Showing papers on "Phase-shift keying published in 2017"

Multiple-Mode Orthogonal Frequency Division Multiplexing With Index Modulation

Abstract: Orthogonal frequency division multiplexing with index modulation (OFDM-IM) performs transmission by considering two modes over OFDM subcarriers, which are the null and the conventional $M$ -ary signal constellation The spectral efficiency (SE) of the system, however, is limited, since the null mode itself does not carry any information and the number of subcarrier activation patterns increases combinatorially In this paper, a novel IM scheme, called multiple-mode OFDM-IM (MM-OFDM-IM), is proposed for OFDM systems to improve the SE by conveying information through multiple distinguishable modes and their full permutations A practical and efficient mode selection strategy, which is constrained on the phase shift keying/quadrature amplitude modulation constellations, is designed Two efficient detectors that provide different tradeoffs between the error performance and detection complexity are also proposed The principle of MM-OFDM-IM is further extended to the in-phase and quadrature components of OFDM signals, and the method of generating multiple modes from the $M$ -ary pulse amplitude modulation constellation for this modified scheme is also introduced Bit error rate (BER) analyses are provided for the proposed schemes Monte Carlo simulations on BER corroborate the analyses and show that the proposed schemes appear as promising multi-carrier transmission alternatives by outperforming the existing OFDM-IM counterparts

Dual-Mode Index Modulation Aided OFDM

Abstract: Index modulation has become a promising technique in the context of orthogonal frequency division multiplexing (OFDM), whereby the specific activation of the frequency domain subcarriers is used for implicitly conveying extra information, hence improving the achievable throughput at a given bit error ratio (BER) performance. In this paper, a dual-mode OFDM technique (DM-OFDM) is proposed, which is combined with index modulation and enhances the attainable throughput of conventional index-modulation-based OFDM. In particular, the subcarriers are divided into several subblocks, and in each subblock, all the subcarriers are partitioned into two groups, modulated by a pair of distinguishable modem-mode constellations, respectively. Hence, the information bits are conveyed not only by the classic constellation symbols, but also implicitly by the specific activated subcarrier indices, representing the subcarriers’ constellation mode. At the receiver, a maximum likelihood (ML) detector and a reduced-complexity near optimal log-likelihood ratio-based detector are invoked for demodulation. The minimum distance between the different legitimate realizations of the OFDM subblocks is calculated for characterizing the performance of DM-OFDM. Then, the associated theoretical analysis based on the pairwise error probability is carried out for estimating the BER of DM-OFDM. Furthermore, the simulation results confirm that at a given throughput, DM-OFDM achieves a considerably better BER performance than other OFDM systems using index modulation, while imposing the same or lower computational complexity. The results also demonstrate that the performance of the proposed low-complexity detector is indistinguishable from that of the ML detector, provided that the system’s signal to noise ratio is sufficiently high.

Joint OSNR monitoring and modulation format identification in digital coherent receivers using deep neural networks

Abstract: We experimentally demonstrate the use of deep neural networks (DNNs) in combination with signals’ amplitude histograms (AHs) for simultaneous optical signal-to-noise ratio (OSNR) monitoring and modulation format identification (MFI) in digital coherent receivers. The proposed technique automatically extracts OSNR and modulation format dependent features of AHs, obtained after constant modulus algorithm (CMA) equalization, and exploits them for the joint estimation of these parameters. Experimental results for 112 Gbps polarization-multiplexed (PM) quadrature phase-shift keying (QPSK), 112 Gbps PM 16 quadrature amplitude modulation (16-QAM), and 240 Gbps PM 64-QAM signals demonstrate OSNR monitoring with mean estimation errors of 1.2 dB, 0.4 dB, and 1 dB, respectively. Similarly, the results for MFI show 100% identification accuracy for all three modulation formats. The proposed technique applies deep machine learning algorithms inside standard digital coherent receiver and does not require any additional hardware. Therefore, it is attractive for cost-effective multi-parameter estimation in next-generation elastic optical networks (EONs).

