Showing papers on "Frequency-division multiplexing published in 2018"

Ultra-broadband on-chip twisted light emitter for optical communications.

Abstract: On-chip twisted light emitters are essential components of orbital angular momentum (OAM) communication devices1, 2. These devices address the growing demand for high-capacity communication systems by providing an additional degree of freedom for wavelength/frequency division multiplexing (WDM/FDM). Although whispering-gallery-mode-enabled OAM emitters have been shown to possess some advantages3, 4, 5, such as compactness and phase accuracy, their inherent narrow bandwidths prevent them from being compatible with WDM/FDM techniques. Here, we demonstrate an ultra-broadband multiplexed OAM emitter that utilizes a novel joint path-resonance phase control concept. The emitter has a micron-sized radius and nanometer-sized features. Coaxial OAM beams are emitted across the entire telecommunication band from 1,450 to 1,650 nm. We applied the emitter to an OAM communication with a data rate of 1.2 Tbit/s assisted by 30-channel optical frequency combs (OFCs). The emitter provides a new solution to further increase capacity in the OFC communication scenario.

Frequency multiplexing for quasi-deterministic heralded single-photon sources.

Abstract: Parametric single-photon sources are well suited for large-scale quantum networks due to their potential for photonic integration. Active multiplexing of photons can overcome the intrinsically probabilistic nature of these sources, resulting in near-deterministic operation. However, previous implementations using spatial and temporal multiplexing scale unfavorably due to rapidly increasing switching losses. Here, we break this limitation via frequency multiplexing in which switching losses remain fixed irrespective of the number of multiplexed modes. We use low-noise optical frequency conversion for efficient frequency switching and demonstrate multiplexing of three modes. We achieve a generation rate of 4.6 × 104 photons per second with an ultra-low g(2)(0) = 0.07 indicating high single-photon purity. Our scalable, all-fiber multiplexing system has a total loss of just 1.3 dB, such that the 4.8 dB multiplexing enhancement markedly overcomes switching loss. Our approach offers a promising path to creating a deterministic photon source on an integrated chip-based platform. The aim of multiplexing is to boost capabilities of probabilistic single photon sources, but is vexed by rapidly increasing switching losses. Here, the authors propose and implement an in-fiber frequency-multiplexing scheme where total losses are independent of the number of multiplexed modes.

0.4 THz Photonic-Wireless Link With 106 Gb/s Single Channel Bitrate

Abstract: To accommodate the demand of exponentially increased global wireless data traffic, the prospective data rates for wireless communication in the market place will soon reach 100 Gb/s and beyond. In the lab environment, wireless transmission throughput has been elevated to the level of over 100 Gb/s attributed to the development of photonic-assisted millimeter wave and terahertz (THz) technologies. However, most of recent demonstrations with over 100 Gb/s data rates are based on spatial or frequency division multiplexing techniques, resulting in increased system's complexity and energy consumption. Here, we experimentally demonstrate a single channel 0.4 THz photonic-wireless link achieving a net data rate of beyond 100 Gb/s by using a single pair of THz emitter and receiver, without employing any spatial/frequency division multiplexing techniques. The high throughput up to 106 Gb/s within a single THz channel is enabled by combining spectrally efficient modulation format, ultrabroadband THz transceiver and advanced digital signal processing routine. Besides that, our demonstration from system-wide implementation viewpoint also features high transmission stability, and hence shows its great potential to not only decrease the system's complexity, but also meet the requirements of prospective data rates for bandwidth-hungry short-range wireless applications.

1.032-Tb/s CPRI-Equivalent Rate IF-Over-Fiber Transmission Using a Parallel IM/PM Transmitter for High-Capacity Mobile Fronthaul Links

Abstract: We report high-capacity intermediate-frequency-over-fiber (IFoF) transmission using parallel intensity/phase modulators (IM/PM). Thanks to the parallel IM/PM transmitter, we can avoid all the null frequencies caused by dispersion-induced RF power fading. Compared to other techniques to avoid RF power fading, the parallel IM/PM transmitter offers a simple solution because it does not rely on any sophisticated digital signal processing. We transmitted 14 $\times$ 1.2-GHz orthogonal-frequency-division-multiplexed signals over a 20-km single-mode fiber using the parallel IM/PM transmitter and achieved a Common Public Radio Interface equivalent data rate of 1.032 Tb/s. Thus, an IFoF system with the parallel IM/PM transmitter shows great potential to be applied to high-capacity mobile fronthaul links in the upcoming fifth-generation mobile system and beyond.

