Coexistence of Wi-Fi and heterogeneous small cell networks sharing unlicensed spectrum

TLDR

Wi‑Fi and cellular networks have evolved separately, yet the growing data demand drives cellular toward dense small‑cell deployments that suffer severe interference from limited licensed spectrum, prompting exploration of shared use of the 2.4 GHz and 5 GHz unlicensed bands. This study investigates how 4G small cells can coexist with Wi‑Fi when both operate in the same unlicensed spectrum. The authors propose a small‑cell architecture that employs an almost‑blank subframe scheme without priority and an interference‑avoidance strategy that estimates nearby Wi‑Fi access‑point density to mitigate co‑channel interference. Simulations demonstrate that the architecture and avoidance schemes markedly boost 4G heterogeneous network capacity while preserving Wi‑Fi service quality.

Abstract

As two major players in terrestrial wireless communications, Wi-Fi systems and cellular networks have different origins and have largely evolved separately. Motivated by the exponentially increasing wireless data demand, cellular networks are evolving towards a heterogeneous and small cell network architecture, wherein small cells are expected to provide very high capacity. However, due to the limited licensed spectrum for cellular networks, any effort to achieve capacity growth through network densification will face the challenge of severe inter-cell interference. In view of this, recent standardization developments have started to consider the opportunities for cellular networks to use the unlicensed spectrum bands, including the 2.4 GHz and 5 GHz bands that are currently used by Wi-Fi, Zigbee and some other communication systems. In this article, we look into the coexistence of Wi-Fi and 4G cellular networks sharing the unlicensed spectrum. We introduce a network architecture where small cells use the same unlicensed spectrum that Wi-Fi systems operate in without affecting the performance of Wi-Fi systems. We present an almost blank subframe (ABS) scheme without priority to mitigate the co-channel interference from small cells to Wi-Fi systems, and propose an interference avoidance scheme based on small cells estimating the density of nearby Wi-Fi access points to facilitate their coexistence while sharing the same unlicensed spectrum. Simulation results show that the proposed network architecture and interference avoidance schemes can significantly increase the capacity of 4G heterogeneous cellular networks while maintaining the service quality of Wi-Fi systems.