Direct downconversion of multiband RF signals using bandpass sampling

Abstract-Bandpass sampling can be used by radio receivers to directly digitize the radio frequency (RF) signals. Although the bandpass sampling theory for single-band RF signals is well established, its counterpart for multiband RF signals is relatively immature. In this paper, we propose a novel and efficient method to find the ranges of valid bandpass sampling frequency for direct downconverting multiband RF signals. Simple formulas for the ranges of valid bandpass sampling frequency in terms of the frequency locations of the multiple RF bands are derived. The result can be used to design a multiband receiver for software defined radios.     

基于软件无线电的导航信号直接带通采样方案研究

航电系统中,软件无线电被认为是实现射频综合的最佳途径。研究了导航信号的射频直接采样方法,对双频段的直接带通采样进行了分析,给出了双频段有效采样频率的计算方法。针对我国北斗卫星1．2GHz和1．5GHz2个频点附近的导航信号,按照文中给出的直接带通采样频率的计算方法确定了有效的采样频率,并进行了相应的Matlab仿真实验...     

导航信号的射频直接采样与数字下变频方法

研究导航信号的射频直接采样与数字下变频方法,并对1.2GHz和1.5GHz2个频点附近的导航信号进行了仿真验证。首先运用带通采样原理,选择合适的采样频率完成对导航信号的射频直接采样,然后结合积分梳状滤波器、半带滤波器,对采样后的信号进行抽取滤波,实现了降采样率的目的。最后,通过Matlab对5个频点的导航信号进行了仿真验证,完成了导航信号的射频直接采样并降低了采样率,恢复且分离了原始导航信号,从而验证了射频直接采样与数字下变频方法是可行的。     

多带通信号直接均匀欠采样技术

该文讨论了宽带数字接收机中对多个复或实的带通信号的直接均匀采样。对这多个通带位置及带宽均是任意的实或复的带通信号给出了采样率应满足的关系,用此采样率采样使输入数据得到有效的压缩,同时结合滤波器将频谱进行搬移,最后给出了实例。     

Direct bandpass sampling of multiple distinct RF signals

A goal in the software radio design philosophy is to place the analog-to-digital converter as near the antenna as possible. This objective has been demonstrated for the case of a single input signal. Bandpass sampling has been applied to downconvert, or intentionally alias, the information bandwidth of a radio frequency (RF) signal to a desired intermediate frequency. The design of the software radio becomes more interesting when two or more distinct signals are received. The traditional approach for multiple signals would be to bandpass sample a continuous span of spectrum containing all the desired signals. The disadvantage with this approach is that the sampling rate and associated discrete processing rate are based on the span of spectrum as opposed to the information bandwidths of the signals of interest. Proposed here is a technique to determine the absolute minimum sampling frequency for direct digitization of multiple, nonadjacent, frequency bands. The entire process is based on the calculation of a single parameter-the sampling frequency. The result is a simple, yet elegant, front-end design for the reception and bandpass sampling of multiple RF signals. Experimental results using RF transmissions from the US Global Positioning System-Standard Position Service (GPS-SPS) and the Russian Global Navigation Satellite System (GLONASS) are used to illustrate and verify the theory     

强干扰情况下用于CDMA系统的时空域联合处理

本文提出了一个时空域联合处理技术来对抗码分多址通信系统中的多址干扰.它由智能天线和多用户联合检测结合而成,智能天线可以压制与有用信号来向不同的干扰,余下的与用户信号来向相同的干扰可以被多用户联合检测系统消除.这种结构在干扰严重的信道仍能得到令人满意的效果.     

