IN-PHASE QUADRATURE DEMODULATOR FOR FRAME SYNCHRONIZATION PROCESS AND DTMF ENCODER IMPLEMENTATION

• Main Author: Dzaki Mubarok, Hilman
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/87736
• Institution: Institut Teknologi Bandung

Rapid evolution in communication technology have not been followed by robust security system. Many user feel worry about the potential for unauthorized third-party access ?ttheir communications. Several communication technologies ojfer security products, none can guarantee absolute and uncompromised security. This has created a vulnerability in voice communication devices and networks, leaving users susceptible to spyware and malware attacks. Recent technologies often offering end-to-end encryption for data protection. However, there is always the possibility of data manipulation or the insertion of additional data that could corrupt the information. Therefore, it is crucial for communication devices and networks to be able to identify all transmitted data ?tprevent unauthorized insertions r? manipulations. Additionally, factors such as the border of data flow and transmission time should be considered. The proposed system aims to secure voice communications by scrambling the audio signal in the frequency domain. After scrambling process, Dual-Tone Multi-Frequency (DTMF) tones are added and transmitted to the receiver device. The receiving device, equipped with a DTMF detection system, is responsible for decoding the scrambled data stream. A DTMF detection system requires a time limit or marker to identify detectable DTMF tones. To fulfill this requirement, a frame synchronization system is necessary to provide markers for the DTMF detection system. Frame synchronization is essential as it allows the receiving device to identify the arrival time of data streams or the border of received data frames. This paper focuses on the use of in-phase quadrature demodulation with an added detection scheme or marker for frame synchronization to determine the border of received DTMF data streams. Furthermore, to support the receiver's process of interpreting the received key, a DTMF encoder is required to process and compare the results of Goertzel's algorithm and send the key data to the descrambling process. The designed frame synchronization process is consists of two blocks: a calculation process using in-phase quadrature demodulation based on a QPSK receiver and a detection block for processing the calculation results and finding the appropriate conditions. The DTMF encoder is designed to compare the received input values. The comparison is performed according to the DTMF frequency groups (low or high), followed by identification using a scheme that represents DTMF as a 3-bit value. The designed system performs as expected, although there are differences in the calculation process that didn 't affect the detection process. The detection process takes 60 ms with a detection shift of 5 batches. The DTMF encoder successfully produces a 24-bit output, representing the 8 detected DTMF tones.