Description
The Start and Length Indicator Value (SLIV) is a key Downlink Control Information (DCI) field in 5G New Radio (NR) used for dynamic time-domain resource allocation. Its primary function is to efficiently signal to a User Equipment (UE) the exact location and duration of its Physical Downlink Shared Channel (PDSCH) or Physical Uplink Shared Channel (PUSCH) transmission within a given slot. Instead of transmitting two separate values for the start symbol (S) and the length in symbols (L), the gNodeB encodes them into a single, compact integer value—the SLIV. The UE decodes this value using a predefined formula or table specified in 3GPP TS 38.214 to derive S and L.
The encoding rule ensures validity: the combination of S and L must define a resource that fits entirely within the slot's 14 symbols (for normal cyclic prefix). The formula is: if (L-1) ≤ 7 then SLIV = 14*(L-1) + S, else SLIV = 14*(14-L+1) + (14-1-S). The UE calculates S and L from the received SLIV by trying both possible interpretations. This joint encoding saves precious bits in the DCI payload, which is crucial for maintaining low control channel overhead, especially for smaller bandwidth parts and for scheduling many users.
SLIV is part of the Time Domain Resource Allocation (TDRA) table. The network can configure a UE with one or more TDRA entries via RRC signaling, where each entry includes parameters like mapping type, slot offset (K0/K2), and the SLIV. During dynamic scheduling, the DCI points to one of these pre-configured entries using a TDRA index field. This two-step process (RRC configuration + DCI indication) provides flexibility: common patterns can be configured semi-statically, while the DCI dynamically selects the appropriate one. SLIV directly determines the time-domain resources, which, combined with frequency-domain resource allocation (via the Frequency Domain Resource Assignment field), gives the UE its complete scheduled resource block set.
Purpose & Motivation
SLIV was created for 5G NR to address the need for highly flexible and efficient time-domain resource allocation. Unlike 4G LTE, which primarily scheduled resources in units of subframes (1 ms), 5G NR introduced a more flexible slot and mini-slot structure with variable numerology (subcarrier spacing). This allows transmissions to start at any symbol and have durations as short as one symbol. Signaling such flexibility with separate start and length fields would require too many bits in the DCI, increasing control channel overhead and reducing scheduling capacity.
The motivation was to minimize control signaling overhead while maximizing scheduling flexibility—a key requirement for 5G's diverse use cases. For enhanced Mobile Broadband (eMBB), it allows efficient packing of user data. For Ultra-Reliable Low-Latency Communications (URLLC), it enables immediate mini-slot scheduling to preempt ongoing eMBB traffic, which is facilitated by the ability to signal a transmission starting at any symbol. The joint encoding of SLIV is an elegant solution from information theory, using the constraint that S+L must be ≤ 14 to reduce the number of possible valid (S, L) combinations, thereby requiring fewer bits to signal them all. This design directly addresses the limitations of LTE's more rigid allocation and is fundamental to NR's dynamic TDD and low-latency capabilities.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (162 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the SLIV function was enhanced through corrections and clarifications to PUSCH resource allocation procedures, including specific fixes for resource allocation table determination for PUSCH with SP CSI. Additionally, alignment changes were made for frequency domain resource allocation when a PUSCH is scheduled by a RAR UL grant, ensuring consistency with the specifications in TS 38.213.
- CR on timing adjustment indicator TS 38.213CR0010
- CR on overlapping of CSI and PUSCH with slot aggregation TS 38.213CR0028
- Correction on PUSCH power scaling TS 38.213CR0039
- Clarification of reference to PDSCH processing capability 1 in TS 38.213 TS 38.213CR0042
- CR to 38.213 on clarification of the RNTI used for scrambling a PUSCH transmission scheduled by RAR UL grant TS 38.213CR0054
- CR on beta_offset values for UCI reporting in PUSCH TS 38.213CR0062
+ 19 more changes
In Release 16, enhancements to SLIV primarily involved corrections and clarifications for more complex scheduling scenarios established in earlier releases. These included handling collisions and multiplexing rules for channels with different priorities, such as between PUCCH/PUSCH transmissions with repetitions, and corrections for the multiplexing of SL HARQ-ACK information on a PUSCH. Additionally, refinements were made to ensure proper operation with features like PDSCH repetitions having different subcarrier spacings in downlink and uplink, and with slot-aggregated SPS PDSCH receptions.
