# Wireless Remote Control for Underwater Vehicles
## 3 Requirements and Definition of Working Modes for ROV Control
### Short-Range Full-Capacity Wireless Mode  
In this section, we describe the short-range full-capacity wireless mode (SRM) with its requirements in terms of supported types of traffic and their respective bit rates. According to the review presented in Section 2, the raw video produced by the BlueROV camera cannot be transmitted with any commercial off-the-shelf underwater communication system for a distance of more than 10 m; therefore, both a lower resolution and video coding should be employed. For example, from our test, a high-definition h264 video with resolution of 704 \(\times\) 578 px at 25 fps can be sent with an average bit rate of 1.3 Mbps and a peak bit rate of 8 Mbps. With h264 compression, the ratio between maximum and average bit rates is higher than in raw videos due to the fact that, while the quasi static parts of the video can be compressed with high efficiency, the frames presenting fast motions cannot be compressed as much. This behavior is caused by the fact that the latter has low correlations between each other and, thus, they require more information to be represented in a smooth video. The video size can be reduced by lowering the frame rate or the video resolution or by forcing a different video bit rate. A solution to achieve a higher compression level without losing quality and resolution is to employ black and white videos: according to our tests, in the same environment, a grey-scale video with the same resolution would require 0.6 Mbps on average and a peak bit rate of 2.93 Mbps. Some ROVs, such as the Ageotec models Pegaso and Perseo [112], in addition to color video can also transmit black and white videos, which sometimes can provide better contrast than color streams. For this reason, in the SRM considered in this paper, we account for the transmission of both a high-quality black and white video and a high-quality color video with average bit rates of 0.6 Mbps and 1.3 Mbps, respectively.  
Ideally, SRM should provide a QoS similar to the one obtained through the umbilical connector, where an operator can control the ROV lighting intensity, the cameras, and a gripper.  
This mode to be supported requires traffic of at least 4.5 kbps from the control station to the ROV, and of approximately 2 Mbps from the ROV to the control station. Video and control delay should be kept as low as possible, and the video delay variance should be minimized. Indeed, it is possible to control a vehicle in real time even video monitoring with a constant delay of up to 1 s, but it is not possible to pilot a vehicle if the video has a variable delay ranging from 0.1 s to 0.5 s [113]. This variation on the delay is called jitter and can be analyzed through the packet delay variation (PDV) metric [114], computed as follows:  
\[PDV=\sum_{i=1}^{N_{v}}\frac{|d(i+1)-d(i)|}{N_{v}}, \tag{1}\]  
where \(N_{v}\) is the number of packets received for the considered video stream and \(d(i)\) is the delay of the \(i\)th packet. If PDV is less than 3 ms [115], the video stream is smooth and can be used for real-time applications; otherwise, a de-jitter buffer [116] is needed to artificially introduce a buffering delay and to mitigate jitter: to obtain a zero-delay jitter video, the buffering delay has to be set equal to the maximum jitter expected by the video.  
This mode can be supported up to a distance of a few tens of meters (depending on the optical range) by the simultaneous use of one optical modem for video streaming and joystic remote control and one acoustic modem with LBL to support ROV navigation and to send the monitoring status.