Military platforms of all types from surveillance aircraft, tanks and helicopters to fighting ships need to distribute video from various TV and Infra-Red (IR) sensor systems to displays. The display operators who will interpret this data make tactical decisions on what they see. Traditionally this class of video has been routed as analog signals using coaxial cables from sensor to display, but this can introduce noise and resolution loss over long distances. Alternatively, the sensor video can be digitized at the source and routed via point-to-point links using Low Voltage Differential Signalling (LVDS), Digital Visual Interface (DVI), or similar technologies.
MPEG video compression
In order to reduce bandwidth requirements on these digital links, video compression such as that created by the Moving Picture Experts Group (MPEG) has been used successfully where dedicated links exist. However, MPEG’s limitations begin to appear if it is used over a network or switched fabric which would be the choice of today’s system designer. MPEG uses multiple, successive frames to convey enough information for the receiver to be able to decompress the signal without loss. If the channel or receiver were to lose one or a number of frames, then errors are introduced into many subsequent frames until the full picture is reestablished. This could happen if, for example, the MPEG video was being transmitted over a busy shared network that denied access to the video for more than a single frame interval. In addition, to support intraframe compression MPEG has to buffer multiple frames of video, introducing latency between the image at the sensor (possibly a real-world threat) and the display. This latency could be critical to the survival of the platform.
The new JPEG2000 standard
JPEG2000 is a new standard for video compression, designed to replace existing Joint Photographic Experts Group (JPEG) and MPEG in many applications, offering better performance and more options. JPEG2000 uses new algorithms and provides much higher quality than JPEG at high rates of compression. JPEG2000 offers a compression ratio of typically 30:1 for TV-rate video and provides no discernable loss of detail at the receiver. This compression rate is quite constant irrespective of the image content of each frame. Like JPEG, JPEG2000 also offers a loss-less mode of compression but the compression rate is very variable as it is directly dependent upon the complexity of the image to be compressed. This makes it less suitable for transmission through a network or fabric because of the unpredictability of each frame size. Loss-less compression is most suited to single frame compression.
JPEG2000 organizes the data stream into packets and layers, which describe all the attributes of the frame within each frame transmission. So JPEG2000 can be used to transmit video just by streaming sequential compressed frames at the frame rate of the sensor. A compressed JPEG2000 non-interlaced video stream only requires a bandwidth of approximately 1 MBps for transmission from sensor to display, meaning that a number of video channels can easily be streamed over a single 100 Mbps Ethernet connection.
Components are now available to both encode and decode TV signals to and from JPEG2000 at frame rates. These can be used, for example, on a PCI Mezzanine Card (PMC) module to take a Phase Alternating Line (PAL)/National Television Committee System (NTSC) TV signal from the sensor and pass it in compressed JPEG2000 format to the PCI bus. The reverse process takes a stream of JPEG2000 data from the PCI bus and decompresses it to PAL/NTSC. As an example, the Orion JPEG2000 PMC module from Curtiss-Wright Controls, Embedded Computing (CWCEC) is illustrated in Figure 1. The Orion includes a video switch allowing selection of any two of 10 input sources to be compressed and can be programmed for different compression rates including loss-less compression.
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A practical application of JPEG2000
In order to build a link from sensor to display subsystem, a PMC module such as the Orion would be mounted on a VME or CompactPCI SBC that includes a network or switched fabric connection. Most current SBCs have two or three 100 Mbps or 1 Gbps Ethernet ports as standard—any of which has more than adequate bandwidth to support a number of JPEG2000 compressed video streams. Existing sensors could be upgraded to provide JPEG2000 capability by means of a simple gateway consisting of a 3U SBC fitted with a JPEG2000 PMC to provide an economical, one card slot network connection. This is illustrated in Figure 2.
