PACKET COMMUNICATION SYSTEM, IRRADIATION CONTROL APPARATUS, ANTENNA CONTROL METHOD AND PROGRAM
Proposed are a packet communication system and others that can achieve automatic adjustment of the antenna directivity without changing the radio interface of a relay radio apparatus even if the relay radio apparatus exhibits fluctuations in packet transmission timing due to CSMA/CA or the like. An interference avoiding unit (9) causes fluctuations in packet transmission timing due to the processing of CSMA/CA or the like. A radio wave irradiating apparatus (5) can control the irradiating direction and/or irradiating intensity. A packet generating unit (7) changes, on the basis of a switching sequence used for determining the irradiating direction and/or irradiating intensity, characteristics other than the content of a switching control packet (e.g., packet length, transmission intensity and so on), thereby generating the switching control packet. A radiation control unit (21) observes, among others, those characteristics other than the content of the switching control packet and determines, as antenna control information, one or more bits. The radiation control unit (21) controls, on the basis of a bit sequence including the determined one or more bits, the directivity of a directivity antenna unit (23) as a whole.