Thompson, John

Davies, Michael

Popoola, Wasiu

Arslan, Tughrul

Zhang, Junkai

2023-11-22T14:22:12Z

2023-11-22T14:22:12Z

2023-11-22

In sixth generation (6G) wireless networks, the severe traffic congestion in the microwave frequencies motivates the exploration of the large available bandwidth in the millimetre-wave (mmWave) frequencies to achieve higher network capacity and data rate. Since large-scale antenna arrays and dense base station deployment are required, the hybrid beamforming architecture and the recently proposed integrated access and backhaul (IAB) networks become potential candidates for providing cost and hardware-friendly techniques for 6G wireless networks. In addition, in-band-full-duplex (IBFD) has been recently paid much more research attention since it can make the transmission and reception occur in the same time and frequency band, which nearly doubles the communication spectral efficiency (SE) compared with state-of-the-art half-duplex (HD) systems. Since 6G will explore sensing as its new capability, future wireless networks can go far beyond communications. Motivated by this, the development of integrated sensing and communications (ISAC) systems, where radar and communication systems share the same spectrum resources and hardware, has become one of the major goals in 6G. This PhD thesis focuses on the design and analysis of IBFD-IAB wireless networks in the frequency range 2 (FR2) band (≥ 24.250 GHz) at mmWave frequencies for the potential use in 6G. Firstly, we develop a novel design for the single-cell FR2-IBFD-IAB networks with subarray-based hybrid beamforming, which can enhance the SE and coverage while reducing the latency. The radio frequency (RF) beamformers are obtained via RF codebooks given by a modified matrix-wise Linde-Buzo-Gray (LBG) algorithm. The self-interference (SI) is cancelled in three stages, where the first stage of antenna isolation is assumed to be successfully deployed. The second stage consists of the optical domain-based RF cancellation, where cancellers are connected with the RF chain pairs. The third stage is comprised of the digital cancellation via successive interference cancellation followed by minimum mean-squared error (MSE) baseband receiver. Multiuser interference in the access link is cancelled by zero-forcing at the IAB-node transmitter. The proposed codebook algorithm avoids undesirable low-rank behaviour, while the proposed staged-SI cancellation (SIC) shows satisfactory cancellation performance in the wideband IBFD scenario. However, the system performance can be affected by the hardware impairments (HWI) and RF effective channel estimation errors. Secondly, we study an FR2-IBFD-ISAC-IAB network for vehicle-to-everything communications, where the IAB-node acts as a roadside unit performing sensing and communication simultaneously (i.e., at the same time and frequency band). The SI due to the IBFD operation will be cancelled in the propagation, analogue, and digital domains; only the residual SI (RSI) is reserved for performance analysis. Considering the subarray-based hybrid beamforming structure, including HWI and RF effective SI channel estimation error, the unscented Kalman filter is used for tracking multiple vehicles in the studied scenario. The proposed system shows an enhanced SE compared with the HD system, and the tracking MSEs averaged across all vehicles of each state parameter are close to their posterior Cramér-Rao lower bounds. Thirdly, we analyse the performance of the multi-cell wideband single-hop backhaul FR2-IBFD-IAB networks by using stochastic geometry analysis. We model the wired-connected next generation NodeBs (gNBs) as the Matérn hard-core point process (MHCPP) to meet the real-world deployment requirement and reduce the cost caused by wired connection in the network. We first derive association probabilities that reflect how likely the typical user-equipment is served by a gNB or an IAB-node based on the maximum long-term averaged biased-received-desired-signal power criteria. Further, by leveraging the composite Gamma-Lognormal distribution, we derive results for the signal to interference plus noise ratio coverage, capacity with outage, and ergodic capacity of the network. In order to assess the impact of noise, we consider the sidelobe gain on inter-cell interference links and the analogue to digital converter quantization noise. Compared with the HD transmission, the designated system shows an enhanced capacity when the SIC operates successfully. We also study how the power bias and density ratio of the IAB-node to gNB, and the hard-core distance can affect system performance. Overall, this thesis aims to contribute to the research efforts of shaping the 6G wireless networks by designing and analysing the FR2-IBFD-IAB inspired networks in the FR2 band at mmWave frequencies that will be potentially used in 6G for both communication only and ISAC scenarios.

https://hdl.handle.net/1842/41226

http://dx.doi.org/10.7488/era/3962

en

The University of Edinburgh

J. Zhang, N. Garg, M. Holm, and T. Ratnarajah, “Design of Full-Duplex Millimeter-Wave Integrated Access and Backhaul Networks”, IEEE Wireless Commun. Mag., vol. 28, no. 1, pp. 60-67, Feb. 2021.

J. Zhang, N. Garg, M. Holm, and T. Ratnarajah, “Nystr¨om Method-Based Hybrid Precoding for mmWave Full-Duplex Integrated Access and Backhaul Systems”, in Proc. IEEE WCNC, Nanjing, China, Mar. 2021.

J. Zhang, H. Luo, N. Garg, M. Holm, and T. Ratnarajah, “Design and Analysis of mmWave Full-Duplex Integrated Access and Backhaul Networks”, in Proc. IEEE ICC, Montreal, Canada, June 2021.

N. Garg, J. Zhang, and T. Ratnarajah, “Rate-Energy Balanced Precoding Design for SWIPT Based Two-Way Relay Systems”, IEEE J. Sel. Topics Signal Process., vol. 15, no. 5, pp. 1228-1241, Aug. 2021.

J. Zhang, N. Garg, and T. Ratnarajah, “Design of In-Band-Full-Duplex IAB Networks for Integrated Sensing and Communications”, in Proc. IEEE ICC, Seoul, South Korea, May 2022.

J. Zhang, H. Luo, N. Garg, A. Bishnu, M. Holm, and T. Ratnarajah, “Design and Analysis of Wideband In-Band-Full-Duplex FR2-IAB Networks”, IEEE Trans. Wireless Commun., vol. 21, no. 6, pp. 4183-4196, June 2022.

J. Zhang, N. Garg, and T. Ratnarajah, “In-Band-Full-Duplex Integrated Sensing and Communications for IAB Networks”, IEEE Trans. Veh. Technol., vol. 71, no. 12, pp. 12782-12796, Dec. 2022.

J. Zhang, and T. Ratnarajah, “Air-Ground OTFS In-Band-Full-Duplex Integrated Sensing and Communications Systems”, in Proc. IEEE ICC, Rome, Italy, May 2023.

J. Zhang, and T. Ratnarajah, “Performance Analysis of In-Band-Full- Duplex Multi-Cell Wideband IAB Networks”, IEEE Trans. Veh. Technol., under review, May 2023.

sixth generation (6G) wireless networks

millimetre-wave (mmWave) frequencies

integrated access and backhaul (IAB) networks

in-band-full-duplex (IBFD)

spectral efficiency (SE)

half-duplex (HD) systems

integrated sensing and communications (ISAC) systems

IBFD-IAB wireless networks

FR2-IBFD-IAB networks

radio frequency (RF) beamformers

Linde-Buzo-Gray (LBG) algorithm

self-interference (SI)

mean-squared error (MSE) baseband receiver

IAB-node transmitter

staged-SI cancellation (SIC)

wired-connected next generation NodeBs (gNBs)

Matérn hardcore point process (MHCPP)

In-band-full-duplex integrated access and backhaul enabled next generation wireless networks

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy