# Big Data Collection in Large-Scale Wireless Sensor Networks
## 2 Overview of WSNs
### Challenges of WSN Design and Deployment  
In most cases, the deployment of a WSN is closely related to the nature of the intended application. There is no generic model for these applications. However, several factors influence WSN design and deployment. The design of the WSN must find a compromise solution for the following challenges:  
* _Energy_. A sensor node, by its size, is limited in energy resources, storage capacity, and processing. One of the most serious concerns is the lifespan of the sensor node, which is entirely determined by the amount of energy available and the rate of energy consumption (that is, the average energy consumption). Since improving the energy capacity of small batteries still requires a lot of effort, the goal of a long service life is difficult to achieve by increasing the amount of available energy. As a result, the design of energy-efficient MAC protocols, communication strategies, operating systems, and energy-efficient routing mechanisms provides effective ways to extend the life of the node [36]. The use of energy-recovery technologies for sensor-node power supplies has also been an alternative in recent years. * _Quality of Service (QoS)_. Quality is defined by the ability to interpret the information collected by the sink. In spite of the fact that the QoS requirements vary according to the different WSN applications, the two main measures of QoS are data reliability and latency [33]. Usually, a successful data-exchange rate between the sensor nodes and the sink must be above a certain threshold to ensure network reliability and functionality. Reliability can be further maximized, but this could be at the cost of increased energy consumption. Therefore, a compromise is necessary. In case of latency, for certain types of applications, the reception of the data detected on the sink is strictly timed, so that latency data can cause delay problems and lead to bad decisions, particularly in industrial-surveillance applications. * _Security and privacy_. WSNs find their applications in various areas of life. Some applications manipulate private data. Moreover, WSNs are networks whose topology is very frequently subject to change. The deployment of sensor nodes is sometimes done in accessible areas; they may encounter technical interference or human intrusion, which can lead to confidentiality issues. Thus, the network should allow the detection of intrusions. It is therefore necessary to design robust and lightweight algorithms for data encryption, authentication mechanisms for privacy protection, and secure routing for data relays to protect the entire network against passive and active attacks, and denials of external service providers [55; 56; 57]. * _Adaptability._ The design of a WSN must be sufficiently flexible and adaptable to be deployable across a wide range of application scenarios. The entire network should be kept functional regardless if the number of sensor nodes is hundreds, thousands, or very small. Due to the mobility of sensor nodes and observed events, as well as the possibility that a sensor node can fail in the network, the overall topology of the network may be subject to frequent change. Therefore, the design of a WSN must be sufficiently intelligent and robust to deal with these dynamic topology scenarios [10; 31]. * _Localization._ WSNs play an important role in the problem of locating elements in a given deployment area. Certainly, GPS is a well-known tracking system and the most used location system. However, it is not satisfactory for this use, because it accumulates handicaps. It is only available outdoors and if no obstacle obstructs the field of view of the receivers. In addition, an operation under dense foliage or in cities with narrow streets is not possible, which are very bad conditions. Moreover, it is particularly expensive, both in terms of hardware, multiplied to many copies in a network with high sensor density. Moreover, signal reception is very energy-greedy, which is not compatible with management problems of battery service life.