Abstract
This paper examines the effectiveness of implicit beamforming (IBF), which enables transmission without channel state information (CSI) feedback in multi-user multiple-input multiple-output (MU-MIMO) systems with a large number of antennas. First, we explain why CSI feedback from terminal stations to the base station produces a very large overhead. A calibration technique is then introduced, which compensates for the difference between the complex amplitudes of the transmitters and receivers to facilitate CSI-feedback-free beamforming; this technique is called IBF. The efficacy of this calibration technique is demonstrated by measuring the amplitude and phase errors obtained using a 16-element array testbed and by performing a channel capacity evaluation. Finally, the throughput under IEEE802.11ac-based massive MIMO transmission, both with and without CSI feedback, is obtained in terms of the medium access control efficiency.
Highlights
IntroductionThe volume of data being transferred over wireless communication channels is almost doubling each year, owing to the popularity of smartphones and wireless local area networks (WLANs)
The volume of data being transferred over wireless communication channels is almost doubling each year, owing to the popularity of smartphones and wireless local area networks (WLANs).high-speed data communication at speeds of faster than 10 Gbps will be required for future wireless communication systems [1,2,3]
In multi-user multiple-input multiple-output (MIMO) (MU-MIMO) systems, the channel capacity C is improved by employing a transmission rate (TR) between a base station (BS) and multiple user equipment (UE) units, where the UE has a small number of antennas [8,9]
Summary
The volume of data being transferred over wireless communication channels is almost doubling each year, owing to the popularity of smartphones and wireless local area networks (WLANs). With a view to further improving the frequency utilization of future wireless systems using MU-MIMO transmission, the concept of massive MIMO has recently been proposed [11,12]. BS antennas that are well suited to TDD communication systems have been proposed in previous studies [20,21].We note that some of these methods allow the transmitter and receiver calibration values to be obtained automatically [20,21,22,23,24]. The calibration method for massive antennas utilizing the channel reciprocity in a TDD system is proposed [25,26,27].
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