Mobile data traffic will continue its tremendous growth in some markets, and has already resulted in an apparent radio spectrum scarcity. There is a strong need for more efficient methods to use spectrum resources, leading to extensive research on increasing spectrum reusability on flexible radio platforms. This study solves this problem in two sub topics, millimeter wave communication on wireless backhaul for spectrum reusability, and flexible prototyping radio platform using software-defined radio (SDR).
Wireless backhaul has received significant attention as a key technology affecting the development of future wireless cellular networks because it helps to easily deploy many small size cells, an essential part of a high capacity system. Millimeter wave is considered a possible candidate for cost-effective wireless backhaul. In the outdoor deployment using a millimeter wave, beamforming methods are key techniques to establish wireless links in the 60 GHz to 80 GHz to overcome pathloss constraints (i.e., rainfall effect and oxygen absorption). The millimeter wave communication system cannot directly access the channel knowledge. To overcome this, a beamforming method based on codebook search is considered. The millimeter wave communication cannot access channel knowledge, therefore alternatively a beamforming method based on a codebook search is considered. In the first part, we propose an efficient beam alignment technique using adaptive subspace sampling and hierarchical beam codebooks. A wind sway analysis is presented to establish a notion of beam coherence time. This highlights a previously unexplored tradeoff between array size and wind-induced movement. Generally, it is not possible to use larger arrays without risking a performance loss from wind-induced beam misalignment. The performance of the proposed alignment technique is analyzed and compared with other search and alignment methods. Results show significant performance improvement with reduced search time.
In the second part of this study, SDR is discussed as an approach toward flexible wireless communication systems. Most layers of SDR are implemented by software. Therefore, only a software change is needed to transform the type of radio system. The translation of the signal processing into software performed by a regular computer opens up a huge number of possibilities at a reasonable price and effort. SDR systems are widely used to build prototypes, saving time and money. In this project, a robust wireless communication system in high interference environment was developed. For the physical layer (PHY) of the system, we implemented a channel sub-bandding method that utilizes frequency division multiplexing to avoid interference. Then, to overcome a further interfered channel, Direct Spread Spectrum System (DSSS) was considered and implemented. These prototyped testbeds were evaluated for system performance in the interference environment.

Millimeter wave beamforming for wireless backhaul and access in small cell networks and practical approaches in software-defined radio

The fifth generation (5G) research and development has been fueled by many new breakthroughs in various areas. The recent progress in carrier aggregation (CA), licensed assisted access (LAA), massive MIMO (MaMi), beamforming techniques, cooperative spectrum sensing (CSS), compressive sensing (CS), machine learning, etc., has provided inspiring and promising approaches to address 5G and beyond challenges. However, at the user equipment (UE) end, limited design budget and hardware resources bring along a series of challenging implementation issues when delivering multi-standard and multi-functional wireless communications. In this paper, we first review recent advances in technical standards and critical enabling techniques, accompanied with several case studies of product developments. After the classification of typical 5G application and deployment scenarios, we propose and analyze a novel hardware reuse and multiplexing solution to facilitate cost-effective and energy-efficient UE design, followed by an investigation of state-of-the-art hardware development from the systems and circuits standpoint. Moreover, wireless UE hardware solutions, UE proof-of-concept (PoC) implementation and field test are proposed and discussed. Finally, the new trends of UE design and terahertz technologies for 5G and beyond applications are investigated and envisioned.

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Enabling Multi-Functional 5G and Beyond User Equipment: A Survey and Tutorial

This article presents an extremely broadband 24.5–43.5 GHz receiver (RX) achieving 32–56-dB instantaneous full-band image rejection (IR), which supports multiple major mm-Wave 5G bands at 24.5/28/37/39/43 GHz. A compact transformer-based I/Q network (0.14 mm2) is proposed to generate high-precision LO I/Q signals at millimeter-wave (mm-Wave) and provide built-in load impedance up-transformation for passive voltage amplification, boosting the LO swing for a higher RX conversion gain (CG). The high-quality differential I/Q generation is measured with phase/amplitude variation less than ±1.8°/±0.15 dB over an instantaneous wide bandwidth of 25–50 GHz without any calibration or switching/tunable elements. The RX is measured with a peak 35.2-dB CG and 18-dB gain tuning to accommodate complex EM environments. The RX modulation tests successfully demonstrate receiving 18-Gb/s 64-QAM and 14.4-Gb/s 256-QAM signals. In addition, the RX is tested with concurrent injection of a desired signal and an image, while the image uses the same wideband modulation scheme and data rate as the desired signal. The RX successfully rejects the wideband images and receives the desired signals of 12-Gb/s 64-QAM with −27.6-dB EVM and 8-Gb/s 256-QAM with −33.47-dB EVM. To the best of our knowledge, this article presents the first CMOS RX front end that covers 24.5–43.5-GHz mm-Wave 5G bands and supports instantaneous full-band IR with no calibration, switching/tuning elements, or external controls, enabling future wideband low-latency 5G MIMOs.

