| SDR (Software Defined Radio) means integrating the modular, systematic hardware modules in a common platform, and this platform through a modular software program loaded on to achieve a variety of different wireless communication functions. It bases on a general used hardware platform and uses software programming to implement different function of wireless broadcasting station, which means reduce analog parts and make the digital processing as much as possible close to the antenna. This technology has many advantages such as reconfigurable, programmable, expandable and easy to upgrade.DQPSK modulation is a base modulation of orthogonal modulation which is a digital modulation has high spectral efficiency and interference immunity. GMSK modulation has excellent feature of frequency spectrum and power. Because of that, GSM which is widely used wireless communication system in the world choose this modulation to be its modulation, π/4-DQPSK modulation has high spectral efficiency, and can resist Doppler frequency shift. It is also the main used modulation in TETRA system. TETRA (Terrestrial Trunked Radio) is a digital trunked standard proposed by ETSI. It has a strong command and control functions, and has high frequency utilization, data security is good, more flexible network control. And the implementation of this modulation is also the preparation for the further implementation of TETRA on this platform.This paper researches the architecture and implementation principle of GNU Radio and USRP platform. And bases on this SDR platform to implement multi-modulations, like DQPSK modulation, GMSK modulation and π/4-DQPSK modulation. In the implementation of GMSK modulation, this paper also makes the speed of the data which is transmitted in the air to obtain the requirement of GSM. And in the implementation of π/4-DQPSK modulation, this paper compares the performance of the different synchronous algorithms in the received side to choose the better one to use, and transmits the data as the structure of the burst which is defined in the TETRA. Besides, this paper also makes the speed of the transmitted data to obtain the requirement of TETRA. |
