There are two fundamental channel models in decode-and-forward (DF) multihop relaying system: one is DF multihop channel and the other is DF multihop diversity channel. The latter outperforms the former at the cost of computational and hardware complexity at each relay. In this study, the authors consider a trade-off of the above two channel models and propose a new channel model, which is DF multihop channel with direct link. The new channel model can exploit partial spatial diversity without any extra request for the receiver of relays. The authors focus on the optimal power allocation problem of their proposed system. The authors first derive the end-to-end outage probability, and then they formulate and evaluate the optimisation problem by minimising the outage probability under the total power constraint. Numerical results demonstrate that their proposed system can improve system performance compared with fundamental multihop relaying system. In addition, their proposed power allocation scheme can effectively enhance the system performance compared with uniform power allocation scheme, especially if the number of relays is large.