Ka-band analog front-end for software-defined direct conversion receiver

A six-port Ka-band front-end architecture based on direct conversion for a software-defined radio application is proposed in this paper. The direct conversion is accomplished using six-port technology. In order to demodulate various phase-shift-keying/quadrature-amplitude-modulation (PSK/QAM) modulated signals at a high bit rate, a new analog baseband circuit was specially designed according to the I/Q equations presented in the theoretical part. An experimental prototype has been fabricated and measured. Simulation and measurement results for binary PSK, quaternary PSK (QPSK), 8 PSK, 16 PSK, and 16 QAM modulated signals at a bit rate up to 40 Mb/s are presented to validate the proposed approach. A software-defined radio can be designed using the new front-end and only two analog-to-digital converters (ADCs) because the I/Q output signals are generated by analog means. Previous six-port receivers make use of four ADCs to read the six-port dc levels and require digital computations to generate the I/Q output signals. With the proposed approach, the load of the signal processor will therefore be reduced and the modulation speed can be significantly increased using the same digital signal processor.     

A Complex Image Rejection Circuit With Sign Detection Only

In direct-conversion receivers, radio frequency (RF) signals are down-converted to low or zero intermediate frequency (IF) using complex in-phase and quadrature (I/Q) mixers with no prior image filtering. Due to I/Q path gain and phase errors, image leaks into the signal band during the down-conversion process. A generic image rejection algorithm is proposed to reject image in the baseband using a zero-forcing sign-sign adaptive feedback concept. The orthonormal property of complex I/Q channels is exploited to update their gain and phase errors by detecting only four signs, and image is corrected with four multiplications and two additions. The proposed image rejection algorithm can be implemented in a digital, analog, or hybrid form. A complex baseband sample and hold (S/H) with a digital error detector, which is a hybrid example, achieves an image rejection of 65 dB while sampling at 40 MS/s. The prototype chip fabricated in 0.18-mum CMOS occupies 800times450 mum², and consumes 23 mW at 1.8 V     

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     

中频直接采样和相干检波

在雷达系统中,一般都需将中频输出信号变为正交的基带信号,即I、Q分量,以获取回波中的相位信息。本文提出的方法是先对中频直接采样,在数字域进行信号处理,来获得中频信号的I、Q正交分量,并给出了实验结果。     

Effect of Phase Mismatch on Image Rejection in Weaver Architecture

In a radio frequency receiver, image signals degrade the sensitivity of the receiver for receiving desired signals. This letter analyzes the effect of phase mismatch on image rejection in the Weaver architecture, which has been proposed to reject image signals. Weaver architecture requires the phase difference between the I signal and Q signal of the first and second local oscillators (LOs) to be 90deg. However, the realization of accurate 90deg phase shifters is very difficult. It is found here that an accurate 90deg phase shifter is not essential in Weaver architecture. Instead, by making the phase mismatch between the I and Q signals of the first LO be equal to that of the second LO, image rejection can be performed, being insensitive to the phase mismatch. The reason for this is mathematically analyzed and simulation results are presented     

A 0.7-3 GHz GaAs QPSK/QAM direct modulator

A single chip I/Q direct modulator for use in digital radio links is presented. This device translates directly the phase and quadrature baseband signals to a microwave frequency that can be chosen between 700 MHz and 3 GHz avoiding the use of IF circuits. It is able to generate any type of digital modulation as QPSK, n-PSK, n-QAM, GMSK, etc., with band-limited spectrum. The bandwidth of the I/Q modulating signals is more than 500 MHz allowing the use of the circuit even in the highest capacity systems. The device has 120 components in a 2.2×2.4 mm chip and has been fabricated using 0.5 μm GaAs MESFET process     

Design of Reader Baseband Receiver Structure for Demodulating Backscattered Tag Signal in a Passive RFID Environment

In this paper, we present a demodulation structure suitable for a reader baseband receiver in a passive radio frequency identification (RFID) environment. In a passive RFID configuration, an undesirable DC‐offset phenomenon may appear in the baseband of the reader receiver, which can severely degrade the performance of the extraction of valid information from the received tag signal. To eliminate this DC‐offset phenomenon, the primary feature of the proposed demodulation structures for the received FM0 and Miller subcarrier signals is to reconstruct the signal corrupted by the DC‐offset phenomenon by creating peak signals from the corrupted signal. It is shown that the proposed method can successfully detect valid data, even when the received baseband signal is distorted by the DC‐offset phenomenon.     

