ИССЛЕДОВАНИЕ ЗАМИРАНИЙ В СИСТЕМЕ СВЯЗИ С ИСПОЛЬЗОВАНИЕМ ТЕХНОЛОГИИ OFDM
A new technique exploited for estimating of fading influence in multipath signal propagation environment for communication system using OFDM (Orthogonal frequency-division multiplexing) technology is proposed. Rayleigh fading model is considered and studied in suggested approach. Wi-Fi network has been selected as a basis system for study performance of OFDM communication system operating in multipath and noisy communication channel. Preliminary experimental measurements and computations have been carried out in order to evaluate received signal parameters after test signal propagation through multipath communication link contaminating transmitted signal under influence of random Rayleigh fading. An algorithm has been developed that makes it possible to perform computations according considered model. Software corresponding to suggested algorithm has been developed. Proposed software contains user interface that is written in order to automate the process of computations. Developed software was examined experimentally for statistical study of interference behavior and its influence on the OFDM communication system performance. The following data were taking into account in investigations: Rayleigh fading; user's motion; number of operating OFDM subcarriers; number of receiving antennas; additive normal noise. The influence of these factors on the communication system performance was evaluated by computation the value of bit error rate (BER) values. Suggested software also gives an opportunity investigating the number of bit errors and appearance of the signal in the time and frequency domains at different stages of transmission. Computer simulations results were obtained for a sequence of test Monte Carlo runs depending on: the speed and angle of the user's traffic; the intensity of the additive Gaussian noise in communication channel; variations of the number of OFDM subcarriers; the number of antennas contained in the user equipment. Computer simulation results demonstrate the following: bit error rate values tend to increasing with increasing the user velocity as well with decreasing the number of antennas and subcarriers. It has been also shown decreasing the signal-to-noise ratio value under influence of additive noise with a Gaussian distribution according to decreasing the number of OFDM subcarriers and number of antennas in MIMO system.
