Load balancing in UDN networks by migration mechanism with respect to the D2D communications and E2E delay

Ultra-Dense Network (UDN) is considered as one of the key technologies of 5G. However, the dense deployment of small cells in UDN hotspots generates an uneven traffic distribution. To address this problem, this paper proposes a load migration mechanism to transfer the extra users from the small cells to the macrocells. In addition, this paper employs the design structure matrix (DSM) method with different approaches in order to balance the load among the small cells and to reduce the inter-communications between the access points. Once the load balancing and the user transfer are achieved, the DSM method is capable of taking the device-to-device (D2D) communications of the users into account. The results prove that the user transfer approaches with the DSM method with respect to the D2D communications can enhance the balancing results in some cases by 24.68% compared to the case without transfer. Additionally, the balance improvement ratio can reach 78.30%. Besides, the average inter-communications ratio between the access points can be reduced by 57.35%.