| Mobile communication technology development of today, has entered the high-speed mobile communication system. With the proliferation of a large number of transmitting information, the spectrum resource has become increasingly tense, and requires more and more mobile communication technology to support high data rate. OFDM main advantage is that it can be effective against frequency selective fading and improve system capacity, spectrum efficiency, suitable for high speed data transmission, has been established as the core of next generation mobile communication systems technology. Since the 90s of the 20th century, due to a series of OFDM has the advantage, has been widely used in many broadband data communication systems, such as digital audio broadcasting, digital television broadcasting and wireless access technologies.This study is built based on the OFDM system, so the OFDM systems principles are introduced emphatically in the second chapter. In the early days of communication transmission system, the serial transmission dominates, with the increasing volume of business, require higher transfer rate, Serial transmission becomes very difficult. Multi-carrier OFDM system using parallel transmission, it will convert a lot of wireless channel orthogonal sub-channels, the high-speed data stream into many parallel low-speed data transmission stream, reducing inter-symbol interference, and enhance the channel capacity to resist fading .Fast Fourier Transform technology uses OFDM modulation and demodulation process of implementation, making the implementation of OFDM technology has become very convenient. In the OFDM symbol cyclic prefix can be used to eliminate inter-symbol interference. In this chapter the key technologies of the OFDM system are introduced, and the system has advantages and disadvantages are analyzed. Because many of the sub-channel OFDM system to produce, the situation is different for each sub-channel fading, this requires the channel state information based on bit and power for effective deployment. Better transmission performance we can increase the channel bit allocation, the poor performance of the channel to reduce bit allocation, the use of such technology can improve system resource utilization, further enhance the system's ability to combat fading. In this paper, with the principle of adaptive allocation, resource allocation algorithm based on the principle of water was introduced. Analysis of the single user case, the three common classical algorithms, according to one of the Chow algorithm, a simplified allocation algorithm is proposed, which is not very different in the case of performance, the original algorithm can effectively reduce the amount of computation.Multi-user adaptive algorithm complex than the single user case, you first need to consider for each user sub-carrier allocation, then the bit and power allocation. Multi-user resource allocation algorithm has better availability, is the focus of much literature. In this paper the case of multi-user system model is described in detail, analyzes the multi-user optimization objective criteria are introduced under the edge of Wong adaptive algorithm, on the basis of the algorithm, combined with follow-up literature, a modified subcarrier allocation algorithm is proposed, the system compares the performance sub-carriers, making the sub-carrier in all reasonable allocation between users and improve the sub-carrier Transmission efficiency, so that the overall system performance can be optimized. Through simulation analysis, to meet certain performance requirements under the conditions, the improved algorithm can effectively reduce the total system transmission power, BER performance of the algorithm are also improved. Finally, the paper summarized the work and made a further need for research. |
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