Modular, portable data collection terminals are disclosed for use in mixed wireless and hard-wired RF communication networks, wherein various radio transmitter modules and associated antennas may be selectively added to a base terminal unit to solve networking problems associated with specific types...http://www.google.de/patents/US6014705?utm_source=gb-gplus-sharePatent US6014705 - Modular portable data processing terminal having a higher layer and lower layer partitioned communication protocol stack for use in a radio frequency communications network
