Description
The Statistical Spatial Channel Model (SSCM) is a comprehensive, geometry-based stochastic channel model (GSCM) standardized by 3GPP for the design, testing, and performance evaluation of New Radio (NR) air interface technologies, particularly those involving advanced multi-antenna systems. Defined in specifications like TR 38.900 and TR 38.901, it provides a mathematical framework to simulate the radio propagation channel between a transmitter (e.g., gNB) and a receiver (e.g., UE) in a statistically accurate manner. The model captures the spatial characteristics of the channel, which are paramount for technologies like Massive MIMO, beamforming, and multi-user MIMO.
The SSCM operates by modeling the propagation path as a combination of multiple clusters. Each cluster represents a group of multipath components with similar delay and angular properties. Key large-scale parameters (LSPs) such as delay spread, angular spread (azimuth and zenith at both arrival and departure), shadow fading, and pathloss are first drawn from statistical distributions that are specific to a defined scenario (e.g., Urban Microcell (UMi), Urban Macrocell (UMa), Rural Macrocell (RMa), Indoor Office). These LSPs are correlated with each other based on real-world measurements. Within each cluster, small-scale parameters like cluster delay, cluster power, and angles are generated. Finally, the channel impulse response (CIR) or channel matrix H is constructed by summing the contributions from all clusters and paths, incorporating antenna patterns and array geometries at both ends.
The model supports a wide frequency range from below 6 GHz up to millimeter-wave (mmWave) bands like 52.6 GHz and beyond. It includes essential features like line-of-sight (LOS) and non-line-of-sight (NLOS) conditions, blockage models for mmWave, and spatial consistency. Spatial consistency ensures that the channel characteristics for a moving UE evolve smoothly over time and space, which is critical for evaluating mobility performance and beam tracking algorithms. By providing a common, realistic reference model, the SSCM enables fair comparison of different antenna schemes, link-level and system-level simulations, and the derivation of key performance indicators (KPIs) for 5G NR systems.
Purpose & Motivation
The development of the SSCM was motivated by the limitations of previous channel models (like the SCM/SCME models for 3G/4G) in addressing the new challenges of 5G. Earlier models were not designed for the higher frequencies (mmWave), the extensive use of beamforming, or the massive scale of antenna arrays envisioned for 5G. There was a need for a unified model that could accurately capture spatial channel properties across a vast range of frequencies, bandwidths, and deployment scenarios.
Its primary purpose is to serve as a reliable tool for the standardization and development of 5G NR physical layer techniques. By using a common, agreed-upon channel model, different companies and researchers can simulate and compare the performance of proposed technologies (e.g., new coding schemes, reference signals, beam management procedures) under consistent and realistic conditions. This is crucial for reaching consensus during 3GPP standardization meetings. Furthermore, it helps network equipment vendors and mobile operators design and optimize their products and deployments by understanding how advanced features like Massive MIMO will perform in real-world environments like dense urban areas or indoor factories. The SSCM addresses the specific propagation challenges of mmWave, such high pathloss and sensitivity to blockages, which was a gap in prior models.
Key Features
- Geometry-based stochastic model supporting frequencies from 0.5 GHz to 100 GHz
- Defines multiple deployment scenarios: UMi, UMa, RMa, Indoor Hotspot, etc., with LOS/NLOS states
- Models large-scale parameters (delay spread, angular spread, shadowing) with inter-parameter correlation
- Generates clusters of multipath components with small-scale fading and spatial consistency
- Includes support for 3D antenna patterns and arbitrary antenna array geometries (ULA, UPA)
- Incorporates blockage and penetration loss models critical for millimeter-wave frequency simulations
Evolution Across Releases
Initially introduced in study item phase as a new channel model for 5G. The initial architecture defined the core GSCM framework, the key scenarios (UMi, UMa, RMa, Indoor), and the basic parameterization for frequencies up to 100 GHz. It established the cluster-based approach with spatial consistency and laid the groundwork for evaluating Massive MIMO and mmWave technologies.
Defining Specifications
| Specification | Title |
|---|---|
| TS 38.900 | 3GPP TR 38.900 |
| TS 38.901 | 3GPP TR 38.901 |