What is a 5G NR DCI (Downlink Control Information) decoder?

A 5G NR DCI decoder converts post-decoding physical-layer control bits transmitted on the PDCCH into scheduling grant parameters. It reveals which PRBs (frequency), OFDM symbols (time), MCS (modulation order & code rate), HARQ process ID, and timing offsets are assigned to a UE for PDSCH (downlink) or PUSCH (uplink) per 3GPP TS 38.212 and TS 38.214 specifications.

Why does a 5G DCI payload require configuration context to decode?

Unlike higher-layer protocols (such as RRC or NAS) that use fixed ASN.1 encoding, DCI payloads do not have one static bit layout. The bit width of fields like Frequency Domain Resource Assignment (FDRA) depends directly on higher-layer RRC parameters—specifically the active Bandwidth Part size (N_BWP_size in PRBs). Without knowing the active BWP size and Time-Domain Allocation (TDRA) tables, a raw bitstream cannot be mapped to actual PRBs or symbols.

How does Resource Indicator Value (RIV) frequency allocation work in DCI 1_0 and 0_0?

In Resource Allocation Type 1, the frequency-domain field uses a single compact integer called RIV (Resource Indicator Value). RIV encodes both the starting PRB (RB_start) and contiguous number of PRBs (L_RBs) using the formula RIV = N_BWP * (L_RBs - 1) + RB_start when (L_RBs - 1) <= floor(N_BWP / 2), and RIV = N_BWP * (N_BWP - L_RBs + 1) + (N_BWP - 1 - RB_start) otherwise. The bit length is calculated as ceil(log2(N_BWP * (N_BWP + 1) / 2)).

Why do DCI format 1_0 and DCI format 0_0 have the exact same bit length in a CORESET?

To prevent UEs from having to perform extra blind decodes on the PDCCH, 3GPP TS 38.212 dictates that fallback DCI Format 1_0 (Downlink) and DCI Format 0_0 (Uplink) monitored in the same search space must have equal bit lengths. If DCI 0_0 is smaller than DCI 1_0, zero padding bits are appended to DCI 0_0 until its total bit length matches DCI 1_0. A 1-bit Identifier field (Bit 0 for DCI 0_0, Bit 1 for DCI 1_0) distinguishes the direction.

How does Time Domain Resource Allocation (TDRA) map to OFDM start symbols and slot offsets?

A 4-bit TDRA field (values 0..15) indexes into a configured or default Time Domain Allocation table (PDSCH Table 5.1.2.1.1-1 or PUSCH Table 6.1.2.1.1-1). Each row specifies: (1) PDSCH/PUSCH Mapping Type A or B, (2) Start Symbol S (0..13), (3) Symbol Length L (1..14), and (4) Slot Offset K0 (for DL PDSCH) or K2 (for UL PUSCH).

How are HARQ process number, NDI, and Redundancy Version (RV) interpreted?

The 4-bit HARQ process number identifies the target HARQ buffer (processes 0..15). The 1-bit New Data Indicator (NDI) signals whether the grant is a new transmission (NDI toggled to 1) or a retransmission (NDI untoggled). The 2-bit Redundancy Version (RV) specifies the LDPC rate-matching starting point (00=RV0, 01=RV2, 10=RV3, 11=RV1).

What is the difference between raw DCI bits and PDCCH blind decoding?

PDCCH blind decoding is the physical-layer receiver operation where a UE monitors candidate CCEs (Control Channel Elements), performs polar decoding, and checks the 24-bit CRC scrambled with its C-RNTI. Once CRC validation passes, the resulting payload bitstream is passed to this DCI Decoder to split fields and extract scheduling coordinates.

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5G NR

Rel-17 Pinned

5G NR DCI Decoder & Scheduling Visualizer

Convert contextual 3GPP Rel-17 DCI payloads into mapped PRB & symbol scheduling allocations with bit-level field inspection.

TS 38.212 / 38.213 / 38.214

1. DCI Configuration & Payload Input

Select DCI format, active BWP parameters, and paste post-decoding payload bits

3GPP Rel-17 Pinned

Presets & Verified Test Scenarios

DCI Format

RNTI Scrambling

Post-Decoding Payload Input

Active BWP & Duplex Context

BWP Size (PRBs)

BWP Start CRB

Subcarrier Spacing

Duplex Mode

2. Decoded Scheduling Allocation

DL Grant: PDSCH

Mapped time-frequency coordinates, MCS efficiency, HARQ state, and timing

Open in RE Grid Mapper

Frequency Allocation

PRB 0..272

273 PRBs (CRB 0..272)

Time Symbol Allocation

Sym 2..13

12 Symbols (TypeA)

MCS & Modulation

MCS 16 (4b/RE)

R=0.643 (SE=2.57)

HARQ Process & NDI

Process 1 (RV0)

NDI = 1 (New Transmission)

14-Symbol Slot Timeline (K0/K2 = +0 slot)1 Slot @ 30 kHz

#0PDCCH

#1PDCCH

#2PDSCH

#3PDSCH

#4PDSCH

#5PDSCH

#6PDSCH

#7PDSCH

#8PDSCH

#9PDSCH

#10PDSCH

#11PDSCH

#12PDSCH

#13PDSCH

Active BWP Span (273 of 273 PRBs)100.0% BWP Span

PRB 00..272 (273 PRBs)PRB 272

Feedback TimingK1 = 2 slots

TPC Command0 dB (01)

DAI / PRIDAI=1 PRI=0

Est. Payload Size12,547 bytes

Send to TBS Send to SLIV

3. Bit-Level Field Inspector

Click any bit field to inspect its raw bits, raw integer, formula, and 3GPP specification reference

Total Payload: 44 Bits

Visual Bit Map (Click to Inspect)MSB Bit [0] → LSB Bit [43]

Selected Field

Identifier for DCI Formats

Bits [0:0] (1 bits)

Raw Bit Slice1

Raw Integer Value1

Interpreted Engineering Meaning

Format 1_0 (Downlink)

3GPP Standard Specification Explanation

Bit value 1 indicates DCI Format 1_0 (PDSCH Downlink assignment).

