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MC và các hệ thống phổ Bá P2
MC-CDMA and MC-DS-CDMA In this chapter, the different concepts of the combination of multi-carrier transmission with spread spectrum, namely MC-CDMA and MC-DS-CDMA are analyzed. Several single-user and multiuser detection strategies and their performance in terms of BER and spectral efficiency in a mobile communications system are examined. 2.1 MC-CDMA 2.1.1 Signal Structure The basic MC-CDMA signal is generated by a serial concatenation of classical DSCDMA and OFDM. Each chip of the direct sequence spread data symbol is mapped onto a different sub-carrier. Thus, with MC-CDMA the chips of a spread data symbol are transmitted in parallel on different sub-carriers, in contrast to a...
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MC và các hệ thống phổ Bá P3
Hybrid Multiple Access Schemes The simultaneous transmission of multiple data streams over the same medium can be achieved with different multiplexing schemes. Most communications systems, such as GSM, DECT, IEEE 802.11a, and HIPERLAN/2, use multiplexing based on either time division, frequency division or a combination of both. Space division multiplexing is applied to further increase the user capacity of the system. The simplest scheme of space division multiplexing is antenna sectorization at the base station where often antennas with 120◦ /90◦ beams are used....
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MC và các hệ thống phổ Bá P4
Implementation Issues A general block diagram of a multi-carrier transceiver employed in a cellular environment with a central base station (BS) and several terminal stations (TSs) in a point to multi-point topology is depicted in Figure 4-1. For the downlink, transmission occurs in the base station and reception in the terminal station and for the uplink, transmission occurs in the terminal station and reception in the base station. Although very similar in concept, note that in general the base station equipment handles more than one terminal station, hence, its architecture is more complex. The transmission operation starts with a stream of...
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MC và các hệ thống phổ Bá P5
The deregulation of the telecommunications industry, creating pressure on new operators to innovate in service provision in order to compete with existing traditional telephone service providers, is and will be an important factor for an efficient use of the spectrum. It is certain that most of the information communicated over future digital networks will be data rather than purely voice. Hence, the demand for high-rate packet-oriented services such as mixed data, voice, and video services, which exceed the bandwidth of conventional systems, will increase. Multimedia applications and computer communications are often bursty in nature....
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MC và các hệ thống phổ Bá P6
Additional Techniques for Capacity and Flexibility Enhancement As shown in Chapter 1, wireless channels suffer from attenuation due to the destructive addition of multipath propagation paths and interference. Severe attenuation makes it difficult for the receiver to detect the transmitted signal unless some additional, lessattenuated replica of the transmitted signal are provided. This principle is called diversity and it is the most important factor in achieving reliable communications. Examples of diversity techniques are: — Time diversity: Time interleaving in combination with channel coding provides replicas of the transmitted signal in the form of redundancy in the temporal domain to the receiver....
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P1)
The term microwaves may be used to describe electromagnetic (EM) waves with frequencies ranging from 300 MHz to 300 GHz, which correspond to wavelengths (in free space) from 1 m to 1 mm. The EM waves with frequencies above 30 GHz and up to 300 GHz are also called millimeter waves because their wavelengths are in the millimeter range (1–10 mm). Above the millimeter wave spectrum is the infrared, which comprises electromagnetic waves with wavelengths between 1 m (10–6 m) and 1 mm. Beyond the infrared spectrum is the visible optical spectrum, the ultraviolet spectrum, and x-rays. Below the microwave...
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P2)
Network Analysis Filter networks are essential building elements in many areas of RF/microwave engineering. Such networks are used to select/reject or separate/combine signals at different frequencies in a host of RF/microwave systems and equipment. Although the physical realization of filters at RF/microwave frequencies may vary, the circuit network topology is common to all. At microwave frequencies, voltmeters and ammeters for the direct measurement of voltages and currents do not exist. For this reason, voltage and current, as a measure of the level of electrical excitation of a network, do not play a primary role at microwave frequencies....
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P3)
Basic Concepts and Theories of Filters This chapter describes basic concepts and theories that form the foundation for design of general RF/microwave filters, including microstrip filters. The topics will cover filter transfer functions, lowpass prototype filters and elements, frequency and element transformations, immittance inverters, Richards’ transformation, and Kuroda identities for distributed elements. Dissipation and unloaded quality factor of filter elements will also be discussed.
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P4)
Transmission Lines and Components In this chapter, basic concepts and design equations for microstrip lines, coupled microstrip lines, discontinuities, and components useful for design of filters are briefly described. Though comprehensive treatments of these topics can be found in the open literature, they are summarized here for easy reference.
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P5)
Lowpass and Bandpass Filters Conventional microstrip lowpass and bandpass filters such as stepped-impedance filters, open-stub filters, semilumped element filters, end- and parallel-coupled half-wavelength resonator filters, hairpin-line filters, interdigital and combline filters, pseudocombline filters, and stub-line filters are widely used in many RF/microwave applications. It is the purpose of this chapter to present the designs of these filters with instructive design examples.
