A spread-spectrum clock generator with triangular modulation

In this paper, a spread-spectrum clock generator (SSCG) with triangular modulation is presented. Only a divider and a programmable charge pump are added into a conventional clock generator to accomplish the spread-spectrum function. The proposed circuit has been fabricated in a 0.35-/spl mu/m CMOS single-poly quadruple-metal process. The proposed SSCG can generate clocks of 66, 133, and 266 MHz with center spread ratios of 0.5%, 1%, 1.5%, 2%, and 2.5%. Experimental results confirm the theoretical analyses.     

Noise stability of time discriminators for spread-spectrum signals with phase and frequency modulation

The noise stability of incoherent and coherent time discriminators of delay tracking systems for promising spread-spectrum signals with phase and frequency modulation is analyzed. Recommendations on the application of the proposed algorithms in tracking correlation receivers of the considered spread-spectrum signals are given.     

Parallel acquisition of spread-spectrum signals with antennadiversity

The use of antenna diversity is investigated for improving the parallel acquisition performance of a direct-sequence spread-spectrum signal in both flat and frequency-selective fading channels. Noncoherent combining techniques are analyzed because coherent diversity techniques, such as maximal ratio combining, cannot be employed prior to initial acquisition. A major application of this work is to cellular communications     

Phase and clock synchronization of the Viterbi demodulator of continuous-phase modulation signals

The possibility of constructing the synchronization system of the Viterbi demodulator of continuous-phase modulation (CPM) signals is analyzed. The concept of multiphase trellis is introduced to provide the phase self-synchronization of a demodulator. The results calculated via computer simulation of the phase synchronization scheme that ensures efficient reception of CPM signals with constant and cyclically varying modulation indices are presented. The clock synchronization scheme whose main component is a delay discriminator is proposed and investigated. Its operability is demonstrated with the use of a minimum frequency-shift keying signal.     

Robust adaptive recovery of spread-spectrum signals with short data records

The problem under consideration is the adaptive reception of a multipath direct-sequence spread-spectrum (SS) signal in the presence of unknown correlated SS interference and additive impulsive noise. An SS receiver structure is proposed that consists of a vector of adaptive chip-based Hampel nonlinearities followed by an adaptive auxiliary-vector linear tap-weight filter. The nonlinear receiver front end adapts itself to the unknown prevailing noise environment providing robust performance over a wide range of underlying noise distributions. The adaptive auxiliary-vector linear tap-weight filter allows rapid SS interference suppression with a limited data record. Numerical and simulation studies under finite-data-record system adaptation show significant improvement in bit-error-rate performance over the conventional linear minimum variance-distortionless-response (MVDR) SS receiver or conventional MVDR filtering preceded by vector adaptive chip-based nonlinear processing.     

A new transmission-line device with double-polarization capabilityfor use in radiated EMC tests

The subject of this paper is the design and performance analysis of a double-polarization transmission line (TL) device for radiated EMC tests, the CrossTEM (X-TEM) cell. The X-TEM cell is a multiwire TL device which has been specifically designed in order to optimize the test-region dimensions while ensuring double-polarization performance and suitable cross-polarization level. Cross-polarization performance is requested by the last modifications of emerging standards. Theoretical and experimental results are shown illustrating the performance of the new device. The selective-absorbing material positioning (SAMP) procedure to suppress resonances is described. The improvements experimentally achieved for both field uniformity and cross polarization are shown     

A low-power spread-spectrum clock generator with three-step frequency and VCO gain calibration for serial-ATA applications

This paper presents a low power ring oscillator-based spread-spectrum clock generator with three-step frequency and voltage-controlled oscillator (VCO) gain calibration for S-ATA applications. To meet the low jitter requirements with a small VCO gain, a ring-type VCO with three step frequency calibration and gain calibration scheme is proposed. The proposed coarse tuning method selects the optimal tuning currents and capacitances of the ring VCO to optimize the phase noise. The gain of ring-type VCO can be reduced and kept constant with the proposed three-step frequency and VCO gain calibration. As a result, it can improve the phase noise characteristics of the ring-type VCO and make it more robust to the PVT variations. Also, charge pump up/down current mismatches are compensated with the current mismatch compensation block. This chip is fabricated with 65 nm CMOS technology, and the die area is 430 × 460 μm². The power consumption is 12 mW at 1.2 V supply voltage. The measured RMS jitter and phase noise are 2.835 ps and ?96.83 dBc/Hz at 1 MHz offset, respectively.     