Design and practical implementation of multifrequency RF front ends using direct RF sampling

The use of direct RF sampling has been explored as a means of designing multifrequency RF front ends. Such front ends will be useful to multifrequency RF applications such as global navigation satellite system receivers that use global positioning system (GPS) L1, L2, and L5 signals and Galileo signals. The design of a practical multifrequency direct RF sampling front end is dependent on having an analog-to-digital converter whose input bandwidth accommodates the highest carrier frequency and whose maximum sampling frequency is more than twice the cumulative bandwidth about the multiple carrier signals. The principle of direct RF sampling is used to alias all frequency bands of interest onto portions of the Nyquist bandwidth that do not overlap. This paper presents a new algorithm that finds the minimum sampling frequency that avoids overlap. This design approach requires a multifrequency bandpass filter for the frequency bands of interest. A prototype front end has been designed, built, and tested. It receives a GPS coarse/acquisition code at the L1 frequency and GPS antispoofing precision code at both L1 and L2. Dual-frequency signals with received carrier-to-noise ratios in excess of 52 dB-Hz have been acquired and tracked using this system.     

A Novel Receiver Architecture for DBF Antenna Array

The developments of the high speed analog to digital converters （ADC） and advanced digital signal processors （DSP） make the smart antenna with digital beamforming （DBF） a reality. In conventional M-elements array antenna system, each element has its own receiving channel and ADCs. In this paper, a novel smart antenna receiver with digital beamforming is proposed. The essential idea is to realize the digital beamforming receiver based on bandpass sampling of multiple distinct intermediate frequency （IF） signals. The proposed system reduces receiver hardware from M IF channels and 2M ADCs to one IF channel and one ADC using a heterodyne radio frequency （RF） circuitry and a multiple bandpass sampling digital receiver. In this scheme, the sampling rate of the ADC is much higher than the summation of the M times of the signal bandwidth. The local oscillator produces different local frequency for each RF channel The receiver architecture is presented in detail, and the simulation of bandpass sampling of multiple signals and digital down conversion to baseband is given. The principle analysis and simulation results indicate the effectiveness of the new proposed receiver.     

二阶非均匀带通采样信号的快速恢复

本文讨论了实带通信号在二阶非均匀采样下的快速频域搬移、恢复,即用FFT方法将实带通信号恢复到两倍带宽(2B)内的复解析信号,而幅度和相位保持不变,最后经过简单的运算,得到原始频率。计算机模拟证实了上述方法。     

软件无线电中的带通采样分析

近年来,软件无线电技术以其强大的通用性和灵活性得到了广泛发展和应用。研究了软件无线电中广泛采用的带通采样技术。在给出带通采样定理一般结论的基础上,重点分析了实现无混叠带通采样的条件,得到了边界频率点上4种不同取值情况下带通采样频率的取值范围,并利用时域内插进行了带通采样信号的完全重建。最后,采用Matlab进行了仿真验证。     

DVB-T接收前端下变频电路设计

介绍了DVB-T接收系统前端下变频的基本原理,设计了DVB-TRF信号到基带信号的下变频电路。电路基本原理为,调谐器将RF信号混频到中频,A/D转换器带通采样,将中频信号搬移到基带部分,得到数字基带信号。电路的控制部分由MCU和D/A转换器组成。本电路实现了对DVB-TRF信号的转换,得到了DVB-T数字基带信号。     

一种特殊的带通信号采样率选取的研究

针对一种特殊的带通信号,即线性调制信号且载波频率与信号带宽之比为整数,研究了采样率的选取问题。此类信号的采样率可超越Nyquist采样定理的限制,文中以二进制幅度键控信号为例进行仿真,验证了结论的正确性。     

Determination of the minimum sampling frequency in bandpass sampling by geometric approach and geometric programming

This paper presents a simple and fast approach to find a minimum sampling frequency for multi-band signals. Instead of neighbor and boundary conditions, constraints on the sampling frequency were derived by using the geometric approach to the bandpass sampling theorem. Reformulation of the constraints on the minimum sampling frequency enabled to represent the problem as an optimization problem which was structured by the geometric programming and mixed-integer nonlinear programming methods. The convex optimization problem was then solved by the proposed algorithm applying interior point approach in the line search framework. It was demonstrated that this unified structure directly linked the geometric approach of the bandpass sampling theorem to the optimization problem. The proposed method was verified through numerical simulations in terms of the minimum sampling frequency and the computational efficiency. Results illustrated the feasibility of the geometric approach and the proposed algorithm in the determination of the minimum sampling frequency by providing the savings in the number of iterations and the decrease in the valid minimum sampling frequency.     

