In a Gigabit Ethernet world, many surveillance sites still need to transmit data using low-bandwidth communication links. Examples include satellite, microwave, VHF, and cellular with bandwidths ranging from a few Mbps to kbps. Low-bandwidth solutions can be found in almost any application including: remote coastal surveillance, offshore platforms, shipboard surveillance, and portable platforms.
The information gathered by these sites may be necessary for the mission at hand, and it is imperative that it gets back in a real-time manner without interruption.
SSR has developed many specialized network communication techniques that allow pertinent data to get back to the command center in real-time.
Key Technologies and Solutions
For most installations, auto-clutter processing and land-masking are utilized and these techniques eliminate unnecessary radar clutter from land and sea. In all cases the radar video is compressed in real-time, allowing high-resolution radar video to be sent using minimal bandwidth. In typical situations these standard techniques reduce the base bandwidth by 75%, allowing most systems to operate without further bandwidth reduction methods.
Adaptive Streaming Radar Video
SSR has recently developed an adaptive streaming radar video algorithm which ensures constant radar video over a connection with fluctuating bandwidth. This technique is well suited for 4G, microwave and some low-bandwidth terrestrial networks. The system continually monitors the health of the network and when it detects a congested state it will reduce the resolution of the radar video, but continue sending it out real-time.
Network messages are typically transmitted between subnets via unicast or multicast. Unicast is not an efficient means to transmit data in bandwidth-constrained environments; however, multicast requires special hardware and qualified network administrators. Within its COMRIC Middleware, SSR has recently developed a hybrid transmission method known as Smartcast. Like multicast, Smartcast efficiently transmits information across subnets, but without the hardware and configuration complexity of multicast.
Synthetic Radar Video
It may not be possible to send full resolution radar video in certain systems with bandwidths below 256 kbps. However, the plot data sent to the tracker can also be used to create a synthetic radar video, which provides an adequate representation of the radar image. Utilizing the synthetic radar video reduces the bandwidth by another 75% over the standard techniques. This technique is typically applied for networks between 56 kbps and 256 kbps.
Track-Only streams are typically used in installations where available bandwidths are below 56 kbps. The tracks are available in proprietary and standard formats, such as NMEA0183 and OTH-Gold. These systems are typically configured with Constant Bit Rate (CBR) settings to ensure the track data does not overwhelm the communication link. In certain cases, when dedicated hardware is not available, this information can even be sent using an AIS Transponder.
Quality of Service
As with many other applications, certain messages and information are more important than others. SSR has developed a means to prioritize message traffic, so when network congestion occurs the most critical messages still get through. This quality of service management is done in the COMRIC Middleware and does not require additional network administration configuration.