With the development of smart terminals and emerging new applications (high-resolution multimedia, social networks, big data analysis etc), current mobile infrastructure (the 3G or 4G mobile networks) cannot gradually meet fast-increasing user requirements. Thus, radical and new technologies are needed for wireless communications, in addition to other candidate technologies, e.g. massive MIMO, wireless caching, etc. Among them, wireless caching increases the system performance with a new strategy. The main idea of wireless caching is to pre-store popular user data near end terminals, e.g. at base stations or the storage memory of user terminals. Thus, the request can be satisfied locally, rather than from remote servers. Then, the network throughput is improved and the response latency is reduced, especially for the multimedia transmission, which will be the dominant application in the 5G mobile.
However, the applications of wireless caching to mobile networks still face many challenges, e.g. impacts of user mobility, reliable transmission in multiple users/nodes, unreliable channels and information security. For instance, since the terminal is moving (as mobiles), the users may have to retrieve data from multiple nodes. Thus, the optimal caching for one node may not be optimal for another node in terms of rates. Moreover, the users may by multiple-accessed by non-orthogonal signals. This will lead to catastrophe. Meanwhile, the transmission medium of wireless communications is time-variant fading channels, which affect download bandwidth and capacity. Also, wireless transmission is unreliable, and efficient error control methods should be taken to fight against transmission errors. The mobility results in uncertainty, and the random in/out network and locations changes of mobile nodes may be frequent and lead to the uncertainty for downloading requested files. The variances of network topology, especially with mmWave communication, cooperative relaying and the integration of heterogeneous networks etc., render the structure of network topology complex. Because of the open air transmission and distributed caching, the security of caching data is also an important problem.
From an overview aspect, we studied information-theoretical performance limits and coding schemes to improve transmission rates, the reliability of transmission, and security. Except the theoretical analysis, we implemented our results in simulation testbed.
