Figure 1From: Performance of opportunistic fixed-beam spatial multiplexing in OFDMA uplinkSchematic description of a 2 × 2 fixed beam MIMO approach. Both the base station (BS) and mobile terminal (MT) have two omnidirectional antennas in an antenna domain MIMO approach (left). In a fixed-beam beam MIMO scheme, a Butler matrix (BM) is applied at BS to create two orthogonal beams (right).Back to article page