الفهرس 
Characteristics of Transmission SystemOnly 14 pages are availabe for public view
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Abstract
The processes of digital data transfer in both the transmitting and receiving operations with high speed represents a big challenge in communication today. The aim of the present work is to design a new technique to accelerate transmitting/receiving data. Digital data can be sent over a very long distance with low cost using the telephone line by converting the voltage levels into tones. This conversion from binary to tones is done with modem (modulator-demodulator). Modulation is the process of changing some property of an electrical wave (called the carrier) in response to some property of another signal (called the modulation signal). The available properties of the carrier that can be changed are the amplitude, frequency, and phase. In serial transmission only one bit of information can be transmitted over the transmission medium at a time. To transmit ‘n’ bits at a time on a single wire with one type of modulation technique we need 2n different modulation levels. Combining two or more types of modulation reduced this number of necessary modulation levels per each type but still with total 2n, as in case of quadrature amplitude modulation, and this will be on the price of circuit accuracy and complexity in both modulation and demodulation processes. The present work introduces the design of a new simple modulation technique to accelerate the process of transmitting/receiving n bits at a time, on one single wire and for very long distance, with much reduced modulation levels. This new modulation technique makes use of a composite bit position based frequency modulation (CBP-FM) where each individual frequency in the composite signal is a bit position based value. This method needs to compose and decompose up to only n/2 different frequencies, where n is the number of bits to be transmitted at a time. The new designed system based on microcontroller and makes use of the pulse width modulation (PWM) technique in the modulation phase to encode the transmitted data. In the demodulation phase the designed system uses tone detectors circuitry in order to decode the incoming composed signal to its original digital form in the receiving process. The composite signal is generated with the summation of no more than four individual frequencies, and decoded by using an intelligent XOR circuitry in the decoding process. By this CBP-FM technique one single composite signal can be used for sending/receiving the information of one complete byte (n=8) on a single wire with speed 8 times faster compared with the normal serial transmission of each individual bit. The brief description of the subjects and contents of each chapter of this thesis are given in the following sections: Chapter 1 introduces the main types of transmission i.e. parallel and serial transmission. This chapter outlines some properties about parallel transmission such as its transmission technique and requirements. It is concerned with serial communication and its format, rate and direction of data transfer, and transmission medium. It also explains the difference between synchronous and asynchronous transfer. Finally, this chapter presents the transmission standards i.e. RS-232 and USB standard demonstrating the cables and connectors, voltage levels, communication, and power supply between computers and electronic devices. Chapter 2 deals with the telephone construction and operation. Dialing modes (pulse dialing and touch tone dialing) are also explained. The modem construction and operation are discussed. Asynchronous operation of the modem and the types of modulation and demodulation of signals are presented. Finally, this chapter introduces the dial-up and broadband Internet v connection and makes a comparison between them demonstrating the cases and conditions of using each type. Chapter 3 introduces the microcontroller structure and operation. A comparison between microprocessor and microcontroller is presented. This chapter is concerned with the microcontroller PIC18F4550 device. It introduces the main parts of microcontroller; ports, oscillator configurations, timers, and pulse width modulation (PWM) module of the device are also discussed. Sine wave generation by using PWM and PIC18F4550 communication with USB are also explained. Finally, this chapter presents the USB HID Library which is used to control the communication of the PIC18F4550 device with the computer USB port supported by MikroC Pro-code. Chapter 4 presents the hardware design of the new system which makes use of a composite bit position based frequency modulation (CBP-FM).The new designed system is divided into three main parts (line interface, tone detector, and microcontroller) and minutely describes the system hardware circuit design and the functions of their components, supported by the schematic diagram of each part. The idea and operation of how the new designed system can transmit/receive data using phone lines is explained by starting with transmitting/receiving two, four and then eight bits at a time, supported by block diagrams and illustrative tables for each case. Chapter 5 explains the design of the Dial-Up software interface program that has been written in Visual Basic 6 to control the communication of the designed system with the computer via the USB port directly. The main window of this Software Interface Program contains the following three parts: a) Title Bar: This bar contains the title name of the main program window (Dial-Up Connection). b) Menu Bar: It consists of four menus for using the Dial-Up system and its applications. c) Working Space: This zone contains the messages (text) or data (decimal) which is sent or received by the Dial-Up system. It also displays the status of USB and line connection. This chapter also explains each of the program menus (File, Dial, Message Transfer and Data Transfer) as well as an illustration of the Dial-Up system processes step by step supported by program flowcharts. In conclusion the present work has been designed and tested over a telephone line; it introduces and approves a new modulation technique for transmitting/receiving digital data with speed 8 times faster compared with the normal serial transmission of each individual bit, and with much reduced modulation levels.