共查询到20条相似文献,搜索用时 15 毫秒
1.
Moeller F Enderlein J Belkerdid MA Malocha DC Buff W 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1999,46(4):842-848
This paper presents the design, fabrication, and experimental results for a differential phase shift keying (DPSK) single SAW-based correlator on GaAs for direct sequence spread spectrum applications. The DPSK modulation format allows for noncoherent data demodulation; the SAW device correlator acts as the despreader. Unlike the conventional technique of using two parallel correlators and a one data bit delay element, this new system uses two inline correlators. When implemented on SAW devices, this in-line structure has the advantage of an inherent one data bit delay, lower insertion loss, and less signal distortion than the parallel structure. The DPSK correlator is fabricated on a {100} cut GaAs substrate with SAW propagation in the 110 direction, Using this cut, which is widely used in electronics, Rayleigh waves are generated with a piezoelectric coupling coefficient of the same order as ST-cut quartz. The piezoelectric semiconductor GaAs is of great interest because it is the only substrate that can be used to integrate SAW devices directly with electronics on the same chip, resulting in smaller packaging, reduction of packaging parasitics, lower cost, and greater system integration. This paper presents experimental results for SAW in-line correlator structures on GaAs along with their despreading system performances. Experimental measurements in both the time and frequency domains were performed and were found to be in good agreement with theoretical predictions. 相似文献
2.
Carter SE Malocha DC 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2000,47(4):967-973
This paper introduces a new weighted stepped chirp code signal for direct sequence spread spectrum (DS/SS) communications systems. This code signal uses the truncated cosine series functions as the chip functions, and it is the result of discretizing a continuous wave (CW) chirp that results in enhanced performance versus a pseudonoise (PN) code and equivalent performance and easier implementation than a CW chirp. This code signal will be shown to have improved compression ratio (CR) and peak sidelobe level (PSL) versus a PN code with identical code length and chip length. It also will be shown to have a similar CR and PSL compared to a CW chirp with identical pulse length and frequency deviation. The code signal is implemented on surface acoustic wave (SAW) devices that will be used as the code generator at the transmitter and the correlator at the receiver. The design considerations for the SAW device implementation of the code signal are discussed, including the effects of intersymbol interference. Experimental data is presented and compared to the predicted results for 8 different SAW devices examining the effects of code length (9 or 13 chips), weighting (uniform, cosine-squared, and Hamming), and sampling on the performance of the code signal. 相似文献
3.
Hikino O Belkerdid MA Malocha DC 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2000,47(4):974-983
This paper introduces a new optimization algorithm for the minimization of the time sidelobes of the correlation function of a pseudonoise (PN) sequence by applying dynamic weighting to the sequence. The resulting optimized time sidelobe level sequences are to be used in direct sequence spread spectrum (DS-SS) systems with digital modulations such as BPSK, DPSK, QPSK, etc. The new optimization algorithm starts with a PN sequence. It first optimizes the correlation time sidelobes for the case where the consecutive data bits are identical (11 or 00). It then optimizes the correlation time sidelobes for the case of alternating consecutive data bits (10 or 01). The suppressed time sidelobe level sequences are derived by iterating these algorithms alternately starting from the initial PN sequence. The derived suppressed time sidelobe sequences show excellent correlation characteristics when compared to conventional PN sequences such as maximal length sequences, Gold sequences and Barker codes. Surface acoustic wave (SAW) devices were used to implement the optimized time sidelobe level sequences in a matched filter pair. The design of the apodized SAW-matched filters and their predicted second order effects are presented. The experimental results for the SAW-matched filters for the optimized time sidelobe level sequences derived from a Barker code were found to be in good agreement with the theoretical predictions from this new algorithm. 相似文献
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基于现场可编程门阵列(FPGA),设计并实现了一个低复杂度的支持码分多址接入(CDMA)机制的水声直接序列扩频(UDSSS)通信系统--UADSSS/CDMA,给出了系统的整体设计和信道编码电路、信号捕获电路的详细设计.信道编码采用规则重复累积(RA)码,解码迭代算法采用低复杂度的最小和算法,给出了一种快速运算的电路设计;信号捕获电路采用延迟相关捕获算法,给出了一种低复杂度的基于流水线结构的电路设计.进行了水声试验平台测试、湖试、海试等性能测试,结果表明,系统在抑制多径干扰和支持多用户通信方面具有良好的性能:试验平台测试显示,单用户通信的误码率为10-4数量级,存在两个用户干扰的误码率为10-3数量级;湖试显示,零误码的数据包为74.8%;海试显示,零误码的数据包为34.4%. 相似文献
5.
