In the frequency dimension, the resources are divided by taking a sub carrier as a unit. In communication, the smallest unit for allocation of frequency-domain resources is resource block (RB) corresponding to a physical resource block (PRB) of physical resources. As shown in FIG. 2, a PRB includes 12 sub carries in the frequency domain, which correspond to a slot in the time domain. A resource corresponding to a sub carrier on each OFDM-SC-FDM symbol is referred to as a resource element (RE).

In LTE/LTE-A cellular communication, a UE discovers an LTE network by detecting a synchronization signal (SS). The synchronization signal includes a primary synchronization signal (PSS) and a secondary synchronization signal (SSS). The UE obtains downlink frequency and time synchronization with a base station by detecting the synchronization signal. Moreover, because the synchronization signal carries a physical cell identity, the detection of the synchronization signal also means that the UE discovers an LTE/LTE-A cell.

On the uplink, when the UE needs to transmit uplink data, it initiates random access (RA) to carry out uplink synchronization and establish a radio resources control (RRC) connection, that is, the UE enters an RRC connected state from an RRC idle state. Upon random access, the UE needs to send a random access preamble, and a network side device detects the random access preamble in a specific time-frequency resource to implement identification of the UE and synchronization of the uplink.