단일 반송파 주파수 분할 다중접속을 위한 주파수 효율적인 상향 링크 전송 시스템 연구

Abstract

This thesis discusses user scheduling and power control for single-carrier frequency division multiple access (SC-FDMA) with iterative multiuser detection, called grouped frequency division multiple access (GFDMA). GFDMA has the advantages of SC-FDMA with respect to power consumption and spectral efficiency. Contrary to the typical FDMA, GFDMA is a non-orthogonal scheme because a same time-frequency resource of GFDMA is shared by multiple users. Previous researches about the user scheduling and power control for SC-FDMA cannot be applied to GFDMA system due to the non-orthogonal feature of GFDMA. Hence, GFDMA requires its own scheduling and power control methods to achieve high spectral efficiency.

Multiple access interference (MAI) can be generated from the users who share the same resource in GFDMA. Both achieving high spectral efficiency and guaranteeing quality-of-service (QoS) of users should be considered to deal with the MAI. Thus, a scheduler for GFDMA should allocate a common set of subcarriers to as many users as possible, while guaranteeing the QoS of each user.

The optimal solution for the scheduling problem is easily obtained by an exhaustive search. However, its complexity of calculation is too enormous to realize practically. A QoS-constrained opportunistic scheduling algorithm was proposed previously, however, its spectral efficiency performance is still a long way from that of the optimal scheduling.

To address this problem, the user selection pattern of optimal user selection via an exhaustive search method is investigated at first. Based on this investigation, a pattern-aware user scheduling algorithm for the optimal user selection is proposed in this thesis. The proposed algorithm follows the observed selection principle of the optimal scheduling, with the jointly performed forward and backward searches. Simulation results show that the proposed algorithm provides higher spectral efficiency than conventional algorithms and achieves the performance of optimal user selection with much reduced computational complexity.

In GFDMA, the uplink signal of a user can be regarded as both a signal and a source of interference. Each user’s signal power should be high enough to ensure reliable signal detection, but not high enough to decrease the user’s interference on other users’ signals. Therefore, to attain efficient detection, the transmit power of each user should be adjusted appropriately. However, the transmit power control for GFDMA have never been discussed in previous researches.

In this thesis, we propose a power control method for uplink GFDMA system to attain high spectral efficiency. The uplink spectral efficiency is improved by limiting each user’s power according to a criterion derived from the non-orthogonal characteristics of GFDMA. The proposed method can maintain the quality-of-service of each user, even with reduced transmit power. Simulation results show that the proposed algorithm provided much higher spectral efficiency than the conventional GFDMA without power control, while reducing transmit energy.