The Future of Wifi

In recent years, the mobile data usage has grown by 70–200 percent per annum. More worryingly, the bursty nature of wireless data traffic makes traditional network planning for capacity obsolete. Amongst both operators and vendors alike, small cells (e.g., picocells, femtocells and relay nodes) have been considered as a promising solution to improve local capacity in traffic hotspots, thus relieving the burden on overloaded macrocells. A lot of research and development efforts have been made to efficiently offload excess traffic from macrocells to small cells, especially in indoor environments [1]. Due to the scarcity of licensed spectrum for cellular networks, small cells are expected to share the same spectrum with macrocells even when they are deployed within the coverage area of a macrocell [2]. A frequency reuse factor of 1 in 3G HSPA+ and 4G LTE/LTE-A systems has proven to yield high gains in network capacity. If without notable amounts of extra spectrum made available for mobile communications, future cellular networks will unsurprisingly continue to explore aggressive frequency reuse methods. Accordingly, the envisaged large-scale deployment of small cells is likely to be hampered by the potentially severe co-channel interference between small cells and the umbrella macrocell and between neighboring small cells in dense deployment. In view of this, the wireless industry is examining the efficient utilization of all possible spectrum resources including unlicensed spectrum bands to offer ubiquitous and seamless access to mobile users [3]. The unlicensed 2.4 GHz and 5 GHz bands that Wi-Fi systems operate in have been considered as important candidates to provide extra spectrum resources for cellular networks. The initially targeted 5 GHz unlicensed band has potentially up to 500 MHz of spectrum available. In USA, Korea and China, deploying LTE-A in unlicensed spectrum does not require changes to the existing LTE-A standards (e.g., 3GPP Rel-10). In most other countries, the regulatory requirements of `Listen Before Talk’ in unlicensed spectrum mandate standard modifications (e.g., candidates for 3GPP Rel-13). Nowadays, most mobile devices such as smartphones and tablets support Wi-Fi connectivity, while the proliferation of Wi-Fi access points continues. The Wi-Fi access point density in developed urban areas has reached over 1000 per square km. Widely deployed Wi-Fi systems are playing an increasingly more important role in offloading data traffic from the heavily loaded cellular network, especially in indoor traffic ABSTRACT