Performance comparison of phase modulated system based on DSSS with HPA nonlinearity

This paper presents a broadband predistortion technique using dual-gate FETs to linearize the Traveling Wave Tube Amplifiers (TWTA) and Solid State Power Amplifiers (SSPA) used in satellite transponders. The results for a linearized TWTA operating over 11.7-12.2 GHz and a linearized SSPA operating over 3.8-4.2 GHz are presented. The improvement in linearity has been achieved over a broad dynamic range of output power.

There has been long-standing debate regarding the comparative reliability of solid-state power amplifiers (SSPAs) versus traveling wave tube amplifiers (TWTAs) for the satellite downlink. High-voltage, thermionic, life-limited emitters operating in a high vacuum enclosure (i.e., a vacuum electronic device) contribute to the TWTA risks and reliability questions. Conventional wisdom espouses the SSPA as an inherently more reliable, solid-state device requiring only low voltages to amplify, with failure resulting in only graceful degradation. However, many trade studies on comparing SSPAs and TWTAs rely on transistor device life test data on the ground for SSPAs due to the lack of statistically significant data on orbit. It is expected that current, on-orbit statistics in the industry would shed relevant light on the debate.

Orthogonal frequency division multiplexing (OFDM) is a multi-carrier digital modulation technique that has been under extensive study and research in recent years, in terms of considering its various advantage in combating the severe effects of the frequency selective fading. However, the OFDM system suffers from the strong sensitivity to the nonlinear distortion, introduced by the transmitting high power amplifier (HPA), since the OFDM system has the high peak-to-average power ratio (PAPR). Clipping is the simple but infective method to low the high PAPR; however, it causes nonlinear distortion too. So in this paper, we propose a new approach to compensate the nonlinearity caused by clipping and HPA. Its performance is verified through computer simulations. Specifically, the enhanced performance in terms of the bit error rate (BER) is documented for both the traveling wave tube amplifier (TWTA) and the solid state power amplifier (SSPA).

OFDM (orthogonal frequency division multiplexing) is usefully applied for DAB (digital audio broadcasting) and DVB (digital video broadcasting) systems due to its high spectral efficiency and robustness to ISI (intersymbol interference) and multipath fading. However, the OFDM signal has a large PAPR (peak-to-average power ratio), which results in significant nonlinear distortion when it passes through an HPA (high power amplifier) such as a TWTA (traveling wave tube amplifier) and a SSPA (solid state power amplifier). We propose a new PAPR reduction method using soft clipping and filtering. Unlike conventional hard clipping, soft clipping has non-zero slope in the clip region. Next, filtering, which uses additional FFT and IFFT processes, is applied in order to reject the out-of-band clip noise. Although the filtering removes the out-of-band noise, it oppositely increases PAPR by a small amount. Since an HPA increases the power consumption according to the linearity range, soft clipping for an SSPA lowers power consumption and is more efficient than the conventional hard clipping method. By the results of the proposed method, the wanted PAPR can be obtained and there is no out-of-band radiation caused by the clipping process.

This paper presents a Ku band analog predistorter linearizer for improving the linearity of high-power radio frequency (RF) amplifiers. This method is applicable for both solid-state power amplifiers (SSPA) and traveling-wave tube amplifiers (TWTA). The designed linearizer consists of analog components, hence it is wideband as compared to the digital predistortion. Moreover, due to most of the passive components, the circuit is simpler and with the advantage of individual control of amplitude modulation to amplitude modulation (AM-AM) and amplitude modulation to phase modulation (AM-PM) conversions. For proof of concept, the designed linearizer is simulated with ZX60-14012L+ class AB SSPA. The S2D SSPA model is extracted using vector network analyzer. The proposed linearizer shows a reduction in third order intermodulation of 37 dB approximately at 4 dB output power backoff for two-tone signal. Similarly, for Long-Term Evolution (LTE) 20 MHz signal after linearization adjacent channel power ratio is approximately 47 dBc and shows a correction of 16 dB.

This paper presents different Solid State Power Amplifiers (SSPAs) with power levels from 3 to 14 W at Ku-Band to be used as Travelling Wave Tube Amplifier (TWTA) replacements and in active array antennae for space application, all developed at MIER COMUNICACIONES.

This study compares current and projected state-of-the-art microwave power amplifiers used in spaceborne transmitter technologies at frequencies through 100 GHz. Projected are future trends in power PHEMTs and in wide bandgap semiconductor devices such as GaN and SiC. Also, the more established InP HEMT low-noise devices are examined for possible power amp applications specifically in the millimeter wave region. Three key power amplifier technologies, including the traveling wave tube amplifier (TWTA), the solid state power amplifier (SSPA), and the microwave power module (MPM), have emerged in varying degrees as heritaged and/or viable components in spaceborne transmitters. Addressed as figures of merit are significant discriminators such as long term reliability, space heritage (failure-free on orbit performance), process/device maturity, size, weight, and efficiency.

The design of code-division multiple-access (CDMA) transmission systems for satellite communications requires an appropriate consideration of the distortion effects due to on-board nonlinear amplification. The aim of this paper is to provide an analytical framework for the evaluation of the in-band nonlinear distortion effects on the performance of CDMA systems. Both synchronous systems with orthogonal codes and asynchronous systems are considered. It is first shown that, when the users accessing the channel have the same power and their number is sufficiently large, the nonlinear distortion in the decision variables at the receiver can be simply described by a complex scale factor, which depends on the high-power-amplifier (HPA) characteristics only, and an additive noise, which is uncorrelated to the useful signal. Moreover, an analytical formulation of the bit error probability and the total degradation as a function of the output back-off and number of users is given. In the results, which are obtained for three classes of HPA models (i.e., the traveling wave tube amplifier, the solid-state power amplifier, and the amplifier with ideal predistortion), the performance and the capacity of power-limited systems is also discussed.

