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Showing papers on "Quadrature amplitude modulation published in 2018"


Journal ArticleDOI
TL;DR: The simulation and analytical results show that the presented SCMA codebook outperforms the existing codebooks and low-density signature, and the proposed design is more efficient for the SCMA Codebook with large size and/or high dimension.
Abstract: In this paper, a novel codebook design method for sparse code multiple access (SCMA) is proposed and an analytical framework to evaluate the bit error rate (BER) performance is developed. In particular, to meet the codebook design criteria based on the pairwise error probability, a novel codebook with large minimum Euclidean distance employing the star quadrature amplitude modulation signal constellations is designed. In addition, with the aid of the phase distribution of the presented SCMA constellations, BER of SCMA system over downlink Rayleigh fading channel is obtained in closed-form expression. The simulation and analytical results show that the presented SCMA codebook outperforms the existing codebooks and low-density signature, and the proposed design is more efficient for the SCMA codebook with large size and/or high dimension. Moreover, the derived theoretical BER results match well the simulation results, especially in the high signal-to-noise ratio regimes.

85 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported the transmission of probabilistically shaped (PS) 64-ary quadrature amplitude modulation (QAM) at 7.46b/s/Hz over a 5523-km in-service trans-Atlantic fiber-optic cable that consists of 65-89km spans of Erbium-doped fiber amplifier only amplified fiber.
Abstract: We report the transmission of probabilistically shaped (PS) 64-ary quadrature amplitude modulation (QAM) at 7.46 b/s/Hz over a 5523-km in-service trans-Atlantic fiber-optic cable that consists of 65–89-km spans of Erbium-doped fiber amplifier only amplified fiber. Using a looped-back system configuration, we achieve 5.68 b/s/Hz over a trans-Pacific-equivalent distance of 11 046 km. Net spectral efficiencies are increased by 18% and 80% by using PS, at 5523 km and 11 046 km, respectively, compared to uniform square QAM. Throughout our experiments, we pay particular attention that our claims are backed by implementable forward error correction schemes. In addition, we demonstrate real-time coherent transmission of single-carrier 200 and 250-Gb/s uniform 8-QAM and 16-QAM at 4 b/s/Hz over the 5523-km cable.

81 citations


Journal ArticleDOI
TL;DR: In this article, the transmit signal vector is optimized for every desired received vector taking into account a relaxed version of the QCE constraint, and the optimization is based on maximizing the safety margin to the decision thresholds of the receiver constellation modulation.
Abstract: Coarsely quantized massive multiple-input multiple-output (MIMO) systems are gaining more interest due to their power efficiency. We present a new precoding technique to mitigate the multi-user interference and the quantization distortions in a downlink multi-user MIMO system with coarsely quantized constant envelope (QCE) signals at the transmitter. The transmit signal vector is optimized for every desired received vector taking into account a relaxed version of the QCE constraint. The optimization is based on maximizing the safety margin to the decision thresholds of the receiver constellation modulation. Due to the linear property of the objective function and the constraints, the optimization problem is formulated as a linear programming problem. The simulation results show a significant gain in terms of the uncoded bit error rate compared to the existing precoding techniques.

70 citations


Journal ArticleDOI
TL;DR: In this paper, the authors derived a tight upper bound for the average symbol error rate (SER) with low-resolution DAC precoding and proposed a low-complexity heuristic algorithm for the one-bit precoder design.
Abstract: The use of low-resolution digital-to-analog converters (DACs) for transmit precoding provides crucial energy efficiency advantage for massive multiple-input multiple-output (MIMO) implementation. This paper formulates a quadrature amplitude modulation (QAM) constellation range and a one-bit symbol-level precoding design problem for minimizing the average symbol error rate (SER) in downlink massive MIMO transmission. A tight upper bound for the SER with low-resolution DAC precoding is first derived. The derived expression suggests that the performance degradation of one-bit precoding can be interpreted as a decrease in the effective minimum distance of the QAM constellation. Using the obtained SER expression, we propose a QAM constellation range design for the single-user case. It is shown that in the massive MIMO limit, a reasonable choice for constellation range with one-bit precoding is that of the infinite-resolution precoding with per-symbol power constraint, but reduced by a factor of $\sqrt{2/\pi }$ or about 0.8. The corresponding minimum distance reduction translates to about a 2 dB gap between the performance of one-bit precoding and infinite-resolution precoding. This paper further proposes a low-complexity heuristic algorithm for the one-bit precoder design. Finally, the proposed QAM constellation range and precoder design are generalized to the multiuser downlink. We propose to scale the constellation range for the infinite-resolution zero-forcing (ZF) precoding with per-symbol power constraint by the same factor of $\sqrt{2/\pi }$ for one-bit precoding. The proposed one-bit precoding scheme is shown to be within 2 dB of infinite-resolution ZF. In term of number of antennas, one-bit precoding requires about 50% more antennas to achieve the same performance as infinite-resolution precoding.