Downlink Design for Spectrum Efficient IoT Network

Abstract: The Internet of Things (IoT) is a new network that connects massive devices which have the communication ability. With the requirement of various services and the wireless spectrums becoming increasingly scarce, we consider a nonorthogonal multicarrier transmission scheme that is spectrum efficient frequency division multiplexing (SEFDM) as the downlink transmission scheme for IoT network. SEFDM has the merit of improved bandwidth usage efficiency, but the serious inter carrier interference (ICI) will be introduced by multiplexing overlapped carriers. Thus, the signal detection is challenged for recovering the signal which is suffered from ICI due to the loss of the orthogonality. In this paper, a low complexity detector based on quasi-orthogonality compensation (QOC) is proposed in the downlink receiver. And the complexity of the QOC detector is also analyzed. Moreover, a novel detector which joint QOC and fixed sphere decoding (FSD) algorithm is proposed. The bit error rate performances of QOC and QOC-FSD detectors are evaluated by numerical simulations. Numerical results show that the QOC and QOC-FSD detectors can achieve better performance than conventional iterative detection (ID) and ID-FSD, respectively. Furthermore, QOC-FSD detector performs a lower complexity than ID-FSD detector.

Modulation Over Nonlinear Fourier Spectrum: Continuous and Discrete Spectrum

Abstract: Nonlinear frequency division multiplexed (NFDM) systems are considered when data are modulated in both parts of the nonlinear Fourier spectrum: Continuous spectrum and discrete spectrum An efficient algorithm is introduced to generate a time-domain signal from a given nonlinear spectrum The transmission of such NFDM symbols is experimentally demonstrated over 1460 km standard single-mode fiber with EDFA-only amplification In each NFDM symbol, the continuous spectrum is modulated by 64 $\times$ 05 Gbaud orthogonal frequency-division multiplexing (OFDM) symbols with 32-QAM format whereas the discrete spectrum contains four eigenvalues with the same imaginary part, each one is modulated by 8-PSK format, resulting a line rate of 553 Gb/s The cross-talk between different nonlinear modes is quantified in terms of cross-correlation and the performance loss is computed in terms of mutual information when each nonlinear modes is detected individually

Bayesian Optimal Data Detector for Hybrid mmWave MIMO-OFDM Systems With Low-Resolution ADCs

Abstract: Hybrid analog–digital precoding architectures and low-resolution analog-to-digital converter (ADC) receivers are two solutions to reduce hardware cost and power consumption for millimeter wave (mmWave) multiple-input multiple-output (MIMO) communication systems with large antenna arrays. In this study, we consider a mmWave MIMO-orthogonal frequency division multiplexing (OFDM) receiver with a generalized hybrid architecture in which a small number of radio frequency (RF) chains and low-resolution ADCs are employed simultaneously. Owing to the strong nonlinearity introduced by low-resolution ADCs, the task of data detection is challenging, particularly achieving a Bayesian optimal data detection. This study aims to fill this gap. By using a generalized expectation consistent signal recovery technique, we propose a computationally efficient data detection algorithm that provides a minimum mean-square error estimate on data symbols and is extended to a mixed-ADC architecture. Considering particular structure of MIMO-OFDM channel matrix, we provide a low-complexity realization in which only fast fourier transform (FFT) operation and matrix-vector multiplications are required. Furthermore, we present an analytical framework to study the theoretical performance of the detector in the large-system limit, which can precisely evaluate the performance expressions, such as mean-square error and symbol error rate. Based on this optimal detector, the potential of adding a few low-resolution RF chains and high-resolution ADCs for a mixed-ADC architecture is investigated. Simulation results confirm the accuracy of our theoretical analysis and can be used for system design rapidly. The results reveal that adding a few low-resolution RF chains to original unquantized systems can obtain significant gains.

