Machine Learning based Adaptive Predistorter for High Power Amplifier Linearization

Satellite communication (SATCOM) system is to be applied in the communication, oceanographic, and meteorological satellite (COMS). ETRI has completed the preliminary design effort for the SATCOM project - an effort which included clarifying requirements, refining mission description and operation, determining the configuration of the payload, and anticipating subsystem performances, schedules, costs, and so on. This paper includes an overview of the project work, and the preliminary design of the Ka-band on-board switching transponder in point of RF performances. A recommendation for future work is also included to aid subsequent projects associated with SATCOM system

High-level linear modulation schemes used in modern digital communication systems exhibit large peak-to-average power ratios (PAPRs). The performance of transceivers is very sensitive to nonlinear distortions, which arise mainly from the high power amplifier (HPA). Also, because of the wideband signals, the nonlinear distortions are frequency-dependent. The paper proposes an algebraic solution to compensate at the transmitter for the HPA nonlinearity. The HPA is represented by a memoryless nonlinear block followed by a linear filter. We first estimate the parameters of the unknown nonlinearity, which is modelled through a polynomial expansion. The frequency response of the unknown filter is then calculated, in order to capture the memory effects in the system. Using the identified nonlinear system parameters, a cascade of the inverse filter and the inverse memoryless nonlinearity is constructed preceding the HPA, in order to predistort the input signals and achieve overall linear transmitter characteristics. The scheme is examined through computer simulations for quadrature amplitude modulation (QAM). Improvements in the bit error rate (BER) and out-of-band spectrum regrowth are demonstrated for the travelling wave tube (TWT) HPA model. The results show that the proposed method is effective in compensating for amplitude-to-amplitude (AM/AM) distortions with memory using a relatively-small number of data points at the identification stage.

Coexistence of satellite and terrestrial wireless communication systems in the same frequency band is quite promising for addressing the challenge of spectrum scarcity. To cope with the inevitable inter-system interference, radio resource allocation at both sides should be carefully re-optimized. In this paper, we focus on a scenario where a satellite communication system and a terrestrial distributed antenna system (DAS) coexist via spectrum sharing. We particularly utilize the radio map (RM) to reduce the system overhead for channel acquisition. Based on the large-scale channel state information at the transmitter (CSIT), which is derived from the RM, we propose an optimized power allocation scheme to improve the achievable sum rate of the terrestrial system. For the satellite side, an opportunistic user scheduling scheme is presented, to reduce the harmful leakage interference to the terrestrial mobile users. Simulation results demonstrate that the proposed RM-based coordination scheme can significantly promote the performance of satellite terrestrial coexistence, although the small-scale channel fading has been ignored in the formulated optimization.

Generalized Frequency Division Multiplexing (GFDM) is a flexible waveform possible choice for the next communication system that offers advantages such as low out-of-band (OOB) and high spectral efficiency. The High Power Amplifier (HPA) is operated close to the saturation region for increased efficiency. However, working in that area will result in nonlinear distortion. We investigated the effect of HPA in the GFDM Multiple Input Multiple Output (MIMO) system. The model used is the Rapp Model. In this paper, the Bit Error Rate (BER) of the MIMO-GFDM system with HPA through the Additive White Gaussian Noise (AWGN) channel will be explored. The output of the simulation shows that the nonlinear distortion effect will cause the signal constellation to propagate. Besides, there was an increase in the BER value for the HPA system.

The monolithic microwave integrated circuit (MMIC) power amplifiers serve an essential and critical role in RF transmit/receive (T/R) modules of phased array radar systems, mobile communication systems and satellite systems. Over recent years, there has been an increasing requirement to develop wideband high-efficiency MMIC high power amplifiers (HPAs) to accommodate wideband operation and reduce power consumption. This paper presents a wideband high efficiency MMIC HPA for Sub-6-GHz applications using a 0.25-μm gate-length D-mode GaN/SiC high electron mobility transistor (HEMT) process. The amplifier consists of two stages with two HEMT cells for the driver stage and eight HEMT cells for the power stage. To obtain a flat gain while maintaining the wideband characteristic, a gain equalization technique is employed in the inter-stage matching circuit. Meanwhile, a low-loss output matching network is utilized to ensure high efficiency. The fabricated HPA occupies a compact chip area of 14.35 mm2 including testing pads. Over the frequency range of 2–6 GHz, measured results of this HPA show a saturated continuous wave (CW) output power of 44.4–45.2 dBm, a power added efficiency (PAE) of 35.8–51.3%, a small signal gain of 24–25.5 dB, and maximum input and output return losses of 14.5 and 10 dB, respectively.

Orthogonal frequency division multiplexing (OFDM) system has been widely used for the high speed digital communication area and it is very promising for the next generation communication standard because of high data rate capability. However, OFDM system has inherent serious problem of high peak-to-average power ratio (PAPR) that makes the OFDM signal be distorted in the nonlinear HPA (high power amplifier). In this paper, CI (carrier interferometry)-OFDM system is considered to overcome this problem and is newly analyzed in the selective fading and narrow-band interference channel. CI-OFDM system distributes each parallel data to all sub-carriers in differently phase-rotated form. So, PAPR becomes lowered and it shows the frequency diversity effects. BER (bit error rate) performance is analyzed in the selective fading and narrow-band interference environment. From the simulation results, it is confirmed that CI-OFDM system calms down the high PAPR problem and CI-OFDM system is more robust than the ordinary OFDM system in the selective fading and narrow-band interference channel.

