Markus Allén

• D.Sc. (Tech.)
• University Teacher at Tampere University

This article presents two novel digital predistortion (DPD) based architectures that jointly mitigate the inphase/quadrature (IQ) modulator impairments and the power amplifier (PA) nonlinear distortion in wireless transmitters. The proposed architectures are multibit cartesian and complex delta-sigma modulator-based joint DPDs, called CDSM-JDPD and...

Wireless communication and radars will play a crucial role for autonomous vehicles in the nearest future. However, the blockage caused by surrounding cars can degrade communication performance, while automotive radars are never aimed to operate in such conditions. Therefore, in this paper, the authors propose the concept of near‐ground propagation,...

In this article, we propose a new robust and highly efficient digital predistortion (DPD) concept for the linearization of wideband RF power amplifiers (PAs). The proposed approach is based on the combination of a parallelized delta-sigma modulator (DSM) and a forward model of the PA. This concept applies multi-rate techniques on a DSM that incorpo...

In this article, we study closed-loop digital predistortion (DPD) systems and associated learning algorithms. Specifically, we propose various low-complexity approaches to estimate and manipulate the inverse of the input data covariance matrix (CM) and combine them with the so-called self-orthogonalized (SO) learning rule. The inherent simplicity o...

Modern millimeter-wave automotive radars are employed to keep a safe distance between vehicles and reduce the collision risk when driving. Meanwhile, an on-board radar module is supposed to operate in the line-of-sight condition, which limits its sensing capabilities in intersections with obstructed visibility. Therefore, this paper investigates th...

We study radio frequency (RF) wireless power transfer (WPT) using a digital radio transmitter for applications where alternative analog transmit circuits are impractical. An important parameter for assessing the viability of an RF WPT system is its end-to-end efficiency. In this regard, we present a prototype test bed comprising a software-defined...

In this article, we study digital predistortion (DPD)-based linearization with a specific focus on millimeter-wave (mmW) active antenna arrays. Due to the very large-channel bandwidths and beam-dependence of nonlinear distortion in such systems, we present a closed-loop DPD learning architecture, lookup table (LUT)-based memory DPD models, and low-...

We study radio-frequency (RF) wireless power transfer (WPT) using a digital radio transmitter for applications where alternative analog transmit circuits are impractical. An important paramter for assessing the viability of an RF WPT system is its end-to-end efficiency. In this regard, we present a prototype test-bed comprising a software-defined r...

In this paper, new digital predistortion (DPD) solutions for power amplifier (PA) linearization are proposed, with particular emphasis on reduced processing complexity in future 5G and beyond wideband radio systems. The first proposed method, referred to as the spline-based Hammerstein (SPH) approach, builds on complex spline-interpolated lookup ta...

This article presents novel solutions for suppressing passive intermodulation (PIM) distortion in frequency-division duplexing (FDD)-based radio transceivers, stemming from nonlinear radio frequency (RF) components and simultaneous transmission and reception, with special emphasis on modern carrier aggregation networks. With certain transmission ba...

In wireless communications, higher transmission power enables higher coverage or higher data rate. However, due to hardware limitations, achieving high power efficiency becomes challenging. The main issue is that at high power region close to power amplifier (PA) saturation point the highly non-linear response of the PA leads to significant spectra...

In this paper, we describe a novel framework for digital predistortion (DPD) based linearization of strongly nonlinear millimeter-wave active antenna arrays. Specifically, we formulate a piecewise (PW) closed-loop (CL) DPD solution and low-complexity gradient-adaptive parameter learning algorithms , together with a region partitioning method, that...

In this paper, we describe a novel framework for digital predistortion (DPD) based linearization of strongly nonlinear millimeter-wave active antenna arrays. Specifically, we formulate a piecewise (PW) closed-loop (CL) DPD solution and low-complexity gradient-adaptive parameter learning algorithms, together with a region partitioning method, that c...

In this paper, a novel digital predistorter concept for power amplifier (PA) linearization is proposed, with particular emphasis on reduced processing complexity in future 5G and beyond wideband radio systems. The proposed method builds on a complex spline interpolated look-up table (LUT) followed by a linear finite impulse response (FIR) filter, c...

In this work, we provide first-in-class measurement results for fast-convolution-based filtered orthogonal frequency-division multiplexing (FC-F-OFDM) processing implemented on a universal software radio peripheral (USRP) software-defined radio (SDR). The fast-convolution-based filter bank is a highly efficient and flexible scheme allowing to achie...

This paper proposes two digital receiver (RX) linearization and in-phase/quadrature (I/Q) correction solutions, where an additional reference RX (ref-RX) chain is adopted in order to obtain a more linear observation, in particular, of the strong incoming signals. This is accomplished with reduced RF gain in the ref-RX in order to avoid nonlinear di...

This paper proposes digital cancellation of nonlinear distortion originating from out-of-band blocking carriers and induced by the analog front-end nonlinearities in direct-conversion receivers (RXs). The cancellation is enabled by employing an additional reference RX for capturing these blockers. In addition, cancellation of mirror-frequency inter...

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 analys...

Reliable spectrum sensing ability is a key factor in cognitive radios. However, there are many aspects that impact the sensing reliability. One important aspect is impairments in the cognitive radio receiver hardware. Received signals tend to have high dynamic range which drives the receiver to the nonlinear zone. This may cause nonlinear distortio...