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At the receiving subsystem, which is likely to be a display console processor, the process is reversed. The received frames are passed from Ethernet to the local PCI bus and then to the PMC module, which regenerates a PAL/NTSC TV signal. The processing overhead of transferring the video over the network is very low as just a simple stack such as User Datagram Protocol (UDP) can be used for transport. The data itself is transparent to the processors at either end of the connection. In order to guarantee delivery of error-free frames in the correct sequence, there is no requirement for top heavy protocol stacks such as TCP/IP as they introduce significant processor overheads and latency into the transmission. Since each JPEG2000 frame is self-contained, recovery from a transient error occurs in the subsequent frame.
Enhanced capabilities
Currently, typical applications of JPEG2000 are to replace analog video distribution and improve digital performance and complexity by replacing MPEG. These applications do not perform any processing on the JPEG2000 stream as it passes from sensor to display. However, JPEG2000 provides a number of possibilities for manipulation of the images in realtime without complete decompression:
- The receiving subsystem might want to record the video while it is still in compressed form but at a lower quality level than that which is being displayed. This might be necessary to save on disk space. The parsing of the JPEG2000 bitstream allows the easy removal of layers affecting image quality. So the receiving subsystem would pass the bitstream unmodified to a PMC module for decompression back to PAL/NTSC, while at the same time creating a further compressed image file in JPEG2000 format for recording.
- JPEG2000 provides spatial accessibility to tiles in the bitstream without decompressing the entire frame. The receiving subsystem could extract regions of interest from the incoming JPEG2000 bitstream, decompress them and process them further while still passing the unmodified bitstream to a PMC module for decompression back to PAL/NTSC.
- JPEG2000 permits cropping, rotation, and flipping of the image without decompression.
Creating a tactical display
Once the video signal is received and decompressed at the display console there are still many operations to be performed before it is finally displayed to the operator. Typical display consoles will have many sources of sensor data available to be displayed such as radar, TV, IR, sonar, and so on. These may vary from scan-converted radar video to fully processed and identified target tracks. Additionally, the display will be built from synthetically generated graphics such as maps and data links. These displays use a windowed approach to generating the overall tactical picture for the operator. Individual sensors may be viewed in windows sized to suit operators’ individual preferences. Hardware scaling and video mixing is used on the incoming video streams to ensure the correct source, size, position, and synchronization of the windows on the display screen.
Network and fabric options
Although Ethernet is probably the most common network of choice in current naval applications, there is no reason why other networks and future switched fabrics such as Fibre Channel, Serial RapidIO, StarFabric, PCI Express or Advanced Switching could not be used just as successfully. The great benefit to system designers and users of the switched fabric approach when compared to traditional analog video routing is that of flexibility and scalability. Video can now be distributed from a single source to one or multiple destinations. Video switching is a simple receiver operation and routing can be changed dynamically to compensate for battle damage or to accommodate multiple mission profiles from day to day.
JPEG2000 can be used successfully to reduce the complexity of video distribution between many of the sensors and display consoles in any multi-sensor tactical/combat display system. In many existing installations the multitude of coaxial video cables can be replaced by a single network cable carrying a number of video streams as well as higher level system data between the video sensors and the display consoles in either direction. JPEG2000 will find many more video distribution applications in the future as products become available to support higher resolutions, faster refresh rates, and other formats such as High-Definition Television (HDTV) and direct display screen capture. JPEG2000 provides the basic technology key to unlock extra capability, reducing noise and building in greater future flexibility into a system to allow for further expansion or reconfiguration of consoles and tactical roles without recabling the platform each time.
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John Wemekamp is chief technology officer for Curtiss-Wright Controls Embedded Computing Group. During his 22-year tenure at Dy 4 Systems (Dy 4 Systems was acquired by CWCEC), John filled a variety of roles beginning as hardware design engineer and various management roles through to his current role at Curtiss-Wright as chief technology officer. Prior to joining Dy 4, John successfully led a team at Bell-Northern Research in the development of a telecommunication’s product. John holds a BS in electrical engineering from Queens University in Kingston, Ontario.
For further information, contact John at:
Curtiss-Wright Controls Embedded Computing
741-G Miller Drive, SE
Leesburg, VA 20175
Tel: 703-779-7800
Fax: 703-779-7805
E-mail: [email protected]
Website: www.cwcembedded.com