Convolutional Neural Networks for Automatic Cognitive Radio Waveform Recognition

Abstract: Cognitive radio technology is an important branch in the field of wireless communication, and automatic identification is a major part of cognitive radio technology. Convolutional neural network (CNN) is an advanced neural network, which is the forefront of application in the digital image recognition area. In this paper, we explore CNN in an automatic system to recognize the cognitive radio waveforms. Excitedly, it is a more effective model with high ratio of successful recognition (RSR) under high power background noise. The system can identify eight kinds of signals, including binary phase shift keying (Barker codes modulation) linear frequency modulation, Costas codes, Frank code, and polytime codes (T1, T2, T3, and T4). The recognition part includes a CNN classifier. First, we determine the appropriate architecture to make CNN effective for proposed system. Specifically, we focus on how many convolutional layers are needed, what appropriate number of hidden units is, and what the best pooling strategy is. Second, we research how to obtain the image features into CNN that based on Choi–Williams time-frequency distribution. Finally, by means of the simulations, the results of classification are demonstrated. Simulation results show the overall RSR is 93.7% when the signal-to-noise ratio is −2dB.

Nonlinear Interference Mitigation: Methods and Potential Gain

Abstract: We explore the potential benefits of digital nonlinearity compensation (NLC) techniques in fully loaded coherent wavelength-division multiplexed (WDM) transmission systems. After providing an overview of the various classes of nonlinear interference noise (NLIN) and digital signal processing approaches for their mitigation, we consider the two practically most relevant digital NLC methods known today: back-propagation (BP) and equalization of nonlinear phase and polarization rotation noise (PPRN). We consider a wide range of system configurations including a variety of modulation formats from quadrature phase-shift keying (QPSK) to 256-ary quadrature amplitude modulation (QAM), single-carrier and digital subcarrier multiplexed (SCM) optical superchannels, as well as both point-to-point line systems and optically routed networks (ORNs). Using theoretical predictions from the time-domain model for NLIN, we show that the gain in peak signal-to-noise ratio in fully loaded WDM systems using single-channel and three-channel joint BP is typically limited to 0.5 and 1 dB. The additional gain provided by increasing the number of jointly back-propagated channels beyond three is limited to 0.1 dB per additional back-propagated channel. The remarkably slow growth of the BP gain with the bandwidth of the back-propagated signal is shown to apply also for systems in which the receiver employs PPRN removal. We additionally explore the potential benefits of SCM across a wide range of system configurations, including the impact of BP and PPRN removal on SCM systems. We show that while the BP gain is similar to single-carrier systems, PPRN removal can have a much stronger effect, particularly for higher order QAM systems, implying that SCM can be advantageous not only for constant modulus formats such as QPSK, but also for high spectral efficiency systems. In the context of ORNs, we find that SCM not only improves system tolerance to nonlinearities, but also induces significantly smaller performance variations in various ORN scenarios.

64-QAM 60-GHz CMOS Transceivers for IEEE 802.11ad/ay

Abstract: This paper presents 64-quadrature amplitude modulation (QAM) 60-GHz CMOS transceivers with four-channel bonding capability, which can be categorized into a one-stream transceiver and a two-stream frequency-interleaved (FI) transceiver. The transceivers are both fabricated in a standard 65-nm CMOS technology. For the proposed one-stream transceiver, the TX-to-RX error vector magnitude (EVM) is less than −23.9 dB for 64-QAM wireless communication in all four channels defined in the IEEE 802.11ad/WiGig. The maximum communication distance with the full rate can reach 0.13 m for 64 QAM, 0.8 m for 16 QAM, and 2.6 m for QPSK using 14-dBi horn antennas. A data rate of 28.16 Gb/s is achieved in 16 QAM by four-channel bonding. The transmitter, receiver, and phase-locked loop consume 186, 155, and 64 mW, respectively. The core area of the transceiver is 3.9 mm2. For the proposed two-stream FI transceiver, four-channel bonding in 64 QAM is realized with a data rate of 42.24 Gb/s and an EVM of less than −23 dB. The front end consumes 544 mW in transmitting mode and 432 mW in receiving mode from a 1.2-V supply. The core area of the transceiver is 7.2 mm2.

An Indoor Visible Light Positioning System Based on Optical Camera Communications

Abstract: We experimentally demonstrate an indoor visible light positioning system based on optical camera communications, in which the transmitted coordinate data are spatially separated and demodulated by a camera. The receiver’s position is calculated based on the coordinates of light-emitting diodes in the real word and in the image. The experimental results show that the proposed system with under-sampled phase shift keying modulation offers an error free data transmission and mean positioning errors of 5.0 and 6.6 cm for $h$ of 120 and 180 cm, respectively.

