Rank filtering and graceful rank switching in base station
A method which i) segregates UEs to different categories of “conforming” and “nonconforming”, and ii) performs rank indicator (RI) filtering and/or switching based on the specific category is provided. Rank indicator (RI) filtering is performed in a SINR-specific manner, e.g., when SINR is low, the rank filtering is performed in such a way to always give an output of 1 or 2, not more. In addition, the Modulation and Coding Scheme (MCS) assigned for a PDSCH is adjusted when the rank switching is performed, thereby achieving graceful rank switching. Furthermore, Outer Loop Rate Control (OLRC) optimization is provided in response to rank switching.
1. A method of providing a rank index (RI) filtering, comprising:
receiving, by one of an eNB or gNB, a rank index (RI) from a user equipment (UE);
determining, by one of the eNB or gNB, whether the UE is one of a conforming UE or a nonconforming UE, based on per-rank-based block error rate (BLER) monitored over a period; and
performing at least one of i) a first type of rank filtering in case the UE is a conforming UE, and ii) a second type of rank filtering in case the UE is a nonconforming UE.
2. The method of claim 1 , wherein the first type of rank filtering is configured for conforming UEs, wherein conforming UEs are defined as UEs reporting correlated RI and Channel Quality Indicator (CQI).
3. The method of claim 1 , wherein the second type of rank filtering is configured for nonconforming UEs, wherein nonconforming UEs are defined as UEs reporting uncorrelated RI and CQI.
4. The method of claim 1 , wherein at least one of:
i) the UE is determined as a nonconforming UE if per-rank-based BLER is greater than the product of a predetermined target BLER and a predetermined offset; and
ii) the UE is determined as a conforming UE if per-rank-based BLER is less than the product of the predetermined target BLER and the predetermined offset.
5. The method of claim 1 , the method further comprising:
adjusting, by one of the eNB or gNB, the RI received from the UE to a final RI rank as part of one of the first type of rank filtering or the second type of rank filtering; and
performing, by one of the eNB or gNB, Outer Loop Rate Control (OLRC) optimization in response to one of the first type of rank filtering or the second type of rank filtering, wherein the OLRC optimization reduces the final RI rank if at least one Physical Downlink Shared Channel (PDSCH) failure occurs on the UE side.
6. The method of claim 1 , further comprising:
in case a filtered RI for a current Transmit Time Interval (TTI) is greater than a filter RI for a previous TTI, and BLER is greater than the sum of a predetermined target BLER and a predetermined offset value, reducing Modulation and Coding Scheme (MCS) index by one.
7. The method of claim 1 , further comprising:
in case a current RI received from the UE for a current Transmit Time Interval (TTI) is greater than a previous RI received from the UE for a previous TTI, and BLER is greater than the sum of a predetermined target BLER and a predetermined offset value, reducing Modulation and Coding Scheme (MCS) index by one.
8. The method of claim 1 , wherein at least one of the first type of rank filtering and the second type of rank filtering comprises:
performing infinite impulse response filtering on the RI received from the UE (UE reported RI) to produce a first filtered RI (FILTERED_RI);
calculating a rounded filtered RI (ROUNDED_FILTERED_RI) using the following function:
ROUNDED FILTERED RI=floor (FILTERED_RI+0.5);
if one of i) ROUNDED_FILTERED_RI>=3, in case the UE has 4 receivers (RXs) with a maximum RI rank of 4, or ii) ROUNDED FILTERED RI>=2, in case the UE has 2 receivers (RXs) with a maximum RI rank of 2, resetting the ROUNDED_FILTERED_RI to 1; and
calculating a final filtered RI (FINAL_RI) using the following minimum function:
FINAL RI=Min (ROUNDED FILTERED_RI, UE reported RI).
9. The method of claim 8 , further comprising:
for the first type of rank filtering, in case FINAL RI for a current Transmit Time Interval (TTI) is greater than FINAL_RI for a previous TTI, and BLER is greater than the sum of a predetermined target BLER and a predetermined offset value, reducing Modulation and Coding Scheme (MCS) index by one.
10. The method of claim 1 , further comprising:
for the second type of rank filtering, performing Modulation and Coding Scheme (MCS) adjustment, wherein said MCS adjustment includes:
in case the RI received from the UE is adjusted to a higher final RI rank, maintaining a code rate for a lower RI rank.