70 citations


Journal ArticleDOI
TL;DR: In this article, a narrowband unitraveling-carrier photodiode (UTC-PD) is used for heterodyne generation of terahertz (THz) communication signals, which is transparent to optical modulation formats.
Abstract: In this letter, we experimentally demonstrate terahertz (THz) photonic wireless transmission of high-speed quadrature-phase-shift-keying (QPSK) and 16 quadrature amplitude modulation (16-QAM) signals in the 350-GHz band, with an effort to extend the wireless reach of ultrafast 100 Gbit/s. In the experiment, a narrowband unitraveling-carrier photodiode (UTC-PD) is used for heterodyne generation of THz communication signals, which is transparent to optical modulation formats. Experimental results show that 30 GBd/s QPSK (60 Gbit/s) and 25 GBd/s 16-QAM signals (100 Gbit/s) are successfully transmitted over a 350-GHz wireless link with an extended distance of 2 m. This enhancement is enabled by combining the techniques of employing cutting-edge narrowband UTC-PD as the photomixing THz emitter, spectrally efficient modulation format and advanced digital signal processing algorithms. The achievement makes 100 Gbit/s THz wireless communication systems promising for future smart wireless services.

66 citations


Journal ArticleDOI
TL;DR: It is observed that multi level QAM has presented better performance than multi level PSK and finally multi level DPSK in optical OFDM systems and OSNR, SNR, and BER are improved using 4-QAM OFDM system than either QPSK or 4-DPSK.
Abstract: This paper shows the trade off between different modulation techniques such as multi level quadrature amplitude modulation, multi level phase shift keying, and multi level differential phase shift keying for upgrading direct detection optical orthogonal frequency division multiplexing systems with possible transmission distance up to 15,000 km and total bit rate of 2.56 Tb/s. The 2.56 Tb/s signal is generated by multiplexing 64 OFDM signals with 40 Gb/s for each OFDM. Variations of optical signal to noise ratio (OSNR), signal to noise ratio (SNR), and bit error rate (BER) are studied with the variations of transmission distance. Maximum radio frequency power spectrum, and output electrical power after decoder are measured for different multi level modulation techniques with carrier frequency. It is observed that multi level QAM has presented better performance than multi level PSK and finally multi level DPSK in optical OFDM systems. Maximum output power after decoder is enhanced with both 32-PSK, and 64-QAM. Quadrature signal amplitude level at encoder is upgraded with 64-QAM. It is noticed that OSNR, SNR, and BER are improved using 4-QAM OFDM system than either QPSK or 4-DPSK.

62 citations


Journal ArticleDOI
TL;DR: This work introduces, for the first time, hierarchical and fuzzy-logic C-means (FLC)-based clustering in optical communications and shows that among the two proposed MLC algorithms, FLC reveals the highest performance at optimum launched optical powers (LOPs), while at very high LOPs, hierarchical can compensate more effectively nonlinearities only for low-level modulation formats.
Abstract: Fiber-induced intra- and interchannel nonlinearities are experimentally tackled using blind nonlinear equalization (NLE) by unsupervised machine-learning-based clustering (MLC) in ∼46-Gb/s single-channel and ∼20-Gb/s (middle-channel) multichannel coherent multicarrier signals (orthogonal frequency-division multiplexing (OFDM) based). To that end, we introduce, for the first time, hierarchical and fuzzy-logic C -means (FLC)-based clustering in optical communications. It is shown that among the two proposed MLC algorithms, FLC reveals the highest performance at optimum launched optical powers (LOPs), while at very high LOPs, hierarchical can compensate more effectively nonlinearities only for low-level modulation formats. When employing binary phase-shift keying and quaternary phase-shift keying, FLC outperforms K-means, fast-Newton support vector machines, supervised artificial neural networks, and NLE with deterministic Volterra analysis. In particular, for the middle channel of a QPSK wavelength-division multiplexing coherent optical OFDM system at optimum −5 dBm of LOP and 3200 km of transmission, FLC outperforms Volterra-NLE by 2.5 dB in Q-factor. However, for a 16-QAM single-channel system at 2000 km, the performance benefit of FLC over inverse Volterra-series transfer function reduces to ∼0.4 dB at a LOP of 2 dBm (optimum). Even when using novel sophisticated clustering designs in 16 clusters, no more than additional ∼0.3-dB Q-factor enhancement is observed. Finally, in contrast to the deterministic Volterra-NLE, MLC algorithms can partially tackle the stochastic parametric noise amplification .