Design of Low-Power DSP-Free Coherent Receivers for Data Center Links

Abstract: Coherent detection offers high spectral efficiency and receiver sensitivity, but digital signal processing (DSP)-based coherent receivers may be prohibitively power hungry for data centers even when optimized for short-reach applications, where fiber propagation impairments are less severe. We propose and evaluate low-power DSP-free homodyne coherent receiver architectures for dual-polarization quadrature phase shift keying (DP-QPSK) for inter- and intradata center links. We propose a novel optical polarization demultiplexing technique, for DP-QPSK and higher-order modulation formats, with three cascaded phase shifters driven by marker tone detection circuitry. We consider carrier recovery based on either optical or electrical phase-locked loops (PLLs). We propose a novel multiplier-free phase detector based on XOR gates, which exhibits less than 0.5 dB power penalty relative to a conventional Costas loop phase detector. We also study the relative performance of homodyne DP-differential QPSK, for which carrier phase recovery is unnecessary. Our proposed DSP-free architectures exhibit ∼1 dB power penalty at small chromatic dispersion compared to their DSP-based counterparts. We estimate conservatively that the high-speed analog electronics of an electrical PLL-based coherent receiver consume nearly 4 W for 200 Gbit/s DP-QPSK, assuming a 90-nm complementary metal-oxide semiconductor process.

Semi-Coherent Detection and Performance Analysis for Ambient Backscatter System

Abstract: We study a novel communication technique, ambient backscatter, that utilizes radio frequency signals transmitted from an ambient source as both energy supply and information carrier to enable communications between low-power devices. Different from existing noncoherent schemes, we here design the semi-coherent detection, where channel-related parameters can be obtained from unknown data symbols and a few pilot symbols. In order to obtain a benchmark for overall detection, we first derive a maximum likelihood detector assuming a complex Gaussian ambient source, and the closed-form bit error rate (BER) is computed. To release the dependence on prior knowledge of the ambient source, we next derive a type of robust design, called an energy detector, with the ambient signal being either complex Gaussian or phase shift keying (PSK). The closed-form detection thresholds, analytical BERs, and outage probability are provided correspondingly. Interestingly, the complex Gaussian source would cause an error floor, while the PSK source does not, which brings nontrivial indication of constellation design as opposed to popular Gaussian-embedded literatures. We also propose an effective approach to estimate detection-required parameters rather than channels themselves. Numerical simulations are finally presented to verify theoretical results.

Symbol-Level Multiuser MISO Precoding for Multi-Level Adaptive Modulation

Abstract: Symbol-level precoding is a new paradigm for multiuser multiple-antenna downlink systems aimed at creating constructive interference among transmitted data streams. This can be enabled by designing the precoded signal of the multiantenna transmitter on a symbol level, taking into account both channel state information and data symbols. Previous literature has studied this paradigm for Mary phase shift keying modulations by addressing various performance metrics, such as power minimization and maximization of the minimum rate. In this paper, we extend this to generic multi-level modulations, i.e., Mary quadrature amplitude modulation by establishing connection to PHY layer multicasting with phase constraints. Furthermore, we address the adaptive modulation schemes which are crucial in enabling the throughput scaling of symbol-level precoded systems. In this direction, we design the signal processing algorithms for minimizing the required power under per-user signal to interference noise ratio or goodput constraints. Extensive numerical results show that the proposed algorithm provides considerable power and energy efficiency gains, while adapting the employed modulation scheme to match the requested data rate.

Constant Envelope Precoding by Interference Exploitation in Phase Shift Keying-Modulated Multiuser Transmission

Abstract: We introduce a new approach to constant-envelope precoding (CEP) based on an interference-driven optimization region for generic phase-shift-keying modulations in the multi-user (MU) multiple-input-multiple-output downlink. While conventional precoding approaches aim to minimize the multi-user interference (MUI) with a total sum-power constraint at the transmitter, in the proposed scheme we consider MUI as a source of additional energy to increase the signal-to-interference-and-noise-ratio at the receiver. In our studies, we focus on two different CEP approaches: a first technique, where the power at each antenna is fixed to a specific value, and a two-step approach, where we first relax the power constraints to be lower than a defined parameter and then enforce CEP transmission. The algorithms are studied in terms of computational costs, with a detailed comparison between the proposed approach and the classical interference suppression schemes from the literature. Moreover, we analytically derive a robust optimization region to counteract the effects of channel-state estimation errors. The presented schemes are evaluated in terms of achievable symbol error rate in a perfect and imperfect channel-state information scenario for different modulation orders. Our results show that the proposed techniques further extend the benefits of classical CEP by judiciously relaxing the optimization region.

