| Aircrafts communicate with each other through wireless network, the master node sends signals to control other nodes. With real-time communication, information like node locations and sensor data can be shared and analyzed as a whole. The paper has designed a wireless communication link to be used on aircrafts, and has accomplished the realization and verification of waveform transmission in physical layer.The paper has studied spread-spectrum communication, digital intermediate frequency, time and frequency synchronization, channel estimation and equalization and other key techniques in wireless communication. Then the paper has analyzed the requirements of the project and put forward the design scheme of waveform transmission in physical layer, consulting the existing technology standards and several typical military communication links. The main work contains the following three parts:Firstly, the communication links’ technology scheme in physical layer is designed and the performance simulation is accomplished. CRC and convolution interleaving technology are used in baseband channel encoding. The modulation mode is QPSK and the communication rate is 137 kbps. Initially, the signals’ base-band-width is 5MHz, and its sampling rate is increased 64 times to be modulated onto the 70 MHz intermediate frequency carrier wave. Training sequence is used in time synchronization and the precision has reached to 1/4 chip. The channel estimation and equalization module uses single-carrier frequency-domain equalization, thus the link can resist 1kHz frequency offset. The simulation results showes that the target BER level can be reached in certain conditions.Secondly, the links’ physical layer are implemented in FPGA circuit chip and the functional simulation is conducted. Each modules’ signal waveforms has been verified. In time-synchronization modules’ implementation, multi phase matched filter structure is used as an effecient way to save hardware resources. The digital intermediate frequency module uses a three stages structure to up-sample or down-sample signal, so each digital filters’ order is not too high.Thirdly, the links’ communication function and BER performance in real hardware platform has been tested. The result shows that the real BER performance of the link is 2 dB worse than the fixed-point simulation.The technology solution designed in the paper has met the demand of the project, according to the test result based on the circuit implementation. The paper has verified many key technologies through test and can be provided as a reference to the similar communication link engineering. |