Non-Orthogonal Narrowband Internet of Things: A Design for Saving Bandwidth and Doubling the Number of Connected Devices

Abstract: Narrowband Internet of Things (NB-IoT) is a low power wide area network (LPWAN) technique introduced in 3GPP release 13. The narrowband transmission scheme enables high capacity, wide coverage, and low power consumption communications. With the increasing demand for services over the air, wireless spectrum is becoming scarce and new techniques are required to boost the number of connected devices within a limited spectral resource to meet the service requirements. This paper provides a compressed signal waveform solution, termed fast-orthogonal frequency division multiplexing (Fast-OFDM), to double potentially the number of connected devices by compressing occupied bandwidth of each device without compromising data rate and bit error rate performance. Simulation is first evaluated for the Fast-OFDM with comparisons to single-carrier-frequency division multiple access (SC-FDMA). Results indicate the same performance for both systems in additive white Gaussian noise channel. Experimental measurements are also presented to show the bandwidth saving benefits of Fast-OFDM. It is shown that in a line-of-sight scenario, Fast-OFDM has similar performance as SC-FDMA but with 50% bandwidth saving. This research paves the way for extended coverage, enhanced capacity and improved data rate of NB-IoT in fifth generation new radio networks.

The First 15 Years of SEFDM: A Brief Survey

Abstract: Spectrally efficient frequency division multiplexing (SEFDM) is a multi-carrier signal waveform, which achieves higher spectral efficiency, relative to conventional orthogonal frequency division multiplexing (OFDM), by violating the orthogonality of its sub-carriers. This survey provides the history of SEFDM development since its inception in 2003, covering fundamentals and concepts, wireless and optical communications applications, circuit design and experimental testbeds. We focus on work done at UCL and outline work done other universities and research laboratories worldwide. We outline techniques to improve the performance of SEFDM and its practical utility with focus on signal generation, detection and channel estimation.

Transmission Experiment of Bandwidth Compressed Carrier Aggregation in a R ealistic Fading Channel

Abstract: This is an invited poster which is based on a paper published in IEEE Transactions on Vehicular Technology, Vol 66, Issue 5, pp 4087-4097 https://ieeexploreieeeorg/abstract/document/7572173/ The paper reports an experimental testbed is designed to evaluate the performance of a bandwidth compressed multicarrier technique, termed spectrally efficient frequency division multiplexing (SEFDM) in a carrier aggregation (CA) scenario Unlike orthogonal frequency division multiplexing (OFDM), SEFDM is a nonorthogonal waveform which, relative to OFDM, packs more subcarriers in a given bandwidth, thereby improving spectral efficiency CA is a long-term evolution-advanced (LTE-Advanced) featured technique that offers a higher throughput by aggregating multiple legacy radio bands Considering the scarcity of the radio spectrum, SEFDM signals can be utilized to enhance CA performance The combination of the two techniques results in a larger number of aggregated component carriers (CCs) and, therefore, increased data rate in a given bandwidth with no additional spectral allocation It is experimentally shown that CA-SEFDM can aggregate up to seven CCs in a limited bandwidth, while CAOFDM can only put five CCs in the same bandwidth In this paper, LTE-like framed CA-SEFDM signals are generated and delivered through a realistic LTE channel A complete experimental setup is described, together with error performance and effective spectral efficiency comparisons Experimental results show that the measured bit error rate performance for CA-SEFDM is very close to CA-OFDM and that the effective spectral efficiency of CA-SEFDM can be substantially higher than that of CA-OFDM

Integration of a GFDM-Based 5G Transceiver in a GPON Using Radio Over Fiber Technology

Abstract: This paper reports the integration and experimental performance analysis of a GFDM-based 5G transceiver in a gigabit passive optical network (GPON), using radio over fiber technology. The proposed architecture enables to simultaneously transport two 5G candidates RF signals through an active GPON under real channel conditions. One signal is generated by a GFDM-based 5G prototype transceiver at 735 MHz, whereas the second one is synthetized by a vector signal generator at 26 GHz. A dual-drive Mach–Zehnder modulator has been utilized in the optical line terminal to modulate both signals, with the purpose of mitigating the interference between them. Particularly for the GFDM-based 735 MHz signal, a modulation error ratio (MER) of 40 dB has been obtained at RF-driven signal up to –9 dBm. Furthermore, the use of a digital predistortion scheme has been efficiently employed to reduce the impact of the nonlinear distortions and enhance MER. The 26-GHz RF signal, aimed for the 5G millimeter wave band, has been investigated as a function of error vector magnitude (EVM) for bitrates up to 1 Gbit/s. ${\text{EVM}}_{{\text{RMS}}}$ of 2.18% and 5.70% have been obtained for 100 Mbit/s and 1 Gbit/s, respectively. Finally, the latency and throughput measurements of the baseband signal originally running over GPON have shown no significant penalties.

