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Cẩm nang dữ liệu không dây P10
MARKET OPPORTUNITY SECOND ERA OF LOW HANGING FRUIT Most carrier business planning personnel and hardware providers have long been captivated by the perceived market opportunity for data. In 1993 AT&T Wireless projected that 1 billion people will use wireless modems for electronic data communications by the year 2000.1 Since that was one-quarter of the population of the earth, only seven years in the future, the number was bound to draw attention. While that particular projection was patently absurd, for the next few years AT&T Wireless continued to espouse greatly reduced but still aggressive forecasts....
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Cẩm nang dữ liệu không dây P11
GREAT EXPECTATIONS When Bell Atlantic Mobile Systems (BAMS) launches its first . . . CDPD . . . system in Washington . . . it will initiate a new business that will impact the . . . bottom line by 1995. . . . The average monthly bill for cellular is dropping, and . . . new services such as data will boost those bills.1 This BAMS management expectation was common to all nascent data carriers of the period. But were their expectations realistic? With multiple carriers bringing increasingly untapped capacity to market, is it reasonable to believe that...
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Cẩm nang dữ liệu không dây P12
COVERAGE VERSUS CAPACITY Paraphrasing the late Tip ONeill: All coverage is local. With 1214-in. full wavelengths it is quite possible to encounter an ARDIS, BSWD, CDPD, or circuit switched cellular dead spot simply by walking to another position in a room. This annoying fact does not mean that all carriers operating near the same frequency band offer essentially the same coverage choices. Design trade-offs are made between area coverage and its close cousin, building penetration, versus subscriber capacity. ...
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Cẩm nang dữ liệu không dây P13
UNDERSTANDING AIRTIME PROTOCOLS THE PACKET REVISITED A packet is the information unit formed when a message is partitioned into more manageable sections for transmission and recovery. Most landline packets have three logical subsections created when control information is added to user data (.igure 13-1). Packets are not required to travel only on packet switched networks. They function quite nicely on circuit switched systems as welloften a source of confusion for persons first encountering adaptive packet assembly in Microcoms protocols sent over circuit switched facilities. ...
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Cẩm nang dữ liệu không dây P14
ESTIMATING AIRLINK CAPACITY: PACKET SYSTEMS The number of variables in a packet switched data radio system are virtually endless. This does not mean that the task of estimating user capacity is hopeless. Directionally accurate but labor-intensive results can be derived if one knows the basic conditions under which the data transfers occur. This most assuredly includes assumptions about the communications software being employed. Examples of the necessary effort are shown here by comparing ARDIS RD-LAP to CDPD. The all-important application example will be the 30-character inbound message whose CDPD component was captured in Appendix C....
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Cẩm nang dữ liệu không dây P15
ENABLING “SOFT” TECHNOLOGIES ALPHABET SOUP Thirty seconds into a review of communication product specifications one encounters a babble of vee-dot (V.) versus MNP variations, and mysterious acronyms such as EC2, ETC, and TX-CEL. It is unwise to dismiss this sometimes unintelligible gibberish as an unimportant attempt to break/protect vendor proprietary interests. These alphabetic designators are often surrogates for key communication developments required for the success of wireless data. This chapter is a simplified look at some nonhardware technologies, protocols, and communication standards that drive both network and device development. The focus is on modulation techniques, error detection/correction, and data compression. ...
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Cẩm nang dữ liệu không dây P16
DEVICE ALTERNATIVES COMBINATIONS AND PERMUTATIONS A bewildering array of subscriber unit options are available for wireless data ranging from fully integrated terminal/modem/radio units to multibox combinations of PCs, external modems, cellular transceivers, and portable faxes. A (too) simple representation of some of the terrestrial variations is illustrated in .igure 16-1. This convoluted collection of hardware alternatives is extraordinarily volatile.
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Cẩm nang dữ liệu không dây P17
CONNECTIVITY Cut the cord. Right now. Unfortunately, simply buying wireless data devices is the least of the problems, especially on packet networks. Actually getting applications to execute over wireless communications links leads to dozens of developmental barriers. Hardware, softwareeven airtime service providersdeliver some application assistance with their products, but the range of offerings, while clearly related, is far from uniform and is never enough. .urther, the terminology is often blurred. One companys toolkit is anothers middleware or operating environment or platform. Packet systems are the least uniform and most complex....
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Cẩm nang dữ liệu không dây P18
SYSTEMS AND SUBSYSTEMS CONTROL APPROACHES The airlink subsystem is defined as the span between the user hosts connection point and the subscriber unit. It includes the service providers message switch/area controller, base stations, and the radio modem. There are (at least!) four current philosophical control approaches: 1. Decentralized: Nearby units are able to communicate with each other with no intervening infrastructure. As the distance increases, disrupting the information flow, nearby nodes pick up the transmitting signal. They hand off the data from node to node until a base capable of connecting to the wireline network is found. The message is...
