Dynamic Broadband Spectrum Refarming for OFDMA Cellular Systems

Conventional spectrum refarming (SR) techniques assemble the legacy services to partial licensed spectrum, and free up the remained spectrum for operating other communication systems. In this paper, we propose a new broadband SR framework in which the orthogonal-frequency division multiple access (OFDMA) system dynamically shares the code division multiple access (CDMA) spectrum, which contains multiple bands in a concurrent manner. The interference margin provided by the downlink isometric random precoded CDMA system is first derived. To protect all the CDMA users, interference constraints that regulate the OFDMA transmission are then formulated. We formulate the joint CDMA load planning and OFDMA resource allocation problem for the SR system. By applying primal decomposition, it is shown that the higher-level problem is non-convex in general. We first propose an efficient algorithm to find the myopic optimal solution by investigating the derivative property of the higher-level problem. Through enhancing the original constrains, the higher-level problem is shown to be convex and solved with another efficient algorithm. Simulation results are provided to evaluate the SR performance, illustrating the significance of the CDMA load planning on the OFDMA throughput, the advantage of the proposed SR model over conventional SR, and the protection to the CDMA system.