Showing papers on "Frequency-division multiplexing published in 2021"
01 Mar 2021
TL;DR: In this article, a dual-channel wireless communication system based on a two-bit space-time-coding digital metasurface was proposed to transmit two different pictures to two users simultaneously in real time.
Abstract: Digitally programmable metasurfaces are of potential use in wireless multiplexing techniques because they can encode and transmit information without using traditional radio-frequency components such as antennas or mixers. Space–time-coding digital metasurfaces can, in particular, manipulate the propagation direction and harmonic power distribution of electromagnetic waves, making them suitable for space- and frequency-division multiplexing. However, while digital metasurfaces have been used for wireless communication, these systems could implement signal modulation only in the time domain. Here, we report a wireless communication scheme that uses space–time-coding digital metasurfaces to implement both space- and frequency-division multiplexing. By encoding space–time-coding matrices through multiple channels, digital messages can be directly transmitted to different users at different locations simultaneously, without the need for digital-to-analogue conversion and mixing processes. To illustrate this approach, we have built a dual-channel wireless communication system based on a two-bit space–time-coding digital metasurface and use it to transmit two different pictures to two users simultaneously in real time. Space–time-coding digital metasurfaces can be used to implement secure and low-cost space- and frequency-division multiplexing in a dual-channel wireless communication system.
147 citations
TL;DR: In this article, a two-dimensional-al modulation scheme referred to as orthogonal time-frequency space (OTFS) modulation is proposed to accommodate the channel dynamics via modulating information in the delay-Doppler domain.
Abstract: Sixth-generation (6G) wireless networks are envisioned to provide global coverage for the intelligent digital society of the near future, ranging from traditional terrestrial to non-terrestri-al networks, where reliable communications in high-mobility scenarios at high carrier frequencies would play a vital role. In such scenarios, the conventional orthogonal frequency division multiplexing (OFDM) modulation, that has been widely used in both the fourth-generation (4G) and the emerging fifth-generation (5G) cellular systems as well as in WiFi networks, is vulnerable to severe Doppler spread. In this context, this article aims to introduce a recently proposed two-dimension-al modulation scheme referred to as orthogonal time-frequency space (OTFS) modulation, which conveniently accommodates the channel dynamics via modulating information in the delay-Doppler domain. This article provides an easy-reading overview of OTFS, highlighting its underlying motivation and specific features. The critical challenges of OTFS and our preliminary results are presented. We also discuss a range of promising research opportunities and potential applications of OTFS in 6G wireless networks.
103 citations
TL;DR: In this paper, the authors proposed a nonorthogonal multiple access (NOMA)-based OTFS system and evaluate its performance from a system-level and link-level perspective.
Abstract: Orthogonal time–frequency space (OTFS) is being pursued in recent times as a suitable wireless transmission technology for use in high-mobility scenarios. In this article, we propose nonorthogonal multiple access (NOMA) based OTFS which may be called NOMA-OTFS system and evaluate its performance from a system-level and link-level perspective. The challenge lies in the fact that while OTFS transmission technology is known for its resilience to high-mobility conditions, while NOMA is known to yield high spectral efficiency (SE) in low-mobility scenarios in comparison to orthogonal multiple access (OMA). We present a minimum mean square error (MMSE)-successive interference cancellation based receiver for NOMA-OTFS, for which we derive expression for symbol-wise postprocessing SINR in order to evaluate system sum SE. We develop power allocation schemes to maximize the sum SE in the high-mobility version of NOMA. We further design a realizable codeword-level SIC (CWIC) receiver using low-density parity check (LDPC) codes along with MMSE equalization for evaluating link-level performance of such practical NOMA-OTFS system. The system-level and link-level performance of the proposed NOMA-OTFS system are compared against benchmark OMA-OTFS, OMA-orthogonal frequency division multiplexing (OMA-OFDM) and NOMA-OFDM schemes. From system-level performance evaluation, we observe interestingly that NOMA-OTFS provides higher system sum SE than OMA-OTFS. When compared to NOMA-OFDM, we find that outage SE of NOMA-OTFS is improved at the cost of decrease in mean SE. The link-level results additionally show that the developed CWIC-based NOMA-OTFS receiver performs significantly better than NOMA-OFDM in terms of block error rate, goodput, and throughout.
