A Blog dedicated to Declutter 3GPP specifications

Monday, November 16, 2020

DL MIMO efficiency enhancements for LTE


MIMO is an effective technique to improve spectral efficiency and increase overall network capacity. SRS can be utilized to improve DL MIMO performance, especially for massive MIMO in TDD. In release-16 SRS capacity and coverage are enhanced by introducing more than one SRS symbol in a UL normal subframe and introducing virtual cell ID for SRS.

More than one symbol for SRS in a UL normal subframe

With the introduction of more than one SRS symbol in a UL normal subframe, the SRS capacity and coverage can be increased. These additional SRS symbol(s) are referred to as trigger type 2 SRS.

1 to 13 symbols of the first 13 symbols of a UL normal subframe can be configured to a UE for aperiodically triggered SRS transmission. Intra-subframe repetition, frequency hopping and antenna switching of the additional SRS symbols can be supported. A guard period of one SC-FDMA symbol can be configured for frequency hopping and antenna switching.

The number of repetitions can be configured from the set {1, 2, 3, 4, 6, 7, 8, 9, 12, 13}. If a UE has more receive antennas than transmit chains (e.g. 1T2R), the UE can be configured to transmit the additional SRS with antenna switching. And a UE can additionally be configured with frequency hopping for the additional SRS. The number of antennas (pairs) to switch is:

-    2 for 1T2R, or the number of pairs is configured as 2 for 2T4R

-    3 if the number of pairs is configured as 3 for 2T4R

-    4 for 1T4R

Both legacy SRS and additional SRS can be configured to the same UE, and transmission of legacy SRS and additional SRS symbol(s) in the same subframe for the UE is supported.

For sequence generation, per-symbol group hopping and sequence hopping are supported.

Independent open loop and close loop power control is supported for additional SRS, and DCI formats 3/3A/3B are used for close loop power control.

UEs not configured with SPUCCH/SPUSCH are not expected to be triggered with additional SRS in the same subframe as PUSCH/PUCCH in the same serving cell. UEs configured with SPUCCH/SPUSCH drop the SRS transmission in the symbols colliding with SPUCCH/SPUSCH in the same serving cell.

The additional SRS transmission in the symbols colliding with PUSCH/PUCCH of another serving cell in the same TAG, the same band and with the same CP, is dropped.

The additional SRS transmission in the symbols colliding with PUSCH/PUCCH of another serving cell in the different TAG is dropped if the total transmission power exceeds the PCMAX in any overlapping portion.

Virtual cell ID

Virtual cell ID within the range from 0 to 503 can be configured for SRS to increase SRS capacity.

The virtual cell ID can be configured to only additional SRS symbol(s) or both legacy and additional SRS symbol(s). If virtual cell ID is not configured, the physical cell ID is used.

0 comments:

Post a Comment