1, Introduction With the increased demand for bandwidth, Communications technology The development of 2.5G and 2.75G was once the middle of the transition on behalf of. When 3G Mobile business has just taken steps, appeared to support voice, data and video transmission technology in three formats High Speed Downlink Packet Access technology. Meanwhile, the real concept of 4G broadband data Rate standards have emerged, which includes fixed broadband wireless access, broadband wireless local area network, broadband systems, each Caozuo the broadcast networks and satellite systems, will be Duogong Neng Ji Cheng's broadband mobile communication systems, can provide data transfer rates of up to 100Mbit / s or even higher, but also broadband access IP system.
From communications technology standards development process, which can be divided into four main line and the two factions. Four main lines which means: 3GPP, 3GPP2, WiMAX and regional standards; two factions refer to: North American and European standards IEEE802.xx the UMTS 3G standard. Standard low-cost construction division increased network complexity. Define the available spectrum resources is another division standard, and this differentiation to facilitate the introduction of new technology standards. Optimal allocation scheme is the global allocation of resources under, but because of radio planning needs and the deployment of heterogeneous spectrum correspond to the spectrum needs of the region with the expansion of the scale, it is difficult to achieve a unified wireless planning. But we can at the same frequency band using a different standard, provided that end-users wireless access to free choice.
2,4 G of the concepts and requirements
Simple terms, 4G is an ultra high-speed wireless network, an information superhighway without cables. This new network allows wireless phone users to achieve all-round form of virtual connection. One of the most prominent feature of 4G is the network transfer rate to an unprecedented 100Mbit / s, fully able to meet the needs of the user's Internet access. The overall technical goal of 4G systems and characteristics can be summarized as: the system should have the higher data rates, better quality of service (QoS), higher spectral efficiency, higher safety, more intelligent, more high transmission quality, greater flexibility; 4G system should be able to support the non-symmetry of business and can support a variety of business; 4G system should reflect the mobile and wireless access network and IP network continues to convergence trends. Following the discussion from different angles 4G systems.
2.1 point from the network
Unified mobility and security management, asked to consider different network entities such as the interaction. The main problem is resolved when the conversation uninterrupted roaming and service mobility, the current solution has emerged a number of programs to accomplish this function, such as mobile IP technology and Session Initiation (SIP).
End to end QoS negotiation support to the network layer and involving over Internet Protocol system. 3GPP UMTS network drafted a comprehensive QoS architecture, QoS is now committed to a common research framework.
Intermediary server with user authentication, authorization and accounting. With the development of IP networks, operators need thousands of concurrent users required to simultaneously access the network via different technologies to provide AAA services, but also must be able to safely support the inter-network AAA services, and should have good scalability, which requires extended AAA function of the existing agreement. In view of this, IETF AAA working on developing the next generation protocol, that is, Diameter protocol. Diameter is a lightweight on the equation of the AAA protocol, using a modified retransmission mechanism to improve network reliability, while also providing a new end to end security mechanism. Figure 1 shows the introduction of an intermediary for the Diameter server to provide AAA services to roaming users. Using an intermediary server can reduce the access network Proxy Workload of the server's configuration, network expansion needs to be updated only when an intermediary server configuration, the agreement will help improve the scalability.
Figure 1 Diameter intermediary server 2.2 point from the terminal
Support multiple communication modes, with the ability to adapt and re-configuration. Terminal can reconfigure itself to change the access mode, open software architecture and standardized environment for this radio could provide. Software radio makes the system flexible and adaptable, able to adapt to different network and air interface. Software radio technology to support different air interface of multi-mode Mobile And the base station, to achieve a variety of applications, variable QoS. Software radio technology will help the integration of different standards and systems. Use of software radio base station can simultaneously achieve multiple network services; when the terminal moves, re-configuration, such as when the mobile terminal moves to a different standard for mobile systems, the terminal system in accordance with the standard automatic configuration of the re- terminal.
ABC connection. ABC (Always BestConnected) to the terminal in different wireless access networks to achieve seamless switching, by giving each user the most appropriate services to achieve optimal overall network performance and resource utilization. ABC key technologies to achieve business is the choice of access network, access network selection QoS impact factors are: accessibility, throughput, time set, reliability, safety and cost. We use X on behalf of the smaller set of possible factors, such as power, bit error rate, the bigger the better with the Y on behalf of the factor sets, such as security, reliability and throughput. Sb is greater than the threshold Ts representatives to meet the requirements of the element set only, such as bandwidth, coverage area, Ss is less than the threshold Tb representatives to meet the requirements of the element set only, such as jitter, delay. This can be attributed to the network selection based on constrained optimization problem:
W1, W2 is the weight, the user can change the shape W1, W2, and Ts, Tb values to select the access network to meet their requirements in order to achieve personal service.
Access network discovery and selection. In the GSM network, base station periodically broadcasts the signal through to the end for business processes, in 4G heterogeneous networks, shown in Figure 2, due to different access protocols and wireless technologies, need to use more complex technology, Here are two reference solutions: One is the use of software radio technology to scan for available networks; the other is the use of broadcast radio channel to reach end-users can access network
