Research On Multi-frequency APD Measurement Technology And Implementation For LTE-R

LTE-R(LTE for railways)is the next-generation of dedicated wireless communication system for railway applications.It is urgent to evaluate the impact of electrified railway electromagnetic interferences on LTE-R.At the same time,the amplitude probability distribution(APD)measurement method can obtain more information about electromagnetic interferences characteristics than traditional quasipeak and other detection methods,and the research shows that the APD of the interference signal is related to the bit error rate of the communication system,so the APD of the interference signal can be used to evaluate its impact on the LTE-R system.However,because the LTE-R system uses orthogonal frequency division multiplexing(OFDM)technology and has a large number of orthogonal subcarriers,and it is difficult to simultaneously measure the APD of the interference signal at each subcarrier frequency.Therefore,based on the NI Flex RIO instrument and the Lab VIEW FPGA software development platform,I studied the key technologies of the multi-frequency APD measurement receiver,and successfully developed the measurement receiver,and I also built a receiver verification platform.In the measurement receiver part,first of all,I used the radio frequency pre-level module to acquire the received signal and transmitted the data to the FPGA through the hardware interface.In the FPGA,in order to realize the multi-frequency point measurement function,I used the FFT and the high-throughput mathematical function to distinguish each frequency point of the signal.For the large dynamic range data output by FFT operation module,I designed a logarithmic compression algorithm that conforms to the Lab VIEW data stream programming mode,and the algorithm used a cyclic shift and a high-throughput natural logarithm arithmetic module to achieve non-uniform quantization of data.At the same time,I used the dual-port random access memory as the real-time data cache to realize simultaneous multi-frequency APD statistical measurement of the compressed data.Finally,I transmitted the measurement results to the host computer through the direct memory access mechanism,and I realized the APD and spectrum display functions after the host computer processed the data.In the part of the receiver verification platform,because of the measurement receiver mainly applied to the interference signal APD statistical measurement requirements of the LTE-R system,I developed a semi-physical simulation platform for the RF transmission and reception of OFDM signals.At the same time,I realized the baseband modulation of the OFDM signal at the host computer of transmitter,and also realized the baseband demodulation of the received signal and the calculation of the bit error rate at the host computer of receiver.In this thesis,I used the single-frequency sinusoidal signal and multi-frequency composite signal to calibrate and pre-verify the multi-frequency APD measurement receiver.The test results show that the error between the maximum probability level measured by the receiver and the theoretical value is usually less than 0.1d B.For the verification platform of the receiver,I constructed the pseudo-noise sequence as the initial bit and observes the constellation and bit error rate of the receiver to test and verify the function of the verification platform.Finally,based on the existing theoretical model of the relationship between the interference signal APD and the system bit error rate,I used the test APD results of the interference signal and the theoretical APD results to estimate the system bit error rate respectively,and I used the receiver verification platform to test the bit error rate under the same interference conditions.Then I verified the function of the measurement receiver by comparing and analyzing the relevant experimental results.The result proves that the error between the measured APD by receiver and the theoretical APD is small,and the relationship between the estimated bit error rate based on the results of the APD measurement receiver and the bit error rate obtained by using the verification platform test is as expected.