In recent years, work has been proceeding on fourth generation (4G) mobile communication systems. The work includes required conditions such as a required frequency band, center frequency band, coexistence with the other systems and carriers, and application of various radio environments. Requirements as a radio access technique are 100 Mbps or more in the downlink in outdoor environments, 1 Gbps in isolated cells/stationary environments, and about 1 Gbps at the maximum even in indoor environments. One of candidates for the system to adopt as a radio access technique is an Orthogonal Frequency Division Multiple Access (hereinafter, referred to as “OFDMA”) communication system using Orthogonal Frequency Division Multiple (hereinafter, referred to as “OFDM”) techniques. Furthermore, the DWCS is proposed as a mobility network configuration (Non-patent Document 1).
FIG. 18 is a diagram showing a configuration outline of the DWCS. The DWCS is comprised of a three-layer structure of a radio access unit (hereinafter, referred to as “RAU”), base station (hereinafter, referred to as “BS”) as an intermediate layer and core network (hereinafter, referred to as “CN”). The RAU has transmission/reception antennas and signal conversion apparatus extracted from the BS that has conventionally been the lowest layer in cellular systems, thus has a simplified configuration, and performs radio transmission/reception with a mobile station (hereinafter, referred to as “MS”). The BS is connected to a plurality of RAUs through radio optical fiber cables RoF (Radio on Fiber: hereinafter, referred to as “RoF”), converts a radio signal from the RAU into a baseband signal, while converting a baseband signal to the RAU into a radio signal, and thus performs high-speed parallel signal processing. High-speed channels are connected between BSs and between the BS and CN, and constitute a mobility network.
As shown in FIG. 18, each RAU (for example, RAU 1, 2, 3, . . . , 10) is installed in a different position corresponding to a geographic position, service request, etc. Each BS (for example, BS 1, 2, 3) is connected to the RAU via RoF. The concept of the cell including a BS as a center in conventional cellular systems is eliminated, and as a substitute, a virtual cell (hereinafter, referred to as “VC”) is constructed using the MS (for example, MS 1, 2) as a center. For example, the MS 1 constructs a VC with RAUs 8 and 9, while the MS 2 constructs a VC with RAUs 3, 4 and 5. The mobility network control system (including the CN) selects a set of antennas i.e. a set of RAUs corresponding to a location position of an MS and service request, and allocates the set to the MS as a VC. The VC is switched according to transmission/reception radio signal environment, moving speed, location position, etc. of the MS. The DWCS enables actualization of user data transmission speeds and system capacity that are higher than in the conventional cellular system, and is considered one of promising candidates for the fourth generation (4G) mobile communication system.
Non-patent Document 1: Shidong Zhou, Ming Zhao, Xibin Xu, Jing Wang. “Distributed Wireless Communication System: A New Architecture for Future Public Wireless Access” IEEE Communications Magazine 2003, 41 (March 3) P 108-113