introduction
With the development of embedded technology, MCU, DSP, ARM and other processors have been widely used in the communication industry, especially in the field of wireless communication has its irreplaceable role. The core device MSP430FG4619 used in this design is the MCU launched by TI, TMS320VC5510 (abbreviated as "VC5510") is TI's 5000 series DSP, and the voice codec chip AMBE-2000 is also based on DSP.
The wireless walkie-talkie is widely used in civil, emergency and other aspects due to its advantages of instant communication, economy and practicality, low cost, convenient use, and no need for communication fees. Especially in the case of emergency handling and the lack of mobile phone network coverage, the two-way radio shows its irreplaceable status. Today, analog walkie-talkies still occupy the vast majority of the market, but because digital communications can provide a richer variety of services, better service quality, confidentiality and connectivity, and higher spectrum efficiency, research and production of digital walkie-talkies And use is advancing with the times, in line with the inevitable trend of information and digital development. The DMR (Digital Mobile Radi0, Digital Mobile Radio) protocol is a new type of digital trunking communication protocol proposed by the European Telecommunications Standards Institute (ETSI) in 2004, and has a very good development prospect.
1 Brief introduction of DMR communication protocol
The DMR protocol uses a dual-slot TMDA access method, with 2 time slots per burst and 30 ms per time slot. Each time slot has a protection time of 1.5 ms. The DMR protocol structure follows a common layered structure, which is suitable for describing reference materials and explaining layered communication structures. The DMR standard defines a model draft, dividing the model into three layers, as shown in Figure 1.
2 Overall design and system working principle
The core devices of the entire baseband system are signal processing devices and control devices. Among them, the signal processing device selects TI's DSP chip VC5510, and the control device is TI's MSP430FG4619 microcontroller.
The main function of DSP is naturally the processing of digital signals. In this design, VC5510 realizes the functions of signaling codec, communication of voice data (with AMBE-2000), frame synchronization, 4FSK modulation and demodulation.
The MCU is the control center of the entire system, and the human-machine interface (keyboard, display) is directly connected to the MCU. MSP430FG4619 realizes communication with the RF module (including baseband signal transmission and reception, RF frequency point control, channel detection, etc.), high-level control (signaling) of the DMR protocol, and interoperability of human-machine interfaces. MSP430FG4619 is an ultra-low-power 16-bit single-chip microcomputer port launched by TI. It has rich on-chip peripheral resources, rich timers, various serial ports, display drivers, AD / DA and other functions. Operation.
The voice codec device is AMBE-2000, and the core is actually DSP. It is a high-performance multi-rate voice codec chip using MBE (AMBE) algorithm, used to encode and decode digital voice data, its codec rate can be controlled by hardware and software, according to the needs of DMR protocol and AMBE The characteristics of 2000, the codec rate selection is 3.6kbps. The AD / DA converter connected to AMBE-2000 is selected as AD73311, and its compatibility is very good. It is widely used to complete the analog / digital conversion of voice signals. The MSP430FG4619FG4619's own AD / DA is connected to the radio frequency interface to complete the digital / analog conversion of the final baseband signal.
The communication mechanism of signaling and voice is different: the sending end of the signaling is initiated by the human-machine interface, framing through the MCU, sent to the DSP code, and then sent to the MCU for D / A conversion, and sent out through the radio frequency module; The signal is sent to the DSP for decoding after the A / D conversion of the MCU, and sent to the MCU for processing after decoding into frames. The encoding and decoding of the voice are completely implemented by AMBE-2000, after the DSP is transferred, the MCU sends or receives.
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