# Opportunistic Sensor Data Collection with Bluetooth Low Energy
## 6 Conclusions  
BLE has become one of the most adopted technologies in the low-power wireless domain. Given its dominant position in several specific markets, such as smartphones and other consumer electronics devices, BLE is a primary candidate to enable OSDC.  
We have investigated the feasibility and the trade-offs of using BLE as a technology for OSDC from a comprehensive perspective, considering the two main approaches that we have identified (namely, advertisement-based, and connection-based approach), and the main BLE configuration parameters. We have developed analytical current consumption and sensor node lifetime models, derived from the behavior of a real BLE platform, as well as maximum amount of collected data models. We have also studied the energy cost of OSDC, and we have explored hardware limitations on the achievable performance.  
Assuming BER = 0, and for a contact time of 45 s, the sensor node lifetime can be as high as 5.3 years and 1.3 years, for the advertisement-based and for the connection-based approaches, respectively, while exploiting the contact interval for data collection. There exists a trade-off with the amount of data that can be collected during the contact interval, which depends on _advInterval_, especially in the advertisement-based approach. If the amount of data to be collected is below \(\sim\)42 kB, the advertisement-based approach suffices. Otherwise, the connection-based approach should be used, which allows the collection of up to 10 to 100 Mbit. The connection-based approach is between 1 and 5 orders of magnitude more efficient in terms of energy consumed per collected bit than the advertisement-based approach. In the former, influence of _comInterval_ on the current consumption and sensor node lifetime is not significant, while an unsuitable setting for this parameter may theoretically decrease the amount of collected data by 13.6%. In the same approach, _advInterval_ has a significant impact on the sensor node lifetime, while influence of this parameter on the amount of data that can be collected is limited to up to 22% in relative terms, for the contact time values we have considered.  
Channel errors do not affect sensor node lifetime in the advertisement-based approach, therefore favoring sensor node lifetime predictability. In this approach, the energy cost per collected bit increases significantly in the presence of channel errors only for very high BER (e.g., \(10^{-3}\)). In the  
Figure 25: Measured amount of collected data as a function of distance between sender and receiver, in the university campus and beach scenarios.  
connection-based approach, both current consumption and amount of data collected decrease with BER, although the latter decreases to a greater extent, leading to significant increase of energy cost per collected bit for moderate BER values (e.g., \(10^{-5}\) to \(10^{-4}\)), compared with error-free scenarios.  
We have also conducted amount of collected data and throughput experiments with a long range BLE platform. We have measured a maximum throughput of 156.5 kbit/s, which can be achieved for _connInterval_ values below 20 ms. Radio buffer limitations, among others, do not allow to achieve the maximum theoretical performance of BLE, thus limiting the maximum amount of collected data per connection interval. On the other hand, link delivery performance only decreases for a distance between the two link endpoints beyond 200 m with the platform considered.  
This work was supported in part by the ERDF and the Spanish Government through projects TEC2012-32531, TEC2016-79988-P, and FEDER.  
[PERSON] evaluated the analytical models, programmed the BLE devices, and performed all experiments and measurements. All authors contributed to the design and writing of the paper, the development of the analytical models, and the analysis of empirical results.  
The authors declare no conflict of interest.