l bandwidth. Right: Dual mode only on the resources allo- cated during link adaptation. Thick curve: best of the two streams with antenna ordering. two streams. This gap indicates that different MCS levels will be assigned to the streams. The right-hand group of curves represents the SINR achieved in dual- stream mode on RBs selected for dual-stream transmission. The curves validate that dual-stream transmission is chosen in MIMO configuration only when the SINR and channel structure are both suitable. Remember that resource blocks are assigned single-stream transmission if dual stream transmission is not optimal. Remark. Dual-stream transmission by means of assigning each stream to a sepa- rate user can be exploited for spatial division medium access (SDMA) operations. The rightmost curve in Figure 11.13, representing the better of two streams, shows a significant SINR increase. In SDMA techniques, a UE is given only the better of the two streams and the second stream is allocated to another UE in the cell. It is well known that a medium to high SINR range allows for dual-stream operation, but at low SINR single-stream transmission is preferable. The probability of finding another user in the medium to high SNR range on a resource block in a cell is, in fact, quite high. Initial trials with only two users have shown that this SDMA mode is chosen quite often. Thus, we expect SDMA multiuser diversity to bring additional throughput gains to the system. The SDMA gain is in addition to the OFDMA multiuser scheduling gains. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology Received power @ Tx1 & Tx2 Throughput per Tx antenna & sum throughput Leave main beam of BS antenna-LOS Enter next room through door-shadowing area 10E-2 Achieved uncoded BER 10E-3 10E-4 10E-5 Time Slot Figure 11.14 Plots of received power (top), throughput (middle), and BER (bot- tom) in an office scenario while the UE is moved from one room to another. 11.2.4.3 Measured Throughput with Link Adaptatio