62 citations


Journal ArticleDOI
TL;DR: A novel dual-function radar-communications (DFRC) strategy to embed quadrature amplitude modulation (QAM) based communication information in the radar waveforms by exploiting sidelobe control and waveform diversity is proposed.

61 citations


Journal ArticleDOI
TL;DR: This is the first time that the 100 GBd mark is reached with an IQ modulator realized on a semiconductor substrate, leading to a single-polarization line rate of 400 Gbit/s.
Abstract: We demonstrate the generation of higher-order modulation formats using silicon-based inphase/quadrature (IQ) modulators at symbol rates of up to 100 GBd. Our devices exploit the advantages of silicon-organic hybrid (SOH) integration, which combines silicon-on-insulator waveguides with highly efficient organic electro-optic (EO) cladding materials to enable small drive voltages and sub-millimeter device lengths. In our experiments, we use an SOH IQ modulator with a π-voltage of 1.6 V to generate 100 GBd 16QAM signals. This is the first time that the 100 GBd mark is reached with an IQ modulator realized on a semiconductor substrate, leading to a single-polarization line rate of 400 Gbit/s. The peak-to-peak drive voltages amount to 1.5 Vpp, corresponding to an electrical energy dissipation in the modulator of only 25 fJ/bit.

59 citations


Journal ArticleDOI
TL;DR: A novel modulation scheme which combines the advantages of filter bank multi-carrier (FBMC)-offset quadrature amplitude modulation and single-carriers frequency-division multiple access (SC-FDMA) with a novel precoding method based on a pruned discrete Fourier transform (DFT) in combination with one-tap scaling.
Abstract: We propose a novel modulation scheme which combines the advantages of filter bank multi-carrier (FBMC)-offset quadrature amplitude modulation and single-carrier frequency-division multiple access (SC-FDMA). On the top of a conventional FBMC system, we develop a novel precoding method based on a pruned discrete Fourier transform (DFT) in combination with one-tap scaling. The proposed technique has the same peak-to-average power ratio as SC-FDMA but does not require a cyclic prefix and has much lower out-of-band emissions. Furthermore, our method restores complex orthogonality, and the ramp-up and ramp-down period of FBMC is dramatically decreased, allowing low latency transmissions. Compared to pure SC-FDMA, the computational complexity of our scheme is only two times higher. Simulations over doubly selective channels validate our claims, further supported by a downloadable MATLAB code. Note that pruned DFT-spread FBMC can equivalently be interpreted as a modified SC-FDMA transmission scheme. In particular, the requirements on the prototype filter are less strict than in conventional FBMC systems.

56 citations


Journal ArticleDOI
TL;DR: The results show the potential for optical pilot tones to reduce both overhead and complexity in systems using comb-based superchannels together with high-order modulation formats.
Abstract: We exploit the coherence of frequency combs for high spectral efficiency superchannel transmission via effective sharing of a single pilot tone. By phase-locking the receiver comb to the transmitted pilot tone, carrier offsets are suppressed while both the overhead and complexity associated with the pilot tone are reduced. We form a 55 carrier superchannel using a 25-GHz spaced electro-optic frequency comb seeded by a 100-kHz linewidth laser. At a pilot tone overhead of $ 2%, the reduction in carrier offsets is shown to facilitate blind DSP-based carrier recovery of all 54 $\times$ 24 Gbaud PM-128QAM data channels. The resulting superchannel spectral efficiency is 10.3 bits/s/Hz assuming a 28% overhead for forward error correction. Our results show the potential for optical pilot tones to reduce both overhead and complexity in systems using comb-based superchannels together with high-order modulation formats.

