Tài liệu miễn phí Kĩ thuật Viễn thông
Download Tài liệu học tập miễn phí Kĩ thuật Viễn thông
TỔNG QUAN MẠNG VIỂN THÔNG TỔNG ĐÀI _ ĐIỆN THOẠI, Chương 6
Mạch hybrid: được thiết kế dựa trên đặc tính của Op-Amp. nhiệm vụ của mạch hibrid là cách ly tín hiệu thu và phát. Tín hiệu trên đường truyền về chỉ đi theo ngõ Rx vào mạch, và tín hiệu từ hệ thống phát chỉ phát ra theo ngõ Tx đi đến đường dây điện thọai. Mục đích là để ngưòi gọi không nghe thấy tiếng nói củ mình trong loa, đồng thời ngăn cách phổ tần của tiếng nói. Mạch lọc: Là lọc thông thấp chủ yếu là lọc lấy tín hiệu thoại (300Hz ÷ 300Hz), nhằm loại bỏ...
8/29/2018 6:17:21 PM +00:00
TỔNG QUAN MẠNG VIỂN THÔNG TỔNG ĐÀI _ ĐIỆN THOẠI, Chương 7
âm hiệu (tone) là các sóng âm thanh mà tổng đài gửi đến các thuê bao nhằm phản hồi, thông báo,… gồm các âm hiệu sau: I. ÂM HIỆU MỜI QUAY SỐ (Dial tone) Dial tone là tín hiệu hình sin có tần số: f= 425 ± 25Hz. Có tác dụng báo cho thuê bao biết tổng đài sẳn sàng nhận số quay. Thuê bao sẻ nghe được âm hiệu này khi nhấc máy, với các điều kiện các đường trung kế không bận. (Busy tone) Âm hiệu này được tổng đài gởi đến cho thuê bao gọi biết...
8/29/2018 6:17:21 PM +00:00
TỔNG QUAN MẠNG VIỂN THÔNG TỔNG ĐÀI _ ĐIỆN THOẠI, Chương 1
Ngày nay,vấn đề thông tin liên lạc luôn được đặt lên hàng đầu. Vì vậy việc xây dựng một mạng viển thông có cấu hình tối ưu nhất, đạt hiệu quả công viêc cao nhất là việc làm cần thiết. Điều cần thiết khi xây dựng một mạng lưới viển thông hợp lý ta phải phân tích ,kết hợp những ưu_khuyết điểm của các cấu hình mạng khác nhau nhằm đạt được một mạnh lưới viển thông hoàn chỉnh.khi đó,mạng viẻn thông hoàn chỉnh là sự kết hợp của mạng hình sao: các tổng đài nội hạt trong vùng nối...
8/29/2018 6:17:20 PM +00:00
TỔNG QUAN MẠNG VIỂN THÔNG TỔNG ĐÀI _ ĐIỆN THOẠI, Chương 2
Quá trình báo hiệu trên đường dây thuê bao được phân thành hai hướng theo giản đồ như sau: Báo hiệu trên đường đây thuê bao gọi Trong các mạng điện thoại hiện nay, nguông tại tổng đài cung cấp đến các thuê bao thường là 48VDC Yêu cầu cuộc gọi: Khi thuê bao rỗi, trở kháng đường dây cao, trở khang đường dây hạ xuống nngay khi thuê bao nhấc tổ hợp kết quả là dòng điện tăng cao. Dòng tăng cao này được tổng đài phát hiện như là một yêu cầu một cuộc gọik mới và sẽ...
8/29/2018 6:17:20 PM +00:00
Chương 2: Các đặc tính của kênh truyền vô tuyến
Kênh truyền tín hiệu OFDM là môi trường truyền sóng giữa máy phát và máy thu. Trong kênh truyền vô tuyến lý tưởng, tín hiệu nhận được bên thu được truyền theo tầm nhìn thẳng. Tuy nhiên trong thực tế, kênh truyền tín hiệu vô tuyến bị thay đổi. Việc nghiên cứu các đặc tính của kênh truyền là rất quan trọng vì chất lượng của hệ thống truyền vô tuyến là phụ thuộc vào các đặc điểm này....
