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A new closed‐form expression of the spectral coefficients of the digital streams obtained by dyadic digital pulse modulation is presented and validated in this letter. The new expression provides in‐depth insight into the spectral properties of dyadic digital pulse modulation, revealing its applicability as an all‐digital bandpass amplitude modulation technique. Simulations and measurements on a proof‐of‐concept dyadic digital pulse modulation amplitude modulator prototype demonstrate the effectiveness of the approach.

Reconfigurable intelligent surface (RIS)‐empowered communications is on the rise and is a promising technology envisioned to aid in 6G and beyond wireless communication networks. RISs can manipulate impinging waves through their electromagnetic elements enabling some sort of control over the wireless channel. The potential of RIS technology is explored to perform a sort of virtual equalization over‐the‐air for frequency‐selective channels, whereas equalization is generally conducted at either the transmitter or receiver in conventional communication systems. Specifically, using an RIS, the frequency‐selective channel from the transmitter to the RIS is transformed to a frequency‐flat channel through elimination of inter‐symbol interference (ISI) components at the receiver. ISI is eliminated by adjusting the phases of impinging signals particularly to maximize the incoming signal of the strongest tap. First, a general end‐to‐end system model is provided and a continuous to discrete‐time signal model is presented. Subsequently, a probabilistic analysis for elimination of ISI terms is conducted and reinforced with computer simulations. Furthermore, a theoretical error probability analysis is performed along with computer simulations. It is analysed and demonstrated that conventional RIS phase alignment methods can successfully eliminate ISI, and the RIS‐aided communication channel can be converted from frequency‐selective to frequency‐flat.

This letter derives an approximate average bit error rate (BER) expression of M‐ary phase shift keying with a noisy phase reference in a Nakagami‐m fading channel. The proposed closed‐form expression is general for the M‐ary case, including previous results for both binary and quadrature phase shift keying. The accuracy of the proposed average BER expression is verified through a comparison with the exact BER.

Here, an enhanced spatial modulation with generalized antenna selection (ESM‐GAS) for multiple‐input single‐output systems is proposed. Unlike the conventional SM systems, in ESM‐GAS, the number of active antennas is not fixed, but varies from only one to all. In ESM‐GAS, a concept called equivalent antennas is introduced to describe the status of the antennas. Out of all the available equivalent antennas, a subset is selected as the candidate antennas for SM, in which additional information bits are used to determine the indices of the activated equivalent antennas. Two criteria are used to select the candidate equivalent antennas. One is ESM‐GAS, where a part of candidate equivalent antennas with larger channel power gains are selected with low computational complexity. To further improve the bit error ratio (BER) performance of ESM‐GAS, the other one is a combination scheme of Euclidean distance antenna selection (EDAS) and ESM‐GAS (ESM‐GAS‐EDAS). Simulation results show that ESM‐GAS has better BER performance than conventional SM, and ESM‐GAS‐EDAS outperforms conventional SM, EDAS‐based SM, and ESM‐GAS, which verifies the effectiveness of the proposed schemes.

One of the critical challenges in multicarrier‐based systems is peak to average power ratio (PAPR). Recently, Filter Bank Multicarrier (FBMC) is proved to be a promising candidate that can replace the traditional orthogonal multiplexing division (OFDM) scheme due to its better spectral efficiency, reducing both inter‐channel interference (ICI) and PAPR. Due to their advantages in reducing the PAPR without impacting the BER, the Hadamard transform was used in the proposed FBMC based VLC system. Furthermore, here, the discreet cosine transform (DCT) precoding is also used to boost the potential for PAPR reduction and the BER efficiency. The negative signals are not clipped off as in traditional asymmetrically‐clipped optical OFDM (ACO‐OFDM) signals to reduce the impact of large‐amplitude signal reduction nor add dc biasing for cancelling negative signals as in traditional DC‐biased optical OFDM (DCO‐OFDM) signals. Furthermore, a Clipping ratio is introduced to allow a trade‐off between bit error rate (BER) and PAPR reduction, and the optimal PAPR reduction is investigated. The obtained results show that the proposed FBMC based VLC system with DCT and clipping technique can reduce the PAPR and achieve good BER efficiency compared to the OFDM based VLC system.