Experimental Demonstration of an Indoor VLC Positioning System Based on OFDMA

Abstract: We propose an indoor visible light communication (VLC) and positioning system using the orthogonal frequency division multiplexing access (OFDMA) scheme, which can provide both indoor positioning and communications. Three subcarriers with the maximum received signal intensity with respect to three light-emitting diodes (LEDs) are selected for indoor positioning based on the trilateration algorithm. The experiment results show that the proposed system with quadrature phase shift keying (QPSK) mapping offers a mean positioning error and an error vector magnitude of 1.68 cm and more than 15 dB, respectively.

Coherent Access: A Review

Abstract: In this paper, we will address the benefits of the coherent detection in future optical access networks. The scarcity of the optical spectrum, the required flexibility, and constant evolution of requirements highlight the effectiveness of coherent techniques toward the future passive optical networks (PON). A set of architectures for coherent optical access networks will be presented and the key attributes of each scenario will be investigated. In addition, as a basis to decrease the cost of the local oscillator (LO) at customer side, we experimentally investigate the possibility of using a low-cost laser as LO with real-time detection of a Nyquist-shaped differential quadrature phase-shift keying (DQPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array. Moreover, we experimentally derive a set of optimized parameters and their impact on the network operation for coherent ultradense wavelength-division multiplexing (UDWDM) systems. The balance between the number of channels, power budget, and dynamic power range will be evaluated. Furthermore, we demonstrate a reconfigurable real-time receiver DSP for future flexible UDWDM-PON systems applying the DQPSK and D8PSK modulation formats. By reviewing some of the motivations for this technology, such as flexibility, spectral efficiency, as well as compatibility with software-defined networking, we show that this technology is approaching the required maturity.

Hierarchical Hypothesis and Feature-Based Blind Modulation Classification for Linearly Modulated Signals

Abstract: This paper presents a hierarchical hypothesis test and a feature-based blind modulation classification (BMC) algorithm for linearly modulated signals. The proposed BMC method is based on the combination of elementary cumulant (EC) and cyclic cumulants. The EC is used to decide whether the constellations are from real, circular, or rectangular class, which is referred to as macro classifier. The cyclic cumulant is used to classify modulation within a subclass, which is referred to as micro classifier. For the micro classification, we use positions of nonzero cyclic frequencies (symbol rate frequency or carrier frequency) of the received signals. A hierarchical hypothesis-based theoretical framework has been developed to find the probability of error for the proposed classification. The method works over a flat fading channel without any knowledge of the signal parameters. The proposed method is more robust than the one based on EC and at the same time it requires lower complexity than the maximum likelihood approach. To validate the proposed scheme, measurement is carried out in realistic scenarios. The performance of the new algorithm is compared with the existing methods. In this paper, we have considered a six-class problem including binary phase-shift keying, quadrature phase-shift keying (QPSK), offset-QPSK, $\pi$ /4-QPSK, minimum shift keying, and 16-quadrature amplitude modulation.

Closed-Form BER Expressions of QPSK Constellation for Uplink Non-Orthogonal Multiple Access

Abstract: Non-orthogonal multiple access (NOMA) is an attractive multiple access technique to achieve the optimal system capacity region. A great deal of recent attention has been devoted to the study of the NOMA system capacity performance. However, the exact bit error rate (BER) expressions of NOMA systems have not been derived yet. We provide the exact closed-form BER expressions of the QPSK constellation for an uplink NOMA system over an additive white Gaussian noise channel. Finally, the validity of our derived BER expressions is verified through simulations.

Quadrature Amplitude Backscatter Modulator for Passive Wireless Sensors in IoT Applications

Abstract: Fully passive wireless networks are a key-enabling technologies for the internet of things. Backscatter radios are a hypothesis to design these passive wireless networks. Backscatter modulation allows a remote device to wirelessly transfer information without requiring a traditional transceiver. Instead, a backscatter device leverages a carrier transmitted by an access point or base station. Nevertheless, the traditional approach is to use amplitude shift keying or phase shift keying backscatter solutions which limits the data rate of the sensors, since it transfers only one bit per symbol period. We propose a novel modulator, which employs a Wilkinson power divider with a phase shift in one of the design branch and two transistors acting as switches in order to generate M-quadrature amplitude modulation backscatter modulation. The design strategy for high level order backscatter modulations will be explained and a design approach will be presented in this manuscript.

