Exponential backoff in frequency-domain for random access in OFDMA femtocells

OFDMA femtocells are considered a key enabler in 3GPP LTE-Advanced networks of very high data rates for indoor users. However, the unmanaged nature of femtocells implies the need for careful modeling (and ultimately, managing) of inter-cell interference especially in dense deployments. So far, co-channel interference in femtocells has been investigated using traditional, cellular resource allocation approaches that usually assume a fully loaded network where the system is insensitive to the activity of a single user. This assumption is not suitable for femtocells which are designed to serve very few users and thus lacks the presumed traffic aggregation. In this paper, we exploit the bandwidth flexibility inherent to OFDMA to design more effective (distributed) random access MAC protocol for femtocells. The proposed Exponential Backoff in Frequency (EBF) algorithm allows femtocells to transmit packets in bulk and resolves collisions in the frequency-domain using a synchronized binary tree branching process over the channels that reduces the accessed bandwidth after every failed attempt. Analysis of the mean packet delay and simulation results show that EBF enjoys considerably less packet delay compared to the basic K-Aloha MAC in which femtocells transmit over a random K-subset of channels.