Link Adaptation for Fair Coexistence of Wi-Fi and LAA-LTE.

As the demand for mobile data traffic increases and cellular network capacity is reaching its theoretical limit, using the unlicensed spectrum is deemed unavoidable. The deployment of the unlicensed spectrum can be a beneficiary solution to increase the capacity of the network and to reduce the cost of the licensed bands that is required. However, the extension of a cellular network, such as Long-Term Evolution (LTE), over the unlicensed spectrum also entails the requirement of a reliable coexistence between other technologies that freely access the unlicensed bands and mainly Wi-Fi. To enable the equal sharing between the so called License Assisted Access (LAA) - LTE and Wi-Fi a number of mechanisms has been introduced by the regulations imposed by standardization organizations such as 3GPP. The process followed by these mechanisms mainly focuses on the Media Access Control (MAC) layer. However, link adaptation is another key factor that can enable high spectral efficiency, reduce the detrimental effect of non-synchronous communications, and increase the overall performance. To this end, in this paper we investigate the contribution of link adaptation in case of LAA-LTE and Wi-Fi coexistence. In particular, we propose a number of enhancements in Wi-Fi link adaptation to increase its adaptability both in terms of changing channel conditions and in terms of LAA-LTE coexistence. Our results show that LAA-LTE can equally and fairly share the channel with Wi-Fi and that the proposed improvements can significantly increase the Wi-Fi performance whether operating alone or coexisting with LAA-LTE. Finally, a detailed description of the fundamental differences in link adaptation between the two technologies is described shedding light to the performance difference noticed.