A new subcarrier-user allocation algorithm for the downlink non-orthogonal multiple access system is presented in this paper. The proposed algorithm aims to enhance the spectral efficiency of the system and the successive interference cancelation performance by guaranteeing a high difference in channel-gain between the paired users per subcarrier. To enhance the spectral efficiency, the proposed algorithm provides a higher priority to the subcarrier that has a higher best (maximum) channel gain value rather than that has a lower best channel gain value. Also, it pairs the strong user with the second minimum channel-gain user rather than the minimum channel gain user. Besides, the proposed algorithm divides the subcarriers into two groups according to the standard deviation of the channel gain of each subcarrier. Then, it gives the priority to the group with low standard deviation values during subcarrier-user allocation to guarantee a high difference in channel-gain between the paired users per subcarrier. Later, fractional transmit power allocation is applied to distribute the subcarrier power between the paired users. Simulation results prove that the proposed algorithm improves the spectral efficiency of the system, and guarantees a significantly higher difference in channel-gain between the paired users per subcarrier compared to the conventional algorithms.

提出了一种新的下行非正交多址系统子载波用户分配算法。所提出的算法旨在通过确保每个副载波的配对用户之间的信道增益之间存在较大差异，来提高系统的频谱效率和连续的干扰消除性能。为了提高频谱效率，所提出的算法为具有较高最佳（最大）信道增益值而不是具有较低最佳信道增益值的子载波提供了更高的优先级。而且，它将强用户与第二个最小频道增益用户而不是最小频道增益用户配对。此外，该算法根据每个子载波的信道增益的标准偏差将子载波分为两组。然后，在子载波-用户分配期间，它会将低标准偏差值的组给予优先级，以确保每个子载波的配对用户之间的信道增益差异很大。随后，应用分数发射功率分配以在配对用户之间分配子载波功率。仿真结果表明，与传统算法相比，该算法提高了系统的频谱效率，并且保证了每个副载波之间成对用户之间的信道增益差异明显更高。