Frequency Response Enhancement of Direct-Detection Phase-Sensitive OTDR by Using Frequency Division Multiplexing

Abstract: The frequency division multiplexing (FDM) technique is first introduced into a direct-detection phase-sensitive OTDR to improve the distributed acoustic sensing performance by using a frequency step sweeping laser source and a dual-pulse heterodyne detection scheme. A raised-cosine-shaped pulse is used to suppress the crosstalk in the FDM technique. By using this technique, a 40-kS/s sampling rate to vibration is realized with a 10-km measurement range, which implies the tradeoff relationship between the frequency response and the measurement range is broken. In the experiment, vibrations with different frequencies are measured to validate the effectiveness of the proposed technique. A 20-kHz frequency response is achieved over a 10-km measurement distance, and the frequency response shows a good flatness with a fluctuation of $\sim$ 0.5 dB.

Nonlinear frequency division multiplexing with b-modulation: shifting the energy barrier.

Abstract: The recently proposed b-modulation method for nonlinear Fourier transform-based fiber-optic transmission offers explicit control over the duration of the generated pulses and therewith solves a longstanding practical problem. The currently used b-modulation however suffers from a fundamental energy barrier. There is a limit to the energy of the pulses, in normalized units, that can be generated. In this paper, we discuss how the energy barrier can be shifted by proper design of the carrier waveform and the modulation alphabet. In an experiment, it is found that the improved b-modulator achieves both a higher Q-factor and a further reach than a comparable conventional b-modulator. Furthermore, it performs significantly better than conventional approaches that modulate the reflection coefficient.

Highly Miniaturized 120-GHz SIMO and MIMO Radar Sensor With On-Chip Folded Dipole Antennas for Range and Angular Measurements

Abstract: This paper describes a highly miniaturized two-channel radar sensor with integrated on-chip folded dipole antennas that exhibit high antenna gain and radiation efficiency due to the use of the selective localized backside etching technique. The sensor can be utilized in single-input multiple-output radar system by combining the two transmit channels to increase the effective isotropic radiated power by 6 dB. This results in an improved standard deviation of range measurements by a factor of 2. The transceiver (TRX) is equipped with binary phase shift keying modulators as well as I/Q receivers and can be utilized in multiple-input multiple-output (MIMO) radar system using time and delta–sigma modulator-based frequency division multiplexing technique. The angular resolution is improved by a factor of 1.5 by the introduction of an additional virtual array element in the MIMO radar system. The TRX also includes a 30-GHz VCO that is complemented with a prescaler and frequency quadrupler to generate a 120-GHz carrier signal. Radar measurements using the digital-beamforming method with 10-GHz modulation bandwidth were performed to show the applicability of the proposed system.

Low Probability of Intercept-Based Optimal OFDM Waveform Design Strategy for an Integrated Radar and Communications System

Abstract: The integration of radar and communications systems can provide great advantages, such as enhanced efficiency, structure simplification, less occupied hardware resources, and interference mitigation, compared with traditional individual radar and communications applications. Extensive studies have presented achieving improved system performance, whereas the problem of low probability of intercept (LPI)-based waveform design for the integrated system is seldom discussed in the literature. In this paper, an LPI-based optimal orthogonal frequency multiplexing modulation (OFDM) waveform design strategy is developed for an integrated radar and communications system (IRCS). The dedicated transmitter in this system transmits integrated OFDM waveform for simultaneously target parameter estimation and downlink communications. The basis of the underlying strategy is to employ the optimization technique to design the integrated OFDM waveform of IRCS in order to minimize the total radiated power, while satisfying the specified requirements of target parameter estimation and data information rate. We analytically show that the resulting optimization problem is convex and can be solved by formulating the Karush–Kuhn–Tuckers optimality conditions. Numerical simulation results demonstrate that our proposed strategy can solve the waveform design problem in the IRCS with low complexity, and the LPI performance of the IRCS can efficiently be enhanced by utilizing the proposed integrated OFDM waveform design strategy.