Minimum probability-of-error perturbation precoding for the one-bit massive MIMO downlink

Abstract: Linear precoders have been shown to perform reasonably well at low SNR when the basestation of a MIMO downlink employs one-bit digital-to-analog converters to quantize the precoder outputs. However, at medium-to-high SNRs, an error floor is encountered due to the coarse quantization. This paper examines methods for slightly perturbing the transmitted signal prior to quantization in an effort to improve downlink performance at higher SNRs. The perturbation is performed with the goal of minimizing the worst-case probability of error among the user terminals, and assumes that the symbols to be transmitted are drawn from a finite alphabet constellation. Two different types of perturbations are studied, and it is found via simulation that the methods can provide dramatic gains in downlink performance.

Subcarrier PSK Performance in Terrestrial FSO Links Impaired by Gamma-Gamma Fading, Pointing Errors, and Phase Noise

Abstract: For terrestrial free-space optical (FSO) communication systems, subcarrier intensity modulation represents an attractive alternative to on-off keying or pulse-position modulation, which is mainly because of the larger spectral efficiency. However, some degradation of the error performance must be taken into account due to nonperfect synchronization of carrier frequency and phase. In a recently published paper, the average bit error probability has been analyzed for $M$ -ary phase-shift keying in the presence of phase noise for a terrestrial FSO link impaired by lognormal fading. In the this paper, we are extending this study to a gamma-gamma model, which is usually applied in case of moderate-to-strong scintillation effects. On top of that, pointing errors, caused by a misalignment between transmitter and receiver of the FSO link, are considered as well. Since a closed-form solution is not available under general conditions and because numerical methods are time-consuming, suffering in part also from serious convergence and stability problems, we provide approximate closed-form expressions, which are accurate enough over a wide signal-to-noise ratio range.

An Integrated Passive Phase-Shift Keying Modulator for Biomedical Implants With Power Telemetry Over a Single Inductive Link.

Abstract: This paper presents a passive phase-shift keying (PPSK) modulator for uplink data transmission for biomedical implants with simultaneous power and data transmission over a single 13.56 MHz inductive link. The PPSK modulator provides a data rate up to 1.35 Mbps with a modulation index between 3% and 38% for a variation of the coupling coefficient between 0.05 and 0.26. This modulation scheme is particularly suited for biomedical implants that have high power demand and low coupling coefficients. The PPSK modulator operates in conjunction with on-off-keying downlink communication. The same inductive link is used to provide up to 100 mW of power to a multi-channel stimulator. The majority of the system on the implant side was implemented as an application specific integrated circuit (ASIC), fabricated in 0.6-[Formula: see text] high voltage CMOS technology. The theory of PPSK modulation, simulated and measured performance evaluation, and comparison with other state-of-the-art impedance modulation techniques is presented. The measured bit error rate around critical coupling at 1.35 Mbps is below 6 ×10(-8).

Real-time video transmission over different underwater wireless optical channels using a directly modulated 520 nm laser diode

Abstract: We experimentally demonstrate high-quality real-time video streaming over an underwater wireless optical communication (UWOC) link up to 5 m distance using phase-shift keying (PSK) modulation and quadrature amplitude modulation (QAM) schemes. The communication system uses software defined platforms connected to a commercial TO-9 packaged pigtailed 520 nm directly modulated laser diode (LD) with 1.2 GHz bandwidth as the optical transmitter and an avalanche photodiode (APD) module as the receiver. To simulate various underwater channels, we perform laboratory experiments on clear, coastal, harbor I, and harbor II ocean water types. The measured bit error rates of the received video streams are 1.0 × 10-9 for QPSK, 4-QAM, and 8-QAM and 9.9 × 10-9 for 8-PSK. We further evaluate the quality of the received live video images using structural similarity and achieve values of about 0.9 for the first three water types, and about 0.7 for harbor II. To the best of our knowledge, these results present the highest quality video streaming ever achieved in UWOC systems that resemble communication channels in real ocean water environments.

