Hybrid Transceiver Optimization for Multi-Hop Communications

Multi-hop communication with the aid of large-scale antenna arrays will play a vital role in future emergence communication systems. In this paper, we investigate amplify-and-forward based and multiple-input multiple-output assisted multi-hop communication, in which all nodes employ hybrid transceivers. Moreover, channel errors are taken into account in our hybrid transceiver design. Based on the matrix-monotonic optimization framework, the optimal structures of the robust hybrid transceivers are derived. By utilizing these optimal structures, the optimizations of analog transceivers and digital transceivers can be separated without loss of optimality. This fact greatly simplifies the joint optimization of analog and digital transceivers. Since the optimization of analog transceivers under unit-modulus constraints is non-convex, a projection type algorithm is proposed for analog transceiver optimization to overcome this difficulty. Based on the derived analog transceivers, the optimal digital transceivers can then be derived using matrix-monotonic optimization. Numeral results obtained demonstrate the performance advantages of the proposed hybrid transceiver designs over other existing solutions.Comment: 32 pages, 6 figures. This manuscript has been submitted to IEEE Journal on Selected Areas in Communications (special issue on Multiple Antenna Technologies for Beyond 5G

Aperture-Level Simultaneous Transmit and Receive (STAR) with Digital Phased Arrays

In the signal processing community, it has long been assumed that transmitting and receiving useful signals at the same time in the same frequency band at the same physical location was impossible. A number of insights in antenna design, analog hardware, and digital signal processing have allowed researchers to achieve simultaneous transmit and receive (STAR) capability, sometimes also referred to as in-band full-duplex (IBFD). All STAR systems must mitigate the interference in the receive channel caused by the signals emitted by the system. This poses a significant challenge because of the immense disparity in the power of the transmitted and received signals. As an analogy, imagine a person that wanted to be able to hear a whisper from across the room while screaming at the top of their lungs. The sound of their own voice would completely drown out the whisper. Approaches to increasing the isolation between the transmit and receive channels of a system attempt to successively reduce the magnitude of the transmitted interference at various points in the received signal processing chain. Many researchers believe that STAR cannot be achieved practically without some combination of modified antennas, analog self-interference cancellation hardware, digital adaptive beamforming, and digital self-interference cancellation. The aperture-level simultaneous transmit and receive (ALSTAR) paradigm confronts that assumption by creating isolation between transmit and receive subarrays in a phased array using only digital adaptive transmit and receive beamforming and digital self-interference cancellation. This dissertation explores the boundaries of performance for the ALSTAR architecture both in terms of isolation and in terms of spatial imaging resolution. It also makes significant strides towards practical ALSTAR implementation by determining the performance capabilities and computational costs of an adaptive beamforming and self-interference cancellation implementation inspired by the mathematical structure of the isolation performance limits and designed for real-time operation

Hybrid Processing Design for Multipair Massive MIMO Relaying with Channel Spatial Correlation

Massive multiple-input multiple-output (MIMO) avails of simple transceiver design which can tackle many drawbacks of relay systems in terms of complicated signal processing, latency, and noise amplification. However, the cost and circuit complexity of having one radio frequency (RF) chain dedicated to each antenna element are prohibitive in practice. In this paper, we address this critical issue in amplify-and-forward (AF) relay systems using a hybrid analog and digital (A/D) transceiver structure. More specifically, leveraging the channel long-term properties, we design the analog beamformer which aims to minimize the channel estimation error and remain invariant over a long timescale. Then, the beamforming is completed by simple digital signal processing, i.e., maximum ratio combining/maximum ratio transmission (MRC/MRT) or zero-forcing (ZF) in the baseband domain. We present analytical bounds on the achievable spectral efficiency taking into account the spatial correlation and imperfect channel state information at the relay station. Our analytical results reveal that the hybrid A/D structure with ZF digital processor exploits spatial correlation and offers a higher spectral efficiency compared to the hybrid A/D structure with MRC/MRT scheme. Our numerical results showcase that the hybrid A/D beamforming design captures nearly 95% of the spectral efficiency of a fully digital AF relaying topology even by removing half of the RF chains. It is also shown that the hybrid A/D structure is robust to coarse quantization, and even with 2-bit resolution, the system can achieve more than 93% of the spectral efficiency offered by the same hybrid A/D topology with infinite resolution phase shifters.Comment: 17 pages, 13 figures, to appear in IEEE Transactions on Communication

Fully-integrated mm-Wave Full-duplexing and MIMO Multi-beamforming Receiver Techniques for 5G and Beyond

