Showing papers on "Keying published in 2023"

Enhancing the security of free space optical communication system by employing chaos-based modulation scheme

Abstract: Abstract Security and privacy are two main dominant features of any communication system. In this paper, physical layer security of free space optical communication system using chaotic modulation scheme i.e., differential chaos shift keying (DCSK) is analyzed, where eavesdropper is actively present near the receiver and interfering between the transmission of secret messages from a transmitter to the receiver. In this manuscript, we have derived analytical expressions for the average secrecy capacity and secrecy outage probability which is used as a metric for secrecy performance analysis. The channel characterization is carried out using gamma–gamma model for weak-to-strong turbulence conditions. The effect of physical layer parameters like transmission link length, spreading length, etc. are considered for evaluating the security performance of the system. Numerical analysis is carried out and graphical results are presented. The results depicted that a very good average secrecy capacity can be achieved even in the presence of eavesdropper, however, it requires a tradeoff between high signal-to-noise ratio of main channel and large values of spreading factor. The proposed system is very promising for the future secured communication systems.

Enhancing Distributed Radar Detection Performance with Reliable Communications

Abstract: Despite their potential to significantly enhance target detection capability, distributed radar networks, with or without a central coordinator, have not been sufficiently examined. In this paper, we propose a generalized likelihood ratio test (GLRT)-based constant false alarm rate (CFAR) detector for distributed detection in a radar network, wherein only neighboring nodes require sharing their GLRT values. We obtain the analytical expression for the local GLRT and employ distributed average consensus-based estimation to reach the global metric in the case of noise-free communications links. The exact analytical expressions for the local probability of false alarm (PFA) and probability of detection (PD) are derived and used to obtain the exact analytical expression for the global PFA as well as an approximate expression for the global PD. In the case of noisy communications links, we demonstrate the effects of quantization and different modulation techniques, such as chirp and phase shift keying, on the global detection probability. Our results show that the proposed detector performs significantly better than the non-CFAR energy detector (ED) and provides performance comparable to that of the non-CFAR matched filter (MF) detector. It is shown that the performance of the chirp and binary phase shift keying (BPSK) modulations is similar but better than that of quadrature phase shift keying (QPSK). Our results also show that the uniform quantization of GLRT values with only 4 bits is sufficient to enable each node to achieve performance similar to the global performance achieved in the case of error-free communications links.

Performance Analysis of Vilnius Chaos Oscillator-Based Digital Data Transmission Systems for IoT

Abstract: The current work is devoted to chaos oscillator employment in digital communication systems for IoT applications. The paper presents a comparative performance analysis of two different chaos data transmission systems: frequency-modulated chaos shift keying (FM-CSK) and quadrature chaos phase-shift keying (QCPSK), and a comparison to their non-chaotic counterparts: frequency-shift keying (FSK) and quadrature amplitude modulation (QAM). For both chaotic communication systems, the Vilnius oscillator and substitution method of chaotic synchronization are chosen due to simple circuitry implementation and low power consumption properties. The performance of the systems in the fading channel with additive white Gaussian noise (AWGN) is evaluated. Also, the systems’ performance in the case phase noise is investigated, and the benefits of chaotic waveforms employment for data transmission are demonstrated.

Optical Amplification-Free High Baudrate Links for Intra-Data Center Communications

Abstract: The enormous traffic growth sets a stringent requirement to upgrade short-reach optical links to 1.6 TbE capacity in an economically viable way. The power consumption and latency in these links should be as low as possible, especially for high-speed computing. This is possible to achieve using high baudrate on-off keying links thanks to a better noise tolerance and a relaxed requirement on linearity for electronics and photonics. In this regard, we demonstrate a 200 Gbaud on-off keying link without any optical amplification using an externally modulated laser with 3.3 dBm of modulated output power operating at 1541.25 nm wavelength. We achieve transmission over 200 meters of single-mode fiber with performance below 6.25% overhead hard-decision forward error correction threshold for each baudrate and all selection of modulation formats. We also show 108 Gbaud on-off keying link with superior performance without decision feedback equalizer up to 400 meters of single-mode fiber. In addition, we benchmark the short-reach optical link with 112 Gbaud four-level pulse amplitude modulation and 100 Gbaud six-level pulse amplitude modulation. For 108 Gbaud on-off keying and 112 Gbaud four-level pulse amplitude modulation, we can achieve an even lower bit error rate.

