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Peer-to-peer (P2P) networks are very popular for large-scale data sharing in today's internet. It is naturally envisioned that the file sharing would also be an important application for civil mobile ad hoc networks in the future. The authors propose the cooperative diversity download methods utilising the wireless medium and common file sources in wireless P2P networks. The designed protocols including multi-source opportunistic direct downloading (MODD) and multi-source opportunistic decode-and-forward downloading (MODFD) can adaptively work in different file distribution scenarios. Both of them rely on the cooperation between the sources or receivers and the proposed distributed source-selection schemes. For the situation with one receiver and multi-source, MODD selects `best` source with most favourite channel condition from available m sources. In the situation with multiple receivers and sources, the multiple receivers could form the cooperative pairs to receive the data from the selected source based on decode-and-forward transmission strategy. Compared with MODD, MODFD saves the source-selection time and provides incentives for the cooperation between the peers. A distributed collision solving scheme for the selection schemes is also proposed. The information theoretic analysis of outage probability shows that the proposed downloading methods can both obtain m times diversity gain.