In recent years, the research community's interest in fully integrated mm-Wave wireless communication systems has increased significantly. With the standards for 5G NR now in place, the focus has shifted to actual deployment. Mm-Wave systems provide wider bandwidths, higher capacity, and lower latency than existing systems such as 4G. Higher path loss and shadowing, however, limit the network coverage at mm-Wave frequencies. The possibility of beamforming due to compact antenna size at mm-Wave and range-extending repeaters help mitigate challenges arising from path loss and relax link budget requirements. In the first part of the thesis, fully integrated scalable MIMO multi-beamforming phased-array to enable unit-tile based densely packed (lambda=2) large scale phased-arrays is demonstrated. Large scale arrays enhance Signal to Noise Ratio (SNR) and/or Effective Isotropically Radiated Power (EIRP) and help meet link budget. In the second part, mm-Wave Full-duplex (FD) receiver (RX) to implement Integrated Access and Backhaul (IAB) and repeaters in a spectrum efficient way is demonstrated. Dense deployment of IAB and repeaters enhances link robustness and range of connectivity. Two Integrated Chips (ICs) are fabricated and measured for demonstration. In the first IC, a 4-element MIMO RX array with multi-beamforming and simplified single wire intermediate frequency (IF) IO is presented. The evolution of mm-wave phased array receivers to MIMO RX promises multi-beamforming and improved capacity. Digital Beamforming (DBF) provides the highest flexibility for multibeamforming. However, it suffers from # of ADCs scaling with the # of elements and absence of spatial filtering prior to the ADCs. Mm-Wave MIMO arrays must also address the challenge of increased IO routing while supporting dense ll-factors with =2 antenna spacing. In this work, a MIMO multi-beamforming RX array architecture with simultaneous spatial filtering and single wire Frequency-domain Multiplexing (FDM) for 5G and beyond is presented. The proposed system preserves full MIMO field-of-view while ensuring a single IF interface. A 28 GHz 4-element RX prototype demonstrates the proposed functionality in 65-nm CMOS. The IC occupies only 3.4mm x 3.1mm for a four-element MIMO 28 GHz array and can form four independent beams with > 400MHz 3 dB BW and FDM on to a single IF interface. Mm-wave MIMO operation is demonstrated by concurrent reception of two wireless 28 GHz beams at 400 Mb/s (100 Msps, 16QAM) data rate. In the second IC, a 26-GHz fully integrated In-band Full-duplex (IBFD) Circulator receiver, which employs passive and active Self-interference Cancellation (SIC) techniques in the mm-Wave domain is presented. Coverage of wireless networks at mm-Wave frequencies can be enhanced by deploying a large number of base stations economically using wireless backhauling. Integrated access and backhaul nodes with spectrum reuse is an efficient way of wireless backhauling. To retain the channel capacity, IAB needs to be implemented using FD schemes that suffers from a strong Transmitter (TX) to RX leakage. This SI leakage can significantly impact the receiver sensitivity and increase the baseband/ADC dynamic range requirements. Canceling SI at mm-Wave applications is challenging given the high frequency of operation, wide bandwidths, and antenna (ANT) impedance sensitivity to the surroundings. Proposed mm-Wave RX with a shared ANT interface based on a Circulator with active SI cancelers provide ~53 dB SIC over 400MHz and ~40 dB SIC over 400MHz to meet the link budget requirements. Proposed architecture achieves SIC by (i) introducing a shared ANT interface based on a hybrid-coupler and a Non-reciprocal Transmission Line (NTL) that provides wideband SIC and additionally creating a SI replica (ii) subsequent active cancellation using SI replica along with variable gain and phase shifters to accommodate SI channel variations. Proposed 26-GHz RX consumes only ~111mW power. The system is implemented in 45nm SOI CMOS and has an active area of 4.54mm². Stand-alone RX NF is ~5.8 dB, and TX to ANT Insertion Loss (IL) is ~3.1 dB. Over-the-Air (OTA) measurements with modulated TX (128 QAM 2.1 Gb/s) and RX (128 QAM 4.2 Gb/s) signals show an EVM of 3.3% when PTX = PRX

Hybrid beamforming with sub-connected structure for MmWave massive multi-user MIMO relay systems

In this paper, we investigate the hybrid beamforming design with sub-connected structure for millimeter-wave (mmWave) massive multi-user multiple-input multiple-output (MU-MIMO) amplify-and-forward (AF) relay systems. Considering the constant-modulus and block-diagonal constraints, an iterative algorithm is proposed to sequentially design the analog beamforming of the base station, relay, and users. Next, the relay baseband combiner is designed by transforming the highly complicated non-convex mutual information maximization problem into an easily tractable weighted minimum mean squared error one. To mitigate the inter-user interference, a successive serial interference cancellation based and a piecewise successive approximation based methods are developed for the uniform sparse distribution and dense distribution scenarios, respectively. Simulation results demonstrate that the two proposed hybrid beamforming schemes can achieve good performance in terms of sum-rate and energy efficiency, and outperform benchmarks significantly. In addition, the two proposed schemes are shown to be robust to imperfect channel state information (CSI), even though they are studied based on perfect CSI