8/29/2018 6:17:16 PM +00:00
Phần mềm xác định radio P10
Software Technology Software – at air interface, applications, protocol and network levels – is at the heart of the promise of software radio. At all levels the potential is vast and the implications are profound – the need for effective design tools to give functional reliability will be key to successful commercialization.
8/29/2018 6:17:02 PM +00:00
Phần mềm xác định radio P11
The subject of software radio emerged as a ‘hot topic’ in mobile communications in the early 1990s, when many people saw the technology as a solution to the problems of complex RF and IF processing required in modern multimode/multiband mobile terminals. Today, software radio is seen more as a technology to enable the reconfiguration of terminals by download. 1 Such reconfiguration can be achieved at all stages from design, through production, to post purchase use by the consumer.
8/29/2018 6:17:02 PM +00:00
Phần mềm xác định radio P12
Visions for systems beyond 3G foresee software defined radio as one of the core enablers of seamless service provision across the boundaries of different wireless transmission platforms. Such visions (e.g. [1]), assume the use of different types of network [2] ranging from fixed (e.g. xDSL) connections via short range wireless (PAN/VAN/HAN) schemes, wireless LANs and cellular radio networks to broadcast systems and beyond. Accessing such a variety of different networks will require highly flexible mobile terminals – a capability expected to be provided by software defined radios....
8/29/2018 6:17:02 PM +00:00
Phần mềm xác định radio P13
The benefits of software defined radios (SDR) are identified in many chapters of this book. SDR will potentially permit new protocols, applications, and air interface waveforms to be flexibly and even dynamically deployed across a variety of implementation platforms and products, sourced from multiple vendors. It will bring the benefits of open standards that have been enjoyed in the PC world to the arena of wireless communications. However, the basic hardware and software technologies, addressed elsewhere in this book, need to be supported by design tools and technologies that enable the simple, flexible, rapid, and cost-effective development, deployment, and reconfiguration...
8/29/2018 6:17:02 PM +00:00
Tín hiệu trong các mạng viễn thông P7
CCITI’ began the specification of the second-generation common-channel signaling system, known as signaling system No.7 (SS7), in the mid-1970s. The system was developed initially for telephony call control, and the first recommendations were published in the CCITT Yellow Books of 1981. During the past decade, the applications of SS7 applications have expanded, and now also include call control in the integrated services digital network (ISDN), and operations in the network that aeennot related to individual trunks. Most of this work has been published in the CCITT Blue Books of 1989. More recent additions have been issued as individual International Telecommunications...
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P8
MTP is divided into three parts, located at levels 1, 2, and 3 of the SS7 hierarchy. The main functions of these parts are outlined below [l-5]. MTP Level 7 (MTp7) is the physical signaling data link (SDL), which consists of a pair of 64 kb/s digital transmission channels, and transports SS7 signal units between two signaling points. MTPl is described in Section 8.2. MTf Level 2 (MTf2).
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P9
The telephone userpart (TUP) is the first SS7 user part defined by CCITT. An early version appeared in the 1980 CCITT Yellow Book. The 1985 Red Book and the 1989 Blue Book include a number of additions and modifications [ 11. The term “telephone” dates back to the beginnings of the TUP development, when all calls were “speech” calls. The calls in the present telecommunication networks can also be used for facsimile, and other data communications.
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P10
DIGITAL SUBSCRIBER SIGNALING SYSTEM NO. 1 Digital subscriber signaling system No. 1 (DSSl) is used for signaling between an ISDN (integrated services digital network) subscriber and his local exchange. This chapter is a brief excursion from the description of signaling system No.7 (SS7), which has been the subject of Chapters 7 through 9, and will continue in Chapter 11, with the description of the integrated services digital network user part (ISUP). This order of presentation has been chosen because DSSl can be discussed without references to ISUP, and because it is helpful to be familiar with DSSl when exploring ISUP, which is...
