## 2 Related Work
### Practical Implementations  
We could end this section by saying that the most objective indicator of the state of the art in CB-DCB is the number of practical applications in which it has been carried out, and we come to the conclusion that its viability is limited, mainly by the difficulties of synchronization [14]. The first work that reports results that are close to 90% of the theoretical estimates uses three emitting nodes with FPGA (Field Programmable Gate Arrays), [20] and synchronizing in closed loop with transmission from the receiver to the WSN of 1-bit, an FPGA presents more complexity for the developer than a commercial mote. The second is for a WSN transmitting at 60 GHz [51], but no details are given of the hardware to reproduce the results. In 2010 with a time-slotted round trip synchronization method, a prototype is built with acoustic signals, called Acoustic Cooperative Communication Experimental Network Testbed [52], but it is not the same to perform beamforming with acoustic signals where the speed of sound is 340 m/s that with radio frequency with the speed of light 2.99792 \(\times\) 10\({}^{8}\) m/s, because the offsets in beamforming are related to the wavelength, \(\lambda\) = \(c/f\). In [53] a WSN was introduced that used analog signals to synchronize but was unstable. Finally, in 2012 [54] the first CB-DCB that synchronizes time phase and carrier with closed-loop synchronization with 1-bit exchange was introduced. It was implemented with Software Defined Radio and used a Kalman filter predictor [54], which is obviously very complex to perform on a simple commercial mote like the ones we use. In a work published in 2011, [55], a prototype was implemented without feedback from the receiver and without synchronization in phase and carrier with two emitting nodes. This work was extended to four nodes later [56].  
From the analysis of the experimental set-ups, it can be seen that Universal Software Radio Peripheral (USRP) are the preferred hardware elements when implementing CB-DCB. The networkscontain at most four elements with a single destination, and the experimental results presented are close to the theoretical calculations on which they are based. But only [PERSON] et al. [55; 56] show experimental results with WSN developed with very simple and basic motes in line with the work presented in this article. In our work we make use of a synchronization signal coming from the BS that reaches all the motes of the WSN, the BS plays the role of master node that requires the synchronization of all the nodes of the WSN.  
In this paper we present a way to circumvent the problem of time synchronization in CB-DCB, with very simple motes, very basic low-cost hardware. In our case the evaluation metric will be SCB gain that is related to RSS in the receiver. We obtain time offsets measured experimentally in low-cost commercial motes and use them to derive the gain under various experimental assumptions. We demonstrate in a semi-empirical way that around 60-80% of the ideal theoretical results could be obtained. The SCB we propose is semi-blind open-loop synchronization, in which a master node is defined within the WSN that coordinates the synchronization of all slave nodes with the information they will transmit [16], when they receive the activation bit from the BS. A simple algorithm is presented and this algorithm is tested by means of a Monte Carlo procedure. This work also presents real measures of signal range in various situations of real deployment to monitor parameters of agricultural interest and the previous procedure is proposed and tested for a future practical implementation, on the ground.