Capacity and coverage enhancement in heterogeneous networks

Disruptive innovations in mobile broadband system design are required to help network providers meet the exponential growth in mobile traffic demand with relatively flat revenues per bit. Heterogeneous network architecture is one of the most promising low-cost approaches to provide significant areal capacity gain and indoor coverage improvement. In this introductory article, we provide a brief overview of heterogeneous network architectures comprising hierarchical multitier multiple radio access technologies (RAT) deployments based on newer infrastructure elements. We begin with presenting possible deployment scenarios of heterogeneous networks to better illustrate the concepts of multitier and multi-RAT. We then focus on multitier deployments with single RAT and investigate the challenges associated with enabling single frequency reuse across tiers. Based on the spectrum usage, heterogeneous networks can be categorized into single carrier usage, where all devices within the network share the same spectrum, and distinct carrier usage, where different types of devices are allocated separate spectra. For single carrier usage, we show that interference management schemes are critical for reducing the resulting cross-tier interference, and present several techniques that provide significant capacity and coverage improvements. The article also describes industry trends, standardization efforts, and future research directions in this rich area of investigation.