Dynamic Resource Allocation In Muliuser OFDM System

Since 1980s, OFDM (Orthogonal Frequency Division Multiplexing) technology has been widely used not only in DAB (Digital Audio Broadcasting) and DVB (Digital Video Broadcasting), but also become a part of local area network standard, such as IEEE802.11a,Hyperlan/2 and so on. OFDM has a high frequency using ratio and good anti-jamming character. OFDM is a widely used multi-carrier modulation scheme which divides the multipath fading channel into a number of parallel frequency dependent flat fading channels. A big advantage is that power and information can be allocate neatly depending on the channel characteristics to get a high resource using ratio. Because the wireless channel is changing from time to time, in order to use the wireless resources more officiously, we need to get the real-time channel status.In multiuser environment, the so-called 'multiuser 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 multiple access (TDMA) and frequency division multiple access (FDMA), assign an independent dimension, e.g. time slot or subchannel, to each user. A fixed resource allocation scheme is rigid regardless of the current channel condition. On the other hand, dynamic resource allocation allocates a dimension adaptively to the users based on their channel gains. Due to the time-varying nature of the wireless channel, dynamic resource allocation makes full use of the multiuser diversity to achieve higher performance. This paper mainly studies the dynamic resource allocation, which bases on a certain power, trying to get the largest rate to solve the problem. Water-filling algorithm and some other classical algorithms have been studied, and a new algorithm with rate control is also proposed. simulations of these algorithms are taken by Matlab. The result shows that dynamic resource allocation algorithms are better than fixed resource allocation algorithm, and the algorithm with rate control can allocate the resources more efficaciously among multiusers.