Dynamic subchannelization for adaptation to multipath fading in mobile WiMAX

Abstract

In Mobile WiMAX based on the IEEE 802.16e wireless MAN technologies using an OFDMA, the system throughput can be improved by subchannelization schemes such as diversity mode in severe multipath fading channel environment. Mobile WiMAX system uses FUSC which is one of the diversity subchannelization schemes in high mobility environment, especially under fast selective fading channel with high mobility environment. The OFDMA frame duration in fast selective fading channel is not shorter than minimum Doppler period in real world. Also, the time diversity gain (between the point of time of reporting CQI from MSs and transmitting frame which is organized by reported CQIs(Channel Quality Indication)) can become rather large. To alleviate this channel state, the FUSC is used for avoiding deep fading and averaging intercell interference by selecting subcarriers pseudo-randomly [1]. And also, this distributed subcarrier permutation mode can get frequency diversity under severe multipath fading channel condition. However, the FUSC scheme in the current standard is not flexible for channel variations inherent to their high mobility channel state, because FUSC allocates subcarriers pseudo-randomly without considering CINR(Carrier to Interference plus Noise Ratio) variation of subchannels. In this thesis, we introduce optimal subchanneliztion problem by making use of channel condition fully and efficiently. Especially, we prove that the effective subchannelization for frame can be guaranteed by making CINR variation of each subchannel low, which means that subchannelization scheme can be adapted to channel condition with severe fading channel fully. Then, we will show the simulation result that the suboptimal subchannelization scheme leads to higher system throughput as compared to conventional subchannelization scheme such as FUSC.