# Area-Efficient Universal Code Generator for Multi-GNSS Receivers
## 5 Experimental Results  
In the experiment, synthesis and implementation were carried out with Xilinx Vivado 2020.2, and the Kintex Ultrascale KCU105 board was used as the field programmable gate array (FPGA) board. Conventional code generators by GNSS and a previous multi-frequency universal code generator were implemented for comparison with the proposed code generator. All codes generated from conventional, previous, and proposed were the same as the as the code provided from official ICD, implying that all the codes can be used for acquisition and tracking in a GNSS receiver. With the results of the synthesis, the look up tables (LUTs) and registers of the existing code generator and the proposed code generator were compared.  
Figure 6 shows a comparison of the normalized hardware resource use of the proposed multi-frequency universal code generator, the previous universal code generator, and the conventional code generators by GNSS, and it can be seen that the hardware complexity was significantly reduced in the proposed multi-frequency universal code generator. As shown in Figure 6a, the LUT use of the proposed multi-frequency universal code generator for GPS signals is reduced by about 13% compared to the previous universal code generator and about 10% compared to the sum of the hardware resource use of the conventional code generators. In addition, since the previous universal code generator and the proposed multi-frequency universal code generator share the shift registers needed to generate the codes, the resistor use is reduced by about 71%. When comparing the hardware resource utilization for BDS, GLONASS, and Galileo signals, it can be seen that in the case of BDS signals, as shown in Figure 6b, the proposed multi-frequency universal code generator reduced LUT utilization by about 11% compared to that of the previous multi-frequency universal code generator and reduced LUT utilization by about 23% and the register utilization by about 78% compared to the sum of the hardware resource utilization of the conventional code generators. In the case of GLONASS signals, as shown in Figure 6c, the proposed multi-frequency universal code generator reduces LUT utilization by about 18% compared to the previous multi-frequency universal code generator and reduces LUT utilization by about 17% and the resistor utilization by about 78% compared to the sum of the hardware resource utilization of the conventional code generators. In particular, in the case of Galileo signals, since the hardwiring technique can be applied to all of Output Tap1, Output Tap2, and Initial ROM1 as shown in Table 5, the proposed multi-frequency universal code generator could save a lot of hardware resources. As shown in Figure 6d, the proposed multi-frequency universal code generator reduced LUT utilization by about 36% compared to that of the previous multi-frequency universal code generator and reduced LUT utilization by about 37% and the register utilization by about 74% compared to the sum of the hardware resource utilization of the conventional code generators. In conclusion, the proposed universal LFSR structure can generate various codes with single hardware that always requires lower hardware resources than existing studies by applying the hardwiring technique.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**GNSS**} & \multicolumn{3}{c}{**Previous [6]/Proposed Universal Code Generator**} \\ \cline{2-4}  & **MUX** & **XOR** & **ROM** \\ \hline GPS & 100\%/57\% & 100\%/61\% & 100\%/96\% \\ \hline BDS & 100\%/71\% & 100\%/71\% & 100\%/95\% \\ \hline GLONASS & 100\%/46\% & 100\%/41\% & 100\%/95\% \\ \hline Galileo & 100\%/27\% & 100\%/31\% & 100\%/93\% \\ \hline \hline \end{tabular}
\end{table}
Table 6: Comparison of normalized hardware resource use of previous code generator and proposed code generator.