海面环境700MHZ频段传输特性测试与模型校正

在海面环境下通过船-岸测量方式对700 MHz频段的无线传输特性进行测量.基于实测数据分析,引入海面双径传输损耗模型对ITU-R P.1546-5标准传输模型进行校正,该校正模型可实现700 MHz频段无线传输损耗预测.在仿真中,分别利用自由空间模型、ITU-R P.1546-5模型和ITU-R P.1546-5校正模型对700 MHz频段的海面无线传输损耗进行预测,通过与实测数据对比分析,证明ITU-R P.1546-5校正模型预测结果准确性更高,能够为海面无线通信系统的设计提供重要依据.     

基于抛物方程的3.6 GHz典型应用场景传播特性分析

文中利用抛物方程(parabolic equation,PE)方法,从纵向剖面和区域覆盖两个维度,对3.6 GHz频点在都市、郊区、乡村三种典型场景下的传播特性进行分析,并将仿真结果与ITU-R P.1546方法仿真结果进行对比分析.分析结果表明:PE方法能够描述信号传输直射、绕射、反射波束,与各场景传播特点相匹配,具...     

调频广播传播预测方法分析与本地应用研究

分析了ITU-R建议所提供地面业务的点对面预测方法,采集了十一套调频广播信号在不同方位、不同距离的测量结果,通过理论与测量结果的对比分析,验证了ITU-R建议方法在中国区域的可用性.基于测试区域,对比城区、郊区、农村不同接收环境,三种不同地形精度,两类不同气象环境和七个不同标准偏差修正量条件下的预测精度,并在此基础上,提出了ITU-R建议方法在中国区域调频广播系统中的应用建议：一是充分考虑地面覆盖物对传播的影响;二是选用高精度的地形剖面数据;三是选用中国区域的大气折射参数的实测或统计分析值;四是针对特定区域分析,调整ITU-R建议方法中的标准偏差修正量.研究成果为ITU-R建议方法中国区域本地化改进以及广播业务规划提供了基础.     

A new family of illumination functions

A family of illumination functions is evaluated. The key property of these functions is that they are everywhere infinitely differentiable in the aperture and at the aperture edge. Patterns are calculated for linear and circular apertures, and results are compared with those given by other illumination functions. Improved performance is given for very low sidelobe designs. Truncated versions of these illumination functions are considered briefly, with encouraging results.     

ITU-R P.1546方法在中国陆地典型区域适用性研究

在解读、剖析ITU-R P.1546方法的基础上，通过对比北京周边平原地区和贵州喀斯特山区的测试结果和预测结果，分析了该方法在两类中国陆地典型区域的适用性.分析结果表明:1）在3 s和30 s高程精度下，平原地区均表现出较好的适应性，但提升高程精度可一定程度上减小预测误差；2）山区在3 s高程精度下具有良好适应性，粗粒度的高程数据将对发射天线等效高度及场强插值、地形余隙角修正值产生较大影响，其中3 s与30 s高程精度下的地形余隙角修正值的均值相差30.85 dB.研究结果可为ITU-R建议所提供传播预测方法的区域性应用及本地化研究等方面提供参考依据.     

Extraction of the aortic and pulmonary components of the second heart sound using a nonlinear transient chirp signal model

The objective of this paper is to adapt and validate a nonlinear transient chirp signal modeling approach for the analysis and synthesis of overlapping aortic (A2) and pulmonary (P2) components of the second heart sound (S2). The approach is based on the time-frequency representation of multicomponent signals for estimating and reconstructing the instantaneous phase and amplitude functions of each component. To evaluate the accuracy of the approach, a simulated S2 with A2 and P2 components having different overlapping intervals (5-30 ms) was synthesized. The simulation results show that the technique is very effective for extracting the two components, even in the presence of noise (-15 dB). The normalized root-mean-squared error between the original A2 and P2 components and their reconstructed versions varied between 1% and 6%, proportionally to the duration of the overlapping interval, and it increased by less than 2% in the presence of noise. The validated technique was then applied to S2 components recorded in pigs under normal or high pulmonary artery pressures. The results show that this approach can successfully isolate and extract overlapping A2 and P2 components from successive S2 recordings obtained from different heartbeats of the same animal as well from different animals.     