Journal ArticleDOI
TL;DR: In this paper, an extensive analysis of an optical Blass-matrix architecture as a beamforming network with potential for multibeam operation in wireless systems is presented, which relies on the use of phase shifters and Mach-Zehnder Interferometers (MZIs) inside an $M\times N$ matrix, and enables the generation of M beams by N -element antenna arrays.
Abstract: We present an extensive analysis of an optical Blass-matrix architecture as a beamforming network with potential for multibeam operation in wireless systems. Its design relies on the use of phase shifters and Mach–Zehnder Interferometers (MZIs) inside an $M\times N$ matrix, and enables the generation of M beams by N -element antenna arrays. We start our analysis from an optical signal with amplitude modulation by discrete microwave tones, and confirm the possibility to translate its optical phase shifts inside the matrix into equivalent phase shifts in the microwave domain. We show this is possible when the input is an optical single-side band signal and the optical carrier is reinserted before photodetection. We extend the conclusions to the case of an optical signal carrying a microwave with quadrature amplitude modulation (QAM) and the case of simultaneous inputs at the M input ports. Based on this analysis, we propose a Blass-matrix configuration algorithm taking into account the properties of the MZIs. Through simulations, we validate the potential for multibeam operation, and evaluate the beamforming performance at 28.5 GHz with respect to the QAM order, symbol rate, and pulse shaping parameters. In all cases with rate up to 3 Gbaud, the bit-error rate remains lower than 10–3, showing that the beam squinting effect, which is present in our design, can be tolerated. Finally, we study the frequency dependence of the beamforming performance due to inevitable asymmetries of the MZIs and length variations of the waveguides, and evaluate the impact of the imperfections in the couplers inside the MZIs and the phase shifters. We show that in all cases the performance degradation is negligible for realistic fabrication and operation conditions.

Journal ArticleDOI
TL;DR: In this article, a three-channel WDM system with two Laguerre-Gaussian modes (LG00 and LG01) was investigated for mitigation of frequency-selective fading under strong atmospheric turbulence, and the performance of four-level quadrature amplitude modulation for orthogonal frequency division multiplexing (OFDM) of radio subcarriers in the WDM-MDMs system was investigated.
Abstract: Radio-over-free-space-optics (Ro-FSO) technology may pave the way towards a ubiquitous platform for seamless integration of radio and optical networks without expensive optical fiber cabling. In this paper, to increase the capacity of Ro-FSO, mode division multiplexing (MDM) of two modes has been capitalized in a three-channel WDM system spaced by 1 nm over a FSO link of 80 km, resulting in a 120 Gbps six-channel Ro-FSO system. The SNR and received power of MDM of two Laguerre-Gaussian modes LG00 and LG01 is compared with respect to MDM of two transverse donut modes. The performance of four-level quadrature amplitude modulation (QAM) for orthogonal frequency division multiplexing (OFDM) of radio subcarriers in the WDM-MDMs system is investigated for mitigation of frequency-selective fading under strong atmospheric turbulence.

Journal ArticleDOI
Jun Tao1
TL;DR: This paper provides a comprehensive investigation on the DFT-precoded OFDM UWA communication with a multiple-input–multiple-output (MIMO) configuration, and corroborates its superiority for implementing a practical UWA Communication modem.
Abstract: The discrete Fourier transform (DFT) precoded orthogonal frequency-division multiplexing (OFDM) has been adopted as the uplink transmission technique in the long-term evolution terrestrial communication standard, for its lower peak-to-average power ratio (PAPR) and similar receiver complexity, compared with the standard OFDM. However, its application in the underwater acoustic (UWA) communications remains doubtful, mainly for the lack of systematic studies as well as sufficient experimental verifications. This paper provides a comprehensive investigation on the DFT-precoded OFDM UWA communication with a multiple-input–multiple-output (MIMO) configuration, and corroborates its superiority for implementing a practical UWA communication modem. The DFT precoding is applied on the data symbols to achieve a lower PAPR than that of the standard OFDM, and it is optional for the pilot symbols. The frequency-domain turbo equalization (FDTE) technique, especially suitable for interference-intensive scenarios, is employed on the receiver side to combat the intersymbol interference (ISI) and the multiplexing interference. Experimental results are provided to demonstrate the performance of the proposed transceiver scheme. It is shown reliable communication is achieved for the two-transducer transmission with a QPSK modulation and the one-transducer transmission with a 16QAM modulation, even without running any iteration for the FDTE. With the help of turbo iterations, a two-transducer transmission with a 16QAM modulation also achieves a satisfactory performance.

Journal ArticleDOI
TL;DR: A physical-layer encryption scheme is proposed and experimentally demonstrated in orthogonal frequency division multiplexing passive optical network (OFDM-PON) and the dynamic parameters of constellation shifting are generated by a 3-D hyper digital chaos.
Abstract: A physical-layer encryption scheme is proposed and experimentally demonstrated in orthogonal frequency division multiplexing passive optical network (OFDM-PON). In the proposed multifold encryption scheme, quadratic-amplitude modulation (QAM) symbols are scrambled and distributed onto the complex plane independently. The dynamic parameters of constellation shifting are generated by a 3-D hyper digital chaos, in which a key space of ~10162 is created to enhance the security level of OFDM data encryption during transmission. An encrypted data transmission of 9.4-Gb/s, 16-QAM optical OFDM signals is successfully demonstrated over 20-km standard single-mode fiber.

