This paper analyzes the signal quality achievable with a novel system architecture for low-power small cell remote units with integrated millimeter-wave wireless backhaul. The data signal on the backhaul link uses the same 3GPP compliant signal as with the access link serving the users. In contrast to existing systems, the small cell remote unit (RU) only consists of a simple frequency conversion from backhaul to access frequencies based on the self-heterodyning mixing concept with suppressed local oscillator (LO) signal. Therefore, it omits the LO source and greatly reduces power consumption and hardware complexity. Its sufficient linearity and phase noise performance at 60GHz was proven with measurements of an LTE signal easily meeting the 3GPP ACLR and EVM requirements, even with varying LO suppression levels on the backhaul link. Moreover, the required frequency stability of the access signal is demonstrated even when using a very unstable LO source.

This paper presents a completely wireless small cell unit for mobile communication systems with lowest possible power consumption. It consists of a simple frequency conversion from millimeter-wave backhaul to access frequencies based on the self-heterodyning concept with only analog amplifiers as active components. This enables an energy autonomous operation based on tiny solar panels, greatly simplifying its deployment. The sufficient linearity and phase noise performance at 60GHz was proven with measurements of an LTE signal easily meeting the access link 3GPP ACLR and EVM requirements. Moreover, a successful system test of our full end-to-end LT E mobile communication system with a commercial user device proved the expected and required high data rates.

Measurements of fixed Massive MIMO links at a carrier frequency of 2.6GHz are reported. The temporal fading at the individual antenna elements is characterized in terms of K-factors and coherence times. We observe ??5dB larger K-factors during night-time as well as ??10dB higher values for the line-of-sight location. The analysis of the fading's cross-correlation between the different antenna elements shows a stronger correlation in the vertical domain than in the horizontal one. However, a horizontal lambda/2-spacing still provides a significant amount of cross-correlation (i.e., values above 0.5 in 6 out of 10 locations), and yields the smallest orthogonality between channel vectors of different locations. The channel hardening effect mitigates the temporal channel gain variations for a 64-antenna link to less than 1dB. The dominant temporal fluctuation of a channel vector is the drift of its subspace, which significantly deteriorates the performance of nullspace-based spatial multiplexing schemes such as zero-forcing.

This paper analyzes the achievable signal quality of a novel system architecture for small cell remote units with integrated millimeter-wave wireless backhaul. In contrast to existing systems, the data signal on the backhaul link uses the same 3GPP compliant signal as with the access link serving the users. The small cell remote unit only consists of a simple frequency conversion from backhaul to access frequencies. We simplified the measurements by using wave guide based variable attenuators to emulate the wireless link in our test setup. Its sufficient linearity and phase noise performance at 60GHz was proven with measurements of a single-carrier WCDMA signal easily meeting the 3GPP ACLR and EVM requirements, even with 10dB dynamic on the backhaul link. Moreover, the required broadband capability is demonstrated using an LTE signal with 20MHz bandwidth.

This paper presents a novel system architecture for small cell base stations with integrated millimeter-wave wireless backhaul. In contrast to existing systems, the data signal on the wireless backhaul uses the same 3GPP compliant signal than on the access link serving the users. The small cell omits the 60GHz local oscillator source completely by using the self-heterodyning mixing approach and transmits only a suppressed carrier. Measurements of a single-carrier WCDMA signal on a simplified setup with lower carrier frequency demonstrated that due to successful phase noise cancellation the 3GPP ACLR and EVM requirements are easily met, even with 15dB dynamic on the backhaul link. Moreover, the required broadband capability is proven using an LTE signal with 20MHz bandwidth.

For supporting a more efficient usage of available spectrum by mobile communication in unlicensed bands, a solution for robust and frequency agile receivers is proposed. Interfering signals of increased power level, expected in these bands, get acceptable as they are reduced by a tunable band-reject filter controlled by the digital receiver unit. The interfering signal position gets identified, the filter stopband gets moved on this position, and distortions of the wanted signal get compensated. A performance evaluation is done on a lab set-up based on hardware prototypes and on implemented control algorithms.

This paper describes a novel concept to encode amplitude and phase information in binary waveforms for switch-mode power amplifiers (SMPAs). A combination of a phase-modulated delta-sigma modulation (DSM) and pulse-width modulation (PWM) makes it possible to adapt signal generation to the power amplifier limits. The proposed system overcomes the inherent signal quality limits of digital systems with fixed clock frequencies by applying a phase modulated clock. We demonstrate that it is possible to achieve the performance of conventional concepts at less than half of the bit rate. Simulation and measurement results are given for important figures of merit of mobile communication signals with high peak-to-average power ratio (PAPR). A proof of concept is implemented in a laboratory setting using a conventional FPGA.

This paper presents the design methodology and the realization of a highly linear and power-efficient reconfigurable dual-band amplifier based on the continuous/Class-ABJ approach. The Class-ABJ theory allows presenting different reactive solutions on both fundamental and second harmonic terminations compared with the standard Class-AB mode. Despite the various terminations, a constant optimum output performance in terms of power, gain, and efficiency can still be achieved. The output impedances are then translated into frequency thus allowing the realization of broadbandpower amplifiers(PAs) at high-power level of 30 W. In this work, the Class-ABJ broadband approach will be used for the realization of a reconfigurable dual-band power amplifier operating in the two frequency bands 2.1–2.2 and 2.5–2.6 GHz. Continuous wave (CW) measurements on the realized PA show power and efficiency greater than 17 W and 55% in the two frequency bands with peak values up to 30 W and 63.7%. Indeed, it is shown that such novel modes can be predistorted and therefore the linearity requirement can also be met.

