Currently, the wireless communication systems such as the mobile telephone systems or the wireless LANs (Local Area Networks) are widely used. In order to further improve the transmission rate and the transmission quality in the wireless communication technologies, next-generation technologies are being actively discussed. Some wireless communication technologies enable communication between two wireless communication devices (e.g., between a wireless base station and a mobile station) by use of multiple carriers. In some cases, the use of multiple carriers is called carrier aggregation, and each carrier in the carrier aggregation is called a component carrier.
In wireless communication, control signals are transmitted from a first wireless communication device to a second wireless communication device. The information transmitted by the control signals may include information which is to be referred to by the second wireless communication device for receiving data transmitted from the first wireless communication device (e.g., information indicating the format used in the data transmission), or information designating a transmission procedure to be used by the second wireless communication device in transmission of data (e.g., information designating a format to be used in the data transmission). For example, information transmitted from a wireless base station to a mobile station may include information to be referred to by the mobile station when the mobile station receives data through a downlink data channel, or information to be referred to by the mobile station when the mobile station transmits data through an uplink data channel.
In the case where wireless communication is performed between two wireless communication devices by use of multiple carriers, a wireless resource used in transmission of a control signal may belong to a carrier different from the carrier to which a wireless resource used in data transmission controlled by the control signal belongs. In this case, the problem is the method for recognition of the carrier to which the control signal is applied.
According to a technique which has been proposed as a recognition method, the carrier to which the control signal is applied is clearly indicated by attaching a bit for carrier recognition (carrier indicator) to the control signal. (See, for example, “Final Report of 3GPP TSG-RAN WG1 #57 v1.0.0”, 3GPP (3rd Generation Partnership Project) TSG RAN WG1 #57bis, R1-092292, July 2009, Section 15.4.)
Another recognition method which has been proposed is applied to a wireless base station scrambling a CRC (Cyclic Redundancy Check) bits attached to a control signal, with a scrambling sequence corresponding to an ID (Identifier) assigned to a mobile station as an opposite party. (See, for example, “Control signaling for carrier aggregation”, 3GPP TSG RAN WG1 #55bis, R1-090375, January 2009.) According to the above recognition method, IDs in the number of carriers are assigned to each mobile station, and the CRC bits are scrambled with a scrambling sequence corresponding to one of the IDs. Therefore, it is possible to concurrently recognize both of the mobile station and the carrier to which the control signal is applied.
However, according to the technique disclosed in 3GPP TSG RAN WG1 #57bis, R1-092292, the wireless resources are excessively spent for attaching the carrier indicator to the control signal, so that the transmission efficiency of the control signal is lowered. In addition, according to the technique disclosed in 3GPP TSG RAN WG1 #55bis, R1-090375, the IDs in the number of carriers are assigned to the opposite party. Therefore, the ID exhaustion becomes a problem. In the case where the length of the bit sequence of the ID is fixed, the number of opposite parties with which communication can be performed in parallel is limited. For example, in the case where five carriers are available in total, the upper limit of the number of opposite parties with which communication can be performed in parallel can become one fifth of the number of opposite parties with which communication can be performed in parallel when only one carrier is used in communication with each opposite party.
Further, in some cases, information indicating a border between the control signal and a data channel is transmitted as a separate control signal. In such cases, when the separate control signal is not correctly received, the border between the control signal and the data channel cannot be correctly detected, so that data cannot be correctly received through the data channel.