In recent years, a plurality of communication standards referred to as the third generation for a high-speed CDMA mobile unit communication system have been employed as IMT-2000 by the International Telecommunication Union (ITU), and as one of them, the commercial service of W-CDMA (FDD: Frequency Division Duplex) has been started in Japan in 2001. The first specification of the W-CDMA scheme was determined as Release 1999 (Version name: 3.x.x) edited in 1999 by the standardization organization 3GPP (3rd Generation Partnership Project). Currently, Release 4 and Release 5 have been specified as a new version of Release 1999. At the same time, Release 6 is under study and in the process of preparation.
Release 1999 has been prepared by assuming mainly continuous data transmission and reception such as verbal communication. In Release 5, the HSDPA (High Speed Downlink Packet Access) technique is added to enable downlink high-speed packet communication, while the uplink uses Release 1999 specification as it is. Even in the case where packet data is transmitted in burst from a mobile station to a fixed station, therefore, an individual dedicated channel (DCH (Dedicated CHannel) and DPDCH (Dedicated Physical Data CHannel) are required to be constantly assigned to each mobile station. Considering the current situation in which demand for packet data transmission such as voice packet transmission has increased, however, a problem has been posed from the viewpoint of effective utilization of radio resources.
Also, the data transmission from a mobile station is conducted under an autonomous transmission control of the mobile station. In this case, the transmission timing from each mobile station is arbitrary (or statistically at random). In a data transmission system with the transmission controlled autonomously by each mobile station, the transmission timing at the mobile station is unknown to the fixed station. In the communication system using the CDMA communication scheme, transmission from other mobile stations all constitute an interference source. In the fixed station managing radio resources, however, an interference noise amount and a change amount thereof can be predicted (managed) only statistically in the reception at a base station. As described above, in the communication system using the CDMA communication scheme, the fixed station managing radio resources is neither informed of transmission timing of mobile stations nor capable of accurately predicting interference noise amounts. The radio resources are assigned in such a manner as to secure a sufficient margin, therefore, in preparation for a case with a large change amount of interference noise. This radio resource management by the fixed station is carried out not by the base station itself but by a base station control unit (RNC: Radio Network Controller) on behalf of a plurality of base stations.
The radio resource management and incidental notifications from the base station control unit (RNC) to mobile stations require a comparatively long processing time (the order of several hundred milliseconds). The radio resources cannot be properly assigned, therefore, in keeping with a sudden change in the radio propagation environment, transmission situation of other mobile stations (interference amounts from other mobile stations), or the like. In view of this, with the aim of realizing effective utilization of radio resources and high-speed radio resource assignment, the E-DCH (Enhanced DCH) technique with a detailed specification has been introduced in Release 6. The E-DCH technique is sometimes referred to as HSUPA (High Speed Uplink Packet Access). In the E-DCH technique, a short transmission time interval (TTI) can be used together with the AMC (Adaptive Modulation and Coding) technique and the HARQ (Hybrid Automatic Repeat reQuest) technique used in the HSDPA (High Speed Downlink Packet Access) technique introduced in Release 5. E-DCH is defined as a transport channel expanded from DCH constituting a transport channel according to the conventional standard, and set independently of DCH.
According to E-DCH, uplink radio resource control operation referred to as “scheduling” is performed on the part of the fixed station. The uplink and the downlink have different radio wave propagation environments and the like, and hence are different in scheduling from HSDPA. The mobile station controls packet data transmission based on the scheduling result notified from the fixed station. The fixed station transmits a receiving determination result (ACK/NACK) for the received packet data to the mobile station. According to 3GPP, the base station (referred to as NodeB in 3GPP) is specified as a device for carrying out the scheduling of the fixed station. A specific example of the E-DCH scheduling method in the base station is disclosed in, for example, Japanese Patent Publication No. 2004-215276 (Patent Document 1).
Also, TS25.309v6.3.0 (Non-Patent Document 1) is available as a 3GPP standard (TS: Technical specification) prepared for E-DCH.
Patent Document 1: Japanese Patent Publication No. 2004-215276
Non-Patent Document 1: 3rd Generation Partnership Project, Technical Specification Group Radio Access Network; FDD Enhanced Uplink; Overall description; Stage 2 (Release 6), 3GPP TS 25.309V6.3.0 (2005-06).
Main channels relating to the specification of Release 6 are briefly described below. As uplink physical channels for E-DCH, Release 6 has added thereto E-DPDCH (Enhanced-Dedicated Physical Data CHannel) constituting a data channel and E-DPCCH (Enhanced-Dedicated Physical Control CHannel) constituting a control channel. E-DPDCH and E-DPCCH are physical channels corresponding to DPDCH and DPCCH, respectively, constituting physical channels before Release 5, in which E-DPDCH is used for data transmission from a high-order layer and E-DPCCH for transmission of control information. Also, as in the DPDCH communication speed setting (referred to as TFC (Transport Format Combination) according to 3GPP), E-TFC (Enhanced-TFC) is provided for specifying communication speed for E-DCH transmission. A gain factor (βed) specifying an E-DPDCH channel amplitude is determined based on the communication speed. Also, as downlink physical channels for E-DCH, Release 6 has added thereto both E-AGCH (Enhanced-Absolute Grant CHannel) and E-RGCH (Enhanced-Relative Grant CHannel) for notifying scheduling results, and E-HICH (E-DCH HARQ Acknowledgment Indicator Channel) for notifying packet data receiving determination results (ACK/NACK).
In data transmission from the mobile station, E-DCH and DCH are each handled as an independent data stream, and the DCH transmission is given priority to the E-DCH transmission. Since E-DCH and DCH are independent data streams and the DCH transmission is given priority over the E-DCH transmission, the mobile station secures transmission power required for DCH transmission and the E-DCH transmission is carried out by selecting E-TFC in a remaining margin of the transmission power as described in Non-Patent Document 1.