A novel method for down-conversion of multiple bandpass signals

Simultaneous down-conversion of multiple band-pass signals is desirable for a number of wireless applications. Bandpass sampling technique can be used for this purpose, but it is difficult to implement and has several drawbacks. In this paper we propose a novel front-end technique to directly down-convert multiple frequency- division multiplexed (FDM) signals separated by certain minimum frequency. A special downconversion function is derived to achieve simultaneous downconversion of the received signals. The technique requires simpler bandpass filters and the ADC has a baseband input as compared to bandpass sampling, which imposes strict requirements on bandpass filters and requires an ADC which can handle RF inputs. The performance of the method has been evaluated by simulating a BPSK receiver employing this technique.     

基带采样率内任意带通信号的正交采样

提出了一种在基带采样率内对任意带通信号的正交采样技术。载频位于ADC(模/数转换器)基带采样率内的任意带通信号,经1/2抽取和(-1)n调制,再由全通线性多相滤波器内插后,得到其复包络的调制输出XI(n)和XQ(n)。     

A NEW QUADRATURE SAMPLING APPROACH FOR ARBITRARY BANDPASS SIGNAL WITHIN BASEBAND SAMPLING RATE

A new quadrature sampling technique for arbitrary bandpass signal within baseband sampling rate is presented. The input bandpass signal whose carrier frequency lies in the A/D baseband sampling rate is first decimated by factor 2 and modulated by (- 1)n, and then is interpolated by a linear phase FIR all-pass filter, finally the modulated complex envelope of bandpass signal can be produced.     

Linear Amplification with Nonlinear Components

A technique for producing bandpass linear amplification with nonlinear components (LINC) is described. The bandpass signal first is separated into two constant envelope component signals. All of the amplitude and phase information of the original bandpass signal is contained in phase modulation on the component signals. These constant envelope signals can be amplified or translated in frequency by amplifiers or mixers which have nonlinear input-output amplitude transfer characteristics. Passive linear combining of the amplified and/or translated component signals produces an amplified and/or translated replica of the original signal.     

SSB-FDM using complementary comb filters

The letter describes single-sideband frequency division multiplex (SSB-FDM) systems using complementary comb filters. A lot of analogue bandpass filters in conventional modulators and demodulators can be replaced by comb filters. In the case of a 12-channel FDM system, SSB modulators can be implemented by 12 product modulators and a pair of complementary comb filters.     

A Novel Circuit Architecture for High Performance of High-order Subharmonic Mixers

A novel circuit architecture for high performance of high-order subharmonic (SH) mixers is proposed in this paper. According to the specified harmonic mixing order, one or more mixer diodes sub-arrays and corresponding power divider as well as phase shift network for RF and LO signals are arranged in the circuit. This proposed SH mixer circuit has improved conversion loss, wide dynamic range and high port isolation for high-order SH mixers. By phase cancellation of idle frequencies, the proposed SH mixer circuit can eliminate complicated design procedure of idle frequency circuits; by phase cancellation of leakage LO power to RF and IF port, and leakage RF power to LO port, the mixer circuit can get high port isolation in LO-IF/RF and RF-LO. The increased antiparallel diode pairs in each sub-array will also lead to well performance by lowering effective series resistance. The proposed SH mixer circuit can be easily realized with power divider and phase shift network for RF and LO signals.     

Time-varying Volterra-series analysis of spectral regrowth andnoise power ratio in FET mixers

This paper presents a direct and robust analysis technique for evaluating nonlinear distortion phenomena in FET mixers excited by multitone signals. Time-varying Volterra-series analysis has previously been proven to be appropriate for small-signal intermodulation-distortion calculations in mixers excited by simple RF signals. Spectral convolutions of the suitably mapped control voltages are introduced in this paper in order to solve the nonlinear current source calculations for narrow-band modulated or broad-band multicarrier RF signals. Simulations and measurements of a properly characterized resistive mixer validate the accuracy of this direct and noniterative analysis tool for spectral regrowth and noise-power-ratio prediction in such applications