Simulation Research On The Adaptive Modulation Algorithm Of OFMD

In recent years, with the continuous development of mobile communication and the increase of wireless service, high speed and reliable data transmission has become the goal and requirement of wireless communication. The basic principle of orthogonal frequency division multiplexing (OFDM) is to divide the frequency selective fading channel into several narrowband flat fading channels, combined with the guard interval and the cyclic prefix, characterized by anti-multipath time delay, anti-fading channel and high spectrum utilization rate. Moreover, OFDM is easy to be combined with multiple input multiple output (MIMO) technology to make a new and high rate data transmission technology, which can significantly improve the system performance.On the other hand, adaptive modulation technology is one that dynamically allocate different transmission information bits and transmit power to sub-carriers, based on the instantaneous channel state information. When the channel is in good condition, high order modulation is taken to increase system throughput rate, otherwise low order modulation is taken on subcarrier to ensure the reliability of the system.This begins with an overview of the research background and the research present situation of adaptive modulation technology, then gives a brief introduction of the content and structural arrangement of this thesis. The characteristics of the wireless fading channel and OFDM technology theory are expounded successively. Afterwards, basic theory of adaptive modulation technology principle and rules are introduced in detail, as well as the implementation of adaptive OFDM system.Then, this thesis focuses on 3 traditional adaptive modulation algorithms, namely Chow algorithm, Hughes-Hartogs algorithm and Fischer algorithm, all of which are simulated in fading channel. BER and throughput performance differences in this system are examined in quantitative analysis in terms of algorithm complexity. Other performance differences, advantages and drawbacks of each algorithm are also compared. Besides, SBLA algorithm in different sub band widths and an improved dynamic sub zone partitioning algorithm based on SBLA algorithm are respectively studied and implemented, complexity, system BER performance and throughput of these two algorithm are analyzed and compared.At last, in order to further improve the performance of the system, this thesis brings in a pre-code technology based on singular value decomposition (SVD), and verifies in detail the feasibility of applying the adaptive modulation to MIMO-OFDM system. In MIMO-OFDM system, the simulation of different adaptive modulation algorithms are completed, and the comparative analysis on performance of different algorithms are also given.Simulation results show that, the combination of OFDM technology, MIMO technology and adaptive modulation technology can significantly improve the system performance.