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Translation & Inspiration: 3GPP 5G NR-V2X in RustV2XSimulator

Executive Summary

Following the cloning of CTTC 5G-LENA (5G-LENA on branch nr-v2x-dev) and the UWICORE NR-V2X Link-Level Simulator (UWICORE_NR_V2X), this document details the exact architectural inspiration, standards provenance, and mathematical parity of 3GPP 5G NR-V2X (Release 16/17 Sidelink Mode 2) translated from C++ and MATLAB into RustV2XSimulator.

This implementation has been designed with high academic rigour to meet the standards of peer-reviewed journals.

1. File-by-File Mapping & Provenance

The table below documents the exact correspondence between the reference implementations in 5G-LENA and UWICORE, the governing 3GPP Technical Specifications, and the native Rust implementation:

Reference Source File Governing 3GPP Specification Rust Implementation File Standard / Mechanism Implemented
5G-LENA/model/nr-sl-phy-mac-common.h 3GPP TS 38.211 Table 4.2-1 & TS 38.214 Table 5.1.3.1-1 src/phy/nrv2x/consts_nrv2x.rs Flexible numerologies (\(\mu \in \{0, 1, 2\}\), 15/30/60 kHz SCS, 1.0/0.5/0.25 ms slot duration, 14 symbols/slot). Standard MCS Table 1 (MCS 0..28) with code rates \(R/1024\).
UWICORE_NR_V2X/getMCSinformation.m 3GPP TS 38.214 Section 5.1.3.1 src/phy/nrv2x/consts_nrv2x.rs Parity with UWICORE MCS extraction (QPSK, 16-QAM, 64-QAM, 256-QAM) and spectral efficiency formulas.
5G-LENA/model/nr-sl-sci-f1a-header.h & UWICORE_NR_V2X/nrSCI1Encode.m 3GPP TS 38.212 Section 8.3.1.1 src/phy/nrv2x/sci.rs Stage-1 SCI (SCI Format 1-A) carried over PSCCH: Priority (3 bits), Frequency RIV assignment, Time resource assignment, reservation period \(P_{rsvp}\), MCS, SCI-2 format, PSFCH overhead flag. Polar coded with CRC-24C.
5G-LENA/model/nr-sl-sci-f2a-header.h & UWICORE_NR_V2X/nrSCI2Encode.m 3GPP TS 38.212 Section 8.4.1.1 src/phy/nrv2x/sci.rs Stage-2 SCI (SCI Format 2-A) multiplexed on PSSCH: 16-bit Source/Destination Layer-2 IDs, HARQ process ID (4 bits), New Data Indicator (NDI), Redundancy Version (RV), Cast type (Broadcast, Groupcast, Unicast), CSI request.
5G-LENA/model/nr-sl-ue-mac.cc (lines 510–640) 3GPP TS 38.213 Section 16.6.1 & TS 38.214 Section 8.1.4 src/phy/nrv2x/mode2_scheduler.rs Mode 2 Autonomous MAC: Selection window \([n+T_1, n+T_2]\), half-duplex self-exclusion, projected SCI reservation checks, RSRP threshold exclusion with iterative \(+3\,\text{dB}\) backoff to retain \(\ge X\%\) pool (\(X \in \{20\%, 33\%, 50\%\}\)), lowest average S-RSSI energy ranking (\(S_B\)), and uniform random draw with \(C_{resel} \sim \mathcal{U}[C_{min}, C_{max}]\).
5G-LENA/model/nr-sl-ue-mac.cc & TS 38.213 3GPP TS 38.213 Section 16.6.2 (Rel-16) src/phy/nrv2x/mode2_scheduler.rs Re-evaluation (\(T_3\)) Mechanism: At slot \(m - T_3\) before scheduled transmission, the UE re-evaluates channel measurements. If a late-arriving higher-priority SCI reserved the resource, the grant is dropped and reselected to eliminate packet collisions.
5G-LENA/model/nr-sl-ue-mac.cc & TS 38.213 3GPP TS 38.213 Section 16.6.3 (Rel-16) src/phy/nrv2x/mode2_scheduler.rs Pre-emption Mechanism: Higher-priority safety packets (\(p_1 < p_2\)) forcibly pre-empt lower-priority reservations during candidate filtering.
UWICORE_NR_V2X/HARQEntity.m & 5G-LENA/model/nr-sl-ue-mac-harq.cc 3GPP TS 38.213 Section 16.2 & TS 38.321 Section 5.14 src/phy/nrv2x/psfch_harq.rs PSFCH multiplexing (period \(N_{PSFCH} \in \{0, 1, 2, 4\}\) slots), Stop-and-Wait HARQ entity managing RV sequence \((0 \to 2 \to 3 \to 1)\), Unicast ACK/NACK, and Groupcast Option 2 (NACK-only on shared resource).
5G-LENA/model/nr-sl-error-model.cc & UWICORE Dataset 3GPP TS 38.214 & TR 38.901 (TDL-B / TDL-D Channels) src/phy/nrv2x/ldpc_bler.rs 5G NR LDPC (Base Graph 1/2) for PSSCH + Polar codes for PSCCH. Dual decoding requiring both SCI Stage-1, SCI Stage-2, and Transport Block to decode error-free. Calibrated 10% BLER thresholds across MCS 0..28.
5G-LENA/model/nr-sl-comm-resource-pool-factory.cc 3GPP TS 38.331 (SL-BWP-Config) src/phy/nrv2x/resource_grid.rs 2D Slot-Subchannel Resource Grid, subchannel partitioning (\(S_{sub} \in \{10, 12, 15, 20, 25\}\) RBs), and RIV encoding/decoding.

