Abstract
Modern day cellular networks are driven by the need to provide ubiquitous connectivity with very high spectral efficiency to both indoor and outdoor users, hence the need to deploy small cells over conventional macrocells in a Heterogeneous Network (Hetnet) deployment. To alleviate the resulting inter-cell and cross-tier interference, effective inter-cell interference coordination (ICIC) schemes such as Fractional Frequency Reuse (FFR) are employed, and have been widely studied in perfect geometry network scenarios which are too idealistic and not easily adaptable to the complexity of Hetnets. This work provides an analytical framework for the performance of such FFR schemes in Hetnets with antenna sectorization employed at the macro tier, by leveraging stochastic geometry tools to model base station locations of both macro and femto tiers using the Poisson Point Process (PPP). We study the effects of varying system parameters and consider cross-tier femto interference commonly ignored in many analytical works in literature. Furthermore, the femtocells employ a sensing algorithm to minimize spectrum sharing with macro users in close proximity, especially at the transition areas of center and edge region where cross-tier interference could be monumental. Numerical simulations are used to evaluate performance of the proposed framework in terms of coverage probability and average user rate, and results are compared with traditional FFR schemes and the No-FFR deployment. To the best of the author’s knowledge, this is the first analytical framework characterizing sectored-FFR schemes using stochastic geometry tools in Hetnets.
Highlights
Over the past few years, the mobile communications industry has experienced unprecedented explosion in data demand by advent of newer, smarter devices and systems, requiring ubiquitous connectivity and seamless quality of experience
Traditional capacity enhancing methods in macro-centric deployments such as increasing spectrum, cell splitting, improved modulation and other physical layer improvements are not sufficient, and a Heterogeneous network (Hetnet) architecture has been proposed by the 3rd Generation Partnership Project (3GPP) which consists of diverse network tiers with varying transmit powers, densities and coverage areas – macrocells, picocells/relays, femtocells and/or distributed antenna systems [1]
To alleviate the inter-cell and cross-tier interference capable of degrading performance of UEs at the boundary of cells or close to restricted access points under closed subscriber group (CSG) mode, an inter-cell interference coordination (ICIC) scheme called Fractional Frequency Reuse (FFR) is used which is very effective for Orthogonal Frequency Division Multiple Access (OFDMA)-based systems such as Long Term Evolution (LTE) and LTE-Advanced (LTE-A) due to its low implementation complexity, minimal signaling overhead and significant performance gains [6]
Summary
Over the past few years, the mobile communications industry has experienced unprecedented explosion in data demand by advent of newer, smarter devices and systems, requiring ubiquitous connectivity and seamless quality of experience. To alleviate the inter-cell and cross-tier interference capable of degrading performance of UEs at the boundary of cells or close to restricted access points under CSG mode, an inter-cell interference coordination (ICIC) scheme called Fractional Frequency Reuse (FFR) is used which is very effective for OFDMA-based systems such as Long Term Evolution (LTE) and LTE-Advanced (LTE-A) due to its low implementation complexity, minimal signaling overhead and significant performance gains [6]. Soft FFR employs power control to improve performance of edge UEs. Sectored FFR is an improvement of Strict FFR where directional antennas are employed by the MeNB to further minimize co-channel interference and improve spectrum efficiency since all available ∆ +1sub-bands are used in each cell. By focusing energy in the desired direction only, received signal quality to intended UEs is significantly increased without the need for complex power control as in Soft FFR
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