Minimum BER Precoding in 1-Bit Massive MIMO Systems

Abstract: 1-bit digital-to-analog (DACs) and analog-to-digital converters (ADCs) are gaining more interest in massive MIMO systems for economical and computational efficiency. We present a new precoding technique to mitigate the inter-user-interference (IUI) and the channel distortions in a 1-bit downlink MUMISO system with QPSK symbols. The transmit signal vector is optimized taking into account the 1-bit quantization. We develop a sort of mapping based on a look-up table (LUT) between the input signal and the transmit signal. The LUT is updated for each channel realization. Simulation results show a significant gain in terms of the uncoded bit-error-ratio (BER) compared to the existing linear precoding techniques.

1-Bit Quantization and Oversampling at the Receiver: Communication Over Bandlimited Channels With Noise

Abstract: A bandlimited additive white Gaussian noise channel is considered where the output is 1-bit quantized and oversampled with respect to the Nyquist rate. We consider root raised cosine filters at the transmitter and receiver. In particular, we focus on a roll-off factor equal to 1 and 0. Because of the oversampling the channel has infinite memory. An auxiliary channel law is proposed which describes the resulting received sequences based on a truncated waveform. The random distortion due to the residual sidelobes can be considered as an additional noise term in the auxiliary channel law. The auxiliary channel law is utilized for computing a lower bound on the achievable rate and in a further step for optimizing a Markov source model. Different signaling schemes have been considered, such as BPSK and ASK. Moreover, Nyquist signaling and faster-than-Nyquist signaling are considered. The resulting achievable rates are superior as compared with results from the literature on bandlimited channels with noise, 1-bit quantization, and oversampling at the receiver.

Massive MIMO downlink 1-bit precoding with linear programming for PSK signaling

Abstract: Quantized massive multiple-input-multiple-output (MIMO) systems are gaining more interest due to their power efficiency. We present a new precoding technique to mitigate the multi-user interference and the quantization distortions in a downlink multi-user (MU) multiple-input-single-output (MISO) system with 1-bit quantization at the transmitter. This work is restricted to PSK modulation schemes. The transmit signal vector is optimized for every desired received vector taking into account the 1-bit quantization. The optimization is based on maximizing the safety margin to the decision thresholds of the PSK modulation. Simulation results show a significant gain in terms of the uncoded bit-error-ratio (BER) compared to the existing linear precoding techniques.

Blind modulation format identification using nonlinear power transformation.

Abstract: This paper proposes and experimentally demonstrates a blind modulation format identification (MFI) method delivering high accuracy (> 99%) even in a low OSNR regime (< 10 dB). By using nonlinear power transformation and peak detection, the proposed MFI can recognize whether the signal modulation format is BPSK, QPSK, 8-PSK or 16-QAM. Experimental results demonstrate that the proposed MFI can achieve a successful identification rate as high as 99% when the incoming signal OSNR is 7 dB. Key parameters, such as FFT length and laser phase noise tolerance of the proposed method, have been characterized.

Mixed-modulated linear frequency modulated radar-communications

Abstract: Increasing congestion of the electromagnetic spectrum has spurred investigation into approaches that provide more efficient spectrum use. While many approaches focus on some type of orthogonality in time, frequency, or coding, another less explored option is mixed modulation of two complementary signals through intentional modulation of pulse. This study discusses intentional modulation of a linear frequency modulated (LFM) chirp radar pulse with a communications signal in order to conduct complementary activities with a combined signal. In order to reduce cross-interference between the signals, the communications message employs spread-spectrum encoding (binary M-sequences) and new modulation scheme with reduced phase change to modulate the LFM waveform. Preferred pair of M-sequences exhibit excellent auto-correlation and low cross-correlation properties that lend themselves to simultaneous transmission of channelised communication signals. The proposed approach is to modulate a radar signal with preferred pair M-sequences using binary reduced phase shift keying modulation that provides a low throughput, communications signal that could be used for administrative or navigation purposes. To measure effect on radar performance, comparison of the radar ambiguity function for the LFM signal is contrasted with combined radar-communication signal.

