Alternatively, a format of preamble signal symbol is as shown in FIG. 3. One preamble signal symbol includes a CP and an information segment. The information segment shares the separate CP. The preamble signal symbol can also be called a preamble signal symbol with a CP. Symbol #n includes 4 preamble signal symbols. That is, a length of one downlink signal symbol is equal to a length of 4 preamble signal symbols. Alternatively, lengths of CPs of the last three preamble signal symbols are same and less than a length of CP of the first preamble signal symbol in the 4 preamble signal symbols. Alternatively, each preamble signal symbol in the 4 preamble signal symbols has a same length of CP.
In FIG. 3, when the network device selects a starting point of a CP or a starting point of a preamble signal symbol as the first time-point, the first time-point can be a starting point of any CP (i.e. a time-point as shown by ↓ in FIG. 3). When the network device selects a starting point of the downlink signal symbol as the first time-point, the first time-point can be a starting point of a CP of the first preamble signal symbol (i.e. the time-point indicated by the first ↓ in FIG. 3).