A 24.5–43.5-GHz Ultra-Compact CMOS Receiver Front End With Calibration-Free Instantaneous Full-Band Image Rejection for Multiband 5G Massive MIMO

Two 4-bit active phase shifters integrated with all digital control circuitry in 0.13-mu m RF CMOS technology are developed for X- and Ku-band (8-18 GHz) and K-band (18-26 GHz) phased arrays, respectively. The active digital phase shifters synthesize the required phase using a phase interpolation process by adding quadrature-phased input signals. The designs are based on a resonance-based quadrature all-pass filter for quadrature signaling with minimum loss and wide operation bandwidth. Both phase shifters can change phases with less than about 2 dB of RMS amplitude imbalance for all phase states through an associated DAC control. For the X- and Ku-band phase shifter, the RMS phase error is less than 10 degrees over the entire 5-18 GHz range. The average insertion loss ranges from -3 dB; to -0.2 dB at 5-20 GHz. The input P-1dB for all 4-bit phase states is typically - 5.4 +/- 1.3 dBm at 12 GHz in the X- and.Ku-band phase shifter. The K-band phase shifter exhibits 6.5-13 degrees of RMS phase error at 15-26 GHz. The average insertion loss is from -4.6 to -3 dB at 15-26 GHz. The input P-1dB of the K-band phase shifter is -0.8 +/- 1.1 dBm at 24 GHz. For both phase shifters, the core size excluding all the pads and the output 50 Omega matching circuits, inserted for measurement purpose only, is very small, 0.33 x 0.43 mm(2). The total current consumption is 5.8 mA in the X- and Ku-band phase shifter and 7.8 mA in the K-band phase shifter, from a 1.5 V supply voltage.

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0.13-mu m CMOS phase shifters for X-, Ku-, and K-band phased arrays - eScholarship

The ever-growing demand for low power, high performance, cost-effective, low-profile, and highly integrated wireless systems for emerging applications has triggered the need for the enormous innovations in wireless transceiver systems, components, architectures and technologies. This is especially valid for the antenna which is an integral component of the wireless transceiver systems and contributes significantly in determining their overall performance. Antenna-on-Chip (AoC) is an alternative antenna technology, which has drawn a substantial attention in recent days because of its various benefits over off-chip antenna technology. A few of these benefits include miniaturization, low power, low cost, and high integration of the wireless modules. Motivated by these valuable advantages and to unveil the true potential of the AoCs, this article presents, for the first time, a comprehensive survey of the suitability, advantages, and challenges of the AoCs for the emerging wireless applications such as 5th generation (5G) Wireless Systems, Internet-of-Things (IoT) Wireless Devices and Systems, Wireless Sensor Networks (WSNs), Wireless Interconnects, Wireless Energy Transfer, Radio Frequency (RF) Energy Harvesting, Biomedical Implants, Unmanned Aerial Vehicles (UAVs), Autonomous vehicles, Innovative characterization methods for Integrated Circuits (ICs) and Antennas, and Smart City. In addition, this article presents the current state-of-the-art of the AoC's applications by classifying their applications in Millimeter-Wave (MM-Wave) band, Terahertz (THz) band, and low-frequency bands. The article also investigates and describes some useful methods for the mitigation of the challenges and issues posed by the emerging applications for the realization of the AoCs in a systematic manner. A concise description of the future directions of the AoCs with respect to each emerging application is also a part of this article. It is expected that this well-structured and organized survey will not only act as an excellent source of scholarship for the relevant research community, but also open up a world of novel research opportunities.

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The Potentials, Challenges, and Future Directions of On-Chip-Antennas for Emerging Wireless Applications—A Comprehensive Survey

The development of next-generation 5G networks is ongoing. The large available bandwidth at mm-waves allows increasing channel capacity well beyond the levels offered by LTE. Wide ranges of spectra, with sub-bands centered at 28GHz, 37GHz, and 39GHz, have been appointed for 5G development to facilitate international roaming and intra-networks connections [1]. In this scenario, generation of ultra-low phase-noise quadrature (IQ) signals with >40dB image rejection ratio (IRR) over >40% fractional bandwidth is key to efficiently deliver extreme data-rates through high-order spectrally efficient modulations. Quadrature voltage-controlled oscillators are disregarded because of their limited tuning range and also due to a severe trade-off between phase noise and phase accuracy. Solutions leveraging single-phase VCOs followed by quadrature generators is seen as a better strategy. Still, the challenging phase noise, required to support higher-order modulations trading-off with tuning range, mandates at least two VCOs covering half bandwidth each. For quadrature generation, distributed couplers, e.g., Lange couplers, are bulky and not amenable to integration. Hybrid couplers based on coupled inductors offer a compact footprint with low loss, but they are disregarded, because a few percent variation in the coupling coefficient, k, leads to unacceptable phase deviations. Polyphase filters (PPFs) and their improvements are widely adopted at RF [2]. In [3], the PPF operation at mm-waves is proven through careful layout techniques. Still, wideband operation can be achieved only by cascading several stages, severely increasing signal loss and power consumption.