30 citations
TL;DR: In this article, an orthogonal frequency division multiplexing (OFDM)-based multi-carrier transmission for cell-free massive multi-input multi-output (CFmMIMO) over frequency-selective fading channels is proposed.
Abstract: This letter presents and analyzes orthogonal frequency-division multiplexing (OFDM)-based multi-carrier transmission for cell-free massive multi-input multi-output (CFmMIMO) over frequency-selective fading channels. Frequency-domain conjugate beamforming, pilot assignment, and user-specific resource allocation are proposed. The CFmMIMO-OFDM system is scalable to serve a massive number of users and is flexible to offer diverse data rates for heterogeneous applications.
27 citations
TL;DR: This article proposes cross-layer design algorithms that exploit frequency-dependent attenuation in the transmission of high-quality video underwater by connecting channel reliability to the structure of the compressed video.
Abstract: We study the transmission of high-quality video underwater. The underwater acoustic medium pathloss attenuation depends not only on transmission distance but also on the frequency occupied by the signal, where lower frequencies have lower attenuation for a given distance. We propose cross-layer design algorithms that exploit this frequency-dependent attenuation by connecting channel reliability to the structure of the compressed video. The video data are categorized based on their importance. Orthogonal frequency-division multiplexing is adopted as the modulation technique, such that different data can be sent on different frequencies. The underlying communications system accompanied with a noise analysis is developed in this article. The signal and noise statistics are used in the simulations to represent the underwater channel. We propose three new techniques and compare them to three baseline techniques. In the proposed techniques, important video information is transmitted on the least attenuated frequencies while less important data are transmitted through higher frequencies. Simulation results show that at least one of our proposed techniques can achieve significant improvements in the peak signal-to-noise ratio in comparison to the baseline techniques.
23 citations
TL;DR: The framework is a generalization of the recently proposed orthogonal time frequency space (OTFS), which fails to achieve the ERC, and proposes the waveform design based on the equal-reliability criterion (ERC), leading to the block multiplexed-orthogonal chirp division multiplexing (BM-OCDM).
Abstract: In this paper, we investigate three different concepts for robust link-level performance under doubly-dispersive wireless channels, namely, i) channel estimation, ii) cyclic prefix (CP)-free transmission, and iii) waveform design. We employ a unique word-based channel estimation, where we decouple the channel related errors into channel estimation error (CEE) and Doppler error (DE). Then, we show that a trade-off between CEE and DE emerges in the frame design, where the system can be optimized to achieve the minimum composite channel error. Another strategy to improve the link-level performance is to suppress the CP of the sub-blocks. This allows for better channel estimation due to the reduced transmission time, with the penalty of requiring the CP-restoration processing at the receiver. Furthermore, we propose the waveform design based on the equal-reliability criterion (ERC), leading to the block multiplexing-orthogonal chirp division multiplexing (BM-OCDM). This waveform is advantageous in the CP-free transmission mode, where the data symbols have equally distributed interference from adjacent sub-blocks. Our framework is a generalization of the recently proposed orthogonal time frequency space (OTFS), which fails to achieve the ERC. The link-level simulations show that at high modulation and coding scheme, the proposed BM-OCDM provides superior link-level performance than OTFS.
21 citations
TL;DR: Experimental results have been demonstrated and confirmed that both downlink and uplinks are capable of providing sufficient bandwidth for a multi-gigabit OWC and the lens-free uplink receiver can alleviate requirements for aligning and improve the mobility of the transmitter.
Abstract: We built a full-duplex high-speed optical wireless communication (OWC) system based on high-bandwidth micro-size devices, for which micro-LED and VCSEL arrays are implemented to establish downlink and uplink, respectively. The high-capacity downlink based on a single-pixel quantum dot (QD) micro-LED can reach a data rate of 2.74 Gbps with adaptive orthogonal frequency division multiplexing (OFDM). VCSEL-based line-of-sight (LOS) and non-line-of-sight (NLOS) uplinks are designed with lens-free receiving functions for a 2.2-m communication distance. Experimental results have been demonstrated and confirmed that both downlink and uplinks are capable of providing sufficient bandwidth for a multi-gigabit OWC. Besides, the lens-free uplink receiver can alleviate requirements for aligning and improve the mobility of the transmitter. The VCSELs implemented for both systems work with low driving currents of 140-mA and 190-mA under consideration of the human eye safety. For non-return-to-zero on-off keying (NRZ-OOK), both uplinks can achieve 2.125 Gbps with bit-error-rate (BER) lower than the forward error correction (FEC) threshold of 3.8×10−3 for Ethernet access.
