A low-power all-digital FSK receiver for space applications

A frequency-shift keying (FSK) receiver has been designed for deep space applications which exhibits potential for ultra low power performance. The receiver is based on a novel, almost all-digital architecture. It supports a wide range of data rates and is very robust against large and fast frequency offsets due to Doppler. The architecture utilizes subsampling and 1-bit data processing together with a discrete Fourier transform-based detection scheme to enable power consumption dramatically lower than implementations reported in the literature. Novel and power-efficient algorithms are derived for frequency and timing tracking. Most of the power saving techniques are applicable to a variety of applications, but some are achieved by taking advantage of the asymmetric power constraints for the receiver and the transmitter as well as the absence of adjacent channel interferers. The worst-case bit-error rate (BER) performance of the receiver is just 2.5 dB below that of the optimal uncoded noncoherent FSK receiver at a BER of 10^-6 and better for lower BERs     

A Subsampling Quadrature Σ∆ Modulator Based on Distributed Resonators for Use in Radio Receiver

The receiver architecture proposed in this brief seizes the subsampling properties of continuous-time sigma-delta (SigmaDelta) modulators based on distributed resonators to construct a quadrature receiver. The proposed architecture is based on a low-pass SigmaDelta modulator that subsamples an intermediate frequency signal around the sampling frequency and does not require quadrature mixers. Instead, the quadrature mixing is replaced by suitably choosing the sampling instants inside the loop. Two practical circuit implementations are proposed. The first one uses separate circuitry for the I and Q paths. The second architecture introduces an innovative way to produce the I and Q outputs that is immune to path mismatch due to the sharing of all the analog circuitry for both paths. The proposed modulator may be feasible for the typical IF frequencies used in cellular base stations.     

Design and Performance of a Digital Multifrequency Receiver

An experimental multifrequency receiver for recognition of digitally encoded multifrequency signaling was designed, constructed and tested. The receiver is based on a quadrature detection technique that consists of digital demodulation followed by second-order, lowpass digital filtering. The post filtering processing produces an estimate of the amplitude of each of the six multifrequency tones and provides suitable information for thresholding and timing measurements. The receiver performs correctly even when subjected to severe environmental conditions including an analog signal range of 23 dB, 10 ms signal interruptions ('hits') and 20 ms signal spacings. The receiver's operation demonstrates the robustness of the digital signal processing techniques employed. The design of the receiver exploits the use of subsampling techniques to increase the efficiency of the hardware through greater multiplexing. When using subsampling, 128 multifrequency receivers with 16-bit words are realized with 6.5 dual-in-line packages per receiver; commercial TTL logic circuits, a 4-bit serial-parallel pipeline multiplier circuit, serial data and a 16.384 MHz clock are assumed.     

A low-power multirate differential PSK receiver for space applications

Wireless communication for deep-space and satellite applications needs to accommodate the Doppler shift caused by the movement of the space vehicle and should consume low power to conserve the onboard power. A low-power phase-shift keying (PSK) receiver has been designed for such applications. The receiver employs double differential detection to be robust against Doppler shift and uses subsampling with a 1-bit A/D converter and digital decimation architecture at the front end to achieve low-power consumption. The receiver is also designed to be programmable to operate using single-stage differential detection instead of double-stage differential detection at low Doppler rates to obtain optimum performance. Furthermore, the baseband can be employed in either direct subsampling or intermediate frequency (IF)-sampling front ends. Both front ends offer minimal power consumption and differ from traditional types by replacing some conventional analog components such as a voltage-controlled oscillator, mixer, or phase-locked loop with their digital counterparts. This eliminates problems due to dc offset, dc voltage drifts, and low-frequency (LF) noise. The paper also includes a brief discussion of the nonidealities existing in real applications. The proposed phase shift keying (PSK) receiver supports a wide range of data rates from 0.1-100 Kbps and has been implemented in a CMOS process.     