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P11
The ISDN user part (ISUP) has been designed for use in the circuit-switched part of ISDN networks (see Fig. 10.1-2). It includes messages and procedures for the control of interexchange calls between two (analog) subscribers, two ISDN users, and between an ISDN user and a subscriber [ 1,2]. As in TUP signaling, ISUP call-control signaling is primarily link-by-link, but also includes procedures for end-to-end signaling. Telecoms that have installed TUP signaling in their networks are gradually converting to ISUP signaling....
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P12
SIGNALI R MOBILE TELECOMMUNICATIONS Cellular mobile telecommunications is one of the most important telecommunication developments of the last decade. The technical concepts underlying this type of communications were developed by Bell Laboratories [1,2], and implemented in the ~dv~~~ed rn~bi~e telephu~e service intern (AMPS). All current cellular systems in the U.S. are descendants of AMPS. Early mobile stations (MS) were designed as car phones. They were too bulky to be carried around, and had to be powered by the battery of the car. Today, there are compact lightweight MSs with internal rechargeable batteries. ...
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P13
INTRODUCTION TO TRANSACTIONS The TUP and ISUP protocols (Chapters 9 and 11) are SS7 protocols for trunkrelated exchange actions (mainly call control). The SS7 signaling takes place between the exchanges at the ends of a TUP or ISUP trunk. Starting with this chapter, the focus is on SS7 signaling for operations that are not trunk-related.
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P14
SIGNALING CONNECTION CONTROL PART The message transfer part (MTP) of SS7 (Chapter 8) was designed to transfer TUP (and later on, ISUP) messages between exchanges at the ends of a trunk. The signaling connection control part (SCCP), in combination with MTP, provides the transfer of messages that are not related to individual trunks, for example, transaction messages [l-3]. The combination of MTP and SCCP is known as the network service part (NSP) of SS7, and is the equivalent of layers 1,2, and 3 of the OS1 (open systems interconnection) protocols in data communication systems (7.1.1)....
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P15
TRANSACTION CAPABILITIES APPLICATION PART The transaction capabilities application part (TCAP) of signaling system No.7, in conjunction with the signaling control connection part (SCCP) and the message transfer part (MTP) [l-3], enables application service elements (ASE) at two nodes (the TCAP term for signaling points) to conduct transact ions.
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P16
The introduction of stored-program controlled exchanges in telecommunication networks has enabled the telecoms to offer call-forwarding, callwaiting, and other supplementary services to their customers [l]. These services are exchange-based: the (software) logic and data for the services reside in the exchanges. Telecommunication networks are evolving into intelliigent networks that offer, in addition to exchange-based services, a number of services whose logic and data reside in a small number of centralized information sources that can be queried (interrogated) by the exchanges....
8/29/2018 6:17:01 PM +00:00
Tín hiệu trong các mạng viễn thông P17
MOBILE APPLICATION PART Chapter 12 has described the signaling between a mobile station (MS) and a mobile switching center (MSC) in a cellular (public land) mobile network (CMN, PLMN). The present chapter describes the mobile application part (MAP) of signaling system No.7 (SS7). MAP defines a number of remote operations (transactions) that support mobile telecommunications. Public switched telecommunication networks (PSTN) are f^lxed networks. A subscriber line is fixed (attached) to a local exchange, which has a record for each of its subscribers. ...
8/29/2018 6:17:01 PM +00:00
Phần mềm xác định radio P1
This chapter offers an introduction to software based radio (SBR), discusses some top-level global drivers for (SBR) designs, and postulates potential evolutionary implications for software radio in one key market space (commercial wireless).
8/29/2018 6:17:01 PM +00:00
Phần mềm xác định radio P2
Front End Technology Front End design – including RF Architecture, Data Conversion and Digital Front Ends – has emerged as a key issue as SDR techniques are finding themselves increasingly embodied by stealth into today’s new products. The radical solution – ‘Pure’ Software Radio, with A/D conversion at the antenna – is not yet feasible at GHz carrier frequencies. However, recent technology advances suggest it may be nearer than had been thought.
