On the capacity of log-normal fading channels

In this letter we provide an analytical expression for the moments of the capacity for the log-normal fading channel. Since the developed expression involves infinite series, we show that the error that results from the truncation of these series is insignificant. We also analyze in more details the ergodic capacity by giving a simpler expression for the remainder of the truncated series. Relying on the fact that the sum of log-normal Random Variables (RV) is well approximated by another lognormal RV, we further utilize the obtained results to approximate the capacity of diversity combining techniques in correlated lognormal fading channels. The results that we provide in this letter are an important tool for measuring the performance of communication links in a log-normal environment.     

A Tight Closed-Form Approximation of the Log-Normal Fading Channel Capacity

The log-normal probability distribution has been commonly used in wireless communications to model the shadowing and, recently, the small-scale fading for indoor ultrawideband (UWB) communications. In this paper, a tight closedform approximation of the ergodic capacity over log-normal fading channels is derived. This expression can be easily used to evaluate and compare the ergodic capacities of communication systems operating over log-normal fading channels. We also utilize this expression to show that the capacity of a multi-antennas UWB system operating over the IEEE 802.15.3a channel can be improved mainly through receive diversity.     

A new power control function for multirate DS-CDMA systems

This paper proposes a closed-form power control function for the reverse link of a multirate single chip-rate variable processing gain DS-CDMA system in a mobile radio environment that assumes a Rayleigh fading channel with log-normal shadowing and path loss. A closed-form open-loop power control function based on a newly defined traffic exponent is proposed, and nonlinear programming is used to perform the optimization. In addition, a user model that allows users to dynamically switch traffic rates for different connection applications is implemented. Results obtained using random chip sequences demonstrate improvement in the system capacity with the new power control function compared to the conventional power control function. Furthermore, the proposed function also simplifies the power control processing     

A general analysis of signal strength handover algorithms withcochannel interference

In this paper, the problem of computing cochannel interference statistics in signal strength measurements in mobile radio systems is presented. In a cellular environment with cross-correlated log-normal shadowings, extensions of Wilkinson's method and Schwartz and Yeh's (1982) method are proposed for evaluating the statistics of differences between signal strengths that a mobile terminal measures on the links to any pair of base stations in the presence of cochannel interferers. The derived statistics are then used in the performance analysis of relative signal strength handover algorithms. Results provided by the two methods are compared with simulation results, in order to assess their accuracy, and computational issues are addressed. From numerical results, it is also seen that handover algorithm performance has a noticeable dependence on both cross correlation among shadow fadings and the interference level. Finally, it is seen that previous approaches to derive cochannel interference statistics in the presence of log-normal shadowing can be obtained as particular cases     

Hopfield神经网络的存贮容量

我们把理论推导与数值模拟相结合得出一个较好的误差函数近似解析式。应用该解析式分析了Ｈｏｐｆｉｅｌｄ神经网络绝对存同容量，得到了一更严格的结果。     

最大比宏分集下的CDMA系统反向容量分析

本文综合考虑快衰落,阴影衰落和路径衰减的影响,建立了最大比宏分集下CDMA系统反向信道分析模型并推导出了中断率(outage probability)表达式.数值结果表明,采用宏分集后反向容量随参与宏分集基站数的增加而大大提高了,而且移动台的反向性能和其位置有关,在小区边界处性能最佳.     

时延约束的冗余通孔插入方法

Redundant via （RV） insertion is a useful mechanism to enhance via reliability. However, when extra vias are inserted into the design, the circuit timing might be changed. Therefore, how to insert RV under the timing constraints is the main challenge. In this paper, we introduce a new model to compute the distance between a RV and the corresponding single via, put forward a new RV type, which is called the long length via （LLV）, and then present an improved RV insertion method considering the timing constraints. This computing model can certify that the timing, which is obtained aider inserting a RV, is not greater than the original timing. Meanwhile, the new RV type LLV can increase the possibility of RV insertion; this method provides a global perspective for the RV insertion. Considering the timing constraints, the total redundant via insertion rate is 85.38% in the MIS-based method, while our proposed method can obtain a high insertion rate 88.79% for the tested circuits.     