Bridging dream and reality: programmable baseband processors for software-defined radio - [integrated circuits for communications]

A programmable radio baseband signal processor is one of the essential enablers of software- defined radio. As wireless standards evolve, the processing power needed for baseband processing increases dramatically and the underlying hardware needs to cope with various standards or even simultaneously maintaining several radio links. Meanwhile, the maximum power consumption allowed by mobile terminals is still strictly limited. These challenges require both system and architecture level innovations. This article introduces a design methodology for radio baseband processors discussing the challenges and solutions of radio baseband signal processing. The LeoCore architecture is presented here as an example of a baseband processor design aimed at reducing power and silicon cost while maintaining sufficient flexibility.     

一种P/L频段高度综合化航空平台的设计

为进一步提升航空平台综合化程度,设计了一种用于航空平台的P/L频段功能高度综合化硬件平台方案。该方案通过射频直接采集2 GHz以下的低频射频信号,在数字域分离出探测、通信、导航、识别以及无源侦察等功能所需基带I/Q信号,最后通过软件完成各种信号的功能处理,实现了对探测、通信、导航、识别以及无源侦察等功能共信道和共信号预处理的高度综合设计。硬件实现验证了该方案能够有效降低硬件系统设计的成本和复杂性,降低系统功耗,有力推进了软件无线电在航空平台综合化中的应用。     

Direct-conversion bandpass sigma-delta modulator

A bandpass sigma-delta modulation analogue-to-digital (A/D) converter that uses direct conversion to baseband with in phase and quadrature paths within the feedback loop is described. The bandpass input signal is processed with continuous-time circuitry and the I/Q baseband signals are processed with switched-capacitor circuits. Experimental and simulation results indicate that the passband centre frequency can be maximised while suppressing the effects of I/Q mismatches     

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。     

Variable-delay, sine/cosine noncoherent detector

The letter describes an all-digital, noncoherent demodulator suitable for the detection of CPFSK and PSK signalling schemes. A single A/D convertor demodulates the input signal and generates baseband in-phase (I) and quadrature (Q) signals. The I and Q signals are then processed with sine and cosine detectors to produce AFC information and the regenerated transmit data.     

Signal Design for the Amplitude-Limited Gaussian Channel by Error Bound Optimization

A necessary and sufficient condition is presented for an input signal alphabet to optimize the random coding exponent for a time-discrete channel with signals restricted in amplitude. It is applied to the white noise Gaussian channel for signals in one and two dimensions. By use of this theorem the best input signal quantizafion is determined by numerical optimization. Results are presented on the number of amplitude or envelope levels needed to maximize the error bound parameter R0at different signal-to-noise ratios. For one-dimensional (baseband) signals a binary antipodal configuration is optimum, in the sense of maximizing R0, for signal-to-noise ratios below 6.9 dB. For two-dimensional (passband) signals with limited envelope, phase modulation is shown to be optimum for signal-to-noise ratios below 7.35 dB.     

System simulations of a 1.5 V SiGe 81–86 GHz E-band transmitter

This paper presents simulation results for a sliding-IF SiGe E-band transmitter circuit for the 81–86 GHz E-band. The circuit was designed in a SiGe process with f _T  = 200 GHz and uses a supply of 1.5 V. The low supply voltage eliminates the need for a dedicated transmitter voltage regulator. The carrier generation is based on a 28 GHz quadrature voltage oscillator (QVCO). Upconversion to 84 GHz is performed by first mixing with the QVCO signals, converting the signal from baseband to 28 GHz, and then mixing it with the 56 GHz QVCO second harmonic, present at the emitter nodes of the QVCO core devices. The second mixer is connected to a three-stage power amplifier utilizing capacitive cross-coupling to increase the gain, providing a saturated output power of +14 dBm with a 1 dB output compression point of +11 dBm. E-band radio links using higher order modulation, e.g. 64 QAM, are sensitive to I/Q phase errors. The presented design is based on a 28 GHz QVCO, the lower frequency reducing the phase error due to mismatch in active and passive devices. The I/Q mismatch can be further reduced by adjusting varactors connected to each QVCO output. The analog performance of the transmitter is based on ADS Momentum models of all inductors and transformers, and layout parasitic extracted views of the active parts. For the simulations with a 16 QAM modulated baseband input signal, however, the Momentum models were replaced with lumped equivalent models to ease simulator convergence. Constellation diagrams and error vector magnitude (EVM) were calculated in MATLAB using data from transient simulations. The EVM dependency on QVCO phase noise, I/Q imbalance and PA compression has been analyzed. For an average output power of 7.5 dBm, the design achieves 7.2% EVM for a 16 QAM signal with 1 GHz bandwidth. The current consumption of the transmitter, including the PA, equals 131 mA from a 1.5 V supply.     