RF Band‐Pass Sampling Frontend for Multiband Access CR/SDR Receiver

Radio frequency (RF) subsampling can be used by radio receivers to directly down‐convert and digitize RF signals. A goal of a cognitive radio/software defined ratio (CR/SDR) receiver design is to place the analog‐to‐digital converter (ADC) as near the antenna as possible. Based on this, a band‐pass sampling (BPS) frontend for CR/SDR is proposed and verified. We present a receiver architecture based second‐order BPS and signal processing techniques for a digital RF frontend. This paper is focused on the benefits of the second‐order BPS architecture in spectrum sensing over a wide frequency band range and in multiband receiving without modification of the RF hardware. Methods to manipulate the spectra are described, and reconstruction filter designs are provided. On the basis of this concept, second‐order BPS frontends for CR/SDR systems are designed and verified using a hardware platform.     

The impact of subsampling on MODIS level-3 statistics of cloud optical thickness and effective radius

The Moderate Resolution Imaging Spectroradiometer (MODIS) Level-3 optical thickness and effective radius cloud product is a gridded 1/spl deg//spl times/1/spl deg/ dataset that is derived from aggregation and subsampling of every fifth pixel, along both spatial directions, of Level-2 orbital swath data (Level-2 granules). The present study examines the impact of this subsampling on the mean, standard deviation, and inhomogeneity parameter statistics of optical thickness and effective radius. The methodology is simple and consists of estimating mean errors for a large collection of Terra and Aqua Level-2 granules by taking the difference of the statistics at the original and subsampled resolutions. It is shown that the Level-3 subsampling does not affect the various quantities investigated to the same degree, with second-order moments suffering greater subsampling errors, as expected. Mean errors drop dramatically when averages over a sufficient number of regions (e.g., monthly and/or zonal averages) are taken, pointing to a dominance of errors that are of random nature. When histograms built from subsampled data with the same binning rules as in the Level-3 dataset are used to reconstruct the quantities of interest, the mean errors do not deteriorate significantly. The results in this paper provide guidance to users of MODIS Level-3 optical thickness and effective radius cloud products on the range of errors due to subsampling they should expect and perhaps account for, in scientific work with this dataset. In general, subsampling errors should not be a serious concern when moderate temporal (e.g., monthly) and/or spatial (e.g., zonal) averaging is performed.     

An 81-MHz IF receiver in CMOS

An 81-MHz CMOS IF receiver for digital wireless applications is presented. The receiver consists of a continuous-time IF amplifier, a subsampling switched-capacitor gain stage, and a sixth-order bandpass ΣΔ A/D converter. Incorporating 24 dB of programmable gain, the receiver achieves 92 dB of dynamic range in a 200 kHz bandwidth. Due to its IF sampling nature, the reciever is immune to de offset, flicker noise, and errors due to mismatches between I and Q signal paths. By utilizing a pseudo two-path resonator architecture in the bandpass ΣΔ A/D converter, a stable passband center frequency which is immune to capacitor mismatch is achieved. Implemented in 0.8-μm CMOS, this chip uses a single 3 V supply and consumes 14.4 mW of power     

A 900-MHz RF front-end with integrated discrete-time filtering

Discrete-time analog filters, rather than off-chip components, have been used to perform frequency selection and down conversion in the integrated front-end for a 900-MHz RF receiver. The first stage of frequency down conversion is implemented with a subsampling switched-capacitor sample-and-hold circuit clocked at 78 MHz. Subsequent stages of discrete-time filtering are realized using switched-capacitor biquadratic filters. An experimental prototype of the front-end had been integrated in a 0.6-μm BiCMOS technology. The circuit provides a system gain of 36 dB and 32 dB suppression of interfering channels over a 40 MHz bandwidth. Referred to the system input, the third-order intercept-point is -16 dBm, and the spot input-referred noise is -82 dBm over a 30 kHz bandwidth. The experimental circuit dissipates 90 mW from a 3.3-V supply and occupies an active area of 1.9×1.9 mm²      

Spatially adaptive subsampling of image sequences

In a spatially adaptive subsampling scheme, the subsampling lattice is adapted to the local spatial frequency content of an image sequence. In this paper, we use rate-distortion theory to show that spatially adaptive subsampling gives a better performance than subsampling with a fixed sampling lattice. A new algorithm that optimally assigns sampling lattices to different parts of the image is presented. The proposed spatially adaptive subsampling method can be applied within a motion-compensated coding scheme as well. Experiments show an increased performance over fixed lattice subsampling.     

