It is noted that energy consumption is not considered

It is noted that energy consumption is not considered for the decompression phase, under the
assumption that the receiver (i.e., the home gateway) is always plugged in the main power supply.
Furthermore, two assumptions are made so as to extract the results presented in following section.
First, it is assumed that when the compression module is not used it is shut down and does not
consume energy; second, it is assumed that when the radio does not transmit it is tuned off and thus
there is no energy consumption.
5.1. Performance Evaluation Setup
In order for the analysis approach presented in the previous section to lead to realistic and useful
results, it is important to present the main hardware components (including the different configuration
options considered) utilized as well as the actual data, comprised by samples taken from real EEG/ECG
signals, which are two of the most demanding modalities in epilepsy monitoring (which represents
our main application scenario).
The most important component influencing our evaluation is the implemented compression
hardware module. As analyzed in Section 4 , the hardware module throughput (thus the delay required
to compress a specific amount of data) depends on the clock frequency based on Equation (1).
The power consumption depends also on the frequency clock. Therefore, we considered four
different clock frequencies; then, we measured the power consumption and based on Equation (5)
the following table has been extracted. Table 5 presents the two main performance metrics of the
compression hardware implementation proposed.
35

Electronics 2017 , 6 , 54
Table 5. Power consumption and throughput performance of compression hardware component.
Clock Frequency
(MHz)
Total Power (mW)
Dynamic Power
(mW)
Static Power (mW)
Throughput
(Mbps)
1 114.27 15.53 98.74 17.09
20 142.38 43.20 99.18 34.19
40 170.07 70.45 99.62 68.39
62.5 198.52 98.45 100.07 106.86
Table 5 depicts also a tradeoff that, as will be proven, comprises a critical factor with respect
to the overall performance evaluation. As depicted, as the clock frequency increases, both power
consumption and throughput also increase. Consequently, when compressing a specific amount of
data increasing the clock frequency implies that, on one hand, the component needs more energy while
active but, on the other hand, it performs its operation much faster, and consequently the time period
required to be active is drastically reduced. A secondary observation concerns the fact that the main
factor of power consumption increase is the dynamic power and not the static power (its influence is
rather negligible).
5.1.1. Short-Range Wireless Communication Radio Characteristics
The second component influencing the system-level performance is the specific off-the-shelf radio
transceivers used to transfer data. In the context of this evaluation, we considered the Shimmer2R
platform [ 25 ] comprising a prominent commercial solution offering highly efficient Bluetooth Class 2.1
as well as IEEE 802.15.4 interfaces.