Selecting a modulation and coding scheme and a transmit block size in long term evolution
A base station for selecting a modulation and coding scheme (MCS) and a total block size (TBS) for a UE is provided. The base station includes a processor and memory storing instructions. The instructions are executable to map a nominal MCS to a TBS index and determine a nominal TBS per resource block value based on the TBS index. The instructions are also executable to determine a target TBS based on the nominal TBS per resource block value and a number of resource blocks allocated to the UE. The instructions are also executable to determine a customized TBS, from a plurality of predefined TBSs, that is closest to the target TBS. The instructions are also executable to map the customized TBS to a customized MCS. The instructions are also executable to use the customized TBS and the customized MCS to transmit to the UE during a downlink transmission time interval.
1. A base station for selecting a modulation and coding scheme (MCS) and a total block size (TBS) for a user equipment (UE), comprising:
a processor;
memory in electronic communication with the processor; and
instructions stored in the memory, the instructions being executable to:
map a nominal modulation and coding scheme (MCS) to a total block size (TBS) index;
determine a nominal TBS per resource block value based on the TBS index;
determine a target TBS by scaling the nominal TBS per resource block value based on at least a number of symbols in a downlink transmission time interval (TTI), an actual CFI used for the downlink TTI, and an actual number of physical data shared channel (PDSCH) reference symbols per resource block, and a number of resource blocks allocated to the UE;
determine a customized TBS, from a plurality of predefined TBSs, that is closest to the target TBS;
map the customized TBS to a customized MCS; and
use the customized TBS and the customized MCS to transmit to the UE during the downlink TTI.
2. The base station of claim 1 , wherein the scaling comprises:
determining an intermediate TBS by multiplying the nominal TBS per resource block value by the number of resource blocks allocated to the UE; and
scaling the intermediate TBS based on:
nominal transmission time interval (TTI) parameters; and
actual TTI parameters comprising the number of symbols in the downlink TTI, the actual CFI used for the downlink TTI, and the actual number of PDSCH reference symbols per resource block.
3. The base station of claim 2 ,
wherein the nominal TTI parameters comprise a nominal number of symbols in a nominal TTI, a control format indicator (CFI) for the nominal TTI, and a nominal number of physical data shared channel (PDSCH) reference symbols per resource block.
4. The base station of claim 1 ,
wherein mapping the nominal MCS to the TBS index comprises using the nominal MCS as a first index in a first lookup table;
wherein determining the nominal TBS per resource block value comprises using the TBS index as a second index in a second lookup table; and
wherein mapping the customized TBS to the customized MCS comprises using the customized TBS as a third index in the first lookup table.
5. The base station of claim 1 ,
wherein a second lookup table comprises the TBS index and a plurality of other TBS indices,
wherein the second lookup table further comprises the nominal TBS per resource block value and a plurality of other nominal TBS per resource block values,
wherein the TBS index is associated with the nominal TBS per resource block value in the second lookup table; and
wherein determining the nominal TBS per resource block value comprises using the TBS index as a second index in the second lookup table.
6. The base station of claim 5 , wherein the instructions executable to determine the customized TBS comprise instructions executable to:
select a column in a third lookup table based on a scaled number of resource blocks allocated to the UE, wherein the third lookup table comprises an entry for each of the plurality of predefined TBSs; and
select the customized TBS as being one of the plurality of predefined TBSs in the third lookup table that is closest to the target TBS in the selected column.
7. The base station of claim 6 ,
wherein the second lookup table is derived from the third lookup table;
wherein the nominal TBS per resource block value in the second lookup table is determined by:
dividing each predefined TBS, in a row indicated by the TBS index, by a corresponding number of resource blocks allocated; and
averaging all the divided predefined TBSs in the row to produce the nominal TBS per resource block value.
8. The base station of claim 6 , further comprising instructions executable to scale the number of resource blocks allocated to the UE by 0.75, based on whether the downlink TTI is a special subframe, to produce the scaled number of resource blocks allocated to the UE.
