In wireless communication systems, one base station (BS) generally provides services to a plurality of user equipments (UEs). The BS schedules user data for the plurality of UEs, and transmits the user data together with control information containing scheduling information for the user data. In general, a channel for carrying the control information is referred to as a control channel, and a channel for carrying the user data is referred to as a data channel. The UE finds control information of the UE by searching for the control channel, and processes data of the UE by using the control information.
In order for the UE to receive user data assigned to the UE, control information for the user data on a control channel must be received. In a given bandwidth, a plurality of pieces of control information for a plurality of UEs are generally multiplexed within one transmission interval. That is, to provide a service to the plurality of UEs, the BS multiplexes the plurality of pieces of control information for the plurality of UEs and then transmits the control information through a plurality of control channels. The UE searches for control channel of the UE among the plurality of control channels.
Blind decoding is one of schemes for detecting specific control information from the plurality of pieces of multiplexed control information. The blind decoding attempts to recover a control channel by using several combinations of information in a state where a UE has no information required to recover the control channel. That is, in a state where the UE does not know whether control information transmitted from the BS is control information of the UE and the UE does not know in which portion the control information of the UE exists, the UE decodes all pieces of given control information until the control information of the UE is found. The UE can use information unique to each UE to detect the control information of the UE. For example, when the BS multiplexes control information of each UE, an identifier unique to each UE can be transmitted by being masked onto a cyclic redundancy check (CRC). The CRC is a code used for error detection. The UE de-masks unique identifier of the UE from the CRC of the received control information, and then can detect the control information of the UE by performing CRC checking.
If the UE cannot correctly detect the control information of the UE from the pieces of multiplexed control information, user data on the data channel cannot be decoded. Therefore, fast and correct detection of the control information has a significant effect on overall system performance. However, it may be difficult to detect the control information when using only blind decoding. Since each UE may require different control information and may use a channel encoding scheme by the use of a different code rate, each UE may have control information with a different size. Therefore, the number of blind decoding attempts may be significantly increased in a control region in which control information is transmitted. Battery consumption of the UE increases in proportion to the number of detection attempts.
Meanwhile, as a mobile communication system of a next generation (i.e., post-3rd generation), an international mobile telecommunication-advanced (IMT-A) system is standardized aiming at support of an Internet protocol (IP)-based seamless multimedia service in an international telecommunication union (ITU) by providing a high-speed data rate of 1 gigabits per second (Gbps) in downlink communication and 500 megabits per second (Mbps) in uplink communication. In a 3rd generation partnership project (3GPP), a 3GPP long term evolution-advanced (LTE-A) system is considered as a candidate technique for the IMT-A system. The LTE-A system is evolved to increase a completion level of the LTE system, and is expected to maintain backward compatibility with the LTE system. This is because the provisioning of compatibility between the LTE-A system and the LTE system is advantageous in terms of user convenience, and is also advantageous for a service provider since existing equipment can be reused.
Accordingly, there is a need for a method in which a BS effectively transmits control information and a UE effectively receives data by using the control information in a next generation mobile communication system such as an LTE-A.