Digital Code-Division Multiplexing Channel Aggregation for Mobile Fronthaul Architecture With Low Complexity

Abstract: A low-complexity mobile fronthaul architecture via digital code-division multiplexing (CDM) is proposed to enable channel aggregation of 4G-LTE signals. In comparison with traditional frequency division multiplexing based aggregation scheme, the fast Fourier transformation/inverse fast Fourier transformation operations are replaced by simple sign selection and addition, leading to the significant reduction of computational complexity. Moreover, synchronous transmission of both the I/Q waveforms of wireless signals and the control words (CWs) used for the purpose of control and management using the CDM approach is also presented to be compliant with the common public radio interface (CPRI). In a proof-of-concept experiment, we demonstrate the transmission of 48 × 20 MHz LTE signals with CPRI equivalent data rate of 59 Gb/s, achieving an average error vector magnitude (EVM) of ∼3.6% and ∼4.3% after 5 and 20 km transmission over standard single-mode fiber (SSMF), respectively. Furthermore, we successfully demonstrate the transmission of 32 × 20 MHz LTE signals together with CPRI-compliant CWs, corresponding to CPRI-equivalent data rate of 39.32 Gb/s, only using single optical wavelength channel with analog bandwidth of ∼1.96 GHz. After transmission over 5 km SSMF, CWs can be error-free recovered while the LTE signals are recovered with an EVM of ∼3.6%.

Time-Domain Neural Network Receiver for Nonlinear Frequency Division Multiplexed Systems

Abstract: The nonlinear Fourier transform is a new approach for addressing the capacity limiting Kerr nonlinearities in optical communication systems. It exploits the property of integrability of the lossless nonlinear Schrodinger equation and thus incorporates nonlinearities as an element of the transmission. However, practical links employing erbium-doped fiber amplifiers include losses/gains and introduce noise which breaks the integrability of the nonlinear Schrodinger equation. Although the lossless path average approximation proposes an integrable model, its imprecision still leads to unintended distortions and thus performance degradation. We propose an alternative receiver for nonlinear frequency division multiplexing optical communication systems using techniques from machine learning. It is highly adaptive as it learns from previously transmitted pulses and thus holds no assumptions on the system and noise distribution. The detection method presented is fully applied in time-domain and omits the nonlinear Fourier transform. The numerical results provide a benchmark for nonlinear Fourier transform based detection of high order solitons for fiber links with losses and noise present.

Performance analysis of analog IF over fiber fronthaul link with 4G and 5G coexistence

Abstract: Fifth generation (5G) mobile communications will require a dense deployment of small cell antenna sites and higher channel bandwidth, in conjunction with a cloud radio access network (C-RAN) architecture This necessitates low latency and high-capacity architecture in addition to energy- and cost-efficient fronthaul links An efficient way of achieving such connectivity is to make use of an opticalfiber- based infrastructure where multiple wireless services may be distributed over the same fiber to remote radio head (RRH) sites In this work, we demonstrate the spectral containment of fourth generation (4G) Long-Term Evolution (LTE) signals and 5G candidate waveforms—generalized frequency division multiplexing and universally filtered orthogonal frequency division multiplexing (UF-OFDM) through a directly modulated link Seventy-five bands of LTEand 10 bands of 5Gwaveforms are successfully transmitted over a 25 km analog intermediate frequency signal over fiber (AIFoF) link through our setup, limited only by the bandwidth of the laser For the first time, to the best of our knowledge, we demonstrate the fronthaul network for providing simultaneous 4G and 5G services by propagating LTE signals in coexistence with UF-OFDM

High Speed Precompensated Nonlinear Frequency-Division Multiplexed Transmissions

Abstract: Nonlinear frequency division multiplexing (NFDM) with the modulation of the nonlinear Fourier spectrum (both discrete and/or continuous parts) have been recently considered as a potential transmission method to combat the fiber nonlinearity impairments. However, due to many challenges in design, digital signal processing (DSP), numerical algorithms, and hardware implementation, reported data rates of NFDM systems have been so far limited to 50 Gb/s. In this paper, we experimentally demonstrate a practical approach for increasing the data rate of NFDM transmission systems by increasing the number of modulated nonlinear subcarriers together with the application of a precompensation technique for the channel-induced phase-shift in the nonlinear Fourier domain. As a result, a record-high data rate of 125 Gb/s and spectral efficiency over 2 bits/s/Hz in burst-mode, single-polarization NFDM transmissions were achieved over 976 km of standard single mode fiber with EDFA-only amplification by transmitting and processing 222 32 QAM-modulated nonlinear subcarriers simultaneously.

