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In the past decade, novel index modulation (IM) has emerged as a promising technology widely employed in wireless communications. In this paper, the subcarrier index modulation super-Nyquist carrierless amplitude phase (SIM-SCAP) modulation scheme is proposed and investigated to enhance the system spectral efficiency (SE) and the energy efficiency of the multiband CAP ( m -CAP) scheme in bandlimited visible light communication (VLC) systems. By innovatively combining the index modulation technique with the non-orthogonal m -CAP technique, the SIM-SCAP scheme can sustain higher system SE than the m -CAP scheme along with a reduced system complexity for transceivers. Furthermore, the ICI mitigation schemes are employed further to enhance the throughput performance of the SIM-SCAP scheme. It is shown that the SIM-SCAP scheme with ICI mitigation DSP achieves ∼30% SE enhancement compared to the non-orthogonal m -CAP scheme. Furthermore, under maximum bandwidth and minimum transmission rate requirements, the SIM-SCAP scheme yields a Q factor gain of 5.5 dB. The results validate the unveiling advantage of the SIM-SCAP scheme in offering high SE transmissions, which is a promising candidate in designing bandlimited multi-user access optical communication systems.

The Quadrature Modulation Scheme (QUAM) uses sine and cosine orthogonality properties to allow the transmission of two different signals in the same carrier, which occupies a bandwidth that is equivalent to the AM signal. The QUAM modulator can be assembled using two DSB-SC modulators. The information is transmitted by both the carrier amplitude and phase.

In this paper, a spectrally efficient version of multiband Carrierless Amplitude Phase modulation (MultiCAP) based on Optical Single-Sideband (OSSB) techniques is proposed for its use in high capacity access links. The proposed system consists of four 2.5 GBd OSSB-MultiCAP bands with quadrature amplitude modulation and uses an insensitive polarization receiver to avoid optical polarization issues and adjustments at the receiver side. This scheme has been experimentally evaluated and can provide an aggregated transmission rate of 50 Gb/s over 50 km of standard single mode optical fiber using only 10G electronic and photonic devices in C-band with a sensitivity of -23.2 dBm and a measured optical power budget of 25.2 dB. 40 Gb/s transmission over 50 km with a sensitivity of -27.5 dBm and a measured power budget of 32.5 dB is also demonstrated.

High-speed interconnects are highly demanded in data centers and high-performance computing, and the use of optical interconnects to replace electrical interconnects has been proposed and widely studied. For medium-range board-to-board communications, free-space based optical interconnects provide the additional advantage of reconfigurability and flexibility, compared with traditional waveguide or fiber-based counterparts. However, the bit rate and interconnection range in free-space optical interconnects are typically limited. In this paper, we propose a carrierless-amplitude-phase (CAP) modulated and space-time coded free-space optical interconnect scheme to overcome these limitations. Up to 80 Gb/s (2 × 40 Gb/s) interconnection with reconfigurability and flexibility is experimentally demonstrated for a maximum error-free distance exceeding 50 cm, showing about 65% improvement over previous demonstrations. The receiver sensitivity of the space-time coded system is measured as well, and results show that the space-time-block code (STBC) is capable of improving the receiver sensitivity and suppressing the inter-channel crosstalk. The impact of air turbulence, which exists in typical interconnect environments, is also experimentally investigated and results show that its impact on the proposed scheme is negligible. The proposed reconfigurable free-space optical interconnects with CAP and STBC can be further scaled up to provide higher speed and further extended interconnection range.

This paper proposes a new technique to increase the symbol rate in Quadrature Amplitude Modulation (QAM) using a new set of orthonormal functions. The proposed technique increases the rate of QAM symbols without increasing the bandwidth of the modulated signal or increasing the modulation order of the QAM symbol. The set of orthonormal functions consists of four shaped-sinusoidal functions. The shaping functions are Hilbert-Transform pair. The proposed QAM modulator modulates two independent complex symbols in the same time. Each modulated symbol uses two different functions from the proposed set. The paper shows the structure of the modulator and demodulator of the proposed system. The paper presents different shaping pulses, which can be used with the proposed system. Keywords: Quadrature amplitude modulation, Orthogonal shaping shapes, Hilbert transform, Complex exponential carriers, Inter-symbol interference

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works In this paper, a combined non-orthogonal multiple access (NOMA) and multiband carrierless amplitude phase modulation (multiCAP) scheme is proposed for capacity enhancement of and flexible resource provisioning in 5G mobile networks. The proposed scheme is experimentally evaluated over a W-band millimeter wave radio-over fiber system. The evaluated NOMACAP system consists of six 1.25GHz multiCAP bands and two NOMA levels with quadrature phase shift keying and can provide an aggregated transmission rate of 30 Gbit/s. The proposed system can dynamically adapt to different user densities and data rate requirements. Bit error rate performance is evaluated in two scenarios: a low user density scenario where the system capacity is evenly split between two users and a high user density scenario where NOMA and multiCAP are combined to serve up to twelve users with an assigned data rate of 2.5 Gbit/s each. The proposed system demonstrates how NOMA-CAP allows flexible resource provisioning and can adapt data rates depending on user density and requirements.

