Handover Management in Femtocell Networks

Abstract

Radio communication has come a long way from 1G Advanced Mobile Phone Systems (Amps) voice to Evolved 3G Enhanced Voice Data Optimized (EVDO), High Speed Packet Access plus (HSPA+) and 4G Long Term Evolution (LTE) now. Spectrum is a scarce resource. While this remains a constant with limited number of frequency bands available, the overall performance of the network is expected to rise many folds. Every instant the need to accommodate more number of users, devices and better quality services increase on the network. Many new technologies help support this ever growing need. Recent advancements in the development of Multiple Input Multiple Output (MIMO), sensitive/directive antennas, modulation schemes like Orthogonal Frequency Division Multiplexing (OFDM), interference mitigation methods like Successive Interference Cancellation (SIC) are good contributions to proper utilization. A technology that holds promise to provide the next leap in performance is a femtocell. Femtocell technology brings the network closer to the user by adding smaller cells, which provide the benefit of higher quality links and more spatial reuse. The benefit of deploying femtocells within cellular networks is established considering the wide acceptance for these networks from several service providers. To fully exploit this diversity realized at the physical layer some challenging issues have to be addressed and smart decision making algorithms need to be implemented. Making a handover decision is one such issue where the user has various power levels available from Macro Base Station (MBS) and Femto Base Station (FBS). From a Base Station's (BS) perspective, there may be many users with close Signal to Noise plus Interference ratio (SINR) values needing service but all users cannot be accommodated due to bandwidth limitation. To make these decisions, appropriate handover mechanisms need to be adapted to fully exploit the advantages of these networks in various deployment scenarios. The area covered by a femtocell is a few tens of meters and hence mobility and speed analysis are important in deciding a favorable FBS for handover. In the work presented, an extensive study of methods to optimize handover decisions under the open access scheme of operation and maintaining Quality of Service (QoS) thresholds to maximize overall network capacity such that fairness among users is maintained. Also, a list of the available parameters and algorithms for making efficient handover decisions are noted and related work by others is mentioned. Two proposed models are introduced namely counter based and stability based schemes; to block temporary requests and to utilize connection times respectively as the methods main theme. The decisions are influenced by a combination factor resulting from SINR. The core contribution in this thesis is the development of algorithms with sound mathematical support and concurrent analysis of their benefits . A detailed description of which parameters are combined and how these are prioritized along with the state models that decide a users choice of FBSs is presented. Finally we evaluate the performance of the methods.