Adaptive modulation for maximum throughput of multi-user SC-FDMA system in doubly selective channel

Performance of multi-user SC-FDMA (single carrier-frequency division multiple access) system varies according to the user allocation and adaptive bit assignment to the subcarriers because each user experiences different channel characteristics. If any specific user suffers from poor channel characteristics in the conventional method of the distributed and localized user mapping, the total communication performance will be degraded. So, in this paper, we like to propose a user allocation method to improve the system performance in the frequency selective fading channel. We allocate users first who have best channel condition in comparison with all users to each subcarrier according to the channel state information. And we increase bandwidth efficiency by improving the modulation level to high order because most users have good channel condition through subcarrier allocation method. Therefore, we improve system performance like the BER performance and throughput effectively. Through the computer simulations, the performance of proposed system is analyzed and compared with existing method.