Patent ID: 7796571

Claim:
A communication system comprising: a communication control apparatus connected to an external network for controlling a communication path with the external network; and a plurality of communication terminal apparatuses that perform radio communications with the communication control apparatus, using any one of a plurality of radio channels by a communication method for communication under a predetermined protocol so as to communicate with the external network via the communication control apparatus, wherein the plurality of communication terminal apparatuses are grouped by each communication method under a different protocol, and a radio channel used in a communication method of each group overlaps a radio channel used in a communication method of at least one of the other groups, the communication system further comprising: channel detecting means for detecting a radio channel currently used by a communication terminal apparatus communicating with the communication control apparatus, a frequency use status memory storing a table indicating one or more frequencies being used for communication where the table has a priority order, radio communication control means controlling communications by selecting a radio channel other than the currently used radio channel so as not to cause interference, before interference is caused, based on the table, at least when establishing communications between a communication terminal apparatus that is not communicating and the communication control apparatus and when switching a radio channel used for communications established between the communication terminal apparatus and the communication control apparatus, and said radio communication control means updating the table in said frequency use status memory when the radio communication control means detects a radio channel in use, wherein said radio communication control means updating the table in said frequency use status memory with a radio channel or channels that are determined to be in use, said radio communication control means selects a radio channel from the table that is assigned a first priority in the priority order as a current channel, said radio communication control means updates the table when it receives information indicating at least one channel as unusable, said radio communication control means compares said current channel with the at least one unusable channel to determine whether the current channel matches the at least one unusable channel, and when said radio communication control means determines that the current channel matches the at least one unusable channel, said radio communication control means randomly selects a new channel and continues to select new channels until a new channel selected does not match the at least one unusable channel.