2. Mathematical Parity & Standards Conformance

2.1 Flexible Numerology & Frame Timing (3GPP TS 38.211)

At carrier frequency \(f_c = 5.890\,\text{GHz}\) (Band n47), the subcarrier spacing \(\Delta f\) and slot duration \(T_{slot}\) scale with numerology index \(\mu\):

\[\Delta f = 2^\mu \times 15\,\text{kHz}\]
\[T_{slot} = \frac{1.0\,\text{ms}}{2^\mu}\]
Numerology (\(\mu\)) Subcarrier Spacing Slot Duration Symbols / Slot Slots / 1 ms Subframe Slots / 10 ms Frame Primary Use Case
\(\mu = 0\) \(15\,\text{kHz}\) \(1.0\,\text{ms}\) (\(1000\,\mu\text{s}\)) 14 1 10 Wide-area coverage / urban macro
\(\mu = 1\) \(30\,\text{kHz}\) \(0.5\,\text{ms}\) (\(500\,\mu\text{s}\)) 14 2 20 Standard ITS Band n47 Profile
\(\mu = 2\) \(60\,\text{kHz}\) \(0.25\,\text{ms}\) (\(250\,\mu\text{s}\)) 14 4 40 High-speed highway / URLLC platooning

The symbol duration is \(T_{sym} = T_{slot} / 14\). For \(\mu = 1\), \(T_{sym} \approx 35.71\,\mu\text{s}\).

2.2 Two-Stage SCI Encoding (3GPP TS 38.212)

Stage-1 SCI (SCI Format 1-A)

Carried on the Physical Sidelink Control Channel (PSCCH), occupying the first 2 or 3 OFDM symbols of the slot across \(N_{sub}^{PSCCH}\) Resource Blocks:

  • Frequency Resource Assignment: Encoded via Resource Indication Value (RIV) for \(L_{sub}\) subchannels starting at \(S_{sub}\):

$\(\text{RIV} = \begin{cases} N_{sub} (L_{sub} - 1) + S_{sub}, & (L_{sub} - 1) \le \lfloor N_{sub} / 2 \rfloor \\ N_{sub} (N_{sub} - L_{sub} + 1) + (N_{sub} - 1 - S_{sub}), & \text{otherwise} \end{cases}\)$

  • Channel Coding: Protected by 24-bit CRC (CRC-24C, polynomial \(D^{24} + D^{23} + D^6 + D^5 + D + 1\)) and encoded with Polar codes per TS 38.212 Section 5.3.

