In an orthogonal frequency division multiple access (OFDMA) communication system, a transmission apparatus connects multiple tiles, which have a 4×3 structure, along a time or frequency axis in an uplink 4-layer partial usage of subchannels (PUSC) mode, and designs pilots corresponding to one layer at one of multiple symbol positions adjacent to a first corner of the tiles and one of multiple symbol positions adjacent to a second corner of the tiles that face the first corner in a diagonal direction. In this case, null symbols are designed at the rest of the symbol positions adjacent to the first corner or the second corner where the pilots are not designed. Accordingly, a receiving apparatus can obtain n channel values from n tiles. Further, n estimated channel values are applied to a linear interpolation method, so that it is possible to estimate the entire channel value of n tiles.