the absence of multipath, the users in the MU group need to be well separated in angle, as observed by the base station array, to ensure sufficiently different spatial signatures. In the presence of rich multipath, the users need less physical separation.

In 1992, R. Roy and others founded ArrayComm Inc. with Marty Cooper as Board Chairman, to commercialize the SDMA technique originally proposed by Beach. The company successfully developed MU technology for the Japanese PHS Handy phone system in 1998,