Precoded Modulo-Precanceling Systems for Simulcasting Analog FM and Digital Data

We present techniques for simulcasting low-power digital data and analog FM over fading channels. Our methods have strong connections to what are referred to as dirty paper coding techniques in that a low-power digital data signal is modulo-added to the host analog FM signal. Due to the low power levels of the digital data and the suppression capability of analog FM, a standard analog FM receiver can be used to reliably recover the analog audio signal. We develop digital receivers that work reliably over fading channels given imperfect channel state information. Spreadresponse precoding is exploited to not only provide rate-1 temporal diversity benefits, but also to simplify the design of the modulo-precanceler and the receiver. Our theoretical and simulation-based performance analysis of the digital receivers and our MSE-based analog FM distortion analysis suggest that precoded modulo-precanceling schemes provide substantially higher data rates than existing precanceling strategies at the cost of transmission delay and transmitter and receiver complexity. The systems we present are also readily compatible with conventional channel coding techniques as well as with analog FM postcancelers, which can improve the digital receiver bit-error-rate performance at the expense of receiver complexity.     

Analysis of FM Systems with Co-Channel Interference Using a Click Model

Rice's click model for ideal FM detection is applied to systems with co-channel interference. Output noise terms consist of a high signal-to-noise ratio (SNR) term due to noise alone, a term due to the desired signal beating with the interferer, and a term due to the clicks. Click rates are determined with and without modulation and it is shown that in the computation of noise due to clicks the interferer can be treated as a simple sinusoid [i.e., an unmodulated carrier] Plots are given for detected SNR versus carrier-to-noise (CNR) with signal-to-interferer ratio (SIR) and modulation index as parameters. The effect of signal suppression is analyzed and for the range of parameters used in this paper it is found to be negligible.     

Analog Implementation of a Robust Control Strategy for Mechanical Systems

An analog implementation of a control structure with disturbance identification for mechanical systems is presented. This control structure is based on a discontinuous observer that estimates the state and the disturbances in the plant, improving the robustness of the closed loop system which also displays a control input free from chattering. The control structure, built with operational amplifiers, is simple, showing good performance for stabilization, regulation, and tracking objectives. The performance of the circuit is compared with a digital implementation based on a real-time data acquisition card to control a simple pendulum. In addition, the circuit performance is illustrated on an industrial 2-DOF robot.      

A New Demodulation Method Improving FM System Interference Immunity

As a result of investigation of interference into FM systems, a new algorithm for the process of demodulation is proposed. When compared to the method using the conventional limiter-discriminator, it offers better immunity against the baseband interference noise. Desired signal processing is performed by the functional devices added to the conventional limiter-discriminator in such a way that this new demodulator can be optimized in the sense of the minimum baseband interference noise. The statistics of the wanted and interfering signals must be known. Several examples involving interference problems in FDM-FM radio-relay systems carrying multichannel telephone signals are elaborated to illustrate the performances of the proposed demodulator. FDM-FM, PSK, or FSK systems are considered the cause of the interference. The noise power ratio (NPR) at the output of the conventional limiter-discriminator and the improvement factor offered by the new demodulator, obtained on digital computer, are presented versus baseband frequency in the form of diagrams. Different IF filters in FDM-FM receiver and transmit filters in the interfering systems are taken into account. The improvement offered by the proposed demodulator is of such a degree that some of the important restrictions in planning different radio systems could be relaxed.     

FPGA-Based Analog Functional Measurements for Adaptive Control in Mixed-Signal Systems

A field-programmable-gate-array (FPGA)-based built-in self-test (BIST) approach that is used for adaptive control in mixed-signal systems is presented. It provides the capability to perform accurate analog functional measurements of critical parameters such as the third-order intercept point, frequency amplitude and phase responses, and noise figure. The results of these measurements can then be used to adaptively control the analog circuitry for calibration and compensation. The BIST circuitry consists of a direct digital synthesizer-based test pattern generator and a multiplier/accumulator-based output response analyzer. The BIST approach has been implemented in an FPGA-based mixed-signal system and used for actual analog functional measurements. The BIST measurements agree quite well with the results obtained with the traditional analog test equipment. The proposed BIST circuitry provides a unique means for high-performance adaptive control in mixed-signal systems.     