Performance evaluation of CSS-APCMA for massive IoT using GNU Radio/USRP

Abstract: Asynchronous Pulse Code Multiple Access (APCMA) is a pulse-based communication system for massive IoT. It enables high-density communication because it can decode messages with a high probability even if they collide. We evaluate the performance of APCMA with Chirp Spread Spectrum-modulated pulses (CSS-APCMA) by comparing it with On-Off Keying APCMA (OOK-APCMA) and LoRa. Our first experiment shows that APCMA has a lower packet error rate (PER) than LoRa in a congested environment. Our second experiment shows that CSS-APCMA has a smaller PER than OOK-APCMA in a noisy environment. Our results confirm that CSS-APCMA is suitable for massive IoT.

Optimal Rotated QPSK Constellation for a Semi-Orthogonal Multiple Access Visible Light Communication System

Abstract: A rotated quadrature phase-shift keying (QPSK) based semi-orthogonal multiple access (SOMA) data transmission is considered for a visible light communication (VLC) system with two users. The rotation of the QPSK constellation at the transmitter followed by a data pre-processing technique at the receiver of each user ensures the elimination of the successive interference cancellation unit. An optimal maximum likelihood receiver is proposed for the system under consideration using which, the closed-form expressions for the symbol error probability (SEP) for both the users in the VLC system are derived. The optimization problem to obtain the optimal angle of rotation of the QPSK constellation which minimizes the SEP of the users is formulated and solved. The dependency of the optimality of the QPSK rotation angle on various VLC system parameters is studied via numerical results which lead to the observation of a value of the signal-to-noise ratio of the system around 8.8 dB about which the dependency of the optimal rotation angle on the other VLC system parameters interchange, thus providing design aspects for a SOMA-VLC system.

A comparative study on channel coding scheme for underwater acoustic communication

Abstract: There are various challenges in underwater acoustic communication (UWA) however bit error rate (BER) is considered as the main challenge as it significantly affects the UWA communication. In this paper, different coding schemes such as convolution, turbo, low density parity check (LDPC), and polar coding based on the t-distribution noise channel are investigated, and binary phase-shift keying (BPSK) modulation with a code rate of 1/2 has considered in the evaluation and analyses. The evaluation of these channel coding schemes is performed based on BER, computational complexity as well as latency. The results have shown the outperform of polar coding in UWA over other channel coding schemes as it has lower BER and lower computational complexity.

Multilevel polarization shift keying modulation for turbulence-robust underwater optical wireless communication.

Abstract: Turbulence is an intractable issue for underwater optical wireless communication (UOWC). Most literature has been mainly focused on the modeling of turbulence channels and performance analysis rather than mitigation of the turbulence effect, especially from the experimental aspects. In this paper, a multilevel polarization shift keying (PolSK) modulation based UOWC system is established utilizing a 15 m-long water tank, and the system performance is investigated under specific temperature gradient-induced turbulence and various transmitted optical powers. Experimental results show the feasibility of the PolSK in alleviating the effect of turbulence, and the bit error rate performance significantly outperforms traditional intensity-based modulation schemes which have difficulty in obtaining an optimal decision threshold in a turbulence channel.

Fully-Integrated SPAD-Based Receiver With Nanosecond Dead Time for Optical Wireless Communication

Abstract: This paper presents the design and characterization of a fully-integrated receiver based on single-photon avalanche diodes (SPADs) with nanosecond dead time for high-speed high-sensitivity optical wireless communication (OWC). The receiver consists of a 4x4 SPAD array that is based on a p-well/deep n-well (DNW) structure, and each SPAD is integrated with a tunable front-end circuit to perform quench and reset. In addition, an OR tree is designed to combine the 16 channels of output from the front-end circuits to generate a single data stream for signal processing, and an output buffer is implemented as the interface to drive 50-Ω loading for testing purpose. Fabricated in a standard 180 nm CMOS process, the receiver achieves a minimum dead time of about 2.5 ns. Bit error rate (BER) measurement of the implemented receiver indicates a sensitivity of −31.6 dBm at 100 Mb/s for a BER of 2 × 10 ⁻³ and a wavelength of 520 nm, where on-off keying (OOK) modulation and a 2 ¹⁵ -1 pseudorandom binary sequence (PRBS-15) are employed. To recover the transmitted data stream from the received signal, a signal processing flow specific for SPAD-based receivers is proposed and implemented.