基于单基站定位的时空调制扩频系统

目前,移动用户对基于无线定位技术的新业务的需求不断增加,提高无线定位系统容量和减少干扰已是一个重要课题,针对智能天线的预多波束切换方式,提出了一种同时测向测距的定位方法。该方法利用接收信号的功率特性估计移动台方位角,利用信号到达时间估计基站与移动台之间的距离。同时研究了多种环境下,信道衰落、非视距、多用户干扰等对这一系统定位精度的影响。该方法提高了同时定位用户数,计算复杂度小,有利于对用户快速定位、跟踪。     

Switched-capacitor filters driven with very low voltage clock signals

It is well known that the switches of a very low voltage (1.5V) switched-capacitor filter in a standard CMOS process must be driven with a clock signal higher than the power supply, often generated on-chip. The authors present, however, a technique to implement very low voltage switched-capacitor filters with switches driven at the same very low voltages.<>     

Bandwidth-efficient coded modulation with optimized linearpartial-response signals

We study the design of optimal signals for bandwidth-efficient linear coded modulation. Previous results show that for linear channels with intersymbol interference (ISI), reduced-search decoding algorithms have near-maximum-likelihood error performance, but with much smaller complexity than the Viterbi decoder. Consequently, the controlled ISI introduced by a lowpass filter can be practically used for bandwidth reduction. Such spectrum shaping filters comprise an explicit coded modulation, for which we seek the optimal design. We simultaneously constrain the bandwidth and maximize the minimum Euclidean distance between signals. We show that under quite general assumptions the problem can be formulated as a linear program, and solved with well-known efficient optimization techniques. Numerical results are presented, and the performance of the optimal signals, measured by their combined bandwidth and noise immunity, is analyzed. The new codes are comparable to set-partition (TCM) trellis codes. Tests of an M-algorithm decoder confirm this and show that the performance occurs at small detection complexity     

The estimation of the directions of arrival of the spread-spectrum signals with three orthogonal sensors

An effective technique in estimating the directions of arrival (DOAs) of incoming signals using three orthogonal sensors is proposed. The channel model with multipath transmissions for code-division multiple access (CDMA) users whose signals are modulated with binary phase-shift keying (BPSK) is used. Utilizing the maximum-likelihood (ML) method, the channel impulse response vectors of the three sensors can be estimated, then all of the corresponding propagation delays and amplitude weights of the three sensors' channels can be obtained. By comparing the propagation delays of the three channels, we can identify the same signal replica, then its DOA can be estimated by the relation of the three corresponding attenuation weights. Calculating results show this method can reach fairly high accuracy, and it needs only three sensors while in other techniques the required number of sensors is greater than the number of estimated signals.     

Performance analysis of direct-sequence spread-spectrum multiple-access communication in an indoor Rician-fading channel with DPSK modulation

The bit error probability for direct-sequence spread-spectrum multiple-access (DS/SS-MA) in indoor radio channels is evaluated, assuming differential phase-shift-keying (DPSK) modulation, both for selection diversity and for maximal-ratio combining. The indoor radio environment is modelled as a Rician fading channel.<>     

The PAM decomposition of CPM signals with integer modulation index

This article presents the solution for decomposing continuous-phase modulated (CPM) signals with integer modulation index into pulse-amplitude modulated components. The notion of main complex pulse is also introduced. A simplified demodulator for CPM signals with integer modulation index is proposed as an application example and simulation results using a quaternary 2 raised cosine (RC) scheme are given.     

多种调制格式微波信号的光学产生方案

提出了一种基于偏振调制器（PolM）和Sagnac环级联的多调制格式微波信号的光学产生方案。理论分析了PolM在基带编码信号的驱动下产生偏振键控（PolSK）信号的基本原理,Sagnac环中嵌有两个马赫增德尔调制器（MZM）,分别对顺时针和逆时针传输的PolSK信号进行独立调制。通过合理调整两个MZM的驱动信号,实现了幅移键控（ASK）、频移键控（FSK）和相移键控（PSK）微波信号的产生。在仿真实验中,产生了比特率为2 Gbit/s的40 GHz ASK信号、20/40 GHz FSK信号和20 GHz PSK信号,同时验证了比特率和载波频率的宽带可调谐性。Sagnac环结构提升了系统的稳定性,并且针对每种调制格式的微波信号,在不改变链路结构的情况下其比特率和载波频率都可以通过控制基带编码信号和MZM的射频驱动来进行独立且灵活的调谐。     