Resources Allocation in Multicell D2D Communications for Internet of Things

Abstract: Device-to-device (D2D) communication can realize the direct communication between mobile users with short distance. It is an enabling technology for realizing Internet of Things in the long-term evolution-advanced system to the future fifth-generation mobile communication system. D2D communication multiplexes the licensed spectrum of cellular users (CUs) to D2D users (DUs) to improve resource utilization of cellular networks. In this paper, a cross-cell fractional frequency reuse-based frequency resource multiplexing (CFRM) scheme is proposed for the multicell D2D communication. In the proposed CFRM, each cell is first divided into two regions, and each region is allocated different spectrum resources to reduce the interference between neighboring cells. Then, the uplink resources of CUs are partially multiplexed by DUs, which can decrease the interference of the DUs to the CUs. The simulation results show that CFRM can reduce the interference, guarantee the quality of service of CUs, and increase the throughput of cellular networks.

A Comparative Study of Unipolar OFDM Schemes in Gaussian Optical Intensity Channel

Abstract: We study the information rates of unipolar orthogonal frequency division multiplexing (OFDM) in discrete-time optical intensity channels (OIC) with Gaussian noise under average optical power constraint. Several single-, double-, and multi-component unipolar OFDM schemes are considered under the assumption that independent and identically distributed. Gaussian or complex Gaussian codebook ensemble and nearest neighbor decoding (minimum Euclidean distance decoding) are used. We obtain an array of information rate result. These results validate existing signal-to-noise-and-distortion-ratio-based rate analysis, establish the equivalence of information rates of certain schemes, and demonstrate the evident benefits of using component-multiplexing at high signal-to-noise-ratio (SNR). For double- and multi-component schemes, the component power allocation strategies that maximize the information rates are investigated. In particular, by utilizing a power allocation strategy, we prove that several multi-component schemes approach the high SNR capacity of the discrete-time Gaussian OIC under average power constraint to within 0.07 bits.

Ultra-Long-Distance Hybrid BOTDA/Ф-OTDR.

Abstract: In the distributed optical fiber sensing (DOFS) domain, simultaneous measurement of vibration and temperature/strain based on Rayleigh scattering and Brillouin scattering in fiber could have wide applications. However, there are certain challenges for the case of ultra-long sensing range, including the interplay of different scattering mechanisms, the interaction of two types of sensing signals, and the competition of pump power. In this paper, a hybrid DOFS system, which can simultaneously measure temperature/strain and vibration over 150 km, is elaborately designed via integrating the Brillouin optical time-domain analyzer (BOTDA) and phase-sensitive optical time-domain reflectometry (Ф-OTDR). Distributed Raman and Brillouin amplifications, frequency division multiplexing (FDM), wavelength division multiplexing (WDM), and time division multiplexing (TDM) are delicately fused to accommodate ultra-long-distance BOTDA and Ф-OTDR. Consequently, the sensing range of the hybrid system is 150.62 km, and the spatial resolution of BOTDA and Ф-OTDR are 9 m and 30 m, respectively. The measurement uncertainty of the BOTDA is ± 0.82 MHz. To the best of our knowledge, this is the first time that such hybrid DOFS is realized with a hundred-kilometer length scale.

Frequency‐Division Multiplexing in Magnonic Logic Networks Based on Caustic‐Like Spin‐Wave Beams

Abstract: Wave-based data processing by spin waves and their quanta, magnons, is a promising technique to overcome the challenges which CMOS-based logic networks are facing nowadays. The advantage of these quasi-particles lies in their potential for the realization of energy efficient devices on the micro- to nanometer scale due to their charge-less propagation in magnetic materials. In this paper, the frequency dependence of the propagation direction of caustic-like spin-wave beams in microstructured ferromagnets is studied by micromagnetic simulations. Based on the observed alteration of the propagation angle, an approach to spatially combine and separate spin-wave signals of different frequencies is demonstrated. The presented magnetic structure constitutes a prototype design of a passive circuit enabling frequency-division multiplexing in magnonic logic networks. It is verified that spin-wave signals of different frequencies can be transmitted through the device simultaneously without any interaction or creation of spurious signals. Due to the wave-based approach of computing in magnonic networks, the technique of frequency-division multiplexing can be the basis for parallel data processing in single magnonic devices, enabling the multiplication of the data throughput.