Phase Alignment of an Array Optical Telescope System Using Balanced Detection

Abstract: Differential phase shift keying (DPSK) modulation and multi-aperture receiving are effective means for suppressing flickering, deviation, and fragmentation of the light spot by atmospheric turbulence. What is challenging in coherent beam combination of such an array receiver system is to detect and compensate for phase deviation of sub-apertures. In this paper, a method of phase alignment of an array optical telescope system using balanced detection was proposed and demonstrated. The improved Mach Zehnder Interferometer (MZI) can demodulate the digital signal and recover the phase difference at the same time. It also brings a 3 dB gain to the receiver and improves the detection sensitivity of the system. Adequate simulations with OptiSystem and MATLAB were carried out to show that the power value remains near the ideal state of 2.75 mW, and the bit error rate is less than 10−9 after phase compensation, which indicates the effectiveness and accuracy of the proposed method. Furthermore, taking the communication interruption difference of ninety degrees as an example, the system bit error rate was reduced from 1 to 10−35, and communication was established again.

65,536-ary orbital angular momentum-shift keying free-space optical communication based on few-shot learning.

Abstract: In an orbital angular momentum-shift keying free-space optical (OAM-SK FSO) communication system, precisely recognizing OAM superposed modes at the receiver site is crucial to improve the communication capacity. While deep learning (DL) provides an effective method for OAM demodulation, with the increase of OAM modes, the dimension explosion of OAM superstates results in unacceptable costs on training the DL model. Here, we demonstrate a few-shot-learning-based demodulator to achieve a 65,536-ary OAM-SK FSO communication system. By learning from only 256 classes of samples, the remaining 65,280 unseen classes can be predicted with an accuracy of more than 94%, which saves a large number of resources on data preparation and model training. Based on this demodulator, we first realize the single transmission of a color pixel and the single transmission of two gray scale pixels on the application of colorful-image-transmission in free space with an average error rate less than 0.023%. This work may provide a new, to the best of our knowledge, approach for big data capacity in optical communication systems.

Towards RIS-aided Non-Coherent Communications: A Joint Index Keying M-ary Differential Chaos Shift Keying System

Abstract: In reconfigurable intelligent surface (RIS)-aided coherent communications, channel state information (CSI) is often assumed to be perfectly estimated at the receiver. However, perfect CSI cannot be available in practice. Furthermore, the complex and ever-changing channel makes the acquisition of accurate CSI unaffordable because of the large overhead in transmitting pilot signals. Motivated by these considerations, a novel non-coherent RIS-aided joint index keying M -ary differential chaos shift keying (RIS-JIK-MDCSK) scheme is proposed in this paper, where the receiver can retrieve information bits by performing non-coherent correlation demodulation without requiring CSI, thereby reducing the system complexity. In RIS-JIK-MDCSK, the states of the reference signal, RIS elements, and information-bearing subcarriers are jointly optimized to devise a joint index keying mechanism, where additional information bits are implicitly transmitted by these state indices, thus increasing the throughput and spectral efficiency. Furthermore, an effective joint index keying detection algorithm is proposed to recover information bits. The analytical bit error rate (BER) of RIS-JIK-MDCSK is derived over a Rayleigh fading channel. Other evaluation metrics, including the throughput, spectral efficiency, and system complexity are also analyzed and compared against benchmark schemes. Numerical simulations are performed to evaluate the superiority of RIS-JIK-MDCSK compared to existing schemes.

