Carrierless Amplitude Phase Modulation Research Articles

90-m/560-Mbps underwater wireless optical communication utilizing subband multiple-mode full permutation CAP combined with an SNR-weighted detector and multi-channel DFE.

In this paper, a joint signal processing scheme including a subband multiple-mode full permutation carrierless amplitude phase modulation (SMMP-CAP), signal-to-noise ratio weighted detector (SNR-WD), and multi-channel decision feedback equalizer (MC-DFE) is proposed to mitigate the bandwidth limitation of a high-speed long-reach underwater wireless optical communication (UWOC) system. Referring to the trellis coded modulation (TCM) subset division strategy, 16 quadrature amplitude modulation (QAM) mapping set is divided into four 4-QAM mapping subsets by SMMP-CAP scheme. An SNR-WD and an MC-DFE are employed to enhance the demodulation effect of this system in a fading channel. In a laboratory experiment, the minimal required received optical powers (ROPs) for data rates of 480 Mbps, 600 Mbps, and 720 Mbps, at hard-decision forward error correction (HD-FEC) threshold of 3.80 × 10-3, are -32.7 dBm, -31.3 dBm, and -25.5 dBm, respectively. Moreover, the proposed system successfully achieves a data rate of 560 Mbps in a swimming pool with a transmission distance up to 90 m and a total attenuation measured to be 54.64 dB. To the best of our knowledge, this is the first time to demonstrate a high-speed, long-distance UWOC system by employing an SMMP-CAP scheme.

Performance Evaluation of NRZ-OOK and Carrier-Less Amplitude Phase Modulation in Li-Fi Environment

Light Fidelity (Li-Fi) is a wireless technology that utilizes light emitting diodes to convey data. Li-Fi has emerged as a promising alternative to radio frequency communication technology in recent years. This paper examines the performance characterisation between NRZ-OOK and carrier-less amplitude-phase modulation (CAP-2, CAP-4 and CAP-8), within a simulated Li-Fi environment. For the parameters of interest, the eye pattern, bit error rate (BER) and constellation diagram are reported. As no distance is specified in the simulation, the BER for CAP is zero, allowing an ideal transmission to be emulated. The scatter diagram increases as the number of CAP modulations increases. For the eye pattern, CAP modulation provides a better visual representation of how noise might affect system performance compared to OOK modulation.

Decision Feedback Kurtosis Minimum Crosstalk Mitigation in Super-Nyquist Multiband CAP Systems

In multiuser access visible light communication (VLC) systems, many multiplex techniques can be utilized to fully exploit the limited bandwidth. In frequency-division multiplexing systems, one possible solution is to dynamically allocate limited bandwidth resources for users to support multiple-service access. To enable high-speed transmissions, the super-Nyquist multiband concept has been proposed in recent years. Specifically, the center frequency spacing is narrowed, and the subcarriers are nonorthogonally overlapped to enable more services and users in multiband systems. Studies have shown that this strategy can support higher spectral efficiency (SE) while simultaneously, introducing intersymbol interference (ISI) and intercarrier interference (ICI). Therefore, a well-designed ICI mitigation scheme is required. In multiband carrierless amplitude phase ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -CAP) modulation systems, it is technically challenging to achieve the SE beyond one baud/s/Hz under the pre-forward error correction (pre-FEC) threshold without increasing the modulation order. Inspired by the distinctive pulse shaping filter (PSF) structure in a non-orthogonal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -CAP scheme, we propose the iterative decision feedback kurtosis minimum (DFKM) scheme and achieve the super-Nyquist SE of approximately 1.06 baud/s/Hz. In contrast to existing ICI mitigation schemes, the theoretical framework reveals that symbol-level crosstalk filters are indispensable to reap the benefit of super-Nyquist transmission, not limited to VLC.

