A Study on Adaptive OVSF Code Allocation Schemes for 2-D Spreading Coded OFCDM Communication Systems

• Main Authors: Chih-Pin Tsai, 蔡智斌
• Other Authors: Yung-Fa Huang
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/41691415453607091802

碩士 === 朝陽科技大學 === 網路與通訊研究所 === 95 === In this paper, we investigate the performance in a 2-D spreading orthogonal frequency coded division multiplexing (OFCDM) communication system over frequency and time selective fading channels. We propose a variance-based diversity gain (VBDG) estimation method from the sub-channels in the 2-D spreading coded OFCDM mobile communication systems. From experiments results, the time and frequency diversity gain in wireless channels can be approximate by proposed VBDG with a linear function. Moreover, an orthogalized code allocation (OCA) method is proposed to assign the OVSF codes to active users for OFCDM mobile communication systems. The proposed OCA scheme can suppress the multiple access interferences (MAI) induced by the non-orthogonality over time and frequency selective fading channels and then can outperform the conventional sequential code allocation (SCA) scheme at all system load. Furthermore, a fuzzy based adaptive code allocation (FBCA) scheme is proposed to dynamically assign the OVSF codes to the users with compromising MAIs minimization and the channel diversity maximization. Simulation results show that the proposed FBCA outperforms the OCA for all the number of active users and varying Doppler shift.