Journal ArticleDOI
TL;DR: This Letter outlines radio-over-fiber combined with radio- over-free-space optics (RoFSO) and radio frequency free-space transmission, which is of particular relevance for fifth-generation networks.
Abstract: This Letter outlines radio-over-fiber combined with radio-over-free-space optics (RoFSO) and radio frequency free-space transmission, which is of particular relevance for fifth-generation networks. Here, the frequency band of 24–26 GHz is adopted to demonstrate a low-cost, compact, and high-energy-efficient solution based on the direct intensity modulation and direct detection scheme. For our proof-of-concept demonstration, we use 64 quadrature amplitude modulation with a 100 MHz bandwidth. We assess the link performance by exposing the RoFSO section to atmospheric turbulence conditions. Further, we show that the measured minimum error vector magnitude (EVM) is 4.7% and also verify that the proposed system with the free-space-optics link span of 100 m under strong turbulence can deliver an acceptable EVM of <9% with signal-to-noise ratio levels of 22 dB and 10 dB with and without turbulence, respectively.

Proceedings ArticleDOI
11 Mar 2018
TL;DR: In this paper, a probabilistic shaping distribution that outperforms the Maxwell Boltzmann distribution for the nonlinear fiber channel was proposed and further gains of 0.1 bit/symbol MI or 0.2 dB SNR were reported for both DP-256QAM and DP-1024QAM.
Abstract: A new probabilistic shaping distribution that outperforms Maxwell-Boltzmann is studied for the nonlinear fiber channel. Additional gains of 0.1 bit/symbol MI or 0.2 dB SNR for both DP-256QAM and DP-1024QAM are reported after 200 km nonlinear fiber transmission.

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

Journal ArticleDOI
TL;DR: Successful self-homodyne detection of all 50 data channels in the 10-nm-wide superchannel demonstrates that the spectral coherence from frequency combs, combined with the use of optical pilots, can overcome limitations arising from frequency offset and phase noise in high-order QAM transmission while keeping the pilot overhead low.
Abstract: We demonstrate transmission of a comb-based 10 Tb/s 50 $\times$ 20 Gbaud PM-64QAM superchannel using frequency comb regeneration to reduce carrier offsets and allow for self-homodyne detection. The regeneration is enabled by transmitting two optical pilot tones which are filtered and recovered in the receiver using optical injection locking and an electrical phase-locked loop. We show that by utilizing frequency combs together with optical pilot tones, self-homodyne detection similar to systems using one pilot tone per wavelength channel, can be achieved. Sharing the overhead for pilot tones reduces the complexity and limits the overhead to 4%. This enabled a total superchannel spectral efficiency of 7.7 b/s/Hz. To evaluate the performance, we perform both back-to-back measurements and transmission over 80 km of standard single-mode fiber. Successful self-homodyne detection of all 50 data channels in the 10-nm-wide superchannel demonstrates that the spectral coherence from frequency combs, combined with the use of optical pilots, can overcome limitations arising from frequency offset and phase noise in high-order QAM transmission while keeping the pilot overhead low.

Journal ArticleDOI
TL;DR: The results demonstrate the suitability of the proposed C-RAN transmitter architecture for next generation 5G wireless communication networks.
Abstract: We propose a digitally linearized radio-over fiber (RoF) downlink transmitter architecture for cloud radio access networks (C-RANs), and we demonstrate its proof of principle in the near-millimeter wave (mm-wave) range (24 GHz). Amplification of input radio frequency signal power is commonly adopted to minimize the impact of photodetection noise on the dynamic range at the receiver. Unfortunately, this amplification causes the RoF system to behave nonlinearly, leading to distortions during the electrical-optical-electrical conversion process that degrades the overall signal quality. To overcome this problem and linearize the RoF link, we propose and implement effective digital predistortion (DPD) using a memory polynomial model. Experimentally, comparing the error vector magnitude (EVM) of a 64-quadratic-amplitude modulation (QAM) 20-MHz bandwidth (BW) long-term evolution (LTE) signal modulated onto a 24-GHz carrier with and without linearization, we found a signal quality improvement by 4.2%, resulting in an EVM value of 2%. Broader LTE signals of BWs up to 100 MHz were experimentally tested to achieve EVM values below 3.5% after DPD, both for 64 and 256 QAM. It is worth highlighting that the remote radio head (RRH) unit does not require any frequency up conversion to generate the mm-wave signals and the centralized baseband unit can serve multiple remote RRHs operating at different frequencies as in C-RANs. Our results demonstrate the suitability of the proposed C-RAN transmitter architecture for next generation 5G wireless communication networks.