This paper presents a novel wideband receiver architecture for base stations. In contrast to existing systems, the analog-digital conversion is done directly in the radio frequency domain and is based on pulse width modulation. Measurements with a 5MHz LTE signal received at carrier frequencies varying between 900MHz and 2350MHz confirm the frequency flexibility of this concept. The captured spectrum of a WCDMA signal with 80MHz bandwidth demonstrates the possible detection of broadband signals. In addition, the capability of supporting instantaneous reception of non-contiguous frequency bands is proven by successfully detecting two signals with carrier frequencies of 900MHz and 2350MHz.

Rising energy consumption and thus equipment operating cost as well as the parallel environmental need to reduce the carbon footprint is a very important issue in mobile radio networks. Beside the needs to reduce the energy consumption, the demand for bandwidth and network capacity is increasing and leading to more standards, frequency bands and applications. The RF transceiver, especially the Power Amplifier as a part of it, is one of the bottlenecks and setscrews for the requirements mentioned. The following paper presents a standard and frequency independent concept as well as a method for energy efficiency optimization of RF Power Amplifiers with voltage controllable power supply to adjust the operating point based on Neural Networks. The system is basically standard independent and can adapt itself to a certain standard with its requirements. The system was designed and simulated.

This paper presents new architectures for RF pulse width modulation (RF-PWM). They allow for very efficient and simple implementation of this class of modulators. Even for the 2.6-Ghz band, the modulator can now be built with standard components. The new concepts support binary and M-ary output alphabets. One variant is capable of generating M-ary RF-PWM signals by only deploying one switching device. The new architectures are derived analytically and are illustrated by simulation results. A recent hardware implementation of this concept proofs the efficiency of this approach.

We show a universal analog signal conditioning approach for switch-mode power amplifiers. Three novel RF-PWM concepts are implemented on PCB, which work with a single RF input. The modulation-inherent distortion is compensated by a dedicated predistortion. We evaluated the performance for base stations of mobile communications in terms of ACLR, EVM, coding efficiency and channel power from 400MHz to 3 GHz. For a standard UMTS signal a coding efficiency of 82%, added EVM of 3% and ACLR of 49 dB are achieved.

A digital switch-mode amplifier MMIC integrating an differential amplifier and driver was realized in an 100 nm GaN technology with a transit frequency of 80 GHz. The circuit operates up to a bit rate of 12 Gbps while it was designed for a current-mode amplifier chain. Each of the two driver output channels delivers an adjustable output voltage swing of up to 5 VPP. Due to the differential amplifier input stage with a very low minimum input voltage swing of 0.5 VPP the MMIC allows a flexible operation used as limiting amplifier or digital pre-amplifier for a GaN final switch-mode stage. The high output power density of the GaN technology allows a further integration of the final switch-mode power amplifier stage which enables for the first time a fully integrated high power digital transmitter in GaN.

This paper discusses RF-PWM for mobile communication applications focusing on maximal achievable coding efficiency. Coding efficiency is one of the most crucial metrics in evaluating modulation concepts for switch mode amplification. It is shown that the achievable efficiency is mostly dependent on the chosen modulator waveform and the magnitude probability density function of the wanted signal. We determine theoretical limits and unveil unexpected benefits of unipolar waveforms. The results are applied to realistic communication test signals with various system parameter sets.

Reducing the power consumed in mobile base stations is an important way to support the effort for energy reduction in communication systems. Mobile base stations are designed for peak load situations, which only occur rarely relative to the overall daily traffic profile. This means, that daily operation of mobile communication networks especially in LTE systems shows a significant amount of time periods without data transmission, leading to reduced average energy efficiency. Sleep modes in base station transceivers, based on the deactivation of components and especially of the power amplifier in time slots of no signal transmission, show a significant potential to reduce the average energy consumption in base stations. This is demonstrated by experimental evaluations, done for different traffic load conditions, on hardware prototypes, dedicated for macro-cell base station.

In era of exploding energy consumption and thus equipment operating cost as well as the parallel environmental need to reduce the carbon footprint, energy efficient mobile radio is a very important issue and future challenge. Additionally, increased number of standards, frequency bands and applications require flexible and sustainable solutions. On both fields the power amplifier constitutes one of the setscrews to be addressed. On the one hand, the power amplifiers cause up to 60 % of the power dissipation of a base station, on the other hand it constitutes a bottleneck concerning transmit bandwidth. The following paper presents a very promising concept of a highly efficient Doherty which supports multiband capability in order to enable future efficient, flexible and sustainable mobile radio applications. The basic functionality of the proposed concept is verified by simulation and promising simulated results, based on AlGaN/GaN-HEMTs from FhG-IAF (Fraunhofer Freiburg) indicate the benefits of the new concept compared to conventional Class-AB and Doherty amplifiers.