HetNets with cognitive small cells: user offloading and distributed channel access techniques

TLDR

Heterogeneous networks combine macrocells with small cells to meet growing capacity demands, but the random deployment, limited power, and coordination gaps make efficient coexistence challenging. The paper aims to show that cognition via spectrum sensing enables small cells to overcome coexistence challenges and to illustrate how stochastic geometry can guide design of load‑balancing and spectrum‑reuse strategies. We model HetNets using stochastic geometry, applying it to evaluate tier loads and offloading strategies, and to design spectrum‑sensing channel access schemes that maximize frequency reuse.

Abstract

Heterogeneous networks, consisting of macrocells overlaid with small cells (e.g., femtocells, picocells, microcells) provide a fast, flexible, cost-efficient, and fine-tuned design and expansion for existing cellular wireless networks to satisfy the ever increasing demand for network capacity. In HetNets, small cells serve as offloading spots in the radio access network to offload users and their associated traffic from congested macrocells. However, due to their large-scale deployment in random locations, limited transmit power, and the lack of complete coordination, the coexistence and efficient operation of small cells is very challenging. In this article, we discuss the coexistence challenges posed to small cells and show that, with cognition capabilities (e.g., achieved through spectrum sensing), small cells can overcome the posed challenges and efficiently coexist in a multitier cellular wireless network. Then we discuss a statistical tool, stochastic geometry, to model and analyze heterogeneous cellular networks. We give two examples where the stochastic geometry tools can be exploited to obtain insightful design guidelines. First, we exploit stochastic geometry to evaluate the load of each network tier and study different offloading techniques used to control this load. Second, we exploit stochastic geometry to maximize frequency reuse efficiency through spectrum sensing design for channel access and compare two channel access techniques based on spectrum sensing.