4G mobile communication technology has entered the commercial stage, and operators need to provide higher capacity and data transmission rate under limited spectrum resources. The introduction of high-bandwidth and high-order modulation technology in LTE makes higher requirements for signal-to-noise ratio, so the coverage of a single LTE base station will be smaller than when 3G technology is used. The requirements of dense networking and cooperation between base stations have brought about a huge demand for the expansion of the number of base station sites, and correspondingly brought great challenges in site selection, power consumption, and massive fiber resources. Therefore, appropriate networking and transmission solutions are the key technologies to promote the popularization of 4G applications.
To this end, major operators are conducting research on new wireless access network networking methods. For example, China Mobile’s C-RAN is a clean system based on Centralized Processing, Collaborative Radio, and Real-time Cloud Infrastructure. Its essence is to reduce the number of sites by placing the baseband unit BBU in a centralized manner, and to extend the outdoor remote radio unit RRU to the area that needs to be covered by a suitable transmission scheme. This networking method greatly reduces the number of computer rooms, thereby reducing construction, operation and maintenance costs. At the same time, collaboration and virtualization technologies can be used to realize resource sharing and dynamic scheduling, improve spectrum efficiency, and achieve low cost, high bandwidth and Flexible operation. Figure 1 shows the networking method of C-RAN (Reference: www.c-ran.com)