A Very Low Complexity Successive Symbol-by-Symbol Sequence Estimator for Faster-Than-Nyquist Signaling

Abstract: In this paper, we investigate the sequence estimation problem of binary and quadrature phase shift keying faster-than-Nyquist (FTN) signaling and propose two novel low-complexity sequence estimation techniques based on concepts of successive interference cancellation. To the best of our knowledge, this is the first approach in the literature to detect FTN signaling on a symbol-by-symbol basis. In particular, based on the structure of the self-interference inherited in FTN signaling, we first find the operating region boundary defined by the root-raised cosine pulse shape, its roll-off factor, and the time acceleration parameter of the FTN signaling where perfect estimation of the transmit data symbols on a symbol-by-symbol basis is guaranteed, assuming noise-free transmission. For noisy transmission, we then propose a novel low-complexity technique that works within the operating region and is capable of estimating the transmit data symbols on a symbol-by-symbol basis. To reduce the error propagation of the proposed successive symbol-by-symbol sequence estimator (SSSSE), we propose a successive symbol-by-symbol with go-back- $K$ sequence estimator (SSSgb $K$ SE) that goes back to re-estimate up to $K$ symbols, and subsequently improves the estimation accuracy of the current data symbol. Simulation results show that the proposed sequence estimation techniques perform well for low intersymbol interference scenarios and can significantly increase the data rate and spectral efficiency. Additionally, results reveal that choosing the value of $K$ as low as 2 or 3 data symbols is sufficient to significantly improve the bit-error-rate performance. Results also show that the performance of the proposed SSSgb $K$ SE, with $K = 1$ or 2, surpasses the performance of the lowest complexity equalizers reported in the literature, with reduced computational complexity.

Prospects for magnetic field communications and location using quantum sensors.

Abstract: Signal attenuation limits the operating range in wireless communications and location. To solve the reduced range problem, we can use low-frequency signals in combination with magnetic sensing. We propose the use of an optically pumped magnetometer as a sensor and realize a proof-of-principle detection of binary phase shift keying (BPSK) modulated signals. We demonstrate a ranging enhancement by exploiting both the magnetometer’s intrinsic sensitivity of below 1 pT/Hz1/2 and its 1 kHz operating bandwidth through the use of BPSK signals.

One-Shot Blind Channel Estimation for OFDM Systems Over Frequency-Selective Fading Channels

Abstract: This paper presents a blind channel estimation (BCE) technique for orthogonal frequency division multiplexing communications systems. The proposed system is based on modulating particular pairs of subcarriers using amplitude shift keying and phase shift keying, which enables the realization of a decision-directed one-shot BCE (OSBCE), with complexity and accuracy that are comparable to pilot-based channel estimation techniques. The performance of the proposed estimator is evaluated in terms of the mean squared error (MSE), where an accurate analytical expression is derived and verified using Monte Carlo simulation under various channel conditions. The obtained results show that the MSE of the proposed OSBCE is comparable to pilot-based estimators, which confirms the efficiency of the proposed OSBCE.

QAM Quantum Noise Stream Cipher Transmission Over 100 km With Continuous Variable Quantum Key Distribution

Abstract: We report the first on-line high-speed and large-capacity secure optical communication system. This was realized by combining a quadrature amplitude modulation/quantum noise stream cipher technology where a coherent multi-level optical signal is hidden in quantum noise and a quantum key distribution technology where secure key delivery is realized with an extremely weak laser light comparable to a single photon. In our security analysis, we adopt a realistic assumption, namely, that an adversary does not have a lossless fiber. To show the advantage of this scheme, we performed a 128 QAM, 70-Gbit/s single-channel transmission over 100 km with a spectral efficiency of as high as 10.3 bits/s/Hz. This is the fastest data rate and highest spectral efficiency yet achieved in quantum cryptography with a realistic assumption.

Faster-Than-Nyquist Signaling With Index Modulation

Abstract: In this letter, we propose a novel faster-than-Nyquist (FTN) transmission scheme relying on the time-domain single-carrier index-modulation (IM) concept. In the proposed FTN with IM (FTN-IM) transmitter, a subset of time-domain FTN symbols are activated, where the combination of the activated symbols conveys additional information further to the classic amplitude phase shift keying. Owing to the explicit benefit of sparse FTN-IM signaling, the FTN-specific inter-symbol interference is mitigated in an effective manner, hence attaining a higher spectral efficiency than the conventional FTN counterpart. Furthermore, a low-complexity noise-whitening frequency-domain equalization is developed for our FTN-IM receiver. In order to demonstrate the performance advantage of the proposed FTN-IM scheme over the conventional FTN counterpart, we show that a minimum Euclidean distance of proposed FTN-IM signaling is higher than that of the conventional FTN signaling, while providing their numerical performance comparisons in terms of error rates.