Performance analysis of channelized cellular systems with dynamic channel allocation

We present an analytical model to compute the blocking probability in channelized cellular systems with dynamic channel allocation. We model the channel occupancy in a cell by a two-dimensional (2D) Markov chain, which can be solved to obtain the blocking probability in each cell. We apply our analytical model to linear highway systems with and without lognormal shadowing and then extend it to 2D cellular systems with lognormal shadowing. We show that, for linear highway systems, distributed dynamic channel-allocation schemes perform similarly to the centralized dynamic channel-allocation schemes in terms of blocking probability. However, for 2D cellular systems, the improvement in the performance is significant and the reduction in the blocking probability in systems with distributed dynamic channel allocation is by almost one order of magnitude, when compared to that in systems with centralized dynamic channel allocation. In practice, our analysis of linear highway systems is applicable to Digital European Cordless Telephony (DECT) and that of 2D cellular systems is applicable to global systems for mobile communications (GSM).     

Systems engineering education

The article discusses some basic principles underlying systems engineering, and the translation of these principles to practices such as to enable the engineering of trustworthy systems of all types that meet client needs. The article is concerned with systems engineering education. Thus, it is inherently also concerned with systems engineering, as this provides a major component of the material that is important for systems engineering education. After setting forth some of the necessary ingredients for success in systems engineering, we devote some comments to objectives for and needs in systems engineering education     

MIMO系统一种新的功率分配算法及容量分析

在不额外增加发射功率和带宽消耗的情况下,注水功率分配算法能够获得最大的多输入多输出(MIMO)系统容量.基于拉格朗日乘数法,推导给出了MIMO系统注水功率分配算法的显式解.利用信道冲激响应矩阵的奇异值分解(SVD)算法,推导给出了注水功率分配算法MIMO系统的容量分析公式.利用数字波束形成(DBF)技术,提出了一种新的功率分配算法,推导给出了该算法MIMO系统的容量分析公式.仿真结果表明,提出的功率分配算法的系统容量虽然略低于注水功率分配算法的系统容量,但它的计算复杂度较低.     

Systems engineering in an age of complexity

This work considers the creation of complex engineered systems (CES) and the systems engineering approach by which they are designed. The changing nature of the challenges facing systems engineering is discussed, with particular focus on the increasing complexity of modern systems. It is argued that modern complexity poses a major challenge to our ability to achieve successful systems and that this complexity must be understood, predicted and measured if we are to engineer systems confidently. We acknowledge previous work, which concluded that in complex systems, failures ("accidents") may be inevitable and unavoidable. To further explore potential tools for increasing our confidence in complex systems, we review research in the field of complexity theory to seek potentially useful approaches and measures and find ourselves particularly interested in the potential usefulness of relationships between the magnitudes of events and their frequency of occurrence. Complexity theory is found to have characterized naturally occurring systems and to potentially be the source of profitable application to the systems engineering challenge, viz., the creation of complex engineered systems. We are left with the tentative conclusion that truly complex systems, with our present understanding of complex behavior, cannot be designed with a degree in confidence that is acceptable given our current expectations. We recommend that the discipline of systems engineering must investigate this issue as a matter of priority and urgency and seek to develop approaches to respond to the challenge.     

Indirect closed-loop systems identification of distributed systems

In many cases it is impossible to remove the feedback during systems identification as it will make the system unstable. This paper presents an identification method for spatially interconnected distributed systems with identical subsystems operating in closed-loop feedback control. The proposed method takes into consideration the boundary conditions. The approach provides parameters estimate with minimum bias for unstable plant models when there is additive colored noise in output data. This yields consistent parameters estimate and, compared with other techniques to identify such systems under similar situations, takes far less time. The method is illustrated for two-dimensional systems (one for time and one for space), but is equally applicable for systems having more dimensions in space. The proposed technique is for general two-dimensional systems which may be causal, semi-causal (spatially interconnected systems) or non-causal. The effectiveness of the approach is demonstrated with a simulation example.     

Performance of binary and quaternary direct-sequencespread-spectrum multiple-access systems with random signature sequences

The performance of synchronous and asynchronous, binary and quaternary (with and without offset) direct-sequence spread-spectrum multiple-access (DS/SSMA) communication systems using random signature sequences and arbitrary chip waveforms is investigated. The average probability of error at the output of the correlation receiver is evaluated using a characteristic-function approach for these systems. Numerical results are presented that illustrate performance comparisons between systems using random and deterministic signature sequences, synchronous and asynchronous systems, systems with rectangular or sinewave chip waveforms, and binary and quaternary systems with the same data rates and bandwidth. In all cases, the accuracy of the Gaussian approximation is also examined     

Capacity of DS/CDMA communication systems with optimum spectraloverlap

We consider frequency overlapped DS/CDMA (FO/CDMA) communication systems where a number of DS/CDMA systems share frequency bands with adjacent systems. We analyze the multiple-access interference from adjacent systems with arbitrary amount of frequency overlap and compare the capacity of FO/CDMA with that of single wideband CDMA (WCDMA). The optimum amount of overlap increases with the number of overlapped systems. However the maximum capacity is obtained when the optimum number of systems are overlapped by half null-to-null bandwidth. It is shown that the FO/CDMA yields higher capacity in the case of relaxed bit error rate requirement and low decay rate of multipath intensity profile. Otherwise, WCDMA is superior     

