Analysis of the fourth generation mobile communication
Introduction The rapid development of mobile communication technology has experienced three major stages of development. Each generation of development is a breakthrough in technology and innovation in concepts. The first generation originated in the 1980s, mainly using analog and frequency division multiple access (FDMA) technology. The second generation (2G) originated in the early 1990s and mainly used time division multiple access (TDMA) and code division multiple access (CDMA) technologies. The third generation mobile communication system (3G) can provide a wider frequency band, not only transmitting voice, but also transmitting high-speed data, thereby providing fast and convenient wireless applications. However, the third-generation mobile communication system is still a regional communication system based on different ground standards. Although its transmission rate can be as high as 2 Mb / s, it still cannot meet the requirements of multimedia communication. Therefore, the fourth-generation mobile communication system (4G) Research is imperative.
1. Definition of 4G and its technical requirements The fourth-generation mobile communication technology can be called Broadband access and distribution network. It has an asymmetric data transmission capacity of more than 2 Mb / s and can provide 150 Mb for full-speed mobile users. / s high-quality image service will realize the high-quality transmission of 3D images for the first time. It includes wideband wireless fixed access, wideband wireless local area network, mobile wideband systems and interoperable broadcast networks (based on terrestrial and satellite systems), integrating different modes of wireless communication, mobile users can roam freely from one standard to another A standard. Its wideband wireless local area network (WLAN) is compatible with B-ISDN and ATM to realize wideband multimedia communication, forming an integrated wideband communication network (IBCN), he can also provide positioning timing, data collection, remote control, etc. in addition to information Comprehensive functions. The main technical requirements are:
(1) The communication speed is increased, the data rate exceeds UMTS, and the Internet speed is increased from 2 Mb / s to 100 Mb / s.
(2) The mobile data-oriented Internet-oriented large-scale coverage of high-speed mobile communication networks has changed the design concept of designing mobile communication networks based on traditional mobile phone services.
(3) The system structure and terminal form using multi-antenna or distributed antenna, support mobile phone mutual assistance function, use wearable radio, downloadable radio and other new technologies.
(4) The transmission power is 10 to 100 times lower than that of the existing mobile communication system, which can better solve the problem of electromagnetic interference.
(5) Support richer mobile communication services, including high-resolution real-time image services and conference TV virtual reality services.
Second, the key technology of 4G 1. OFDM (Orthogonal Frequency Division Multiplexing)
OFDM technology is actually a kind of MCM (MulTI-Carrier ModulaTIon, multi-carrier modulation). The main idea is to divide the channel into several orthogonal sub-channels, convert the high-speed data signals into parallel low-speed sub-data streams, and modulate each sub-channel for transmission. Orthogonal signals can be separated by using relevant techniques at the receiving end, which can reduce mutual interference (ICI) between sub-channels. The signal bandwidth on each sub-channel is smaller than the associated bandwidth of the channel, so each sub-channel can be regarded as a flat fading, which can eliminate inter-symbol interference. And because the bandwidth of each sub-channel is only a small part of the original channel bandwidth, channel equalization becomes relatively easy. Because OFDM technology has the above characteristics, it is a potential solution to high-speed data transmission, so it is recognized as one of the core technologies of 4G.
2. Software Defined Radio (Software Defined Radio, SDR for short) is the use of digital signal processing technology on a programmable programmable general hardware platform, using software to define the functions of each part of the radio station: including front-end reception, intermediate frequency processing And signal baseband processing. That is, the entire radio station is completed by software programming from high frequency, intermediate frequency, baseband to the control protocol. The core is to use a broadband "digital / analog" converter as close to the antenna as possible to complete the digitization of the signal as early as possible, so that the functions of the radio station can be defined and implemented in software as much as possible. Software radio is a brand-new wireless communication architecture based on digital signal processing (DSP) chip with software as the core.
3. Smart antenna Smart antenna is a multi-beam or adaptive array antenna without switching between beams. Multi-beam antennas use multiple fixed beams in a sector, while in an adaptive array, the received signals of multiple antennas are weighted and combined together to maximize the signal-to-noise ratio. Compared with the fixed beam antenna, the advantage of the antenna array is that in addition to providing a high antenna gain, it can also provide a corresponding multiple of diversity gain. Smart antennas have intelligent functions such as suppression of signal interference, automatic tracking, and digital beam adjustment. The basic working principle is to adaptively adjust the pattern according to the direction of signal arrival, track strong signals, and reduce or cancel interference signals. The core of a smart antenna is an intelligent algorithm, and the algorithm determines the complexity of the circuit implementation and the instantaneous response rate. Therefore, it is necessary to select a better algorithm to achieve intelligent control of the beam.
4. IPv6 protocol The 4G communication system chose to use IP-based full packet to transmit data streams, so IPv6 technology will become the core protocol of the next generation network.
(1) Huge address space. In a foreseeable period, it can provide a globally unique address for all conceivable network devices.
(2) Automatic control. Another basic feature of IPv6 is that it supports stateless and stateful address auto-configuration methods. The stateless address auto-configuration method is the key to obtaining an address. In this way, the node that needs to configure the address uses a neighbor discovery mechanism to obtain a local connection address. Once this address is obtained, it uses another plug-and-play mechanism to obtain a globally unique routing address without any human intervention.
(3) Service quality. Quality of service (QoS) contains several aspects. From the perspective of the protocol, IPv6 and the current IPv4 provide the same QoS, but the advantage of IPv6 is that it can provide different services. The newly added field "flow flag" in the IPv6 header, with this 20-bit field, during the transmission process, each node in China can identify and handle any IP address flow separately.
(4) Mobility. Mobile IPv6 (MIPv6) provides greater flexibility in terms of new functions and new services. Each mobile device has a fixed home address (home address), this address has nothing to do with the location of the device currently connected to the Internet. When the device is used outside the hometown, a care-of address is used to provide the current location information of the mobile node. Each time a mobile device changes location, it must tell its home address and its corresponding communication node of its care-of address.
3. Conclusion 4G will become the focus of the industry due to its advantages of faster communication speed, wider network spectrum, more flexible communication, higher intelligent performance and smoother compatible performance compared with 1 ~ 3G. It is believed that in the near future, 4G will unify the world of mobile communications and generate huge social and economic benefits.
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