Efficient MIMO Transmission of PSK Signals With a Single-Radio Reconfigurable Antenna

Crucial developments to the recently introduced signal-space approach for multiplexing multiple data symbols using a single-radio switched antenna are presented. First, we introduce a general framework for expressing the spatial multiplexing relation of the transmit signals only from the antenna scattering parameters and the modulating reactive loading. This not only avoids tedious far-field calculations, but more importantly provides an efficient and practical strategy for spatially multiplexing PSK signals of any modulation order. The proposed approach allows ensuring a constant impedance matching at the input of the driving antenna for all symbol combinations, and as importantly uses only passive reconfigurable loads. This obviates the use of reconfigurable matching networks and active loads, respectively, thereby overcoming stringent limitations of previous single-feed MIMO techniques in terms of complexity, efficiency, and power consumption. The proposed approach is illustrated by the design of a realistic very compact antenna system optimized for multiplexing QPSK signals. The results show that the proposed approach can bring the MIMO benefits to the low-end user terminals at a reduced RF complexity.Comment: 30 pages, 6 figures. IEEE Transactions on Communications, 201

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

RF and Millimeter-wave Techniques to Improve Scalability and Efficiency of Digital Beamforming Arrays

Spectrum overcrowding, ever increasing demand for high data rate and increased mobility requirements are three major challenges 5G-technology is trying to address. In this thesis I start with a RF front-end technique that deals with blocker interference arising from spectrum overcrowding both across frequency bands and within the same frequency bands. Chapter 3 presents a single wire IF interface design for phased array receivers which enables simple IF backhaul for high data volume MIMO systems. Finally a outphasing power amplifier(PA) design is presented in chapter 4 along with a driver amplifier with digital amplitude modulation to achieve state of the art power back off efficiency, which reduces battery usage and thus increases mobility. The first part of this thesis demonstrates the use of orthogonal sequences along to N-path filters to achieve reconfigurable select/reject filtering of signals based on their spatial, spectral and code-domain properties. A frequency/code-domain reject and select filtering is proposed and implemented using N-path switching with passive inductors as correlators. Using inductors instead of capacitors in N-path filters is challenging because of large inductance value required for our application demands use of off-chip inductors, which comes with associated parasitics and lower self-resonance frequency. In this design a cascaded inductor approach and differential N-path filtering is used to overcome inductor parasitics and enable operation at 1 GHz. A code-domain notch filter followed by a code-domain select receiver is designed and implemented in 65-nm CMOS technology. Measurements demonstrate 0.5 GHz to 1.0 GHz filter tuning range, with a maximum 26dB rejection for a blocker signal with 8dBm power, while consuming 60mW (at 1GHz operation frequency) and occupying 1.2mm2 of die area. Second part of this thesis demonstrates a single wire IF interface to simplify scaling of millimeter-wave(mm-Wave) phased array systems while preserving the data from each element, this enables spatial multiplexing, virtual arrays for radar, digital beamforming(DBF), etc. However, per-element digitization results in a formidable I/O challenge in large-scale tiled MIMO mm-Wave arrays. This dissertation demonstrates a 28 GHz 4-element MIMO RX with a single-wire interface that multiplexes the baseband signals of all elements and the LO reference through code-domain multiplexing. System considerations are presented and the approach is validated through DBF after de-multiplexing of the baseband signals from the single wire. Each element in the array achieves 16 dB conversion gain and ∼ 7 dB noise figure(NF) while consuming 60 mA from 1.2 V. The IC occupies 5.75 mm² in 65-nm CMOS. Final part of this thesis describes the design and implementation of a digital outphasing PA at 28 GHz to achieve state of the art back of efficiency. Outphasing PA require branch PA units to act as voltage sources(very low output impedance), which is challenging at mm-Wave frequencies. In this PA design an approximate class-F operation is achieved by tuning PA load network for up to 3rd harmonic. A stacked PA architecture is used for individual PA units to achieve high maximum power output. Output-power further improved by utilizing a novel diode connected stack bias circuit to improve out-put swing. PA delivers a maximum output-power of 20 dBm with a peak power added efficiency(PAE) of 27% (PA along with driver stages) and 6 dB back-off PAE of 16.5%

Direction of Arrival Estimation for Radio Positioning: a Hardware Implementation Perspective