Subcarrier Index Modulation Super-Nyquist Carrierless Amplitude Phase Modulation for Visible Light Communication Systems

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 ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -CAP) scheme in bandlimited visible light communication (VLC) systems. By innovatively combining the index modulation technique with the non-orthogonal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -CAP technique, the SIM-SCAP scheme can sustain higher system SE than the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -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.

50 Gb/s Transmission using OSSB-MultiCAP Modulation and a Polarization Independent Coherent Receiver For Next-Generation Passive Optical Access Networks

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.

A Bat Optimized Reliable Elm (Bore) For an Efficient Throughput of Cap-VLC System

Indoor Visible light communication (VLC) is considered one of the most famous communication technologies in today’s industrial life, showing importance in data broadcasting and glowing instantly with the cost-effective source of light-emitting diode (LED). This kind of high-speed network’s properties is controlled by the source device’s shortened bandwidth (LED). Therefore, it is considering highly efficient modulation technique and extreme adaptive demodulation technique for better data rate in visible light communication. Carrier less amplitude-phase (CAP) modulation is an eminent modulation scheme that increases implementation ease and places good position inefficiency. Somehow, the CAP-VLC system’s impact is signal jamming, poor sensitivity, scattering, and noise issues. To overrule this problem, it witnesses the implementation of VLC system with CAP modulation using advanced neural network system of High-Speed Feed Forward Neural Network, which works based on the principle of Extreme Learning Machine (ELM). The same is adopted and extended using the BAT algorithm. Along with this, algorithm optimization technique has been integrated to enhance the entire CAP-VLC system’s performance. Altogether, it can be named as bat-optimized reliable ELM (BORE). The proposed new learning-based algorithm for CAP-VLC has shown better performance in received power distribution of 90.6% at various modulation indexes, better BER of about 97.6% in the voltage level of 3V, and different distances between transceivers, respectively.

200-Gb/s Direct Modulation of a 50-GHz Class Laser With Advanced Digital Modulations

Directly modulated lasers (DML) dominate the short reach optical interconnect market. For years, the bandwidth of commercial DMLs has been limited to a level of 25 GHz, which can support a speed up to around 100 Gb/s via advanced modulations like Nyquist-shaped 4-ary pulse amplitude modulation (PAM-4), carrier-less amplitude phase (CAP) modulation, subcarrier multiplexing, and discrete multitone (DMT). To scale with the capacity evolution of interconnect applications, it is in urgent demand to develop DMLs operated at 50G class and even beyond. In this article, we exploit a newly designed 50G-class short-cavity distributed Bragg reflector (DBR) laser, called the two- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">κ</i> DBR laser, and demonstrate its capability of supporting 200 Gb/s per wavelength direct modulation and direct detection transmissions. Combining high-speed electronics with the 50G-class DML, we demonstrate a variety of advanced digital modulations including Nyquist-shaped 100-GBaud PAM-4, 80-GBaud PAM-8, and 50-GHz DMT signals, with the maximum net bit rate of 236 Gb/s. The DML exhibits an ultra-low chirp parameter of 1.0, which enables isolator-free operation and dispersion-tolerant transmission over tens of kilometers at O-band.

Ultra‐wideband technology: Prospective solution for 5G ultra‐small cell networks

SummaryExhaustive research is being done to establish the technologies and standards of the fifth generation (5G) of wireless communication systems. Some of the most challenging requirements of 5G systems are to increase the spectral efficiency and the capacity by a factor of 10 and 1,000, respectively. New technologies must offer an adequate framework for the 5G uses cases, which will enable higher capacities and the flexibility to adapt to dynamic scenarios. To cope with these challenging demands, a compelling approach is to exploit the current radio service bands by means of spectrum sharing and cooperation techniques, which alleviate the bandwidth requirements. In addition, advanced modulation schemes have a fundamental role in ensuring the best usage of the spectrum available in band‐limited systems. In this manuscript, we present the ultra‐wideband (UWB) technology as a prospective solution for 5G picocells and femtocells. Its main feature is its capability to operate simultaneously, without introducing interference, with current radio services on an unlicensed basis. We report experimental results reaching data rates up to 35 Gbit/s using the multiband approach of carrierless amplitude phase (MB‐CAP) modulation. To validate the versatility of the proposed system, our experimental tests were performed under the UWB regulations defined by the United States' Federal Communications Commission (FCC), the European Electronic Communications Committee (ECC), and the Russian State Committee for Radio Frequencies (SCRF). The regulations chosen provide diversity enough to demonstrate the capacity of MB‐CAP modulation to comply with worldwide regulations.

