In high acoustic reverberation environments, such as shallow-water areas, the fiber- 

 optic link promises to allow offshore inspections even when acoustic Unk systems would 

 tend to be rendered ineffective by high error rates. 



2.2 COMMUNICATION REQUIREMENTS FOR SUPERVISORY-CONTROLLED 

 VEHICLES 



The supervisory-controlled vehicle, as part of a closed-loop (in fact, man-in-the-loop) 

 system, by definition requires a duplex communication Hnk. This duplex link may be divided 

 for discussion purposes into downUnk (support platform to vehicle) and uphnk (vehicle to 

 support platform) communications. The former carries command-control infomiation, while 

 the latter, in addition to closing the command-control loop, also carries sensor information. 

 Full duplex operation over a single optical fiber is readily achieved by the use of wavelength 

 multiplex techniques, which obviate the need for cables containing more than one fiber. 



Command-control information consists of obvious propulsion commands as well as 

 the exchange of navigation and system status information (ie, depth, state of battery charge, 

 etc). With the advent of the integrated circuit microprocessor, it is apparent that command- 

 control functions are best carried out in a serial, digital format, and when so reahzed can be 

 implemented readily via software. This approach excels in cost flexibility, effectiveness, and 

 rehabihty. When microprocessors are employed, all synchronization, display, data transfer, 

 time division multiplexing, and control are under the command of the processors. Recon- 

 figuration of the system is easily accomphshed by employing a universal data bus and simple 

 software changes, which allow the vehicle to be quickly and efficiently reconfigured and 

 optimized for the performance of diverse missions. 



A proposed approach would place one microprocessor aboard the vehicle and another 

 on the support platform. The former would locally manage affairs such as navigation, attitude 

 compensation, homing and guidance functions, and the Uke, while the latter would oversee 

 such functions as display and operator interfacing. The two units would communicate via 

 UARTs (Universal Asynchronous Receiver/Transmitters), which would allow reprogramming 

 and interaction as well as status reporting. The UART provides all formatting and synchroniza- 

 tion to transfer data efficiently between the processors. Data transfer rates from 1 10 to 9600 

 baud are standard for such devices. Such an approach was adopted early in the design of the 

 NOSC-developed EAVE WEST submersible. 



Probably the single most valuable sensor for the inspection vehicle is a television 

 camera. Such cameras, packaged and ruggedized for operation to depths of several thousand 

 feet, are only slightly larger than a beer can and are available from several manufacturers. All 

 such units employ standard composite video waveforms that satisfy RS-170 specifications. 

 It is expected that the CCD (charge-coupled device) camera will soon become commercially 

 available, and will allow a further reduction in camera size. Transmission of RS-170 real-time 

 video requires a channel with a bandwidth of 2—5 MHz and a dynamic range of at least 40 dB. 

 (Home-quality monochrome television occupies approximately 3.8 MHz with a dynamic range 

 of 40 55 dB.) 



Slow-scan converters are available which trade off frame rate, resolution, and dynamic 

 range to decrease the required transmission bandwidth. For example, a commercial unit has 

 been evaluated at NOSC which allows slow-scan television transmission via an acoustic channel 

 with a bandwidth of only 3 kHz. One frame is transmitted every 8 seconds, and has a spatial 

 resolution 20% that of RS-170 TV with 6% as much gray-scale rendition. Some apphcations 

 may be tolerant of the loss of motion and resolution inherent in slow-scan TV. 



14 