Energy E fficiency Oriented Full Duplex Wireless Communication Systems

Full-duplex (FD) transmission is a promising technique for fifth generation (5G) wireless communications, enabling significant spectral efficiency (SE) improvement over existing half-duplex (HD) systems. However, FD transmission consumes higher power than HD transmission, especially for millimetre wave band. Therefore, energy efficiency (EE) for FD systems is a critical yet inadequately addressed issue. This thesis addresses the critical EE challenges and demonstrates promising solutions for implementing FD systems, as detailed in the following contributions. In the first contribution, a comprehensive EE analysis of the FD and HD amplify-and-forward (AF) relay-assisted 60 GHz dual-hop indoor wireless systems is presented. An opportunistic relay mode selection scheme is developed, where FD relay with different self-interference (SIC) techniques or HD relay is opportunistically selected. Together with transmission power adaptation, EE is maximised with given channel gains. A counter-intuitive finding is shown that, with a relatively loose maximum transmission power constraint, FD relay with two-stage SIC is preferable to both FD relay with one-stage SIC and HD relay, resulting in a higher optimised EE. A full range of power consumption sources are considered to rationalise the analysis. The effects of imperfect SIC at relay, drain efficiency and static circuit power on EE are investigated. Simulation results verify the theoretical analysis. In the second contribution, EE oriented resource allocation for FD decode-of-forward (DF) relay-assisted 60 GHz multiuser systems is investigated. In contrast to the existing SE oriented designs, the proposed scheme maximises EE for FD relay systems under cross-layer constraints, addressing the typical problems at 60 GHz. A low-complexity EE-orientated resource allocation algorithm is proposed, by which the transmission power allocation, subcarrier allocation and throughput assignment are performed jointly across multiple users. Simulation results verify the analytical results and confirm that the FD relay systems with the proposed algorithm achieve a higher EE than the FD relay systems with SE oriented approaches, while offering a comparable SE. In addition, a much lower throughput outage probability is guaranteed by the proposed resource allocation algorithm, showing its robustness against channel estimation errors. In the third contribution, it is noticed that in wireless power transfer (WPT)-aided relay systems, the SE of the source-relay link plays a dominant role in the system SE due to limited transmission power at the WPT-aided relay. A novel asymmetric protocol for WPT-aided FD DF relay systems is proposed in multiuser scenario, where the time slot durations of the two hops are designed to be uneven, to enhance the degree of freedom and hence the system SE. A corresponding dynamic resource allocation algorithm is developed by jointly optimising the time slot durations, subcarriers and transmission power at the source and the relay. Simulation results con rm that, compared to the symmetric WPT-aided FD relay (Sym-WPT-FR) and the time-switching based WPT-aided FD relay (TS-WPT-FR) systems in the literature, the proposed asymmetric WPT-aided FD relay system achieves up to twice the SE and higher robustness against the relay's location and the number of users. In the final contribution, to strike the balance between high SE and low power consumption, a hybrid duplexing strategy is developed for distributed antennas (DAs) systems, where antennas are capable of working in hybrid FD, HD, and sleeping modes. To maximise the system EE with low complexity, activation/deactivation of transmit/receive chain is first performed, by a proposed channel-gain-based DA clustering algorithm, which highlights the characteristics of distributed deployment of antennas. Based on the DAs' con figuration, a novel distributed hybrid duplexing (D-HD)-based and EE oriented algorithm is proposed to further optimise the downlink beamformer and the uplink transmission power. To rationalise the system model, self-interference at DAs, co-channel interference from uplink users to downlink users, and multiuser interference in both uplink and downlink are taken into account. Simulation results confirm that the proposed system provides significant EE and SE enhancements over the colocated FD MIMO system, showing the advantages in alleviating high path loss as well as in cutting the carbon footprint. Compared to the sole-FD DA system, the proposed system shows much higher EE with marginal loss in SE. Also, the SIC operation in the proposed system is much more simplified compared to the two benchmarks

Advanced Tri-Sectoral Multi-User Millimeter-Wave Smart Repeater

Smart Repeaters (SR) can potentially enhance the coverage in Millimeter-wave (mmWave) wireless communications. However, the angular coverage of the existing two-panel SR is too limited to make the SR a truly cost-effective mmWave range extender. This paper proposes the usage of a tri-sectoral Advanced SR (ASR) to extend the angular coverage with respect to conventional SR. We propose a multi-user precoder optimization for ASR in a downlink multi-carrier communication system to maximize the number of served User Equipments (UEs) while guaranteeing constraints on per-UE rate and time-frequency resources. Numerical results show the benefits of the ASR against conventional SR in terms of both cumulative spectral efficiency and number of served UEs (both improved by an average factor 2), varying the system parameters