# Compression of GNSS Data with the Aim of Speeding up Communication to Autonomous Vehicles
## 7 Results  
This compression method contains three steps:  
1. The difference method is based on H.264. 2. Mapping. 3. Huffman coding. One of the significant advantages of this compression method (compared to zip compression) is that ours has error resilience because of the Huffman Codes [5]. ZIP does not have this attribute of error resilience, and it is almost impossible to recover damaged files. In addition, if the files using ZIP were sent in parts and one part were not received, then the information could not be recovered at all [57]. In each message transmission using the method proposed in this paper, we send a first packet that is always original and without any changes. Therefore, because of this feature, we recover the subsequent packets. If some of the packages are lost, because of the Huffman property of synchronization, we would recover the rest of the information at a relatively high speed. In addition, the first packet is transmitted at a certain frequency each time the number of messages in the GPGSV protocol changes. Therefore, when there is a change in the GPGSV protocol, the existing file is closed, and a new file is opened in a renewed procedure, and thus we create additional error resilience to information loss due to the repeatability of the first package. This durability does not exist in the Zip compression method (not in real time). If some of the information does not arrive or goes wrong in transmission, ZIP will not be able even partially to restore the information. The suggested method of compression has been evaluated by several benchmark tests employing real GNSS information obtained from the GNSS of real vehicles. We tried Zip as it is, as well as Diff' the method employing the concept of H.264 described above. The output of Diff was sent to [PERSON], Zip, and a mapping of repeated strings before doing the Zip. We have marked in bold in the following tables the method we propose in this study, the winning method among all those tested and reviewed. The results of the first benchmark are detailed in Table 1 (GNSS data file and compression results). In the next results, we will be able to see a slight improvement with larger files, but at a certain stage, the improvement is not significant, and the results remain about the same numbers. We see that after calculating and using the difference method (Diff file), which is a preprocessing stage, we get a reduction of 28%. The significant gain is not just the gain \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Name and Pure**} & \multicolumn{5}{c}{**Compression Method and Ratio.**} \\ \cline{2-6}  & \multirow{2}{*}{**Size of File:**} & \multicolumn{3}{c}{**Ratio=100 – \(\frac{\text{result}}{\text{Total}}\times\)100**} \\ \cline{3-6}  & & Zip & Diff & **Diff\&Huff\&Zip & Diff\&Mapping\&Zip \\ \cline{2-6} Test 1 = 286 KB & 28 KB & 207 KB & **37 KB** & 25 KB & 19 KB \\ (Total) & 90.21\% & 27.62\% & **87.1\%** & 91.26\% & 93.36\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison between different compression methods–source file is 286 KB. of 28% but the number of zeros we get after the differences. These help us to compress the information more efficiently using the Huffman code and achieving better significant compression percentages. After using the difference method, which is a preprocessor for Huffman coding, we will get a significantly better compression ratio (compared to the original file), of about 87%.Nevertheless, if we want to improve and compete with ZIP, first we perform the difference method, which preprocesses for Huffman, and then directly apply ZIP compression and thus get a better compression percentage of about 91.3% compared to about 90% by directly using ZIP on an original file  
Furthermore, it is possible to compress even better after performing the difference method, then using the mapping method, and then Zip; the result is significantly better--93.4%. Naturally, we must take into account that the world is not perfect and sometimes successes come at the expense of something else.