基于DEHT的伪码引信中多分量FM干扰抑制方法研究

在介绍离散进化变换(DET)和离散进化哈夫变换(DEHT)的基本原理基础上,详细分析了伪码引信中基于DEHT的多分量FM干扰抑制方法。接收信号首先通过DEHT估计干扰瞬时相位,并通过递归校正方法减小相位估计误差,利用估计出的干扰瞬时相位设计了一时变级联滤波器,逐个消去FM干扰。对不同干信比(ISR)情况下的干扰抑制前后的相关输出进行了仿真分析。分析结果表明,该方法能有效地去除干扰,相关输出得到显著改善。     

Mixed Power Control with Directed Assignment (MPCDA), a Method for Interference Reduction in Channelized Wireless Systems

Power control, often coupled with dynamic channel assignment, has been viewed as a promising answer to the challenge of reducing interference and increasing capacity. Indiscriminate use of power control, however, may exacerbate the near-far-end problem on the down link, and give rise to other complications when users are mobile. We propose a power control policy that can alleviate the near-far-end interference caused by the use of either the same channel or neighbor channels inside the same cell, while at the same time aiding in the reduction of interference from different cells through user matching. We present a heuristic algorithm for user matching, which is distributed and simple to implement. The method can be combined with an array of either fixed or dynamic channel assignment algorithms and applies to both circuit-based and packet-based traffic. It is ideal for fixed or slow circuit-based traffic and for packet-based traffic.A duality relationship is derived for the proposed power control policy between the signal-to-interference ratio of two interfering users experienced in the two communication directions. This relationship enables one to validate channel assignment decisions on both communication directions by analyzing only the decisions for one.     

调频广播发射机定位民航甚高频台干扰源的一种方法

介绍一种在线测试调频广播发射机定位民航干扰源的方法,阐述了工作背景,重点讨论了测试内容、方法、依据和测试系统的连接,对测试数据和结果进行了详细分析,最后强调了此方法对确定调频广播发射机干扰民航甚高频电台的重要意义.     

一种简化的模拟电路测试性评价方法

模拟电路的测试性是进行故障诊断和定位的重要依据.采用基于符号化的分析方法来进行测试性评价,相对于数值计算的方法更有优势.提出了一种测试性矩阵的构建方法,同时给出并证明了基于该测试矩阵进行测试性评价的方法.该评价方法的特点是计算简单实用,且消除了计算误差.最后,通过电路实例,验证了该方法的有效性及其实现上的简洁性.     

Interference coordination for LTE-Advanced and FM broadcasting interoperability

The surest way to guarantee that multiple wireless systems can concurrently exist harmlessly, when operating in the same or adjacent channel, is by analyzing spectrum overlapping. This paper proposes a more accurate model to evaluate the interference power from co-channel and adjacent channel of orthogonal frequency division multiplexing-based long term evolution-advanced (LTE-Advanced) towards broadcasting frequency modulation systems at 800?MHz. Power spectral density overlapping factor is employed, and closed form of the interference power loss is derived. Numerical results demonstrate that the proposed method evaluates more exact interference power than the advanced minimum coupling loss (A-MCL) method, where the co-channel and adjacent channel interference powers are reduced by 1.3 and 3?dB, correspondingly, compared to that obtained using the A-MCL method. This decreases the minimum separation distance between the two systems, which can eventually lead to efficient radio spectrum resources utilization.     

一种新的应用于多载波码分多址系统的干扰对消算法

本文提出了一种适用于多载波直扩码分多址系统(MC-DS-CDMA)上行信道的低复杂度部分并行干扰对消(LC-PPIC)算法.该算法充分利用MC-DS-CDMA系统的信道估计与子载波分集,在各个子载波上将用户分为可靠,普通和无效三类,对可靠用户进行干扰对消处理并消去后,再对普通用户进行相同操作,并放弃无效用户,最后将各个子载波上的结果通过最大比合并(MRC)输出.这样,在降低运算复杂度的同时,更好地抑制了多址干扰(MAI).通过仿真比较,可以看出LC-PPIC算法的误码率(BER)性能明显优于置于载波合并前后的两种部分并行干扰对消(PPIC)算法,特别是在系统负载较重和信噪比较高的情况下,这种优势十分显著.     

Application of Coded Modulation to 1.544-Mbit/s Data-in-Voice Modems for FDM FM and SSB Analog Radio Systems

The technical issues relevant to providing high-quality digital service over analog radio using 1.544-Mbit/s DS-1 data-invoice modems operating through analog supergroup channels with 256-QAM modulation are reviewed. By means of a typical example, the desirability of increasing the fading margin when operating over FM radio systems is demonstrated. This motivates the consideration of coded modulation as a means of extending the threshold of the modem System, so that operation of the modem can be achieved in supergroup channels located higher in the radio baseband. It is found that trellis coded modulation provides better improvement of threshold performance than lattice coded modulation when the actual coding gain realized near the R0channel bound is used rather than the high signalto-noise-ratio (SNR)asymptotic coding gains. Using Ungerboeck's eight-state trellis code [3], a coding gain of approximately 2 dB is found for operation at 28 dB SNR (1 dB from the R0bound). Furthermore, it is found that even at this low operating SNR (where error events at the coded modulation receiver ouput can be long), high-rate, interleaved Reed-Solomon codes, used for burst noise protection at high SNR, still provide over 2 dB of additional coding gain.     

