Có 20+ tài liệu thuộc chủ đề "Hệ thống không dây"
312623.pdf
dlib.hust.edu.vn Xem trực tuyến Tải xuống
VŨ VĂN TOẠI NGHIÊN CỨU MÃ KHỐI KHÔNG GIAN TẦN SỐ CHO HỆ THỐNG MIMO-OFDM VỚI ĂNG-TEN TÁI CẤU HÌNH LUẬN VĂN THẠC SĨ KỸ THUẬT KỸ THUẬT VIỄN THÔNG Hà Nội – 2018 VŨ VĂN TOẠI * KỸ THUẬT VIỄN THÔNG * KHOÁ 2015B BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƯỜNG ĐẠI HỌC BÁCH KHOA HÀ NỘI. VŨ VĂN...
312623-tt.pdf
dlib.hust.edu.vn Xem trực tuyến Tải xuống
Tóm tắt Luận VănTốtNghiệp TÓM TẮT LUẬN VĂN THẠC SĨ Đề tài:Nghiên cứu mã khối không gian tần số cho hệ thống MIMO-OFDM với ăng-ten tái cấu hình. Tác giả luận văn:Vũ Văn Toại. Kỹ thuật MIMO kết hợp với kỹ thuật điều chế OFDM là một trong những kỹ thuật được các nhà khoa học tìm tòi và nghiên...
tailieu.vn Xem trực tuyến Tải xuống
Hertz demonstrated radio frequency (RF) generation, propagation, and reception in the laboratory. Marconi's wireless communications using the telegraph meant that a ship was no longer isolated in the open seas and could have continuous contact to report its positions. In the early 1900s, most wireless transmission occurred at very long wavelengths.. In the 1920s, the one-way broadcast was made to...
tailieu.vn Xem trực tuyến Tải xuống
At low RF, a wire or a line on a printed circuit board can be used to connect two electronic components. They can be classi®ed into two categories: conventional and integrated circuits. They can be used for wired communications to connect a transmitter to a receiver (Cable TV is an example).. FIGURE 2.2 The currrent distribution within a wire operating...
tailieu.vn Xem trực tuyến Tải xuống
The antenna is a key component in any wireless system, as shown in Fig. FIGURE 3.1 Typical wireless system.. FIGURE 3.2 Various antennas [2].. If the source transmitting power is P t , the power density P d in watts per square meters at a distance R from the source can be calculated by. At a distance far from the...
tailieu.vn Xem trực tuyến Tải xuống
Various Components and Their System Parameters. Figure 4.1 shows a brief history of microwave technologies. These components can be represented by the symbols shown in Fig.. FIGURE 4.1 History of microwave techniques: (a) technology advancements. FIGURE 4.2 Symbols for various components.. A directional coupler is a four-port device with the property that a wave incident in port 1 couples power...
tailieu.vn Xem trực tuyến Tải xuống
The input signal to the receiver is in the frequency range of 20–470 MHz. Other receiver examples are shown in Fig. Most components shown in Figs. This chapter will discuss the system parameters of the receiver.. The performance of the receiver depends on the system design, circuit design, and working environment. For the output signal to be useful, the signal...
tailieu.vn Xem trực tuyến Tải xuống
Figure 6.1 shows a typical transmitter block diagram. The output signal could be upconverted to a higher frequency.. The power amplifiers are used to increase the output power before it is transmitted by an antenna. To have a low phase noise, the oscillator or local oscillator can be phase locked to a low-frequency crystal oscillator. Power output and operating frequency:...
tailieu.vn Xem trực tuyến Tải xuống
The nature of an echo signal provides information about the target—range, direction, and velocity.. Although radar cannot reorganize the color of the object and resolve the detailed features of the target like the human eye, it can see through darkness, fog and rain, and over a much longer range. It can also measure the range, direction, and velocity of the...
tailieu.vn Xem trực tuyến Tải xuống
Three such satellites can provide services covering all major population centers in the world. Wireless personal and cellular communications have enjoyed the fastest growth rate in the telecommunications industry. The received power is P r and the distance is R. The received power can be calculated in the following if we assume that there is no atmospheric loss, polarization mismatch,...
tailieu.vn Xem trực tuyến Tải xuống
The lower frequency is called the modulating signal, the higher frequency signal is called the carrier, and the output signal is called the modulated signal. The benefits of the modulation process are many, such as enabling communication systems to transmit many baseband channels simultaneously at different carrier frequencies without their interfering with each other. Some simple modulation can be achieved...
tailieu.vn Xem trực tuyến Tải xuống
Multiple-Access Techniques. 10.1 INTRODUCTION. Three commonly used techniques for accommodating multiple users in wireless communications are frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). Frequency division multiple access and TDMA are old technologies and have been used for quite a while. Code division multiple access is the emerging technology for many new...
tailieu.vn Xem trực tuyến Tải xuống
11.1 RADIO NAVIGATION AND GLOBAL POSITIONING SYSTEMS Radio navigation is a method of determining position by measuring the travel time of an electromagnetic (EM) wave as it moves from transmitter to receiver. 11.1 and 11.2.. Figure 11.1 shows an example of an active radio navigation system. Several typical radio navigation systems are shown in Table 11.1 for comparison. FIGURE 11.1...
tailieu.vn Xem trực tuyến Tải xuống
Currently the field of wireless communications is one of the fastest growing segments of the telecommunications industry.. From the point of view of these people, mobility is also highly beneficial: the mobile user can be contacted by dialing the very same number irrespective of the user’s physical location. We then proceed to briefly highlight the major technical challenges in implementing...
tailieu.vn Xem trực tuyến Tải xuống
2.1.1 Scope of the Chapter. Section 2.2 describes the various bands of the electromagnetic spectrum and discusses the way spectrum is licensed. This refers to the distance between two consecutive maximum or minimum peaks of the electro- magnetic wave and is measured in meters. As a result, there is not a clear distinction between some bands of the electromagnetic spectrum....
tailieu.vn Xem trực tuyến Tải xuống
The use of the cellular concept greatly improved spectrum usage, for the reasons mentioned in the previous chapters. The moral lesson from this fact is obvious and has been seen in other areas of technology as well – the market does not entirely follow technological developments. As in the case of AMPS, all of the above systems employ FM for...
tailieu.vn Xem trực tuyến Tải xuống
2G systems overcome many of the deficiencies of 1G systems mentioned in the previous chapter. The frequency of the first channel is known as the uplink (or reverse link) and that of the second channel is known as the downlink (or forward link). Due to the fact that pairs of uplink/downlink channels are allocated by regulation agencies, most of the...
tailieu.vn Xem trực tuyến Tải xuống
Returning to the example of the previous paragraph, the presentation transfer would take only 8 s over the 2 Mbps link of a 3G system, which results in a significant performance improvement over 2G. The outcome of the standardization effort, called International Mobile Tele- communications 2000 (IMT-2000), comprises a number of different 3G standards. Most of the protocols used today...
tailieu.vn Xem trực tuyến Tải xuống
Furthermore, 3G networks will have, in the best case, an upper capacity limit of 2 Mbps. Although more than enough for the application demands of the years to come, 3G networks will most likely need to evolve in order to meet the mobile application demands of the next decades. As seen later in the chapter, the vision for 4G and...
tailieu.vn Xem trực tuyến Tải xuống
These ideas seemed to be too ambitious at the time of the publication due to the fact that technology was not advanced enough to allow for reliable transceivers and easy deployment of satellites. Two years later the ECHO project offered single hop radio coverage of the entire US area through a passive reflector that was carried by a balloon at...