Synthesis of bandlimited signals with independent amplitude and phase modulation

The synthesis of a bandpass bandlimited signal with independent AM and PM channels is considered, where the bandwidth of each of the two information signals is required to be less than or equal to half the bandwidth of the bandpass signal. A simple iterative algorithm for generation of the bandpass signal is proposed, and sample results are presented. It is shown that this approach may be useful in simultaneous amplitude phase transmission systems even when the number of iterations is small.     

基于马赫-曾德尔调制器的多种调制格式微波信号的光学生成研究

提出了一种基于马赫-曾德尔调制器(MZM)的 多种调制格式微波信号的光学一体化生成方案。 在本文方案中,微波信号和编码矩形波信号经合路器同时输入到MZM中,通过合理设置编码 信号的幅值使 MZM能够工作在其传输曲线的不同传输点,分别实现了频移键控(FSK)、二进制相移键控(BPSK)和 二倍频BPSK微波信号一体化生成。本文方案仅需要1个MZM而不需要额外加电的或光的选频器 件, 因此具有结构简单、可大范围调谐的优势。特别的,本文方案还可以产生二倍频的BPSK微波 信号,从 而使能够满足更高频的应用需求。在仿真和实验中,分别得到10/20 GHz的FSK、10GHz的BPSK 微波信号,同时产生了20GHz的二倍频BPSK微波信号,有效验证了本 文方案的可行性。     

同频同调制信号的瑞利信道系统仿真设计

为了解决通信系统仿真模型的不完备性,利用Matlab的组件Simulink搭建了一套模拟信号的传输、接收、分离的接收机通信仿真模型。该模型以同频同调制信号为信源,选取多径瑞利衰落信道模拟仿真实际接收机的工作流程,并且包括信源模块、调制解调模块、信道模块、模拟接收模块、采样滤波模块、信号分离模块等。此外,系统测试了瑞利信道的路径增益对信号盲分离的影响,仿真结果表明信道增益越大,信号越集中,分离效果也相对较好。因此,该仿真系统可以与硬件系统原型相结合,为测试信号提供功能验证,为实际接收机系统运行环境提供参考建议。     

Algorithms of synchronization and detection of continuous-phase modulated signals with cyclically varying modulation index

Algorithms of simultaneous superbaud, clock, and phase synchronization for the detectors of continuous-phase modulated signals with cyclically varying modulation index are considered. The algorithms are based on the theory of nonlinear filtering and optimized with respect to the minimum mean-square error. A closed-loop model of the synchronization system is constructed and comprehensively studied with the aid of computer simulation.     

Injection-locked Fabry-Pe/spl acute/rot laser with electronic feedback for clock recovery from high-speed OTDM signals

We demonstrate the use of an injection-locked Fabry-Pe/spl acute/rot laser diode with electronic feedback for base-rate clock recovery in N/spl times/10 Gb/s optical time-division-multiplexing (OTDM) systems. Injection-locking enhances the resonance frequency of the laser and the electrical feedback achieves strong resonance at the base-rate frequency of the injected data streams, enabling ultrastable electrical clock signal generation at the base rate of 10 GHz. Experimental demonstrations for clock recovery at 10 GHz from 40-Gb/s OTDM data streams and 4-1 demultiplexing of the data using the extracted clock after fiber transmission is presented. The timing jitter measured in the recovered electrical clock is less than 0.25 ps.     

Decision feedback differential detection for differential orthogonal space-time modulation with APSK signals over flat-fading channels

Differential orthogonal space-time modulation (DOSTM) with amplitude/phase shift keying (APSK) signals has been recently proposed to improve the data throughput of the DOSTM with PSK signals over quasi-static channels. In this letter, decision feedback differential detection (DF-DD) based on linear prediction is presented for the DOSTM with APSK Signals (DOSTM-APSK) over flat-fading channels. The proposed DF-DD offers better performance than the differential detection when the channel experiences fast fading. The coefficients of the linear prediction based DF-DD can be obtained by an adaptive recursive least-squares algorithm, where the channel statistics are not needed. The proposed DF-DD is also applicable to the general unitary differential space-time modulation.