Performance Analysis of 6G Multiuser Massive MIMO-OFDM THz Wireless Systems with Hybrid Beamforming under Intercarrier Interference

TL;DR

This work analyzes 6G-like THz multiuser MIMO-OFDM systems employing fully connected hybrid beamforming under carrier frequency offset–induced intercarrier interference. It develops a two-stage design where analog beamforming is optimized on a Riemannian manifold and digital precoding uses zero-forcing, with a complexity-reduction shift from rate maximization to interference minimization. By incorporating a three-dimensional wideband THz channel model with molecule absorption and CFO-driven ICI, the approach demonstrates substantial latency reductions while maintaining near-optimal spectral efficiency, especially as the number of RF chains and antennas grows; spectral efficiency declines with more users due to increased ICI. The results underscore the necessity of modeling ICI in THz MU-MIMO-OFDM and highlight practical trade-offs between RF-chain count, antenna numbers, and user load for 6G-scale networks, guiding future improvements in latency, adaptive power allocation, and AI-enabled cross-layer design.

Abstract

6G networks are expected to provide more diverse capabilities than their predecessors and are likely to support applications beyond current mobile applications, such as virtual and augmented reality (VR/AR), AI, and the Internet of Things (IoT). In contrast to typical multiple-input multiple-output (MIMO) systems, THz MIMO precoding cannot be conducted totally at baseband using digital precoders due to the restricted number of signal mixers and analog-to-digital converters that can be supported due to their cost and power consumption. In this thesis, we analyzed the performance of multiuser massive MIMO-OFDM THz wireless systems with hybrid beamforming. Carrier frequency offset (CFO) is one of the most well-known disturbances for OFDM. For practicality, we accounted for CFO, which results in Intercarrier Interference. Incorporating the combined impact of molecular absorption, high sparsity, and multi-path fading, we analyzed a three-dimensional wideband THz channel and the carrier frequency offset in multi-carrier systems. With this model, we first presented a two-stage wideband hybrid beamforming technique comprising Riemannian manifolds optimization for analog beamforming and then a zero-forcing (ZF) approach for digital beamforming. We adjusted the objective function to reduce complexity, and instead of maximizing the bit rate, we determined parameters by minimizing interference. Numerical results demonstrate the significance of considering ICI for practical implementation for the THz system. We demonstrated how our change in problem formulation minimizes latency without compromising results. We also evaluated spectral efficiency by varying the number of RF chains and antennas. The spectral efficiency grows as the number of RF chains and antennas increases, but the spectral efficiency of antennas declines when the number of users increases.

Figures (29)

• Figure 1: Mobile data traffic per smartphone (GB per month) ericsson2020ericsson
• Figure 2: Evolution of Wireless Mobile Generations ranaweera20224g.
• Figure 3: A user's perception of the different communications networks, from 1G to the hypothetical 6G. In 1G and 2G, voice and text are available. In 3G and 4G, pictures and video become commonplace. In 5G, live ultra-high-definition three-dimensional data can be employed. In 6G, it is expected that we could have a ubiquitous virtual existence dang2020should.
• Figure 4: Representation of multiple KPIs of 6G use cases, together with the improvements with respect to 5G networks 9040264.
• Figure 5: Possible 6G Communication Architecture Scenario chowdhury20206g.