20 citations
TL;DR: The reconfigurable weighted multi-phase mixing based beam-space RX scheme achieves both: 1) multi-beam formation/spatial filtering and 2) FDM of multiple beam- space outputs, preserving full MIMO field-of-view while ensuring a single IF interface.
Abstract: The evolution of mm-wave phased array receivers (RX) to MIMO RX promises multi-beamforming and improved capacity. Although digital beamforming (DBF) provides the highest flexibility, digitization in the beam space as opposed to element space enables ADC digitization scalability with number of beams ( $\le $ 4) and spatial filtering prior to the ADC. mm-Wave MIMO arrays must also address the challenge of increased IO routing while supporting dense fill-factors with $\lambda /2$ antenna spacing. In this work, an MIMO beam-space RX array architecture with simultaneous spatial filtering and single wire frequency-domain multiplexing (FDM) is presented. The reconfigurable weighted multi-phase mixing based beam-space RX scheme achieves both: 1) multi-beam formation/spatial filtering and 2) FDM of multiple beam-space outputs, preserving full MIMO field-of-view while ensuring a single IF interface. A 28-GHz four-element RX prototype demonstrates the proposed architecture in 65-nm CMOS. The IC occupies only 3.4 mm $\times $ 3.1 mm for a four-element MIMO 28-GHz array and can form four independent beams with >400-MHz 3-dB BW and FDM on to a single IF interface. The array consumes 450 mW and achieves >27-dB beam-to-beam isolation over 150-MHz BW, while consuming 28.1 mW/stream/beam for 28 GHz. Concurrent MIMO measurements with two wireless 28-GHz beams are shown at 400 Mb/s (100 Msps, 16QAM) data rate demonstrating mm-wave MIMO operation.
18 citations
TL;DR: A novel frequency-domain (FD) digital predistortion (DPD) solution for orthogonal frequency division multiplexing (OFDM) transmitters (TXs) is proposed, which allows to flexibly control the linearization performance, in FD, such that different degrees of linearization can be provided at different parts of the spectrum.
Abstract: In this letter, a novel frequency-domain (FD) digital predistortion (DPD) solution for orthogonal frequency division multiplexing (OFDM) transmitters (TXs) is proposed. The proposed approach allows to flexibly control the linearization performance, in FD, such that different degrees of linearization can be provided at different parts of the spectrum. Such a feature can be of special interest in the millimeter-wave (mmWave) bands, where the inband signal quality requirements can limit the feasible TX power, while also varying across the active subcarriers due to frequency multiplexing of different users with different modulation and coding schemes. The performance of the proposed FD DPD is demonstrated and validated through over-the-air (OTA) measurements on a 64-element phased-array operating at 28-GHz carrier frequency.
15 citations
TL;DR: A photonics-aided MMW communication system is demonstrated that can be successfully transmitted over 1-m wireless link, and a hybrid time-frequency domain least mean square (LMS) equalizer is proposed to eliminate the crosstalk in the adjacent OFDM symbols and subcarriers.
Abstract: Millimeter-wave (MMW) transmission has the advantage of larger available bandwidth compared with traditional wireless communications. Compared with the electrical algorithms, photonics-aided MMW signals generation can support a large modulation bandwidth and is regarded as a potential candidate for future RoF link. In this experiment, we demonstrate a W-band (75 GHz ∼ 110 GHz) photonics-aided MMW communication system. To overcome the high-frequency power loss induced by the limited bandwidth of photoelectric devices, we adopt orthogonal frequency division multiplexing (OFDM) signal with hybrid quadrature amplitude modulation (QAM) formats. Moreover, the probabilistic constellation shaping (PCS) technique is used to further improve the system capacity. In the offline digital signal processing (DSP), a time-domain Volterra series based nonlinear equalizer with I/Q multiple input multiple output (MIMO) structure can compensate for the nonlinearity during the fiber and wireless transmission. Finally, a hybrid time-frequency domain least mean square (LMS) equalizer is proposed to eliminate the crosstalk in the adjacent OFDM symbols and subcarriers. With the aid of advanced modulation and hybrid time-frequency domain equalization, 30 Gbaud OFDM MMW signals with hybrid PS-512QAM and PS-128QAM at 92.5 GHz can be successfully transmitted over 1-m wireless link, whose raw transmission rate is 208.4 Gbit/s. It is worth noting that the hybrid time-frequency domain LMS equalizer can increase the maximal AIR to 178.8 Gbit/s.
