IEEE Journal on Emerging and Selected Topics in Circuits and Systems

A novel methodology for designing highly-efficient broadband harmonic-tuned power amplifiers (PAs) with more than one octave bandwidth is presented in this paper. Continuous class-F power amplifiers with resistive second-harmonic impedance is for the first time analyzed and employed in a multi-sub-band mode to enhance the bandwidth of a conventional continuous class-F PA. The load-pull method is e... View full abstract»

Digitally modulated power amplifiers (DMPA) are a promising architecture for practical and highly efficient software-defined radio transmitters. Signal encoding schemes for DMPAs have primarily focused either on amplitude or time domain encoding, neither of which can simultaneously provide high coding efficiency, high dynamic range and low design complexity. In this paper, we propose, analyze and ... View full abstract»

Linearization of user equipment power amplifiers driven by orthogonal frequency division multiplexing signals is addressed in this paper. Particular attention is paid to the power efficient operation of an orthogonal frequency division multiple access cognitive radio system and realization of such a system using compressed sensing. Specifically, precompensated overdriven amplifiers are employed at... View full abstract»

In this paper, key design considerations in self-demodulators at millimeter wave range for short-range software-defined transceivers are presented. Oscillator-less demodulators are used to achieve a wide operating range with low power consumption. The proposed demodulator, featured with a new single-input differential-output low noise amplifier and implemented in 0.18- μm SiGe BiCMOS techno... View full abstract»

In this paper, the optimized design, characterization and applications of a broadband 300-800 MHz (~ 91% fractional bandwidth) digitally-controlled tunable matching network is presented. The design employs PIN diodes as switching components and a repetitive structure of basic cells using lumped reactive elements. After an intensive and complex optimization process, a Smith chart coverage (return l... View full abstract»

Detecting the presence of primary users and ability to find white spaces in the spectrum are the key enablers of the opportunistic communication. This paper analyzes the trade-offs in cyclostationary-based spectrum sensing algorithm implementations in terms of performance, hardware complexity, and power consumption. The evaluation of the algorithm implementations is performed on field-programmable... View full abstract»

One of the key tasks in cognitive radio and communications intelligence is to detect active bands in the radio-frequency (RF) spectrum. In order to perform spectral activity detection in wideband RF signals, expensive and energy-inefficient high-rate analog-to-digital converters (ADCs) in combination with sophisticated digital detection circuitry are typically used. In many practical situations, h... View full abstract»

Dynamic spectrum access relying on spectrum sensing requires reliable detection of signals in negative signal-to-noise ratio (SNR) conditions to prevent harmful interference to licensed users. Energy detection (ED) is a quite general solution, which does not require any knowledge of the signals to be detected. Unfortunately, it suffers from noise uncertainty in the receiver, which results in an SN... View full abstract»

Among the primary challenges of designing a flexible and efficient wideband receiver for cognitive radio (CR) are harmonic distortion caused by the hard-switching commutating mixers, the need for wide tuning range frequency synthesizer to span the frequency band of interest, and the use of power-hungry high-speed analog-to-digital converters to reduce the sensing time. In this paper, the harmonic ... View full abstract»

This paper presents an effort-reduced approach for calibrating the reconfigurable six-port based receiver (SPR) systems for cognitive radio/software defined radio applications that accounts for all the known imperfections and impairments of an SPR system. The state-of-the-art calibration method requires estimation of more than 100 calibration parameters on-the-fly. The proposed calibration method ... View full abstract»

This paper proposes a new linearization algorithm, discrete level gain adjustment (DLGA), for linearized high efficiency multi-level delta sigma modulator (ΔΣM)-based transmitter architectures adequate for wideband multi-standard software defined radio (SDR) applications. The new simple linearization DLGA algorithm is deployed instead of using a full digitally predistorted to maintai... View full abstract»

In multimode transceivers, the transmitter for one communication standard may induce a strong interference in the receiver for another standard. Using linear filtering techniques to suppress this interference requires a receiver with a very large dynamic range, leading to an excessive power consumption. A much more power efficient approach suppresses the interference using an adaptive nonlinear in... View full abstract»

A novel low complexity active interference cancellation (AIC) scheme for primary user (PU) protection is presented for application to cognitive orthogonal frequency division multiplexing (OFDM) systems, in which out-of-band radiation spilling over the PU protected band is to be minimized. A set of cancellation subcarriers are modulated by appropriate linear combinations of the remaining data subca... View full abstract»

Opportunistic interference alignment (OIA) is a technique that enables the multiple-input multiple-output (MIMO) secondary user (SU) to exploit the inherent spatial spectrum holes of the MIMO primary user's (PU) communication link while the PU transmissions remain interference free, thus generalizing the concept of interweave cognitive radio (CR) systems. A typical characteristic of an interweave ... View full abstract»

Space-time spectral white spaces in a cognitive radio environment are defined based on multidimensional spatio-temporal spectral properties of radio waves received by a planar array of antennas. Spectral occupancy of a given carrier frequency pertaining to a particular direction in space is expressed by the volume of a semi-cone shaped geometrical region in the 3-D spatio-temporal frequency space ... View full abstract»

In the above titled paper (ibid., vol. 3, no. 3, pp. 322-329, Sep. 2013), equations (17a) and (17b) should have appeared as presented here. View full abstract»