## 8 Conclusions  
In this paper, we have analyzed the requirements of CB in WSNs in order to achieve long distance communications. We went through the frequencies utilized in the usual commercial motes that operate according to the standard IEEE 802.15.4 and presented the synchronization precision level required in order to adjust the phases of the signals to coherently interfere in the BS and substantially increase the received SNR.  
We have analyzed the obstacles that stand in the way of attaining the required precision, which, in general, contribute to degrading the overall precision of the motes, and, in return, reduce the possibility of achieving the required phase offsets.  
Different alternatives are presented, such as integrating GPS low power chips, atomic clocks and/or external modules to modify the capacity of the antenna to achieve phase offsets on the order of nanoseconds. Unfortunately, these options are not technically feasible or do not provide enough accuracy to perform CB.  
Finally, by relaxing the requirements to perform CB in WSN, we propose and suggest a feasible solution based on random communications, where, under certain circumstances, we could successfully implement a CB to reach a BS located in the far field. In particular, we have suggested a receiver (BS) placed at an LEO satellite. In this case, we found that sending the same message many times from the motes once they have received a beacon signal from the satellite increases the probability of doing beamforming and the superposition of signals could be properly received with adequate equalizing techniques at the satellite. In addition, we find that the same gain is achieved pointing to other angles. We have analyzed both a uniform linear array (1D) and a planar array (2D). From these results, we conclude that the increase in the number of motes given by a 2D array makes it more difficult to attain coherence, and although there is an increase in the CB gain, there is not a linear increase with the number of motes.  
Then, as the main conclusion of this feasibility study, these findings suggest that although optimal CB has some drawbacks, some CB is feasible by repeating the process of symbol transmission; however, the real CB gain is much lower than the expected gain for a perfect array with perfect synchronization.  
This work was supported by the Universitat de Valencia under the projects UV-INV-PRECOMP14-207134 and UV-INVAE15-339582, by the Generalitat Valenciana under the project GV-2016-002, and by the Spanish Ministry of Economy under the project BIA2016-76957-C3-1-R.  
**Author Contributions:** [PERSON] and [PERSON] conceived the idea, proposed the scientific methodology and wrote the paper. [PERSON] performed the simulations and [PERSON] provided the experimental measurements. [PERSON] and [PERSON] contributed to the technical improvements. All authors participated in the review of the related works, analysis of the results, elaboration of the manuscript and its revision.  
**Conflicts of Interest:** The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.