This study proposes an online deep learning‐based channel state estimator for OFDM wireless communication systems by employing the deep learning long short‐term memory (LSTM) neural networks. The proposed algorithm is a pilot‐assisted estimator type. The proposed estimator is initially offline trained using simulated data sets, and then it follows the channel statistics in an online deployment, where finally the transmitted data can be recovered. A comparative investigation is performed using three different optimisation algorithms for deep learning to evaluate the performance of the proposed estimator at each. The proposed estimator provides a superior performance in comparison to least square (LS) and minimum mean square error (MMSE) estimators when limited pilots are used, thanks to the outstanding learning and generalisation capabilities of deep learning LSTM neural networks. Also, it does not require any prior knowledge of channel statistics. So, the proposed estimator is promising for channel state estimation in OFDM communication systems.

A modified load‐modulation network to design a fully integrated wideband Doherty power amplifier (DPA) from 4.6 to 5.5 GHz is presented in this letter. The modified load‐modulation network uses only two π‐type high‐pass equivalent quarter wavelength transmission lines (QWTLs). Unlike the existing methods, the bandwidth of the load‐modulation network composed of two merged π‐type equivalent QWTLs is broadened. Furthermore, a drain bypass capacitor compensation method is proposed to reduce the leakage of RF power after the drain supply inductors are merged. For verification, a wideband monolithic microwave integrated circuit DPA was designed and fabricated using a 0.25‐μm gallium nitride based high‐electron‐mobility transistor process. Measurement results show that a saturated power of 41.6–42.4 dBm, a saturated drain efficiency (DE) of 65.3–72%, and a 6‐dB back‐off DE of 45–55.4% are achieved from 4.6 to 5.5 GHz. Using a 160‐MHz orthogonal frequency‐division multiplexing signal with a peak‐to‐average power ratio of 6.2 dB, the high average efficiency of 49% with an adjacent channel leakage ratio of –47.2 dBc after linearisation was obtained at an average output power of 35 dBm at 4.9 GHz.

This letter derives the probability distribution function (PDF) of received symbols for orthogonal frequency‐division multiplexing (OFDM) based massive multiple‐input, multiple‐output (MMIMO) systems, which uses maximal‐ratio combining (MRC) detection. The effects of noise and interferences are evaluated through random variables, and the PDF is then derived from their joint probability and characteristic functions. The bit error rate (BER) using Binary and Quadrature Phase Shift Keying (BPSK, QPSK), and M‐ary Quadrature Amplitude Modulation (QAM) waveforms is then analyzed by using this PDF. Simulation and analytical results confirm that the derived equations provided accurate PDF and BER, and therefore, can be used efficiently to evaluate performance of OFDM‐MMIMO systems.

This paper deals with the peak to average power ratio of duplex multicarrier signals. A simple but accurate expression of the complementary cumulative distribution of the peak to average power ratio is suggested, based on both empirical and theoretical analyses of the mean peak to average power ratio of such a continuous duplex signal. To this end, it is shown that the mean peak to average power ratio can be written in function of the frequency distance between the two signals composing the duplex one. The relevance and the accuracy of the suggested analysis are shown through simulations, and a discussion paves the way to further analyses involving general multiplex signals with different powers and subcarriers numbers.

For improving the anti‐interference performance and compatibility of a navigation‐augmented signal in future BeiDou Global Navigation Satellite Systems, a new modulation based on chirp subcarriers is proposed, named binary offset chirp carrier modulation, which is formed by multiplying a periodic binary chirp subcarrier with a spreading code signal. And it can make use of the time‐varying frequency for shaping the spectrum and have superior performance in anti‐interference, similar advantage in tracking accuracy, anti‐multipath capability and compatibility compared with binary offset carrier modulations. The binary offset chirp carrier modulations proposed in this paper provide a potential signal design for the future low earth orbit (LEO) navigation‐augmented Global Navigation Satellite Systems.