Nowadays multiple antenna wireless systems have gained considerable attention due to their capability to increase performance. Advances in theory have introduced several new schemes that rely on multiple antennas and aim to increase data rate, diversity gain, or to provide multiuser capabilities, beamforming and direction finding (DF) features. In this respect, it has been shown that a multiple antenna receiver can be potentially used to perform radio localization by using the direction of arrival (DoA) estimation technique. In this field, the literature is extensive and gathers the results of almost four decades of research activities. Among the most cited techniques that have been developed, we find the so called high-resolution algorithms, such as multiple signal classification (MUSIC), or estimation of signal parameters via rotational invariance (ESPRIT). Theoretical analysis as well as simulation results have demonstrated their excellent performance to the point that they are usually considered as reference for the comparison with other algorithms. However, such a performance is not necessarily obtained in a real system due to the presence of non idealities. These can be divided into two categories: the impairments due to the antenna array, and the impairments due to the multiple radio frequency (RF) and acquisition front-ends (FEs). The former are strongly influenced by the manufacturing accuracy and, depending on the required DoA resolution, have to be taken into account. Several works address these issues in the literature. The multiple FE non idealities, instead, are usually not considered in the DoA estimation literature, even if they can have a detrimental effect on the performance. This has motivated the research work in this thesis that addresses the problem of DoA estimation from a practical implementation perspective, emphasizing the impact of the hardware impairments on the final performance. This work is substantiated by measurements done on a state-of-the-art hardware platform that have pointed out the presence of non idealities such as DC offsets, phase noise (PN), carrier frequency offsets (CFOs), and phase offsets (POs) among receivers. Particularly, the hardware platform will be herein described and examined to understand what non idealities can affect the DoA estimation performance. This analysis will bring to identify which features a DF system should have to reach certain performance. Another important issue is the number of antenna elements. In fact, it is usually limited by practical considerations, such as size, costs, and also complexity. However, the most cited DoA estimation algorithms need a high number of antenna elements, and this does not yield them suitable to be implemented in a real system. Motivated by this consideration, the final part of this work will describe a novel DoA estimation algorithm that can be used when multipath propagation occurs. This algorithm does not need a high number of antenna elements to be implemented, and it shows good performance despite its low implementation/computational complexity

Low-Cost Beam Steerable Antennas Using Parasitic Elements

Beam steerable antennas are considered as a possible solution for meeting challenges in military and civilian systems such as satellite communication networks, automotive collision avoidance radar, base stations and biomedical applications. Phased array antennas are a natural choice as the foundation for many steerable antenna platform due to its exibility and gain scalability. The implementation of a phased array requires a large number of electronic components, tending to drive the cost of phased arrays and limit their usage to military applications. The electrically steerable parasitic array radiator (ESPAR) has been introduced as an antenna which is capable of adaptively controlling its beam pattern using parasitic elements loaded with varactors. ESPAR has attracted the attention of researchers from the desire for electrically scanned beams with inexpensive fabrication and has found as a suitable candidate for communication systems applications, including advanced radars, cellular base stations and space communications. The ultimate goal of this research is to design and propose state of the art designs in the �eld of ESPAR that can satisfy the requirements of today's advanced communication systems, which should be cost-e�ective and can compete with other rival technologies. Considering the potentials of ESPAR, it can be proved that it is a good candidate for modern wireless communications. The thesis presents several contributions related to the design and analysis of ESPAR technology using dielectric resonator antenna (DRA) as the main radiator element. First, the thesis presents solutions to alleviate the problems associated in implementing a large ESPAR. The large array is useful in many applications since some required recon�gurable radiation characteristics may not be achievable with a single ESPAR element. The proposed structure consists of 240 perforated DRAs, whichare uniformly excited by a parallel-series feeding network. By employing the perforation technique, the need for aligning and bonding individual DRA is eliminated. The subarrays are placed in an interleaved arrangement to suppress the grating lobes. The proposed large ESPAR can incredibly reduce the number of phase shifter by 80% in comparison with the conventional phased array, which makes it inexpensive. Second, the thesis investigates potentials of ESPAR for massive multi-input multiple output (MIMO) communication. Massive MIMO technology has attracted tremendous interest due to its capabilities in enhancing the data transmission capacity, increasing the reliability, and reducing the multipath fading. However, in this technology for feeding each individual antenna, one radio frequency chain is required that can increase the power consumption and complexity of the structure. Moreover, to obtain decorrelated channels and to reduce mutual coupling, the antenna should be spaced suffciently far from each other that imposes increased physical dimensions. In contrast to the conventional MIMO structures, in ESPAR only one RF chain is needed and the small size constraint turns to be an advantage as the mutual coupling is exploited to form the desired signals. Furthermore, by controlling the tunable loads at each parasitic antenna element, different radiation patterns can be formed which can signi�cantly improve the performance of a MIMO antenna system operating in a changing environment. Thus, by using the advantages of ESPAR, a design approach to address the size and cost issues is proposed through this work. The proposed design is validated by simulation and measurement of a prototype, and results include the antenna and MIMO �gure of merits such as radiation patterns, efficiency, S-parameters, signal correlations, total active reection coeffcient (TARC), and channel capacity. These results have demonstrated that the proposed ESPAR design can be successfully implemented for a massive MIMO structure. Finally, the thesis presents an effective method to design a ESPAR with a circularly polarized (CP) beam-scanning feature. Circular polarization is an ideal polarization due to its advantages in signal propagation properties, which can address the di�culties associated with mobility, inclement weather conditions, and immunity to multi path distortion. In this work, the CP beam steering is achieved by adopting a sequential rotation approach for placing the parasitic antennas that are loaded with tunable varactors. The proposed CP-ESPAR technique eliminates the need of expensive phase shifters, which signi�cantly reduces cost and fabrication complexity. For performance evaluation, a prototype of the proposed antenna is designed, fabricated, and measured. It is observed that the proposed antenna has a monotonic CP beam scanning from { 22 to 22 operating at 10.5 GHz

