LTE / LTE-Advanced
3GPP TS 36-series · EPC · eNodeB · UE
The NetSim LTE model library is a packet-level simulation of 4G and 4.5G cellular networks to the 3GPP TS 36-series. It models the EPC, eNodeB and UE with a full RRC-to-PHY stack, MIMO, HARQ, link adaptation, carrier aggregation and handover. Each protocol ships as source in C.
What NetSim models
NetSim models a complete LTE network, from the EPC down to the radio interface. The standards-based detail lets you study capacity, scheduling, link adaptation and end-to-end performance.
Radio access
An eNodeB serves UEs over an OFDMA downlink and an SC-FDMA uplink, with QPSK to 64QAM, FDD and MIMO transmission modes TM1 to TM5.
Full protocol stack
RRC, PDCP, RLC, MAC scheduling and PHY follow the 3GPP 36-series. They run with IPv4, TCP and UDP transport, and standard application traffic.
EPC and IP core
The Evolved Packet Core bundles the MME, SGW and PGW. It gives end-to-end IP connectivity from the UE through the eNodeB to routers, switches and servers.
Own the source
Each protocol ships as C source. Modify it in Visual Studio to implement and test your own scheduling, link adaptation or PHY ideas.
Devices
You can add three LTE-specific nodes to the topology and connect them to the standard NetSim devices.
EPC
The Evolved Packet Core (EPC) node bundles the MME, SGW and PGW. It provides end-to-end IP connectivity and connects to routers, switches, access points and servers in the core.
Macro cell eNB
The Evolved NodeB is the LTE base station. Each eNB serves at least one UE. You can put an eNB inside a building to study indoor and outdoor coverage.
UE
Each User Equipment is always associated with exactly one eNB. Move UEs with mobility models to study how the link and the scheduler respond.
These nodes work with the standard NetSim routers, L2 / L3 switches, access points, and wired and wireless nodes.
The LTE protocol stack
The control and user plane go from RRC down to MAC scheduling. Each layer follows its 3GPP specification, and its source is open.
Control plane
- System information: MIB and SIB1 acquisition
- RRC connection establishment
- RRC Idle, Connected / Active, and Inactive states
Convergence
- Sequence numbering and PDCP association
- ROHC robust header compression
- Discard timer and duplicate discard
Radio link control
- Transparent Mode (TM)
- Unacknowledged Mode (UM)
- Acknowledged Mode (AM) with retransmission
Scheduling
- Round Robin
- Proportional Fair
- Max Throughput
PRBs allocated per slot per carrier. MCS from the reported CQI.
Physical layer
Standard 3GPP TS 36.213. You can configure the bandwidth, transmission mode and antenna configuration of the air interface.
Transmission modes
SISO
The eNodeB has a single antenna. With round-robin scheduling, all flows get equal throughput.
Transmit diversity
MIMO transmit diversity (TxD) sends copies of the same data over multiple antennas for higher reliability at the same throughput.
Open-loop SU-MIMO
Single-user spatial multiplexing, open loop. The eNodeB splits the data across antennas to raise the data rate.
MU-MIMO
Multi-user spatial multiplexing per the LTE standard, raising throughput across multiple users.
MU-MIMO (2 Rx)
Multi-user MIMO with the number of receive antennas fixed at two.
Resource block
12 subcarriers of 15 kHz over 0.5 ms (7 OFDMA symbols). Modulation: QPSK (2 bits), 16QAM (4) and 64QAM (6).
| Channel bandwidth (MHz) | 1.4 | 3 | 5 | 10 | 15 | 20 |
|---|---|---|---|---|---|---|
| Resource blocks (NRB) | 6 | 15 | 25 | 50 | 75 | 100 |
| Occupied subcarriers | 73 | 181 | 301 | 601 | 901 | 1201 |
| FFT size | 128 | 256 | 512 | 1024 | 1536 | 2048 |
| Sampling rate (MHz) | 1.92 | 3.84 | 7.68 | 15.36 | 23.04 | 30.72 |
| Downlink / uplink access | OFDMA / SC-FDMA |
|---|---|
| Duplexing | FDD (carrier aggregation also supports TDD) |
| Subcarrier spacing | 15 kHz |
| Frame / subframe / slot | 10 ms / 1 ms / 0.5 ms |
| Operating bands | 3GPP TS 36.101 LTE / LTE-A bands |
| Modulation | QPSK, 16QAM, 64QAM |
Link adaptation and error modelling
This section explains how NetSim chooses a modulation and coding scheme, models block errors and recovers from them. These functions set the LTE throughput.