Nowadays, Carrier less Amplitude and Phase (CAP) Modulation has been used in various industrial applications because of its simplicity and bandwidth efficiency. In this paper, a novel CAP modulation technique has been used for OFDM in wireless communication system. To reduce the spectrum efficiency losses and improving the speed of the data transmission are the main requirements of the wireless communication systems. In conventional technologies transmitter takes long time to modulate and encode the signal, the time delay occurred during the conversion is suffers the total Li-Fi networks. In order to overcome this problem, novel modulation techniques have been proposed such as Carrier less amplitude and phase modulation (CAP) and Quadrature Phase Shift Keying (QPSK) Modulation. The design simulation is carried out in ModelSim XE III 6.3C and Synthesized in Xilinx ISE 10.1 by using Verilog HDL Language.

Union modulation scheme is proposed and analyzed based on trellis-coded modulation, orbital angular momentum (OAM), and quadrature amplitude modulation (QAM). Specifically, source data symbols are mapped to a 3-D constellation diagram consisting of OAM modes and QAM constellation. Moreover, the constellation point is jointly detected by an OAM single-point detector and a pruned Viterbi decoder at the receiver. Compared with standalone modulation schemes, larger Euclidean distance with lower bit error rate (BER) and lower complexity can be obtained. Furthermore, the simulation results show that the single-point detection is more robust than the phase-gradient detection at a large receiving distance.

A low complexity maximum likelihood (ML) detection method is proposed for the square quadrature amplitude modulation (QAM) constellation. In order to reduce the implementation complexity of ML detection, set-partition, subset-selection, and subset-shift are recursively applied to the square QAM constellation. The estimated square QAM symbol is finally given in a closed form as a function of the received signal and the estimated channel. Complexity analysis and numerical simulation confirm that the proposed detection method reduces the implementation complexity substantially and achieves exactly the same performance as the conventional ML detection irrespective of the channel estimation error.

A cognitive tri-band transmitter (TX) with a forwarded clock using multiband signaling and high-order digital signal modulations is presented for serial link applications. The TX features learning an arbitrary channel response by sending a sweep of continuous wave, detecting power level at the receiver side, and then adapting modulation scheme, data bandwidth, and carrier frequencies accordingly based on detected channel information. The supported modulation scheme ranges from nonreturn to zero/Quadrature phase shift keying (QPSK) to Pulse-amplitude modulation (PAM) 16/256-Quadrature amplitude modulation(QAM). The proposed highly reconfigurable TX is capable of dealing with low-cost serial channels, such as low-cost connectors, cables, or multidrop buses with deep and narrow notches in the frequency domain (e.g., a 40-dB loss at notches). The adaptive multiband scheme mitigates equalization requirements and enhances the energy efficiency by avoiding frequency notches and utilizing the maximum available signal-to-noise ratio and channel bandwidth. The implemented TX prototype consumes a 14.7-mW power and occupies 0.016 mm2 in a 28-nm CMOS. It achieves a maximum data rate of 16 Gb/s with forwarded clock through one differential pair and the most energy efficient figure of merit of 20.4 $\mu \text{W}$ /Gb/s/dB, which is calculated based on power consumption of transmitting per gigabits per second data and simultaneously overcoming per decibel worst case channel loss within the Nyquist frequency.

The multidimensional constellations of quadrature amplitude modulation (QAM) signals are proposed. Each symbol incorporates the blocks of QAM signals not only carrying the same information content but also composed of the symbols of different higher order constellations (in contrast to the simple 1D modulation where each QAM symbol carries its intrinsic information). The multidimensional constellations of QAM signals are synthesized using the optimization algorithm based on the criteria for enhancing the energy or spectral efficiency of digital data transmission systems. The characteristics of interference immunity of the proposed signals are estimated with the help of analytical calculations and simulation. The relationships making it possible to consider faster-than-Nyquist signaling technology as a particular case of the multidimensional constellations of QAM signals are derived. It is demonstrated that the obtained signals provide an energy gain with respect to traditional 1D signals, in particular, ensure the operability at SNRs smaller than those inherent to binary phase-shift keying signals.

A simplified soft demapper for non-square quadrature amplitude modulation (QAM) provided by fifth generation of high-speed data-over-cable systems (DOCSIS 3.1) is proposed. By using the geometric tendency of the non-square QAM constellation and “fold-and-overlap” approach, the non-linear log likelihood ratio (LLR) equation based on the max-log maximum a posteriori (MAP) algorithm can be approximated to linear equations. With this approximation, the proposed method can be applied to high-order non-square QAM, up to 8192 QAM, with negligible bit error rate performance degradation under additive white Gaussian noise and multipath flat-fading channels. Computational complexity is reduced by at least 93% compared to the LLR calculation based on the max-log MAP algorithm.

