Modified-SEP 通过修改了族头的筛选条件，以及考虑筛选族头时，各个族头相对于基站的位置，对SEP协议进行了优化-Modified-SEP： In this protocol, the remaining energy and distance　node to base station have been taken under consideration while selecting optimal cluster-heads at each round in Stable Election Protocol(SEP). Meanwhile, an energy threshold is set for cluster head to avoid that the nodes which have too low energy are selected as cluster head.