In a 3GPP (3rd Generation Partnership Project, 3rd generation partnership project) LTE (Long Term Evolution, long term evolution)/LTE-A (LTE-advanced, LTE-advanced) system, an OFDMA (Orthogonal Frequency Division Multiple Access, orthogonal frequency division multiple access) manner is usually adopted for a downlink multiple access manner. Downlink resources of a system are divided into OFDM (Orthogonal Frequency Division Multiple, orthogonal frequency division multiple) symbols in terms of time, and divided into subcarriers in terms of frequency.
According to the LTE Release 8/9/10 standard, a normal downlink subframe includes two slots (slot), each slot includes 7 OFDM symbols, a normal downlink subframe includes 14 or 12 OFDM symbols in total, and the size of an RB (Resource Block, resource block) is defined: an RB includes 12 subcarriers in a frequency domain and is half of a subframe duration (one slot) in a time domain, that is, it includes 7 or 6 OFDM symbols, where the length symbol of a normal CP (Cyclic Prefix, Cyclic Prefix) is 7 OFDM symbols and the length symbol of an extended cyclic prefix is 6 OFDM symbols. A subcarrier in an OFDM symbol is referred to as an RE (Resource Element, resource element), so an RB includes 84 or 72 REs. In a subframe, a pair of RBs of two slots is referred to as a resource block pair, namely, an RB pair (RB pair).
For various data carried on a subframe, mappings are organized by dividing physical time-frequency resources of the subframe into various physical channels. The various physical channels generally involve two types: a control channel and a service channel. Correspondingly, data carried by a control channel may be referred to as control data (or control information), whereas data carried by a service channel may be referred to as service data. The fundamental objective of communications is to transmit service data, and the function of a control channel is to aid the transmission of service data, so in the design of a communication system, resources occupied by a control channel should be minimized.
Generally, resources used for transmitting service data in an OFDMA system are allocated flexibly, that is, to a UE (User Equipment, user equipment), the number of RBs occupied by the service data sent to the UE by each subframe, and the initial positions of the RBs in all RBs in the entire system are changeable. Therefore, when service data is sent to the UE, the UE needs to be notified at which RBs the UE should receive the service data sent to the UE. Similarly, for a UE, a modulation and coding scheme adopted by each subframe to send the service data to the UE is also changeable, and also needs to be notified to the UE. Information such as RA (Resource Allocation, resource allocation) and MCS (Modulation and Coding Scheme, modulation and coding scheme) is to aid or control the transmission of service data, so it is referred to as control information and is transmitted on a control channel.
According to the LTE Release 8/9/10 standard, a control channel in a subframe may occupy the front 3 OFDM symbols of all RBs in the entire system. By taking a PDCCH (Physical Downlink Control CHannel, physical downlink control channel) carrying control information such as scheduling as an example, a complete PDCCH is formed by one or more CCEs (Control Channel Element, control channel element), a CCE is formed by 9 REGs (Resource Element Group, resource element group) and an REG occupies 4 REs. According to the LTE Release 8/9/10, a PDCCH may be formed by 1, 2, 4 or 8 CCEs, which are approximately evenly distributed in time and frequency domains. In the present LTE Release 8/9/10, the demodulation of the PDCCH is based on a CRS (Common Reference Signal, common reference signal). In the LTE Release 11, the number of UEs in one cell may increase, so the PDCCH channel needs to be enhanced, and more resources need to be allocated to the PDCCH or the performance of the PDCCH needs to be improved, so as to adapt to the scheduling of more UEs in one cell. An enhanced PDCCH channel may also be referred to as an E-PDCCH (enhanced-PDCCH).
In the prior art, some RB pairs are separated from the area of a PDSCH (Physical Downlink Shared Channel, physical downlink shared channel) to serve as an area where E-PDCCH control information is sent, where the granularity is in unit of an RB pair. However, a basic unit of a PDCCH is a CCE, and an RB pair may be equivalent to resources of multiple CCEs. Therefore, the granularity of the basic unit using an RB pair as the E-PDCCH is too large, thereby causing a waste of resources.