# Enabling Trustworthy Multicast Wireless Services through D2D Communications in 5G Networks
## 5 Performance Evaluation  
A simulative analysis in MATLAB (MathWorks, Natick, MA, USA) has been performed to study the performance of the proposed eCMS-sD2D protocol. The considered scenario consists of a variable number of users uniformly distributed in a single LTE-A cell of dimensions 100 m \(\times\) 100 m, with available bandwidth of 20 MHz, which corresponds to 100 RBs. A Time Division Duplex (TDD) LTE frame type 2 configuration 3 is used. Each slot (or Transmission Time Interval, TTI) in the frame lasts 1 ms, so the entire frame has a duration of 10 ms. The inband D2D mode is chosen, so uplink slots are reserved to D2D communications. In the downlink slots, a multicast transmission allows for sending data to in-coverage devices. The performance of the proposed eCMS-sD2D protocol is evaluated on the basis of the following metrics:  
* _Data loss_ in D2D communications because of an unreliable transmitter;
* _Mean Throughput_, measured as the mean data rate value experienced by the D2D receivers. It is independent of the nature of the communication transmitter (i.e., if it is malicious or not). In particular, even if the data transmitter is a malicious user, the amount of data it delivers is counted in the throughput computation;
* _Mean Goodput_, measured as the mean useful data rate value experienced by the D2D receivers (i.e., rate of data that has been forwarded by non malicious transmitters). This metric takes into account the reputation of the user. In fact, if an RN behaves maliciously, the amount of data that it delivers does not cause a goodput increase;
* _Aggregate Data Rate (ADR)_, computed as the sum of the data rates experienced by the D2D receivers;
* _Good Aggregate Data Rate (ADR)_, computed as the sum of the useful data rates experienced by the D2D receivers;
* _Mean number of malicious nodes_ accounting for malicious D2D receivers that have been served and selected relay nodes;
* _Mean number of malicious relays_ that have been selected to transmit data in D2D communications. In the following simulation results, we will compare our proposed eCMS-sD2D with respect to the existing protocol presented in [5], in which the security of D2D communications is not guaranteed. Under eCMS-sD2D, we analyze its performance with three different values of the maliciousness threshold (equal to 0, 40, and 80). We assign to each node a nature (malicious or non-malicious) and we assume that it does not change over time. Thus, our analysis can be seen as a sort of worst case analysis. The results in terms of mean throughput and goodput are presented in Figure 3a,b, respectively, under increasing percentage of malicious UE. By looking at Figure 3a, we can notice that curves are almost overlapping because throughput does not depend on security. In fact, D2D-SF and our proposed eCMS-sD2D achieved really similar throughput values and the experimented data rate is independent from the percentage of malicious users. Differently, the results in terms of goodput depicted in Figure 3b are substantially different. In fact, D2D-SF exhibits significantly lower performance with respect to eCMS-sD2D that achieves goodput values as close to the throughput as the maliciousness threshold is lower. In detail, as the threshold increases, eCMS-sD2D becomes less selective, therefore more similar to D2D-SF, in which no selection is applied in the choice of RNs. On the contrary, when the maliciousness threshold is set to zero, eCMS-sD2D shows the better results since nodes that behaved maliciously just once are also not selected as RN. A similar reasoning holds for the ADR metric. In fact, we can appreciate in Figure 4 that, while the ADR is almost identical for eCMS-sD2D (under all maliciousness thresholds under analysis) and D2D-SF, the good ADR is significantly lower than ADR when no security mechanism is implemented (see the last pair of bars). Furthermore, we highlight that the increment of the maliciousness threshold causes a performance degradation since security mechanisms are less stringent.