Cooperative device-to-device communications in the downlink of cellular networks

We propose a cooperative device-to-device (D2D) communications framework in order to combat the problem of congestion in crowded communication environments. The idea is to allow a D2D transmitter to act as an in-band relay for a cellular link and at the same time transmit its own data by employing superposition coding in the downlink. Cooperation between the cellular link and D2D transmitter eases down the requirement on the interference. The main benefit of the proposed method is in increasing the number of connections per unit area with the same spectrum usage. It could also be beneficial to offload over-loaded cells. We formulate our problem to minimize the assigned power for cooperation while making sure the cellular user´s performance does not degrade. Our results show that cooperation possibilities and improvement in overall cell capacity increase with the number of cellular users within the cell as well as the cell size.