Spatial Multidimensional Cooperative Transmission Theories And Key Technologies. Lin Bai
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antenna constellation
Chapter 1
Introduction
With the rapid development of wireless broadband communication and the swift progress in the Internet industry, mobile Internet is showing a booming trend with its unprecedented way to change people’s social lives and lifestyles, and it has become one of the necessary means for modern human information interaction. Traditional wireless communication is mostly based on ground-based cellular communication. However, with the continuous improvement of aerospace technology and the rapid growth of the types and quantities of space-based and air-based platforms, the space–air–ground integrated information network consisting of satellites, stratospheric balloons, and various aerospace vehicles is developing rapidly. The resulting space–air–ground integrated mobile Internet will become an information bridge for human beings to understand, enter, use, and develop space in the future.
Since the birth of wireless communication, the shortage of spectrum resources has been the biggest bottleneck restricting its development. The efficient use of spectrum resources and the development of the corresponding spatial multidimensional cooperative transmission technology have brought new growth points for future wireless communication and also provided theoretical and technical guarantee for the healthy development of the space–air–ground integrated mobile Internet in the future. This chapter will outline the characteristics and development history of ground-based, air-based, and space-based wireless communication.
1.1Overview of Ground-based Wireless Communication System
Since the concept of mobile communication was proposed by Bell Labs in the United States in 1947,1 mobile communication technology has made rapid progress in the past 30 years and has become one of the indispensable communication means in modern ground-based communication networks. In this section, we will first expound the development of the four generations of ground-based mobile communications and the corresponding key technologies.2
1.1.1The first generation of mobile communication system
The first generation of mobile communication systems (1G) was born in the 1970s and 1980s when the integrated circuits, microcomputers, and microprocessor technologies were rapidly developed. In 1978, Bell Labs of the United States introduced an analog cellular mobile communication system, extending mobile communication into personal field. In 1983, the US advanced mobile phone service (AMPS)1 was put into commercial use. The AMPS system employed a 7-cell multiplexing mode and could use “sectorization” and “cell splitting” to increase capacity when needed. At the same time, Europe and Japan had also established their own mobile communication networks, including the UK’s extended total access communication system (ETACS) and Japan’s narrowband total access communication system (NTACS). The wireless communication system of this period mainly used analog modulation and frequency division multiple access (FDMA) technology. There is no doubt that the first generation of mobile communication system has many shortcomings, such as limited user capacity, difficulty in system expansion, mixed modulation methods, inability to achieve international roaming, poor confidentiality, low call quality, and inability to provide data services.
1.1.2The second generation of mobile communication system
In 1992, with the birth of the first digital cellular mobile communication network, namely the global system for mobile (GSM) communications, mobile communication entered the second generation (2G). Due to its superior performance, GSM made rapid progress worldwide. In 1993, the first all-digital mobile phone GSM system was completed in China, and then both China Telecom and China Unicom adopted GSM. The GSM system has the following main characteristics: microcell structure, digitalization of voice signals, new modulation methods (GMSK, QPSK, etc.), the use of FDMA or time division multiple access (TDMA) technology, high spectrum utilization, high confidentiality, etc.
In 1995, Qualcomm proposed another digital cellular system technology solution using code division multiple access (CDMA), which is IS-95 CDMA. It is currently used in Hong Kong, South Korea, and North America with good reviews from users. The CDMA system mainly has the following characteristics: the user access mode adopting CDMA, soft capacity, soft cut-in, large system capacity, anti-multipath fading, voice activation, and diversity reception, etc.
Compared with the 1G system, 2G system has higher spectrum utilization, stronger security, and better voice quality. Up to now, the 2G system standards have become more and more perfect, and the technology is relatively mature. However, as people’s demand for data services continues to increase, the rate provided by the 2G system is no longer sufficient, and a stronger system is needed to support high-speed mobile communications.
1.1.3The third generation of mobile communication system
The concept of the third-generation mobile communication system was proposed by the ITU in 1985 and it was named the future public land mobile telecommunications system (FPLMTS). In 1996, it was renamed the international mobile telecommunications 2000 (IMT-2000) system, which worked in the 2000-MHz band and could provide a data transmission rate of up to 2000 kbit/s. The purpose of 3G is to achieve a unified standard for cellular mobile communication and establish a globally popular seamless roaming system. Meanwhile, it can support high-quality multimedia services and enhance network capacity and multiple-user management capabilities. Therefore, IMT-2000s requirements for 3G technology are as follows: (1) high data transmission rate including the minimum rate of satellite link 9.6 kbit/s, indoor environment at least 2 Mbit/s, outdoor walking and vehicle environment at least 384 kbit/s and 144 kbit/s, respectively, (2) transmission rate allocation on demand, (3) uplink and downlink adapting to the needs of asymmetric services, (4) simple cell structure and easy-to-manage channel structure, (5) flexible frequency and radio resource management, system configuration, and service facilities, and (6) the combination of wireless network and wired network, trying to achieve the same transmission quality as that of the wired network.
On October 19, 2007, the ITU officially approved the IEEE 802.16-based worldwide interoperability for microwave access (WiMax) to become the 3G standard. WCDMA and cdma2000 have been commercialized on a global scale, and China also began commercialization based on TD-SCDMA 3G system in 2008. However, 3G has its limitations which are as follows: (1) Using CDMA it is difficult to achieve high communication rate due to multi-user interference, (2) due to the limitation of the air interface to the core network, the dynamic range of service rates provided by 3G is not large enough to meet various service types, (3) the frequency resources allocated to 3G have become saturated, (4) the voice switching architecture adopted by 3G still inherits 2G circuit switching rather than pure IP, and (5) the applications of streaming media are not satisfactory. Therefore, more advanced technologies are needed to further improve the quality of mobile services.
1.1.4The fourth generation of mobile communication system
Along with the rapid development of the first three generations of mobile communication systems and intelligent mobile terminals, the users’ demand for services has changed from voice-based to Internet-based communication modes based on high-speed data streams. As users’ demand for transmission rate continues to increase, people are beginning to develop