The combined effect of partial band jamming and imperfect channel estimation on the analysis of the performance of MC-FH/BFSK receiver over a Rayleigh fading channel is often neglected in the literature. In this study, this missing analysis is provided. The authors derive closed form bit error probability (BEP) expressions for studying the effect of partial band and broad-band jamming on the performance of a coherent uncoded MC-FH/ BFSK receiver over a Rayleigh fading channel where the effect of channel estimation errors is not neglected. The considered model of the channel estimation errors does not assume independency between amplitude and phase estimates. Computer simulations are provided to validate the theoretical developments. It is shown that the smart partial band jammer should be present in all sub-bands of the system in order to be effective. 相似文献
6.
Small deviations from perfect circular symmetry in the core region of single mode fiber (SMF) cause optical pulses to become broadened as they propagate. This phenomenon is referred to as polarization mode dispersion (PMD), which leads to intersymbol interference and becomes a major impediment for the high speed long-haul fiber-optic links. We present here the theoretical complement for evaluating the performance of a line-coded continuous phase frequency shift keying (CPFSK) optical transmission system with a direct detection receiver. The analysis is carried out for two different line-coding schemes, i.e. alternate mark inversion (AMI) and order-1 coding, to investigate the effectiveness of the line coding in counteracting the effect of PMD in a CPFSK direct detection transmission system in the presence of group velocity dispersion (GVD) and receiver noise in a single mode fiber. The average bit error rate (BER) performances are evaluated without and compared to that of line codes at a bit rate of 10 Gb s?1 considering Maxwellian distribution for the mean differential group delay (DGD). We found that the amount of power penalty improvement of line-coded systems is within 0.65 to 2.25 dB with respect to NRZ data at a BER of 10?9. 相似文献
7.
An octave bandwidth millimetre wave gallium arsenide (GaAs) MMIC modulator is demonstrated, wherein a novel method for directly producing QPSK/OQPSK/BPSK modulation directly from baseband IQ signals is presented. A key feature of the architecture is the absence of mixers. Expressions detailing the overall modulator error vector magnitude (EVM) performance with regard to its constituent components are derived. The dc power consumption of the circuit is less than 50 mW, and its 1 dB compression point is above 7 dBm. Frequency operation is between 30 and 66 GHz, over which QPSK EVM is below 15 , BPSK EVM 3 and data rates of greater than 500 MB/s are possible. 相似文献
8.
New high performance SAW convolvers used in high bit rate and wideband spread spectrum CDMA communications system 总被引:4,自引:0,他引:4
Hikita M Takubo C Asai K 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2000,47(1):233-241
New surface acoustic wave (SAW) convolver structures with high conversion efficiency and self-temperature compensation characteristics have been developed. Strong piezoelectric substrates, regardless of temperature coefficients of delay (TCD), can be used in these convolvers. New demodulation techniques using the developed SAW convolver for high bit rate and wideband spread spectrum code division multiple access (CDMA) communications have also been developed. I- and Q-channel demodulation data can be derived directly from binary phase shift keying (BPSK) or quadri-phase shift keying (QPSK) CDMA signals. In an experiment using a 128 degrees YX-LiNbO(3) substrate, CDMA signals of 9 Mbps (megabits per second) with 60 Mcps (megachips per second) spread by 13-chip Barker code and 11 Mbps with 140 Mcps spread by 25-chip Shiba's code were clearly demodulated, demonstrating the effectiveness of these techniques for use in future CDMA communications. 相似文献
9.
Binary joint transform correlator based on differential processing of the joint transform power spectrum 总被引:6,自引:0,他引:6
A novel binary joint transform correlator with differential processing in the joint transform power spectrum is proposed. The new model of the binary joint transform correlator can eliminate the dc component and sharpen the correlation intensity peaks, hence increasing its discrimination ability but with a lower complexity of computation. Preliminary results are shown by computer simulations. 相似文献
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Stankovic L. Djukanovic S. 《IEEE transactions on instrumentation and measurement》2005,54(6):2156-2162
Methods for jammer rejection in the spread spectrum communications, based on the time-frequency representations, have been proposed in order to improve the desired signal receiving performances. In this paper nonstationary jammers were considered and the local polynomial Fourier transform (LPFT) was used to represent the received corrupted signal. Time-varying filtering was implemented in optimal LPFT domain, having in mind that the LPFT is linear with respect to the signal. An order adaptive algorithm of the LPFT calculation is presented. Performance of the proposed nonparametric method is tested in the presence of linear and sinusoidal FM interferences in the noisy signal, without any a priori assumption about the jammer form. The proposed method may be successfully extended to the case of multiple jammers. Obtained results in terms of the bit error rate (BER) values show the achieved improvements. Procedure for an efficient optimization of the first-order LPFT is presented. 相似文献
12.
Phase unwrapping still plays an important role in many data-processing chains based on phase information. Here, we introduce a new phase unwrapping approach for noisy wrapped phase maps of continuous objects to improve the accuracy and computational time requirements of phase unwrapping using a rotational compensator (RC) method. The proposed algorithm is based on compensating the singularity of discontinuity sources. It uses direct compensation for adjoining singular point (SP) pairs and uses RC for other SP pairs. The performance of the proposed method is tested through both simulated and real wrapped phase data. The proposed algorithm is faster than the original algorithm with the RC and has proved efficiency compared to other phase unwrapping methods. 相似文献
13.
