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With significantly growing demand for wireless networks and services in recent years, the issue of spectrum efficiency has taken a more and more important role in the design of communication systems. To achieve more dynamic, efficient and intelligent use of the scarce wireless spectrum resource, the concept of cooperation has been formalized into several hierarchical network models in future mobile networks, including cognitive radio networks and Internet of Things. Cooperative communications, such as cooperative relaying, can potentially increase communication efficiency and spectrum utilization by overhearing and cooperating with the transmission due to the broadcast nature of wireless networks. On the other hand in hierarchical networks, cooperation of users may lead to a better support for diverse communication modes with flexible spectrum sharing. In this thesis, we investigate the cooperation between users with different priorities in hierarchical wireless networks. Especially, by coinciding the idea of relaying and network coding, we explore cooperation schemes from several aspects. First we discuss orthogonal time-frequency access for cooperation between primary and secondary users in a cognitive radio network, where two binary network coding schemes are developed over packet-based wireless links. We analyze the transmission process and propose a novel methodology for performance evaluation by approximating the distribution of the number of transmission attempts. From the study in two cases of different definitions on frame size, the performance evaluation method provides an efficient way to estimate spectrum …