Theoretical Research And Algorithm Realization Of Subcarrier And Power Allocation In OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier modulation technology, which is good at anti-noise and resisting the route disturbance from multiple paths as well as having high use ratio of frequency spectrum. So it is regarded as a key technique of the next generation mobile communication system, and it gets more and more attention.In OFDM systems, the resources allocation (including subcarrier, bit and power allocation) is very important for the performance of systems. The logical allocation schemes can reduce the BER and power dissipation, heighten the use ratio of frequency spectrum, and improve the capacity of the systems. Now there are many ways to solve how to allocate the resources. They can be divided into two classes: fixed resource allocation and dynamic resource allocation. The fixed resource allocation scheme includes the time division multiple access (TDMA) and frequency division multiple access (FDMA). This scheme is rigid regardless of the current channel gains and the use ratio of resources is very low.In this paper, we mostly analyze dynamic allocation algorithms, which consist of three adaptive rules: Rate Adaptive, Margin Adaptive and BER Adaptive. On the base of classical algorithms, we tend to syncretize the Rate Adaptive and Margin Adaptive, and propose an improved algorithm for subcarrier and bit allocation in multi-user OFDM systems. The simulation result shows that this algorithm is better than the static algorithm. Compared with the prevenient dynamic algorithms, it has higher data rate and lower power dissipation. In addition, aiming at the BER adaptive, we propose an algorithm for bit and power allocation, which uses Lagrange function and the upper limit of BER function to get the ultimate solution. The simulation result shows that this algorithm has better performance in the situation of low SNR, and it can improve the holistic capability of the systems.