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Cẩm nang dữ liệu không dây P19
USER APPLICATIONS VERTICAL VERSUS HORIZONTAL The trade press is rife with conventional wisdom reports on vertical versus horizontal markets. ARDIS is known to focus only on the verticals because of its heritage and infrastructure limitations1 or its genetic differences.2 BSWD is thought to focus only on horizontals. In reality, during 1996 roughly 90% of BSWDs revenues came from vertical applications.3 CDPD carriers work for the horizontal market with credit card processing4 or Smartphone plans, but sell in the verticals, especially public safety. It is fair to say their focus is highly variable, with some exceptions: GTE is concentrating on vertical markets....
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Cẩm nang dữ liệu không dây P20
NETWORK MYTHOLOGIES As we reach the end of the book, it is useful to consider the veracity of some of the common old wives tales that abound in the packet radio arena. These pronouncements are often accepted as gospel when they are anything but. A realistic appraisal of some of these claims will surely help one make more hard-eyed, useful business decisions. Given the state of the wireless data business, a little realism will be a refreshing conclusion. 20.2 CDPD IS AN OPEN STANDARD; ARDIS AND BSWD ARE PROPRIETARY The claim is ubiquitous. AT&T Wireless says: AirData is based upon an...
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P1
Overview The goal of a control system is to enhance automation within a system while providing improved performance and robustness. For instance, we may develop a cruise control system for an automobile to release drivers from the tedious task of speed regulation while they are on long trips. In this case, the output of the plant is the sensed vehicle speed, y, and the input to the plant is the throttle angle, u, as shown in Figure 1.1. Typically, control systems are designed so that the plant output follows some reference input (the driver-specified speed in the case of our...
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P2
Engineers have applied knowledge gained in certain areas of science in order to develop control systems. Physics is needed in the development of mathematical models of dynamical systems so that we may analyze and test our adaptive controllers.
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P3
Few technologies have been used for such a vast variety of applications as neural networks and fuzzy systems. They have been found to be truely interdisciplinary tools appearing in the fields of economics, business, science, psychology, biology, and engineering to name a few. Based upon the structure of a biological nervous system, artificial neural networks use a number of interconnected simple processing elements (“neurons”) to accomplish complicated classification and function approximation tasks....
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P4
As humans, we are intuitively familiar with the process of optimization because of our constant exposure to it. For instance, in business investments we seek to maximize our profits; in recreational games we seek to maximize our own score or minimize that of our opponent. It is not surprising that optimizaStion plays a key role in engineering and many other fields. In circuit design we may want to maximize power transfer, in motor design we may want to design for the highest possible torque delivery for a given amount of current, or in communication system design we may want to...
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P5
Overview The use of function approximation actually has a long history in control systems. For instance, we use function approximation ideas in the development of models for control design and analysis, and conventional adaptive control generally involves the on-line tuning of linear functions (linear approximators) to match unknown linear functions (e.g., tuning a linear model to match a linear plant with constant but unknown parameters) as we discussed in Chapter 1. The adaptive routines we will study in this book may be described as on-line function approximation techniques where we adjust approximators to match unknown nonlinearities (e.g., plant...
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P6
The purpose of this chapter is to summarize a collection of standard control design techniques for certain classes of nonlinear systems. Later we will use these control techniques to develop adaptive control approaches that are suitable for use when there is additional uncertainty in the plant dynamics. Since the linear concept
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P7
In Chapter 6 we found that it is possible to define static (non-adaptive) stabilizing controllers, u = V,(X) with u E R”, for a wide variety of nonlineas plants. In addition to being able to define control laws for systems in input-output feedback linearizable and strict-feedback forms, it was shown how nonlinear damping and dynamic normalization may be used to compensate for system uncertainty. In this and subsequent chapters we will h consider using the dynamic (adaptive) controller u = Y, (z, 6) where now e(t) is allowed to vary with time. In general, we will consider two different approaches...
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P8
In the previous chapter we explained_how to develop stable direct adaptive controllers of the form u = .F(z, O), where .F is an approximator and 8 E RP is a vector of adjustable parameters. The approximator may be defined using knowledge of the system dynamics or using a generic universal approximator. We found that as long as there exists a parameter set for the approximator such that an appropriate static stabilizing controller may be represented, then the parameters of the approximator may be adjusted on-line to achieve stability using either the a-modification or the e-modification. In this chapter we will...
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P9
In Chapters 6, 7 and 8 we discussed certain important classes of continuous time nonlinear systems, and presented general methods based on state feedback for control of such systems, including in particular direct and indirect adaptive control methods. Here, we will illustrate these adaptive approaches by applying them to the problem of controlling a rotational inverted pendulum apparatus. Moreover, we will compare the performance of these methods with that of “conventional” adaptive control techniques. The direct and indirect adaptive control approaches of Chapters 7 and 8 are general enough that they can be applied to a wide class...