11. The method of claim 1 , wherein the second type of rank filtering comprises:
performing Modulation and Coding Scheme (MCS) adjustment, wherein said MCS adjustment includes:
in case the RI received from the UE is adjusted to a different final RI rank,
i) calculating new efficient bit rate (newEffBitrate) based on new target code rate (newTargetCodeRate), the final RI rank (newEffRank) and new modulation order (newModOrder), as follows:
newEffBitRate=newTargetCodeRate*newEffRank*newModOrder,
and
ii) calculating current efficient bit rate (currEffBitrate) based on current target code rate (currTargetCodeRate), the RI rank received from the UE (currEffRank) and current modulation order (currModOrder), as follows:
currEffBitRate=currTargetCodeRate*currEffRank*currModOrder;
determining whether the following condition is satisfied:
(newEffBitRate/currEffBitRate)−1>predetermined threshold; and
if the condition is satisfied,
calculating at least one of a target efficient bit rate per rank
(“targetEffbitRatePerRank”), a target signal-to-interference-and-noise ratio (targetSINR) and target MCS (targetMCS), and
updating current SINR (currSINR) as new SINR (newSINR), and updating code word MCS as new MCS.
12. The method of claim 1 , further comprising:
monitoring the per-rank-based BLER occurring over a plurality of RI-receiving periods, wherein only the RI-receiving periods in which RI rank is adjusted from a lower rank to a higher rank are monitored.
13. The method of claim 6 , further comprising:
adjusting, by one of the eNB or gNB, the RI received from the UE to a final RI rank as part of one of the first type of rank filtering or the second type of rank filtering; and
performing, by one of the eNB or gNB, Outer Loop Rate Control (OLRC) optimization in response to one of the first type of rank filtering or the second type of rank filtering, wherein the OLRC optimization reduces the final RI rank if at least one Physical Downlink Shared Channel (PDSCH) failure occurs on the UE side.
14. The method of claim 1 , further comprising:
performing, by one of the eNB or gNB, Outer Loop Rate Control (OLRC) optimization in response to one of the first type of rank filtering or the second type of rank filtering, wherein the OLRC optimization includes:
calculating an OLRC offset for at least one code word when a downlink transmission shifts between one code word and two code words, wherein the one code word case has a first code word-to-layers mapping, and the two code words case has a second, different code word-to-layers mapping.
15. The method of claim 14 , wherein:
in case RI rank is adjusted from RI rank 1 to RI rank 2 in a scenario requiring one code word for RI rank 1 and two code words for RI rank 2, one OLRC offset value for one code word for RI rank 1 is evenly divided into two equal halves used as OLRC offset values for the two code words for RI rank 2.
16. The method of claim 14 , wherein:
in case RI rank is adjusted from RI rank 1 to RI rank 2 in a scenario requiring one code word for RI rank 1 and one code word for RI rank 2, one OLRC offset value for one code word for RI rank 1 is cut by half for use as an OLRC offset value for the code word for RI rank 2.
17. The method of claim 14 , wherein:
in case RI rank is adjusted from RI rank 2 to RI rank 3 in a scenario requiring two code words for RI rank 2 and two code words for RI rank 3, one of two OLRC offset values for the two code words for RI rank 2 is cut by half for use as an OLRC offset value for one of the two code words for RI rank 3.
18. The method of claim 14 , wherein:
in case RI rank is adjusted one of i) from RI rank of 2 to RI rank of 1, ii) from RI rank of 3 to RI rank of 1, or iii) from RI rank of 4 to RI rank of 1, in a scenario requiring one code word for RI rank 1 and two code words for RI rank of 2, 3 and 4, then a single OLRC offset value for one code word for RI rank 1 is determined by:
calculating a maximum code word OLRC offset (MaxCW-OLRC offset) using a maximum function of first code word OLRC offset (CW0-OLRC offset) and second code word OLRC offset (CW1-OLRC offset), as follows:
MaxCW-OLRC offset=MAX(CW0-OLRC offset,CW1-OLRC offset);
calculating a minimum code word OLRC offset (MinCW-OLRC offset) using a minimum function of first code word OLRC offset (CW0-OLRC offset) and second code word OLRC offset (CW1-OLRC offset), as follows:
MinCW-OLRC offset=MIN(CW0-OLRC offset,CW1-OLRC offset); and
calculating the single OLRC offset (CW OLRC offset) value for one code word for RI rank 1 as follows:
CW OLRC offset=(MaxCW-OLRC offset/2)+(MinCW-OLRC offset/2).