## 3 Performance Evaluation of Combinations of Modulation and Spreading Code Techniques
### Combinations of Modulation and Spreading Code Techniques
The transmission power of the pulse is inversely proportional to the number of transmitted pulses. The number of time slots \(L_{max}\), the number of pulses \(N_{p}\), and the pulse peak power \(E_{TX}\) were determined for each measurement point depending on the combinations of block partitioning, modulation scheme, and spreading code. According to combinations of these techniques, the \(L_{max}\) and \(N_{p}\) used for each measurement point are shown in Table 12, and \(E_{TX}\) is described in Table 13. OOK allocates one time slot per bit, so the number of time slots was constant regardless of the partitioning of the block. PPM, DPPM, and DPIM were different from each other in their numbers of '1's and their average block sizes, but their number of time slots was the same according to the maximum block size, indicating whether a transmission is possible within a given time. These three modulation methods are identical regarding the parameters required to measure the performance of the LIDAR system, even though the symbol representation is different. DH-PIM had the advantage that the average and maximum block sizes were both smaller than those of PPM, DPPM, and DPIM. However, it had the disadvantage that the number of '1's required for representing a block was large. If the number of slots corresponding to '1' was larger, the pulse peak power was smaller. Unlike other modulation methods, in which the number of '1's is fixed, DH-PIM changes the number of '1's according to the block. MPPM had the advantage that the average and maximum block sizes were the smallest among the modulation schemes. However, as in the case of DH-PIM, the number of '1's needed to represent a symbol was increased, so the pulse peak power was reduced. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Block Partitioning** & **OOK** & **PPM** & **DPPM** & **MPPM** & **DPIM** & **DH-PIM\({}_{2}\)** \\ \hline
**1:2:2:2:2** & 9, 9 & 5, 17 & 5, 17 & 9, 17 & & \\
**2:2:2:2:1** & & & & & 5, 17 & 9, 17 \\
**1:2:3:3** & 9, 9 & 4, 21 & 4, 21 & 7, 15 & & \\
**2:3:3:1** & & & & & 4, 21 & 7, 17 \\
**1:4:4** & & 9, 9 & 3, 33 & 3, 33 & 5, 13 & & \\
**4:4:1** & & & & & 3, 33 & 5, 21 \\
**1:5:3** & 9, 9 & 3, 41 & 3, 41 & 5, 15 & & \\
**5:3:1** & & & & & 3, 41 & 5, 25 \\
**1:6:2** & 9, 9 & 3, 69 & 3, 69 & 5, 17 & & \\
**6:2:1** & & & & & 3, 69 & 5, 29 \\
**1:7:1** & 9, 9 & 3, 131 & 3, 131 & 5, 21 & & \\
**7:1:1** & & & & & 3, 131 & 5, 70 \\
**1:8** & 9, 9 & 2, 257 & 2, 257 & 3, 25 & & \\
**8:1** & & & & & 2, 257 & 3, 131 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Possible block partitioning according to block partitioning and modulation techniques. A bold ’**1’** shows a leading ’1’ or a trailing ’1’. Each cell expresses the modulated results as a 2-tuple \(\left(N_{p},L_{max}\right)\). The combination of using OOK as the modulation technique and PC or MPC as the spreading code technique had the smallest number of time slots. In this case, the number of time slots was always 225, regardless of the size of the block partition. The highest number of time slots was required when the block was divided into eight bits, the PPM was used as the modulation method, and the OOC was used as the spreading code technique. In this case, a total of 7969 time slots were required, and since