On the Use of FFH-MFSK for Ultra-Low Power Communications in a Jamming Environment

Abstract: We are interested in a communication system that operates in the presence of an intelligent jammer, under stringent power constraints, but with flexible bandwidth constraints.We optimize some of the key elements in the transceiver design for low power consumption, and thus high complexity components of the system, such as matched filters (MF), forward error correction (FEC) that employs iterative decoders, coherent demodulators, and bandwidth-efficient modulation formats, are not feasible for this research. Rather, our system is designed using M -ary frequency shift keying (MFSK) with non-coherent detection and fast frequency hopping (FFH), optimized two-pole bandpass filters (BPF), and Reed-Solomon (RS) codes with hard-decision decoding. Among other things, we show that by properly optimizing the key parameters of the BPFs and RS codes, we can design the system to be significantly less complex than the MF system with a performance loss of less than 1.4 dB for most scenarios that we considered. Further, the 2-pole BPF system can actually outperform the corresponding MF system by up to 2.4 dB in the presence of multi-tone jamming.

Experimental Demonstration of Modulation Format Recognition Using Reservoir Computing Based on VCSEL With Gradient-like Boosting

Abstract: We present a simple experimental approach based on a photonic time delay reservoir computing (RC) system for modulation format recognition. Here an optically injected vertical cavity surface emitting laser with single feedback is trained with the cross sequence of instantaneous characteristics of modulation signals. Three widely used modulation formats including on–off keying, binary phase shift keying, and binary frequency shift keying, where the optical signal-to-noise ratio varies from 4 dB to 36 dB are considered. Besides, we propose a post-processing method of using multiple gradient-like boosting operations for the time delay RC system, in which the residual value between the target value and the actual value is regarded as the target value for multiple training. Experimental and numerical results demonstrate that using multiple gradient-like boosting operations for post-processing can efficiently identify all three modulation formats with the highest accuracy of 100% after optimizing the control parameters such as the feedback strength, injection strength, and number of virtual nodes of the time delay RC system. The simple experimental approach with the proposed multiple gradient-like boosting operations offers a resource-efficient alternative approach to modulation format recognition of future communication.

Receiver Design in Full-Duplex Joint Radar-Communication Systems

Abstract: Full-duplex (FD) integrated sensing and communication (ISAC) has great potential in future vehicular networks. However, the FD requirement and the ISAC functions make the receiver processing extremely complicated, particularly when multiple transmissions are uncoordinated. In this paper, we study frequency-hopping (FH) based receivers in an FD ISAC system, where the arrivals of backscattered signals from one node may overlap with those of signals from another node. To mitigate the interferences caused by the overlapping signals, we consider two receiver options based on either conventional communications or frequency-modulated continuous-wave radars, and two signal modulations based on either fast FH or un-slotted ALOHA FH. Based on the different signal modulations, we develop two parameter estimation schemes via using FH-decoding and dechirp operations, respectively. To further improve the sensing accuracy, we proceed to propose an iterative algorithm, which refines the estimates of all parameters via using short-time-Fourier transform and maximizing the received power in desired frequency bands. After obtaining all channel parameters in sensing, bilateral communications between two nodes are realized by differential phase-shift keying. Finally, simulation results are provided and verify that the proposed FD ISAC can obtain parameters in high resolution and realize robust communication links.

Radar-Centric Photonic Terahertz Integrated Sensing and Communication System Based on LFM-PSK Waveform

Abstract: The radar-centric terahertz integrated sensing and communication (THz-ISAC) is identified as a significant application in future wireless access networks. Up to date, previously reported demonstrations regarding radar sensing performance lack sufficient support in a complex environment with a strong target masking effect. This work tacks this problem by proposing a radar-centric waveform combining linear frequency modulation (LFM) waveform and phase shift keying (PSK). We first derive sensing metrics of the LFM-PSK waveform through theoretical analysis, including range resolution, peak sidelobe ratio (PSLR), and Cramér-Rao lower bound (CRLB). Then a proof-of-concept experiment on a photonics-assisted integrated sensing and communication (ISAC) system operating at 330 with 18 GHz bandwidth is conducted to verify the performance of the proposed LFM-PSK waveform. In the experiment, the proposed waveform can reach a PSLR of up to 20.9 dB and a range resolution of 1.3 cm, simultaneously accommodating a data transmission of 6 Gbit/s. In addition, the effect of embedding symbols on sensing metrics is also discussed, and by comparing the range solution and PSLR with various data rates, around $\sim$ 6 dB gain in the PSLR without any deterioration of range resolution is observed.