Equalization of tdma links using in-service impulse response measurement

This paper describes a method of measuring the frequency response of a digital radio link given the received (modulated) message signal, suitable for the incremental commissioning and in-service monitoring of links in a QPSK/TDMA system. The method applies least squares estimation techniques to samples of the I and Q baseband components in order to derive a linear equivalent model for the channel. Results obtained by computer simulation of an INTELSAT V channel demonstrate that the method can provide a better basis for linear equalization of a non-linear channel than the frequency response measurements provided by conventional techniques. A mathematical formulation and an implementation overview are also given.     

Adaptive digital/RF predistortion using a nonuniform LUT indexing function with built-in dependence on the amplifier nonlinearity

This paper reports on an integrated adaptive digital/RF predistorter using a nonuniform spaced lookup table (LUT) and in-phase/quadrature (I/Q) RF vector multiplier (VM). The LUT contents are directly deduced from the baseband input and output signals of the power amplifier (PA). In addition, a new nonlinear indexing function of the predistortion LUT with built-in dependence on the PA nonlinearity is proposed. This function is made to be robust to the input signal statistics. A comparison of this new indexation method with conventional approaches, namely, power and logarithmic power indexation functions, is carried out. The superiority of the proposed scheme is demonstrated in particular for class-AB amplifiers where the gain of the PA varies over the whole input range of the drive signal. The measured output spectrum of a linearized 90-W peak lateral double-diffused metal-oxide-semiconductor PA reveals a significant reduction of the power emission at the adjacent channels of approximately 15 dB under IS95, single-carrier, and multicarrier wide-band code-division multiple-access signals. The experimental evaluation is carried out using an RF/digital predistorter prototype that mainly includes an envelope detector, a linear I/Q RF VM, field-programmable gate array and digital signal processor, and fast analog/digital and digital/analog converters.     

一种基于MATLAB+正交上变频的模拟通信信号设计方法

文中提出了一种利用MATLAB 产生模拟通信信号的基带I/ Q 调制数据,通过FPGA+DAC 数字正交上变频来实现中频模拟通信信号产生的设计方法。该方法实现电路简单,不需要专门的模拟器件。通过该方法来实现模拟通信信号的产生,为构建更加复杂的电磁环境,实现雷达电子战和通信电子战领域的交织融合提供了有力保障,具有很强的实用价值。     

A 925–960 MHz I/Q modulator in a 8 GHz 1.2 μm BiCMOS process

An integrated I/Q modulator has been implemented in a commercially available 8 GHz 1.2 m double metal double poly BiCMOS process. The circuit converts baseband signals from 60 kHz to 500 kHz directly to a carrier frequency which can be selected between 925 MHz and 960 MHz. It has an internal 90° phase shifter for the LO signal, the phase shift of which can be adjusted automatically using a control signal generated inside the circuit. The size of the circuit is 2.9 mm×2.9 mm and it consumes about 50 mA. Measurements suggest that the specified LO suppression and image rejection of 35 dBc can be achieved under optimal operating conditions.     

Linearisation of RF PA by even-order nonlinear baseband signal processed in digital domain

This paper represents, for the first time, the linearisation method of RF power amplifiers, which is based on using the second- and fourth-order nonlinear signals shaped by digital signal processing in a baseband domain. The linearisation signals are generated by the second- and fourth-order nonlinear modifications of the baseband signal in the proposed manners. The composite second- and fourth-order linearisation signals modulate carrier second harmonics, and the modulated signals are then driven to the gate and drain of the amplifier transistor. The linearisation effects of the proposed method are evaluated on a single stage power amplifier for the simulated QAM and OFDM digitally modulated signals at diverse input power levels up to the 1 dB compression point. Moreover, the FPGA implementation of a system for the generation and processing of the fundamental signal, and the second-order linearisation signals is presented in the paper, and the proposed technique is verified for the generated QAM signal. In addition, the linearisation of the two-way asymmetrical Doherty amplifier is performed in the experiment by using software defined radio platforms for synthesising the fundamental signal and the second-order linearisation signals.     

用水平天线消除天波干扰的算法研究

天波电台干扰导致探测距离下降是高频地波探海雷达面临的主要问题,虽然用水平天线能够消除天波干扰,但要消除多个干扰需要使用多根水平天线,这在海边有限的场地条件下是不可行的.基于对干扰特性的分析,提出了一种将水平天线的信号两次混频、在时域分段滤波的新算法,可以用较少的水平天线消除多个干扰,理论和仿真证明了算法的有效性,从而为在有限场地条件下,用水平天线消除天波干扰的工程应用提供了实现方案.