# A Survey on Monitoring Quality Assessment for Wireless Visual Sensor Networks
## 7 Research Trends and Directions

Table 5: _Cont._* _Content and dependable quality for barrier coverage applications_: the performed literature review showed the absence of articles approaching content and dependable quality for barrier coverage in WVSN applications. These are very important issues in order to be able to classify and identify the object or intruder violating a barrier, as well as to determine the barrier lifetime and successful operational application behavior. Metrics to assess these quality categories should be proposed specifically for barrier coverage applications. At least, feasibility studies should be developed about the adaptation and application of metrics used for area and target coverage to barrier coverage applications. For instance, which metrics from Table 2 could be used to assess quality in barrier coverage applications? Maybe _occlusion range_, indicating how much of the expected barrier can be indeed covered, or _distance rate_, since as closer the camera is to the barrier, more content quality the application will get. What about the remaining metrics? How to apply the concept of _angle of view_, for example, in this context? Does this make sense, once an intruder can break into the barrier from any direction? More than that, could we define a quality metric specific for barrier coverage applications (since an intruder could break into the barrier from any edge)? Maybe it would be useful to evaluate these applications with respect to a full-view barrier coverage, which means a 360\({}^{\circ}\) coverage. Regarding to dependable quality in barrier coverage applications, redundancy should be considered as a determining factor, since a visual sensor failure can create a hole in the barrier. This approach will lead to the computing of the overlapped area among the camera's FoV composing the barrier. This assessment could help to design and schedule preventive or contingency measures;
* _Minimum sensors set in area coverage applications_: as mentioned before, since the monitored area is a continuous space, it is difficult to state which region has been covered by which visual sensors, which makes the definition of the minimum sensors set in area coverage a challenging task. However, this issue should be discussed in order to enhance the usage of resources to provide a high quality area coverage with the minimum effort. This is a NP-complete problem [95], which requires the development of heuristics to find or verify a solution in an reasonable computational time. Maybe a possible solution could be to find an optimal sensors set and reduce the problem;
* _Trade-off associated with redundancy in area coverage applications_: dealing with area coverage implies in the definition of the best position and orientation of the visual nodes to cover a wider area. This is intrinsically related to the reduction of the coverage redundancy among the visual nodes. On the other hand, in the sense of generating high dependable quality, redundancy can be increased. This can be done through the usage of spare nodes, even whether this measure means that resources are underused or wasted. At this point, it is necessary to consider the trade-off between increasing redundancy and saving power, as well as between increasing redundancy and increasing area coverage. To address this problem, an optimization method should be proposed based on a multi-objective function. That way, a solution that tries to equalize opposite aspects could be found. ;
* _Multiple coverage metrics_: one of the objectives of this work is to foster the comparison among different WVSN implementations. In this sense, new quality metrics could be proposed integrating aspects of more than one quality category. This would allow broader analysis of the compared networks.