Experimental Demonstration of a Visible Light Communications System Based on Binary Frequency-Shift Keying Modulation: A New Step toward Improved Noise Resilience

Abstract: Visible light communications (VLC) are an emerging technology that is increasingly demonstrating its ability to provide wireless communications in areas where radio frequency (RF) technology might have some limitations. Therefore, VLC systems offer possible answers to various applications in outdoor conditions, such as in the road traffic safety domain, or even inside large buildings, such as in indoor positioning applications for blind people. Nevertheless, several challenges must still be addressed in order to obtain a fully reliable solution. One of the most important challenges is focused on further improving the immunity to optical noise. Different from most works, where on–off keying (OOK) modulation and Manchester coding have been the preferred choices, this article proposes a prototype based on a binary frequency-shift keying (BFSK) modulation and non-return-to-zero (NRZ) coding, for which the resilience to noise is compared to that of a standard OOK VLC system. The experimental results showed an optical noise resilience improvement of 25% in direct exposure to incandescent light sources. The VLC system using BFSK modulation was able to maintain a maximum noise irradiance of 3500 µW/cm2 as compared with 2800 µW/cm2 for the OOK modulation, and an improvement of almost 20% in indirect exposure to the incandescent light sources. The VLC system with BFSK modulation was able to maintain the active link in an equivalent maximum noise irradiance of 65,000 µW/cm2, as opposed to the equivalent 54,000 µW/cm2 for the OOK modulation. Based on these results, one can see that based on a proper system design, VLC systems are able to provide impressive resilience to optical noise.

A Novel ML-Based Symbol Detection Pipeline for Molecular Communication

Abstract: Molecular Communication (MC) is the process of sending information by the use of particles instead of electromagnetic (EM) waves. This change in paradigm allows the use of MC in areas where EM transmission is undesirable. These include underground, underwater and even intra-body communications. While this novel paradigm promises new areas for communication, one of the major setbacks is its relatively low throughput caused by the propagation speed. This can be improved by decreasing the symbol duration; however, this can be a detriment to the correct decoding of symbols. This paper proposes a novel symbol detection pipeline to increase the possible throughput without increasing the error rate of the communication. This is based on a machine-learning algorithm for classification tasks using an L-point discrete time moving average filter and a wide range of features. Extensive simulations with long sequences at different signal-to-noise ratio (SNR) values were performed to determine how well the proposed method detects symbols. The results show that our method can detect symbols received when On-Off Keying (OOK) modulations are used with a 10 dB gain, even when transmissions with untrained SNR values occur.

Efficient FPGA Implementation of Phase Shift Keying

Abstract: Digital modulation schemes have been an essential part of wireless communication technologies for data transmission. Existing works that implement M-ary PSK using digital logic either have a greater computational complexity due to using arithmetic operations or a more significant area due to using a higher number of LUTs. This paper presents a two look-up table-based modulator capable of generating up to 8-ary PSK at different sampling frequencies with only memory-read operations. From the simulation, it is obtained that the proposed architecture reduces both computational complexity and area without compromising on the characteristics of phase-shift keying.

On the UOWC Performance Under Location Uncertainty

Abstract: More often than not, currents due to gravity, wind friction, and heterogeneous water density cause frequent drifts of the end-users to random locations creating transmission problems in an underwater optical wireless communication (UOWC) network. The location uncertainty effect on the overall network performance in harsh environments, including submarine ones, is an appealing issue that needs to be adequately addressed in the existing technical literature. The present work takes account of a vertical UOWC link where a fixed transmitter at the sea surface illuminates towards the seabed following a Lambertian pattern. In this way, a randomly placed receiver inside a spherical cone is served, and the problem is treated with three-dimensional stochastic geometry methods. In the sequel, the complete statistical behavior of the random distributions of the channel gain and the instantaneous electrical signal-to-noise ratio is estimated. Moreover, some critical network performance metrics, including the outage probability and the bit-error rate for intensity modulation/direct detection with on-off keying and M -ary pulse position modulation, are derived, whereas indicative numerical results are illustrated adequately through a series of appropriate figures.

