A primary synchronization signal (PSS) and a secondary synchronization signal (SSS) are transmitted at a period of 5 subframes, the frequency domain is located within a frequency domain width of 6 resource blocks in the center of a carrier, and the time domain occupies two symbols. A time domain of a physical broadcast channel (PBCH) occupies the first four symbols of the second time slots in subframe 0, and the frequency domain thereof is also located within a frequency domain width of 6 resource blocks in the center of a carrier. The PBCH carries downlink carrier bandwidths, therefore, before the PBCH is detected, a user equipment (UE) only can identify a downlink carrier bandwidth within a frequency domain width of 6 resource blocks in the center of a currently-detected carrier, that is, both the synchronization signals and the PBCH must be placed in the downlink resource bandwidth within a frequency domain width of 6 resource blocks in the center of carrier. A system information block (SIB) can be divided into SIB1 through SIB13, the SIB1 is transmitted at a period of 20 ms, and is located on a subframe 5 of an even radio frame in time, the frequency domain resources are scheduled based on a physical downlink control channel (PDCCH), and the PDCCH is located in a common search space, i.e., the search space that all the UEs should detect; a time window for transmitting other SIB is allocated via the SIB1, but specific time and frequency domain resources are also scheduled based on the PDCCH. The PDCCH is located within a control area, which is at the first n symbols of one subframe, n is one of natural numbers from 1 to 4, the frequency domain thereof occupies the whole bandwidth of the carrier, and the transmitted PDCCH is broke up into the whole bandwidth through interleaving to obtain frequency diversity gain.
The UE is accessed to a base station in a process as follows: the PSS is firstly detected, and then the SSS is detected through the time domain positional relationship of the PSS and the SSS, to make initial synchronization of the time domain, including synchronization of symbol, subframe and frame; a physical cell identifier (PCI) also can be acquired through the sequence combination of detected PSS and SSS, a cyclic prefix length is determined through an time interval between PSS and SSS, and etc.; then the system information is read, PBCH is firstly read to acquire a bandwidth of a downlink system, an antenna port for a cell-specific reference signal (CRS), a system frame number, a physical hybrid automatic repeat request indicator channel (PHICH) configuration information and etc.; then SIB1 is read, and other SIBs are read according to configuration of the SIB1; and a random access signal is finally transmitted to establish radio resource control connection with the base station, and afterwards, normal data transmission can be performed.
In one deployment scenario, massive base stations, especially micro base stations, are deployed in a dense manner. In this scenario, interference between cells administrated by each mirco base station is rather severe, especially as for synchronization information, so that it is even more difficult for the UE to read the common control channel or even impossible to acquire, including PBCH and a control channel for scheduling the SIB.
In order to solve the problem of detecting the common control channel in an interference restricted scenario, one direct solution is to perform inter-cell interference coordination, that is, neighboring cells respectively transmit the common control channels of their respective cells with orthogonal resources, such as PBCH, SIB and so on, and the orthogonal resources mentioned above can be at least one of time domain, frequency domain, codeword domain and spatial domain. However, the PBCH carries the downlink carrier bandwidth based on the current design of the system, that is, before the PBCH is detected, the UE has no idea about the downlink carrier bandwidth of the current carrier, and therefore, the interference coordination only can be performed within a predefined bandwidth, for example, the predefined bandwidth in the current long term evolution (LTE) system is the frequency domain width of six resource blocks in the carrier center. It can be seen that such interference coordination has a rather low degree of freedom, and the above problems of detecting the common control channel cannot be completely solved, especially in a scenario where the cells are deployed in a dense manner.
USPTO Backgrounds
USPTO Backgrounds