Reconfigurable Antennas for Beam-Space MIMO Transmission with a Single Radio

MIMO techniques allow remarkable improvements in the reliability and/or transmission rate of wireless communication systems. However, there are several major challenges towards the implementation of conventional MIMO concept in terminals with size, cost, and power constraints. Firstly, insufficient space impedes the design of efficient and decorrelated MIMO antennas. Second, MIMO traditionally demands each antenna to be fed by its own RF chain, which in turn results in greater hardware complexity, larger power consumption, and higher implementation cost. Among all reduced-complexity and antenna-decoupling schemes proposed so far, the so-called beam-space MIMO has attracted a great deal of interest as a potential solution for addressing both problems concurrently. The key idea therein is to engineer the radiation pattern of a single-feed antenna structure for each symbol period, such that multiple independent symbols directly modulate a predefined set of orthogonal virtual patterns in the far-field, therefore allowing true MIMO transmission using a single RF chain and a compact antenna structure. More important in practice, the transmitted information can be retrieved using a conventional MIMO receiver. However, the transformation of this idea into reality entails dealing with various practical aspects that are commonly overlooked in theoretical and conceptual developments. This dissertation explores the beam-space MIMO concept from the perspective of the antenna engineering, and aims at addressing several key issues associated with the actual design and implementation of beam-space MIMO systems. The early developments of beam-space MIMO concerned switched parasitic arrays. However, the requirement of utilizing several physically-separate radiators is inconvenient for practicable implementation in compact portable devices. To solve this problem, a single-radiator load-modulated antenna solution is proposed in this dissertation. Another primary challenge consists in emulating high-order modulation schemes such as PSK with realistic hardware. Here, an efficient beam-space MIMO strategy is developed, which allows transmitting PSK data streams of any modulation order using only purely reactive reconfigurable loads, and without the need for a symbol-rate dynamic matching network. The approach is illustrated by the design and fabrication of a realistic antenna for QPSK signaling. The performance of a beam-space MIMO system which utilizes the fabricated antenna is then investigated through over-the-air experiments, and compared with conventional MIMO in realistic environments. Embedding information in the radiation patterns, beam-space MIMO systems are expected to be inherently prone to multiplexing performance degradation in the presence of external field perturbation. This makes the study of near-field interaction influence on beam-space MIMO distinct from those carried out for the case of conventional systems. This issue is considered for the first time in this dissertation. Moreover, like any reconfigurable system, a beam-space MIMO system may suffer from bandwidth expansion of the transmitted signals. The final part of the work is directed towards this important issue. To reduce out-of-band radiation effect, a solution based on shaping the time-domain response of the reconfigurable components is presented. The studies presented in this thesis constitute a crucial step towards MIMO with simpler and cheaper hardware for real-life terminals