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P10
In Chapter 6 we introduced non-adaptive control design tools for certain classes of nonlinear systems. All of them were based on the assumption that the state of the plant is available for feedback. The scope of this chapter is to remove this restriction by dealing with the case when the state of the system is not available for
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P11
In Chapters 7 and 8 we saw how adaptive control may be used as a systematic design tool to develop dynamic controllers for systems with a great deal of uncertainty while still being able to achieve good closed-loop performance. The techniques presented there, however, assumed that full state information is available for feedback. In this chapter we will extend these tools to develop adaptive output-feedback controllers for both stabilization and tracking. First, for systems with parametric uncertainties, we will provide a brief account of the adaptive output-feedback backstepping technique developed by Kanellakopoulos, Kokotovi6, and Morse...
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P12
In Chapters 10 and 11 we discussedtechniques for output-feedback control of nonlinear systems both via non-adaptive and adaptive methods. In this chapter we apply these techniques to three illustrative examples. In the first example we consider the problem of controlling stall and surge in a jet engine compressor and we seek to find a controller which only employs the measurement of the differential pressure acrossthe compressor to reject stall and surge while regulating the pressure at a desired value. This design presents an interesting challenge in that, when there is no mass flow through the compressor, the system looses observability....
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P13
Thus far we have discussed how to control continuous-time systems for both state-feedback and output-feedback problems. With today’s high performance real-time systems, the control algorithms developed in the continuous-time framework are typically implemented on a sampled-data system. As long as the sampling rate of the controller is high with
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P14
In this chapter, we will study the control of MIMO systems where constraints are placed on the flow of information. In particular we will consider the control of decentralized systems where there are constraints on information exchange between subsystems. Decentralized control systems often arise from either the physical inability of subsystem information exchange or the lack of computing capabilities required for a single central controller. Furthermore, at times it may be more convenient to design a controller in a decentralized framework since each subsystem is often much more simple than the composite MIMO system. Within a decentralized framework,...
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Kiểm soát và ổn định thích ứng dự toán cho các hệ thống phi tuyến P15
Adaptive fuzzy and neural systems do not exist as an isolated topic devoid of relationships to other fields. It is important to understand how they relate to other fields in order to strengthen your understanding of them, and to see how general the ideas on adaptation are. We have emphasized that the methods of this book have their foundations in conventional adaptive control and that there are many relationships to techniques, ideas, and methodologies there. Adaptive fuzzy and neural systems are also an “intelligent control” technique, and hence there are certain relationships between them and other intelligent control...
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Đo nhiệt độ P1
Temperature Scales and Classification of Thermometers 1.1 Temperature - Historical Background The concept of temperature makes one think of physiological experiences whilst touching or approaching some solid. Some of them may be described as cold, cool or tepid, others as hot or warm. Warmer bodies transfer heat to other cooler bodies . Both bodies tend to equalise their temperatures, approaching a new common intermediate temperature . Thus the correctness of the definition, given to temperature by the Scotsman James Clerk Maxwell, may be seen . He stated that the temperature ofa body is its thermal state, regarded as a measure of its...
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Đo nhiệt độ P2
Non-Electric Thermometers 2.1 Liquid-in-Glass Thermometers Liquid-in-glass thermometers are based upon the temperature dependent variation of the volume of the liquid which is used . The thermometer consists of a liquid filled bulb connected to a thin capillary with a temperature scale as shown in Figure 2.1 . Assuming that the bulk volume, Vb, is much greater than that of the liquid contained in the capillary, the volume variation, AV, of the liquid corresponding to the measured temperature variation, d6, is: AV = V/3.;AO (2.1) where /3a is the average apparent coefficient of cubic thermal expansion of the thermometric liquid in the given glass....
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Đo nhiệt độ P3
Thermoelectric Thermometers Physical Principles Thermoelectric force It was T. Seebeck who discovered, in 1821, the effect which now bears his name . He observed that a current flows in a closed loop oftwo dissimilar metals when theirjunctions are at two different temperatures. As Ohm's law was not formulated by G. S. Ohm until 1826, the quantitative description of this phenomenon was not possible at the time of its discovery . In 1834, I.C.A. Peltier, discovered that a junction of two dissimilar metals is respectively heated or cooled when a current is passed through it either in one direction or the other. This phenomenon...
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Đo nhiệt độ P4
Resistance Thermometers General and Historical Background Resistance thermometers, which change their resistance with temperature, are based on modulating sensors described in Chapter 1 . These sensors, which are also referred to as resistance thermometers detectors and thermo-resistors, require the supply of energy to support the flow of acquired temperature information . When Sir Humphrey Davy, the English chemist who invented the Davy Safety Lamp for use in coal mining, investigated the properties of platinum in 1821, he reported the temperature dependence of its resistance....
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