Traffic-aware graph-based dynamic frequency reuse for heterogeneous Cloud-RAN

In order to allocate frequency resource among users in heterogeneous Cloud-RAN (Het-Cloud-RAN) as well as avoid the co-channel interference, we propose a traffic-aware graph-based dynamic frequency reuse scheme. Cloud-RAN is a new network structure comprised of baseband units (BBU) and remote radio heads (RRH), which has the ability to reduce the energy costs of network. Two kinds of RRHs, including macro RRHs and pico RRHs, are considered to form the two tiers of the Het-Cloud-RAN. We construct the interference graph where the vertices represent different RRHs in the network, and then apply our proposed scheme in it. We use a graph coloring method to allocate different length of bandwidth to cells in different tiers based on their traffic demands. Our scheme also considers the time varying traffic and can adjust the frequency allocation based on the change of traffic demands in each cell without re-performing the whole scheme. With the application of our scheme in Het-Cloud-RAN, we can not only improve the spectrum utilization and efficiency, but also reduce the energy consumption through reducing the number of working BBUs. The system level simulation results show clearly that our new scheme in Het-Cloud-RAN outperforms the existing frequency allocation scheme based on traditional cellular system in many ways including throughput and energy efficiency.