Radio interface evolution towards 5G and enhanced local area communications

The exponential growth of mobile data in macronetworks has driven the evolution of communications systems toward spectrally efficient, energy efficient, and fast local area communications. It is a well-known fact that the best way to increase capacity in a unit area is to introduce smaller cells. Local area communications are currently mainly driven by the IEEE 802.11 WLAN family being cheap and energy efficient with a low number of users per access point. For the future high user density scenarios, following the 802.11 HEW study group, the 802.11ax project has been initiated to improve the WLAN system performance. The 3GPP LTE-advanced (LTE-A) also includes new methods for pico and femto cell´s interference management functionalities for small cell communications. The main problem with LTE-A is, however, that the physical layer numerology is still optimized for macrocells and not for local area communications. Furthermore, the overall complexity and the overheads of the control plane and reference symbols are too large for spectrally and energy efficient local area communications. In this paper, we provide first an overview of WLAN 802.11ac and LTE/LTE-A, discuss the pros and cons of both technology areas, and then derive a new flexible TDD-based radio interface parametrization for 5G local area communications combining the best practices of both WiFi and LTE-A technologies. We justify the system design based on local area propagation characteristics and expected traffic distributions and derive targets for future local area concepts. We concentrate on initial physical layer design and discuss how it maps to higher layer improvements. This paper shows that the new design can significantly reduce the latency of the system, and offer increased sleeping opportunities on both base station and user equipment sides leading to enhanced power savings. In addition, through careful design of the control overhead, we are able to improve the channel utilization when compared- with LTE-A.