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P6)
Highpass and Bandstop Filters In this chapter, we will discuss some typical microstrip highpass and bandstop filters. These include quasilumped element and optimum distributed highpass filters, narrow-band and wide-band bandstop filters, as well as filters for RF chokes. Design equations, tables, and examples are presented for easy reference.
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P7)
Advanced Materials and Technologies High-temperature superconductors (HTS), ferroelectrics, micromachining or microelectromechanical systems (MEMS), hybrid or monolithic microwave integrated circuits (MMIC), active filters, photonic bandgap (PBG) materials/structures, and low-temperature cofired ceramics (LTCC) are among recent advanced materials and technologies that have stimulated the rapid development of new microstrip and other filters. This chapter summarizes some of these important materials and technologies, particularly regarding the applications to microstrip or stripline filters. ...
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P8)
Coupled Resonator Circuits Coupled resonator circuits are of importance for design of RF/microwave filters, in particular the narrow-band bandpass filters that play a significant role in many applications. There is a general technique for designing coupled resonator filters in the sense that it can be applied to any type of resonator despite its physical structure. It has been applied to the design of waveguide filters [1–2], dielectric resonator filters [3], ceramic combline filters [4], microstrip filters [5–7], superconducting filters [8], and micromachined filters [9]. ...
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P9)
CAD for Low-Cost and High-Volume Production There have been extraordinary recent advances in computer-aided design (CAD) of RF/microwave circuits, particularly in full-wave electromagnetic (EM) simulations. They have been implemented both in commercial and specific in-house software and are being applied to microwave filter simulation, modeling, design, and validation [1]. The developments in this area are certainly stimulated by increasing computer power. In the past decade, computer speed and memory have doubled about every 2 years [2]....
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P10)
Advanced RF/Microwave Filters There have been increasing demands for advanced RF/microwave filters other than conventional Chebyshev filters in order to meet stringent requirements from RF/microwave systems, particularly from wireless communications systems. In this chapter, we will discuss the designs of some advanced filters. These include selective filters with a single pair of transmission zeros, cascaded quadruplet (CQ) filters, trisection and cascaded trisection (CT) filters, cross-coupled filters using transmission line inserted inverters, linear phase filters for group delay equalization, extracted-pole filters, and canonical filters....
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P11)
Compact Filters and Filter Miniaturization Microstrip filters are themselves already small in size compared with other filters such as waveguide filters. Nevertheless, for some applications where the size reduction is of primary importance, smaller microstrip filters are desirable, even though reducing the size of a filter generally leads to increased dissipation losses in a given material and hence reduced performance.
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Microstrip bộ lọc cho các ứng dụng lò vi sóng RF (P12)
Case Study for Mobile Communications Applications Microstrip filters play various roles in wireless or mobile communication systems. This chapter is particularly concerned with a case study of high-temperature superconducting (HTS) microstrip filters for the cellular base station applications. The study starts with a brief discussion of typical HTS subsystems and RF modules, including HTS microstrip filters for cellular base stations. This is followed by more detailed descriptions of the developments of duplexers and preselect bandpass filters, including design, fabrication, and measurement. ...
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Điện thoại di động mạng lưới Radio P1
During the first half of this century, the transmission of human voice through the telephone was the dominant means of communication next to telegraphy. Radio-supported mobile communication has constantly grown in importance during the last few decades and particularly the last few years to technical advances in transmission and switching technology as well as in microelectronics. Table 1.1 presents an overview of the chronological development of mobile radio systems. In contrast to wireline networks, mobile radio networks that comply with the wish for geographically unrestricted communication can be used anywhere where it is not economic or possible to install cabling....
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Điện thoại di động mạng lưới Radio P2
Fundamentals of Radio Transmission In mobile radio systems, unlike wired networks, electromagnetic signals are transmitted in free space (see Figure 2.1). Therefore a total familiarity with the propagation characteristics of radio waves is a prerequisite in the development of mobile radio systems. In principle, the Maxwell equations explain all the phenomena of wave propagation. However, when used in the mobile radio area, this method can result in some complicated calculations or may not be applicable at all if the geometry or material constants are not known exactly....
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Điện thoại di động mạng lưới Radio P3
The GSM Recommendation The early 1980s were marked by the development of a number of national and incompatible radio networks in Europe; see Table 1.2 and Figure 1.3. The seven different mobile radio networks made the prospect of the mobile telephone unattractive to many potential customers because of high tariffs and equipment costs. For this reason, at its general meeting in Vienna in June 1982, CEPT (see Appendix B.2.2) decided to develop and standardize a Pan-European cellular mobile radio network. The aim was for the new system to operate in the 900 MHz frequency band allocated to land mobile radio....