基于欠采样的宽带线性调频信号参数估计

基于中国余数定理解频率模糊和解线调方法,提出一种无模糊欠采样的宽带线性调频信号的调频斜率和初始频率的估计算法.首先,欠采样宽带线性调频信号与其两路不同延迟共轭相乘,根据两路输出信号的单频特性,利用FFT、谱峰检测(PSD)和中国余数定理进行宽带线性调频信号的调制斜率无模糊估计;其次,根据估计的调制斜率数字合成无载波的线性调频信号对另外两路不同延迟的欠采样宽带线性调频信号解线调处理,利用类似方法进行宽带线性调频信号的初始频率无模糊估计.利用频谱细化技术,参数估计精度可进一步提高.计算机仿真证实了算法的有效性.     

A 60-dB 246-MHz CMOS variable gain amplifier for subsampling GSM receivers

A variable gain amplifier (VGA) is designed for a GSM subsampling receiver. The VGA is implemented in a 0.35-/spl mu/m CMOS process and approximately occupies 0.64 mm/sup 2/. It operates at an IF frequency of 246 MHz. The VGA provides a 60-dB digitally controlled gain range in 2-dB steps. The overall gain accuracy is less than 0.3 dB. The current is 9 mA at 3 V supply. The noise figure at maximum gain is 8.7 dB. The IIP3 is -4 dBm at minimum gain, while the OIP3 is -1 dBm at maximum gain. The group delay is 1.5 ns across 5-MHz bandwidth.     

基于AD9244和PCI9054的虚拟无线电接收子系统

虚拟无线电是软件无线电技术一种新的发展趋势,基本思路是利用计算机取代传统软件无线电系统中的DSP芯片,一般采用直接中频采样技术,将采样结果通过PCI总线送入主机内存,由用户软件做后续的信号处理.本文讨论了欠采样技术在中频信号接收系统中的应用,由此提出了一种虚拟无线电接收子系统实现的硬件设计方案,然后对系统中重要芯片的性能进行了介绍,并对系统的控制过程进行了详细说明,最后简要介绍了一些注意事项.     

Multiband RF-sampling receiver front-end with on-chip testability in 0.13 μm CMOS

In this paper a flexible RF-sampling front-end primarily intended for WLAN standards operating in the 2.4 GHz and 5–6 GHz bands is presented. The circuit is implemented with on-chip Design for Test (DfT) features in 0.13 μm CMOS process. The front-end consists of a wideband LNA, a sampling IQ down-converter implemented as switched-capacitor decimation filter, test attenuator (TA), and RF detectors. The architecture is generic and scalable in frequency. It can operate at a sampling frequency up to 3 GHz and RF carrier up to 6 GHz with 2× subsampling. The selectable decimation factor of 8 or 16 makes the A/D conversion feasible. The frequency response, linearity, and NF of the whole front-end have been measured. The power consumption of complete RF front-end is 176 mW. The on-chip DfT features are helpful in reduction of overall test cost and time in volume production. The measurement results show the feasibility of DfT approach for multiband radio receiver design using standard CMOS process.     

Phase-noise-induced performance limits for DPSK modulation with andwithout frequency feedback

The effect of phase noise on the performance of differential phase shift keying (DPSK) is analyzed for four different receiver structures. The phase noise model used is more general than the standard Brownian motion model. It allows the observation of the effect of frequency feedback stabilization on system performance. The asymptotic performance in the limit as the signal-to-noise ratio tends to infinity is considered. The results show that feedback stabilization results in a considerable performance improvement. For example, in a narrowband receiver this scheme results in an effective linewidth reduction by a factor of 12.5 when the feedback bandwidth is 0.8 times the bit rate, and by a factor of 42 when the feedback bandwidth is 1.6 times the bit rate. Therefore, frequency feedback reduces the minimum required data rate for a given laser linewidth, or increases the maximum linewidth allowed for a given data rate. The performance of the narrowband receiver in the presence of both additive and phase noises is determined and a dramatic improvement with feedback is shown     

Interpolative BTC image coding with vector quantization

The authors suggest two interpolative block truncation coding (BTC) image coding schemes with vector quantization and median filters as the interpolator. The first scheme is based on quincunx subsampling and the second one on every-other-row-and-every-other-column subsampling. It is shown that the schemes yield a significant reduction in bit rate at only a small performance degradation and, in general, better channel error resisting capabilities, as compared to the absolute moment BTC. The methods are further demonstrated to outperform the corresponding BTC schemes with pure vector quantization at the same bit rate and require minimal computations for the interpolation     

