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Limited linearity and local oscillator (LO) harmonics mixing are two major issues that ultra-wideband receivers, and a cognitive radio (CR) in particular, are dealing with. Direct-conversion schemes, based on current-driven passive mixers, have shown to improve the linearity but unable to resolve the LO harmonic mixing problem. They are usually limited to third and fifth harmonics rejection or require a very complex and power hungry circuitry for a higher number of harmonics. This paper presents a heterodyne conversion scheme in the 180-nm CMOS technology for CR applications (54–862 MHz band) that robustly mitigates the harmonic mixing issue for all the harmonics, while by employing an active feedback loop, a comparable state-of-the-art $\mathrm {IIP_{3}}$ of better than +10 dBm is achieved. Measurements show an average noise figure of 7.5 dB when the active feedback loop is OFF (i.e., in the absence of destructive interference) and of 15.5 dB when the feedback loop is active and a 0-dBm interferer is applied, respectively. [ABSTRACT FROM AUTHOR]

Real-time spectrum sensing refers to searching for possible signals at a specific time and location, which is applicable to cognitive radio for primary signal detection. The simplicity and low sensing time of phaser-based spectrum sensors, implemented in a discrete manner previously, provided the incentive for this paper. In this paper, an integrated CMOS wideband real-time spectrum sensor with a novel on-chip phaser in 57–354-MHz band, as part of VHF/UHF TV broadcast bands, is presented. The proposed approach provides a fast, simple, area-efficient analog solution for real-time spectrum sensing with low noise figure and power consumption. The integrated chip has been fabricated in a standard 0.18- \mu \textm CMOS IBM technology and has achieved a sensing time of as low as 2.5 \mu \texts for 27-MHz frequency resolution. [ABSTRACT FROM PUBLISHER]

This paper presents the development of the wideband power amplifier (PA) for application to intelligent cognitive radios. The load-tracking based on the frequency-varied load-pull technique is proposed for the PA design. The load impedance tracking is realized by filter network synthesis. A 3-7.5-GHz broadband PA is demonstrated in 0.15-μm InGaAs pseudomorphic HEMT technology. Operated at 3.5 V, the P1 dB and power-added efficiency of the PA are better than 21.4 dBm and 20%, respectively. [ABSTRACT FROM AUTHOR]

Sensitivity and sensing time are the key features for spectrum sensing in a cognitive radio (CR) which detects empty bands within VHF/UHF television broadcast bands and uses them as a secondary user. In this paper, an integrated CMOS CR spectrum sensor for a CR receiver in the 54–862 MHz band is presented. A quasi-cyclostationary feature (QCF) detector is proposed based on both energy and feature detection methods and can take advantage of both methods to reach a fast and accurate decision without the need for an analog-to-digital converter for decision making. The integrated chip has been fabricated in a standard 0.18\mathchar"702D\mu\ m CMOS IBM technology and has achieved minimum detection signal-to-noise ratio of as low as -24~\ dB and dynamic range (DR) of 39 dB. [ABSTRACT FROM PUBLISHER]

Software-defined radio technology is experiencing more and more attention in modern communication and radar systems. The main practical challenge in deploying such technology is related to achieving sufficient linearity and spurious-free dynamic range in the RF front-end, especially in low-cost mass-product devices. This paper focuses on the analysis and digital mitigation of nonlinear distortion in software-define radio devices, building on wideband multicarrier/multiradio direct-conversion receiver principle where a wide collection of radio frequencies is in-phase/quadrature down-converted as a whole. A complete behavioral model for the total nonlinear distortion of the whole receiver chain is first derived, taking into account the third-order nonlinear distortion effects in all individual components, namely, RF low-noise amplifier, in-phase/quadrature mixer, and baseband in-phase/quadrature amplifiers. Stemming from this modeling, an adaptive digital feed-forward linearization structure is then developed to efficiently mitigate the joint nonlinear distortion of the whole receiver. The effectiveness of this approach is verified through extensive simulations and actual RF system measurements with a commercially available software-defined radio platform, which clearly outperforms the existing state-of-the-art methods that do not jointly consider RF and baseband nonlinearities. [ABSTRACT FROM PUBLISHER]

This paper presents a novel frequency-offset technique to enhance operating range of frequency synthesizers for long-term evolution-advanced and cognitive-radio applications. Conventional wideband frequency synthesizers typically have complex architectures, such as multiple phase-locked loops (PLLs), multiple voltage-controlled oscillators, and multiple mixers, to increase operating range. These complex architectures have high cost and power consumption. In this study, the proposed technique substantially increases the operating range of the frequency synthesizer by using only a single PLL to simultaneously lock two mixing oscillators. The presented frequency synthesizer is implemented using \ 0.18-\mu\ m CMOS technology. Performance tests demonstrate that the frequency synthesizer achieves a very wide operating frequency range from 50 MHz to 4.8 GHz with a phase noise lower than -\ 100 dBc/Hz at a frequency offset of 100 kHz. The period of stability for a switching frequency of 40 MHz is shorter than \ 40~\mu\ s. [ABSTRACT FROM AUTHOR]

This paper presents a wideband power amplifier (PA) for the application of intelligent cognitive radios. Resistive feedback and transformer matching network are proposed in this PA design to enhance the broadband frequency response. The broadband load impedance match is realized using series stack topology. The limitation of stack PA in both GaAs and CMOS processes are discussed. A high-efficiency broadband PA in commercial 0.18 \mum CMOS process with the best P1\,dB of 20 dBm and PAE of 30% are demonstrated to verify the design concepts. This PA also shows the widest fractional bandwidth performance among CMOS PAs below 10 GHz. [ABSTRACT FROM AUTHOR]

A new linearity optimization (LO) technique is proposed to improve the input third-order intercept point (IIP3) of the wideband noise-canceling (NC) low-noise amplifiers (LNAs) without any influence on input impedance matching. Furthermore, this technique can be combined with the ${gm}$ -boost technique and achieve LO with low power consumption. Fabricated in the 65-nm CMOS technology, the proposed wideband LNA occupies a small chip area of 0.0062 mm2. This LNA achieves 4–9.4-dBm IIP3, 17-dB voltage gain, and 2.09–3.2-dB noise figure (NF) over the entire frequency range from 100 MHz to 3.5 GHz. Furthermore, the core circuit draws only 6.6 mA from a single 1-V power supply. [ABSTRACT FROM AUTHOR]

This article presents the design of an integrated system involving multiple-input–multiple-output (MIMO) and cognitive radio (CR) technologies for sub-6 GHz applications. Two types of CR techniques, i.e., interweave and underlay CR, have been discussed in this article. The design model has a four-port multifunctional MIMO antenna system involving lumped elements for three selectable operation choices. Based on the switching conditions, the MIMO antenna system can operate as a wideband antenna (for sensing purpose), or narrowband frequency tunable antenna (for communicating purpose in interweave CR), or a wideband antenna with frequency tunable band notch (for communicating purpose in underlay CR). The sensing frequency range is 2.45–5.3 GHz. The interweave CR communicating antenna frequency tuning range is 3.6–4.2 GHz. To cover the entire desired spectrum range, i.e., from 2.5 to 4.2 GHz, another four-port narrowband MIMO antenna system with resonance frequency tuning from 2.5–3.6 is designed on the other/backside of the substrate. In the underlay CR communicating antenna, the stopband frequency tuning range is 3.1–3.85 GHz. The complete structure is having dimensions of 110 $\times $ 70 $\times $ 1.52 mm3. The measurements are performed, and good matching is found between simulated and measured results. [ABSTRACT FROM AUTHOR]