15 citations
TL;DR: This proposed MP-DSA system based on FDM technique provides an efficient and cost-effective way for upgrading a conventional single DAS into an integrated DAS network, which shows great potential in many applications such as modern city civil structure monitoring with different demands.
TL;DR: C coded MIMO OFDM waveforms are proposed and investigated that allow continuous and simultaneous wideband transmission for all transmitters of a multiple transmit and receive antenna array for spatial radar environment perception.
Abstract: Emerging digital radar concepts such as orthogonal frequency-division multiplexing (OFDM) allow flexible signal generation. This opens up new opportunities in waveform design in a multiple-input multiple-output (MIMO) system such as introducing coding for signal multiplexing. In this article, coded MIMO OFDM waveforms are proposed and investigated that allow continuous and simultaneous wideband transmission for all transmitters of a multiple transmit and receive antenna array for spatial radar environment perception. Challenges for coded MIMO OFDM radar operation are derived, and three coded MIMO strategies are introduced and analyzed. Their potential is validated and compared to the standard subcarrier interleaving OFDM approach using simulations and measurements of an experimental 4 × $ 4$ MIMO OFDM radar at 77GHz.
06 Sep 2021
TL;DR: In this article, the authors show that affine frequency division multiplexing (AFDM) offers significant throughput and reliability gains over state-of-the-art multicarrier modulation.
Abstract: Affine Frequency Division Multiplexing (AFDM) is a new multi-chirp waveform that can be generated and demodulated using the discrete affine Fourier transform (DAFT). DAFT is a generalization of discrete Fourier transform characterized with two parameters which can be adapted to better cope with both doubly dispersive channels and impairments at high-frequency bands. DAFT domain impulse response can indeed convey a full delay-Doppler representation of linear time-varying (LTV) channels, which allows AFDM to achieve the full diversity. Moreover, AFDM signals are maximally spread in time and frequency, thus providing a coverage gain that turns out to be robust against radio frequency impairments, such as carrier frequency offset and phase noise. In this paper, we show that AFDM offers the aforementioned advantages while being compatible with practical pilot-aided channel estimation and low-complexity channel equalization. Our analytical and simulation results evince that AFDM achieves significant throughput and reliability gains over state-of-the-art multicarrier modulation.
TL;DR: A novel two-stage joint hybrid precoder and combiner design for maximizing the average achievable sum-rate of frequency-selective millimeter-wave massive MIMO-OFDM systems is proposed.
Abstract: Hybrid beamforming design for OFDM systems is hugely challenging since their analog precoders and combiners are shared among all subcarriers. This paper proposes a novel two-stage joint hybrid precoder and combiner design for maximizing the average achievable sum-rate of frequency-selective millimeter-wave massive MIMO-OFDM systems. In the proposed approach, the analog precoder and combiner design is formulated as a constrained Tucker2 tensor decomposition problem, which allows maximizing the sum of the effective baseband gains over every subcarrier while suppressing inter-user and intra-user interferences. The solution is obtained by a projected alternate least-square-based algorithm, which is suitable for both single-user (SU) and multiuser (MU) systems. The digital precoder and combiner for SU systems is obtained from the effective baseband channel’ SVD. In contrast, for MU systems, it is obtained from the regularized channel diagonalization method, which balances multiuser interference and noise suppression. Numerical simulation results validate the effectiveness of the proposed method.
TL;DR: In this article, a compact, highly integrated multiplexing filtering antenna operating at 4.7/5.2/6.6 GHz is proposed for multiservice wireless communication systems.
Abstract: In this communication, a compact, highly integrated multiplexing filtering antenna operating at 4.7/5.2/6.0/6.6 GHz is proposed for the first time. Different from traditional antennas, the proposed antenna has one shared radiator but four ports working in different frequency bands, and thus, it can simultaneously support four different transmission channels. The proposed multiplexing antenna is composed of a patch with a U-shaped slot, two substrate integrated waveguide (SIW) cavities, and four resonator-based frequency-selective paths. The resonator-based paths can not only enhance the interchannel isolations but also improve the impedance bandwidth. The design principles and the methods of controlling the four operating bands are studied. Measurement results agree reasonably well with the simulations, showing four channels from 4.5 to 4.8 GHz, 5.1 to 5.3 GHz, 5.85 to 6.3 GHz, and 6.4 to 6.6 GHz, respectively. The antenna also exhibits high isolation of over 25 dB between the channels. In addition, the proposed antenna has a consistent broadside radiation pattern and polarization in the four bands, and manifesting the proposed multiplexing filtering antenna can be a promising candidate for multiservice wireless communication systems.