基于FRFT的线性调频信号欠采样快速检测方法

采用分数阶Fourier变换对线性调频信号(Linear Frequency Modulation,LFM)进行检测与参数估计时,由于信号的特征未知,需要运用二维搜索方法确定分数阶Fourier变换的最佳旋转角度.该方法运算量巨大.为减少运算量,本文推导了欠采样前后LFM信号的分数阶Fourier变换最佳能量聚集旋转角度关系,证明了无噪LFM信号的调频率估计可以完全不受Nyquist采样定理的限制;通过推导分析欠采样含噪LFM信号在最佳分数阶Fourier域的信噪比,给出了欠采样倍数M对LFM信号检测的影响及其选取原则;最终提出一种基于欠采样理论的LFM信号快速检测方法.实验结果表明,当M选取合适时,利用原始信号的欠采样样本即可对LFM信号实现有效检测,快速确定其调频率.     

基于USRP的DVB-T接收机实现

为提高地面数字电视广播(DVB-T)接收机的实现灵活性,基于由通用软件无线电外设(Universal Software Radio Peripheral,USRP)和通用计算机组成的软件无线电平台,实现DVB-T接收机。接收机以USRP作为射频前端,在通用计算机中完成全部基带信号处理、视频解码与显示等。测试结果表明,接收机可实现对DVB-T信号的接收,为接收机算法开发、验证与评估提供了更为灵活的方法。     

Signal analysis and compression performance evaluation ofpathological microscopic images

Digitizing high-quality microscopic images and developing input/output technology for displaying those results is critical to telepathology in which pathological microscopic images are transferred to remote locations where they are diagnosed by specialists. Here, the authors discuss the results achieved by directly digitizing (nonfilm process) pathological microscopic images at a 2 k×2 k resolution, and then using a super-high-definition imaging system to analyze the signals and evaluate compression performance. The authors start off by digitizing samples that a pathologist actually uses in making a diagnosis. They then analyze the images' color distribution and spatial frequency characteristics by comparing them to general images. This makes it apparent that such pathological images characteristically contain high spatial frequencies in their chrominance components. The authors also discuss the evaluation results of color differences for L ^*a^*b^* space and compression ratios achieved when using JPEG to encode pathological images. Finally, the authors present a subjective evaluation of the influence that subsampling of chrominance components has on image quality     

Space-time signaling for high data rates in EDGE

Several space-time coding and processing techniques have been introduced in the literature for enhancing the capacity of wireless systems through antenna diversity or spatial multiplexing. We study the application of such techniques to an adaptive coded modulation system in multipath channels with intersymbol interference. One of the key requirements for application of these schemes is the use of appropriate training symbols for channel estimation at the receiver. We determine the training requirements for coherent receiver operation when multiple transmit antennas are used. We show that for the special case of the delay diversity scheme, transmitting the same training sequence from the two antennas is optimal. For more general schemes, we present training sequences that have good auto-correlation and cross-correlation properties that can be used in a practical system such as Enhanced Data for GSM Evolution (EDGE). We present detailed link level simulations that include channel estimation for the proposed schemes. We then determine the system throughput that is achieved for packet data with ideal link adaptation for deployment scenarios with 1/3, 3/9, 4/12, and 7/21 frequency reuse. We conclude that the gains from transmit diversity are not significant when there is frequency hopping as in an EDGE system and that a factor of 3 gain in throughput can be achieved when four transmit and four receive antennas are available using simple space-time transmission and receiver processing.     

脉冲超宽带(UWB)跳时系统的频域信道估计

提出一种基于序列和的最大似然(ML)频域信道估计算法,该算法可适用于对跳时UWB通信系统进行基于训练序列的信道估计和盲信道估计,大大简化了运算的复杂性。在仿真中比较了基于理想信道估计、基于一般的频域信道估计以及基于序列和的ML频域信道估计的性能。结果显示,在频域的估计过程中,对发射信号的频谱设定适当的可信门限后,可以获得与直接进行频域信道估计相似的性能。