A new modulation scheme — single sideband quadrature amplitude modulation (SSB QAM) is proposed. This scheme allows to decrease the spectral width of the transferred signal by two times as opposed to the traditional quadrature amplitude modulation, while maintaining its spectral efficiency. This allows transmitting the modulated signal with the spectral width, which is equal to the spectral width of the modulating signal, and providing an energy gain of about 3 dB.

The current constant growth in mobile networks’ traffic demands, owing to the popularization of cloud and streaming services on personal devices, requires architectural changes to fulfill all the new 5G mobile network requirements and specifications. Cloud access radio network (C-RAN) architecture in combination with the massive deployment of small cell antenna sites has recently been proposed as a promising solution, though demanding, for high-capacity mobile fronthaul links. An efficient way to perform that connectivity is to make use of the deployed passive optical networks (PONs) where wireless and wired services may be converged for distribution purposes. Non-orthogonal multiple access (NOMA) combined with multi-band carrierless amplitude phase modulation (NOMA-CAP) has recently been proposed as a promising 5G and beyond modulation format candidate to increase the capacity and flexibility of future mobile networks. In this paper, for the first time we 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 power levels—hence doubling the capacity—transmit 15 Gb/s multiplexed with a digital 10 Gb/s fourlevel pulse amplitude modulation (PAM-4) signal for downlink application. The results show that the crosstalk interference can be minimized by controlling the amplitude relation between the NOMA-CAP and PAM-4 signals to maximize the wireless transmission bandwidth. Moreover, successful transmission over 25 km of standard single-mode fiber is also demonstrated with negligible transmission penalty.

We propose a new transceiver solution named KK-CAP-NQAM that combines Kramers-Kronig (KK) reception with carrierless amplitude/phase modulation (CAP) technology. This system's KK receiver operates without extra digital upsampling. © 2020 The Author(s)

We report experimental results of a semiconductor optical amplifier (SOA) for optical amplification in a 50-90 Gb/s IM-DD optical access system using non-orthogonal multiple access multiplexing combined with multi-band carrierless amplitude phase modulation format (NOMA-CAP). Specifically, the SOA has been investigated as both booster and pre-amplifier for downstream applications in PONs. The measured optical power budgets resulting from performing booster amplification and pre-amplification simultaneously, assuming a BER threshold at 2.2 × 10 -3 , are 28.7(23.7) dB and 23.6(18.9) dB at 50(90) Gb/s for the strong and weak NOMA levels, respectively, compared to the budgets for the strong and weak NOMA levels of 12.4(8.7) dB and 9.4(5.2) dB when no optical amplification is used. This work was supported in part by ALLIANCE (TEC2017-90034-C2-2-R) project co-funded by FEDER, the European Union’s Horizon 2020 research and innovation programme under grant agreement no 780997 (plaCMOS), as well as MINECO FPI-BES-2015-074302.

Coherent technologies are exhibiting the flexibility and performance required to address the next generation of optical access networks, where the residential, business and mobile backhaul will converge. The use of these technologies for access networks is approached from several angles, including affordable photonic integrated circuits (PICs) and cost-effective transceivers are met. In this work, we will present different technologies we have been working on lately, as a low cost 2x3 coherent PIC receiver, which allows an increment of the overall capacity of the network. We will also show cost-effective coherent transceiver components, e.g. directly-phase modulated VCSELs transmitters and/or quasi-coherent receivers, which can play an important role in reducing cost while still fulfilling the future capacity. New advanced modulation formats may also contribute to this goal, by allowing the introduction of new concepts as pay-as-you-grow upgrades through the employment of non-orthogonal multiple access (NOMA) technique combined with e.g. carrierless amplitude phase modulation (CAP). Finally, we will also study the use of intensity modulated spectrally efficient formats as OFDM, FBMC, UFMC and GFDM in an optical access network architecture.

A filter-bank multicarrier–quadrature amplitude modulation (FBMC-QAM) system with two prototype filters for transmitting QAM symbol is proposed, and the orthogonality conditions for the FBMC-QAM system without the intrinsic interference is derived. The proposed transmitter performs the individual filtering for the even and odd-numbered sub-carrier symbols, respectively. In order to satisfy the derived orthogonality conditions, we perform a sub-block wise reverse ordering procedure for the outputs of the odd-numbered sub-carrier filter. Also, this paper shows that the proposed FBMC-QAM system satisfies the suggested orthogonality conditions and can use the multiple-input multiple-output transmission schemes as the conventional orthogonal frequency division multiplexing (OFDM) systems. The signal-to-interference power ratio and the bit error rate (BER) for the proposed FBMC-QAM system are evaluated. Numerical results show that the proposed FBMC-QAM system has almost the same BER performance compared with the FBMC-OQAM and OFDM systems.

