With more users, more mobile phones and tablets, more connections to homes and offices, and richer content sharing over wireless communication networks, the industry is facing an exponential increase in mobile broadband traffic in the frequency spectrum from 700 MHz to 2.6 GHz. To meet this demanding challenge, an intuitive idea is to add more licensed spectrum, which would ensure predictable performance in terms of mobility. However, for various reasons, it is possible that sufficient additional licensed spectrum will not be available in the near future. On the other hand, the amount of unlicensed spectrum already assigned or planned to be assigned is comparable or even more than the licensed spectrum. By taking full advantage of the unlicensed spectrum, the burden on the licensed spectrum can be relieved. Unlicensed spectrum has already been utilized in multiple technologies, such as Wi-Fi and Bluetooth, and now there is a new member of the unlicensed family at 5 GHz for mobile broadband. By extending the benefits of Long Term Evolution-Advanced (LTE-A) to the unlicensed spectrum, we can boost the capacity, while maintaining seamless mobility and predictable performance.
Although it has great potential, LTE-Unlicensed is still in its infancy and faces some major challenges. Only by careful design can the LTE-Unlicensed technique truly benefit us with tremendous advantages. Thus, in this chapter, we give a comprehensive introduction to the benefits and design principles of LTE-Unlicensed. In addition, two specific implementation cases are provided for illustration purposes. This chapter is organized as follows. In Section 20.1, the motivation for proposing the LTE-Unlicensed technique will be stated. Then the design challenges in and potential solutions for LTE-Unlicensed will be discussed in Section 20.2. Two distributed resource allocation applications utilizing matching-based approaches will be introduced in Section 20.3. Finally, conclusions are drawn in Section 20.4.
Currently, technologies such as IEEE 802.11 (Wi-Fi), 802.15.1 (Bluetooth), and 802.15.4 (ZigBee) are implemented in the 2.4 GHz ISM (Industry, Scientific, and Medical) and 5 GHz U-NII (Unlicensed National Information Infrastructure) bands, more commonly referred to as the unlicensed bands. Some operators have deployed a large number of Wi-Fi access points (APs) to offload cellular traffic to the unlicensed spectrum. Wi-Fi offloading strikes a trade-off between capacity and performance.