Handover Simulation

Simulates the UE measurement reports that trigger handover decisions. Models the configurable A3, A4, A5, and B1/B2 events defined in 3GPP specifications, including hysteresis margins, time-to-trigger (TTT) counters, and L3 filtering coefficients. The simulation must accurately reproduce the delay between a radio condition change and the gNB receiving the measurement report, as this latency directly impacts the radio link failure (RLF) rate at cell edges.

Tests algorithms that dynamically tune handover parameters to minimize failures. Key optimization targets include:

• Too-early handover: UE loses connection in target cell and re-establishes in source
• Too-late handover: RLF occurs in source cell before handover completes
• Handover to wrong cell: UE re-establishes in a cell other than the intended target Simulation enables safe tuning of cell individual offsets (CIO) and TTT without impacting live users.

Models complex handover scenarios beyond simple intra-frequency transitions. Includes PSCell change in EN-DC and NR-DC architectures, SCell addition/release during mobility, and make-before-break handover sequences. The simulation must coordinate the signaling between Master Node (MN) and Secondary Node (SN) while maintaining data continuity across multiple component carriers operating at different frequencies.

Simulates transitions between different radio access technologies, such as NR to LTE handover, LTE to 3G reselection, or EPS fallback for voice services. Requires modeling of measurement gap configurations, compressed mode operations, and the translation of QoS profiles between RATs. Critical for testing coverage continuity in multi-layer deployments where 5G coverage may be limited to urban hotspots.

Deliberately introduces adverse conditions to stress-test handover robustness. Scenarios include:

• T304 timer expiry: Target cell fails to complete handover within the configured window
• Reconfiguration failure: UE cannot apply the target cell's RRC configuration
• RACH failure: UE cannot complete random access on the target cell
• SCG failure: Secondary cell group link breaks during dual connectivity Each failure type triggers specific recovery procedures that must be validated.

Models the 3GPP Release 16 feature where the network pre-configures a handover command with an execution condition (e.g., A3 event threshold). The UE stores the command and executes it autonomously when the condition is met, eliminating the vulnerable period where the UE is sending measurement reports on a deteriorating link. Simulation validates CHO preparation, candidate cell selection, and execution condition evaluation under high-mobility scenarios.

A mathematical formulation that predicts the path loss and signal characteristics of radio waves as they travel through an environment. The accuracy of a handover simulation is fundamentally bounded by the fidelity of its propagation model.

• Empirical Models (e.g., Okumura-Hata, COST 231): Fast, based on measurement campaigns, but less accurate for specific environments.
• Semi-Deterministic: Combine empirical path loss with a stochastic component for diffraction and scattering.
• Ray Tracing: Computationally intensive but highly accurate, modeling individual wave paths using 3D geometry.
• Key Output: The Reference Signal Received Power (RSRP) and Signal-to-Interference-plus-Noise Ratio (SINR) at the UE, which directly feed the handover decision algorithm.

A logical function in a base station that allocates time-frequency radio resources to user equipment. In a handover simulation, the scheduler's behavior dictates the resource availability at the target cell, which directly impacts admission control and handover success.

• Resource Block Allocation: The scheduler assigns Physical Resource Blocks (PRBs) based on channel quality and demand.
• QoS Enforcement: Ensures Guaranteed Bit Rate (GBR) and non-GBR bearers meet their latency and throughput targets during and after the handover.
• Scheduling Algorithms: Common strategies include Proportional Fair, Round Robin, and Max C/I, each creating different load profiles for the target cell.
• Simulation Integration: The scheduler model must accurately reflect the load state of the target cell to determine if a handover can be admitted without degrading existing users.

The modeling of the network function that decides whether to accept or reject a new bearer request based on available resources and the required Quality of Service (QoS). This is the final gatekeeper in a handover procedure.

• Resource Check: The algorithm verifies if the target cell has sufficient PRBs, power, and backhaul capacity.
• QoS Preservation: A handover is rejected if admitting the new UE would cause existing GBR bearers to drop below their guaranteed rate.
• Priority and Preemption: Models the ability to preempt lower-priority bearers to admit an emergency call or a high-priority handover.
• Failure Modeling: A realistic simulation must model admission rejection, triggering a handover failure and potentially a Radio Link Failure (RLF) for the UE.

The process of replicating the real-world behavior and impairments of a wireless channel in a controlled laboratory environment. For handover testing, this is often integrated with a Hardware-in-the-Loop (HIL) setup.

• Fading Emulation: Artificially introduces multipath fading, Doppler shift, and shadow fading to test receiver robustness during a handover.
• MIMO Channel Emulation: Replicates the complex spatial correlation and cross-polarization effects for multi-antenna systems.
• Scenario Replay: Recorded real-world RF measurements are injected into the emulator to recreate a specific field handover failure for root-cause analysis.
• HIL Integration: A physical UE and gNB can be connected through a channel emulator, with the simulation controlling the fading profiles to trigger handover events on real hardware.

A property of a channel model ensuring that channel parameters evolve smoothly and realistically for closely spaced or moving terminals. This is critical for handover simulation to avoid generating false, abrupt events.

• Correlated Shadowing: The shadow fading experienced by a UE should be correlated in space; a UE moving 1 cm should not experience a 20 dB drop.
• Birth-Death Process: Models the appearance and disappearance of multipath clusters as a UE moves, preventing sudden changes in the channel impulse response.
• Handover Stability: Without spatial consistency, a simulation might generate a rapid ping-pong handover sequence that is an artifact of the model, not a real network condition.
• GSCM Integration: Geometry-Based Stochastic Channel Models inherently provide spatial consistency by tying scatterer locations to a geometric environment.