Research On Dynamic Subcarrier And Power Allocation For OFDM Systems

OFDM (Orthogonal Frequency Division Multiplexing) has outstanding advantages because that it could utilize frequency resource sufficiently and robust against channel delay spread. It is suitable for high speed and broadband wireless communication. It modulates the signals to subcarriers which are orthogonal and increase the time for sending signals, so it can reduce the effect of inter-symbol interference (ISI) effectively. But OFDM is sensitive to the frequency offset because the orthogonality between subcarriers resulting inter-carrier interference (ICI) which gives rise to an irreducible error floor of the system's bit error rate (BER). This paper mainly researches on dynamic resource allocation in OFDM systems. In broadband OFDM system over mobile fading channels, which have different channel capacity, if a fixed modulation scheme is applied to all subcarriers, the whole system's capacity and the transmitted power have not been full used. In this paper, various dynamic subcarrier, bit and power allocation schemes are discussed. This algorithm distributes the information bits, the signal constellations and transmitting power adaptively to different subcarriers according to channel instantaneous attenuations to satisfy average power and BER constraints. Besides, a dynamic subcarrier and power allocation scheme based on embedded constellation is proposed in this paper. With the goal of minimizing the overall transmit power while ensuring the fulfillment of each user's transmission rate and QoS requirement, embedded constellation based algorithm allows that a subcarrier could be shared by multiple users. It can also achieve high performance with low compute complexity by theory and Matlab simulations.