06 Jun 2021
TL;DR: The first transparent Optical-THz-Optical link providing record-high line-rates up to 240 and 190 Gbit/s over distances from 5 to 115m is demonstrated.
Abstract: The first transparent Optical-THz-Optical link providing record-high line-rates up to 240 and 190 Gbit/s over distances from 5 to 115m is demonstrated. The link is based on direct data-conversion from optical to sub-THz and vice-versa.
TL;DR: In this article, an end-to-end optimization through autoencoders is applied to define symbol-towaveform (modulation) and waveform-tosymbol (detection) mappings.
Abstract: Optimizing modulation and detection strategies for a given channel is critical to maximizing the throughput of a communication system. Such an optimization can be easily carried out analytically for channels that admit closed-form analytical models. However, this task becomes extremely challenging for nonlinear dispersive channels such as the optical fiber. End-to-end optimization through autoencoders (AEs) can be applied to define symbol-to-waveform (modulation) and waveform-to-symbol (detection) mappings, but so far it has been mainly shown for systems relying on approximate channel models. Here, for the first time, we propose an AE scheme applied to the full optical channel described by the nonlinear Schrodinger equation (NLSE). Transmitter and receiver are jointly optimized through the split-step Fourier method (SSFM) which accurately models an optical fiber. In this first numerical analysis, the detection is performed by a neural network (NN), whereas the symbol-to-waveform mapping is aided by the nonlinear Fourier transform (NFT) theory in order to simplify and guide the optimization on the modulation side. This proof-of-concept AE scheme is thus benchmarked against a manually-optimized NFT-based system and a three-fold increase in achievable distance (from 2000 to 6640 km) is demonstrated.
14 Jun 2021
TL;DR: In this article, a tensor-based precoding scheme for MIMO GFDM systems is proposed, where the input and output are modelled as order 3 tensors where the three modes correspond to space, time and frequency domains.
Abstract: Generalized Frequency Division Multiplexing (GFDM) is a multi-domain communication scheme where data symbols are transmitted over a time-frequency block. Tensors, which are multi-way arrays, can be efficiently used to model such systems. This paper presents a system model for a multiple input multiple output (MIMO) GFDM system using the Einstein product of tensors. The input and output are modelled as order 3 tensors where the three modes correspond to space, time and frequency domains. The equivalent channel between the input and output obtained from a cascade of transmit filter, physical channel and receive filter, is defined as an order 6 tensor which takes into account interference across all the domains. An information theoretic analysis of such a tensor channel is presented which is then used to develop a tensor based precoding scheme for MIMO GFDM systems. The effect of various GFDM pulse shape parameters on the capacity of the equivalent channel is explored. A multi-linear minimum mean square error (MMSE) receiver using the tensor framework is also presented.
TL;DR: In this article, a geometric shaped (GS) 64-ary amplitude phase shift keying (64-APSK) eigenvalue transmission was demonstrated, where the signal is modulated on the scatter coefficient of a single eigen value and linear minimum mean square error estimator is used to reduce the noise.
Abstract: We experimentally demonstrated a geometric shaped (GS) 64-ary amplitude phase shift keying (64-APSK) eigenvalue transmission. The signal is modulated on the scatter coefficient of a single eigenvalue and linear minimum mean square error (LMMSE) estimator is used to reduce the noise. The channel response is estimated by transmitting a normally distributed 64-APSK constellation through a communication link. Based on the polar coordinates distribution of the received constellation, the diameter distributions for each circle can be obtained so that circles with larger noise can obtain larger judgment width. After optimization, the experimental results show that the Q-factor gain is 1.13 dB under 22 dB received optical signal to noise ratio (OSNR) configuration and 0.88 dB after 900 km transmission compared with normally distributed APSK configuration.
TL;DR: In this article, an artificial neural network (ANN)-based scheme was proposed to improve the performance of nonlinear frequency division multiplexing (NFDM) optical transmission systems in both time and frequency domain.