Large peak-to-average power ratio (PAPR) of the signal is an imperative problem in orthogonal frequency division multiplexing (OFDM) systems, as it impedes the efficient design of their analog front end. Companding is a well-known technique that reduces the PAPR by using a deterministic amplitude transform, which is designed by assuming Rayleigh distribution for the signal amplitude. But in OFDM systems employing higher order QAM, like 16- or 64-QAM, this probabilistic model is insufficient to model the true characteristics of the signal. This is due to the stochastic nature of average symbol power, which alters the complete amplitude distribution from one OFDM symbol to another. This leads to degradation in the companders’ PAPR reduction performance. In this paper, we propose two novel schemes that modify the companding operation to accommodate the randomness of symbol power. Probabilistic analysis of symbol’s average power, in relationship with the amplitude of its constituent samples, is carried out. This yields the theoretical framework employed in the design of the proposed low-complexity solutions. The proposed schemes essentially make the companding operation itself nondeterministic/adaptive, i.e., it adjusts to comply with the changing symbol amplitude distribution during application runtime.

Multi-dimensional carrierless amplitude phase (CAP) modulation attracts a lot interest in recent optical communications as an advanced modulation format with improved performance. In this paper, we have demonstrated a multiband three-dimensional CAP (3D-CAP) modulation scheme and investigated its applications in short reach optical communication systems. Corresponding digital filters are designed by minimax algorithm with additional linear constraint to avoid the coding intersymbol interference. The performance of the digital filters is analyzed for optical fiber links with data rate over 100 Gb/s based on simulations. Similar to discrete multitone technique, several independent bands can be loaded with different 3D-CAP signals in the proposed multiband 3D-CAP system, offering improved tolerance to non-flat channels. 2-km single mode fiber transmission at total bit rate of 112.5 Gb/s is investigated through simulations and the results indicate better performance of multiband 3D-CAP compared with conventional 3D-CAP in short reach optical communication.

We consider the design of the optimum detector for two-dimensional amplitude/phase modulated signals received in additive white Gaussian noise (AWGN) and a Gaussian distributed phase reference error (PRE) due to imperfect carrier phase estimation. We propose a novel approach of using the amplitude and phase information of the received signal, based on viewing the AWGN as an equivalent additive observation phase noise (AOPN) whose statistics is derived in our earlier work. This allows the AOPN to be combined with PRE, and the maximum $a\ posterior$ probability (MAP)/maximum-likelihood (ML) detection scheme to be readily derived in amplitude-phase form. This amplitude-phase approach is simpler and more convenient than the conventional method of using the in-phase and quadrature components of signals in phase noise. For $M$ -ary phase-shift keying, which only has one ring of signal points, the ML detector here turns out to be the same as the conventional minimum Euclidean distance (MED) detector which is derived without taking the PRE into account, and leads to angular bisector decision boundaries (DB). However, for constellations which have multiple rings, e.g., $M$ -ary quadrature amplitude modulation ( $M$ -QAM) and amplitude phase-shift keying ( $M$ -APSK), the ML detector here is very computationally inefficient. Thus, simpler and closed-form approximations to the ML detector for equiprobable signals are given, which can be easily implemented online. All these simplified ML detectors are shown via simulations to perform almost the same as the exact one and perform much better than the MED detector. The approximate ML DB for both 8-star QAM and rotated 8-star QAM are illustrated as examples and shown to be not necessarily straight lines. As the variance of PRE or the signal-to-noise ratio (SNR) or both increases, the DB between two signal rings asymptotically becomes circular. This leads to an annular sector as the decision region for each signal point. For annular-sector decision regions, simple, accurate, and closed-form approximations to the symbol error probability (SEP) are obtained for both 8-star QAM and the rotated case, 16QAM and even general $M$ -APSK. These expressions provide explicit insight into how the PRE variance affects the performance. Within a wide range of PRE variances, our SEP approximations agree very well with the Monte Carlo simulations for all SNR values of interest. For the special case of an $M$ -APSK constellation which has the same number of points and the same phase values on each ring, such as 8-star QAM, one of the suboptimal ML detectors further simplifies to a structure that performs ring detection and phase detection separately, and the decision regions are always annular sectors.