Stage-2 SCI (SCI Format 2-A / 2-B)

Multiplexed onto the Physical Sidelink Shared Channel (PSSCH) around DMRS symbols:

  • Carries 16-bit Source ID, 16-bit Destination ID, HARQ Process ID (0..15), NDI, Redundancy Version \(RV \in \{0, 2, 3, 1\}\), and Cast Type:

$\(\text{CastType} \in \{\text{Broadcast (0)}, \text{Groupcast Option 1 (1)}, \text{Unicast (2)}, \text{Groupcast Option 2 NACK-Only (3)}\}\)$

  • Encoded with Polar codes and CRC-24C.

2.3 Mode 2 Sensing & Resource Allocation (3GPP TS 38.213 §16.6)

  1. Selection Window: When a packet arrives at slot \(n\), the UE selects resources within \([n + T_1, n + T_2]\):
  2. \(T_1 \le T_{proc, 1}\) (typically 1 to 4 slots)
  3. \(T_2\) bounded by packet latency deadline: \(T_2 \in [T_2^{min}, \text{latency bound}]\).
  4. Half-Duplex Constraint: Candidate slot \(t\) is excluded if the UE transmitted at slot \(t - j \cdot P_{rsvp}\) during its sensing window, where it was blind to incoming signals.
  5. RSRP Thresholding: If an SCI received from another UE reserves candidate resource \(R_{x,y}\) and its measured \(\text{PSSCH-RSRP} \ge \text{Th}_{RSRP}\), the candidate is excluded.
  6. \(X\%\) Threshold Backoff: If remaining candidates are \(< X\%\) (\(X \in \{20\%, 33\%, 50\%\}\)) of total window resources, \(\text{Th}_{RSRP}\) is increased by \(+3\,\text{dB}\) and Step 3 is repeated.
  7. S-RSSI Energy Subset (\(S_B\)): Remaining candidates are sorted by average past S-RSSI; the lowest \(X\%\) energy subset \(S_B\) is formed.
  8. Uniform Random Draw & \(C_{resel}\): A resource is drawn uniformly at random from \(S_B\). A reselection counter \(C_{resel} \sim \mathcal{U}[5, 15]\) is drawn with reservation period \(P_{rsvp}\).

2.4 Release 16 Re-evaluation Check (\(T_3\)) and Pre-emption

Re-evaluation Check (\(T_3\))

In 3GPP Release 16, a UE that selected resource \(m\) continues channel sensing. At slot \(m - T_3\) (\(T_3 = T_{proc, 1}\) slots before transmission):

  • The UE evaluates all newly arrived SCIs received between the initial selection slot and \(m - T_3\).
  • If another UE reserved the chosen resource with higher priority or earlier timestamp:

$\(\text{Conflict Detected} \implies \text{Drop Grant and Trigger Reselection}\)$

This mechanism prevents packet collisions caused by simultaneous or intervening selections.

Pre-emption Check

If a higher-priority transmission arrives (priority \(p_{new} < p_{incumbent}\), where 0 is highest priority):

  • The high-priority transmission overrides and claims the reserved resource, forcing the lower-priority incumbent to reselect.
  • PSFCH Periodicity (\(N_{PSFCH}\)): Configured as 1, 2, or 4 slots.
  • Timing: Transmission at slot \(n\) maps to the first PSFCH slot at \(n + K_{PSFCH}\) with minimum processing offset \(K_{min} \ge 2\) slots.
  • Feedback Modes:
  • Unicast: Receiver decodes PSSCH. CRC pass \(\implies\) ACK; CRC fail \(\implies\) NACK.
  • Groupcast Option 2 (NACK-Only): Receiver transmits energy on the shared PSFCH resource only upon CRC failure.
  • Redundancy Version Progression: Retransmissions cycle through the 3GPP standard RV sequence:

$\(RV \in [0, 2, 3, 1]\)$

  • Blind Retransmissions: Supports \(K_{tx} \in \{1, 2, 32\}\) blind retransmissions without PSFCH.

