Spectral Efficiency of Precoded 5G-NR in Single and Multi-User Scenarios under Imperfect Channel Knowledge: A Comprehensive Guide for Implementation

Abstract

Digital precoding techniques have been widely applied in multiple-input multiple-output (MIMO) systems to enhance spectral efficiency (SE) which is crucial in 5G New Radio (NR). Therefore, the 3rd Generation Partnership Project (3GPP) has developed codebook-based MIMO precoding strategies to achieve a good trade-off between performance, complexity, and signal overhead. This paper aims to evaluate the performance bounds in SE achieved by the 5G-NR precoding matrices in single-user (SU) and multi-user (MU) MIMO systems, namely Type I and Type II, respectively. The implementation of these codebooks is covered providing a comprehensive guide with a detailed analysis. The performance of the 5G-NR precoder is compared with theoretical precoding techniques such as singular value decomposition (SVD) and block-diagonalization to quantify the margin of improvement of the standardized methods. Several configurations of antenna arrays, number of antenna ports, and parallel data streams are considered for simulations. Moreover, the effect of channel estimation errors on the system performance is analyzed in both SU and MU-MIMO cases. For a realistic framework, the SE values are obtained for a practical deployment based on a clustered delay line (CDL) channel model. These results provide valuable insights for system designers about the implementation and performance of the 5G-NR precoding matrices.

Fluid Antenna System—Part II: Research Opportunities

“…The number of selected regions depends on the number of radio frequency (RF) chains of the transceiver. 7 The handling of the current distribution is therefore reduced to controlling only the current feeds to the selected regions, similar to a standard MIMO transceiver, and existing MIMO techniques can also be employed.…”

“…2 shows a downlink system where the BS is equipped with a 2D multi-port FAS 10 to transmit signals to U UEs each with a 2D multi-port FAS. In this case, ( 6) can be extended to express the received signals at the u-th UE as (7) in which all the variables follow the same definitions as before except the index u is introduced to specify the UE. Note that all the UE signals share the same port selection A T at the BS.…”

“…Upsizing MIMO comes with complexity in channel estimation and beamforming optimization. In 5G, the Type II New Radio (NR) multiuser MIMO precoder is not a simple solution [7] and pushing it to serve many more users implies serious overheads. It is also fair to evaluate that it will take time to realize CP-MIMO in the future as this will require a technology that can produce any arbitrary, steerable current distribution over a two-dimensional (2D) antenna surface.…”

Fluid Antenna System—Part III: A New Paradigm of Distributed Artificial Scattering Surfaces for Massive Connectivity

“…To obtain the performance gain, there is a need to jointly optimize the precoding matrix at the BS and the phase shifters at the RIS [4], [5], let alone the acquisition of channel state information (CSI) of the cascaded channel. Note that the 5G Type II NR multiuser multiple-input multiple-output (MIMO) precoder is already complicated [7] and incorporating the RIS phase shifters optimization will be extremely difficult. Furthermore, the beamforming-based RIS approach is hardly scalable because if there are more than one RISs in the vicinity, the phase shifters of all the RISs need to be coordinated.…”

Fluid Antenna System—Part I: Preliminaries

“…Despite its brilliance, MIMO, or more accurately multiuser MIMO, is not a simple solution, not in terms of the overhead for acquiring the channel state information (CSI) to be known at the BS and not the complexity for obtaining the precoding matrix. Although massive MIMO promises to be theoretically simple [14], in 5G, a more complex codebook-based precoding design that uses quantized CSI feedback is adopted [15]. Even if the overhead and complexity can be afforded, the Type II 5G New Radio (NR) multiuser MIMO precoding is not easily upgradable to support more users than it is designed to without another standardization effort.…”