Design and Implementation of Control System in a Satellite Voice Communication Terminal

A control system in satellite communication terminal of low information rate is designed via program based on ATmega128 system controller, which has realized the function of operation control in the satellite communication terminal of low information rate. The synchronization signal of clock is simulated via Mcu I/O interface to voice-coder. Mcu controls the input and output of analog signal and digital signal of voice-coder and acquires and transmits the digital signal from voice-coder. Serial communication mode is adopted between the satellite communication baseband and Mcu and the information exchange is carried out according to the system communication protocol. Introduction Satellite communication has some advantages such as wide coverage, high safety, high reliability, etc., which can be used as a strong supplement for ground mobile communication. Especially the establishment and development of satellite voice communication has important practical value and social significance for disaster relief and some field [1, 2]. To improve the utilization of satellite bandwidth is one of the main directions of the development of satellite communication. Low information rate satellite voice communication can reduce the use of satellite frequency bandwidth and improve the user capacity of satellite communication voice communication system [3, 4]. A low information rate satellite voice communication system platform is constructed based on this idea. According to the operation characteristics of satellite voice communication, we design and achieve a control system in satellite communication terminal, which realizes information exchange between voice-coder and satellite communication baseband and satellite communication function of operation control. Hardware Design ATmega128 MCU is a 8-bit AVR microcontroller with high performance and low power [5], which is comprised by advanced RISC architecture, has powerful instruction system, integrated with large RAM of non-volatile program, data and working memory, a SPI interface, two USART interface programming, a variety of power saving modes controlled by software. It can be facilitate to achieve functions such controlling and data transmitting [6, 7]. A satellite voice communication terminal of low information rate is composed of ATmega128 microcontroller, voice-coder, LCD, keyboard and other circuits, which is connected to transceiver baseband through an asynchronous serial communication interface. The systematic block diagram is shown in Fig.1. 6th International Conference on Electronic, Mechanical, Information and Management (EMIM 2016) © 2016. The authors Published by Atlantis Press 315 Atmega128MCU Transceiver baseband vocoder Key & monitor Voice analog signal Figure 1. Systematic block diagram Voice-coder. The hardware interface of voice-coder is defined as shown in Table 1. Table 1 Hardware interface definition Number Characteristics Control Function Description Signal Direction 1 Voice_Out Analog voice signal out ← 2 Voice_In Analog voice signal in → 3 PTT PTT request, active at low level → 4 V_Rst Voice-coder reset signal, active at low level → 5 GND GND, not distinguish between analog and digital ground 6 7 VCC Power(+5V), not distinguish between analog and digital power 8 9 RTS Send request, active at low level ← 10 TXD Digital signal output (for voice-coder ) ← 11 RXD Digital signal input (for voice-coder ) → 12 TXC Synchronous clock signal → 13 14 CD Carrier monitoring signal, active at low level → Table 1 shows the interface definition and control function of the voice-coder and points out each pin direction (input or an output) for voice-coder. PTT is an input signal from controller to voice-coder. When it is pressed the signal is set low level by controller and the analog voice begin transmitting [8]. When RTS is set low level, the output bit stream is effective. CD is a input signal from controller to voice-coder, when it is set low level, the bits data inputting voice-coder is effective. TXD and RXD is coded bit stream with synchronization bits. The voice-coder is coded by fixed frame length. The bit stream has strict frame format. The communication channel is regarded to be transparent for voice-coder, so there is not strict frame format requirement to communication channel for the coder bit stream [9]. Interface between MCU and Voice-coder. ATmega128 control unit simulates synchronous clock signal of voice-coder transmitted via I/O [10], controls voice-coder analog signal and digital signal input and output and acquires digital signal from voice-coder and transmits digital signal to voice-coder. The interface connected circuit between MCU and voice-coder is shown in Fig. 2.