- Aperiodic CSI-RS Triggering for UE reporting beamSwitchTiming values of 224 and 336 TS 38.214CR0060
- Clarify starting slot within DCI 2_5 indication TS 38.213CR0126
- CR to 38.213 on HARQ-ACK processing timeline for DCI format 1_1 with Scell dormancy indication without scheduling PDSCH TS 38.213CR0135
- Correction on PUSCH processing capability for DAPS handover TS 38.213CR0150
- Correction of NRU HARQ procedure in the presence of SPS PDSCH TS 38.213CR0163
- Correction on UL grant Type 2 PUSCH release for search space sharing TS 38.213CR0169
+ 33 more changes
In Release 17, the SLIV function was updated to support new features including intra-UE multiplexing and the handling of overlapping configured grant (CG) and dynamic grant (DG) PUSCH transmissions. Specific enhancements were made to ensure proper HARQ-ACK codebook construction and reporting for PDSCH scheduled by DCI format 4_1, and to manage PUSCH frequency hopping with DMRS bundling. These changes also included corrections to the UE's PUSCH preparation and PDSCH processing procedure times for operation with shared spectrum channel access in the FR2-2 band.
- Corrections on the value of slot configuration period in TS 38.213 for the features extending NR operation to 71 GHz TS 38.213CR0335
- CR on default PUSCH power control parameters for mTRP PUSCH TS 38.213CR0344
- CR for power control of mTRP PUSCH repetition TS 38.213CR0345
- CR on HP DG PUSCH and LP CG PUSCH collision resolution TS 38.213CR0355
- Correction on parallel transmission of PRACH and SRS/PUCCH/PUSCH TS 38.213CR0386
- CR on HARQ-ACK feedback for PDSCH scheduled by DCI format 4_1 TS 38.213CR0389
+ 46 more changes
In Release 18, the SLIV function itself was not a primary focus for new feature introduction. The enhancements were instead concentrated on corrections and clarifications for related physical channel procedures, such as corrections on the determination of the starting RB set for PSSCH and on the CPE starting position for PSSCH/PSCCH. These updates ensure proper resource mapping and timing for sidelink and uplink transmissions in various configured grant and multi-cell scheduling scenarios.
- Introduction of RS for pathloss determination of Type 1 CG PUSCH [PL RS Type 1 CG] TS 38.213CR0567
- Introduction of multiplexing in a PUSCH with repetitions HARQ-ACK associated with DL assignments received after an UL grant for the PUSCH [HARQ-ACK MUX on PUSCH] TS 38.213CR0568
- Introduction of multi-cell PDSCH / PUSCH scheduling TS 38.214CR0442
- Correction on sidelink starting symbol index for indications of UL slots in PSBCH in SL-U TS 38.213CR0616
- Multicast MBS PDSCH bandwidth for eRedCap UE in RRC inactive state TS 38.213CR0629
- Clarification on not multiplexing UCI on MSG3 PUSCH TS 38.213CR0631
+ 35 more changes
In Release 19, the SLIV function was updated to support the multiplexing of UEIRI into PUSCH, as indicated in the corresponding CR title. Furthermore, corrections were made to the determination of the HARQ Process Number for multi-PDSCH and multi-PUSCH scheduling to ensure proper operation.
- CR on UEIRI multiplexed into PUSCH in TS 38.213 TS 38.213CR0762
- Correction on HPN determination for multi-PDSCH and multi-PUSCH scheduling TS 38.214CR0747
- Correction on TBS determination for SPS PDSCH TS 38.214CR0748
- Msg4 PDSCH repetition and retransmission TS 38.214CR0749
- CR on SRI in STxMP SFN non-codebook PUSCH TS 38.214CR0710
Explore further
Broader topics and technologies where SLIV plays a role.
Defining Specifications
3GPP specifications that define or reference SLIV, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 38.213 vj10 | NR Physical Layer Control Procedures | Rel-19 |
| TS 38.214 vj10 | NR Physical Layer Procedures for Data | Rel-19 |