8/29/2018 6:17:01 PM +00:00
Phần mềm xác định radio P3
All wireless communication systems have traditionally employed a radio frequency front end (RF FE) (see Figure 3.1), located between the antenna and the baseband subsystem, the latter commonly implemented with digital signal processing technology. While ‘pure’ software radios anticipate analog-to-digital conversion at the antenna, dispensing with the need for this element of the radio, today’s ‘pragmatic’ software defined radios (SDRs), still (and as will be seen later in this chapter, for the foreseeable future) require an RF FE and place stringent demands thereon....
8/29/2018 6:17:01 PM +00:00
Phần mềm xác định radio P4
Data converters are one of the key enabling technologies for the software defined radio (SDR). Regardless of the interpretation of the definitions – software radio, software defined radio, software based radios – the challenge of moving the analog-digital boundary closer to the antenna is the critical step in establishing the foundation for increasing the content and capability of digital signal processing (DSP) in the radio. SDR technologies have provided the incentives for the breakthrough in converter technologies pushing the state-of-the-art [1]....
8/29/2018 6:17:01 PM +00:00
Phần mềm xác định radio P5
When the concepts of ‘pure’ software radio 1 were first introduced they were immediately recognizable to those who had worked on military systems at very low frequencies – at a carrier frequency of 16 kHz, A/D conversion of the RF carrier directly at the antenna was becoming feasible in the 1970s. However, only 10 years ago the prospect of ‘pure’ software radio implementations for commercial wireless systems, operating at carrier frequencies of 2 GHz and beyond, was seen as being decades away....
8/29/2018 6:17:01 PM +00:00
Phần mềm xác định radio P6
The Front End of a Digital Transceiver The first question that might arise is: What is the digital front end? The notion of the digital front end (DFE) has been introduced by the author in several publications (e.g. [13]). Nonetheless it is useful to introduce the concept of the DFE at the beginning of this chapter. Several candidate receiver and transmitter schemes have been presented by Beach et al. in Chapter 2. They all have in common that they are different from the so-called ideal software radio insofar as the signal has to undergo some signal processing steps before the baseband...
8/29/2018 6:17:01 PM +00:00
Phần mềm xác định radio P7
Baseband Technology ‘Software runs on Silicon’ – and in the case of SDRs today, the competition between approaches and technologies for exponentially increasing baseband processing requirements is proving a fertile ground for innovation, in both conceptual approaches and implementation architectures.
8/29/2018 6:17:01 PM +00:00
Phần mềm xác định radio P8
Parametrization – a Technique for SDR Implementation Friedrich Jondral University of Karlsruhe Mobile communications is mainly a service driven business. But there are important marginal conditions from physics and technology that may not be ignored when developing a mobile communications system; the frequency spectrum is a scarce resource. Therefore terminals, mobile as well as base station transceivers, have to work efficiently with respect to spectrum. Mobile radio channels are complicated due to multipath propagation, reflections, scattering, time, or frequency dispersion, etc. ...
8/29/2018 6:17:01 PM +00:00
Phần mềm xác định radio P9
Practical implementation of software defined radio (SDR) for mobile wireless devices will place significantly increased demands on design approaches and integrated circuit (IC) technology. Next generation wireless terminals, third generation (3G) and beyond, are required to provide much higher levels of features, functions, and services than their second generation (2G) counterparts. Examples include such capabilities as higher throughput, multiband, multimode, multimedia, and location-based services. This demand for new capabilities is occurring simultaneously with the demand for portability driving key physical requirements of long battery life, small size, light weight, etc....
8/29/2018 6:17:01 PM +00:00
Mạng lưới giao thông và đánh giá hiệu suất P10
One of the major challenges in designing modern communication networks is providing quality of service to the individual users. An important part of this design process is understanding statistical characteristics of network traf®c streams and their impact on network performance. Unlike the conventional voice traf®c, modern data traf®c exhibits an increased level of ``burstiness'' that spans over multiple time scales. It was observed that sample paths of these data sequences show evidence of self-similarity....
8/29/2018 6:17:00 PM +00:00