Real-time Fourier-domain optical vector oscilloscope

Abstract: To meet the constant demands of high-capacity telecommunications infrastructure, data rates beyond 1 terabit per second per wavelength channel and optical multiplexing are widely applied. However, these features pose challenges for existing data acquisition and optical performance monitoring techniques because of bandwidth limitation and signal synchronization. We designed an approach that would address these limitations by optically converting the frequency limit to an unlimited time axis and combining this with a chirped coherent detection to innovatively obtain the full-field spectrum. With this approach, we demonstrated a real-time Fourier-domain optical vector oscilloscope, with a 3.4-terahertz bandwidth and a 280-femtosecond temporal resolution over a 520-picosecond record length. In addition to on-off keying and binary phase-shift keying signals (128 gigabits per second), quadrature phase-shift keying wavelength division–multiplexed signals (4 × 160 gigabits per second) are simultaneously observed. Moreover, we successfully demonstrate some high-precision measurements, which indicate them as a promising scientific and industrial tool in high-speed optical communication and ultrafast optical measurement.

First Demonstration of 512-Color Shift Keying Signal Demodulation Using Neural Equalization for Optical Camera Communication

Abstract: This paper experimentally demonstrates 512 color shift keying (CSK) signal transmission for optical camera communication (OCC). We achieved error-free operation with a CMOS image sensor module and a multi-label classification neural network-based equalizer.

Non-Coherent Chaotic Communications Aided by RIS: A Performance-Enhanced Approach

Abstract: In non-coherent chaotic communications, traditional code-index-modulation-aided differential chaos shift keying (DCSK) schemes face limited gains in bit-error-rate (BER) performance, despite incurring substantial time-frequency resources. To address this challenge, we propose a new reconfigurable intelligent surface (RIS)-aided DCSK (RIS-DCSK) scheme in this letter. The proposed scheme deploys an RIS close to the transmitter antenna to enhance the signal-to-noise ratio (SNR) of the received signal, significantly improving the BER performance. We analyze the BER performance of the RIS-DCSK scheme and demonstrate its superiority. Furthermore, we propose two performance-enhanced algorithms to further improve the BER performance, though with increased computational complexity. Through simulations and comparisons, we show that the proposed RIS-DCSK scheme and its performance-enhanced variants outperform existing benchmarks in terms of BER performance.

Ratio Shift Keying Modulation for Time-Varying Molecular Communication Channels

Abstract: Molecular Communications (MC) is a bio-inspired communication technique that uses molecules to encode and transfer information. Many efforts have been devoted to developing novel modulation techniques for MC based on various distinguishable characteristics of molecules, such as their concentrations or types. In this paper, we investigate a particular modulation scheme called Ratio Shift Keying (RSK), where the information is encoded in the concentration ratio of two different types of molecules. RSK modulation is hypothesized to enable accurate information transfer in dynamic MC scenarios where the time-varying channel characteristics affect both types of molecules equally. To validate this hypothesis, we first conduct an information-theoretical analysis of RSK modulation and derive the capacity of the end-to-end MC channel where the receiver estimates concentration ratio based on ligand-receptor binding statistics in an optimal or suboptimal manner. We then analyze the error performance of RSK modulation in a practical time-varying MC scenario, that is mobile MC, in which both the transmitter and the receiver undergo diffusion-based propagation. Our numerical and analytical results, obtained for varying levels of similarity between the ligand types used for ratio-encoding, and varying number of receptors, show that RSK can significantly outperform the most commonly considered MC modulation technique, concentration shift keying (CSK), in dynamic MC scenarios.