Power control, capacity, and duality of uplink and downlink in cellular CDMA systems

Accurate power control is an essential requirement in the design of cellular code-division multiple-access (CDMA) systems. In this paper, we contribute three main themes to the power control problem. First, we derive an efficient algorithm for computing minimal power levels for large-scale networks within seconds. Nice and intuitive conditions for the existence of feasible power solutions follow from this approach. Second, we define the capacity region of a network by the set of effective spreading gains, or data rates, respectively, which can be supplied by the network. This is achieved by bounding the spectral radius of a certain matrix containing system parameters and mutual transmission gain information. It is shown that the capacity region is a convex set. Finally, we reveal an interesting duality between the uplink and downlink capacity region. In a clear-cut analytical way, it substantiates the fact that the uplink is the more restricting factor in cellular radio networks. The same methods carry over to certain models of soft handover. In the case that the channel gains are subject to log-normal shadowing, we introduce the concept of level-/spl alpha/ capacity regions. Despite the complicated structure, it can still be shown that this set is sandwiched by two convex sets coming arbitrarily close as variance decreases.     

Variable-Range Transmission Power Control in Wireless Ad Hoc Networks

In this paper, we investigate the impact of variable-range transmission power control on the physical and network connectivity, on network capacity, and on power savings in wireless multihop networks. First, using previous work by Steele (1988), we show that, for a path attenuation factor a = 2, the average range of links in a planar random network of A m² having n nodes is ~aradicA/n1. We show that this average range is approximately half the range obtained when common-range transmission control is used. Combining this result and previous work by Gupta and Kumar (2000), we derive an expression for the average traffic carrying capacity of variable-range-based multihop networks. For a = 2, we show that this capacity remains constant even when more nodes are added to the network. Second, we derive a model that approximates the signaling overhead of a routing protocol as a function of the transmission range and node mobility for both route discovery and route maintenance. We show that there is an optimum setting for the transmission range, not necessarily the minimum, which maximizes the capacity available to nodes in the presence of node mobility. The results presented in this paper highlight the need to design future MAC and routing protocols for wireless ad hoc and sensor networks based, not on common-range which is prevalent today, but on variable-range power control     

LMS Markov model and its use for power control error impact analysis on system capacity

We present a wideband land mobile satellite channel model based on a three-state Markov chain model valid for any kind of satellite constellation and for L, S, and Ka bands. Data from measurement campaigns was used to extract the parameters for the statistical distributions involved in the model. We also present a methodology describing how to use the proposed channel model to interface with system-level analysis. We use the time series generated by the model to parameterize power control (PC) imperfection as a function of the environment and user speed by acting upon the time series through a seven-level PC algorithm. We then apply the obtained parameterization to the analysis of a direct sequence-code division multiple-access scenario with users requiring different quality-of-service (QoS). It is shown that request of different QoS produces an unbalance in the users power distribution and less users can be served with the most demanding QoS. PC error worsens this effect and considerably reduces capacity efficiency which is highly dependent on the environment and mobile speed. Bit-error rate statistics are also investigated through the log-normal characterization obtained by using the channel model obtaining results on the effect of required E/sub b//(N/sub o/+I/sub o/) of a particular user.     

Macroscopic diversity performance measured in the 800-MHz portableradio communications environment

Analysis of 816 MHz residential propagation data is presented, demonstrating the usefulness of macroscopic selection diversity in combatting shadow fading produced by buildings and other large geographic features in the portable radio communication environment. Macroscopic diversity can reduce the link margin needed for 99% reliability by 10 dB. The analysis of these data indicates that log-normal shadow fading is partially correlated on the paths between a portable user and several surrounding ports. A two-component shadow-fading model duplicates this behavior. One log-normal term is identical for all paths from a given location and characterizes the propagation losses associated with the location. A second log-normal component is independent for each path and characterizes the remainder of the path to the port. The model fits the propagation data as well. A standard deviation of 8 dB for the path-specific term fits subsets of the available data well and is consistent with the standard deviation of shadow fading in the mobile (vehicular) communication environment     

Spectrum efficiency for log-normal shadowed Rician/Rician channels

Analysis is carried out on the spectrum efficiency in a microcellular mobile radio environment using a fourth power path loss law. A new technique for evaluating outage probabilities for channels affected by Rician fast fading and log-normal shadowing is presented, and new spectrum efficiency against outages probability curves for these channels is obtained and discussed     

