## 1 Introduction  
Wireless Sensor Networks (WSNs) is a group of small devices called nodes or motes. These nodes or motes contain a microcontroller to which a multitude of sensors can be attached and which have the capacity to communicate mainly using the IEEE 802.15.4 [1] standard in the ISM (Industrial Scientific Medical) band. The interest in these types of networks lies in the simplicity of their implementation, the nodes are autonomous elements powered by batteries (AA or AAA of 1.5 Volts), which can be deployed implementing virtually any type of network topology. Once the nodes are installed and working, they transmit the information provided by the sensors to the Base Station (BS), also known as sink or gateway, which in turn can supply the information to an external server. WSNs thus allow monitoring of physical or environmental conditions, such as temperature, sound, humidity, pressure, noise, movement or pollutants. WSN were initially developed for military applications, such as battlefield surveillance. They are now used in a multitude of industrial and civil applications [2], in industrial process monitoring and control, machine monitoring, environmental parameter monitoring, traffic control, healthcare, and automation and habitat monitoring in home automation applications. These networks can also be deployed in areas of difficult access or under very adverse conditions, such as mountainous areas, jungles, deserts, mines, skyscrapers, etc. The duration of the batteries determines the duration of its correct operation which can be months or years, depending on the sensors consumption and the energy used by the transmissions within the WSN for different issues, such as data exchange, routing, synchronization, etc. In many applications the motes have been distributed by means of an aerial procedure in inaccessible spaces, or they have been hidden due to their small size and the difficulties of the terrain, or merely there has not been interest in recovering them after exhausting their batteries. For those cases, the motes are designed to be self-destructible, biodegradable, and sometimes a new deployment is made to change or continue monitoring. The motes used at WSNs are relatively cheap and are designed specifically for these applications. Mainly, the communications between the motes follow the standard IEEE 802.15.4 which imposes limitations to the maximum power of emission, that is 100 mW of power, and this has constrained its development, that among other things allows its operation with batteries AA and AAA using antennas of theoretical gain 0 dBi. This limitation in power has repercussions in the maximum distance that allows the correct communication between two motes. They normally communicate by exchanging packets following a multi-hop routing protocol, in which the motes send the information wirelessly. Commercial motes such as TelosB are said to allow a theoretical maximum distance of 100 m in open spaces. Actually, the experimental tests presented in this article that have been performed with the Cypress CY3271 kit [3] allow up to 80 m in a ground level deployment. This communication range limits the WSN's access possibilities within a radius of at most 100 m of the nearest mote. Notice that communication at great distances would be possible with a \"line\" of motes or WSN deployed in a line that would establish a kind of \"virtual cable\" linking to the BS in a multihop fashion, but this solution is not scalable or flexible. Thus, in this paper we propose an alternative long range communications, by a kind of synchronized transmission in phase from all the motes of the WSN, known as Collaborative Beamforming, Cooperative Beamforming (CB) or Distributed Beamforming [4; 5; 6]. In particular, we propose a way to transmit from WSN to get CB from a limited spatial distribution of motes that must perform a data transmission to a BS located hundreds of kilometers from the monitoring area [7].