QoS-Aware Multi-RAT Resource Allocation with Minimum Transmit Power in Multiuser OFDM System

A novel analytical framework of multiple radio access technologies (Multi-RAT) communication system is proposed where a small cell serves K mobile users via IEEE 802.11 Wireless Local Area Network (WLAN) and 3GPP Long Term Evolution (LTE) access technologies. A scheduler at the small cell is proposed in order to minimize the total transmission power subject to quality of service constraints on the users transmission rates. An optimal solution to the resulting nonconvex optimization problem is proposed to reach the optimal value by solving a group of convex problems using a proposed iterative optimal algorithm. Furthermore, the offloading transmission scenario is considered where each user is assigned either to WLAN or LTE and a solution of two steps is proposed. The first step finds the user-to-RAT assignment while the second step allocates the resources to the WLAN and LTE users. Numerical simulations are presented to demonstrate the superior performance of the proposed Multi-RAT scheduling schemes (saving 43% of the total transmission power) compared to the conventional Single-RAT LTE system.