Hybrid Limited Feedback in 5G Cellular Systems With Massive MIMO

Abstract

Massive multiple input multiple output (MIMO) is one of the promising technologies to address the growing capacity requirement in fifth-generation cellular systems. However, the massive MIMO deployed at base stations (BSs) or relay stations (RSs) brings new challenges on channel state information (CSI) feedback because of its large-scale complex channel matrix. In this paper, we propose a hybrid limited feedback with selective eigenvalue information (HLFSEI), which adopts the individual quantized feedback and the codebook-based feedback jointly. In HLFSEI, we feed back only selective eigenvalue elements for power allocation by individual quantized feedback and the precoding matrix by codebook-based feedback. Furthermore, we study the optimal feedback bit allocation of the aforementioned two feedback methods to minimize the throughput loss with the feedback-link capacity constraint. Specifically, the feedback bits are allocated according to the properties of the throughput loss in high-and low-signal-to-noise regimes. Both the BS-RS communications and the BS/RS-user-equipment communications in cellular systems are taken into consideration. Finally, we evaluate the performance of the proposed HLFSEI strategy by simulation and show its performance gain compared with conventional feedback strategies.Index Terms-Fifth-generation cellular systems, limited feedback, massive multiple input multiple output (MIMO), power allocation. Manuscript

Feedback-Aware Precoding for Millimeter Wave Massive MIMO Systems

“…Thereby, OMP is a widely-adopted algorithm, which can efficiently find the best K elements of basis matrix Ψ(C φ ) ∈ C M×| C φ | to approximate F opt [18]. Once φ is derived, the optimization problem in (7) reduces to the well-known least square problem for G whose closedform solution is known. Algorithm 1 summarizes the proposed Algorithm 1 Feedback-Aware Precoding via OMP Require: F opt , C φ 1: φ = Empty vector 2: F res = F opt for i = 1 : K do 4:…”

“…Next, the transmitter can fully implement this precoder based on Lemma 1 for the hybrid MIMO architecture introduced in Section II. The structure of precoderF implies that the required feedback scales with K(1 + S), which is not only independent of the number of transmit antennas M, but can also be controlled with the proposed design parameter K. Therefore, the solution of optimization problem (7) ensures that the set of the best K vectors for spanning the channel's row space and their corresponding combining matrix are fed back to the transmitter. Consequently, the optimal precoder can be better approximated by choosing a larger K at the cost of increased feedback overhead, while choosing a smaller K can lower the overhead when the feedback link bandwidth is limited.…”

“…The existing CSI feedback strategies for MIMO systems can be classified into two categories: i) codebookbased feedback, where an index from a known codebook is fed back, and ii) individual quantized feedback, where each CSI value is quantized and send back [6]. Both approaches have shortcomings when it comes to systems with large antenna arrays [7], such as mmWave systems, and thus the limitation of the feedback channel should be taken into account for the design of precoding algorithms [8]- [12]. In [9] and [10], multiresolution codebooks are proposed to minimize the training power and feedback overhead during channel estimation.…”

Robust full-dimension MIMO transmission based on limited feedback angular-domain CSIT

“…Since the spatial resolution of the 50 element ULA considered here is better, we increase the angular CSI resolution to 1 • . 7 The definition of σ 2 e here is slightly different as compared to (8), in order to keep the energy of the estimated channel constant irrespective of σ 2 e .…”

“…Currently, most implementation proposals of FD-MIMO transceivers are based on hybrid architectures, where part of the signal processing is performed in base band and part in the analog radio frequency (RF) domain in order to limit the number of required RF chains. This approach is especially important in the millimeter wave band, where hardware complexity is a limiting factor [4][5][6][7][8]. When designing hybrid precoding systems, several challenges need to be addressed [9][10][11]: the design freedom of RF precoders is commonly restricted by hardware limitations, such as discrete angular resolution and constant modulus of the phase-shifting elements, as well as partial connectivity of the phase-shift network to limit insertion loss.…”