Immittance-domain Levinson algorithms

Several computationally efficient versions of the Levinson algorithm for solving linear equations with Toeplitz and quasi-Toeplitz matrices are presented, motivated by a new stability test. The new versions require half the number of multiplications and the same number of additions as the conventional form of the Levinson algorithm. The saving is achieved by using three-term (rather than two-term) recursions and propagating them in an impedance/admittance (or immittance) domain rather than the conventional scattering domain. One of the recursions coincides with recent results of P. Delsarte and Y. Genin (IEEE Trans., Acoust. Speech, Signal Proc., vol.ASSP-34, p.470-8, June 1986) on split Levinson algorithms for symmetric Toeplitz matrices, where the efficiency is gained by using the symmetric and skew-symmetric versions of the usual polynomials. This special structure is lost in the quasi-Toeplitz case, but one still can obtain similar computational reductions by suitably using three-term recursions in the immittance domain     

Comparison of diversity combining techniques for Rayleigh-fadingchannels

Several methods of diversity combining for a Rayleigh-faded channel are evaluated and compared. The methods considered are, for coherent reception, maximal ratio combining (MRC), selection combining (SC), and a generalization of SC, whereby the two (three) signals with the two (three) largest amplitudes are coherently combined. We will call this method second (third) order SC, and denote it SC2 (SC3). Similar techniques are also investigated for noncoherent reception, with equal gain combining (EGC) replacing MRC, and noncoherent versions of SC2 and SC3. Numerical results indicate that SC2 and SC3 significantly enhances the bit-error rate (BER) performance relative to that achievable with SC, and under certain conditions approaches the performance achieved by MRC or EGG. The performance enhancement of SC2 and SC3 is especially noticable for noncoherent reception, where EGC is seen to provide the best performance only for low BER values. In fact, when the BER is 10 ^-3 or greater, SC2 and SC3 performed comparably to EGG, and in some cases performed better than EGC     

An analysis of the effect of multiversions on the performance oftimestamp algorithms

The performance of a multiversion conservative timestamp algorithm is evaluated by analyzing the response time of operations in a distributed database system. The random communication delay in the transmission channels of a long-haul network supporting the distributed database system causes transmitted operations to be received out of order. According to rules that are dependent on the number of versions, the scheduler reorders the operations to preserve the consistency of the database. Operations encounter extra delay in the process of reordering. The system is modeled by a queuing network. Response-time distributions are obtained analytically. Numerical results are presented to show the effect of the number of versions on the performance     

The null field approach to electromagnetic scattering fromcomposite objects

An improved null-field approach to scattering from composite objects is reported. Several alternative expressions for the transition matrix of a composite object are derived that partly or completely avoid the geometrical constraints inherent in previous null-field results for a composite scatterer. Some of the new versions make use of Q-matrices for the open surfaces which are defined by the interfaces between the different parts of the composite scatterer. The numerical performance of the various alternatives is investigated for a number of test cases. Comparisons between alternative versions for the same scattering problem are made to provide a measure of the absolute accuracy of the computed null-field results. Whenever possible, the results are compared with other computed or measured results     

中央节目无线数字化覆盖工程规划试算电波传播模型研究

本文简要介绍了三种常用的电波传播模型,包括ITU-R P.1546、ITU-R P.526和Okumura-Hata,提出了一种用于对中央工程广播电视发射台站的场强覆盖进行仿真试算时使用的电波传播模型的方法,给出了模型确定的总体思路,并以广东省阳江市望瞭岭为典型案例,按照“三步走”原则,采用理论推导结合现场实测的方法,详细介绍了确定电波传播模型的过程,并给出结论。     

Efficient calculation of finite Gabor transforms

The Gabor transform may be viewed as a collection of localized Fourier transforms and as such is useful for analysis of nonstationary signals and images. We present a new approach to analyzing the Gabor transform and use it to study the various critically sampled discretizations that form the infinite-discrete, periodic finite-discrete, and nonperiodic finite-discrete versions of the transform. In particular, we distinguish between the analysis and synthesis forms of the transform, and introduce an intermediate operation that decomposes both forms into collections of independent Toeplitz operators. In the continuous, the infinite-discrete, and the periodic finite-discrete cases, this decomposition allows us to show that, for appropriate windows, the analysis and synthesis transforms are inverses of each other. In the nonperiodic finite-discrete case this relation no longer holds, but we are still able to use the decomposition and results on Toeplitz matrices to show that both the transform and the inverse transform of P discrete samples are computable in O(P log P) operations (after a setup cost of O(Plog²P)). Furthermore, we use the decomposition to study in detail the differences between the periodic and nonperiodic versions of the transform and to compare their conditioning     

CDMA系统中2D-RAKE接收机性能比较

该文探讨了CDMA系统中2D-RAKE接收机的各种可能形式,并对其性能进行了分析比较,最后给出了数值模拟结果。     

傅里叶红外光谱研究光敏剂5-氨基酮戊酸的光动力作用机制

本文测定了光敏剂5-氨基酮戊酸对人宫颈癌细胞HeLa光敏作用后的傅里叶红外光谱。结果显示：光敏作用后,HeLa细胞磷酸二酯基团的对称伸缩振动峰1085cm。和不对称伸缩振动峰1246cm。蓝移,强度下降;蛋白质酰胺Ⅰ带1656cm。发生蓝移,酰胺Ⅱ带1546cm^-1出现红移;CH2对称伸缩振动峰2858cm^-1,峰位蓝移2cm^-1,峰值明显减弱。结果表明：DNA、蛋白质和磷脂是5-氨墓酮戊酸光敏作用的主要靶分子。     

