## 5 Latency and Reliability Performance Evaluation in Wearable-Based MCPTT Applications
### Evaluation Methodology and Parameters  
We utilized network simulator 3 (ns-3) for the performance evaluation of MCPTT application requirements. Specifically, this evaluation was conducted based on the LTE-EPC network simulator (LENA) updated with D2D communications and MCPTT services. Such updates are supported by the research community and were first published in [41]. Further, we extend the LENA module with the features needed for the simulation of public safety scenarios and wearable devices. In detail, we consider scenarios in which the cellular network is deployed in the 700 MHz frequency band. In terms of wearable device modeling, an empirical off-body propagation loss model is implemented to better capture the signal propagation between wearable devices [42]. We also updated LENA's adaptive modulation and coding model with the reduced baseband capabilities that are provided by the 3 GPP physical layer specifications [43]. In 3 GPP specifications, the term bandwidth-reduced low-complexity (BL) is used to indicate the implementation of LTE-M device categories. More precisely, 3 GPP TS 36.213 provides the recommendations for complexity reduction and baseband configuration of these devices. As part of these recommendations, BL UEs have a maximum bandwidth of 5 MHz, a 16 QAM maximum modulation scheme in both uplink (UL) and downlink (DL), and one Tx/Rx antenna. These and other wearable device-related parameters are declared in Table 3 along with D2D and MCPTT application-related parameters. \begin{table}
\begin{tabular}{l l} \hline \hline
**Wearable Device-Related Parameters** & **Value** \\ \hline UE category & LTE Cat M2 \\ \hline Max. bandwidth & 5 MHz \\ \hline Max. UL/DL modulation order & 4 (16-QAM) \\ \hline UE transmission mode & 1 (1 Tx/Rx antenna) \\ \hline UE power class & 5 \\ \hline UE transmit power & 20 dBm \\ \hline UE noise figure & 9 dB \\ \hline
**D2D-Related Parameters** & **Value** \\ \hline Sidelink transmission mode & Mode-2 (autonomous) \\ \hline Sidelink MCS & 10 \\ \hline Sidelink allocation size & 5 RBs \\ \hline kTRP & 1 \\ \hline PSCCH period & 40 ms \\ \hline PSCCH/PSSCH ratio & \(1/3,1,3\) \\ \hline
**MCPTT Application-Related Parameters** & **Value** \\ \hline Functional mode & Off-network \\ \hline Types of calls & private and basic group calls \\ \hline Message size & 60 bytes \\ \hline Inter-packet interval & 20 ms \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Performance evaluation parameters. In terms of the network layout and the MCPTT functional mode adopted in this performance evaluation, we focus on off-network MCPTT services with out-of-coverage UEs. An illustration of the evaluation scenario can also be seen in Figure 1. As discussed in Section 3.1, out-of-coverage UEs are restricted to using sidelink transmission mode-2. Notably, the resource allocation approach without the network side's assistance is widely applied in public safety scenarios [44]. Therefore, we utilize this autonomous mode for resource allocation in D2D communications as depicted in Table 3. MCPTT off-network mode supports several types of calls [45]. In this paper, we focus on MCPTT private and basic group calls. A private call is established between two MCPTT applications for two users to communicate. A basic group call is a call where a group of users that are associated with a particular group ID contend to talk. The term \"basic\" is used in 3 GPP specifications to point out the difference between these types of calls and broadcast group calls. In the rest of the paper, MCPTT basic group calls will be simply referred to as MCPTT group calls. Five UEs participated in our MCPTT group calls. Before a D2D communication takes place on the Physical Sidelink Shared Channel (PSSCH), a sidelink grant needs to be preconfigured.