Abstract
This paper deals with the problem of maximizing the spectral efficiency in a massive multi-user MIMO downlink system, where a base station is equipped with a very large number of antennas and serves single-antenna users simultaneously in the same frequency band, and the beamforming training scheme is employed in the time-division duplex mode. An optimal resource allocation that jointly selects the training duration on uplink transmission, the training signal power on downlink transmission, the training signal power on uplink transmission, and the data signal power on downlink transmission is proposed in such a way that the spectral efficiency is maximized given the total energy budget. Since the spectral efficiency is the main concern of this work, and its calculation using the lower bound on the achievable rate is computationally very intensive, in this paper, we also derive approximate expressions for the lower bound of achievable downlink rate for the maximum ratio transmission (MRT) and zero-forcing (ZF) precoders. The computational simplicity and accuracy of the approximate expressions for the lower bound of achievable downlink rate are validated through simulations. By employing these approximate expressions, experiments are conducted to obtain the spectral efficiency of the massive MIMO downlink time-division duplexing system with the optimal resource allocation and that of the beamforming training scheme. It is shown that the spectral efficiency of the former system using the optimal resource allocation is superior to that yielded by the latter scheme in the cases of both MRT and ZF precoders.
Highlights
The use of massive multiple-input multiple-output (MIMO) systems, where a number of users communicate with the base station (BS) with a very large number of antennas, is viable approach for achieving significant improvement in spectral efficiency (SE) [1]–[6]
We have derived an approximate expression for the achievable downlink rate and the accuracy of this approximation has been verified by obtaining numerical results
We have proposed a resource allocation method in order to maximize the spectral efficiency and evaluated the performance of the proposed scheme conducting simulations
Summary
The use of massive multiple-input multiple-output (MIMO) systems, where a number of users communicate with the base station (BS) with a very large number of antennas, is viable approach for achieving significant improvement in spectral efficiency (SE) [1]–[6]. In case of multiuser TDD MIMO systems, an attempt has been made in [28] to deal with the problem as to how much time should be spent in training for a given number of transmit antennas, number of receive antennas, and length of the channel coherence time It has been shown in [29] that, by varying the transmit powers for the pilot and data sequences, the optimal number of pilot symbols is equal to the number of transmit antennas. In this paper, a resource allocation scheme that maximizes SE in DL massive MU-MIMO transmission assuming the pilot and data powers to be different, and in which MRT or ZF precoding is employed. It should be pointed out that in this paper the same symbols are used for the derivation of the achievable rates for both the MRT and ZF precoders
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
