Distributed coordination of co-channel femtocells via inter-cell signaling with arbitrary delay

To achieve high spatial reuse of spectrum resources with limited inter-layer/cell interference, co-channel femtocells must be coordinated with the underlying macro- and other femto-cells in using radio resources. While inter-cell signaling can coordinate femtocells by providing the status information of neighbor cells explicitly, signaling delay - which may result from a limited signaling rate to reduce the resulting overhead, network latency, etc. - and its impact on the behavior of distributed coordination has not been explored before. In this paper, we propose a new architecture for the distributed coordination of co-channel femtocells based on asynchronous inter-cell signaling, called asynchronous coordination of co-channel femtocells (ACoF). ACoF improves solutions iteratively; femtocells update radio resource usage based on the received information, which usually gets outdated due to delayed signaling and asynchronous update behavior. ACoF allows each femtocell to adjust its signaling rate depending on its local conditions for fine-grained cost minimization, but at the expense of higher degree of inconsistency of femtocells' knowledge. Despite such asynchrony and inconsistency, the solution yielded by ACoF is guaranteed to converge to a global optimum under a certain condition of configuration parameters, which we prove theoretically. We design the optimization method of per-cell signaling rate for both wired and over-the-air signaling. Finally, we present a joint muting and transmit power adjustment scheme designed for ACoF and evaluate its convergence behavior and performance gain.