多领航者网络化系统的动态群集运动

针对时变动态切换拓扑下具有多个领航者的网络化系统群集运动问题,本文分别给出了一阶／二阶网络化系统的控制算法,并对所提出的控制算法进行了理论分析。运用现代控制理论、代数图论和矩阵论等分析工具,研究了当通信拓扑为动态联合连通时,系统可以实现群集运动,即系统的运动轨迹都收敛到由多个领航者构成的凸包中。通过对系统信息拓扑连通部分的进一步研究,得到了二阶网络化系统群集运动的约束条件。最后应用仿真实验验证了结论的正确性。     

A comparison of systems engineering programs in the United States

Given the length of time systems engineering has been taught in the US, it is now appropriate to examine the types of programs being offered and to compare and contrast these programs. The paper provides this comparison with a view toward the future of systems engineering education in the US. In particular, we first examine the US undergraduate and graduate programs in systems engineering in order to understand what is taught and how it is taught. Using cluster analysis, we identify four distinct types of systems engineering undergraduate programs, and an informal analysis examines the directions in the systems engineering graduate programs. Next we look at issues in systems engineering education, which have shaped the development of the curricula over the last thirty years. These include the definition of systems engineering, associated professional societies, similar degree types, the role of an undergraduate systems engineering degree, and the role of information technology in systems engineering. We conclude with opportunities for systems engineering education within the US with regard to curricula directions and job opportunities     

Performance analysis of atmospheric optical subcarrier-multiplexing systems and atmospheric optical subcarrier-Modulated code-division multiplexing systems

This paper analyzes the performance of the atmospheric optical subcarrier multiplexing (AO-SCM) systems and the atmospheric optical subcarrier-modulated code-division multiplexing (AO-CDM) systems. The average received carrier-to-interference-plus-noise ratio (CINR) of the AO-SCM systems and the AO-CDM systems on a turbulence channel with the scintillation and the nonlinearity of a laser diode is derived. It is shown that the received CINR of the AO-CDM systems is larger than that of the AO-SCM systems when the number of channels is four for the same optical modulation index (OMI), and vice versa, when the number of channels is 16 for the same OMI.     

Regulation of Photovoltaic Voltage

Manufacturing systems changed towards higher degrees of automation in the 1980s. Today's manufacturing systems again face a fundamental change. One of the key matters of this change is going to be the modularity of tomorrow's manufacturing systems. This article analyzes the industrial and technological background of this change from the perspective of a large manufacturing company in the automotive, consumer goods and automation industry. A seminal definition of modularity for manufacturing systems is given. A new categorization of manufacturing systems based on the granularity of their modules is presented. Within this categorization manufacturing systems are divided into standard-machine-based production systems, cell-based production systems, workstation-based production systems, and unit-based production systems. Advantages and disadvantages of the different concepts are discussed with respect to future requirements. Finally, challenges and trends of the future manufacturing technology are outlined.     

Active optics: A new technology for the control of light

Active optical systems are those in which real-time control over optical wavefronts is employed to optimize system perference in the presence of random distrurbances. Applications include 1) outgoingwave systems for maximizing the power density of a laser beam on a target and 2) received-wave systems for maximizing the angular resolving power of a telescope viewing a distant object through a turbulent atmosphere. In this tutorial-review paper, the basic concepts of active optics systems and their historical evolution are discussed, from early figurecontrol systems with a servo bandwidth of less than 1 Hz to the recently developed high-bandwidth systems for atmospheric compensation with bandwidths of several hundred hertz. A critical comparison of the various approaches to wavefront sensing is then made covering both coherent (laser) and incoherent (white-light)systems. Current techniques for wavefront correction including Bragg cells, segmented mirrors, thin-plate deformable mirrors, monolithic mirrms, and membrane mirrors are described. The performance analysis and optimization of closed loop systems is covered using two basic models. The paper concludes with a review of the design and performance of five current experimental active optical systems, with some comments on future applications.     

Reliability for Sparsely Connected Consecutive-k Systems

We introduce the system of consecutive failures with sparse d which is a natural extension of consecutive-k systems. Then a series of generalizations of consecutive-k systems are discussed, such as consecutive-k-out-n:F systems with sparse d, M consecutive-k-out-of-n:F systems with sparse d, and (n, f, k) :F systems with sparse d. We present the formulation for the system reliability of these generalized consecutive-k systems with various component settings in terms of the finite Markov chain imbedding idea, along with two numerical examples.     