Journal ArticleDOI
TL;DR: In this paper, the performance of probabilistically shaped 64QAM with uniform 16QAM and 32QAM modulation formats at the same net data rate in long-haul coherent optical communications systems was compared, with offline postprocessing of the data performed using either an ideal or a realistic carrier phase estimation (CPE) scheme.
Abstract: In this paper, we compare the performance of probabilistically shaped 64QAM with uniform 16QAM and 32QAM modulation formats at the same net data rate in long-haul coherent optical communications systems. Experimental results at 16 GBaud are shown, with offline postprocessing of the data performed using either an ideal or a realistic carrier phase estimation (CPE) scheme. We show that the choice of the CPE algorithm at the receiver is crucial, since, as predicted by current models, most of the additional nonlinear noise introduced by the shaping is nonlinear phase noise (NLPN). Thanks to the use of probabilistic shaping (PS), maximum reach gains ranging from 15.5% and $\text{34}\%$ are obtained over pure silica-core fiber, where the NLPN can be efficiently compensated for by standard CPE algorithms, while over nonzero dispersion-shifted fiber, the gain of PS is drastically reduced, due to residual short-correlated NLPN.

Journal ArticleDOI
TL;DR: A I/Q RF-DAC featuring two 6-bit DAC elements driven in quadrature, each with its own on-die antenna, and a total effective isotropic radiated power (EIRP) of 13.2 dBm, is demonstrated in a 45-nm SOI-CMOS technology.
Abstract: A ${D}$ -band I/Q RF-DAC featuring two 6-bit DAC elements driven in quadrature, each with its own on-die antenna, and a total effective isotropic radiated power (EIRP) of 13.2 dBm, is demonstrated in a 45-nm SOI-CMOS technology. The carrier signal is first amplified by the 30-dB gain LO path and is directly modulated by the 12 baseband bit streams, without linear upconversion or power amplification. QPSK, 8-PSK, 16-QAM, 32-QAM, and 64-QAM single-carrier (SC) and OFDM constellations are formed in free space and measured above the die at data rates up to 12 Gb/s and at distances over 15 cm. The large-signal bandwidth—from the carrier input pad to the output of the transmitter above the antennas—is 130–142 GHz and was obtained by sweeping the frequency of the ${D}$ -band external carrier, modulating it on die at 0.4 Gb/s using 16-QAM format, and measuring the error vector magnitude (EVM) with an instrumentation receiver. The highest data rate of 12 Gb/s was measured for QPSK SC modulation with a corresponding EVM of −12.2 dB. Lower maximum data rates of 7 Gb/s with −14.3-dB EVM and 3.6 Gb/s with −19-dB EVM were observed for 16-QAM and 64-QAM formats, respectively. Spectral shaping and OFDM transmission were also demonstrated at up to 2.5 Gb/s. The prototype consumes a total of 1.25 W, with an energy efficiency of 104 pJ/b.

Journal ArticleDOI
TL;DR: A spectral-efficient GenSM-based hybrid dimming scheme with layered asymmetrically clipped optical OFDM is proposed for VLC, which combines the spatial-domain and time-domain dimming strategies.
Abstract: Visible light communication (VLC) is regarded as one of the promising candidates to complement the conventional radio frequency communication as it can potentially perform communication and illumination simultaneously. Recently, VLC is combined with the generalized spatial modulation (GenSM) technology to improve spectral and energy efficiencies. In order to provide high-speed communication and flexible dimming control simultaneously, in this paper, a spectral-efficient GenSM-based hybrid dimming scheme with layered asymmetrically clipped optical OFDM is proposed for VLC, which combines the spatial-domain and time-domain dimming strategies. The channel capacities of the proposed scheme are analyzed and the closed-form expressions of the channel capacity are derived in both the rich scattering scenario and highly correlated scenario. According to the required illumination level, the spatial-domain and time-domain strategies are realized based on the maximization of the channel capacity. Simulation results substantiate the superior performance of the proposed dimming scheme over the state-of-art dimming schemes.