A >40dB IRR, 44% fractional-bandwidth ultra-wideband mm-wave quadrature LO generator for 5G networks in 55nm CMOS

Precise generation of quadrature signals over a wide frequency range is a key function for the next-generation 5G communication systems. In this paper, we present a wideband quadrature generator based on a single-stage polyphase filter (PPF). A phase detector senses the phase error from quadrature signals generated by a single-stage PPF, and a feedback circuit continuously tunes the filter center frequency to the input signal frequency by varying the polyphase resistance of an nMOS device in triode. Transformer-based resonant circuits at the input and output of the PPF ensure wide bandwidth and low loss. Prototypes have been realized in a 55-nm CMOS technology. Tailored to the next-generation 5G systems for cross-network interoperability requirements, the measured quadrature generator shows an image rejection ratio IRR > 40 dB over a bandwidth from 28 to 44 GHz. The power consumption is 36 mW for the PPF and buffers, and 3 mW only for the calibration loop. One key aspect of the proposed solution is its robustness over process, voltage and temperature (PVT), one of the weak aspects of alternatives proposed in the literature. This solution compares favorably with the state of the art and shows the largest fractional bandwidth (44%) among the quadrature generators at frequencies greater than 20 GHz, to authors’ knowledge.

A PVT-Tolerant >40-dB IRR, 44% Fractional-Bandwidth Ultra-Wideband mm-Wave Quadrature LO Generator for 5G Networks in 55-nm CMOS

The development of 5G communication systems is underway. When employing 64 QAM, very low phase noise levels are required to limit EVM — i.e. less than −117dBc/Hz at 1MHz offset from f=20GHz. In this paper, the challenges of achieving such a low phase noise are discussed in detail. The choice between CMOS vs BJT devices is investigated and the impact of the base resistance intrinsic in BJT-based VCOs is addressed. BJT-based VCO shows ∼2dB better phase noise when compared to CMOS-based VCO and low supply is employed. When higher supply is leveraged, BJT-based VCO advantage is kept, while CMOS-based VCO is not able to reach the targeted tuning range due to thick-oxide devices parasitics. To further minimize phase noise, emphasis is on the minimization of L/Q inductor versus quality factor ratio. Prototypes in a 55nm BiCMOS technology were operated at 2.5V supply with the largest amplitude allowed by reliability constraints. Measurements show a phase noise as low as −119dBc/Hz at 1MHz from a 20GHz carrier offset with a tuning range (TR) of 19% and FoM=-187dBc/Hz. Power consumption is 56mW. To the best of authors' knowledge, the presented VCO shows the lowest reported phase noise among state-of-the-art BiCMOS VCOs with TR>10%.

A K-Band low-noise bipolar Class-C VCO For 5G backhaul systems in 55nm BiCMOS technology

A K-band low-noise bipolar class-C VCO for 5G backhaul systems in 55 nm BiCMOS technology

Next-generation 5G communication systems require adaptive high-order modulations to increase spectral efficiency. To limit EVM, very low phase noise levels are required — i.e. less than −117dBc/Hz at 1MHz offset for 64QAM at f=20GHz. In this paper, the design and measurements of a low-noise K-Band VCO are presented. The challenges of achieving such a low phase noise are discussed in detail, with particular emphasis on the minimization of L/Q, inductor versus quality factor ratio. Prototypes have been realized in a 55nm BiCMOS technology. Operated at 2.5V supply with the largest amplitude allowed by reliability constraints, measurements show a phase noise as low as −119dBc/Hz at 1MHz from a 20GHz carrier offset with a tuning range (TR) of 19% and FoM=−187dBc/Hz. Power consumption is 56mW. To the best of authors' knowledge, the presented VCO shows the lowest reported phase noise among state-of-the-art BiCMOS VCOs with TR>10%.

Niccolo Lacaita

Papers

A >40dB IRR, 44% fractional-bandwidth ultra-wideband mm-wave quadrature LO generator for 5G networks in 55nm CMOS

A PVT-Tolerant >40-dB IRR, 44% Fractional-Bandwidth Ultra-Wideband mm-Wave Quadrature LO Generator for 5G Networks in 55-nm CMOS

A K-Band low-noise bipolar Class-C VCO For 5G backhaul systems in 55nm BiCMOS technology

A K-band low-noise bipolar class-C VCO for 5G backhaul systems in 55 nm BiCMOS technology

A low-noise K-band class-C VCO for E-band 5G backhaul systems in 55nm BiCMOS technology