1. Technical Field
Example embodiments of the present invention relate in general to technology for a packet-based mobile communication system, and more particularly, to methods of managing a terminal performed in a base station and the terminal to support mobility management and low-power operation of the terminal in a heterogeneous network (HetNet) environment.
2. Related Art
In a packet-based cellular mobile communication system, mobility management is intended to maintain continuity of a connection of a radio bearer (RB), which is a logical channel established between a base station and a terminal.
A general mobility management method uses a backward handover procedure in which a terminal establishes a connection for a control channel through preliminary information exchange between a source base station from which the terminal has originally received service and a target base station that will provide the service through a new connection according to movement of the terminal, accesses the target base station to set a connection for a data channel, and then closes a connection with the source base station.
In particular, in a HetNet environment in which various types of base stations, cells or transmission points such as macro base stations, micro or pico base stations, home base stations, closed subscriber group (CSG) cells or remote radio heads (RRHs) coexist, ping-pong handover frequently occurs between adjacent base stations/cells, and load of a system increases. Also, the quality of a radio channel deteriorates due to interference at a cell boundary, and radio link failure (RLF) occurs due to the deterioration, so that the overall performance of a mobile communication system is hindered.
To improve performance of a mobile communication system, there is a necessity for a method capable of reducing signaling overhead caused by message transmission or state switching (e.g., switches between a connected state and an idle state) of terminals, which are smart phones intermittently generating a small amount of data such as instant message (IM) traffic, machine type communication (MTC) terminals generating traffic such as smart metering data, or terminals generating a small amount of data at long intervals, and minimizing power consumption of the terminals.
Terminals supporting a device-to-device (D2D) communication function are required to perform a measurement for checking whether or not there are adjacent terminals and whether or not it is possible to communicate, and thus it is necessary to improve a measurement procedure such as measurement setup, measurement execution, and measurement reporting for D2D communication, and a method and a control procedure for measurement triggering.
Meanwhile, to improve performance of a terminal located at a cell boundary in a packet-based cellular mobile communication system, a coordinated multipoint transmission and reception (CoMP) function in which a plurality of base stations, cells or transmission nodes located at geographically the same point or different points cooperate to provide service is taken into consideration. CoMP may be classified as a CoMP function provided by one or more micro base stations in a macro base station having a relatively large arbitrary service area, a CoMP function provided by two or ore macro base stations, a CoMP function provided by two or more macro base stations and micro base stations belonging to the macro base stations, and so on.
In addition, CoMP functions may be classified into a joint processing (JP) scheme in which a plurality of transmission nodes transmit the same packet information all together, and a coordinated scheduling/beamforming (CS/CB) scheme in which a plurality of transmission nodes cooperate to support minimization of interference at one transmission node.
According to the JP scheme, in general, a plurality of transmission nodes transmit the same information using the same radio resources (which means that radio resources consisting of the same frequency band and transmission time are allocated to a CoMP-target terminal) and the same modulation and coding scheme (MCS).
The CS/CB scheme is a control method in which a plurality of transmission nodes share radio resources and information for MCS to transmit data to an arbitrary terminal using optimal radio resources and MCS, and exchange related information (e.g, the magnitude of an interference signal, the magnitudes of a signal from a serving cell and a signal of an adjacent cell, optimal transmission and coding information such as a pre-coding matrix indicator (PMI) in consideration of the adjacent cell) so that provision of service and allocation of radio resources can be made through interference control.
The JP scheme may be classified into a joint transmission (JT) scheme in view of a downlink from a base station to a terminal, and a joint reception (JR) scheme in view of an uplink from a terminal to a base station. Also, the JP scheme may include a dynamic cell selection (DCS) method or a dynamic point selection (DPS) method of dynamically selecting transmission nodes participating in CoMP.
The DCS/DPS method is intended to select an optimal point (or cell) at an arbitrary transmission time from among a plurality of cells or points set to participate in CoMP in consideration of radio channel quality, the load statuses of base stations, transmission/reception power and an interference state between a terminal and the base stations, etc., thereby improving performance.
In order to improve performance of a mobile communication system in a HetNet environment supporting a CoMP function in which a plurality of base stations cooperate to provide service as described above and a carrier aggregation (CA) function, it is necessary to improve a measurement operation required for connection control between one or more base stations and a terminal, and a discontinuous reception (DRX) operation control procedure. In addition, to improve the performance of the system, it is necessary to improve a mobility control procedure of a terminal, a measurement method for an MTC terminal, a terminal generating traffic having a variety of profiles, and a terminal supporting the D2D communication function, and a control procedure for minimizing power consumption of a terminal.