We propose and fully analyze a compact structure for DAC-free pure optical QAM modulation. The proposed structure is the first ring resonator-based DAC-free QAM modulator reported in the literature, to the best of our knowledge. The device consists of two segmented add-drop Mach Zehnder interferometer-assisted ring modulators (MZIARM) in an IQ configuration. The proposed architecture is investigated based on the parameters from SOI technology where various key design considerations are discussed. We have included the loss in the MZI arms in our analysis of phase and amplitude modulation using MZIARM for the first time and show that the imbalanced loss results in a phase error. The output level linearity is also studied for both QAM-16 and QAM-64 not only based on optimizing RF segment lengths but also by optimizing the number of segments. In QAM-16, linearity among levels is achievable with two segments while in QAM-64 an additional segment may be required.

This paper proposes a new technique for soft information relaying, which is based on a soft decode–compress–forward relay protocol. The proposed system provides a means of using distributed low-density parity-check (LDPC) coding in conjunction with higher order modulation, such as pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM), which is effective even under poor source–relay link conditions. Ordinarily, such schemes suffer from error propagation to the destination caused by incorrect decoding at the relay when the signal-to-noise ratio (SNR) on the source–relay link is low; however, our system avoids this problem by generating soft versions of the additional (parity-bearing) PAM symbols for transmission from the relay. The proposed technique of soft compression does not suffer from parity log-likelihood ratios (LLRs) converging to zero, as do many soft re-encoding techniques for turbo and LDPC codes. In the case of Gray-coded PAM/QAM signaling, we also propose a method of performing exact expectation-based soft modulation with low computational complexity. Furthermore, we propose a new model, which we refer to as the soft scalar model, for the overall source-to-destination channel encountered by the constellation symbols, and this model is used at the destination to compute LLRs for joint decoding of the distributed LDPC code. Simulation results demonstrate that the proposed scheme can provide good coding gain, diversity gain, and spectral efficiency under poor source–relay SNR conditions.

We report on the first experimental demonstration of carrierless amplitude/phase modulation in a flexible multiband approach for ultrawideband high-data-rate wireless communications. An effective bitrate of 2 GB/s is achieved while complying with the restrictions on the effective radiated power established by the Russian State Commission for Radio Frequencies. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1603–1607, 2016

Optical technologies have been widely studied to satisfy the interconnect demand in high-performance computers and data centers, and free-space optical interconnects have been investigated for flexible card-to-card applications. To increase the interconnect speed and range, in this Letter we propose a reconfigurable free-space optical interconnect with 16-carrierless-amplitude-phase (16-CAP) symbol modulation and filter-enhanced spatial modulation (FE-SM). The 16-CAP increases the interconnect speed in the symbol domain, and the FE-SM scheme increases the speed in the spatial domain, even under highly correlated optical interconnect channels. A 50 Gb/s reconfigurable optical interconnect is experimentally demonstrated. The results show that the impact of FE-SM on the bit error rate (BER) is negligible, while the speed is significantly improved. Compared with the conventional SM scheme, the BER is improved by over one order of magnitude. The proposed scheme is also capable of extending the interconnect range. The results show that over 70% range extension and 50% speed increase can be achieved simultaneously. The proposed scheme with a 16-CAP and FE-SM provides a promising solution in free-space optical interconnects.

Low-complexity carrier phase recovery (CPR) for M-ary offset quadrature amplitude modulation (OQAM) formats is proposed and numerically verified, based on the technique of constellation classification. Although the OQAM signal has very poor tolerance to the laser linewidth due to the phase noise-induced crosstalk, we find that both even and odd samples of OQAM signal only have conventional constellation rotation with respect to phase noise. Through linear fitting of the classified constellation, carrier phase estimation can be derived from the slope of linear fitting function. Compared with our recently proposed modified blind phase search scheme, the computational complexity (CC) of proposed CPR does not increase much with the OQAM modulation level of M. Taking the CPR of 16-OQAM into account, we show that the CC can be significantly reduced by a factor of 8.47 (or 7.34) in the form of multipliers (or adders) with performance comparable to MBPS (B = 24) under the condition of Δf × T S = 5 × 10 -6 . In particular, a tolerance of linewidth and symbol duration product of 8 x 10-5, under the condition of CD = 300 ps/nm and DGD = 10 ps, can be secured for 16-OQAM, given 0.7-dB required-OSNR penalty.

In this letter, we experimentally demonstrate a 1024-quadrature-amplitude-modulation (QAM) optical camera communications (OCC) system using a dual light-emitting diode (LED) and a commercial digital single-lens reflex camera. An undersampled QAM subcarrier modulation (UQAMSM) is proposed to support a high-efficiency and non-flickering OCC system. Owing to the built-in gamma correction function of the camera, pre- and post-compensation techniques are successfully applied to compensate for the non-linear impairment. A dedicated framing structure is also designed to support the proposed UQAMSM and compensation techniques. The experimental results show that this system is able to achieve a data rate of 500 b/s using a dual LED and a 50 ft/s commercial camera over a transmission span of 1.5 m, which is suitable for the transmission and reception of location-based information.

