Rob Helliar, the Head of Customer Solutions at Cambridge Pixel, presents an insightful article on the measurement of radar video latency—the duration it takes for radar data to reach a display—and its meaning.
understanding Radar Video Latency
Radar video latency refers to the interval between the radar signal’s generation and its visualization on a screen. this latency is typically quantified in milliseconds, with lower values indicating better performance.
The Importance of Measuring Latency
Excessive latency can lead to discrepancies between the actual movement of radar targets and their depiction on the display. By the time the targets are rendered, their positions may have shifted considerably. At Cambridge Pixel, our engineers frequently receive inquiries such as, “How can I quantify the latency from the moment a radar video signal is received by an HPx card to when it is displayed?” The answer hinges on several factors:
- Input buffering and acquisition within the HPx hardware
- Processing and packetization in the transmitting software
- Delays in the network
- Scan conversion buffering and refresh rates
Considering these stages, one might anticipate approximately 40ms of latency during the analogue acquisition and buffering phase, followed by a few milliseconds for processing, around 5ms for unpredictable network delays, and roughly 30ms for scan conversion. Cumulatively, this results in an estimated total latency of about 80ms from the moment data is received at the HPx card to its appearance on the client display. In most scenarios, a latency of around 100ms is a practical benchmark. However, there are instances where precise measurement is necessary, such as for compliance verification or to ensure the proper functioning of downstream systems.
our Approach to Latency Measurement
To accurately estimate end-to-end latency, we utilize a suitable test source, an oscilloscope, and a video camera.In our Cambridge Pixel laboratory, we established a test setup using an HPx-300 card to generate radar signals, which were then processed by an hpx-346 unit. The HPx-300 is designed to create analogue radar signals based on software input, while the HPx-346 manages both the acquisition and distribution of radar video data.
Step-by-Step Measurement process
- The HPx-300 card is configured to emit a specific test pattern, producing a strobe pulse at 0 degrees azimuth, which serves as a clear reference point on both the oscilloscope and the computer display.
- An instance of SPx Server is executed on the client PC to facilitate the scan conversion and visualization of the radar video data.
- The video output from the HPx-300 card is routed to an oscilloscope, with both the oscilloscope and PC displays captured by a single video camera feed.
- By reviewing the recorded footage frame-by-frame, we can measure the time difference between the strobe pulse appearing on the oscilloscope and its subsequent appearance on the PC screen. This time difference represents the latency we aim to quantify.
Results of Our Testing
During our laboratory tests, we recorded a latency of 100ms. It is crucial to note that the camera used for capturing the oscilloscope and PC displays operated at a frame rate of 30 frames per second (FPS), introducing a potential error margin of approximately ±30ms. Ideally, a higher frame rate camera would enhance the precision of the latency measurement.
This testing procedure takes about five minutes to conduct, with a preparation time of a couple of hours. While this is not a routine task, a latency of 100ms is generally acceptable. However, further reductions can be achieved by:
- Minimizing buffering on the acquisition card (though this may reduce processing efficiency and network bandwidth).
- Reducing network latency (which can be challenging and often beyond our control).
- Shortening the scan conversion update interval (which may increase the processing load on the display).
At Cambridge Pixel, our engineers possess extensive expertise in radar interfacing, processing, target tracking, camera integration, and user interface advancement across both Windows and Linux platforms.With our advanced hardware and software capabilities, we deliver remarkable solutions tailored to our clients’ needs.If you have a project where we can assist, we would be eager to collaborate.