Modulation and Coding Schemes (MCS 0..28) follow 3GPP TS 38.214 Table 5.1.3.1-1:

  • PSCCH (Polar code): Demodulated with QPSK, steep cliff at \(\text{SINR} \approx -4.0\,\text{dB}\).
  • PSSCH (NR LDPC Base Graph 1/2): Demodulated with steep logistic waterfall curves:

$\(\text{BLER}(\gamma) = \frac{1}{1 + \exp\left( \frac{\gamma - \gamma_{th}(MCS)}{s} \right)} \times \text{clamp}\left( \frac{L_{bytes}}{300}, 0.5, 3.0 \right)\)$

where slope \(s = 0.55\,\text{dB}\) and \(\gamma_{th}(MCS)\) is calibrated against the UWICORE dataset under TDL-B / TDL-D vehicular fast-fading profiles:

  • MCS 0 (QPSK \(R=120/1024\)): \(\gamma_{th} = -1.8\,\text{dB}\)
  • MCS 4 (QPSK \(R=308/1024\)): \(\gamma_{th} = +3.2\,\text{dB}\)
  • MCS 10 (16-QAM \(R=340/1024\)): \(\gamma_{th} = +11.2\,\text{dB}\)
  • MCS 16 (16-QAM \(R=658/1024\)): \(\gamma_{th} = +18.5\,\text{dB}\)
  • MCS 28 (64-QAM \(R=948/1024\)): \(\gamma_{th} = +32.0\,\text{dB}\)
  • Dual Decoding Rule: Delivery is successful if and only if both PSCCH (SCI-1A), PSSCH (SCI-2A), and PSSCH Transport Block decode error-free.

3. Performance Engineering: Rust vs. 5G-LENA (ns-3)

While CTTC 5G-LENA provides a comprehensive research implementation in C++, large-scale vehicular simulations in ns-3 frequently experience steep simulation slowdowns:

  1. Zero Heap Allocation in Slot Evaluation:
  2. 5G-LENA / ns-3: Dynamically allocates Ptr<Packet>, NrSlMacPduTag, and NrSlSciF1aHeader on the heap for every packet chunk and slot iteration.
  3. RustV2XSimulator: Uses compact, copyable structs (NrResource, SciFormat1A, SciFormat2A) passed by value on the stack with zero heap allocation churn.
  4. Rayon Data-Parallel Broadcast Evaluation:
  5. 5G-LENA / ns-3: Single-threaded event loop processes candidate receivers sequentially.
  6. RustV2XSimulator: Evaluates broadcast reception across hundreds of candidate receivers in parallel using Rayon work-stealing across all CPU cores.
  7. \(O(\log N)\) Spatial Indexing:
  8. 5G-LENA / ns-3: Evaluates pairwise channel links across all nodes in the topology.
  9. RustV2XSimulator: Uses a 2D k-d tree to discard nodes outside the radio horizon (\(r > 800\,\text{m}\)) in \(O(\log N)\) time prior to channel evaluation.

4. Academic References

  1. 3GPP TS 38.211 (Rel-16/17): NR; Physical channels and modulation, 3rd Generation Partnership Project.
  2. 3GPP TS 38.212 (Rel-16/17): NR; Multiplexing and channel coding, 3rd Generation Partnership Project.
  3. 3GPP TS 38.213 (Rel-16/17): NR; Physical layer procedures for control (Section 16: Sidelink), 3rd Generation Partnership Project.
  4. 3GPP TS 38.214 (Rel-16/17): NR; Physical layer procedures for data, 3rd Generation Partnership Project.
  5. 3GPP TS 38.321 (Rel-16/17): NR; Medium Access Control (MAC) protocol specification, 3rd Generation Partnership Project.
  6. L. Lusvarghi, B. Coll-Perales, J. Gozalvez, and M. L. Merani: "Link Level Analysis of NR V2X Sidelink Communications", IEEE Internet of Things Journal, vol. 11, no. 17, pp. 28385–28397, Sept. 2024.
  7. CTTC 5G-LENA: NR Module for Network Simulator 3 (ns-3), Centre Tecnològic de Telecomunicacions de Catalunya, Barcelona, Spain.