A scheme for fully polarimetric MIMO multiuser detection

Multiple-Input Multiple-Output (MIMO) functionality has been shown to dramatically increase the capacity of wireless communication systems when the environment provides rich multipath scattering. In a predominantly Line-of-Sight (LOS) environment, the loss of diversity reduces the potential gain considerably. Recent studies have shown that systems which use a fully -polarimetric antenna such as triad antenna at the both end of the link can provides stability in performance across a full range of propagation environments from LOS to pure Rayleigh scattering. These systems also provide resilience to arbitrary rotations of the transmit and receive antennas. This paper considers the multiuser downlink where both the base station and each user is equipped with a triad antenna. The system uses a CDMA transmitting scheme in which each user is assigned a two dimensional subspace and the transmitted information symbol for each user is coded across this subspace. The received signal for each user after despreading is equivalent to the decoding problem of a single user with space-time block code (STBC) system. We demonstrate that the transmitted information symbols can be chosen to have the structure of STBC with full rate, full-diversity and low complexity decoding. We also show how to generalize our basic MIMO CDMA scheme to apply to an inhomogeneous multiuser scenario where the base station has two transmit antennas, but each user is equipped with either one or two receive antennas and wish to use different STBCs.