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 the next-generation system based on the first three generations of mobile communication systems to better support high-speed broadband mobile communication services. The World Radio Conference in 2007 allocated spectrum for IMT-Advanced, and IMT-Advanced standards began to be collected in March 2008. By October 2009, a total of six candidate proposals were collected, which can be classified into 3GPP LTE-Advanced3 and IEEE802.16m.4 At present, international standards for 4G mobile communication technologies mainly include FDD-LTE, FDD-LTE-Advance, TD-LTE, and TD-LTE-Advanced. Among them, TD-LTE and TD-LTE-Advanced are 4G international standards led by China.
LTE is an evolution of 3G. It improves 3G air access technology, using orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output (MIMO) technologies as its wireless evolution technology. The LTE mobile communication system can provide a downlink rate of 100Mbit/s (TD-LTE) or 150Mbit/s (FDD-LTE), an uplink rate of 50 Mbit/s (TD-LTE) or 40 Mbit/s (FDD-LTE), and peak rates in a 20-MHz spectrum bandwidth. TD-LTE is the 4G international standard led by China, and it is adopted by China Mobile.
LTE-Advanced can be divided into FDD-LTE-Advanced and TD-LTE-Advanced. It is optimized for indoor environments and uses technologies such as carrier aggregation. It flexibly allocates spectrum for a wider spectrum bandwidth and effectively supports new frequency band and large-bandwidth applications. It can provide a downlink rate of 1 Gbit/s and an uplink rate of 500 Mbit/s in a 100-MHz spectrum bandwidth.
WiMax is an IEEE 802.16 standard that provides a maximum access rate of 70 Mbit/s and a working frequency range of 2–66 GHz without authorization. The main advantages of WiMax are as follows: (1) it is beneficial to avoid known interference, (2) it is beneficial to save spectrum resources, (3) flexible bandwidth adjustment capability is beneficial for operators to coordinate spectrum resources, and (4) wireless signal transmission distance can be up to 50 km. However, it cannot meet the seamless connection of wireless networks under high speed in terms of mobile performance. Therefore, WiMax is not a wireless mobile communication technology, but only a wireless broadband LAN technology.
Wireless MAN-Advanced is an upgraded version of WiMax, namely the IEEE 802.16m standard, which has the ability to seamlessly switch under high speed. It can effectively solve mobile performance problems of WiMax. IEEE 802.16m is compatible with 4G networks. Its advantages are as follows: (1) expand network coverage to achieve seamless network connectivity, (2) improve spectrum efficiency, (3) provide 1 Gib/s wireless transmission rate in roaming mode or high-efficiency/strong signal mode.
1.1.5The fifth generation of mobile communication system
The