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Điện thoại di động mạng lưới Radio P4
Other Public Mobile Radio Systems 4.1 Airline Telephone Network for Public Air–Ground Communication In 1993 ETSI RES 5 submitted a standard for the Terrestrial Flight Telephone System (TFTS), specifying the radio interface and the interfaces to public telecommunications networks. At the same time the European Airlines Electronic Committee (EAEC) specified the airline equipment and interfaces to cabin facilities. Commercial operations began in 1994. In July 1994, after inviting international tenders, the Ministry of Post and Telecommunications granted a licence to DeTeMobil for the operation of TFTS. DeTeMobil was to supply radio coverage to all airspace up to an altitude of 4500 m....
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Điện thoại di động mạng lưới Radio P5
Dramatic developments have been taking place in the mobile radio area all over the world during the last couple of decades. Mobile communications is one of the fastest growing markets in the telecommunications area. According to projections, there will be a linear increase in the number of subscribers to the major GSM networks operated in Europe by the end of the decade. The political environment in Europe is the main reason for the rapid development. Without a free exchange of information, the concept of an internal market striving for a free flow of goods between EU states would be inconceivable....
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Điện thoại di động mạng lưới Radio P6
Trunked Mobile Radio and Packet Data Radio In addition to the public radio telephone service and the paging service, there are other radio services that are not accessible by the public. These radio systems, called the non-public land mobile radio network , have access to frequencies that cannot be used by the public but only by specific users or groups of users. Probably the best known non-public mobile radio service is analogue Private Trunked Mobile Radio (PTMR), which has been used for many years by large firms such as airlines, taxi and transport companies, the railways, and ports, as well...
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Điện thoại di động mạng lưới Radio P7
Paging Systems It is often important to be able to reach certain people very quickly. The conventional telephone network is not always optimal, because a line may be engaged or the person being called might not be available. Mobile telephone systems offer a high degree of reachability of a mobile subscriber, but MSs are not always switched on and are expensive to use. Paging systems fill a particular gap (see Table 7.1). They allow unidirectional transmission of information in the form of a tone or a numeric or alphanumeric message to the person being contacted, whose location area is not known...
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Điện thoại di động mạng lưới Radio P8
Cordless Telephone Systems Cordless telephone systems are mobile radio systems that, although their transmission range is not suitable for wide-area coverage, are attractive to many users because of the services offered and their low cost. Cordless telephony (CT) can be used within the area of a subscriber line, and provides a radio link within a radius of approximately 50 m inside a building or 300 m outdoors between the fixed terminal and a mobile part. This requires the fixed terminal, as the base station, and the mobile part each to be equipped with transmitting and receiving capabilities. ...
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Điện thoại di động mạng lưới Radio P9
Besides cellular mobile radio networks that are primarily envisaged for use outdoors, systems that have been specifically designed for use in buildings are also important. In recent years cordless telephones with a range of a few hundred metres have become increasingly popular in private households. There is (along with CT2/CAI) a digital alternative to these analogue devices that offers better voice quality and a greater security against eavesdropping, as well as other advantages: the DECT system....
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Điện thoại di động mạng lưới Radio P10
10 Wireless Local Loop Systems Wireline communications networks are expensive and time-consuming to configure. Growing demand for telecommunications services and the imminent liberalization of the telecommunications market in Europe have greatly increased the interest in radio-based communication (Wireless Local Loops, WLL), also referred to as Radio in the Local Loop (RLL), see [3]. Future competitors of telecommunications monopoly service providers, such as power suppliers who already have their own wide-area networks, will usually lack access networks to the end users....
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Điện thoại di động mạng lưới Radio P11
Development of the Personal Handyphone System in Japan At the end of the 1980s, two cordless telephone systems, CT2 and DECT, had entered the second step of their development process. At that time, Japan had not yet developed any comparable technology; therefore work began in 1989 on a Japanese cordless standard, which has become known as the Personal Handyphone System (PHS). Disadvantages of conventional cellular telephone systems, such as high costs of infrastructure and cell-planning resulting in high communication fees, had motivated the development of a less expensive system. ...
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Điện thoại di động mạng lưới Radio P12
Wireless Broadband Systems and Wireless ATM∗ Broadband systems are generally those systems that provide a high transmission rate besides other features like integration of services. An exact definition of this term can be found in ITU Rec. I.113, which characterizes broadband services as having a higher transmission rate than a primary multiplex connection in ISDN (2048 kbit/s). A brief overview of the current state of development of wireless broadband systems, particularly in Europe, including the fundamentals of ATM in BISDN, is given below. This is followed by important aspects of development of wireless ATM for movable and mobile stations. ...
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Điện thoại di động mạng lưới Radio P13
Wireless Local Area Networks∗ Since the introduction of lightweight portable computers (laptops, notebooks), a great deal of attention has been focused on the development of wireless computer networks (Wireless Local Area Network, WLAN). Thanks to standardization in the field of local area networks, it is comparatively easy to find systems that will still be upgradable even in a few years’ time. Around 70 % of all computers connected to networks are compliant with the IEEE 802.3 (Ethernet) and IEEE 802.5 (Token Ring) standards. Connection is normally over a permanent wireline link....
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