Enhanced 3D-CAP modulation with information-inserted time slots for seven-core fiber transmissions.

An enhanced three-dimensional carrier-less amplitude phase (3D-CAP) modulation with information-inserted time slots is proposed in this paper. Compared with the traditional 3D-CAP, the proposed scheme can reduce the value of the up-sampling factor by loading information on the time slots position, thus achieving better bit error rate (BER) performance under the same bit rate. An experiment demonstrating 43.75 Gb/s MIMO-free transmission employing the proposed enhanced 3D-CAP modulation over 2 km weakly coupled 7-core fiber is successfully carried out. The experimental results show that the difference between the best and worst core is about 1.7 dB in receiver sensitivity at a BER of 1 × 10-3 due to the geometrical reason, and the proposed scheme outperforms the traditional 3D-CAP-16 by 2.7 dB in core-1.

Optical Power Budget Enhancement in 50–90 Gb/s IM-DD PONs With NOMA-CAP and SOA-Based Amplification

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 $2.2\times 10^{-3}$ , 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.

Zero Guard Band Multi-Twin-SSB System in Single Fiber Bidirectional PON Transmission

We propose a novel zero guard band (ZGB) multi-twin-SSB bidirectional passive optical network system which combines the multiband carrier-less amplitude phase and twin single sideband (SSB) modulation techniques. The multi-twin-SSB signal is generated at the downlink transmitter side with zero guard band between the left-sideband and right-sideband. A weak local oscillator which is extracted from the uplink optical source aids the downstream signal detection. Kramers-Kronig algorithm is used at both downlink and uplink receiver sides to reconstruct the SSB signal and eliminate the signal-signal beat interference. The downstream and upstream signals are transmitted in a single fiber without any spectral overlap between them and the Rayleigh backscattering noise is removed by the optical band-pass filter. The proposed scheme is extensively investigated and analyzed with four sub-bands using 50 Gbps 16-QAM modulation for each sub-band over a bidirectional 50 km transmission. The results show that, compared with the conventional multi-twin-SSB scheme, the proposed ZGB multi-twin-SSB scheme can improve the spectral efficiency by about 11%. The required optical signal to noise ratio (OSNR) and the required received optical power (ROP) can be reduced by more than 15 dB and 7 dB respectively at the 7% hard decision forward error correction (HD-FEC) threshold (bit error rate of $3.8\times 10^{-3}$ ), respectively. For the uplink transmission, the required ROPs for the inner and outer sub-bands at 7% HD-FEC are about −10 dBm and −11 dBm, respectively. And the signal to noise ratio to the corresponding ROPs for the inner and outer sub-bands are 15.4 dB and 15.3 dB, respectively.

Three-Dimensional Probabilistically Shaped CAP Modulation Based on Constellation Design Using Regular Tetrahedron Cells

This article proposes a novel 3-D probabilistically shaped carrier-less amplitude phase (3D-PS-CAP) modulation based on constellation design using regular tetrahedron cells, which is capable of being applied in short reach communication. Geometric shaping based on regular tetrahedron cells for 3D constellation, combined with probabilistic shaping, can increase the constellation figure of merit (CFM) of the 3D constellation and improve the bit error rate (BER) performance of the 3D-PS-CAP modulation scheme. An experiment demonstrating 4 Gb/s 3D-PS-CAP-16 data transmission over 25 km standard single-mode fiber (SSMF) is successfully carried out. Results show that at the BER of $\text{1} \times \text{10}^{ -\text{3}}$ , the proposed uniform 3D-CAP-16 outperforms the traditional counterparts by 1.1 dB receiver sensitivity gain. Moreover, in the entropy of 3.6 bits/symbol, the proposed 3D-PS-CAP-16 obtains 0.6 and 1.0 dB receiver sensitivity gains compared to the two traditional 3D-PS-CAP-16, respectively. The experimental results indicate the proposed scheme a bright prospect for future short reach communication.

