US Patent 7693038 OFDM radio communications system, transmitter and receiver

Each of a general chunk to which pilot signals are allocated at a general density, and a high-density chunk to which pilot signals are allocated at a higher density than the density of the general chunk, is transmitted in a frequency band common to OFDM transmitters. Each of the OFDM transmitters allocates the high-density chunk to any one of OFDM receivers, which notifies poor receiving quality.