Communication at millimeter wave (mmWave) frequencies is defining a new era of wireless communication. The mmWave band offers higher bandwidth communication channels versus those presently used in commercial wireless systems. The applications of mmWave are immense: wireless local and personal area networks in the unlicensed band, 5G cellular systems, not to mention vehicular area networks, ad hoc networks, and wearables. Signal processing is critical for enabling the next generation of mmWave communication. Due to the use of large antenna arrays at the transmitter and receiver, combined with radio frequency and mixed signal power constraints, new multiple-input multiple-output (MIMO) communication signal processing techniques are needed. Because of the wide bandwidths, low complexity transceiver algorithms become important. There are opportunities to exploit techniques like compressed sensing for channel estimation and beamforming. This article provides an overview of signal processing challenges in mmWave wireless systems, with an emphasis on those faced by using MIMO communication at higher carrier frequencies.

An Overview of Signal Processing Techniques for Millimeter Wave MIMO Systems

Integrins are cell adhesion molecules that mediate cell-cell, cell– extracellular matrix, and cell-pathogen interactions. They play critical roles for the immune system in leukocyte trafficking and migration, immunological synapse formation, costimulation, and phagocytosis. Integrin adhesiveness can be dynamically regulated through a process termed inside-out signaling. In addition, ligand binding transduces signals from the extracellular domain to the cytoplasm in the classical outside-in direction. Recent structural, biochemical, and biophysical studies have greatly advanced our understanding of the mechanisms of integrin bidirectional signaling across the plasma membrane. Large-scale reorientations of the ectodomain of up to 200 ˚ A couple to conformational change in ligand-binding sites and are linked to changes in α and β subunit transmembrane domain association. In this review, we focus on integrin structure as it relates to affinity modulation, ligand binding, outside-in signaling, and cell surface distribution dynamics.

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Structural Basis of Integrin Regulation and Signaling

Integrins are heterodimeric cell adhesion molecules that link the extracellular matrix to the cytoskeleton. The integrin family in man comprises 24 members, which are the result of different combinations of 1 of 18 alpha- and 1 of 8 beta-subunits. Alternative splicing of mRNA of some alpha- and beta-subunits and postranslational modifications of integrin subunits further increase the diversity of the integrin family. In their capacity as adhesion receptors that organize the cytoskeleton, integrins play an important role in controlling various steps in the signaling pathways that regulate processes as diverse as proliferation, differentiation, apoptosis, and cell migration. The intracellular signals that lead to these effects may be transduced via cytoplasmic components, which have been identified as integrin-binding proteins in yeast two-hybrid screens and which could mediate the coupling of integrins to intracellular signaling pathways. In this review an overview is given of the function and ligand-binding properties of integrins as well as of proteins that associate with integrins and may play a role in their signaling function.

Function and interactions of integrins.

This tutorial presents an overview of the technological advances in millimeter-wave (mm-wave) circuit components, antennas, and propagation that will soon allow 60-GHz transceivers to provide multigigabit per second (multi-Gb/s) wireless communication data transfers in the consumer marketplace. Our goal is to help engineers understand the convergence of communications, circuits, and antennas, as the emerging world of subterahertz and terahertz wireless communications will require understanding at the intersections of these areas. This paper covers trends and recent accomplishments in a wide range of circuits and systems topics that must be understood to create massively broadband wireless communication systems of the future. In this paper, we present some evolving applications of massively broadband wireless communications, and use tables and graphs to show research progress from the literature on various radio system components, including on-chip and in-package antennas, radio-frequency (RF) power amplifiers (PAs), low-noise amplifiers (LNAs), voltage-controlled oscillators (VCOs), mixers, and analog-to-digital converters (ADCs). We focus primarily on silicon-based technologies, as these provide the best means of implementing very low-cost, highly integrated 60-GHz mm-wave circuits. In addition, the paper illuminates characterization techniques that are required to competently design and fabricate mm-wave devices in silicon, and illustrates effects of the 60-GHz RF propagation channel for both in-building and outdoor use. The paper concludes with an overview of the standardization and commercialization efforts for 60-GHz multi-Gb/s devices, and presents a novel way to compare the data rate versus power efficiency for future broadband devices.

http://faculty.poly.edu/~tsr/wp-content/uploads/publications/abstract17.pdf

State of the Art in 60-GHz Integrated Circuits and Systems for Wireless Communications

Cell adhesion is critical for the genesis and maintenance of both three-dimensional structure and normal function in tissues. The biochemical entities mediating cell adhesion are multiprotein complexes comprising three broad classes of macromolecules: the adhesion receptors, the extracellular matrix

Signal Transduction and Signal Modulation by Cell Adhesion Receptors: The Role of Integrins, Cadherins, Immunoglobulin-Cell Adhesion Molecules, and Selectins