HARQ
Hybrid ARQ in MAC and PHY, in downlink and uplink, with up to 8 processes per direction per component carrier. Chase combining stores and combines failed transmissions.
BLER and MCS selection
Zero-BLER mode picks the MCS from an ideal Shannon or attenuation-factor rate (TR 36.942). BLER-enable mode transmits with errors from the NetSim BLER-MCS-SINR curves.
OLLA and AMC
Outer-loop link adaptation tunes the MCS toward a target BLER using HARQ ACK / NACK feedback. AMC works from a wideband SNR averaged over a configurable window.
Code block segmentation
NetSim splits each transport block into code blocks, and groups them into code block groups (CBGs) for selective retransmission. It retransmits CBGs at the original MCS. The LTE model uses the shared NR engine, so it has this CBG-based retransmission.
Spectrum, interference, and propagation
Aggregate carriers for more bandwidth, model intercell interference, and drive the link with standards-based propagation models.
Carrier aggregation
Aggregate up to five component carriers of 1.4 to 20 MHz, for up to 100 MHz. Intra-band contiguous and non-contiguous, and inter-band non-contiguous, over FDD and TDD.
Downlink interference
The default is no interference. You can also select a graded distance-based Wyner model, which includes interference from any number of base stations and the location of the UE.
Propagation models
3GPP TR 38.901 path loss for rural macro, urban macro, urban micro and indoor office. The models include LOS / NLOS, outdoor-to-indoor loss, log-normal shadow fading and Rayleigh fading.
Network, transport, applications, and mobility
The LTE radio sits under a full IP stack, so you can drive it with realistic traffic, routing, movement and handover.
Network layer
IPv4 across the core, with RIP and OSPF routing in the EPC and core network.
Transport layer
TCP with Old Tahoe, Tahoe, Reno, New Reno and BIC CUBIC variants, plus UDP.
Application layer
HTTP, CBR, email, video, voice, FTP and other application traffic models.
Mobility and handover
Random walk, random waypoint, group and file-based mobility. The serving and target SNR and a time-to-trigger control eNB-to-eNB handover.
Metrics and logs
Summary statistics give quick answers, and per-event logs give detailed analysis of the radio link.
Network and LTE metrics
Network-wide statistics and LTE cell metrics, which include PDSCH and PUSCH throughput per eNB interface.
IP, TCP / UDP, application
IP metrics, TCP and UDP transport metrics, and per-application performance statistics.
Dynamic metrics
Time-series plots of an attribute, including application throughput and individual link throughput, plus the LTE packet trace.
Radio measurements log
Per-slot SNR, received power, path loss and the CQI / MCS on the link.
Radio resource allocation log
PRB allocation per slot and carrier, with the scheduler's per-UE decisions.
Handover log
Time, UE, serving and target cell, serving and target SNR, and time-to-trigger remarks. The SNR columns have the label SSB SNR, because the LTE model uses the shared NR engine.
Code block log
Process ID, TB size, modulation, code rate, code block size, BLER and CBG ID per transmission.
OLLA log
CQI with and without OLLA, PHY SINR, SINR delta and virtual SINR per carrier and layer.
Packet and event traces
Per-packet and per-event records across the network for end-to-end debugging.
Next generation
From LTE to 5G NR
LTE is the 4G baseline, and NetSim builds it on the same engine as 5G NR. When you are ready to model 5G, the NR library adds the new radio, with the same workflow and C source model. It adds flexible numerology, mmWave (FR2), massive MIMO and beamforming, 16 HARQ processes and network slicing.
- Flexible numerology and wide bandwidths
- FR1 and FR2 (mmWave)
- Massive MIMO and beamforming
- Network slicing and AI/ML in the RAN
Useful links
Use the documentation, the knowledge base, the file exchange and support to take an LTE project further.