3GPP Standard ReferenceTS 38.212 Rel-17 Clause 7.3.1.1.2

Decoded Field Table

Identifier for DCI Formats

Bits [0:0] (1b)

Frequency Domain Resource Assignment

Bits [1:16] (16b)

545

0000001000100001

Time Domain Resource Assignment

Bits [17:20] (4b)

0000

VRB-to-PRB Mapping

Bits [21:21] (1b)

Modulation and Coding Scheme

Bits [22:26] (5b)

10000

New Data Indicator

Bits [27:27] (1b)

Redundancy Version

Bits [28:29] (2b)

HARQ Process Number

Bits [30:33] (4b)

0001

Downlink Assignment Index

Bits [34:35] (2b)

TPC Command for Scheduled PUCCH

Bits [36:37] (2b)

PUCCH Resource Indicator

Bits [38:40] (3b)

000

PDSCH-to-HARQ Feedback Timing Indicator (K1)

Bits [41:43] (3b)

010

Frequently asked questions

3GPP TS 38.212 & TS 38.214 specifications guidance and engineering reference

5G NR DCI Decoder & Scheduling Visualizer

Convert contextual 3GPP Rel-17 DCI payloads into mapped PRB & symbol scheduling allocations with bit-level field inspection.

TS 38.212 / 38.213 / 38.214

1. DCI Configuration & Payload Input

Select DCI format, active BWP parameters, and paste post-decoding payload bits

3GPP Rel-17 Pinned

Presets & Verified Test Scenarios

DCI Format

RNTI Scrambling

Post-Decoding Payload Input

Active BWP & Duplex Context

BWP Size (PRBs)

BWP Start CRB

Subcarrier Spacing

Duplex Mode

2. Decoded Scheduling Allocation

DL Grant: PDSCH

Mapped time-frequency coordinates, MCS efficiency, HARQ state, and timing

Open in RE Grid Mapper

Frequency Allocation

PRB 0..272

273 PRBs (CRB 0..272)

Time Symbol Allocation

Sym 2..13

12 Symbols (TypeA)

MCS & Modulation

MCS 16 (4b/RE)

R=0.643 (SE=2.57)

HARQ Process & NDI

Process 1 (RV0)

NDI = 1 (New Transmission)

14-Symbol Slot Timeline (K0/K2 = +0 slot)1 Slot @ 30 kHz

#0PDCCH

#1PDCCH

#2PDSCH

#3PDSCH

#4PDSCH

#5PDSCH

#6PDSCH

#7PDSCH

#8PDSCH

#9PDSCH

#10PDSCH

#11PDSCH

#12PDSCH

#13PDSCH

Active BWP Span (273 of 273 PRBs)100.0% BWP Span

PRB 00..272 (273 PRBs)PRB 272

Feedback TimingK1 = 2 slots

TPC Command0 dB (01)

DAI / PRIDAI=1 PRI=0

Est. Payload Size12,547 bytes

Send to TBS Send to SLIV

3. Bit-Level Field Inspector

Click any bit field to inspect its raw bits, raw integer, formula, and 3GPP specification reference

Total Payload: 44 Bits

Visual Bit Map (Click to Inspect)MSB Bit [0] → LSB Bit [43]

Selected Field

Identifier for DCI Formats

Bits [0:0] (1 bits)

Raw Bit Slice1

Raw Integer Value1

Interpreted Engineering Meaning

Format 1_0 (Downlink)

3GPP Standard Specification Explanation

Bit value 1 indicates DCI Format 1_0 (PDSCH Downlink assignment).

3GPP Standard ReferenceTS 38.212 Rel-17 Clause 7.3.1.1.2

Decoded Field Table

Identifier for DCI Formats

Bits [0:0] (1b)

Frequency Domain Resource Assignment

Bits [1:16] (16b)

545

0000001000100001

Time Domain Resource Assignment

Bits [17:20] (4b)

0000

VRB-to-PRB Mapping

Bits [21:21] (1b)

Modulation and Coding Scheme

Bits [22:26] (5b)

10000

New Data Indicator

Bits [27:27] (1b)

Redundancy Version

Bits [28:29] (2b)

HARQ Process Number

Bits [30:33] (4b)

0001

Downlink Assignment Index

Bits [34:35] (2b)

TPC Command for Scheduled PUCCH

Bits [36:37] (2b)

PUCCH Resource Indicator

Bits [38:40] (3b)

000

PDSCH-to-HARQ Feedback Timing Indicator (K1)

Bits [41:43] (3b)

010

Frequently asked questions

3GPP TS 38.212 & TS 38.214 specifications guidance and engineering reference

5G NR DCI Decoder & Scheduling Visualizer

1. DCI Configuration & Payload Input

2. Decoded Scheduling Allocation

3. Bit-Level Field Inspector

Identifier for DCI Formats

Frequently asked questions

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5G NR DCI Decoder & Scheduling Visualizer

1. DCI Configuration & Payload Input

2. Decoded Scheduling Allocation

3. Bit-Level Field Inspector

Identifier for DCI Formats

Frequently asked questions

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