统中只存在发射机I/Q不平衡和多径信道干扰的分析,得到一种频域均衡器;然后再考虑同时存在接收机I/Q不平衡和CFO的情况,得到了2个时域均衡器;最后把2个时域均衡器变换到频域,并结合消除发射机I/Q不平衡和多径信道干扰的频域均衡技术,提出了一种全面的联合均衡技术即频域子载波均衡器。仿真结果表明,针对MIMO OFDM系统提出的频域子载波均衡技术不仅能扩展到其他高阶STBC系统,而且使均衡后的系统BER性能得到了明显的提高。     

A 5-6-GHz polyphase filter with tunable I/Q phase balance

A tunable polyphase filter with integrated input and output buffers was designed and fabricated in a 0.4 /spl mu/m SiGe BiCMOS technology with a 5-6-GHz bandwidth. Series tunable capacitors (varactors) provide phase tunability for the differential quadrature outputs of the polyphase filter. The tunable phase can be used to improve image rejection in Weaver or Hartley architectures, or mitigate in-phase and quadrature (I/Q) phase error in direct conversion or low-IF receivers. The die area of the fabricated circuit with pads is 920 /spl mu/m/spl times/ 755 /spl mu/m. Based on measurements, approximately 15/spl deg/ of I/Q phase imbalance can be tuned out using the fabricated polyphase filter, proving the concept of tunable phase. To the authors' knowledge, this is the first reported tunable I/Q balance polyphase network.     

正交调制器的校准设计

在当前许多复杂调制射频信号源中,随着数字基带信号越来越多的加入．需要正交凋制器将其调制到需要的载波信号上。正交调制器原理简单：将生成好的I/Q两路基带信号调制到两路正交的载波上,合路后输出。但是在实现时,想获得好的指标就需要考虑载波相位误差,I/Q基带信号幅度不平衡以及载波泄漏等问题。文章给出了一种正交调制器的校准方案,可以减少和模拟以上三种现象造成的调制误差,并给出自动校准和手动校准两种方法。     

The application of complex quantized feedback in integrated wireless receivers

Integrated wireless receiver architectures, such as direct-conversion receivers, offer many advantages over the conventional heterodyne receivers including smaller size, lower cost, and reduced power consumption. However, the design of monolithic receivers, using direct-conversion, involves many challenges including dealing with low-frequency disturbances, namely, dc-offset and 1/f noise (especially in CMOS implementations), in-phase (I) and quadrature (Q) amplitude and phase mismatch, local oscillator (LO) leakage, and even-order distortions. A cost-effective method to minimize the low-frequency disturbances is to use ac-coupling in the baseband signal path. However, it results in baseline wander effects, especially in spectrally efficient modulation schemes such as quadrature amplitude modulation (QAM) where the baseband signal spectrum contains a significant amount of energy near dc. A system solution to mitigate the effects of low-frequency disturbance is presented in this paper. The quantized feedback (QFB) technique is used in conjunction with ac-coupling to minimize the baseline wander effects. A cross-coupled (CC) QFB extension to compensate for the receiver local oscillator phase error as well as the IQ mismatch is also described. Simulation results are presented to demonstrate the effectiveness of this complex QFB technique.