This paper presents experimental results for multiuser-multiple input multiple output (MU-MIMO) with a two-dimensional antenna configuration. MU-MIMO can increase spectral efficiency significantly by employing many antennas at the base station (BS). However, the performance is upperbounded when many antennas are arranged in a line because antenna spacing has to be small to maintain the required span for antenna arrangement. In order to overcome the problem, this paper evaluates a two-dimensional antenna configuration, where multiple antennas are set in both the horizontal and vertical directions using the testbed developed by the authors. The experimental results show that the spectral efficiency with a twodimensional antenna configuration is 12.8 % higher than that with conventional linear array configuration when the span for the antenna arrangement in the horizontal direction is constrained to 7λ, where λ indicates the wavelength of carrier frequency.

No abstract

SC-FDMA is a multiple access technique adopted in LTE uplink transmission. SC-FDMA, as well as OFDMA, can improve system throughput by assigning different frequency portions of system bandwidth to different user equipments (UEs) adaptively based on their channel quality information. In SC-FDMA uplink cellular system, interference arising from UEs in neighboring cells degrades system performance, especially the performance of the cell-edge UE. To overcome this drawback, many papers propose the Fractional Frequency Reuse (FFR) technique and analyze its influence. However, these studies have different conclusions on the effectiveness of FFR, and the throughput gain of FFR depends on the evaluating conditions. In this paper, we reveal the conditions where FFR is effective by demonstrating the throughput gain of FFR in SC-FDMA uplink cellular system. In order to analyze the throughput gain of FFR, we focus on the performance relationship between FFR and frequency selective scheduling (FSS). From the analysis, the throughput gain of FFR is small because of the degradation of the FSS gain, and FFR is effective when the following conditions are met; (i) the number of UEs is small, (ii) the multipath delay spread is large or equal to 0.

No abstract

No abstract