地海面复合场景的杂波建模方法

地海杂波对采用前视以及下视成像的机载、弹载雷达具有十分重要的影响,对港口成像,会同时受到地杂波和海杂波的影响。文章提出复合场景杂波的后向散射系数模型,推导了复合场景杂波的幅度分布公式,并对由对数正态杂波与韦伯杂波组成的复合杂波分布进行了仿真。仿真中,地海杂波功率比选取了0.001到50之间的一系列典型值,并将不同情况下复合杂波的幅度分布与单一对数正态分布模型和Weibull分布模型得到的杂波分布进行了比较,结果表明二者的复合杂波分布依赖于二者的功率比。     

On the Applicability of Average Channel Capacity in Log-Normal Fading Environment

The statistical characterization of channel capacity in slow fading environment modeled by log-normal probability density function is considered. The probability density function of channel capacity is found to be positively skewed and significantly departs from bell shaped curve for higher values of σ _dB . The computation of first two moments of channel capacity provides a measure for relative fluctuation in terms of coefficient of variation (CV). It is noted that the value of CV is quite high in lower range of SNR and starts declining with increasing SNR. This may question the applicability of average channel capacity as a performance measure in slow fading scenario and accordingly a more appropriate measure is based on outage capacity. A simple procedure based on three-point estimate is outlined to obtain the approximate expression for higher order moments of channel capacity and they are found to be in excellent agreement with exact results.     

On the inverse symbol-error probability for diversity reception

This paper addresses the problem of finding the inverse symbol-error probability (SEP) expression for coherent detection of M-ary phase-shift keying with multichannel reception and maximal ratio combining in Rayleigh fading. To this aim, we derive upper and lower bounds on SEP that are simply invertible and uniformly tight for all values of signal-to-noise ratio. This enables us to obtain tight bounds on the inverse SEP and on the symbol-error outage (SEO), i.e., SEP-based outage probability. As an example of application to digital mobile radio, the SEO in a log-normal shadowing environment is analyzed.     

Diversity Improvement in Frequency-Hopping Multilevel FSK Systems Under the Influence of Rayleigh Fading and Log-Normal Shadowing

Recently, various frequency-hopping schemes have been proposed for possible application to digital mobile radio telephony. While the advantage of the inherent frequency diversity against fading is well known, the improvement in the system performance due to the use of space diversity has not been studied. In this paper we analyze the performance of FH-MFSK under the influence of Rayleigh fading and log-normal shadowing due to the combined use of frequency and space diversities. It is shown by analysis that the system capacity can be increased from the corresponding nondiversity figure by 26.3 percent relative to the full system capacity (i.e., 209 users) with the use of two diversity branches at channel condition of 10 dB normalized area mean and worst case of shadowingsigma = 12dB. Also, graphical results are given for different channel environments, and required signal-to-noise ratio.     

Cochannel Interference in High-Capacity Mobile Radio Systems

The probability of cochannel interference is evaluated for a mobile radio system operating in Rayleigh fading and log-normal shadowing environment. All cochannel cells surrounding the base station are taken into consideration in this evaluation. The results obtained are used to calculate the reuse distance and the cluster size (number of cells in a group). The blocking probability, the number of channels in each cell, the protection ratio, and the standard deviation are taken as parameters in this evaluation. The results show that shadowing has a severe effect on the interference level and on the channel reuse distance ratio.     

Delay spread statistics in vicinity of same-frequency repeater

The statistics of the delay spread in a two-path mobile radio environment where every path is subject to log-normal shadowing are derived. The channel profile thus considered consists of two delta functions whose power levels are in addition, correlated. Analytical expressions for the probability density function, the mean and the standard deviation of the resulting delay spread are obtained and compared with simulation results     

Reverse Link Performance of a DS-CDMA System With Both Fast and Slow Power Controlled Users

In this paper the performance of the reverse link of a multicell DS-CDMA system with coexisting open-loop and closed-loop power controlled users transmitting heterogeneous traffic is analyzed. Real-time and non-real-time traffic performance expressions are obtained. The analysis includes a different channel coding scheme for each traffic type selected in accordance to their specific QoS requirements. Moreover, the study takes into account the effect of frequency-selective Nakagami-m fading with arbitrary parameters, correlated log-normal shadowing, power control imperfections and selection-based macroscopic diversity. How the power control imperfections, the number of resolvable paths, or the proportion of simultaneous open-loop and closed-loop power controlled users affect the reverse link capacity of the system is discussed in detail. Analytical results are also given for systems with different processing gains and for propagation environments with different multipath intensity profile (MIP) distributions.