9. The base station of claim 1 , wherein the downlink TTI is a normal subframe or a downlink pilot time slot (DwPTS), wherein the downlink TTI carries control data and PDSCH data.
10. The base station of claim 1 , wherein the base station and the UE operate in a Citizens Broadband Radio service (CBRS) system that implements a Long-Term Evolution (LTE) system using time-division duplexing (TDD).
11. A method for selecting a modulation and coding scheme (MCS) and a total block size (TBS) for a user equipment (UE), wherein the method is performed by a base station, the method comprising:
mapping a nominal modulation and coding scheme (MCS) to a total block size (TB S) index;
determining a nominal TBS per resource block value based on the TBS index;
determining a target TBS by scaling the nominal TBS per resource block value based on at least a number of symbols in a downlink transmission time interval (TTI), an actual CFI used for the downlink TTI, and an actual number of physical data shared channel (PDSCH) reference symbols per resource block, and a number of resource blocks allocated to the UE;
determining a customized TBS, from a plurality of predefined TBSs, that is closest to the target TBS;
mapping the customized TBS to a customized MCS; and
using the customized TBS and the customized MCS to transmit to the UE during the downlink TTI.
12. The method of claim 11 , wherein the scaling comprises:
determining an intermediate TBS by multiplying the nominal TBS per resource block value by the number of resource blocks allocated to the UE; and
scaling the intermediate TBS based on:
nominal transmission time interval (TTI) parameters; and
actual TTI parameters comprising the number of symbols in the downlink TTI, the actual CFI used for the downlink TTI, and the actual number of PDSCH reference symbols per resource block.
13. The method of claim 12 ,
wherein the nominal TTI parameters comprise a nominal number of symbols in a nominal TTI, a control format indicator (CFI) for the nominal TTI, and a nominal number of physical data shared channel (PDSCH) reference symbols per resource block.
14. The method of claim 11 ,
wherein mapping the nominal MCS to the TBS index comprises using the nominal MCS as a first index in a first lookup table;
wherein determining the nominal TBS per resource block value comprises using the TBS index as a second index in a second lookup table; and
wherein mapping the customized TBS to the customized MCS comprises using the customized TBS as a third index in the first lookup table.
15. The method of claim 11 ,
wherein a second lookup table comprises the TBS index and a plurality of other TBS indices,
wherein the second lookup table further comprises the nominal TBS per resource block value and a plurality of other nominal TBS per resource block values,
wherein the TBS index is associated with the nominal TBS per resource block value in the second lookup table; and
wherein determining the nominal TBS per resource block value comprises using the TBS index as a second index in the second lookup table.
16. The method of claim 15 , wherein the determining the customized TB S comprises:
selecting a column in a third lookup table based on a scaled number of resource blocks allocated to the UE, wherein the third lookup table comprises an entry for each of the plurality of predefined TBSs; and
selecting the customized TBS as being one of the plurality of predefined TBSs in the third lookup table that is closest to the target TBS in the selected column.
17. The method of claim 16 ,
wherein the second lookup table is derived from the third lookup table;
wherein the nominal TBS per resource block value in the second lookup table is determined by:
dividing each predefined TBS, in a row indicated by the TBS index, by a corresponding number of resource blocks allocated; and
averaging all the divided predefined TBSs in the row to produce the nominal TBS per resource block value.
18. The method of claim 16 , further comprising scaling the number of resource blocks allocated by 0.75, based on whether the downlink TTI is a special subframe, to produce the scaled number of resource blocks allocated to the UE.
19. The method of claim 11 , wherein the downlink TTI is a normal subframe or a downlink pilot time slot (DwPTS), wherein the downlink TTI carries control data and PDSCH data.
20. The method of claim 11 , wherein the base station and the UE operate in a Citizens Broadband Radio service (CBRS) system that implements a Long-Term Evolution (LTE) system using time-division duplexing (TDD).