In recent years, small base station apparatuses placed in houses and offices have been under consideration. A small base station apparatus is connected to a fixed line or the like in a house and used to expand the communication area or provide user-specific services. The small base station apparatus being developed in a standardization group 3GPP (3rd Generation Partnership Project) is referred to as a Home Node B (or Home e Node B). In addition, the Home Node B that restricts users who can use it by preliminarily registering users who can access it is specifically referred to as a CSG (Closed Subscriber Group) cell (see Non-patent Document 1). On the other hand, an ordinary base station apparatus is referred to as a macro cell and distinguished therefrom.
In 3GPP, CSG cells are under consideration for Evolved Universal Terrestrial Radio Access (referred to as “EUTRA”, hereinafter) which has evolved the third generation mobile communication system, and Advanced EUTRA which is its further developed system.
A mobile station apparatus may waste power consumption and radio resource by trying access to an inaccessible CSG cell unless it can distinguish a CSG cell in which the mobile station apparatus is already registered as a subscriber (registered CSG cell), a CSG cell in which it is not registered (unregistered CSG cell), and a macro cell. Therefore, a method of including a CSG cell identifier in broadcast information (see section 6.3.1 of Non-patent Document 2) has been proposed as a method for a mobile station apparatus to distinguish a CSG cell from a macro cell.
FIG. 19 is a sequence chart showing an initial access procedure of a mobile station apparatus when a registered CSG cell is placed among neighboring cells. First, a mobile station apparatus CSG_UE acquires CSG cell information from the CSG cell (step S191). The CSG cell information is acquired from a CSG cell to distinguish a macro cell from the CSG cell, and corresponds to a CSG cell identifier, a cell ID, and frequency band of the broadcast information. The mobile station apparatus determines, in a idle determination process (step S192), whether or not the CSG cell detected from the acquired CSG cell information is a registered CSG cell. If, according to the result of this determination, it is a registered CSG, a wireless connection request message is transmitted to the registered CSG cell (step S193). The CSG cell which received the wireless connection request transmits a wireless connection request permission message (step S194), and subsequently a wireless connection completion message is transmitted from the mobile station apparatus (step S195).
The mobile station apparatus subsequently performs a location registration process (step S196). It thereby notifies the network of an area where it waits for an terminated call signal, and enters a idle state. Entering the idle state is referred to as “camping on a cell”. When the mobile station apparatus subsequently starts a originated call procedure for data communication according to an instruction from an upper layer or the like, it transmits a originated call request message to a CSG cell on which it is camping (step S197), and the CSG cell responds with a originated call request permission message (step S198).
FIG. 20 is a sequence chart showing an initial access procedure when an unregistered CSG cell is placed among neighboring cells, or when the mobile station apparatus does not support a CSG cell. First, a mobile station apparatus Non-CSG_UE acquires CSG cell information from the CSG cell (step S201). The mobile station apparatus determines, in the idle determination process (step S202), whether or not the CSG cell detected from the acquired CSG cell information is a registered CSG cell. If, according to the result of the determination, it is not a registered CSG, or the mobile station apparatus does not support a CSG cell, it transmits a wireless connection request message to a macro cell (step S203). The macro cell which received the wireless connection request transmits a wireless connection request permission message (step S204), and subsequently a wireless connection completion message is transmitted from the mobile station apparatus (step S205).
The mobile station apparatus subsequently performs a location registration process (step S206), and notifies the network that it will camp on the macro cell. Subsequently, when starting a originated call procedure, the mobile station apparatus transmits a originated call request message to the macro cell on which it is camping (step S207), and the macro cell responds with a originated call request permission message (step S208). Although there may be a case where a random access procedure is actually required for an uplink resource request prior to transmission of a wireless connection request message and a originated call request message in FIGS. 19 and 20, description thereof is omitted for simplicity.
FIG. 21 is a flow chart showing a procedure of the idle determination process shown in FIGS. 19 and 20. When selecting a cell to be camped on, the mobile station apparatus first receives signals from neighboring cells and selects one or more neighboring cells satisfying a reception quality suitable for camping (step S211). Next, it is determined, based on the CSG cell information, whether or not a CSG cell is placed among neighboring cells and a signal of the CSG cell is included in the reception signal (step S212). If a CSG cell is placed among neighboring cells, it is next determined whether or not the CSG cell is a registered CSG cell (step S213). If the CSG cell is a registered CSG cell, the registered CSG cell is selected as the cell to be camped on (step S214). On the other hand, if no CSG cell is placed among neighboring cells in step S212, or if only unregistered CSG cells are placed in step S213, the macro cell is selected as the cell to be camped on (step S215).
In addition, there is made a proposal in Non-patent Document 3 enabling a priority call (urgent call, emergency communication) to camp even on an unregistered CSG cell in a cell environment where only CSG cells are observed.    Non-patent Document 1: 3GPP TS36.300, Overall description; Stage2.V8.4.0 http://www.3gpp.org/ftp/Specs/html-info/36300.htm    Non-patent Document 2: 3GPP TS36.331, Radio Resource Control (RRC); Protocol specification V8.2.0 http://www.3gpp.org/ftp/Specs/html-info/36331.htm    Non-patent Document 3: Huawei, R2-083555, 3GPP TSG-RAN2 Meeting #62bis, Warsaw, Poland, Jun. 30-Jul. 4, 2008