The cytoplasmic domains of integrins are essential for cell adhesion. We report identification of a novel protein, ICAP-1 (integrin cytoplasmic domain- associated protein-1), which binds to the 1 integrin cytoplasmic domain. The interaction between ICAP-1 and beta1 integrins is highly specific, as demonstrated by the lack of interaction between ICAP-1 and the cytoplasmic domains of other beta integrins, and requires a conserved and functionally important NPXY sequence motif found in the COOH-terminal region of the beta1 integrin cytoplasmic domain. Mutational studies reveal that Asn and Tyr of the NPXY motif and a Val residue located NH2-terminal to this motif are critical for the ICAP-1 binding. Two isoforms of ICAP-1, a 200-amino acid protein (ICAP-1alpha) and a shorter 150-amino acid protein (ICAP-1beta), derived from alternatively spliced mRNA, are expressed in most cells. ICAP-1alpha is a phosphoprotein and the extent of its phosphorylation is regulated by the cell-matrix interaction. First, an enhancement of ICAP-1alpha phosphorylation is observed when cells were plated on fibronectin-coated but not on nonspecific poly-L-lysine-coated surface. Second, the expression of a constitutively activated RhoA protein that disrupts the cell-matrix interaction results in dephosphorylation of ICAP-1alpha. The regulation of ICAP-1alpha phosphorylation by the cell-matrix interaction suggests an important role of ICAP-1 during integrin-dependent cell adhesion.

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ICAP-1, a Novel β1 Integrin Cytoplasmic Domain–associated Protein, Binds to a Conserved and Functionally Important NPXY Sequence Motif of β1 Integrin

57-65 GHz differential and transformer-coupled power and variable-gain amplifiers using a commercial 90 nm digital CMOS process are presented. On-chip transformers combine bias, stability and input/interstage matching networks to enable compact designs. Balanced transmission lines with artificial dielectric strips provide substrate shielding and increase the effective dielectric constant up to 54 for further size reduction. Consequently, the designed three-stage power amplifier occupies only an area of only 0.15 mm2. Under a 1.2 V supply, it consumes 70 mA and obtains small-signal gains exceeding 15 dB, saturated output power over 12 dBm and associated peak power-added efficiency (PAE) over 14% across the band. The variable-gain amplifier, based on the same principle, achieved a peak gain of 25 dB with 8 dB of gain variation.

60 GHz CMOS Amplifiers Using Transformer-Coupling and Artificial Dielectric Differential Transmission Lines for Compact Design

A self-healing two-stage millimeter-wave broadband power amplifier (PA) with on-chip amplitude/phase compensation is realized in 65-nm CMOS. The amplitude and phase compensations are accomplished by using feedback bias/capacitive schemes to extend the linear operation region and optimize the PA efficiency. Tunable control knobs are inserted in the linearization block to enhance the PA performance yield against process/temperature variations and device ageing effects. This prototype shows a 5.5-dB improvement of the output 1-dB compression point (P1dB) and a less than 2% chip-to-chip gain variation. At a 1-V supply, the differential PA achieves a saturation output power (Psat) of 14.85 dBm with a peak power-added-efficiency (PAE) of 16.2%. With the amplitude compensation, P1dB is increased to 13.7 dBm. With the phase compensation, the output phase variation is decreased to less than 0.5°. To the best of our knowledge, this prototype provides the highest Psat and P1dB with simultaneously high PAE from a single PA reported to date. The PA delivers a linear gain of 9.7 dB and has a 7-GHz 3-dB bandwidth from 55.5 to 62.5 GHz with a compact total area of 0.042 mm2.

Millimeter-Wave Self-Healing Power Amplifier With Adaptive Amplitude and Phase Linearization in 65-nm CMOS

This study presents an inverter-based inductorless single-to-differential (S2D) wideband low-noise amplifier (LNA). The proposed LNA has three inverter-based gain stages with a global shunt feedback resistor for wideband input impedance matching. Moreover, a shunt capacitor with a current bias transistor in the third gain stage enhances the gain/phase imbalances and the linearity of the pseudo-differential outputs. When implemented in a TSMC $0.18$ - $\mu {\rm m}$ CMOS process, this wideband LNA covering DC-1.4 GHz achieves a ${\rm S}_{21}$ of 16.4 dB, a minimal input third-order intercept point (IIP3) of $ -13.3~{\rm dBm}$ , and a minimal noise figure (with output buffers) of 3 dB. The output gain and phase imbalances are less than 1 dB and 2.5 $^{\circ}$ , respectively, within 1 GHz. The chip consumes 12.8 mW from a 1.8 V supply.

Jenny Yi-Chun Liu

Papers

ICAP-1, a Novel β1 Integrin Cytoplasmic Domain–associated Protein, Binds to a Conserved and Functionally Important NPXY Sequence Motif of β1 Integrin

60 GHz CMOS Amplifiers Using Transformer-Coupling and Artificial Dielectric Differential Transmission Lines for Compact Design

Millimeter-Wave Self-Healing Power Amplifier With Adaptive Amplitude and Phase Linearization in 65-nm CMOS

A Wideband Inductorless Single-to-Differential LNA in $0.18 \mu{\rm m}$ CMOS Technology for Digital TV Receivers

Molecular Basis for Interaction between Icap1α PTB Domain and β1 Integrin