In this paper, we specially propose some improved packet-level aggregation (PA) mechanisms which can enhance energy efficiency in WSNs. Firstly, the PA models are classified as SISO (single input single output), MISO (multiple input single output) and MIMO (multiple input multiple output) in WSNs. And then, motivated by SISO and MISO, we improve the PA mechanism by proper packet size solution for a single voice delivering and propose an efficient PA mechanism with asynchronous waiting algorithm for small data communication. Furthermore, we conduct some simulations to evaluate the performance of these proposed solutions in WSNs.