Journal ArticleDOI
TL;DR: The proposed blind and fast modulation format identification (MFI) enabled by the digital frequency-offset (FO) loading technique for hitless coherent transceiver brings no performance degradation, in term of tolerance of amplified spontaneous emission (ASE) noise, laser linewidth, and fiber nonlinearity.
Abstract: We propose a blind and fast modulation format identification (MFI) enabled by the digital frequency-offset (FO) loading technique for hitless coherent transceiver. Since modulation format information is encoded to the FO distribution during digital signal processing (DSP) at the transmitter side (Tx), we can use the fast Fourier transformation based FO estimation (FFT-FOE) method to obtain the FO distribution of individual data block after constant modulus algorithm (CMA) pre-equalization at the receiver side, in order to realize non-data-aided (NDA) and fast MFI. The obtained FO can be also used for subsequent FO compensation (FOC), without additional complexity. We numerically investigate and experimentally verify the proposed MFI with high accuracy and fast format switching among 28 Gbaud dual-polarization (DP)-4/8/16/64QAM, time domain hybrid-4/16QAM, and set partitioning (SP)-128QAM. In particular, the proposed MFI brings no performance degradation, in term of tolerance of amplified spontaneous emission (ASE) noise, laser linewidth, and fiber nonlinearity. Finally, a hitless coherent transceiver enabled by the proposed MFI with switching-block of only 2048 symbols is demonstrated over 1500 km standard single mode fiber (SSMF) transmission.

Journal ArticleDOI
TL;DR: Polarization (pol) selectivity has been widely adopted in modern RF transceivers to enable the channel diversity and this paper utilizes orthogonal pol modes to support simultaneous independent data streams on the same frequency channel, thereby doubling the effective channel capacity.
Abstract: Polarization (pol) selectivity has been widely adopted in modern RF transceivers to enable the channel diversity. This paper utilizes orthogonal pol modes to support simultaneous independent data streams on the same frequency channel, thereby doubling the effective channel capacity. The energy-efficient 60-GHz transceiver prototype uses two transmit/receive (TX/RX) chains with a single printed circuit board (PCB) antenna to demonstrate over-the-air (OTA) 2 $\times $ 13.9 Gb/s 16 quadrature-amplitude modulation (QAM) dual-pol (DP) multiplexing-based multi-input and multi-output (MIMO), thus achieving 2 $\times $ higher communicated bits/symbol than a single-pol transceiver. At these multi-Gb/s rates, multi-path ISI and cross-pol effects limit the feasibility of DP–MIMO. To mitigate these channel effects, a mixed-signal 384-coefficient feed-forward equalizer (FFE)- and 2400-coefficient decision-feedback equalizer (DFE)-based area- and energy-efficient RX baseband is also presented. The baseband supports DP–MIMO up to 40 Gb/s for line-of-sight (LOS) 16QAM and 14 Gb/s non-line-of-sight (NLOS) QPSK, at 3 $\times $ to 38 $\times $ better energy efficiency per coefficient than state of the art.

Journal ArticleDOI
TL;DR: A unified error analysis of multi-antenna systems with orthogonal space-time block coding (OSTBC) using transmit antenna selection (TAS) over Nakagami-–LaTeX channels in the presence of feedback delay and channel estimation error is presented, where the number of transmit antennas is arbitrarily selected.
Abstract: A unified error analysis of multi-antenna systems with orthogonal space-time block coding (OSTBC) using transmit antenna selection (TAS) over Nakagami- $m$ channels in the presence of feedback delay and channel estimation error is presented, where the number of transmit antennas is arbitrarily selected. For imperfect channel state information (CSI), the Nakagami- $m$ channel is modeled as the sum of Nakagami- $\hat{m}$ channel and independent Gaussian channel error. By this model, accurate and closed-form approximate bit error rate (BER) expressions of TAS-OSTBC for M-ary quadrature amplitude modulation and M-ary phase-shift keying are derived by using the moment generating function of received SNR. With the approximate BER formula, the number of antennas to be selected for transmission can be adapted by minimizing the BER of the system with imperfect CSI. The diversity and coding gains of TAS-OSTBC with $K$ receive antennas and $M$ antennas selected from $N$ transmit antennas for transmission are analyzed at high SNR. For noninteger $mK$ , the upper and lower bounds of the diversity gain for different CSI and estimation error scenarios are derived. But for integer $mK$ , the results indicate that the upper and lower bounds are equal achieving the full diversity order of $mKN$ for perfect CSI, zero diversity order and partial diversity order of $mMK$ for estimation error variance being fixed and being a decreasing function of average SNR, respectively. The coding gain is affected by $M$ , $N$ , $K$ , Nakagami parameter $m$ , code rate, modulation, and channel correlation coefficients. Simulation results verify the validity of the theoretical analysis and effectiveness of the adaptive antenna selection scheme.

