1. A radio communication system in a network comprising:
a plurality of source nodes (2), which are transmitting sources of information; and
a sink node (1) that collects the information,
the source nodes (2) and the sink node (1) having radio communication functions and being connected using radio multi-hop when the source nodes (2) and the sink node (1) cannot directly perform radio communication,
characterized in that
the sink node (1) includes a multi-polling control unit (14) that requests the source nodes (2) to transmit information,
the source nodes (2) each includes a polling-response control unit (24) that sends back the information in response to the request, and
in the sink node (1), the multi-polling control unit (14) divides the source nodes (2) into a plurality of groups for spatially avoiding radio interference, selects all or several groups of the divided groups, and performs, for each of the selected groups, polling in order for the source nodes (2) in the group to simultaneously or continuously perform multi-polling.
2. The radio communication system according to claim 1, wherein, in the sink node (1), the multi-polling control unit (14) divides, on the basis of positional information of the source nodes (2) with respect to the own node, the source nodes (2) into a plurality of groups for spatially avoiding radio interference.
3. The radio communication system according to claim 1, wherein, in the sink node (1), the multi-polling control unit (14) divides, on the basis of information concerning the number of hops or route information from the own node to the source nodes (2) or these two kinds of information, the source nodes (2) into a plurality of groups for spatially avoiding radio interference.

4. The radio communication system according to claim 1, wherein, in the sink node (1), the multi-polling control unit (14) divides, on the basis of positional information of the source nodes (2) with respect to the own node and information concerning the number of hops or route information from the own node to the source nodes (2) or these two kinds of information, the source nodes (2) into a plurality of groups for spatially avoiding radio interference finer than dividing the source nodes (2) using only the positional information or only the information concerning the number of hops or the route information or these two kinds of information.
5. The radio communication system according to claim 1, wherein, in the sink node (1), the multi-polling control unit (14) collects, concerning each of the source nodes (2), interference degree information between adjacent nodes for each of the source nodes (2) and divides the source nodes (2) into a plurality of groups such that the source nodes (2) having a high interference degree belong to a same group.
6. The radio communication system according to claim 3 or 4, wherein, in the sink node (1), when performing the polling for the source nodes (2) of a selected plurality of the groups, the multi-polling control unit (14) performs multi-polling in order from the polling for the source nodes (2) of the group having a large number of hops to the polling for the source nodes (2) of the group having a small number of hops.
7. The radio communication system according to claim 3 or 4, wherein, in the sink node (1), when performing the polling for each of the source nodes (2) of a selected plurality of the groups, the multi-polling control unit (14) selects a next source node for each of the groups and performs the polling after receiving responses from the source nodes (2) requested to transmit information or, when the responses cannot be received, after reception waiting time is timed out.

8. The radio communication system according to claim 3 or 4, wherein, in the sink node (1), when performing the polling for each of the source nodes (2) of a selected plurality of the groups, the multi-polling control unit (14) sets the number of pollings for the source nodes (2) of the group having a small number of hops to be larger than the number of pollings for the source nodes (2) of the group having a large number of hops.
9. The radio communication system according to claim 3 or 4, wherein, in the sink node (1), when performing the polling for each of the source nodes (2) of a selected plurality of the groups, the multi-polling control unit (14) selects a next source node individually for each of the groups and performs the polling without waiting for responses from the source nodes (2) of other groups after receiving responses from the source nodes (2) of the groups requested to transmit information or, when the responses cannot be received, after reception waiting time is timed out.
10. The radio communication system according to claim 2, 3, or 4, wherein,
in the sink node (1), when source nodes (2) are added or deleted in the radio
communication system, the multi-polling control unit (14) cyclically collects and
calculates the route information and performs correction of a divided state of the
groups.
11. The radio communication system according to claim 3 or 4, wherein, in the sink node (1), when the number of hops is changed because of a route change in the radio communication system, the multi-polling control unit (14) cyclically collects and calculates the route information and performs correction of a divided state of the groups.
12. The radio communication system according to any one of claims 2 to 5, wherein, in the sink node (1), the multi-polling control unit (14) measures a