Abstract: We propose an artificial neural network (ANN)-based scheme to improve the performance of nonlinear frequency division multiplexing (NFDM) optical transmission systems in both time and frequency domain. Through two-stage ANN equalization at the receiver side, time-domain distortions between adjacent bursts and frequency-domain cross talk between neighboring subcarriers can be jointly mitigated. Burst ANN and Subcarrier ANN equalizers are characterized and validated by numerical simulations of a dual-polarization NFDM transmission system. Compared with the basic detection scheme, the proposed two-stage ANN achieves a Q-factor gain of 3.01 dB for an NFDM system with 256 Gb/s gross data rate transmitting over 960 km standard single-mode fiber (SSMF). The two-stage ANN approach offers an effective way to jointly equalize the signal in multiple dimensions.
TL;DR: The F-TDM system is a compromise method that combines the advantages of both and has no obvious disadvantage at the detection limit and is the most time-saving system based on FDM technology.
Abstract: Multi-gas tunable diode laser absorption spectroscopy (TDLAS) system based on time division multiplexing (TDM) demodulation technology which combine with frequency division multiplexing (FDM) technology is proposed, called F-TDM (frequency- time division multiplexing) system. In addition, traditional TDM technology and FDM technology are introduced to analyze and compare their performance. As for the performance of F-TDM system, multi-gas detection of CH4 and C2H2 has been accomplished with minimum detection limits of 10.24 ppmv for CH4 at 1653.72 nm and 0.763 ppmv for C2H2 at 1532.83 nm respectively. The relationships (CH4: R-square = 0.9989; C2H2: R-square = 0.9995) between gas concentration and second harmonic signal amplitude are proved as a good linear response. It is consistent with the data obtained by traditional TDM and FDM demodulation methods, indicating that the F-TDM system is feasible. By comparison, it is known that different methods have their advantages in different applications. The TDM system uses less equipment and is the most cost-effective. The system based on FDM technology is the most time-saving. The F-TDM system is a compromise method that combines the advantages of both and has no obvious disadvantage at the detection limit.
TL;DR: In this paper, a CNN model operating on the fast Fourier transformation window bank (FWB) was proposed to extract the useful symbol length in OFDM, which represents the identification of each OFDM-based wireless communication technology.
Abstract: Automatic modulation classification (AMC) is an essential factor in dynamic spectrum access to fulfill the spectrum demand of 5G wireless communications for achieving high data rate and low latency. Many deep learning (DL)-based AMC methods have achieved improved accuracy for classifying analog modulation schemes, single-carrier-based modulation schemes, and multi-carrier signals using several DL architectures such as the convolutional neural network (CNN) and long-short term memory (LSTM). However, most conventional DL-based AMC methods have confused the orthogonal frequency multiplexing division (OFDM)-based signals with different OFDM useful symbol lengths. To resolve the issue, we propose a CNN model operating on the fast Fourier transformation window bank (FWB) to extract the useful symbol length in OFDM, which represents the identification of each OFDM-based wireless communication technology. After extracting the OFDM useful symbol length, we propose a DL-based AMC system combined with FWB and in-phase and quadrature-phase signals to classify the OFDM symbol length and single-carrier modulation schemes simultaneously. Furthermore, we explore the constraints of the FWB parameters according to the length and the fast Fourier transformation (FFT) size of the OFDM signal to achieve good classification accuracy through the experiment. We constructed a dataset by generating OFDM signals of different lengths while changing the FFT size in a fixed bandwidth and selecting only quadrature amplitude modulation (QAM) schemes from RadioML2016.10a. Experimental results show the improved classification accuracy by about 30% over conventional classifiers in additive white Gaussian noise, synchronization impairments, and fading environments.
TL;DR: This work experimentally demonstrate the convergence of a NOMA-CAP wireless waveform with a single-carrier wired signal in a PON scenario using radio-over-fiber (RoF) technology.
