Mobility Management and Handover for Beyond 3G and 4G Mobile Communication Systems

Mobility management (MM) comprises the mechanisms needed to allow wireless terminals to move while staying connected to the radio network. This includes, e.g., keeping track of idle terminals and performing seamless handovers of active terminals to the most appropriate base station. With the transition towards Beyond 3G (B3G) and 4G mobile communication systems comes several grounds why to modernize traditional methods for radio resource management (RRM) and MM. For example, it is likely that the B3G/4G systems will be characterized by the following features that all benefit from new solutions for MM and handover: • new Radio Access Technologies (RAT), • distributed RRM, • multitude of RATs, • IP based architecture. The use of WCDMA in the European 3G system requires that a complex soft handover scheme is used. A new RAT and architecture for B3G/4G systems might permit the development of a high performance handover schemes without the complexity of soft handover. To guarantee high system performance it is necessary with joint optimization of all RRM functions which requires a high degree of interaction between different RRM functions. Since B3G/4G systems are likely to be composed of different types of RATs with characteristics that are optimized for different environments it is a challenge to devise a handover scheme that selects optimum RAT for each situation and to design an access architecture that provides efficient inter-working between the different RATs. Pure IP cannot handle mobile terminals and therefore several solutions combining Mobile IP with routing at lower layers have been proposed. When designing a handover concept for a particular network architecture the split of mobility functionality between IP layer and lower layers must be considered . Below we list projects at Cellular Systems Division addressing the problems described above: Cross-layer handover performance in IP-based architectures The performance of handover in packet based systems is not only affected by the handover decision algorithm’s ability to react to changes in radio environment, but also on how efficiently mobility is handled in the access network. Handover performance has been extensively studied with respect to radio conditions for circuit switched systems, and the access network behavior during a single handover in packet based systems has also been covered. However, the merge of these two disciplines has not been thoroughly addressed yet. This project focuses on the dynamic cross-layer behavior in the access network during handover in environments with varying radio conditions. Examples of studied issues are: • handover performance in radio environments where the terminal is exposed to ping-ponging between base stations, • handover performance for different hierarchical MM architectures (functional split between network-, and link layer routing), • differences in handover performance for various handover schemes (hard handover, soft handover or hybrids). The results of the studies will emanate in guidelines how to design handover decision algorithms, how to split handover functionalities in the access network, and how to select handover concept for best cross-layer performance in various radio environments. Mobility Management and Handover for EUTRAN EUTRAN is 3GPP’s proposal of an evolution of the 3G WCDMA system towards a B3G system. This system will be optimized for packet data traffic and characterized by reduced latency, higher user data rates, improved system capacity and coverage, and lower cost. Improved performance will be achieved by means of a new air interface and network architecture. The Cellular Systems Division currently has two projects regarding MM for EUTRAN. One project focuses primarily on network architectures, inter-system handover and related issues at link- and higher layers, and the other project studies issues mainly at link- and lower layers for intra-system handover. The results will be used as input to standardization in 3GPP. IP and Link Layer Mobility Management for EUTRAN This project focuses on intra-system handovers within EUTRAN and inter-system handovers to and from other systems. In particular we study the split of MM functionalities between the link layer and IP layer. Strategies for lossless handover are developed and their performances are evaluated with respect to the trade-off between usability, cost and quality. The results of the project will show how to: • achieve mobility within EUTRAN (Intra System Mobility), • achieve multi access mobility (Intra Operator mobility), • perform RAT selection in a multi RAT environment, • achieve mobility without packet loss (seamless) between EUTRAN with other existing systems (Inter System Mobility). The study will give recommendations for solutions and strategies for intra-, and inter-system MM in various radio environments and network topologies. Interaction between handover algorithm and other RRM functionalities in EUTRAN This project addresses intra-system handover within EUTRAN mainly at link-, and lower layers. This encompasses the interaction between the handover algorithm and other RRM functions such as: admission-, power-, interference control, packet scheduling, and the influence on physical layer performance. In the first phase the focus will be on uplink handover performance. Some of the activities in this project are: • design of handover algorithms for different handover concepts in the uplink, e.g., hard handover and soft handover so as to optimize QoS • investigation of the interaction between handover and other RRM functionalities and optimization of the aggregate performance • a detailed dynamic simulator that can be used as a framework for future research projects The outcome of this project will be proposals of handover concepts and algorithms mainly from a RRM perspective together with guidelines for how the handover algorithm interacts with other RRM functionalities.