# Simplified Derivative-Based Carrierless PPM Using VCO and Monostable Multivibrator
## 1 Introduction
### Literature Review  
PPM has evolved across various communication domains, including optical fiber, free-space optics, and underwater laser communication [3; 4; 5; 6; 7]. It has been implemented in analog and digital forms [8], with innovations targeting improved synchronization [9], demodulation accuracy [10], and bandwidth efficiency [11; 12]. Recent designs have integrated PPM with OFDM, PWM, and other hybrid schemes [13; 14], aiming to increase spectral efficiency and robustness.  
Traditional PPM demodulation involves converting received signals into PWM, then applying low-pass filtering or integrating them for message recovery [15; 16]. These methods are straightforward for carrier-based PPM, but carrierless variants require additional processing, such as carrier reconstruction using PLLs or time-to-voltage conversion techniques [17; 18; 19; 20; 21; 22]. Other studies explore PFM and selective pulse methods to improve demodulation flexibility [23; 24].  
Spectral analyses confirm that both PWM and PPM belong to the phase modulation family, though practical implementations remain complex. Hybrid modulation schemes and energy-efficient transceivers have shown performance gains, but with increased circuit intricacy [25; 26; 27; 28; 29].  
While the building blocks used in this study--taking the derivative of the message signal, voltage-controlled oscillators, and monostable multivibrators--are well-established, this work draws insight from common principles across multiple PPM demodulation strategies to construct a new, low-complexity carrierless PPM modulation scheme. The resulting architecture eliminates carrier reconstruction and aligns well with compact, cost-sensitive platforms such as Internet of Things (IoT) systems [30]. By integrating foundational concepts in a novel configuration, this approach addresses implementation challenges in carrierless PPM and demonstrates practical advantages.  
Several studies have analyzed pulse position modulation (PPM) in terms of bandwidth trade-offs, implementation complexity, and modulation comparisons. While many existing techniques rely on digital processing, complex synchronization, or hybrid signal processing, the proposed method adopts a refined analog design with a differentiator, VCO, and monostable multivibrator. Table 1 provides a concise overview of relevant works, including various implementation approaches. In contrast, the proposed technique leverages a practical design, offering a carrierless and hardware-optimized solution for pulse position modulation.  
\begin{table}
\begin{tabular}{p{42.7 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Ref. No.** & **Authors/Title (Year)** & **Application/System Context** & **Advantages** & **Limitations** & **Comparison to Proposed Method** \\ \hline \multirow{4}{*}{[2]} & \multirow{4}{*}{[PERSON] et al. (2009)} & PLL-based analog PPM circuit with carrier/no-carrier options & Simple tuning, carrier/no-carrier options & Requires PLL, RS implementation complexity & Proposed system eliminates PLL and flip-flop, yielding lower complexity and fewer analog blocks \\ \cline{1-1}  & & & & & \\ \cline{1-1}  & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of selected related works on PPM and their comparison to the proposed method.