Patent ID: 7830838

Claim:
A wireless sensor network ( 100 ) comprising a first headnode ( 101 ) a first subnode ( 102 ) adapted to communicate with the first headnode ( 101 ), thus making the first headnode ( 101 ) and the first subnode ( 102 ) members of a first cluster ( 103 ) a second headnode ( 111 ) and a second subnode ( 112 ) adapted to communicate with the second headnode ( 111 ), thus making the second headnode ( 111 ) and the second subnode ( 112 ) members of a second cluster; characterized in that the first headnode ( 101 ) is adapted to select a first frequency for use in wireless communications within the first cluster ( 103 ) the first subnode ( 102 ) is adapted to communicate with the first headnode ( 101 ) on said first frequency, using a time slotted channel access scheme to allow also other nodes to communicate with the first headnode ( 101 ) on said first frequency the second headnode ( 111 ) is adapted to find out the first frequency selected by the first headnode ( 101 ), and to select a second frequency—different from said first frequency—for use in wireless communications within the second cluster the second subnode ( 112 ) is adapted to communicate with the second headnode ( 111 ) on said second frequency, using a time slotted channel access scheme to allow also other nodes to communicate with the second headnode ( 111 ) on said second frequency, for communicating information from the first cluster ( 103 ) to the second cluster, the first headnode ( 101 ) is adapted to find out the second frequency selected by the second headnode ( 111 ) and to communicate with the second headnode ( 111 ) on said second frequency, using the same time slotted channel access scheme as said second subnode ( 112 ), and the first headnode ( 101 ) and the second headnode ( 111 ) are additionally adapted to repeatedly transmit network beacon signals ( 331 , 332 ) on a third frequency, which is different from said first frequency and said second frequency.