Estimating local mean signal strength of indoor multipathpropagation

We explore techniques for the measurement of local mean signal strength at 900 MHz and 2 GHz. In particular, we characterize the impact of transmitter and receiver antenna rotation on the estimated local mean. Then, we explore the collection of high resolution data while moving along a linear trajectory and using linear averaging techniques to estimate the local mean. With this information, the best measurement techniques can be chosen depending on the required speed versus accuracy tradeoff. Finally, we use a ray tracing propagation model to evaluate different methods of calculating the local mean signal strength for indoor environments     

Exact symbol error probability of a Cooperative network in a Rayleigh-fading environment

In a distributed spatial diversity wireless system, not all antennas are located at one station as in classical transmit diversity systems, but are dispersed at different, possibly mobile, stations in the network. Transmit diversity is created when the selected stations assist a sender by relaying its information signal to the destination. In this letter, we present an exact average symbol error rate analysis for the distributed spatial diversity wireless system with K amplifying relays in a Rayleigh-fading environment. The average symbol error rate formula allows us to clearly illustrate the advantage that the distributed diversity system has in overcoming the severe penalty in signal-to-noise ratio caused by Rayleigh fading. Using simple bounds on the probability of error, we show that the cooperative network presented in this letter achieves full diversity order.     

Wavelet-based estimation of the nonstationary mean signal inwireless systems

A new technique is described for estimating the nonstationary mean signal received at a mobile station in a Rayleigh fading environment. The estimate is based on samples taken at the midpoints between the local minima of the received envelope. The continuous wavelet transform is used to estimate the local minima. An estimate of the mean signal is obtained using a fixed number of local minima. This technique requires neither an estimate of the mobile speed nor an adaptive temporal averaging window in contrast to other estimators. Simulations show that the mean signal is estimated well in a nonstationary environment with variable mobile speed     

Turbo-BLAST: performance evaluation in correlated Rayleigh-fading environment

Theoretical investigations of spatially correlated multitransmit and multireceive (MTMR) links show that not only independently and identically distributed links, but also spatially correlated links can offer linear capacity growth with increasing number of transmit and receive antennas. We explore the suitability of the turbo-BLAST architecture in correlated Rayleigh-fading MTMR environments. In particular, for an MTMR system with a large number of receive antennas, a near optimal performance can be achieved by the turbo-BLAST architecture in spatially and temporarily correlated Rayleigh-fading environments. The performance of turbo-BLAST, in terms of both bit-error rate and spectral efficiency, is analyzed empirically in indoors and correlated outdoor environments.     

基于射线跟踪的小区信号强度估计

基于经验模型的无线信号强度估计方法无法针对具体物理场景,估计结果精度低,无法满足移动通信网络规划和优化的需要。射线跟踪技术能依据场景信息跟踪电波传播路径,但现有的反向跟踪方法在进行室外成片区域信号强度估计时复杂度高,无法实用。为提高估计结果的精度,降低估计方法的复杂度,提出了一种正向跟踪信号强度估计方法,将基站天线处发射的电磁波模拟成离散的射线,在考虑建筑物形状、分布信息的基础上采用基于网格的搜索算法跟踪射线路径,在接收点处对反射、绕射射线接收合并,最终得到基站覆盖区域的信号强度分布。仿真结果表明该方法的场强估计结果和实测数据吻合程度远大于经验模型估计方法,并且80%左右的估计结果和实测数据的误差在12 dBm以内,可应用于移动通信网络规划和优化。     

Spatial spectrum estimation in a coherent signal environment using an array in motion

Spatial spectrum estimation utilizing an array in motion is here investigated for dealing with coherent arrivals in a multiple signal environment. The effect of estimating the spatial correlations while the array is moving is studied in terms of the decorrelation it produces, the change it causes in the eigenvalues of the correlation matrix, and the improvements obtained in the measured spectrum. Cases of both fixed and varying angle of arrival are investigated, The former arises with distant sources and will, with a sufficiently long estimation interval, emulate uncorrelated sources and given correspondingly sharp spectra. The latter arises with nearby sources and will allow them to be distinguished but will be attended by spectral shift and broadening, and loss of resolution. It is shown that meaningful estimates of the arrival angles can nevertheless be made. Specific illustrations are worked out using a seven-element, sparse, nonuniformly spaced linear array utilizing the well-known superresolution spectral estimators-the maximum likelihood (ML) method, the method of linear prediction (LP), and the method of multiple signal classification (MUSIC).     