A Novel Forward-Link Multiplexed Scheme in Satellite-Based Internet of Things

Abstract: Satellite communication has the potential to play a key role in many applications of Internet of Things (IoT). In this paper, we consider a satellite-based IoT and investigate the technology that can improve the spectral efficiency. In general, one beam in satellite systems serves one user. To serve multiple users, time division multiplexing or frequency division multiplexing is usually used. In this paper, we propose a novel forward-link multiplexed scheme, by which the signals of different users can be transmitted simultaneously using the same frequency band. Specifically, at the transmitter, we first map each combination of the users’ constellation points to a higher-order constellation point, which is referred to as constellation coding, and then transmit such higher-order modulation signals. At the user side, after receiving and detecting the transmitted signal, each user obtain its own signal by the corresponding demapping, which is referred to as constellation decoding. The total system capacity over an additive white Gaussian noise channel is analyzed in this paper. Simulation results demonstrate that the proposed scheme can greatly improve the spectral efficiency.

Dual-Polarization NFDM Transmission Using Distributed Raman Amplification and NFT-Domain Equalization

Abstract: Transmission systems based on the nonlinear Fourier transform (NFT) can potentially address the limitations in transmission reach and throughput set forth by the onset of Kerr-induced nonlinear distortion. Whereas this technique is at a preliminary research stage, a rapid progress has been shown over the past few years leading to experimental demonstrations of dual-polarization systems carrying advanced modulation formats. The lossless transmission required by the NFT to ensure the theoretical validity of the scheme is a fairly strong requirement considering practical transmission links. Here, we address it by using optimized distributed Raman amplification to minimize the power variations to approximately 3 dB over 200 km, thus approaching the lossless transmission requirement. Additionally, we experimentally evaluate the improvement provided by equalization schemes applied to the signals in the NFD. By combining distributed Raman amplification and NFD equalization, we show transmission reaches for dual-polarization nonlinear frequency division multiplexing systems transmitting both two eigenvalues (8 bit/symbol) up to 2200 km and three eigenvalues (12 bit/symbol) up to more than 600 km at hard-decision and soft-decision forward error correction threshold, respectively.

Deep Learning for Interference Cancellation in Non-Orthogonal Signal Based Optical Communication Systems

Abstract: Non-orthogonal waveforms are groups of signals, which improve spectral efficiency but at the cost of interference. A recognized waveform, termed spectrally efficient frequency division multiplexing (SEFDM), which was a technique initially proposed for wireless systems, has been extensively studied in 60 GHz millimeter wave communications, optical access network design and long haul optical fiber transmission. Experimental demonstrations have shown the advantages of SEFDM in its bandwidth saving, data rate improvement, power efficiency improvement and transmission distance extension compared to conventional orthogonal communication techniques. However, the achieved success of SEFDM is at the cost of complex signal processing for the mitigation of the self-created inter carrier interference (ICI). Thus, a low complexity interference cancellation approach is in urgent need. Recently, deep learning has been applied in optical communication systems to compensate for linear and non-linear distortions in orthogonal frequency division multiplexing (OFDM) signals. The multiple processing layers of deep neural networks (DNN) can simplify signal processing models and can efficiently solve un-deterministic problems. However, there are no reports on the use of deep learning to deal with interference in non-orthogonal signals. DNN can learn complex interference features using backpropagation mechanism. This work will present our investigations on the performance improvement of interference cancellation for the non-orthogonal signal using various deep neural networks. Simulation results show that the interference within SEFDM signals can be mitigated efficiently via using properly designed neural networks. It also indicates a high correlation between neural networks and signal waveforms. It verifies that in order to achieve the optimal performance, all the neurons at each layer have to be connected. Partially connected neural networks cannot learn complete interference and therefore cannot recover signals efficiently. This work paves the way for the research of simplifying neural networks design via signal waveform optimization.