A Probabilistically Shaped CAP Modulation Method Employing Multiple Subsets Mapping With Symbol Classification for a Short Reach Communication

This paper proposes a novel probabilistically shaped carrierless amplitude/phase (CAP) modulation method employing multiple subsets mapping with symbol classification for a short reach communication. This method can classify the original data into multiple subsets of symbols carrying different amounts of bits, and then, map the symbols with different probabilities in the subsets to the different regions of the constellation to reduce the average signal power, thus improving the system bit error rate (BER) performance. An experiment demonstrating 21.8 Gb/s PS-CAP-12 data transmission employing the proposed method over 25 km standard single-mode fiber is successfully carried out. Experiment results show that the proposed scheme outperforms the traditional CAP-16 modulation by 2 dB improvement in receiver sensitivity at a BER of 1 × 10 -3 , which suggests the superiority of our proposed scheme for a future short reach communication.

Real-time investigation of CAP transceivers with hybrid digital equalization for visible light communication

In a practical light emitted diodes (LEDs)-based visible light communication (VLC) system, high-speed transmission is generally limited by the LED bandwidth. To address the bandwidth limitation, a hybrid digital linear and decision-feedback equalization (DFE) is investigated to improve the transmission performance (or spectral efficiency) in the carrier-less amplitude phase modulation (CAP)-based VLC systems. A real-time CAP-VLC transceiver with the hybrid digital equalization is designed, based on which 200 Mb/s transmission is successfully demonstrated over a 15 m VLC link with the commercial red LEDs (bandwidth: 6.5 MHz). In the real-time CAP-VLC system, the baseline wander (BLW) is observed, due to the removal of the low-frequency components with a direct current (DC) block. The BLW effect can be mitigated by increasing the roll-off factor. However, this roll-off factor affects the equalization performance, due to an increased loss in the signal spectrum beyond the system bandwidth. Optimization of the roll-off factor and filter length is required. Experimental results show that, with the optimized real-time transceiver design, the hybrid Wiener/recursive least squares (RLS) and DFE significantly improves the error vector magnitude (EVM) performance compared with the DFE. In addition, the digital signal processing (DSP) complexity is discussed.

Enhanced performance of odd order square geometrical shaping QAM constellation in underwater and free space VLC system

Visible light communication(VLC) employing light-emitting diodes(LED) as light source has become a promising field for underwater wireless communication. However, due to the complex underwater environment and scattering, absorption and diffusion effects during optical transmission in water, the underwater VLC system will suffer from poor SNR and highly nonlinear distortion. In this paper, we proposed and experimentally demonstrated a novel Square Geometrical Shaping(SGS) odd order QAM discrete multitone(DMT) and carrier-less amplitude phase(CAP) modulation based VLC system. Unlike to traditional odd order QAM constellation aiming at the minimum Euclidean distance but without Gray coding at edge constellation points, the new SGS constellation boasts acceptable Euclidean distance and thoroughly Gray coding for every constellation point. Therefore, the system performance can be effectively enhanced by SGS constellation for low SNR and high nonlinearity cases. Both numerical and experimental results verify that SGS 32QAM and 128QAM constellations can outperform traditional QAM constellation by mitigating nonlinearity in a blue LED based underwater and free space VLC system using DMT modulation or CAP modulation. By employing SGS 128QAM, we successfully demonstrate 2.534Gb/s 1.2meter underwater transmission at the driving voltage of 1.1Vpp.