Local mean signal estimation over Nakagami‐m fading channels

Accurate and fast algorithms for the local mean signal level estimation are very important for the successful implementation of many wireless communication enabling techniques such as handoff, power control, and adaptive gain control schemes. In this paper, we present on‐line simple‐to‐implement (i) minimum variance unbiased and (ii) maximum likelihood estimators for the local mean signal power estimation in the decibel domain. We consider a generalized Nakagami‐m fading environment and show that these estimators are asymptotically efficient in the number of samples and in the fading parameter m. Numerical and simulation results confirm that these estimators outperform the sample mean estimator and quickly approach the Cramer–Rao lower bounds. Copyright © 2006 John Wiley & Sons, Ltd.     

多径环境下TDDM-BOC信号伪码周期估计

针对低信噪比下存在多径效应的时分数据调制二进制偏移载波( TDDM-BOC )调制信号的伪码周期估计难题,提出了一种基于二次谱的TDDM-BOC信号伪码周期估计算法。该算法首先推导出多径环境下TDDM-BOC信号模型,然后求出多径TDDM-BOC信号的功率谱,再求其二次谱,最后通过检测二次谱的尖峰脉冲间的间距得到多径环境下TDDM-BOC信号的伪码周期。实验过程中采用累加平均的方法可以达到降噪和精确估计的目的。仿真结果表明：该算法能够在多径环境下对TDDM-BOC信号伪码周期进行有效估计,且估计性能与多径环境有密切关系,这为今后我国“北斗冶导航接收设备的开发提供了一定的理论参考。     

基于功率估计的高动态GNSS抗干扰零陷展宽算法

全球卫星导航系统(GNSS)接收机在高速运动状态下时,干扰来向的快速变化会导致阵列抗干扰算法性能下降,为此,提出一种基于功率估计的抗干扰零陷展宽算法。根据特征值将采样协方差矩阵划分为信号子空间与噪声子空间,通过子空间投影确立信号导向矢量与功率的线性关系;利用线性关系估计干扰功率,并根据零陷展宽需求重新设定干扰区域内的信号功率;最后,以干扰区域内功率的估计值为基础重构干扰加噪声协方差矩阵,求解阵列权矢量。仿真表明,相比其他零陷展宽算法,所提算法在相同展宽下具有更深的零陷,阵列输出信干噪比也有所提升。     

Estimation of the mean of a quantized signal

The accuracy with which the mean of an analog signal can be estimated from the mean after quantization by an analog/digital converter is examined. The mean of the quantized signal is a good measure of the mean of the input, down to lower values of input noise than is commonly supposed.     

Statistical properties of the RMS delay-spread of mobile radiochannels with independent Rayleigh-fading paths

The statistical properties of the RMS delay-spread for mobile radio channels with independent Rayleigh-fading paths are investigated. We give analytical formulas for the statistical distribution of the local RMS delay-spread for two independent paths (two-delay model). We show that there is a considerable difference between the mean RMS delay-spread and the expected value of the local RMS delay-spread if the number of paths is small; however, this difference vanishes for a large number of paths     

Source enumeration in a correlated signal environment

The authors present a simple method for determining the number of signals impinging on a uniform linear array that is applicable even in the extreme case of fully correlated signals. This technique uses what they term modified rank sequences, which is a modification of the construction implicit in the matrix decomposition method of Di (1981). They prove that if a particular rank sequence stabilizes (the last two terms of the sequence are equal) to a value strictly less then the common row size of the defining block matrices, then this value equals the number of signals, provided that the number of signals has not exceeded a Bresler-Macovski (1986) type bound. Using the above characterization of stability, they formulate an algorithm that either determines the number of signals or indicates that the resolution capability of the algorithm has been exceeded. They also provide theorems that show that under certain conditions, a rank sequence can stabilize to a value strictly less than the number of signals. This result allows them to find simple counterexamples to all of the existing rank sequence methods     

