Many key pre-distribution techniques have been developed recently to establish pairwise keys for wireless sensor networks. To further improve these schemes, researchers have proposed to take advantage of sensors' expected locations to help pre-distributing keying materials. However, it is usually very difficult, and sometimes impossible, to guarantee the knowledge of sensors' expected locations. In order to remove the dependency on expected locations, this paper proposes a practical deployment model, where sensor nodes are deployed in groups, and the nodes in the same group are close to each other after the deployment. Based on this model, the paper develops a novel group-based key pre-distribution framework, which can be combined with any of existing key predistribution techniques. A distinguishing property of this framework is that it does not require the knowledge of sensors' expected locations and greatly simplifies the deployment of sensor networks. The analysis also shows that the framework can substantially improve the security as well as the performance of existing key predistribution techniques.