Research On Adaptive Modulation Techniques In OFDM System

Reliable data transmission with high-speed is the aim of wireless communication OFDM with the advantage of high spectrum efficiency and easy realization, can strongly combat multi-path delay and fading, and is remarkable in recent years. In OFDM systems, the adaptive modulation which is adopted based on the accuracy estimation of subchannels can improve system efficiency and lead the system to achieve optimal performance. This paper first introduces the basic theory, channel model of OFDM systems. Channel estimation techniques and channel interpolation filtering technologies for OFDM system is researched, and the performance simulation is taken. To overcome the shortcoming of fixed packet in SBLA algorithm, a dynamic packet grouping adaptive modulation SBLA algorithm is given. Simulation shows that the dynamic SBLA adaptive algorithm can improve system adaptability. In addition, a dynamic threshold is applied in SBLA adaptive algorithm to overcome the shortcoming of fixed threshold。The simulation shows that the SBLA algorithm has a good adaptive performance. The channel estimation error of adaptive modulation has significant impact on the adaptive algorithm. Simulation results show that the channel estimation error will lead to the increase of system error when the channel estimation SNR is bigger than the real situation, which can influence the communication quality greatly. The BER will decrease with the increase of SNR error.