Robust parameter estimation of a deterministic signal in impulsivenoise

This paper presents a robust class of estimators for the parameters of a deterministic signal in impulsive noise. The proposed technique has the structure of the maximum likelihood estimator (MLE) but has an extra degree of freedom: the choice of a nonlinear function (which is different from the score function suggested by the MLE) that can be adjusted to improve robustness. The effect of this nonlinear function is studied analytically via an asymptotic performance analysis. We investigate the covariance of the estimates and the loss of efficiency induced by nonoptimal choices of the nonlinear function, giving special attention to the case of α-stable noise. Finally, we apply the theoretical results to the problem of estimating the parameters of a sinusoidal signal in impulsive noise     

Statistical suppression of interference with diversity in a mobile-radio environment

In a small-cell mobile-radio system different base stations transmit different signals simultaneously, and at the same carrier frequency, to mobile vehicles in their respective cells. It is desirable that these cochannel stations be placed as close to one another as possible without creating undue interference. However, as a vehicle moves within a cell, both the desired and undesired signals exhibit Rayleigh (local) fading, creating a relatively high probability that the interference exceeds the signal. On the other hand, at the frequencies contemplated it is relatively simple to construct additional antennas that provide independently fading signals, thereby offering the use of diversity techniques. Three different switch diversity techniques are considered, and the improvements produced by each are calculated. It is also shown that some are effective in combating an additional difficulty of the mobile-radio environment; this difficulty is that while the signal received in a moving vehicle is locally Rayleigh, the mean of this Rayleigh process changes slowly with time.     

Statistical modeling of the received signal envelope in a mobileradio channel

Propagation loss measurements taken in the Ottawa region in the 900-MHz frequency band are reported and discussed. Significant statistical parameters for a mobile radio channel, such as the mean, the standard deviation of the signals, the level crossing rates and the fading distance, are presented. The signal is first transformed from a time scale to a distance scale; it is then separated into slow and rapid variation components, a low-pass filter with a cutoff point corresponding to 0.125 cycle per wavelength being used to estimate the slow variation component. The statistical analysis of the rapid variation is related to the Rice probability law and to a direct-component-to-multipath-component ratio. For the medium-density urban area under consideration, this ratio is shown to change from around 5 dB to around 9 dB as one moves from medium-density urban to the surrounding open areas     

Statistical analysis of jitter estimation in ADC

Analytical expressions for jitter estimation under conditions of sinusoidal signal at ADC input are obtained for the case of no prior knowledge of jitter value. Statistical analysis of the obtained estimates is conducted. Numerical modeling results are presented. Applicability limits for the suggested estimates are obtained.     

Mobile location using signal strength measurements in a cellular system

In a high-capacity mobile telephone system using cellular technology, a mobile location technique which determines the radio zone in which a moving vehicle exists is one of the most important techniques for the system control. A mobile location technique using a signal strength measurement scheme is described. The probability that a mobile is judged to exist in a certain zone (zone selection rate) is first defined. Dependency of this rate on land mobile propagation characteristics is then discussed in detail. A field test for the justification of this location technique was carried out in the Tokyo metropolitan area in which the field test results agreed well with the estimated values.     

Statistical properties of the instantaneous frequency for a noisy signal

In this paper a comprehensive study of the statistical properties of the instantaneous frequency is presented. A rather crude estimate is given in the both situation where the signal to noise ratio tends respectively towards zero or infinity. For an intermediate state a more refined and exact computation, which recovers the asymptotic situations, has been performed. Two main results must be emphasized; the first deals with the bias of the instantaneous frequency and the second with the good immunity of this frequency against the noise.