With the development of multimedia communications, people need a higher speed, greater coverage and mobility of wireless broadband access, the emergence of WiMAX technology just meets people's demand for wireless Internet. If the wireless local area network technology solves the "last one hundred meters" access problem, then WiMAX technology is the best solution for the "last mile" access.
1. WiMAX technology
Global Interoperability for Microwave Access (WiMAX) is a wireless metropolitan area network (WMAN) technology with higher data transmission rates, more flexible deployment, more scalable and safer configurations, and wider coverage. The advantage of WiMAX network determines that it will be an important part of the future wireless communication network.
In the future, WiMAX and other wireless network technologies are likely to coexist in the market, just like the coexistence of GSM and CDMA standards for mobile communications today. WiMAX can adopt the same networking mode as Wi-Fi / 3G in terms of networking structure, and can adopt hierarchical, flat, Mesh network structure, and a flexible combination of the three. In the future wireless communication field, there will be a pattern in which various wireless access technologies coexist and various mobile communication systems are compatible and cooperative with each other.
2. Hybrid networking of TD-SCDMA and WiMAX
The third generation mobile communication technology mainly includes WCDMA, cdma2000, TD-SCDMA, etc., mainly voice communication. Although it can maintain communication under high-speed mobile, the highest data transmission rate is only 2 Mbit / s, which cannot meet the requirements of mobile cities. WiMAX is suitable for providing high data rates in local hot spots, and 3G can achieve wide area coverage. Therefore, 3G and WiMAX are destined to be two complementary technologies, and their integration is of great significance.
The WiMAX mobile communication system is mainly positioned for packet data service transmission. Its peak data transmission rate can reach 75 Mbit / s, which is much higher than the 3G system. However, its main application is for fixed, portable, or low-speed mobile user access. The early and middle stages of network construction do not support seamless roaming under high-speed mobile. The 3G mobile communication system has the advantages of supporting fast roaming and calling service functions that can provide full network coverage. If WiMAX and 3G systems are combined during networking, WiMAX focuses on broadband wireless to meet the needs of high-speed data services in hot spots, while 3G focuses on achieving high-quality voice communication and seamless roaming requirements for mobile communications. Realize the advantages and disadvantages of the two major systems and complement each other's advantages. Therefore, the investment cost of the two can be saved, a win-win situation can be achieved, and the user's demand for one card for multiple uses can be met [1]. Although there is a big difference in technology between the two, TD and WiMAX both use the TDD method in the air interface part, which gives TD the possibility of drawing on WiMAX air interface technology. TD can learn from WiMAX while maintaining its own advantages. The technology of air interface develops TDD-OFDM technology, so that it can better evolve to B3G and even 4G in the future. Therefore, 3G and WiMAX joint networking is feasible, and it is a very advantageous hybrid networking system.
The weaknesses of TDD (TD-SCDMA) separate networking:
(1) The receiving and sending channels are on the same frequency, and interference isolation cannot be achieved with the help of frequency selectivity.
(2) In order to implement coexistence electromagnetic compatibility with different FDD networks, the larger guard bands generally need to be reserved affect the overall spectrum utilization efficiency.
(3) There is no global TDD large-scale networking experience.
(4) Global roaming services still face greater challenges [4].
In other words, TD considers channel calculation and base station construction. To build high-quality and high-speed data seamless coverage requires that the cell radius cannot be too large, otherwise the investment scale is too large, and it is not suitable for supporting hot spots in terms of economic benefits. Data service coverage. WiMAX technology can solve these problems. The ideal joint networking solution is: use WiMAX's ability to support high-speed data services, use WiMAX to cover high-speed data service-intensive urban areas, and use TD-SCDMA to support fast roaming and the advantages of calling services that can provide full network coverage to achieve voice and low speed Continuous coverage of data, and can also use WiMAX system to provide E1 interface to achieve the interconnection of TD base stations, see Figure 1. In this way, the advantages of the two systems can be complemented. Specifically, for 3G users, the combined WiMAX and 3G network can provide higher-speed broadband data services and cheaper broadband access prices; for WiMAX users, the combined WiMAX and 3G network can provide Wider-area wireless access service and better mobile performance. In addition, the integration of WiMAX technology and 3G helps reduce the construction and operating costs of 3G networks and improve the quality of service for mobile and wireless broadband services.
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