## 5 Performance Analysis of Proposed Schemes: MRS-ST-BL and MRS-SD-BL
### Results
#### 5.3.3 Comparison of Average Relay Power of Proposed Scheme MRS-ST-BL with MRS-ST-FB and MRS-ST-WFB  
This section presents the comparison of average power of relay device used in our proposed scheme MRS-ST-BL with MRS-ST-FB and MRS-ST-WFB. The average power of relay selected in HRS (HRS-FB, HRS-WFB, HRS-BL) schemes are not compared because we can see from results obtained in Section 5.3.1 that the performance HRS (HRS-FB, HRS-WFB, HRS-BL) schemes are significantly lower than that of MRS-ST-BL in all the scenarios considered. We show that our proposed scheme MRS-ST-BL enhances the throughput by selecting relay with higher transmission power compared to MRS-ST-WFB, and is the focus of this section. The analysis is done for different social trust scenarios and different node densities. The main result from our analysis is that our proposed scheme MRS-ST-BL selects relay with higher transmission power compared to that of HRS-ST-WFB. As a result, our proposed scheme MRS-ST-BL significantly enhances the throughput of D2D communications. Figure 8 shows the average transmission power of relay of MRS-ST-FB, MRS-ST-WFB and MRS-ST-BL for different social trust scenarios in square network having width of 100 m. The average transmission power of a relay is on the y-axis and radius of search ring is on the x-axis in each of  
the graphs. Each of the schemes analyzed are represented by a line. The blue line with squares represents transmission power of relay for MRS-ST-FB scheme. This scheme is same as that proposed in Reference [10] and has devices with full battery level in the network. The blue line with triangles represents transmission power of relay for MRS-ST-WFB scheme. This scheme is also same that proposed in Reference [10]. The only difference is that devices in the network have variable battery levels and transmit at lowest power possible when their battery level is lower than battery threshold. The blue line with crosses represents transmission power of MRS-ST-BL, a relay selection scheme proposed in this paper. Figure 7(a) shows that the average transmission power of a relay increases with the increase in search radius for all the schemes. The transmission power of relay in MRS-ST-WFB (blue line with triangles) is lower than that of MRS-ST-FB (blue line with squares), as expected. As our proposed scheme MRS-ST-BL (blue line with crosses) also takes battery level into consideration while selecting a relay, it selects a relay with high transmission power compared to MRS-ST-WFB. The selection of higher transmission power can be observed only for large values of search radius. This is because the scenario considered here has very weak social trust among users in the network. Therefore, most of the devices do not transmit at high power even though their battery level is above the threshold value. Figure 7(b) shows that the transmission power of all the schemes increases with the increase in search radius. The transmission power of MRS-ST-BL gradually increases and becomes higher than that of MRS-ST-WFB, which can be observed when the search radius is greater than 20 m. However, for larger search radius, the difference in transmission power of MRS-ST-BL and MRS-ST-WFB becomes small. Figure 7(c) depicts that the transmission power of relay increases with the increase in search radius for MRS-ST-FB and our proposed scheme MRS-ST-BL. Our proposed scheme MRS-ST-FB selects relay with high transmission power by probing devices having high social trust as well as device battery level above battery threshold. The importance of the battery threshold is quite evident in the transmission power of a relay in MRS-ST-WBL. Interestingly, the transmission power of relay in MRS-ST-WFB is not improved for larger search radius. MRS-ST-WFB filters devices based on social trust, not based on battery level. Therefore, when a device having high social trust but with low battery power is selected as a relay, it transmits at a low power. As a result, throughput of D2D communication is reduced compared to our proposed scheme MRS-ST-BL.