Lexicographic Codebook Design for OFDM With Index Modulation

Abstract: In this paper, we propose a novel codebook design scheme for orthogonal frequency-division multiplexing with index modulation (OFDM-IM) to improve system performance. The optimization process can be implemented efficiently by the lexicographic ordering principle. By applying the proposed codebook design, all subcarrier activation patterns with a fixed number of active subcarriers will be explored. Furthermore, as the number of active subcarriers is fixed, the computational complexity for estimation at the receiver is reduced and the zero-active subcarrier dilemma is solved without involving complex higher layer transmission protocols. It is found that the codebook design can potentially provide a tradeoff between diversity and transmission rate. We investigate the diversity mechanism and formulate three diversity-rate optimization problems for the proposed OFDM-IM system. Based on the genetic algorithm, the method of solving these formulated optimization problems is provided and verified to be effective. Then, we analyze the average block error rate and bit error rate of the OFDM-IM systems applying the codebook design. Finally, all analyses are numerically verified by the Monte Carlo simulations. In addition, a series of comparisons are provided, by which the superiority of the codebook design is confirmed.

A Unified System With Integrated Generation of High-Speed Communication and High-Resolution Sensing Signals Based on THz Photonics

Abstract: Multifunctional convergence is one of the key physical features in future generation networks and Internet of things architectures. In this paper, we propose and experimentally demonstrate a unified terahertz (THz) system operating in the 300 GHz band, with a potential of simultaneously enabling high-speed communication and high-resolution ranging over a common optical infrastructure. Both THz communication and THz sensing signals are generated based on THz photonics and cutting-edge terahertz transceiver technologies. In the experiment, 16-quadrature amplitude modulation modulated THz signal is generated by photo-mixing two free running lasers for the communication, and linear frequency modulated (LFM) THz pulses are generated based on optical interferometer-based frequency-to-time mapping (FTM) for sensing. The experimental results show that up to 56 Gbit/s net rate is successfully transmitted over a 2 m free-space line-of-sight link, and the THz LFM pulses with a time-bandwidth product of up to 207 are successfully generated, which is potentially able to enable a cm-scale range resolution. We also investigate the frequency multiplexing schemes for two signals by changing the channel gap at the transmitter side. To the best of our knowledge, such a system represents the first demonstration of integrated generation system in the THz region above 300 GHz, which has great potential in prospective applications of future converged networks.

SEFDM over satellite systems with advanced interference cancellation

Abstract: For high data rates satellite systems, where multiple carriers are frequency division multiplexed with a slight overlap, the overall spectral efficiency is limited. This work applies highly overlapped carriers for satellite broadcast and broadband scenarios to achieve higher spectral efficiency. Spectrally efficient frequency division multiplexing (SEFDM) compresses subcarrier spacing to increase the spectral efficiency at the expense of orthogonality violation. SEFDM systems performance degrades compared to orthogonal signals, unless efficient interference cancellation is used. Turbo equalisation with interference cancellation is implemented to improve receiver performance for variable coding, compression and modulation/constellation proposals that may be applied in satellite communications settings. Such parameters may be set to satisfy pre-defined spectral efficiency values for a given quality index or associated application. Assuming low-density parity check coded data, the work proposes two approaches to receiver design: a simple matched filter approach and an approach utilising an iterative interference cancellation structure specially designed for SEFDM. Mathematical models and simulations studies are presented indicating promising gains to be achieved for SEFDM transmission with advanced transceiver architectures at the cost of increased complexity at the receiver.

Generalized DFT-s-OFDM Waveforms Without Cyclic Prefix

Abstract: This paper deals with generalized discrete Fourier transform—spread—orthogonal frequency division multiplexing (G-DFT-s-OFDM) waveforms, which replace the cyclic prefix of traditional OFDM/DFT-s-OFDM with an internal guard period. Such waveforms feature significant benefits in terms of flexibility, spectral containment, and low peak-to-average power ratio. Aspects related to reference sequence design and mapping for channel estimation are thoroughly addressed, and a new estimator for the specific zero-tail DFT-s-OFDM case is proposed. Furthermore, we address the opportunity of exploiting the internal guard period at each symbol for frequent channel state information updates, thus enabling the possibility of tracking rapidly varying propagation conditions.