Coverage and Interference for Second-Adjacent Channel FM Broadcast Stations

The coverage and interference of seven Los Angeles area FM broadcast stations are analyzed. The area and population coverages predicted by the FCC methods described in the rules are compared with a method that considers the intervening terrain in some detail. We also show that the criteria for deciding second-adjacent-channel interference threshold of -50 dB (rather than the present -20 dB) adequately protects modern receivers, based on data available in FCC filings and on the performance of these stations. We believe the techniques used in this analysis could be widely applied, and would result in more efficient spectrun use.     

CDMA移动通信系统中的多址干扰及抑制技术

相对于FDMA及TDMA，CDMA具有一系列的优点，这些优点使得CDMA技术在日新月异的移动通信领域中所处的地位越来越重要，已经成为新一代移动通信以及未来个人通信中最具竞争力、最具发展前景的无线多址技术。但在CDMA已经成为第三代移动通信主流技术的时候，要真正达到预定的目标，还有许多关键技术要解决，其中最为关键的就是要突破克服CDMA系统中多址干扰(MAI)的技术。     

Synchronization Receiver for OFDM-Based FM Broadcasting Systems

The digital radio mondiale (DRM) consortium is now preparing to test and verify the design of DRM plus, prior to standardization, produce a revision to the existing DRM system specification. This paper presents an overview of the OFDM-based DRM system, planned to operate in FM bands, utilizing important receiver aspects, such as timing and frequency synchronization, which can provide benefits to the overall system performance. In particular, algorithms are devised or selected for the sequential estimation of symbol timing and carrier frequency offsets by exploiting the structure of the data and pilot. The performance of using the proposed algorithms is demonstrated via several examples in the channel models for FM bands.     

Interference Evaluation of Bluetooth and IEEE 802.11b Systems

The emergence of several radio technologies, such as Bluetooth and IEEE 802.11, operating in the 2.4 GHz unlicensed ISM frequency band, may lead to signal interference and result in significant performance degradation when devices are colocated in the same environment. The main goal of this paper is to evaluate the effect of mutual interference on the performance of Bluetooth and IEEE 802.11b systems. We develop a simulation framework for modeling interference based on detailed MAC and PHY models. First, we use a simple simulation scenario to highlight the effects of parameters, such as transmission power, offered load, and traffic type. We then turn to more complex scenarios involving multiple Bluetooth piconets and WLAN devices.     

Maximum A Posteriori Estimator for Suppression of Interchannel Interference in FM Receivers

In this paper an FM detector capable of suppressing the degradation in receiver performance due to the presence of an interfering signal is presented. Optimum receiver structures based on maximum-aposteriori estimation procedures are first derived and then a practical demodulator based on the optimum receivers is examined. The receiver consists of two phase-locked loops (PLL) interconnected in a manner to permit one PLL to lock onto and track the Stronger received FM signal while the other loop tracks the weaker of the two received FM signals. The detector has the capability of demodulating both the desired received FM as well as the interferer even for the case when both signals are co-channel. Experimental results demonstrating such capability even in the presence of strong input Gaussian noise are presented.     

Analog Impairments in MIMO-OFDM Systems

MIMO-OFDM is being considered for communication systems where high throughput and spectral efficiency are important factors. Analog impairments like I/Q mismatch and phase noise significantly degrade and limit the performance of communication systems. In this paper, we analyze the impact of I/Q mismatch and phase noise in MIMO-OFDM systems as a function of the number of antennas. We show the improvement in performance that is possible when these impairments are cancelled. We also discuss the impact of correlated and uncorrelated phase noise in MIMO-OFDM systems. Finally, we show the results of I/Q mismatch and phase noise cancellation in wireless measurements performed using a 2times2 MIMO-OFDM testbed     

模拟视频滤波技术

本文详细介绍Maxim满足多种视频应用需求而提供的各种集成视频滤波放大器.     

A Pulsed Control Method for Chaotic Systems

In this paper, it is proposed a method for controlling chaotic systems; where the main goal is to obtain a periodic behaviour for a chaotic system. In our approach, the system to control is considered as a black-box, and therefore it is not necessary to know a mathematical model of the system, only experimental measurements are used. Our method employs pulses with adjustable amplitude and width, and it is implemented in discrete time. In order to generate pulses control, a variable Poincaré section is used; which is computed on-line using a moving average sampling signal. Measurement noise is considered too, by means of an additional controller parameter (hold-off time), resulting that controller tuning is made using four parameters: proportional gain, sampling time, pulse width and hold-off time. In order to test the proposed method, computer simulations with several representative chaotic systems (Lorenz, Chua, Chen, Colpitts and others) are carried out and satisfactory results are obtained.