Harmonized co-existence with robust interference management in femto-macro cellular architectures
Date of Issue2014
School of Computer Engineering
Centre for Multimedia and Network Technology
Today's wireless communication systems are driven by the need for ubiquitous wireless services at high capacity. This has led to the search for a promising solution to provide better user experience by offloading traffic through a supplemental infrastructure to augment the macrocellular network. These growing demands are driving them to use smaller cell sizes to offer better service to higher number of users. Bringing the network closer to the user by reducing the radio transmission range through small cells assures a significant leap in system performance via higher data rates and extended battery life. The HetNets that incorporate different kinds of small cells such as micro, pico, femto, metro cells, relays, and others, all integrated with Wi-Fi, are instrumental in meeting this anticipated performance enhancements. Considering these deployments, the concept of end-user installed femtocell has become a hot topic since it is the most economical solution with lower upfront costs that assures high quality indoor coverage to home users, while backhauling their traffic over the IP network. If the indoor traffic can be routed into the cellular network using a femtocell base station, the connected users will experience an increase in capacity along with ubiquitous coverage while macrocell base station resources might be spared. This in turn implies a reduction in network maintenance and deployment cost for the operator. At the same time, the key technical challenge of managing inter-tier radio interference inherent in the femto-macro network grabs significant attention. It urges the researchers to devise a viable alternative to support the spectrum sharing strategy in the current deployment in an effective manner. Keeping these challenges in mind, the main focus of this thesis is on developing advanced co-existence techniques that support inter-cell cooperation and decentralized interference management in two-tier femto-macro network. It aims at devising solutions that can diminish the interference, enhance the system capacity and at the same time encourage mutually beneficial co-existence with the current cellular architectures. The first contribution mainly aims at improving the current cellular framework in terms of capacity, coverage and dead-zone reduction without bringing in prominent changes in the network architecture. Hence, it introduces the concept of Femto-Relays which proposes the coverage extension of existing femtocell network even beyond the home environment through relaying, which not only reduces the load on the macrocell network but also proves to limit the interference significantly. The idea involves the exploitation of under-utilized femtocells to serve high data rate requests of many macrocell user equipments and reduce the probability of their outage with significant energy savings. Relaying, however demands more operational spectrum which points towards the need for devising a superior inter-tier spectrum sharing strategy resulting in the second contribution -Reverse Frequency Allocation (RFA). RFA is proposed as a key solution to mitigate the cross-tier interference and at the same time enhancing the spectral efficiency and coverage probability by reversing the uplink and downlink transmission frequencies between the femto-macro networks. Interference mitigation accomplished through incorporation of orthogonal transmission in wireless cellular networks is not a novel idea. However, independent operation of two-tier networks can be facilitated through orthogonal polarized transmission which results in the third contribution aimed at alleviating cross-tier interference in a two-tier femto-macro network. Orthogonal Polarized Transmission can be adopted as an effective method to assure network isolation by permitting femtocell network to transmit along right hand circular polarization and macrocell network to transmit along left hand circular polarization, which control interference and thereby enhance the system performance. Fourth and the last, the much-expected futuristic scenario of Self-Organized Femtocells is considered, where each femtocell is expected to be intelligent enough to autonomously integrate into the radio access network without causing any impact on its immediate cellular neighborhood. Hence each femtocell is embedded with a cognitive capability by means of a radio resource allocation algorithm called Cross-Polarized Complementary Frequency Allocation strategy (CPCFA) which enables it to select its own operational frequency. Here it exploits both frequency and polarization diversity by incorporating reverse frequency allocation within an orthogonally polarized transmission network to maintain its interference to the macrocell user under a pre-determined threshold. To summarize, the goal of this thesis is to inspire and motivate the use of advanced co-existence techniques coupled with efficient interference management solutions requiring minimal network overhead in ongoing and future deployment of tiered cellular architectures. It addresses key technical challenges inherent in a femtocell-aided cellular network, with focus on managing radio interference and providing reliable coverage at either tier, for different physical layer technologies.
DRNTU::Engineering::Computer science and engineering