In this letter, we propose a quasi-quadrature phase shift keying (QPSK) partitioning to replace the conventional QPSK partitioning in the first stage of the carrier phase estimation (CPE) algorithms for 32-QAM optical systems. By using the proposed quasi-QPSK-partitioning method, the ability of the CPE algorithms to track changes of phase is greatly enhanced. For 1-dB SNR penalty at bit error rate of 1E-2, the proposed method can achieve an improvement of 85% in combined linewidth symbol duration product tolerance when compared with the conventional method for single stage. With the help of the fine estimation stages, the maximum tolerable combined linewidth symbol duration product can be up to 5.1E-5.

A novel optical high order quadrature amplitude modulation (QAM) transmission system for high-speed short links is described. Dual-polarization (DP) QAM and twin local lights are generated from one light source in the system, and these lightwaves are simultaneously transmitted via standard single mode fiber. The receiver can be constructed simply because it does not require a coherent light source under wavelength control. The system enables a 3.1 Gbaud DP-16-QAM signal to be successfully demodulated after 80-km transmission without using an optical dispersion compensator. It also achieves high tolerance against phase noise in the signal light source.

A new coded modulation scheme is proposed. At the transmitter, the concatenation of a distribution matcher and a systematic binary encoder performs probabilistic signal shaping and channel coding. At the receiver, the output of a bitwise demapper is fed to a binary decoder. No iterative demapping is performed. Rate adaption is achieved by adjusting the input distribution and the transmission power. The scheme is applied to bipolar amplitude shift keying (ASK) constellations with equidistant signal points and it is directly applicable to two-dimensional quadrature amplitude modulation (QAM). The scheme is implemented by using the DVB-S2 low-density parity-check (LDPC) codes. At a frame error rate of 1e-3, the new scheme operates within less than 1 dB of the AWGN capacity 0.5log2(1+SNR) at any spectral efficiency between 1 and 5 bits/s/Hz by using only 5 modes, i.e., 4-ASK with code rate 2/3, 8-ASK with 3/4, 16-ASK and 32-ASK with 5/6 and 64-ASK with 9/10., 13 pages, 11 figures, 10 tables

A theoretical model for transmission of advanced modulation schemes [pulse amplitude modulation (PAM), carrierless amplitude-phase (CAP), and discrete multitone (DMT)] in visible light communications (VLC) link using white phosphorescent LEDs is presented. The model extends and adapts the Randel et al. , framework for advanced modulation format transmission in intensity-modulated direct-detection for the VLC channel. The main contributions are: CAP modulation, effect of transmit signal spectral shaping in PAM and CAP, analytical calculation of crest factor for CAP, and analysis of inter-symbol and cross-carrier interference due to an insufficient cyclic-prefix in DMT. Based on this model, the impact of blue filtering at the receiver is studied in the context of spectrally efficient modulation formats. The results indicate that blue filtering has a marginal effect on the performance for all the investigated modulation formats, while PAM with decision feedback equalizer shows the best performance. Without blue filtering, slightly higher data rates can be achieved, but at a price of extensive signal processing.

As a new three-dimensional (3-D) modulation, Polarization Quadrature Amplitude Modulation (PQAM) can be regarded as the combination of Pulse amplitude modulation (PAM) and Quadrature Amplitude Modulation (QAM) Modulation. It can better improve the digital communication efficiency and reduce the Symbol error rate (SER) of the system than one-dimensional or two-dimensional modulation scheme. How to design a feasible constellation is the most concerned problem of PQAM currently. This paper first studies the relationship between the SER theoretical value of PQAM and the distribution of M and N, proposes a new M, N allocation scheme. Secondly, a new and straightforward design method of constructing higher-level 3-D signal constellations, which can be matched with the PQAM, and the constellation can divided into three different structures according to the ary for PQAM. Finally, the simulation results show that: in PQAM system, the modulation scheme and the constellation mapping scheme are proposed in this paper which can effectively reduce the system SER and improve the anti-noise performance of the system.

We numerically and experimentally investigate and compare photonic constant- and multi-amplitude quadrature-amplitude-modulation (QAM) vector signal generation at radio frequency (RF) bands enabled by a Mach-Zehnder modulator (MZM)-based optical carrier suppression (OCS) modulation. In order to attain an electrical vector RF signal displaying multi-amplitude QAM modulation, such as 8 QAM and 16 QAM, after square-law photodiode detection, the driving RF signal carrying multiamplitude QAM transmitter data, should be both amplitude- and phase-precoded before used to drive the MZM. However, for constant-amplitude QAM modulation, such as quadrature-phase-shift-keying (QPSK), only phase precoding is needed. We experimentally demonstrate 1-GBd vector signal generation at 12 GHz enabled by an MZM-based OSC modulation, adopting QPSK, 8 QAM, and 16 QAM modulation, respectively. We also experimentally compare the bit error rate performance of the three different vector signals, and the QPSK case is the best, while the 16 QAM case is the worst.