采用相位差校正法进行频谱校正,对幅值进行校正需要依赖于窗函数的谱函数。而实际上很多窗函数都十分复杂,其谱函数的解析表达式难以取得。该文提出基于相位差法取得频率修正量后,可以将原加窗序列乘以一个由频率修正量产生的复数序列,相当于进行一个小的频移,产生一个新的序列。新序列的信号频率正好对准离散频谱上的某一根谱线,不会产生泄漏。因此在幅值校正时不需要依赖窗函数的谱函数,通用性好。仿真研究和应用实例表明,采用该文提出的方法,选择合适的窗函数,即使是密集分布的频谱,也可以达到理想的校正精度 相似文献
14.
A special sampling structure based on double exposure technology is proposed to achieve dual-wavelength lasing in the distributed feedback fiber laser. This structure is composed of two grating pitches in one sampling period, which could be realized by changing the fiber's length in the fabrication. Through employing an equivalent phase shift, only a submicrometer-level precision is required for precise phase control. Then a stable dual-wavelength laser with the spacing of 400?pm is obtained in the experiment successfully. The output power is 30.46?μW and the sidemode suppression ratio is 46?dB under a pumped power of 146?mW. 相似文献
15.
提出了一种利用辐射噪声强度和线谱多普勒频移联合估计匀速直线运动目标的速度和正横距离的方法。该方法基于单水听器观测,首先在球面波近似下利用目标辐射噪声强度估计出正横时刻并确定目标速度和正横距离之间满足的线性关系;然后利用线谱多普勒频移,通过对一个新定义的代价函数进行一维搜索的方法估计出目标速度和正横距离。与现有各种基于噪声强度和线谱多普勒频移进行测距测速的方法相比,该方法具有以下优点:(1)要求更少的先验知识,易于确定参数搜索范围;(2)参数估计过程中仅需一维搜索,并且算法可应用于需对目标参数进行预报的场合。数值仿真给出了不同参数条件下目标运动参数估计结果的统计误差。湖试结果验证了该方法的有效性。 相似文献
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针对单矢量水听器多重信号分类(Multiple Signal Classification,MUSIC)算法在低信噪比条件下,存在谱峰宽度变宽、估计精度变低等性能恶化的问题,提出一种基于单矢量水听器空间谱增强的改进MUSIC算法。该算法的基本原理是:单声源入射到单只矢量水听器上时,加一参考信号源,若两者方位相同,则同方位叠加使空间谱增强;若两者方位不相同,则两方位合成,使空间谱估计产生偏差。因此,改变参考信号源的方位,当参考信号源的方位与信号源的方位一致时,将使谱峰得到增强,此时空间谱达到最大值,其对应的角度即为信号源的方位角。仿真分析及实验数据处理结果表明,与常规MUSIC算法相比,该算法具有更尖锐的谱峰、更高的估计精度,能够实现更好的空间谱估计。 相似文献
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The transmission spectrum of single-crystal silicon in the range of 2.75?C3.25 eV has been obtained experimentally. An empirical formula is proposed to describe the spectral dependence of the optical density. The energy of the direct transition at the saddle point is found to be E(??15) ? E(??25??) = 3.43 eV. Analysis of the spectral dependence showed that the observed absorption corresponds to direct transitions to the van Hove singularity M 1 of the conduction band. 相似文献
20.
Adsorptive removal of direct azo dye from aqueous phase onto coal based sorbents: a kinetic and mechanistic study 总被引:12,自引:0,他引:12
Venkata Mohan S Chandrasekhar Rao N Karthikeyan J 《Journal of hazardous materials》2002,90(2):189-204
This communication presents the results pertaining to the investigation conducted on color removal of trisazo direct dye, C.I.Direct Brown 1:1 by adsorption onto coal based sorbents viz. charfines, lignite coal, bituminous coal and comparing results with activated carbon (Filtrasorb-400). The kinetic sorption data indicated the sorption capacity of the different coal based sorbents. The sorption interaction of direct dye on to coal based sorbents obeys first-order irreversible rate equation and activated carbon fits with the first-order reversible rate equation. Intraparticle diffusion studies revealed the dye sorption interaction was complex and intraparticle diffusion was not only the rate limiting step. Isothermal data fit well with the rearranged Langmuir adsorption model. R(L) factor revealed the favorable nature of the isotherm of the dye-coal system. Neutral solution pH yielded maximum dye color removal. Desorption and interruption studies further indicated that the coal based sorbents facilitated chemisorption in the process of dye sorption while, activated carbon resulted in physisorption interaction. 相似文献