14.3 Multiantenna Evolution
3GPP Release 7 introduced 2 × 2 MIMO operation with 16QAM modulation to the standards in 2007, Release 8 extended the MIMO support to operate with 64QAM modulation and Release 9 and 10 further extended the MIMO + 64QAM operation with simultaneous two- and four-carrier operations respectively. 3GPP Release 11 extended the HSDPA MIMO to 4 × 4 antenna configurations. Figure 14.4 illustrates the MIMO support in 3GPP standard releases.
Figure 14.4 Multi-antenna evolution.
The need for two (or four) receive antennas in the device and two (or four) transmit antennas in the base station have somewhat slowed down the enthusiasm for practical MIMO deployments. Furthermore the additional overhead introduced in the MIMO enabled cell due to the second antenna pilot transmission slightly degrades the performance of the non-MIMO devices operating in the cell.
Figure 14.5 illustrates the virtual antenna mapping integrating the two transmit antennas of 2 × 2 MIMO with the single-transmit-antenna signals understandable to the non-MIMO devices. The Pilot 2 and Data 2 represent the MIMO signals only understood by the MIMO receivers. Both pilot signals need to be present for a MIMO UE to be able to estimate the channel quality and provide MIMO Channel Quality Indicator (CQI) reports in the uplink. Both data signals are only present when a MIMO UE is scheduled with dual-stream ...
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