In recent years, various proposals have been made concerning UWB (Ultra Wide Band) radio communication methods. As UWB radio communication is broadband communication exceeding 1 Gbps, its application to video transmission and the like with large transmission capacity has been investigated. On the other hand, UWB cannot be said to be easy to use in an office environment due to the narrowness of its possible communication range, and it can be said to be better suited to PANs (Personal Area Networks) that are attracting attention nowadays. However, PANs are still in their early days, and there are very few major applications. This is because a device exploiting the broadband characteristics generally uses a lot of power, but in the case of a PAN, movement is difficult while carrying a large number of batteries.
One application that uses a PAN and requires the broadband characteristics of UWB is a file exchange (file-swapping, file-sharing) application. The basic operating principle of a file exchange application is disclosed in Patent Document 1, for example. It is possible to create a mini-community with random file exchange in a mobile environment (referred to as message exchange in Patent Document 1). Although not mentioned in Patent Document 1, exchanged data is not limited to text documents, and the exchange of music, image, video, and suchlike files is also possible. With UWB in particular, since the effective transmission speed is 100 Mbps to several Gbps, it is possible to exchange large files that bypass each other, and this kind of file exchange can be said to be an application suited to UWB.
Various discussions concerning transmitting methods used in this UWB have emerged in IEEE802.15. There are many cases in which a MAC protocol implemented in a PAN (and more particularly, a mobile PAN) environment is a method using autonomous distributed processing. This is because, in a PAN environment in which terminals constantly pass by each other, constructing a master-slave relationship each time, and starting communication after setting up a communication environment, such as assigning data slots, is a major overhead.
Non-patent Document 1 discloses a radio communication method in an autonomous distribution type PAN.
FIG. 1 is a drawing showing the configuration of a super-frame in TDMA (Time Division Multiple Access).
In FIG. 1, a super-frame is divided into a beacon period 2201 and a data period 2202.
Beacons 2203 are transmitted from radio communication apparatuses within beacon period 2201, and it is guaranteed that beacons of neighbor nodes propagate to neighbor nodes without colliding.
Data period 2202 is divided equally into slots 2204, and slot IDs are assigned in that order, but this is not a limitation, and data periods may be unequal, and need not be contiguous.    Patent Document 1: Unexamined Japanese Patent Publication No. 2001-298406    Non-patent Document 1: “Towards High Speed Wireless Personal Area Network-Efficiency Analysis of MBOA MAC”, Yunpeng Zang, et al, Internet URL: http://www.ctr.kcl.ac.uk/IWWAN2005/papers/88_invited_Philips.pdf