Interference Aware Medium Access in Cellular OFDMA/TDD Networks

In this paper a novel decentralized and interference aware medium access control (MAC) protocol combined with a dynamic subchannel selection algorithm for OFDM (orthogonal frequency division multiplexing) is presented. The protocol resolves several drawbacks of the existing radio resource allocation techniques for OFDM systems, such as the hidden and exposed node problem, and the requirement for a time-invariant channel. The proposed scheme enables the transmitter to determine the level of interference it would cause to already active links prior to any transmission. This is achieved through a busyslot signaling that exploits the channel reciprocity offered by the TDD mode. Compared to existing radio resource allocation schemes the required signaling overhead is significantly reduced. The interference awareness allows the system to avoid significant co-channel interference (CCI) and to operate with full frequency reuse. When applied to a broadband OFDM air interface, this principle can also exploit the frequency selective fading channel on the intended as well as the interference links. This results in an autonomous subcarrier allocation algorithm which can dynamically adapt to time-varying channels. Due to its decentralized nature, the algorithm can be utilized in both cellular and ad hoc networks. Simulation results for a cellular system show that the new decentralized medium access and channel assignment algorithm is capable of achieving spectral efficiencies of up to 2.25 bits/Hz/cell using 16 QAM (quadrature amplitude modulation).