Journal ArticleDOI
TL;DR: The design and optimization of the optical single side-band (SSB) Nyquist four-level pulse amplitude modulation (PAM-4) transmission using dual-drive Mach-Zehnder modulator (DDMZM) modulation and direct detection (DD), aiming at the C-band cost-effective, high-speed and long-distance transmission is presented.
Abstract: We present the design and optimization of the optical single side-band (SSB) Nyquist four-level pulse amplitude modulation (PAM-4) transmission using dual-drive Mach-Zehnder modulator (DDMZM)modulation and direct detection (DD), aiming at the C-band cost-effective, high-speed and long-distance transmission. At the transmitter, the laser line width should be small to avoid the phase noise to amplitude noise conversion and equalization-enhanced phase noise due to the large chromatic dispersion (CD). The optical SSB signal is generated after optimizing the optical modulation index (OMI) and hence the minimum phase condition which is required by the Kramers-Kronig (KK) receiver can also be satisfied. At the receiver, a simple AC-coupled photodiode (PD) is used and a virtual carrier is added for the KK operation to alleviate the signal-to-signal beating interference (SSBI).A Volterra filter (VF) is cascaded for remaining nonlinearities mitigation. When the fiber nonlinearity becomes significant, we elect to use an optical band-pass filter with offset filtering. It can suppress the simulated Brillouin scattering and the conjugated distortion by filtering out the imaging frequency components. With our design and optimization, we achieve single-channel, single polarization 102.4-Gb/s Nyquist PAM-4 over 800-km standard single-mode fiber (SSMF).

Journal ArticleDOI
TL;DR: To the authors' knowledge, the ratio between the bit rate achieved and the switching frequency of the dc–dc power converter presented in this paper is the highest that can be found in the literature.
Abstract: A dc–dc power converter based on a two-phase synchronous buck converter that reproduces single-carrier digital modulation schemes by controlling the first switching harmonic of the output voltage ripple is presented in this paper. The dc–dc power converter carries out both the lighting and the transmission functionalities of visible light communication transmitters. Control of both the amplitude and the phase of sinusoidal currents injected toward high-brightness LEDs enable the use of efficient modulation schemes, such as quadrature amplitude modulation, carrierless amplitude and phase modulation, amplitude-shift keying, and phase-shift keying. These modulation schemes achieve higher spectral efficiency (i.e., more data can be transmitted using the same bandwidth) than previously proposed modulation schemes performed by visible light communication transmitters based on the use of dc–dc power converters. To the authors' knowledge, the ratio between the bit rate achieved and the switching frequency of the dc–dc power converter presented in this paper is the highest that can be found in the literature.

Proceedings ArticleDOI
11 Mar 2018
TL;DR: PDM-QPSK transmission over 4480 km is demonstrated at a record all-electronically multiplexed symbol rate of 180 GBaud, providing a line rate of 720 Gb/s on a single optical carrier enabled by high-speed InP-DHBT selectors.
Abstract: We demonstrate PDM-QPSK transmission over 4480 km at a record all-electronically multiplexed symbol rate of 180 GBaud, providing a line rate of 720 Gb/s on a single optical carrier enabled by high-speed InP-DHBT selectors.

Journal ArticleDOI
TL;DR: The closed-form expression of outage probability for a dual-hop variable-gain amplify-and-forward relay network is derived from the maximal ratio combining receiver over independent and non-identically distributed frequency flat Nakagami-m fading channels with integer-valued fading parameter and imperfect channel state information.
Abstract: In this letter, we derive the closed-form expression of outage probability for a dual-hop variable-gain amplify-and-forward relay network. The maximal ratio combining receiver over independent and non-identically distributed frequency flat Nakagami-m fading channels with integer-valued fading parameter and imperfect channel state information (CSI) is considered. Asymptotic analysis on outage probability is also performed. Average symbol error rate (ASER) expressions are derived for general-order hexagonal and rectangular QAM schemes using the cumulative distribution function-based approach. The impact of the fading parameter and imperfect CSI are highlighted on the system performance. Comparative analysis of ASER performance for different QAM constellations is also illustrated. Monte Carlo simulations are performed to validate the derived analytical results for both perfect and imperfect CSI.