Receiver, transmitter, radio communication system, and radio communication method

A receiver includes a reception antenna, a reception unit, and a demodulation unit. The reception unit sequentially receives modulated signals resulting from spread spectrum via the reception antenna. The demodulation unit demodulate a first signal received by the reception unit by performing despreading using a short-period spreading code, the first signal including information for identifying a long-period spreading code. The demodulation unit identifies the long-period spreading code on the basis of the information obtained from the first signal. The demodulation unit then demodulates a second signal received by the reception unit after the first signal by performing despreading using the long-period spreading code.