Hybrid TOA–AOA Location Positioning Techniques in GSM Networks

Positioning algorithms and their implementation in mobile networks are being investigated in the literature due to their importance in location services. Nowadays, the need for superior accuracy has cast attention to hybrid positioning techniques. In this paper, we introduce a novel algorithm for the identification of NLOS propagation using both angle and time estimates, which leads to enhanced versions of the Time of Arrivals and Angle of Arrivals positioning methods. Furthermore, a novel GSM procedure for the implementation of the latter techniques is proposed. In contrast to specified network-based GSM solutions (U-TDOA), the proposed requires minimum modifications in the GSM Phase 2+ infrastructure and protocol stack, and therefore increases the upgrade flexibility and minimizes the implementation cost. The proposed GSM positioning procedure has been experimentally validated using a GSM emulator and the modified signalling messages given by a measurement tool of the emulator are exhibited. Finally, the enhanced cost functions are experimentally evaluated using several GSM-like, high-capacity simulation environments and the results have shown significant reduction of the location error compared to the conventional techniques.     

Comments, with reply, on 'Solving the generalized eigenvalue problem with singular forms by M.D. Zoltowski

The above-titled letter (ibid., vol.75, no.11, p.1546-8, Nov. 1987) proposed two numerical algorithms for the solution of generalized eigenvalue problem Ax= lambda , where it is assumed that the matrix B is Hermitian. It was claimed by the author that standard algorithms are not available if the matrix B is singular. The commenters draw attention to the literature in this field based on the QZ algorithm. The author thanks the commenters for supplying the information but points out to prospective readers certain caveats with regard to use of the QZ algorithm.<>     

Reversible integer-to-integer wavelet transforms for imagecompression: performance evaluation and analysis

In the context of image coding, a number of reversible integer-to-integer wavelet transforms are compared on the basis of their lossy compression performance, lossless compression performance, and computational complexity. Of the transforms considered, several were found to perform particularly well, with the best choice for a given application depending on the relative importance of the preceding criteria. Reversible integer-to-integer versions of numerous transforms are also compared to their conventional (i.e., nonreversible real-to-real) counterparts for lossy compression. At low bit rates, reversible integer-to-integer and conventional versions of transforms were found to often yield results of comparable quality. Factors affecting the compression performance of reversible integer-to-integer wavelet transforms are also presented, supported by both experimental data and theoretical arguments.     

An efficient algorithm for superresolution in medium field imaging

In this paper, we study the problem of reconstruction of a high-resolution (HR) image from several blurred low-resolution (LR) image frames in medium field. The image frames consist of blurred, decimated, and noisy versions of a HR image. The HR image is modeled as a Markov random field (MRF), and a maximum a posteriori (MAP) estimation technique is used for the restoration. We show that with the periodic boundary condition, a HR image can be restored efficiently by using fast Fourier transforms. We also apply the preconditioned conjugate gradient method to restore HR images in the aperiodic boundary condition. Computer simulations are given to illustrate the effectiveness of the proposed approach. This research was conducted with support from the Army Research Office Grant DAAD 19-03-1-0261 and the National Science Foundation Grant CCF-0429481. Research supported in part by RGC Grant Nos. 7130/02P, 7046/03P, 7035/04P and 7035/04P and FRG/04-05/II-51.     

Performance analysis of multiple access protocols for multimediasatellite networks

In this paper, several TDMA-based packet multiple access protocols are studied and evaluated in the geostationary satellite environment. The distributed queueing random access protocol, DQRAP, originally proposed for HFC networks is adapted to the satellite environment. Another protocol, the announced retransmission random access protocol, ARRA, proposed for wireless networks is also studied. Both protocols are modeled and simulated in a VSAT network context. We then propose a new protocol which combines the advantages of both studied schemes and is more adapted to interactive multimedia applications over satellite uplinks. The generalized retransmission announcement protocol, GRAP, regroups the immediate access by contention at low loads, and the reservation access. At higher loads, to achieve a better channel efficiency. An analytical model is proposed to calculate the channel throughput obtained by GRAP under different loading conditions. Simulation results illustrate an improved throughput/delay characteristics and a higher protocol stability compared to both DQRAP and ARRA. Enhanced versions of the protocol are also proposed and evaluated to further improve its efficiency, with reasonable additional complexity     

Multichannel operation of an integrated acoustooptic wavelengthrouting switch for WDM systems

Polarization independent acousto-optic tunable filters (PIAOTF's) can operate as transparent wavelength-selective crossconnects to route signals in wavelength division multiplexed optical networks. In this paper, a new low power PIAOTF is characterized as a switch in multiwavelength operation, using four equally spaced lightwave signals with wavelengths between 1546 nm and 1558 nm. Interchannel interference due to sidelobe excitation is lower than -11 dB for single wavelength switching and is equal to -6 dB in the extreme case of simultaneous switching of all wavelength channels. Sources of interport and interchannel crosstalk for single and multiple wavelength switching are identified