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In 3GPP Release 12, 256QAM (Quadrature amplitude modulation) is expected to be adopted in downlinks of the LTE-Advanced standard as a new modulation order for the purpose of further enhancement in frequency efficiency. However, if a UE (user equipment) is configured to be able to select 256QAM in downlink transmission, the UE cannot select several MCSs (modulation and coding schemes), which was possible in the previous standard. This point is one of the performance deterioration factors associated with 256QAM. Evaluating and clarifying the impact which this deterioration factor has on system performance is of commercial significance because it leads to the development of an effective application method for 256QAM, which will be required in the deployment phase after standardization completion. Therefore, this paper presents some actual methods by which 256QAM is configured to UEs in LTE-Advanced heterogeneous networks, and evaluates their performance by computer simulation, so as to clarify the above-mentioned impact. The results of the simulation make it clear that it is desirable to configure UEs in small cells so that 256QAM can always be selected. |
