As a next-generation system of the W-CDMA (Wideband Code Division Multiple Access) system, HSDPA (High Speed Downlink Packet Access) system, HSUPA (High Speed Uplink Packet Access) system and the like, an LTE system has been studied by 3GPP (3rd Generation Partnership Project) which is a standards body of the W-CDMA. In the LTE system as a radio access system, an OFDM (Orthogonal Frequency Division Multiplexing) scheme and an SC-FDMA (Single-Carrier Frequency Division Multiple Access) scheme have been studied as prospective candidate schemes to be applied to the downlink communications system and the uplink communications system, respectively (see, for example, Non Patent Document 1).
The OFDM scheme is a multi-carrier transmission scheme in which a frequency band is divided into plural sub-carriers having narrower frequency bands, and data are mapped onto the sub-carriers. By closely and orthogonally arranging the sub-carriers along the frequency axis, faster transmission is expected to be achieved and the efficiency of using the frequency band is also expected to be improved.
The SC-FDMA scheme is a single carrier transmission scheme in which a frequency band is divided with respect to user equipment (hereinafter may be referred to as user equipment (UE) terminal or mobile station) in a manner so that different frequencies can be separately used among plural terminals (user equipment terminals); and as a result, interference between terminals may be easily and effectively reduced. Further, preferably, in the SC-FDMA scheme, a range of transmission power fluctuation may be made smaller; therefore lower energy consumption of terminals can be achieved and a wider coverage area can be obtained.
In both uplink and downlink of the LTE system, communications can be performed by allocating one or more resource blocks to the mobile station. More specifically, the resource blocks may be shared among plural mobile stations in the system. In the LTE system, the base station (hereinafter may be referred to as base station apparatus) determines which resource blocks are to be allocated to which mobile station from among plural mobile stations with respect to each Sub-frame having 1 ms period (this allocation process may be called Scheduling). The Sub-frame may also be called a TTI (Transmission Timer Interval). In downlink, the base station apparatus transmits a shared channel using one or more resource blocks to the mobile station selected by the Scheduling. The shared channel is called a Physical Downlink Shared Channel (PDSCH). In uplink, the mobile station selected by the Scheduling transmits the shared channel using one or more resource blocks. This shared channel is called a Physical Uplink Shared Channel (PUSCH).
In a communication system using the shared channels, it is required to perform (report) Signaling designating which shared channel is allocated to which user equipment terminal. In the LTE system, a control channel is used for the Signaling, and the control channel is called a Physical Downlink Control Channel (PDCCH) or a Downlink L1/L2 Control Channel (DL-L1/L2 Control Channel). The Physical Downlink Control Channel (PDCCH) may include information items such as Downlink Scheduling Information, Acknowledgement information (ACK/NACK), Uplink Scheduling Grant, an Overload Indicator, Transmission Power Control Command Bit and the like (see, for example, Non Patent Document 2).
The Downlink Scheduling Information and Uplink Scheduling Grant correspond to the information on which the Signaling is to be performed. The Downlink Scheduling Information includes the information of the shared channel in downlink. More specifically, the Downlink Scheduling Information includes allocation information of the Resource Blocks in downlink, identification information of the user equipment (UE-ID), the number of streams, information of Precoding Vector, data size, modulation scheme, information of Hybrid Automatic Repeat reQuest (HARQ) and the like.
The Uplink Scheduling Grant includes information of the shared channel in uplink. More specifically, the Uplink Scheduling Grant includes allocation information of the Resources in uplink, the UE-ID, data size, modulation scheme, information of transmission power in uplink, information of a Demodulation Reference Signal in Uplink MIMO and the like.
In downlink, a Common Control Physical Channel (CCPCH) is also transmitted. The Common Control Physical Channel (CCPCH) includes a Broadcast Channel (BCH). The Broadcast Channel (BCH) transmitted in the Common Control Physical Channel (CCPCH) may be called a static Broadcast Channel. In addition to the static Broadcast Channel, there is also provided a dynamic Broadcast Channel (Dynamic part). The dynamic Broadcast Channel is mapped to the Physical Downlink Shared Channel (PDSCH). In this case, the Physical Downlink Shared Channel (PDSCH) transmits the Downlink Scheduling Information for the dynamic Broadcast Channel.
An uplink control channel transmits a downlink Channel Quality Indicator (CQI), the Acknowledgement information with respect to the Physical Downlink Shared Channel (PDSCH) and the like. The Channel Quality Indicator (CQI) is used in, for example, the Scheduling process and an Adaptive Modulation and Coding Scheme (AMCS) with respect to the Physical Downlink Shared Channel (PDSCH).
As described above, in the proposed mobile communication system, basically, the information indicating which shared channel is allocated to which user equipment terminal with respect to each Sub-frame is required to be reported by Signaling using the Downlink L1/L2 Control Channel (DL-L1/L2 Control Channel). Further, this Scheduling is to be required (reported) regardless of the length of the packet data to be transmitted. Therefore, even when the packet data having a short length are required to be frequently transmitted, it is required to perform Signaling designating which shared channel is allocated to which user equipment terminal with respect to each packet data transmission using the Downlink L1/L2 Control Channel (DL-L1/L2 Control Channel). As a result, the ratio of the radio resources allocated to the control channel increases, the overhead rate may be accordingly increased, and the number of radio resources to be allocated to the data channel may be reduced. Typical examples of the packet data that have a short length and that are generated frequently may be voice packet data, VoIP, real-time data, and the like.
To overcome the problems, a method called Persistent Scheduling has been proposed. In this method, a downlink data channel (typically, the voice packet data) is transmitted using a certain fixed transport format based on a specific cycle such as 20 ms. The transport format includes information items necessary to decode the data channel, the information items indicating the modulation scheme, the channel coding rate and the like. For example, the modulation scheme and the channel coding rate are fixed to QPSK and ⅓, respectively, and the data are known to (i.e., shared between) the base station and the user equipment terminals. Therefore, the user equipment terminals may adequately receive the downlink shared channel (DL-SCH) even when the control channel such as the L1/L2 control channel with respect to each Sub-frame is not reported. Such Persistent Scheduling is described in, for example, Non Patent Documents 3 and 4.                Non Patent Document 1: 3GPP TR 25.814 (V7.0.0), “Physical layer Aspects for Evolved UTRA,” June 2006        Non Patent Document 2: 3GPP R1-070103, Downlink L1/L2 Control Signaling Channel Structure: Coding        Non Patent Document 3: R1-051511, 7-11th Nov., 2005, 3GPP TSG-RAN WG1 #43, Qualcomm Europe, pp 2, Section 3        Non Patent Document 4: R2-060550, 13-17 Feb., 2006, 3GPP TSG-RAN WG2 #51, Qualcomm Europe, pp 1, Section 2