October 2012
Intermediate to advanced
248 pages
7h 54m
English
Content preview from LTE Advanced: 3GPP Solution for IMT-Advanced
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7.2 Uplink MIMO Enhancements Overview
In contrast to the downlink MIMO operation in LTE Release 8, there is no multi-antenna uplink as part of the Release 8 or 9 LTE specifications. In the early days of LTE studies uplink MIMO was also considered but then it was decided to focus the Release 8 LTE specification work in the downlink-only MIMO solutions. In the uplink direction there is already the possibility to perform so called virtual MIMO or uplink Multi-User MIMO (MU-MIMO) in Release 8 anyway by allocating two users the same set of physical resource blocks, while those users are transmitting using mutually orthogonal reference signal (RS) sequences. Additionally, antenna selection transmit diversity was included in Release 8 as an optional feature. Release 10 now provides a lot of extra functionality both to add more flexibility to the earlier defined MU-MIMO operation as well as to introduce the Single User MIMO (SU-MIMO) in the uplink direction as well. The following key new areas are introduced on top of the Release 8 MIMO capabilities as shown in Figure 7.1.
Figure 7.1 LTE uplink MIMO developments in different releases.
- Introduction of the two- and four-antenna uplink SU-MIMO transmission, with the overall principle rather similar to the downlink MIMO operation, with the two-antenna MIMO operation illustrated in Figure 7.2.
- More flexible reference signal sequence allocation ...
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