In this paper the main motive is to study the Electromagnetic Interference which is very prominent field in today's life. Electromagnetic interference also called radio frequency interference (RFI) is a disturbance that affects an electrical circuit due to either electromagnetic conduction or electromagnetic radiation emitted from an external source. EMI problems have been increasing with the proliferation of mobile electronic systems, wireless communication systems, and computer networks. The electromagnetic spectrum is becoming increasingly crowded. After this the reasons are elaborated; why electromagnetic interference takes place and how it affects the system. The presence of electrical field contributes to the surrounding levels of electrical and electromagnetic noise and interference. The increasing demand and dependence on the use of electromagnetic transmission systems for information technology applications has enabled revolutionary communications capabilities to include cordless communication devices, wireless networking, and satellite communication systems. As the number of these devices increases, there is an increase in electromagnetic radiation within the segments of the electromagnetic spectrum in which these systems operate. These emissions have the potential to interfere with the normal operation of electronic communication links and systems. The electromagnetic energy disrupting the normal operation or function of electronic devices is known as environmental interference (El). The source of El can be categorized as environmental (naturally occurring), incidental or intentional. The effects of El can be significant regardless of their source, however, engineering design and other considerations that can be used to limit the impact and disruption of El on electronic, communication and information systems. As we are aware of the bad impacts of Electromagnetic Interference so main concentration will be on Negative Effects of EMI. In the end of this paper different methods for reducing the EMI and selecting the best one will be discussed.

The satellite communications (SatCom) system is a representative technology for global coverage and seamless communications in next-generation communication systems. This paper is a survey of basic studies and recent research trends for multiple input multiple output (MIMO) SatCom. Specifically, we describe and provide the differences between terrestrial networks and SatCom. Furthermore, we categorize the scenarios mainly considered in the MIMO SatCom systems and major research topics in those scenarios. We also summarize the most important technical issues currently being researched in MIMO SatCom systems, and list future works to be studied based on this. This survey is recommended for researchers who are starting research on SatCom systems or those who wish to understand the research trends associated with MIMO SatCom systems.

Satellite communication is one of the key focuses of the sixth generation (6G) mobile communication systems, and aerial hybrid reconfigurable intelligent surface (AHRIS) -assisted satellite communication has recently emerged as a promising candidate for practical deployment in the 6G wireless networks. System design and gain rely heavily on accurately modeling of the underlying channel characteristics, which is challenging due to the high mobility of AHRIS and the unique properties of satellite communication. In this paper, we propose a novel three-dimensional (3D) non-stationary wideband geometry-based stochastic model (GBSM) for AHRIS-assisted satellite communication systems, where AHRIS movements and satellite trajectories are specifically considered. Moreover, two AHRIS phase correction schemes are proposed based on the characteristics of AHRIS in satellite communication systems. Following this, channel correlation function, Doppler power spectral density (PSD) and channel capacity are derived according to the proposed model. Simulation results show that the proposed model can accurately capture the characteristics of the AHRIS-assisted satellite communication systems, and the proposed phase correction schemes can effectively improve the channel statistical characteristics and increase the system capacity.

For the design of the QPSK‐TDMA satellite communication system, analyses and experiments of modem systems have been made. When the burst‐mode QPSK signals with white Gaussian noise are input into the demodulation system, the demodulation system including the carrier recovery circuit, is influenced by noise. In this paper, the symbol error rate in the CPSK transmission, the code error rate in the DCPSK transmission, the unique word error rate (UWER) [for PSK transmission for both C and DC] which is important for the frame timing synchronization signal extraction, and occurrence probability of cycle slip in CR as well as its effect on the UWER, have been analyzed. Furthermore, experiments have been made and their results have been compared with the results of the analyses. Also, it has been shown by examples that the modem system of the QPSK‐TDMA system can easily be designed by using the results of the analyses.

