 is a fixed two-receive-antenna MRC with transmission over the full bandwidth. Alternatively, one could also employ transmit antenna selection based on feedback from the UE. The other two curves represent this tech- nique. It is straightforward that choosing the better single stream achieves effective SINR gain compared to a fixed choice of the transmit antenna. The gap between the worst single stream and the best single stream is 6 dB in Figure 11.12. In the figure (right), SINR plots on those resources allocated single-stream mode are shown. There is ambiguity as to whether the selected single stream is, in fact, the best single stream. This is because the bit-loading algorithm has addi- tional constraints, such as protocol data unit (PDU) size matching over the entire bandwidth. To verify this, we plot the third curve showing the effective SINR on the selected single stream. Observe that the selected single stream coincides with the best single stream choice. The gap between the worst single stream and the best single stream is 3 dB. Dual-stream mode. Figure 11.13 compares the SINR for dual-stream transmis- sion. The left-hand bunch of curves represents achieved SINRs with dual-stream operation on the entire bandwidth. This is obtained with a linear MMSE algorithm. The other two curves show plots for Tx1 and Tx2, which transmit simultaneously on a time-frequency resource. The effective SINR shows a longer tail toward the left. This happens because a second stream has to be separated at the receiver. The plot also shows a significant gap between the worst of two streams and the best of © 2009 by Taylor & Francis Group, LLC Early Real-Time Experiments and Field Trial Measurements Dual Stream Mode Worst single stream Single stream Tx1 Single stream Tx2 Best single stream Effective SINR when full bandwidth is allocated in dual stream mode Effective SINR on selected resource blocks Effective SNR at QAM Demodulator (dB) Figure 11.13 SINR distribution for the dual-stream mode. Left group of curves: dual mode over ful