Recently, a multiple input multiple output (MIMO) system has received much attention as a broadband wireless communication technology. The MIMO system means a system that enhances communication efficiency of data by using a plurality of antennas. The MIMO system can be divided into a spatial multiplexing scheme and a spatial diversity scheme depending on transmission of same data.
The spatial multiplexing scheme means a scheme that can transmit data at high rate without even increasing a system bandwidth by simultaneously transmitting different data through a plurality of transmitting antennas. The spatial multiplexing scheme means a scheme that can obtain transmission diversity by transmitting same data from a plurality of transmitting antennas. An example of the spatial diversity scheme includes a space time channel coding scheme.
Also, the MIMO system can be divided into an open loop system and a closed loop system depending on feedback of channel information from a receiving side to a transmitting side. An example of the open loop system includes a space-time trellis code (STTC) system in which a transmitting side transmits information in parallel while a receiving side detects a signal by repeatedly using a zero forcing (ZF) scheme and a minimum mean square error (MMSE) scheme and obtains transmission diversity and encoding gain by using a blast and spatial area that can increase information as much as the number of transmitting antennas. An example of the closed loop system includes a transmit antenna array (TxAA) system.
FIG. 1 is a conceptional diagram illustrating a CoMP system of intra eNBs and an inter eNB according to the related art.
Referring to FIG. 1, intra base stations 110, 120 and inter base station 130 exist under a multi cell environment. According to a long term evolution (LTE) system, the intra base stations include several cells (or sectors). Cells that belong to a base station to which a specific mobile station belongs are in the relation of intra base stations 110, 120 with a specific mobile station. Namely, cells that share a base station to which a mobile station belongs are cells corresponding to the intra base stations 110 and 120 while cells that belong to other base stations are cells corresponding to the inter base station 130. In this way, although cells based on the same base station as that of a specific mobile station transmit and receive information (for example, data, channel state information (CSI)) through x2 interface, cells based on a base station different from that of a specific mobile station can transmit and receive information through a backhaul 140.
As illustrated in FIG. 1, a single cell MIMO user 150 located within a single cell performs communication with a single serving base station in one cell (sector), and a multi-cell MIMO user 160 located at the cell edge performs communication with a plurality of serving base stations in multiple cells (sectors).
A coordinated multi-point system (hereinafter, referred to as ‘CoMP system’) is the system for improving throughput of a user located at the cell edge by applying improved MIMO transmission under the multi-cell environment. If the CoMP system is applied, inter-cell interference can be reduced under the multi-cell environment. In case of the CoMP system, a mobile station can commonly be supported with data from multi-cell base stations. Also, each base station can improve system throughput by supporting same radio frequency resource to one or more mobile stations (MS1, MS2, . . . , MSK) at the same time. Also, the base station can perform a space division multiple access (SDMA) method based on channel state information (CSI) between the base station and the mobile station.
The CoMP system can be divided into a coordinated MIMO (Co-MIMO) type joint processing (JP) scheme through data sharing and a coordinated scheduling scheme/beamforming (CS/CB) scheme.
In the cooperative MIMO system, a serving base station and one or more cooperative base stations are connected with a scheduler through a backbone network. The scheduler can be operated in such a manner that channel information is fed back to the scheduler through the backbone network, wherein the channel information is measured by each of the base stations (BS1, BS2, . . . , BSM) and relates to channel status information between each of the mobile stations (MS1, MS2, . . . , MSK) and the cooperative base station. For example, the scheduler schedules information for cooperative MIMO operation with respect to the serving base station and one or more cooperative base stations. Namely, the scheduler directly commands cooperative MIMO operation to each base station.
The CoMP system includes transmission processes (for example, multiple antennas) locally spaced apart from one another as well as the inter-cell joint processing and the coordinated scheduling scheme/beamforming scheme.
FIG. 2 is a diagram illustrating transmission of a physical downlink shared channel (PDSCH) and a physical downlink control channel (PDCCH) in a process of performing downlink CoMP system.
As illustrated in FIG. 2, some or all of individual transmission points (Tx points) may be configured within a random base station (eNodeB) or on different base stations. As illustrated in FIG. 2, if a total of N (N>1) transmission points (Tx points) exist, one transmission point is regarded as an anchor point (reference point), and the PDSCH is transmitted from the N transmission points, whereas the PDCCH is transmitted from the anchor point. This is to prevent overhead for receiving the PDCCH in a user equipment (UE) from occurring when considering that a control channel element (CCE) of the PDCCH and CCE of a resource element (RE) to RE mapping is configured differently per transmission point and the user equipment receives control information individually through blind decoding.
Since a downlink control information (DCI) format of the PDCCH transmitted through the anchor point includes full control information on PDSCH transmission of a total of N transmission points, payload size of the DCI format may be increased. This may cause deterioration of reliability in receiving the PDCCH due to increase of a useful code rate.
Accordingly, when the PDCCH of a single anchor point is transmitted with respect to PDSCH transmission of N transmission points of FIG. 2, a method for transmitting downlink CoMP for effective control signaling and a method for configuring control information should be considered.