A quadrature ΣΔ analog-to-digital converter (ADC) is a promising solution for intermediate frequency digitizing software defined cognitive radio (CR) receivers because of, e.g., multiband capability and power efficiency. However, inherent coefficient mismatches between the in-phase and quadrature rails can severely damage the performance of such re...

This article proposes a recon#64257;gurable wideband transfer function design for quadrature sigma-delta A/D converters combined with digital post-compensation of frequency-selective mirror-frequency interference (MFI) induced by the inherent mismatches between the in-phase (I) and quadrature (Q) rails of the receiver. When receiving wideband wavef...

Following the design trend of integrated receivers, the direct downconversion (DD) principle is investigated from radar system-level perspective, but with a strong focus on the analog mechanisms. While most modern radar receivers favor a digital downconversion to avoid I/Q mismatches, they demand discrete realization and larger form factors. Recent...

Over the last years ongoing advances in ADC technology have enabled RF signals to be sampled at IF frequencies. Undersampling is nowadays employed in software-defined radio or radar receivers and offers the possibility to relieve requirements in the analog receiver partition. Unfortunately, when moving to higher IF concepts, this becomes demanding...

This article proposes a novel frequency-agile transfer function design for quadrature ΣΔ modulators (QΣΔMs), allowing digital post-compensation of mirror-frequency interference generated by the mismatches between the receiver I and Q branches. In addition to mitigating the interference created inside the QΣΔM, doing the compensation in digital doma...

Emerging wireless communications concepts, such as cognitive radio, bring various challenges in the implementation of radio receivers. One of the concerns is the dynamic range of the receiver front-end, which might be insufficient in certain situations, e.g., if strong blocker signals are present concurrently with weaker interesting signals. Overdr...

In modern wideband communication receivers, the large input-signal dynamics is a fundamental problem. Unintentional signal clipping occurs, if the receiver front-end with the analog-to-digital interface cannot respond to rapidly varying conditions. This paper discusses digital postprocessing compensation of such unintentional clipping in multiband...

This article addresses the design, analysis, and parameterization of reconfigurable multi-band noise and signal transfer functions (NTF and STF), realized with multistage quadrature ΣΔ modulator (QΣΔM) concept and complex-valued in-phase/quadrature (I/Q) signal processing. Such multi-band scheme was already proposed earlier by the authors at a prel...

Sigma-delta basics The principle of oversampling the analog-to-digital converter (ADC) with negative feedback has been invented decades ago and is still being developed further by scientists all over the world. Today’s state-of-the-art converters have come a long way from the first ADCs employing the ΣΔ principle in the 1960s. There is quite a broa...

The analog-to-digital converter (ADC) is one of the key components in modern radio front-end design. Real-world ADC components always have certain trade-offs in performance which have to be taken into account. One reason for that is the rather slow development of ADCs compared to other technical achievements in radio technology [22], [33]. The fund...

Large input signal dynamics is an essential problem in modern wideband communication receivers such as cognitive radios. If the receiver front-end and analog-to-digital interface cannot respond to varying conditions, a high amount of nonlinear distortion is caused due to the clipping. This paper proposes a robust digital signal processing method to...

This article discusses the applicability of quadrature ΣΔ modulator (QΣΔM) based analog-to-digital (A/D) conversion in cognitive radio (CR) receivers. First, unavoidable in-phase/quadrature (I/Q) mismatch effects, limiting the dynamic range, are analyzed in closed-form in the case of a first-order modulator. In addition, using the derived analytica...

In this article, a novel analytical closed-form model is derived for second-order quadrature I:A modulators (QI:AM) taking implementation inaccuracies of QI:AM coefficients into account. The model enables analytical examination of the mod­ ulator I1Q imbalance effects on input-output relation as well as signal and noise transfer functions (STF and...

In this article, the design and analysis of sophisticated multi-band quadrature ΣΔ modulators (QΣΔM) are addressed, offering a high-performance and easily-reconfigurable solution for the analog-to-digital (A/D) interface of cognitive radio receivers. Based on spectrum sensing information, the multi-band principle stemming from multi-stage converter...

The cognitive radio concept has gained widespread interest to avoid spectral scarcity in next generation mobile communications systems. However, there are major challenges from the radio transceiver electronics point of view. This paper addresses the analog-to-digital converter saturation problem due to highly-varying signal conditions in wideband...

This article discusses the reduction of nonlinearities in analog-to-digital (A/D) converters using digital signal processing (DSP). Also modeling of certain essential nonlinearities is considered in detail. The main focus is on wideband radio receivers, such as the emerging cognitive radio applications, where a collection of signals at different fr...

This article focuses on the in-phase/quadrature (I/Q) imbalance problem in quadrature ΣΔ modulators (QΣΔM). In the literature, such quadrature modulators have been seen as a promising possibility for software defined radio (SDR) receivers, but matching the quadrature circuits is an inevitable problem for this kind of systems. In this article, an an...

This article addresses the reduction of analog-to-digital (A/D) converter nonlinearities in radio receivers using digital signal processing (DSP). The main focus is on wideband A/D conversion where a collection of different waveforms at different frequency channels is digitized as a whole. The overall dynamic range in such composite signal can easi...