The free space optical (FSO) communication system has attracted many researchers from different countries, owning to its advantages such as high security, high speed and anti-interference. Among all kinds of the channels of the FSO communication system, the atmosphere channel is very difficult to deal with for two typical disadvantages at least. The one is the scintillation of the optical carrier intensity caused by the atmosphere turbulence and the other is the multipath effect by the optical scattering. A lot of studies have shown that the MIMO (Multiple Input Multiple Output) technology can overcome the scintillation of the optical carrier through the atmosphere effectively. So the background of this paper is a MIMO system which includes multiple optical transmitting antennas and multiple optical receiving antennas. A number of particles such as hazes, water droplets and aerosols exit in the atmosphere widely. When optical carrier meets these particles, the scattering phenomenon is inevitable, which leads to the multipath effect. As a result, a optical pulse transmitted by the optical transmitter becomes wider, to some extent, when it gets to the optical receiver due to the multipath effect. If the information transmission rate is quite low, there is less relationship between the multipath effect and the bit error rate (BER) of the communication system. Once the information transmission rate increases to a high level, the multipath effect will produce the problem called inter symbol inference (ISI) seriously and the bit error rate will increase severely. In order to take the advantage of the FSO communication system, the inter symbol inference problem must be solved. So it is necessary to use the channel equalization technology. This paper aims at deciding a equalizer and designing suitable equalization algorithm for a MIMO free space optical communication system to overcome the serious problem of bit error rate. The reliability and the efficiency of communication are two important indexes. For a MIMO communication system, there are two typical equalization methods. The first method, every receiving antenna has an independent equalizer without the information derived from the other receiving antennas. The second, the information derived from all of the receiving antennas mixes with each other, according to some definite rules, which is called space-time equalization. The former is discussed in this paper. The equalization algorithm concludes training mode and non training mode. The training mode needs training codes transmitted by the transmitter during the whole communication process and this mode reduces the communication efficiency more or less. In order to improve the communication efficiency, the blind equalization algorithm, a non training mode, is used to solve the parameter of the equalizer. In this paper, firstly, the atmosphere channel is described focusing on the scintillation and multipath effect of the optical carrier. Then, the structure of a equalizer of MIMO free space optical communication system is introduced. In the next part of this paper, the principle of the blind equalization algorithm is introduced. In addition, the simulation results are showed. In the end of this paper, the conclusions and the future work are discussed.

This paper presents simulation results which illustrate the performance of a fast frequency hopped - frequency division multiple access (FFH-FDMA) satellite communication system using a partial processing dehop-rehop transponder (DRT) under jamming. In the simulated system, convolutional coded symbols (using rates 1/2 or 1/4) are hopped with time diversity to enhance the anti-jamming (AJ) capacity. This study examines the combined effect of time diversity and channel coding under the influence of TWTA nonlinearity, jammer strength and up/down link channel noises on the end-to-end bit error rate (BER) of the DRT system. The simulated results show that under the considered jamming environments of partial band noise jamming (PBNJ) and band multi-tone jamming (BMTJ), excessive TWTA input back-off (IBOF) does not necessarily enhance the performance; rather, it greatly degrades the BER, particularly when channel noise is non-negligible. It was also verified that under the same conditions, time diversity and convolutional coding must be carefully combined to avoid possible degradation in FH-FDMA satellite channel.

In the past few years, non-geostationary orbit (NGSO) satellite communication constellations have regained popularity due to their conspicuous advantages. Nevertheless, with more NGSO satellites getting involved in communications, the spectrum resources should become much more scarce. Multi-beam high throughput satellite and spectrum sharing are two major techniques in communication design. The two techniques can significantly mitigate interference and highly augment the capacity of the communication system. Thus, they are commonly used in satellite communication systems nowadays. With a massive number of NGSO satellites comprising the communication system and moving in their orbits, interference scenarios are pretty complex. In this article, the relationship between the level of interference and the beam distance is deduced. Moreover, for beams with different tilting angles, the different off-axis angles may correspond to the same beam distance, which is directly related to the interference level. Through the interference analysis, we propose a channel allocation method that uses a beam search algorithm to optimize the channel allocation problem and achieves outstanding time efficiency. The performance of the proposed method is validated by a coexisting scenario of the geostationary orbit and NGSO satellite communication systems. The results show that the level of interference can be largely mitigated, and the capacity of communication systems is significantly augmented.

The spread spectrum technology has been widely used in ground communication systems. With the development of global satellite communication, spread spectrum communication has also been widely used in satellite communication system. However, spread spectrum communication has many challenges to address, such as multi-user interference, near-far effect, random phase, delay and so on. Multi-user detection technology makes use of spreading sequence, delay, amplitude and phase information of each user for joint detection, which can effectively suppress multiple access interference, make full use of the frequency spectrum resources at the uplink and improve system capacity. Thus, the multiple user detection is one of the key technologies in CDMA communication systems. This paper adopts the multiple user detection scheme that is based on convolution coding block parallel iteration interference cancellation and conducts MATLAB simulation on multiple user detection algorithms. Though the study of three different data rate scenarios, this paper verifies that the multiple user detection algorithm can reduce the bit error rate of the reference user and improve system capacity.

Nonlinearities play an imperative role in performance of wireless communication systems. In this paper, High Power Amplifiers (HPA) have been used to check the performance of the proposed system by analyzing its amplitude, phase and their joint distortions using Multiple-Input Multiple-Output (MIMO) wireless communication system. This paper takes-in account the overall effects of HPA that provokes nonlinearities at the transmitter's end in a communication system. Therefore, a novel method for the HPA nonlinearities mitigation has been proposed to improve the performance of amplitude, phase and joint distortions in MIMO communication systems. The simulation results show an improvement in the overall effect of the MIMO system and enhance the input response on the transmitter side. Furthermore, this method has been proposed to exploit the benefits of the MIMO system to improve the Symbol Error Rate (SER) versus Signal to Noise Ratio (SNR) curves for amplitude, phase and their joint distortions.