BER performance of turbo-coded PPM CDMA systems on optical fiber

We obtain upper bounds on the bit error rate (BER) for turbo-coded optical code-division multiple-access (CDMA) systems using pulse position modulation (PPM). We use transfer function bounding techniques to obtain these bounds, so our results correspond to the average bound over all interleavers of a given length. We consider parallel concatenated coding (PCC) schemes that use recursive convolutional codes as constituent codes. We consider systems using an avalanche photodiode (APD), and treat APD noise, thermal noise, and multi-user interference using a Gaussian approximation. We compare the performance of turbo-coded systems with that of BCH-coded systems with soft-decision decoding, and that of concatenated coding systems with outer Reed-Solomon (RS) code and inner convolutional code. We show that turbo-coded systems have better performance than BCH-coded systems. We also show that concatenated systems have better performance than turbo-coded systems when the block length is small and the received laser power is somewhat large     

Expert systems: Artificial intelligence applied

This article provides an overview of expert systems, the topic of greatest current interest in Artificial Intelligence (AI). The article describes what an expert system is and sketches the mechanisms by which several of the better known systems operate. The prerequisites for constructing an expert system are given and the state of the art of current expert systems is indicated, with an extensive listing of these systems being provided. The article concludes with a forecast of the nature and applications of future expert systems.     

On the Calculation of Overflow Systems with a Finite Number of Sources and Full Availiable Groups

This paper deals with the calculation of loss probabilities in overflow systems with a finite number of sources and full available groups. An exact, explicit solution is derived for overflow systems with only one primary group. Furthermore, an exact method is applied in case of overflow systems with two primary groups. For overflow systems with an arbitrary number of primary groups an approximate method is developed which takes into account the variance of offered overflow traffic. This approximate method yields results which are in good agreement with exact calculations and simulation results.     

Low-complexity multiuser detectors for time-hopping impulse-radio systems

Impulse radio (IR) and especially time-hopping IR (TH-IR) systems have attracted considerable attention since their introduction in the context of ultra wide-band (UWB) systems in the early 1990s. Recently, with the U.S. Federal Communications Commission actions allowing for the wide-spread use of UWB radio systems, the interest in these systems has grown further. These systems promise to deliver high data rates in multiple access communication channels with very simple transmitter and receiver designs. The importance of multiuser detection for achieving high data rates with these systems has already been established in several studies. This paper studies several low-complexity multiuser detectors specifically designed for TH-IR radio systems. It is demonstrated that many multiuser detectors developed primarily for direct-sequence code division multiple access (DS-CDMA) systems can be used essentially without any change in TH-IR receivers. Further, several novel, low-complexity multiuser detectors that exploit the special signal structure used for transmission by TH-IR systems are developed. These novel detectors are analyzed both theoretically and via simulations. It is shown that a very simple iterative multiuser detector yields performance that is similar to that of a single-user system.     

Spectral analysis of instantaneous powers in single-phase and three-phase systems with use of p-q-r theory

Three linearly independent instantaneous powers have been defined in the time domain in three-phase four-wire systems with the use of p-q-r theory. Any three-phase circuit can be transformed into three single-phase circuits by the p-q-r transformation. Thus the instantaneous powers in any three-phase systems can be analyzed as the same way of instantaneous power in single-phase systems. This paper analyzes the instantaneous powers spectrally in the frequency domain for single-phase systems and three-phase systems. Each instantaneous power in three-phase systems has its own spectral pattern that is characterized by the spectral distribution of the system voltages and currents. The instantaneous power in single-phase systems has its own spectral pattern different from that of three-phase systems. From the spectral analysis of the instantaneous powers, powers are newly defined in the frequency domain. The definition of the powers is consistent through single-phase systems and three-phase systems and agrees well with the traditional definition of powers in sinusoidal single-phase systems. Based on the defined powers, some useful power quality factors are defined to evaluate power qualities for various circuit conditions.     

Performance of Noncoherent Direct-Sequence Spread-Spectrum Multiple-Access Communications

The performance of noncoherent reception in direct-sequence spread-spectrum multiple-access communications systems is investigated for additive white Gaussian noise channels. Analytical and numerical results on the probability of error are presented for binary andM-ary frequency-shift-keying data modulation with noncoherent demodulation and differential-phase-shift-keying data modulation with differentiallycoherent demodulation. Both synchronous and asynchronous systems are analyzed. Systems which employ deterministic as well as random signature sequences are considered. The multiple access capability of noncoherent DS/SS systems is evaluated and compared to that of coherent DS/SS systems with the same parameters. The comparison shows that the loss in the performance of DS/SSMA systems due to noncoherent reception can be considerably larger than the loss incurred to noncoberent single-user systems operating in additive Gaussian noise.     

Noncoherent Hybrid DS-SFH Spread-Spectrum Multiple-Access Communications

The performance of noncoherent reception in synchronous and asynchronous hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access communication systems operating through additive white Gaussian noise channels is investigated. Systems with binary andM-ary frequency-shift-keying modulation and noncoherent demodulation, as well as systems with differential-phase-shift keying modulation and differentially coherent demodulation, are examined and their probability of error is evaluated for random frequencyhopping patterns and signature sequences. The multiple-access capability of noncoherent hybrid spread spectrum is shown to be superior to that of noncoherent purely frequency-hopped spread spectrum and inferior to that of noncoherent purely directsequence spread spectrum for systems with the same bandwidth expansion. Comparison of hybrid systems with coherent and noncoherent demodulation shows a considerable loss in the performance of the noncoherent systems.