Abstract
Millimeter-wave and terahertz technologies have been attracting attention from the wireless research community since they can offer large underutilized bandwidths which can enable the support of ultra-high-speed connections in future wireless communication systems. While the high signal attenuation occurring at these frequencies requires the adoption of very large (or the so-called ultra-massive) antenna arrays, in order to accomplish low complexity and low power consumption, hybrid analog/digital designs must be adopted. In this paper we present a hybrid design algorithm suitable for both mmWave and THz multiuser multiple-input multiple-output (MIMO) systems, which comprises separate computation steps for the digital precoder, analog precoder and multiuser interference mitigation. The design can also incorporate different analog architectures such as phase shifters, switches and inverters, antenna selection and so on. Furthermore, it is also applicable for different structures, namely fully-connected structures, arrays of subarrays (AoSA) and dynamic arrays of subarrays (DAoSA), making it suitable for the support of ultra-massive MIMO (UM-MIMO) in severely hardware constrained THz systems. We will show that, by using the proposed approach, it is possible to achieve good trade-offs between spectral efficiency and simplified implementation, even as the number of users and data streams increases.
Highlights
Over the last few years, significant advances have been made to provide higherspeed connections to users in wireless networks, with several novel technologies being proposed to achieve this objective
We proposed an iterative algorithm for hybrid precoding design which is suitable for multiuser UM-multiple-input multiple-output (MIMO) systems operating in millimeter wave (mmWave) and THz bands
The adopted approach replaces unfeasible fully-digital precoders/combiners relying on a dedicated RF chain per antenna with a hybrid architecture comprising low dimension digital blocks with only a few RF chains which are complemented by analog blocks supported solely on networks of phase shifters and switches
Summary
Over the last few years, significant advances have been made to provide higherspeed connections to users in wireless networks, with several novel technologies being proposed to achieve this objective. Unlike [10], where we only considered the adoption of phase shifters, in this paper we present explicit solutions for some of the most common architectures, namely FC, AoSA and DAoSA structures based in either Unquantized Phase Shifters (UPS), Quantized Phase Shifters (QPS), Switches (Swi), Switches and Inverters (SI), Antenna Selection (AS) or Double Phase Shifters (DPS); To cope with the large bandwidths available in mmWave/THz bands, where practical MIMO systems likely have to operate in frequency selective channels, the proposed hybrid design considers the application in a multicarrier context, where the same analog precoder is applied at different frequencies; We explicitly show how the proposed design can be applied to a DAoSAs approach where a reduced number of switches are inserted at each AoSA panel, which allows the connections to the RF chains to be dynamically adjusted. The superscript (.)T and (.)H denote the transpose and conjugate transpose of a matrix/vector, · p is the p- norm of a vector, · 0 is its cardinality (i.e., the number of non-zero elements in a vector which is sometimes referred to as the 0- norm in the literature) and In is the n × n identity matrix
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