We propose a novel two-stage carrier phase estimation (CPE) algorithm for 64-ary quadrature amplitude modulation (64-QAM) coherent optical systems. It makes use of a new quadrature phase shift keying partitioning (QPSK-partitioning) approach and an enhanced maximum likelihood (ML) detection. 36/64 of the 64-QAM symbols are statistically employed by the modified QPSK-partitioning approach to estimate phase noise in the first stage. The proposed enhanced ML detection is used in the second stage to improve linewidth tolerance performance. The simulation results show that, our proposed VVPEc1&c2 + EML algorithm can achieve much higher linewidth tolerance performance than the modified V&V + MLE algorithm at high laser linewidth level. A combined laser linewidth symbol duration product as high as $5.6 \times 10^{- 5} $ is achieved by the proposed two-stage CPE algorithm at a target BER of $1 \times 10^{- 2} $ with 1 dB SNR sensitivity penalty.

A novel low-complexity two-stage digital feed-forward carrier phase estimation algorithm based on the rotation of constellation points to remove phase modulation for a 64-ary quadrature amplitude modulation (QAM) system is proposed and analyzed both experimentally and through numerical simulations. The first stage is composed of a Viterbi and Viterbi (V&V) block, based on either the standard quadrature phase shift keying (QPSK) partitioning algorithm using only Class-1 symbols or a modified QPSK partitioning scheme utilizing both Class-1 and outer most triangle-edge (TE) symbols. The second stage applies the V&V algorithm after the removal of phase modulation through rotation of constellation points. Comparison of the proposed scheme with constellation transformation, blind phase search (BPS) and BPS+MLE (maximum likelihood estimation) algorithm is also shown. For an OSNR penalty of 1 dB at bit error rate of $10^{-2}$ , the proposed scheme can tolerate a linewidth times symbol duration product ( $\Delta \hbox{$\nu $}\cdot T_{s}$ ) equal to $3.7\times 10^{-5}$ , making it possible to operate 32-GBd optical 64-QAM systems with current commercial tunable lasers.

In this letter we propose simple and robust features to distinguish continuous-phase frequency shift keying from quadrature amplitude modulation and phase shift keying modulations. The features are based on sample mean and sample variance of the imaginary part of the product of two consecutive complex signal values. Root raised cosine pulses are used to generate the linearly modulated signals. Support vector machines are employed to distinguish the signals. One benefit of using support vector machines is that it requires very few realizations for training. Moreover, no a priori information is required about carrier amplitude, carrier phase, carrier offset, symbol rate, pulse shape, initial symbol phase (timing offset) and channel impulse response. Effectiveness of the features and signal separation by support vector machines is tested by observing the joint effects of additive white Gaussian noise, carrier offset, lack of symbol and sampling synchronization, and either fast or slow fading. In the course of doing that, the proposed classifier is compared to the wavelet based classifier, equipped by support vector machines.

Four-dimensional (4-D) set-partitioning quadrature amplitude modulation (4-D SP-QAM) has emerged as an interesting option for cost- and resource-efficient realization of bandwidth variable transceivers in elastic optical networks. In this invited paper, we review the principles for generation of 4-D SP-QAM signals, and describe options for forward error correction coding of 4-D SP-QAM signals and for realization of the digital signal processing in the coherent receiver. Furthermore, we report on the experimental realization of 4-D 512-ary and 2048-ary SP-QAM signals at a symbol rate of 28 GBd and investigate their performance in a Nyquist-WDM scenario. In transmission experiments over standard single-mode fiber, we compare the reach and spectral efficiency of five-carrier Nyquist-WDM signals modulated by various 4-D SP-QAM formats and polarization-division multiplexed (PDM) QAM formats. Of these modulation formats, the one with the lowest spectral efficiency is 128-ary SP-QAM encoding 7 bits/4-D symbol and the one with the highest spectral efficiency is PDM-64QAM encoding 12 bits/4-D symbol. By switching the modulation format, the spectral efficiency can be optimized for a specific reach with a granularity of 0.56 bit/s/Hz.

Next generation wireless communication systems face many challenges to increase the capacity and spectral efficiency of current solutions. The worldwide mobile data traffic increased 4000-fold over the last decade, and is forecast a 7-fold increase between 2016 and 2021. To cope with these stringent demands, prospective solutions are millimeter-wave (mmWave) technology and ultradense small cell networks, given that today most of the mobile traffic is offloaded from mobile networks, i.e., most of mobile users are connected to fixed networks. In addition, enabled by the fast development of electronics, digital signal processing has become essential to enhance the capacity and the performance of current communication systems. In this paper, by using the benefits of multiband modulation schemes and independent sideband (ISB) modulation, high-speed mmWave wireless transmissions in the D-band (110-170 GHz) are reported. D-band radio frequency carrier is generated by means of optical heterodyning, and ISB modulation is applied by means of the Hilbert transform and a double-nested Mach-Zehnder modulator. Total data rates up to 352 Gb/s and spectral efficiencies up to 7.7 bit/s/Hz are experimentally achieved in a single 2 × 2 multiuser multiple-input multiple-output system.

