## 5 WSN Application Design
### Node Placement Constraints  
The appropriate placement for the WSN nodes is an important issue dealt by different authors who select the node localization as a function of different constraints such as energy consumption and transmission range. The goal is to find a proper balance between system lifetime, functionality and cost. Focusing on the network lifetime, many authors suggest the use of short range links between nodes, considering that short hops are associated to less transmission power and that several short hops are preferable than a single long hop. However, this assertion, for limited power consumption devices such as those used in WSNs, is examined in several works, and short hops have been proven not to be effective. For instance, in [71] it is shown that, for short hops, the power consumed by the transceiver's internal circuitry is bigger than that radiated, therefore wasting a considerable amount of energy. The authors provide experimental results of the utilization of commercial devices such as the Mica2 and MicaZ motes, which reveal that variations in the transmission power (and consequently in the transmission range) have little effect on the total power consumption. Many works follow this approach, setting large node separations that still allow small packet losses [12]. Similarly, it is also possible to use long-haul transmissions but relying on smaller node separation, thus allowing transmissions between one node and several of its neighbors. In spite of increasing cost, this adds robustness to the network since multiple paths to a same destination are available. As an example, in [65] this is achieved by selecting the farthest reachable node from all of the closest neighbors as the next-hop (in multi-hop transmissions), and dynamically adjusting the procedure according to packet losses and passive listening of neighbors' transmissions. Some works propose the use of cooperative transmission techniques such as cooperative MIMO (Multiple Input, Multiple Output), SIMO (Single Input, Multiple Output) and MISO (Multiple Input, Single Output) in order to reduce power consumption in WSNs and increase system capacity. In [72] it is shown that two cooperative nodes reduce power consumption in comparison with a single node when they transmit to a location which is at a distance greater than 60 m from them. The employment of more cooperative nodes improves power consumption when transmitting to locations at even larger distances. For example, three cooperative nodes consume less power than two nodes for transmissions to distances greater than 80 m, four nodes consume less than three for distances greater than 140 m, and so on. WSN-based ITS applications are good candidates to benefit from cooperative transmission techniques since there are many situations where it is possible to find nodes close enough to cooperate. This may happen when nodes are deployed at both sides of a road or at intersections. The intersections deployment case has been studied in [73], considering the deployment of nodes at road signs in crossroads. The purpose is to achieve low power communications between crossroads (applyingMIMO techniques) and between crossroads and vehicles (MISO, SIMO), with the latter being equipped with directive antennas in order to establish communication with crossroads even at further distances. Another consideration about the placement of nodes is related to the position of nodes within the road. For single lane and two-lane roads, nodes may be deployed either by the roadside or at the center of the lanes. The differences between both options regarding their respective performance were mentioned above, in Section 4. For multi-lane roads, placement at the center of the lane is required. Emplacing nodes at the center of the lanes, where vehicles may pass, implies that these nodes require special encapsulations and protections and that the nodes have to be installed aligned with the pavement.