We propose a novel detection method for non-coherent synchronization (signal acquisition) in multi-access UWB impulse radio (IR) networks. It is designed to solve the IUI (Inter-User Interference) that occurs in some ad-hoc networks where concurrent transmissions are allowed with heterogeneous power levels. In such scenarios, the conventional detection method, which is based on correlating the received IR signal with a Template Pulse Train (TPT), does not always perform well. Our proposal has similar complexity as the conventional method. We evaluate its performance with the Line Of Sight (LOS) office indoor channel model proposed by the IEEE P802.15.4a study group and find that the improvement is significant.