1) Targets in the framework include users, terminals, networks, and applications, which compass the entire technical domain and operating environment of 4G.
2) Core features of 4G are described as diversity and adaptability of the targets, leading to seamless integration.
3) The feature of diversity includes both external and internal diversity, in which adaptability is caused by external diversity and is solved by internal diversity.
Technical perspectives are presented for each of the features in the paper, in which also some promising techniques and possible research issues of 4G are introduced. The proposed framework provides a layout view on future communication systems, and challenging research topics are figured for guiding systematic research of 4G.