# An Experimental Study on D2D Route Selection Mechanism in 5G Scenarios
## 3 Related Work
### USRP/GNU Radio and RP3 Testbeds
#### 3.2.2. USRP/GNU Radio with RP3 Testbeds  
In [15; 28; 31; 32; 33; 34; 35], testbeds consist of USRP/GNU radio nodes equipped with separate RP3 processing unit, which serves as the decision-making engine. This enables both control messages and data packets to be transmitted over wireless medium. The effect of criteria, such as the ambient noise, as well as interference from other devices, are naturally affecting the end-to-end delay and packet delivery ratio. All experimental results were gathered in the same operating environment in the laboratory. The nodes use similar devices, specifically USRP with GNU radio units connected to RP3 to minimize the differences in signal volatility and inconsistency in communication. Experiment has been conducted under the similar operating environment in the literature [13; 14; 15; 24; 28; 33; 34; 35]. In the literature, RP3 has been used to:  
* generate frequency modulation (FM) signals within a range of frequency bands [38]. Measurement using a spectrum analyzer shows that the FM signals, despite being transmitted using a lower transmission power, have close quality to the signals transmitted by radio stations. Energy consumption has shown to reduce at the expense of a lower throughput. * perform channel sensing to detect white spaces [29; 39], and subsequently access the available channels to reduce interference to PUs' activities [29]. Measurement shows that RP3 consumes energy in computation (e.g., using the available memory in kernel to run GNU radio libraries) and software initialization [39]. Energy consumption has shown to reduce at the expense of a higher delay [14; 39], which is up to twice the amount of energy consumption in a PC [Unclear] [29]. * send location information from an unmanned aerial vehicle (UAV), which is a dynamic node, to a ground BS, which is a static PC, so that the ground station can monitor the location of the UAV [40]. Energy consumption has shown to reduce, while the communication and information processing capabilities of RP3 are sufficient [40]. * generate and exchange signals between a RP3 embedded in a register transfer level (RTL) dangle and a PC embedded in a USRP/GNU radio unit using the 915 MHz bands, the 40.68 MHz FM bands [41], and the 24-1850 MHz bands. In [42], pulse width modulation signals are generated. Investigations show that: (a) energy consumption reduces, and it is less than 3 watts [42], which can be sufficiently powered by batteries; (b) the quality of the received signals depends on the height of the antenna and the transmission power [40]; and (c) the communication capability of RP3 is sufficient [40]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Experimental Testbed in the Literature**} & \multicolumn{2}{c}{**Use of USRP/GNU Radio with RPS**} & \multicolumn{2}{c}{**Number of Nodes**} & \multicolumn{2}{c}{**Number of Links for**} & \multicolumn{2}{c}{**Network Scenario with Heterogeneous Nodes**} \\  & **(Represents That This Type of Testbed Is Used)** & **in the Testbed** & **D2D Communication** & **(Represents That the Network Scenario Has Heterogeneous Nodes)** \\ \hline [PERSON] et al. (2017) [14] & Yes & 1 & 0 & No \\ \hline [PERSON] and Unibert (2016) [15] & No & 6 & 0 & No \\ \hline [PERSON] et al. (2016) [25] & No & 5 & 4 & Yes \\ \hline [PERSON] et al. (2014) [26] & No & 6 & 5 & Yes \\ \hline [PERSON] et al. (2014) [27] & No & 9 & 8 & Yes \\ \hline [PERSON] et al. (2016) [31] & Yes & 3 & 2 & Yes \\ \hline [PERSON] et al. (2015) [35] & No & 5 & 0 & No \\ \hline [PERSON] et al. (2014) [37] & No & 6 & 0 & No \\ \hline [PERSON] et al. (2019) [38] & Yes & 2 & 0 & No \\ \hline [PERSON] et al. (2018) [39] & Yes & 2 & 0 & No \\ \hline [PERSON] et al. (2017) [25] & Yes & 4 & 3 & Yes \\ \hline [PERSON] et al. (2018) [40] & Yes & 2 & 2 & Yes \\ \hline [PERSON] et al. (2016) [30] & No & 10 & 0 & No \\ \hline Our testbed & Yes & 9 & 8 & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Experimental testbed comparison between literature and this paper.