Study On Subcarrier And Bit Allocation In Multiuser OFDM System

OFDM (Orthogonal Frequency Division Multiplexing) has outstanding advantages because that it could utilize frequency resource sufficiently and robust against channel delay spread. It's suitable for high speed and broadband wireless communication. In broadband OFDM system over mobile fading channels, each individual sub channel has its own attenuation. So each sub channel has different channel capacity. A more efficient radio resource allocation and management scheme should be proved to transmit with higher spectrum and power efficiency and higher system performance. Adaptive allocation of resource gains more and more attention and becomes one of the focuses in OFDM research.In multiuser environment, the so-called 'mutiuser diversity' by dynamically allocating subcarriers among the users can be used. Since the subcarriers that appear to be in deep fade for one user may not be in deep fades for others, spectral efficiency can be improved, and equivalently, transmit power can be reduced.Now, there are many ways to solve how to allocate the resources. Generally, they can be divided into two classes: fixed resource allocation and dynamic resource allocation. Fixed resource allocation schemes, such as time division access (TDMA) and frequency division multiple access (FDMA), assign an independent dimension, e.g. time slot or sub channel, to each user. A fixed resource allocation scheme is rigid regardless of the current channel condition. This paper mostly analyzes dynamic allocation algorithm. From the total data rate to be under the conditions of the overall transmission power to minimize the problems and limitations of transmission power under the condition of maximum data rate of two angles on the issue of OFDM system resource allocation problem. This paper studies on an improved algorithm for subcarrier and bit allocation in multiuser OFDM systems. The algorithm uses the idea of step-by-step for dynamic allocation of resources and tries to minimize the total transmission power with given BER and each user's requirement on minimum rate. Simulation result shows that the proposed algorithm is simple in calculation and high in efficiency.