Abstract: Network architectural changes to satisfy all the 5G+ mobile network specifications and requirements are necessary due to the popularization of streaming and cloud applications on omnipresent portable devices. The combination of massive installation of micro-cell antenna sites with the cloud access radio network (C-RAN) architecture has recently been nominated as a promising technology for high-capacity mobile fronthaul links, albeit at a high cost. An alternative approach for next-generation fronthaul networks is to utilize the already deployed passive optical networks (PONs) where wireless and wired services may coexist in a converged manner. Non-orthogonal multiple access (NOMA) modulation with multi-band carrierless amplitude and phase modulation (NOMA-CAP) has recently been investigated as a promising 5G+ modulation format candidate to increase the capacity and flexibility of future mobile networks. Here, we experimentally demonstrate the convergence of a NOMA-CAP wireless waveform with a single-carrier wired signal in a PON scenario using radio-over-fiber (RoF) technology. Specifically, fifteen NOMA-CAP bands, with two NOMA power levels to double the capacity, transmit 15 Gb/s multiplexed with a digital 10 Gb/s four-level pulse amplitude modulation (PAM-4) signal for downlink application. Two converged system implementations have been considered, first using electrical frequency division multiplexing (EFDM) and secondly using the hybrid EFDM-wavelength division multiplexing (EFDM-WDM). Successful transmission through a 25 km span of standard single-mode fiber is achieved with negligible transmission penalty for both proposed converged solutions.
TL;DR: The development of a method of active control of military radio communication systems through the use of multifunctional radios, which allow through control of the parameters of militaryRadio Network Parameters is developed.
Abstract: A method of adaptive control of military radio network parameters has been developed. This method allows predicting suppressed frequencies by electronic warfare devices, determining the topology of the military radio network. Also, this method allows determining rational routes of information transmission and operating mode of radio communications. Forecasting of the electronic environment is characterized by recirculation of input data for one count, resampling on a logarithmic time scale, finding a forecast for the maximum value of entropy and resampling the forecast on the exponential time scale. The developed method allows choosing a rational network topology. The choice of topology of the military radio communication system is based on the method of ant multi-colony system. The main idea of the new option of ant colony optimization is that instead of one colony of the traditional ant algorithm several colonies are used that work together in a common search space. However, this procedure additionally takes into account the type of a priori uncertainty and the evaporation coefficient of the pheromone level. The proposed method allows choosing a rational route for information transmission. The proposed procedure is based on an improved DSR algorithm. This method uses several operating modes of radio communications, namely the technology of multi-antenna systems with noise-like signals, with pseudo-random adjustment of the operating frequency and with orthogonal frequency multiplexing. The developed method provides a gain of 10‒16 % compared to conventional management approaches
TL;DR: In this article, a method for suppressing crosstalk noise by compressed sensing under multi-frequency optical time domain reflectometer (ϕ-OTDR) is proposed, and the frequency domain is chosen as the sparse domain.
Abstract: The frequency division multiplexing (FDM) is an effective method to improve the detection ability of high-frequency disturbance in phase-sensitive optical time domain reflectometer (ϕ-OTDR). However, as the probe channels increase, crosstalk between channels will be generated. As a result, the recovery phase signal-to-noise ratio (SNR) will be deteriorated, which will reduce the detection capability of ϕ-OTDR. Therefore, a novel method for suppressing crosstalk noise by compressed sensing under multi-frequency ϕ-OTDR is proposed in this paper. The band-limited characteristics of vibration are deeply analyzed, and the frequency domain is chosen as the sparse domain. Noise without sparsity is discarded in the compression process. Furthermore, the noise cannot be recovered in the reconstruction process which uses the critical information containing the global property of phase signal. Consequently, the influence of crosstalk noise is reduced effectively. In experiments, compared with the restored signals without the proposed method, the average SNRs of the reconstructed 12 kHz sinusoidal vibration are respectively enhanced by 18.57 dB, 40.47 dB, and 41.67 dB in the sensing system with 6, 7, and 8 channels. In addition, the 24 kHz triangular wave signal and the disturbance composed of several different frequencies with random amplitudes can be detected and reconstructed. The proposed crosstalk noise suppression method provides a potential choice for ϕ-OTDR performance enhancement.
TL;DR: A novel and low-cost echo separation technique for the multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) is presented, based on the orthogonal frequency-division multiplexing (OFDM) chirp waveforms.
Abstract: In this letter, a novel and low-cost echo separation technique for the multiple-input multiple-output (MIMO) synthetic aperture radar (SAR) is presented, based on the orthogonal frequency-division multiplexing (OFDM) chirp waveforms. The proposed scheme allows the generation of multiple OFDM chirp waveforms on common spectral support. In the new scheme, a series of simple time-domain operations including replica, T-shift, and superposition is applied to eliminate the interference waveform within a limited time. Then, a combination with a bandpass filter instead of a matched filter to focus signal power and digital beamforming (DBF) on receive in elevation enables the suppression of interference signals for a realistic spaceborne SAR scenario, where the swath width exceeds the spatial extension of the transmitted pulse. Furthermore, the distributed scene simulation results are presented to verify the practicability of the proposed scheme.