collection time of information for each of the groups and reduces the number of nodes in the group when the collection time is long or increases the number of nodes in the group when the collection time is short, to perform correction of the group division.
13. The radio communication system according to claim 2, 3, or 4, wherein, in the sink node (1), the multi-polling control unit (14) collects, concerning each of the source nodes (2), interference degree information between adjacent nodes for each of the source nodes (2) and performs correction of the group division such that the source nodes (2) having a high interference degree belong to a same group.
14. The radio communication system according to any one of claims 2 to 5, wherein, in the sink node (1), to preferentially use a stable radio link, after ending the polling for all the source nodes (2) in a same group, the multi-polling control unit (14) shifts to the polling for the source nodes (2) of a next group.
15. The radio communication system according to any one of claims 2 to 5, wherein, in the sink node (1), when fluctuation of a radio environment or a route failure occurs, if there is no response of information from the source nodes (2) in response to a transmission request for information to each of the source nodes (2), the multi-polling control unit (14) performs the polling for the source nodes (2), from which responses of information have not been received, again immediately or after elapse of a fixed time or after the polling for other source nodes (2) in a same group ends.
16. The radio communication system according to any one of claims 2 to 5, wherein, in the sink node (1), when fluctuation of a radio environment or a route failure occurs, if there is no response of information from the source nodes (2) in response to a transmission request for information to each of the source nodes (2) and, even if the polling is performed again, responses have not been sent back a

fixed number of times or there are a large number of the source nodes (2) from which responses have not been sent back, the multi-polling control unit (14) determines that a radio state near the groups, to which the source nodes (2) belong, is temporarily bad and collectively shifts polling targets to perform the polling for another group.
17. The radio communication system according to claim 2, 4, or 5, wherein, in the sink node (1), the multi-polling control unit (14) selects, as order of the polling for each of the source nodes (2) in the group, on the basis of positional information and interference degree information, in each of the groups, the source nodes (2) present in positions where relative positions in the group with respect to the own node are similar and thereafter sequentially selects the source nodes (2) present in unified directions from the selected source nodes (2) to perform the polling for the source nodes (2), the relative positions of which with respect to the own node are similar, in each of the groups.
18. The radio communication system according to claim 3 or 4, wherein, in the sink node (1), the multi-polling control unit (14) sequentially selects, as order of the polling for each of the source nodes (2) in the group, on the basis of information concerning the number of hops, in each of the groups, the source nodes (2) from the source node having a large number of hops to the source node having a small number of hops or sequentially selects the source nodes (2) from the source node having the small number of hops to the source node having the large number of hops to perform the polling for the source nodes (2) having a same degree of ranking of the number of hops in each of the groups.
19. The radio communication system according to any one of claims 2 to 5, wherein, in the sink node (1), when performing the polling for each of the source nodes (2) of a selected plurality of the groups, concerning the group in which the polling for all the target source nodes (2) in the group ends, the multi-polling

control unit (14) selects another group replacing the group and continues the multi-polling for a plurality of the groups including the group selected anew.
20. The radio communication system according to claim 1, wherein the network is a sensor network, an ad-hoc network, or a wireless mesh network.
21. A sink node (1) of a radio communication system in a network including a plurality of source nodes (2), which are transmitting sources of information, and a sink node (1) that collects the information,
the source nodes (2) and the sink node (1) having radio communication functions and being connected using radio multi-hop when the source nodes (2) and the sink node (1) cannot directly perform radio communication,
the sink node (1) comprising a multi-polling control unit (14) that requests the source nodes (2) to transmit information, characterized in that
the multi-polling control unit (14) divides the source nodes (2), which send back the information in response to the request, into a plurality of groups for spatially avoiding radio interference, selects all or several groups of the divided groups, and performs, for each of the selected groups, polling in order for the source nodes (2) in the group to simultaneously or continuously perform multi -polling.
22. A radio communication method for a radio communication system in a
network including a plurality of source nodes (2), which are transmitting sources
of information, and a sink node (1) that collects the information,
the source nodes (2) and the sink node (1) having radio communication functions and being connected using radio multi-hop when the source nodes (2) and the sink node (1) cannot directly perform radio communication,
the radio communication method comprising:
group dividing in which the sink node (1) divides the source nodes (2) into a plurality of groups for spatially avoiding radio interference;

group selecting in which the sink node (1) selects all or several groups of the divided groups;
polling requesting in which the sink node (1) requests, for each of the selected groups, in order, the source nodes (2) in the group to transmit information; and
polling responding in which the source nodes (2) send back information in response to the request, wherein
multi-polling is simultaneously or continuously performed between the sink node (1) and the source node (2).