Enhanced performance of a multiband super-Nyquist CAP16 VLC system employing a joint MIMO equalizer.

In this paper, we have experimentally demonstrated the feasibility of a LMS-Volterra based joint MIMO equalizer in multiband super-Nyquist carrierless amplitude phase modulation visible light communication system. To obtain higher spectrum efficiency, overlapping between different sub-bands is introduced in this experiment. By using joint MIMO equalizer, an aggregate data rate of 1.26 Gb/s is successfully achieved in 1-m indoor free space transmission with the BER below the 7% FEC limit of 3.8 × 10-3. To our best knowledge, this is the first time that our proposed joint MIMO equalizer is used to equalize multiband super-Nyquist data in VLC system.

A Carrierless Amplitude Phase (CAP) Modulation Format: Perspective and Prospect in Optical Transmission System

The explosive demand of broadband services nowadays requires data communication systems to have intensive capacity which subsequently increases the need for higher data rate as well. Although implementation of multiple wavelengths channels can be used (e.g. 4 × 25.8 Gb/s for 100 Gb/s connection) for such desired system, it usually leads to cost increment issue which is caused by employment of multiple optical components. Therefore, implementation of advanced modulation format using a single wavelength channel has become a preference to increase spectral efficiency by increasing the data rate for a given transmission system bandwidth. Conventional advanced modulation format however, involves a degree of complexity and costly transmission system. Hence, carrierless amplitude phase (CAP) modulation format has emerged as a promising advanced modulation format candidate due to spectral efficiency improvement ability with reduction of optical transceiver complexity and cost. The intriguing properties of CAP modulation format are reviewed as an attractive prospect in optical transmission system applications.

Nonorthogonal Multiple Access and Carrierless Amplitude Phase Modulation for Flexible Multiuser Provisioning in 5G Mobile Networks

In this paper, a combined nonorthogonal 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 NOMA-CAP system consists of six 1.25-GHz 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 12 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.

Adaptively loaded SP-offset-QAM OFDM for IM/DD communication systems.

In this paper, we propose adaptively loaded set-partitioned offset quadrature amplitude modulation (SP-offset-QAM) orthogonal frequency division multiplexing (OFDM) for low-cost intensity-modulation direct-detection (IM/DD) communication systems. We compare this scheme with multi-band carrier-less amplitude phase modulation (CAP) and conventional OFDM, and demonstrate >40 Gbit/s transmission over 50-km single-mode fiber. It is shown that the use of SP-QAM formats, together with the adaptive loading algorithm specifically designed to this group of formats, results in significant performance improvement for all these three schemes. SP-offset-QAM OFDM exhibits greatly reduced complexity compared to SP-QAM based multi-band CAP, via parallelized implementation and minimized memory length for spectral shaping. On the other hand, this scheme shows better performance than SP-QAM based conventional OFDM at both back-to-back and after transmission. We also characterize the proposed scheme in terms of enhanced tolerance to fiber intra-channel nonlinearity and the potential to increase the communication security. The studies show that adaptive SP-offset-QAM OFDM is a promising IM/DD solution for medium- and long-reach optical access networks and data center connections.

Flexible MultiCAP Modulation and its Application to 850 nm VCSEL-MMF Links

In this paper, we introduce a flexible scheme for the multiband approach of carrierless amplitude phase (flexible MultiCAP) modulation. The proposed modulation scheme can adapt to different data traffic demands and transmission link conditions, with advantages of variable bit rate and, therefore, power consumption adaptivity. First, simulations results are presented to show the capacity of the proposed scheme under different bandwidth restrictions, and then, as a proof of concept, its feasibility is experimentally demonstrated in 850 nm vertical-cavity surface-emitting laser based transmissions over 100 m of OM4 multimode fiber. Data rates up to 40.6 Gb/s with spectral efficiencies up to 4 bit/s/Hz are achieved. All measured bit error rates were below the 7% overhead forward error correction threshold of 3.8 × 10−3.