Uplink capacity and interference avoidance for two-tier femtocell networks

Abstract

Two-tier femtocell networks-comprising a conventional cellular network plus embedded femtocell hotspots-offer an economically viable solution to achieving high cellular user capacity and improved coverage. With universal frequency reuse and DS-CDMA transmission however, the ensuing cross-tier interference causes unacceptable outage probability. This paper develops an uplink capacity analysis and interference avoidance strategy in such a two-tier CDMA network. We evaluate a network-wide area spectral efficiency metric called the operating contour (OC) defined as the feasible combinations of the average number of active macrocell users and femtocell base stations (BS) per cell-site that satisfy a target outage constraint. The capacity analysis provides an accurate characterization of the uplink outage probability, accounting for power control, path loss and shadowing effects. Considering worst case interference at a corner femtocell, results reveal that interference avoidance through a time-hopped CDMA physical layer and sectorized antennas allows about a 7x higher femtocell density, relative to a split spectrum two-tier network with omnidirectional femtocell antennas. A femtocell exclusion region and a tier selection based handoff policy offers modest improvements in the OCs. These results provide guidelines for the design of robust shared spectrum two-tier networks.

Opportunistic distributed channel access for a dense wireless small‐cell zone

“…From the above assumption and since the SAPs in the zone are close to each other with respect to the coverage area of the macrocell, the sum of MUE interference received at each SAP can be modeled by identically distributed random variables [33]. In other words, defining γ km := l∈N g k lm with the probability density f γ km , we have that…”

Adaptive geolocation based interference control for hierarchical cellular network with femtocells

“…Co-channel operation of femtocell with existing macro-cellular network can significantly improve the spectral efficiency in comparison with dedicated channels assignment to each macrocell and femtocell users [6,7,8]. Open access femtocell, one of the operating mode of femtocell, allows cellular users to connect to near-by base-station (macrocell or femtocell base-station) with the best signal quality.…”

“…This study shows that open access femtocell gives the opportunity to mobile user to connect to base-station with the best signal quality but at the expense of increased handovers between base-stations. References [12,8] discusses femtocell interference problems to macrocell user when femtocell is operating in closed access mode.…”

Interference management for multimedia femtocell networks with coalition formation game

“…Cheung et al in [4] proposed a resource allocation algorithm to deal with inter-tier and intra-tier interference by considering both open-access and closed-access femtocell networks. Chandrasekhar et al in [5] analyzed the uplink capacity in a shared spectrum two-tier direct sequence code division multiple access (DS-CDMA) femtocell network. An interference avoidance technique based on time hopping code division multiple access (TH-CDMA) physical layer and sectorized receive antenna was proposed.…”