# Performance Evaluation of Bluetooth Low Energy: A Systematic Review
## 3 BLE Performance
### Power Consumption  
The main innovative characteristic of BLE, in comparison with Classic Bluetooth and other wireless technologies, is the low power consumption. Indeed, as described in Section 2.2, both in _broadcasting_ and _connection_ mode, the RF module turns on to send or receive data and then turns off in order to save energy consumption. Bluetooth SIG affirms BLE has a current consumption, on average, lower than ANT+ by a factor of 1.5\(\times\) and ZigBee of 2\(\times\)[74]. STMicroelectronics provides a simulator [68] to evaluate and measure the power consumption during all possible states of the BLE IC RF module, BlueNRG-MS [69], also managing all the parameters. To evaluate the power consumption of a BLE IC, it is necessary to evaluate the average current absorbed during the active phase in each modality of communication. In fact, on the other side, when the radio is in the sleep phase, the current consumption is approximately 1 \(\upmu\)A (with 3 V of reference voltage level) [75]. In _broadcasting_ mode, the _advertiser_ sends a packet on the three advertising channels in each _advInterval_. Therefore, it is easy to notice that the consumption is directly proportional to the packet data length and to the number of channels used to communicate, while it is inversely proportional to the _advInterval_. In scanning mode, the average current consumption is only related to the _Scan Window_, which determines the active phase, and the _scanInterval_, which indicates the time between two active phases. Moreover, the energy consumption during the active scanning is higher than the passive scanning, described in Section 2.3, because the _advertiser_ is set to listen to other requests from the _scanner_. An analysis of the power consumption of a BLE _broadcasting_ mode during the discovery process has been done by [PERSON] et al. in [76]. They measured in detail the current consumption in each phase during the advertising mode using the BLE IC CC2541 [77] by Texas Instruments (using 3 V of reference voltage level). The results show that the current consumption in the active phase of advertising is ~10.9 mA. That means that the total current consumption during advertising, with the minimum _advInterval_ of 20 ms, is ~2.3 mA. Moreover, they validated an analytical model of energy  
Figure 15: Theoretical maximum number of _slaves_ per piconet for various types of interaction between devices, scheduling schemes and _connInterval_. The different types of interaction examined are the _one-way_ and _round-trip_ communications (described in Section 2.2.2). Moreover, the analysis has been done in the ideal case of non-overlapping communications, as well as in the case of overlapping, which denotes the upper bound limit. Adapted from [50]. consumption in advertising mode, depending on the variable parameters that define this type of communication (_advInterval_, _scanInterval_ and _Scan Window_). A comparison and a new model to evaluate power consumption during the discovery process has been proposed by [78]. They found that the results about the energy consumption are comparable with [76], but they proposed a more precise model when the _advInterval_ is higher than the _Scan Window_; see Figures 16 and 17. They assumed that the operating voltage of a device is constant, so that the energy consumption can be assessed as the device current multiplied by the elapsed time. Figure 16: Average discovery latency and energy consumption of the _advertiser_ according to \(T_{a}\) (\(T_{s}\) = 1.28 s and \(T\) = 10.24 s) [78]. The green line shows the model proposed by [76], while the black and blue lines positioned in the lower part show the models analyzed in [78]. The crosses represent the simulation based on the theoretical model. As can be noticed, when \(T_{a}>T_{s}\), the two results do not agree anymore. On the other side, the red line [79] and the two blue and black lines positioned in the upper part of the figure represent the data relative to the latency, analyzed in Section 3.4.