Multi-hop extension is fulfilled by constructing child or neighbor piconets in IEEE 802.15.3 standard. This approach does not consider the multi-channel capability in the physical layer. The scalability of the design is limited. This paper discusses how to construct a multi-piconet network and improve the performance of UWB multi-hop WPANs in the existing 802.15.3 standard based on a bridge device (BDEV). BDEV is a member of all interconnected piconets. The coverage extension by BDEVs follows the 802.15.3 standard and it takes benefit from the space reuse. BDEV with only one network interface is cheap and simple to extend a flexible construction of ad hoc networking of WPANs. Furthermore, a distributed scheduling scheme on BDEV is proposed to improve the delay performance. Through detailed simulations, the proposed distributed BDEV scheduling scheme are shown to be effective to extend network coverage.