 first case is referred to as space division multiplexing (SDM) and is applied in order to increase user data rates. On the other hand, multiple code words can also provide multiple access (i.e., different code words are allocated to different users sharing the same radio resource). © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology Frequency Channel 1 Channel 2 Code word #1 AAAABBBB eNode Code word #2 AAAABBBB Channel User A User B Figure 3.23 Example of single-user MIMO with two code words. 3.3.3.1 Space Division Multiplexing (SU-MIMO) The basic idea of space division multiplexing, also referred to as single-user MIMO (SU-MIMO), is to transmit several code words to the same user in the same radio resource ("time frequency") in order to increase user peak data rates. As depicted in Figure 3.23, there is only one scheduled user on each channel or frequency sub-band. SU-MIMO transmission allows for applying the so-called per stream rate control by independently adapting each of the transmitted code words. The mobile terminal reports channel quality indicators for each of the received code words; this informa- tion is used to adapt the modulation and coding rates independently per code word. Also, the fact that several streams are transmitted to the same user allows for imple- menting a stream-by-stream successive interference cancellation (SIC) strategy at the receiver (Wubben and Kammeyer 2006, 2183; Kyungchun, Chun, and Hanzo 2007, 2438). Successfully decoded streams are suppressed from the received signal (interference cancellation), thus avoiding error propagation in the reception of the remaining streams. Hence, the application of SIC strategies allows efficient recov- ery of the different data streams. SU-MIMO is very suitable for users experiencing good channel conditions and, in general, throughput is increased in the center of the cell (near the eNodeB). 3.3.3.2 Multiple Access When multiple antennas are used to support spatially multiplexed users in the same