The half-cycle subcarrier modulation (SCM) with 64/128-quadrature-amplitude modulation (QAM) format in short-reach optical communications system is experimentally demonstrated. Without utilizing erbium-doped fiber amplifier, we have demonstrated the transmission of single-polarization 64/128-QAM half-cycle SCM using cost-effective directly modulated laser and also transmission of dual-polarization signal using a pair of external modulators. The experiment is enabled by spectral-efficient overlap frequency-domain-equalization and polarization division multiplexing channel estimation based on a pair of time-interleaved training sequences. Utilizing an electrical bandwidth of only 3 GHz, the bit-error rate (BER) of the 32.5-Gb/s dual-polarization 64-QAM format after 20-km fiber transmission is under $3.8 \times 10^{-3}$ , and BER of the 38-Gb/s dual- polarization 128-QAM format is under $2.4 \times 10^{-2}$ .

A simulation-based assessment is made of the benefits of using advanced modulation formats including pulse amplitude modulation (PAM) and carrierless amplitude/phase modulation (CAP) to ease laser control requirements of a recently proposed novel uncooled multiple-input and multiple-output wavelength-division multiplexing (WDM) system. At a per channel bit rate of 25 Gb/s, the spectral efficiency improvements inherent to these schemes provide additional optical system power margin over non-return-to-zero (NRZ) modulation (0.4 dB for PAM-4 and 4.4 dB for CAP-16) for a link distance of 20 km. This allows the minimum channel spacing between channels to be reduced from 0.4 nm (NRZ) to 0.3 nm for PAM-4 and to 0.14 nm for CAP-16, this in turn allowing for a more stable operating region to be realised. Compared with a traditional 16 × 25 Gb/s dense WDM system, a power consumption saving of 30% can be realised using NRZ whereas PAM-4 and CAP-16 offer 29 and 27% savings, respectively.

A multistage carrier phase estimation (CPE) scheme for any $m$ -ary quadrature amplitude modulation (QAM) formats is proposed and analyzed in coherent optical communication systems. The scheme is based on the crossed constellation transformation algorithm that is transparent to all modulation formats whose constellations are on the square grid. Simulation results show that the hardware complexity of the proposed CPE scheme can be significantly reduced by the group factors of 6.1/8.6, 4.7/6, and 2.6/3.3 (in the form of multipliers/adders) for 32-QAM, 64-QAM, and 128-QAM compared with the single-stage blind phase search algorithm. In 32-QAM, 64-QAM, and 128-QAM, coherent optical communication systems with 1-dB SNR penalty at bit error rate is $1\times 10^{-2}$ , the comparable linewidth symbol duration can be reached with the values of $6\times 10^{-5}$ , $4\times 10^{-5}$ , and $8\times 10^{-6}$ , respectively.

Carrierless amplitude and phase (CAP) modulation is generating increasing interest for short-reach optical communications. Polarization multiplexing (PolMux) is a good way to improve the CAP system’s data rate further with the limited bandwidth of electrical devices. In this Letter, we experimentally demonstrate a 56 Gb/s direct-detection PolMux CAP system over a 15 km fiber link for the first time, to our best knowledge. Two-band CAP modulation with different modulated orders for each band is employed. An optical filter at the receiver is utilized to realize the polarization separation. No extra digital signal processing for polarization-dependent distortion is required.

An equalization algorithm is proposed for carrier-less amplitude and phase (CAP) modulation system, which is regarded as a good candidate for short range optical communications, like electrical power optical fiber communication, optical access network. The constant module algorithm (CMA) combined with support vector machine (SVM) performs the equalization function. The simulation system was setup for both single-band 16-CAP signal at 10Gbps and multi-band M-CAP (4-CAP, 16-CAP, 64-CAP) signal at 100Gbps. After the CMA-SVM equalization, the impaired CAP signals are compensated effectively. The phase rotation is recovered and the centralization of each constellation points is improved obviously, which demonstrate the feasibility of the proposed equalization algorithm.

Quadrature Amplitude Modulation (QAM) is an important modulation scheme with many practical applications, including current and future wireless technologies. The performance of a mobile communication system can be improved by using a doubly iterative decoding scheme for space-time turbo codes with a large number of transmit and receive antennas, where the decoder uses preliminary soft values of the coded symbols. In this paper, the soft estimates for a high QAM order are derived and explained.