Addressing C-V2X Congestion with Keysight Director Software.
In my previous blog, I introduced Cellular Vehicle-to-Everything (C-V2X) technology, which enables direct and network-based communication modes including vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle-to-pedestrian (V2P), and vehicle-to-network (V2N). C-V2X is engineered to support safety, efficiency and traffic management applications. Time-sensitive applications like collision avoidance, emergency braking alerts, intersection movement assist, and vulnerable road user protection require extremely reliable and low latency message delivery.
In a controlled lab environment with only a limited number of C-V2X devices such as Roadside Units (RSUs) or Onboard Units (OBUs) are operating, system performance is typically stable and free from major concerns. However, real-world deployments present a much more complex scenario. In dense traffic environments such as highways, busy intersections or urban downtown areas, there may be dozens or even hundreds of vehicles and infrastructure nodes transmitting simultaneously. This high node density led to congestion. In these situations, the likelihood of packet collisions, delays, or dropped safety-critical message increases. Such impairments are particularly concerning the time-sensitive applications I mentioned above, where even small delays in message delivery could compromise system effectiveness and directly impact road safety. Therefore, evaluating devices and system performance under congestion is crucial to ensure compliance with standards, validate congestion control mechanisms, and guarantee that C-V2X communications remain reliable and scalable in real-world conditions.
Congestion testing methodologies typically involve simulating a high-density vehicular environment with tens to hundreds of simultaneous transmitters, while monitoring key performance indicators such as packet error rate, end to end latency, channel busy ratio, and overall link reliability under varying load conditions. In this blog, we will examine the use of Keysight’s C-V2X Director software to simulate congestion scenarios.
Keysight Director software is part of the SA8700A C-V2X test solution. It provides a controlled framework for congestion testing by generating large number of virtual ITS stations across multiple formats (IEEE, ETSI, and SAE-C). The tool is capable of producing standards-compliant Basic Safety Messages (BSMs, IEEE/SAE-C) or Cooperative Awareness Messages (CAMs, ETSI) at configurable transmission rates, with 10 Hz as the nominal default. The software supports two spatial distribution models - Radial and Host Path patterns, which facilitate the emulation of realistic deployment scenarios.
Figure 1: Keysight Director Software Congestion GUI, it allows users to select either Radial or Host Path as the congestion distribution mode.
You can emulate up to 500 stations across both distribution models. That said, the limit can be lower when the secure congestion is enabled, since the number of available certificate collections will determine the upper limit. In secure congestion mode, every congestion station message is digitally signed using the certifications provided in the Certificate Files folder. This feature adds the IEEE 1609.2 security header to the payload for North American standards or Secured Message header for European (GeoNet) standards. The software also allows you to define the congestion generation time in seconds, and the amount of variation in a station’s location from its prescribed point.
Radial Congestion
Figure 2: Radial Congestion Settings
In radial congestion mode, Director software places stations in a pseudo-random pattern around a defined central point. This center can be set to the host’s position or a user-defined latitude and longitude. To make the setup even more flexible, you can also specify outer and inner boundaries, allowing you to control how far the congestion data spread from that central point.
Figure 3: Inner and Outer Limits for Radial Congestion generation
Host Path Congestion
In the Host Path congestion mode, Director places stations along the same route as the host, arranging them in front, behind, or alongside depending on the user-defined lane patterns. You have full control over lane widths, spacing between vehicles, traffic direction and even speed variations. This makes it easy to create highly realistic roadway scenario. For instance, simulating forward and reverse traffic lanes moving at different speeds.
Figure 4: Host Path Congestion Settings
You can define the lane pattern or road layout by using a sequence of letters to dictate traffic direction, speed and host location.
- H – Must appear exactly once, and dictates where the host station is located.
- F – Forward lanes, i.e. lanes whose traffic is moving in the same direction as the host station
- f – Forward lanes whose speed is twice that of the host station
- R – Reverse lanes, i.e. lanes whose traffic is moving in the opposite direction to the host.
- f – Reverse lanes whose speed is twice that of the host station.
- X – Empty lanes, typically used to defined the median strip or central reservation for highways and similar.
Once you define the lane pattern, then you can enter the lane width which is the distance to the right or left of the host station where each adjacent lane appears, and separation which is the distance between each station in the same lane, including the host.
Because the host path has a finite length, there isn’t always enough space to generate all stations at once. Therefore, when Show Out Of Range Stations is turned off, stations that are too far ahead of the host simply stop being emulated, and those falling behind won’t appear until the host moves further along its path. This approach creates more realistic traffic patterns, though it may not produce the required amount of congestion.
Conversely, if Show Out of Range Stations is enabled, then any stations beyond the host path will still be displayed. Those too far ahead will stay frozen at the path’s end, while those behind will appear at the starting point. This ensures you have the full number of congestion stations needed for RF or stack testing, though it also means some stations may overlap in the same physical location.
Figure 4: Example Host Path Congestion
Traffic congestion in C-V2X networks isn’t just an annoyance. It’s a real challenge that can impact safety-critical applications. To keep connected mobility safe and reliable, we need tools that go beyond theory and actually recreate the pressures of real-world traffic. That’s exactly what Keysight’s C-V2X Director software delivers. The true strength of Keysight Director lies in its ability to bridge the gap between lab testing and real-world conditions. By simulating hundreds of virtual vehicles, supporting global standards, and even layering in secure message handling, it gives engineers a powerful way to stress-test their systems before they hit the road.
In short, C-V2X Director takes the guesswork out of congestion testing. It helps you validate performance, uncover bottlenecks, and ensure your solutions are ready for the toughest traffic conditions out there. If you’re building for the future of connected vehicles, this is one tool you don’t want to overlook.
If you have questions or comments regarding what you have just read, feel free to send me a message.