TL;DR: In this paper, a photonic ELM based on a frequency-multiplexed fiber setup is presented for classification tasks and a nonlinear channel equalization task, which can be performed either offline on a computer, or optically by a programmable spectral filter.
Abstract: The optical domain is a promising field for physical implementation of neural networks, due to the speed and parallelism of optics. Extreme Learning Machines (ELMs) are feed-forward neural networks in which only output weights are trained, while internal connections are randomly selected and left untrained. Here we report on a photonic ELM based on a frequency-multiplexed fiber setup. Multiplication by output weights can be performed either offline on a computer, or optically by a programmable spectral filter. We present both numerical simulations and experimental results on classification tasks and a nonlinear channel equalization task.
TL;DR: In this article, a time-and-frequency hybrid multiplexing technique for a multiple-input multiple-output (MIMO) orthogonal frequency division multiple-division multiple-radio (OFDM) radar is proposed.
Abstract: A time-and-frequency hybrid multiplexing technique for a multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) radar is proposed. Discrete Fourier transform (DFT)-coded OFDM waveforms are introduced, which allow it to be free from range-dependent angle errors. These are readily used to provide both time-domain multiplexing and frequency-domain multiplexing in the MIMO OFDM radar. The DFT- coded frequency-domain multiplexing shortens the maximum unambiguous range, while the DFT- coded time-domain multiplexing lowers the maximum Doppler ambiguity. A hybrid of both domain multiplexing techniques can mitigate the respective limitations by adaptively selecting the proper DFT matrix size in each multiplexing domain. This allows to solve the intrinsic range and Doppler ambiguity problems of MIMO radars by controlling the hybrid ratio of the two kinds of DFT- code based multiplexing methods. Range-Doppler and range-angle maps of four examples with different hybrid multiplexing ratios are simulated with a MIMO OFDM radar numerical platform.
TL;DR: In this paper, a new configuration of radio over fiber-passive optical network (RoF-PON) including two 60 GHz multiple-input multiple-output (MIMO) based on a 5G universal filtered multicarrier waveform and wired signal utilizing orthogonal frequency division multiplexing (OFDM), is described.
Abstract: Next-generation integrated fiber-wireless access networks will require low-cost and high-capacity deployment to meet customer demand. A new configuration of radio over fiber–passive optical network (RoF-PON) architecture, including two 60 GHz multiple-input multiple-output (MIMO) based on a 5G universal filtered multicarrier waveform and wired signal utilizing orthogonal frequency division multiplexing (OFDM), is described. At the optical line terminal, MIMO signals are integrated as upper and lower sidebands of the wired OFDM signal. This integration approach, employing single-sideband frequency translation, reduces the complexity of the transceiver design and provides high spectral efficiency because the two MIMO-RoF and wired signals transmit at the same frequency. Improved techniques are also employed to upconvert and downconvert the 60 GHz millimeter wave (MMW), being remote optical heterodyning and self-heterodyning, respectively. The MIMO-RoF signals are therefore transmitted at low frequency over the standard single-mode fiber to avoid the impairments induced at higher frequencies, and the remote optical local oscillator is reused to downconvert the two 60 GHz MMWs, producing a cost-effective system. Simulation results demonstrate very satisfactory network performance when using a downstream link over a 20 km span standard PON.
TL;DR: In this paper, a joint probabilistic shaping (PS) and neural network (NN) equalizer was proposed to improve the performance of the b-modulated nonlinear frequency division multiplexing (NFDM) system.
Abstract: A joint scheme introducing probabilistic shaping (PS) at the transmitter and utilizing a neural network (NN) equalizer at the receiver is proposed to improve the performance of the b-modulated nonlinear frequency division multiplexing (NFDM) system. Through a numerical simulation, we demonstrate that PS plays a leading role for low launch power case, which improves the performance of the system effectively, while the NN equalizer’s superiority appears in a high launch power region, whose main role is to weaken the correlation among subcarriers for improving system performance. The proposed scheme would enlighten the optimum modulation and detection schemes of the NFDM system.