In this paper, we investigate the impact of nonlinear distortion on the overall system outage probability of simultaneous wireless information and power transfer enabled two-way amplify-and-forward relaying network by employing three different nonlinear power amplifier (NLPA) models such as traveling wave tube amplifier, soft envelope limiter, and solid-state power amplifier at the relay node. We consider a time-switching based protocol at the energy-constrained relay node to harvest energy and information transmission. We derive the closed-form expression of the system outage probability by utilizing the selection combining technique at the source nodes over Nakagami-m fading channels. System throughput and energy efficiency of the network are also investigated. The impact of NLPA, threshold data-rate, fading severity, and time-switching factor are highlighted on the network's performance. Finally, the derived analytical results are validated by the Monte Carlo simulations.

Several well-known simple behavioral models for solid state power amplifier (SSPA) devices are reviewed and compared. This paper proposes an improvement to White et al's model and discusses their use of the Rapp model for AM/AM and AM/PM device modeling. Furthermore an improvement to Honkanen & Haggman's phase shift addition to Rapp's model is given thus allowing phase shifts greater than zero degrees to be considered. Finally a review of several models' performances beyond available data and into the saturation region is presented. These simple model improvements and additions, combined with the extension of the modeling into the saturation region, thus allow for faster and more accurate system level analysis, enabling better crucial output device selections to be made.

This paper describes the development of an L-Band (f0= 1.575 GHz) high power and efficient solid state power amplifier (SSPA) designed for the European satellite navigation system (i.e. Galileo). The amplifier, developed in the framework of the European Project named SLOGAN, exploits the GH50-10 GaN technology available at United Monolithic Semiconductor foundry. The aim of the project is to offer, using as much as possible European technologies, a valid alternative to replace traveling wave tube amplifiers with more compact and reliable systems. All the SSPA functionalities, i.e. power supply, power conditioning and radio frequency amplification, are integrated in the developed architecture and accommodated in a single box with limited volume and mass. The required output power level is achieved by parallelizing several GaN die power bars of 12 and/or 25.6 mm. In continuous wave operating mode, the overall SSPA delivers an output power higher than 250 W at less than 2 dB of gain compression in the whole E1-band. Moreover, the registered gain and efficiency are higher than 67 dB and 54%, respectively.

Main lobe shifting and splitting phenomena of Airy beams are theoretically investigated based on the spatial light modulator (SLM) method. By digitally modulating the phase masks on the SLM, the single main lobe of the 2D symmetric Airy beam shifts to its neighboring side lobe. This results in the main-lobe splitting and the formation of a two-main-lobe state. These two main lobes further split into four while appropriately setting the phase modulation parameters. Meanwhile, the main lobe intensity decreases from 1.529 to 0.361a.u. as the incident Gaussian beam's amplitude is 1. Therefore, one, two, or four main lobes can be obtained in Airy beams, and the corresponding intensity can be flexibly modulated by digital phase masks without moving the obstacle. Furthermore, a set of Airy beams with single main lobes and their corresponding splitting are realized by periodically setting the propagation distance. This further improves the modulation flexibility of the main lobe intensity. In our work, the number and intensity modulations of main lobes in Airy beams may have significant potentials for optical communication devices, such as tunable lasers and optical demultiplexers.

Precise signal processing schemes for resonator fiber optic gyro (R-FOG) with bipolar digital serrodyne phase modulation technique are proposed. One scheme is to suppress the noise induced by higher harmonics of the frequency used to extract the rotation signal when the bipolar digital serrodyne modulation technique is used. The other scheme is to increase the stability of the control signal for the amplitude adjustment of the phase modulation waveform, in which a lock-in reference waveform with 90° out of phase compared with the modulation waveform is introduced.

Radio transmitters are evolving towards digital-intensive solutions to exploit reconfigurability and benefit from CMOS process scaling. Outphasing has been identified as a suitable candidate for digital wideband transmitters. However, with recent digital-intensive outphasing transmitters the achieved performance in terms of adjacent channel leakage ratio (ACLR) has been limited. This paper identifies the sampling images of the modulating phase signal as the main factor limiting the ACLR of digital outphasing transmitters. We present a new digital interpolating phase modulator architecture, capable of providing significantly better sampling image attenuation. When evaluated in outphasing configuration with a 100 MHz OFDM signal at the carrier frequency of 2.46 GHz, and 10-bit phase resolution, the proposed solution achieves an ACLR of $-$ 59 dBc, compared to $-$ 43 dBc achievable with the phase modulator architecture utilized in state-of-the-art digital outphasing transmitters. The proposed digital interpolating phase modulator is also capable of custom carrier generation, a straightforward method for generating an arbitrary carrier frequency up to 1.25 times the phase modulator sampling rate.

This paper presents a low power, high speed SiGe DDS MMIC with 9-bit phase and 7-bit amplitude resolutions. This DDS MMIC is the first reported GHz range output DDS with direct digital frequency and phase modulation capabilities. Using more than eight thousand transistors, the DDS MMIC includes a 9-bit CLA accumulator for phase accumulation, a 9-bit CLA adder for phase modulation and a 7-bit sine-weighted DAC. The core area of the DDS occupies 1.7times2.0 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The DDS consumes low power of 2.0 W under a 3.3 V single power supply even with the added modulation blocks. The narrow band spurious-free-dynamic range (SFDR) is measured as 35 dBc with the maximum update frequency of 2.9 GHz. The DDS MMIC is packaged and tested in an LCC-44 cavity.