So far, 3G standards and specifications have been agreed and have entered commercial use. However, we should also see that 3G systems also have their limitations, such as: the lack of global unified standards; 3G's voice exchange architecture still inherits the second generation (2G) circuit switching, rather than pure IP; due to Multi-user interference, CDMA is difficult to achieve high communication rates and the like. However, for the above various shortcomings, the fundamental task of the 4G mobile network is to be able to receive and acquire calls to the terminal, establish its most effective communication path between multiple operating networks (platforms) or between multiple wireless interfaces, and Real-time positioning and tracking. In the process of mobile communication, the mobile network must maintain a good seamless connection capability to ensure high quality and high speed of data transmission. The 4G mobile network will be based on a multi-layer cellular structure, providing multimedia services by multiple service providers and numerous network operators through multiple wireless interfaces. The core network is an all-IP-based network. Therefore, the core network is independent of various specific wireless access solutions and can provide end-to-end IP services, which can coexist with the existing core network and PSTN. Various access systems for different services are connected to the IP-based core network through a multimedia access system to form a public, flexible, and scalable platform, as shown in the figure.
Figure: 4G system network structure
First, discuss the three key technologies of 4G technologyOFDM technology
OFDM is the most suitable multiple access scheme for 4G systems. The main idea of ​​this technology is to divide a given channel into many narrow orthogonal subchannels in the frequency domain, using one subcarrier for modulation on each subchannel, and each subcarrier is parallel. Transmission, so interference between signal waveforms can be greatly eliminated. OFDM can also adaptively allocate transmission loads on different subchannels, which optimizes the overall transmission rate. OFDM technology can also combat frequency selective fading or narrowband interference. In the OFDM system, since the carriers of the respective subchannels are orthogonal to each other, their spectrums overlap each other, which not only reduces the mutual interference between the subcarriers, but also improves the spectrum utilization.
2. Smart Antenna (SA) and Multiple Input Multiple Output Antenna (MIMO) Technology
Smart antennas have intelligent functions such as suppression of signal interference, automatic tracking, and digital beam conditioning, and are considered to be key technologies for future mobile communications. Smart antenna shaped beam can suppress crosstalk in the spatial domain and enhance the wanted signal in a special range. This technology can improve signal quality and increase transmission capacity. The basic principle is to use antenna array and coherent wireless transceiver at the wireless base station. The signal is used to receive and transmit RF signals. At the same time, through the baseband digital signal processor, the signals received on the respective antenna links are combined according to a certain algorithm to realize the uplink beamforming. At present, there are two main ways in which smart antennas work: a fully adaptive method and a pre-multi-beam based beam switching method.
3. Software Radio Technology (SDR)
Software radio technology is considered to be the only technology that can effectively link different forms of communication technology together. In 4G mobile communication systems, software will become very complicated. To this end, experts propose to introduce software radio technology as a bridge from second-generation mobile communications to third-generation and fourth-generation mobile communications. Software radio technology can digitize the analog signal as close as possible to the antenna, that is, the A/D and D/A converters are as close as possible to the RF front end, and the DSP is used for channel separation, modulation and demodulation, and channel coding and decoding. It aims to establish a radio communication platform on which various software systems can be run to enable multi-channel, multi-level and multi-mode wireless communication.
Second, putting the 4G system into practical application will encounter challenges in both technology and market.1. The various core technologies used in 4G systems are still not perfect. The gradual improvement of these technologies is a long-term process. In addition, the integrated service/RSVP technology and differentiated service technology used in QoS in the mobile IP environment are also one of the important issues to be solved. And these technologies are not optimal on mobile IP platforms.
2. The maximum speed of the 4G system, in practical applications, it is difficult to reach the theoretical value. The demand for future 4G communication is that its communication transmission speed will be greatly improved, theoretically up to 100Mbps, but the transmission speed of mobile phones will be limited by the capacity of the communication system.
3. The development and implementation of 4G will also be affected by market pressure. Some experts predict that after 10 years, 2G multimedia services will enter the third stage of development. At this time, 3G networks covering the whole world have basically taken shape. At least 25% of the world's population use 3G systems. By that time, the entire industry. The third generation technology is being digested and absorbed, and the improvement and improvement of 3G using 4G related technology will also be carried out at the same time. The acceptance of 4G system also requires a gradual transition process. In addition, during the transition process, the technology known as 5G is likely to threaten the 4G profit plan at any time.
4. Although the fourth-generation mobile communication technology has stronger advantages than 3G, if the 4G is put into practical application, the existing mobile communication infrastructure needs to be updated, which will lead to a series of funds and concepts. And so on, so to a certain extent will slow down the speed of 4G officially entering the market.
Although the development path of 4G systems is bumpy, it is also full of variables. However, with the emergence of new technologies and new demands, 4G will inevitably replace 3G and become the leading technology in the future of mobile communications. 4G will definitely make our future mobile communications business a better prospect.
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