An Emerging Detection Design Adopting Two-Keying Technique in SAC-OCDMA-Based MDW Code

Abstract: This paper aims to enable the two-keying approach in spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) system that employs modified double weight (MDW) code. To achieve this goal, two-keying subtraction detection (TKSD) is suggested, which also declines the impact of multiuser interference (MUI) and phase-induced intensity noise (PIIN). The results of simulation test demonstrate that the TKSD is efficient in realizing the two-keying detection feature in SAC-OCDMA system with superior bit-error rate (BER) performance, security, and transmission rate.

Reconciliation Efficiency Impact on Discrete Modulated CV-QKD Systems Key Rates

Abstract: Continuous variable quantum key distribution (CV-QKD) allows the distribution of symmetric keys in a secure manner. CV-QKD systems can extract keys at its maximum rate when using Gaussian modulation (GM). Nonetheless, GM demands high-capacity random number sources and tends to be very hard to approach in practice. To circumvent these disadvantages, higher-order probabilistic -shaped discrete modulation (DM) can be used. State-of-the-art works compute the key rates of DM-CV-QKD systems considering a fixed value for the reconciliation efficiency and do not take into account the frame error rate (FER) of the system, thus over or under estimating the key rates. In this work, we study the security bounds of CV-QKD systems considering probabilistic shaped DM formats with 256-symbols in the finite-size regime. This accounting for the true value of the reconciliation efficiency, and the FER of the information reconciliation step. Both conventional and hexagonal 256-quadrature amplitude modulation (QAM) constellations yield higher key rates than 256-amplitude and phase shift keying (APSK) constellations, with 256-QAM constellations being indistinguishable in performance with GM for high transmission distances. Minimum signal-to-noise ratio (SNR) values were fixed from a FER analysis through a CV-QKD simulation allowing for key extraction considering different FER levels. Lower FER values are associated with higher SNRs in the system and thus lower achievable transmission distances. Nonetheless, the FER maximizing the extraction key rate is not null. Our results show that the extraction key rate is maximized by SNR adjustment which should have in account both the reconciliation efficiency and the FER.

Дослідження програмної фільтрації цифрового сигналу на базі стандарту psk-31

Abstract: Системи цифрового зв'язку стають усе більше привабливими внаслідок постійно зростаючого попиту і через те, що цифрова передача пропонує можливості обробки інформації, не доступні при використанні аналогової передачі. В основі сучасних систем передачі цифрової інформації через радіоканали лежить кодування кожного символу за допомогою сегмента опорного коливання з певними значеннями базових параметрів — амплітуди, частоти, початкової фази. Відповідно до змінюваного параметра розрізняються основні сімейства — амплітудна маніпуляція (AM, ASK — Amplitude Shift Keying), частотна маніпуляція (ЧМ, FSK — Frequency Shift Keying) і фазова маніпуляція (ФМ, PSK — Phase Shift Keying). Крім базових видів маніпуляції також широко застосовуються комбінаційні — наприклад, квадратурно амплітудна (КАМ, QASK — Quadrature Amplitude Shift Keying). З розвитком обчислювальної техніки, програмного забезпечення і інтегральних мікросхем, з'явилися нові види зв'язку. Одним з них є PSK-31. Спочатку робота в режимі PSK-31 були засновані на використанні дорогих інтегральних мікросхем цифрової обробки сигналу (DSP). Початок стрімкого поширення режиму PSK-31 почалося в 1998 p., коли англійський радіоаматор Пітер Мартінез створив комп'ютерну програму PSK31 SBW, що реалізує обробку цифрових сигналів. Відмінною рисою систем цифрового зв'язку (digital communication system — DCS) є те, що за кінцевий проміжок часу вони посилають сигнал, що складається з кінцевого набору елементарних сигналів (на відміну від систем аналогового зв'язку, де сигнал складається з нескінченної безлічі елементарних сигналів). У системах DCS завданням приймача є не точне відтворення переданого сигналу, а визначення на основі перекрученого шумами сигналу, який саме сигнал з кінцевого набору був посланий передавачем. Важливим критерієм продуктивності системи DCS є ймовірність помилки (РЕ). Розроблена та реалізована у вигляді лабораторного макету практична схема приймача PSK-31. Проведені дослідження основних параметрів і характеристик розробленого зразка. Додатково проведено комп'ютерне моделювання стандарту цифрового зв'язку PSK-31.