# From Sensor Networks to Internet of Things. Bluetooth Low Energy, a Standard for This Evolution
## 3 Related Work  
Although BLE is a very recent technology, and its standard has not a specification for a mesh network topology yet, there are interesting works analyzing the BLE standard and related applications: the Array of Things project of Chicago [22]; inter-vehicular communications [23]; power management in smart homes [19]; passengers control [24] or remote lock system [25]. However, our main focus is on papers related with mesh transmission using BLE. In [26], authors propose BLEMesh, a mesh network topology for BLE that takes advantage of the broadcasting capabilities of wireless networks. To reduce  
Figure 5: Paper road map.  
the number of packets retransmitted through the network, BLEMesh uses an opportunistic routing method. However, this proposal does not satisfy the Zero fails requirement of Industry 4.0. In [27] a light evaluation of a prototype of CSR mesh has been showed using the metric packet delivery ratio. After a not very clear study case, authors use the Octave simulator. They conclude that more studies are needed. In [28] authors implement a synchronization protocol. With this protocol nodes can not transmit in broadcast mode and then it will be impossible the free movement of the nodes such as smartphones, smartbands or different tools or instruments in the industry 4.0 environment.  
On the other hand, the Bluetooth Special Interest Group (SIG) has officially announced the formation of the Bluetooth Smart Mesh Working Group, which will build the architecture for standardized mesh networking capability for Bluetooth Smart technology [29]. A new Bluetooth specification, Bluetooth 5 [30], has just been appeared, but there is no extra information about the mesh topology.  
Well-known companies have also shown interest in incorporating this new functionality to BLE technology. The most important initiatives are the Nordic Semiconductor [31] and Cambridge Silicon Radio (CSR) [32]:  
* The Nordic project [33] was created in collaboration with the Norwegian University of Science and Technology [34] as part of a thesis and is not part of the official SDK of Nordic Semiconductor. This is an open project, which uses the broadcast data transmission. This project uses Nordic series nRF51 [35] devices. These devices use BLE version 4.0, which causes packet loss in the mesh, because devices are not able to receive packets while they are retransmitting those already received.
* CSR is a company that has opted for the development of a mesh network topology for BLE. CSR has developed devices which use BLE version 4.1: the smart Bluetooth CSR101x family [36], as well as a proprietary protocol built on BLE, called CSRmesh [37]. This protocol allows to create a mesh topology by transmitting and receiving broadcast packets, like other projects.  
However, mesh topology is not an exclusive BLE topology: ZigBee uses mesh topology to deploy low-power WSN [13; 38], it is also well-known in Wi-Fi [39; 40] and it allows connections among smartphones or tablets. However, BLE technology allows us to unify the advantages of both alternatives: to create low-power WSNs which are able to connect directly with users, using their smartphones.  
This BLE network topology proposals open a new possibility in the Industry 4.0, because it will allow us to cover large areas completely. Thus, static or mobile (users) devices which are in the mesh can communicate with the mesh server or any other mesh device, regardless of their location.