Showing papers on "Phase-shift keying published in 2014"
TL;DR: This work shows that systematic adjustment of pump conditions for low phase noise enables coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the comb and offers an attractive solution towards chip-scale terabit/s transceivers.
Abstract: Optical frequency combs have the potential to revolutionize terabit communications1. Generation of Kerr combs in nonlinear microresonators2 represents a particularly promising option3 enabling line spacings of tens of GHz. However, such combs may exhibit strong phase noise4-6, which has made high-speed data transmission impossible up to now. Here we demonstrate that systematic adjustment of pump conditions for low phase noise4,7-9 enables coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the comb. In a first experiment, we encode a data stream of 392 Gbit/s on a Kerr comb using quadrature phase shift keying (QPSK) and 16-state quadrature amplitude modulation (16QAM). A second experiment demonstrates feedback-stabilization of the comb and transmission of a 1.44 Tbit/s data stream over up to 300 km. The results show that Kerr combs meet the highly demanding requirements of coherent communications and thus offer an attractive solution towards chip-scale terabit/s transceivers.
606 citations
TL;DR: In this paper, a q-plate-based mode (de)multiplexer for vector modes based on a liquid crystal technology referred to as a qplate is introduced, and four vector modes are used to increase the information capacity of free space optical communication via the method of optical communication referred as mode division multiplexing.
Abstract: Vector modes are spatial modes that have spatially inhomogeneous states of polarization, such as, radial and azimuthal polarization. They can produce smaller spot sizes and stronger longitudinal polarization components upon focusing. As a result, they are used for many applications, including optical trapping and nanoscale imaging. In this work, vector modes are used to increase the information capacity of free space optical communication via the method of optical communication referred to as mode division multiplexing. A mode (de)multiplexer for vector modes based on a liquid crystal technology referred to as a q-plate is introduced. As a proof of principle, using the mode (de)multiplexer four vector modes each carrying a 20 Gbit/s quadrature phase shift keying signal on a single wavelength channel (~1550nm), comprising an aggregate 80 Gbit/s, were transmitted ~1m over the lab table with <-16.4 dB (<2%) mode crosstalk. Bit error rates for all vector modes were measured at the forward error correction threshold with power penalties < 3.41dB.
239 citations
23 Jun 2014
TL;DR: Both theoretical analysis and simulation results are presented to show that the proposed OFDM with interleaved sucarrier-index modulation (OFDM-ISIM) can achieve better system performance than conventional OFDM-IM and OfDM with low-order modulation schemes such as binary phase shift keying, quadrature phase shiftkeying and 16 quadratures amplitude modulation.
Abstract: Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is a recently developed technique which modulates part of the information bits using the indices of OFDM subcarriers. In this letter, a simple and efficient subcarrier-level interleaving scheme is introduced to improve the performance of conventional OFDM-IM through enlarging the Euclidean distances among the modulated symbols. Both theoretical analysis and simulation results are presented to show that the proposed OFDM with interleaved sucarrier-index modulation (OFDM-ISIM) can achieve better system performance than conventional OFDM-IM and OFDM with low-order modulation schemes such as binary phase shift keying, quadrature phase shift keying and 16 quadrature amplitude modulation.
233 citations
TL;DR: A time-modulated 4-D array with constant instantaneous directivity is proposed for directional modulation and two enhanced methods are presented to improve the feasibility of directional modulation by using random time sequences and random time modulation frequency.
Abstract: Four-dimensional (4-D) antenna arrays are formed by introducing a fourth dimension, time, into traditional antenna arrays. In this paper, a time-modulated 4-D array with constant instantaneous directivity is proposed for directional modulation. The main idea is that the 4-D array transmits correct signal without time modulation in the desired direction, while transmitting time-modulated signals in other directions. As longs as the time modulation frequency is less than the bandwidth of the transmitted signal, the time-modulated signals cannot be demodulated correctly due to the aliasing effect, implying that time-modulated signals go distorted. Thus, the 4-D array can be used to transmit direction-dependent signals in secure wireless communications. The proposed idea is verified by experiments based on AM signal transmission through the 4-D array. Moreover, BPSK signal transmission through the 4-D array is studied and the bit error rate (BER) performance is investigated. Simulation results show that the BERs of time-modulated BPSK (TM-BPSK) signals transmitted through the sidelobes of the 4-D array are much higher than those of BPSK signals and almost keep unchanged even under higher SNR. Finally, two enhanced methods are presented to improve the feasibility of directional modulation by using random time sequences and random time modulation frequency.
152 citations
TL;DR: The simulations suggest that major improvements can be expected in the achievable rates of optical networks with high-order QAM, and a mapping function for turbo-coded bit-interleaved coded modulation is proposed based on optimization of the mutual information between the channel input and output.
Abstract: In this letter, the fiber-optic communication channel with a quadrature amplitude modulation (QAM) input constellation is treated. Using probabilistic shaping, we show that high-order QAM constellations can achieve and slightly exceed the lower bound on the channel capacity, set by ring constellations. We then propose a mapping function for turbo-coded bit-interleaved coded modulation based on optimization of the mutual information between the channel input and output. Using this mapping, spectral efficiency as high as 6.5 bits/s/Hz/polarization is achieved on a simulated single channel long-haul fiber-optical link excluding the pilot overhead, used for synchronization, and taking into account frequency and phase mismatch impairments, as well as laser phase noise and analog-to-digital conversion quantization impairments. The simulations suggest that major improvements can be expected in the achievable rates of optical networks with high-order QAM.
122 citations
TL;DR: In this article, the nonlinear inverse synthesis (NIS) method is proposed for the continuous nonlinear signal spectrum, which can provide an effective eigenvalue division multiplexing with high spectral efficiency thanks to highly suppressed channel cross talk.
Abstract: In linear communication channels, spectral components (modes) defined by the Fourier transform of the signal propagate without interactions with each other. In certain nonlinear channels, such as the one modelled by the classical nonlinear Schr\"odinger equation, there are nonlinear modes (nonlinear signal spectrum) that also propagate without interacting with each other and without corresponding nonlinear cross talk; effectively, in a linear manner. Here, we describe in a constructive way how to introduce such nonlinear modes for a given input signal. We investigate the performance of the nonlinear inverse synthesis (NIS) method, in which the information is encoded directly onto the continuous part of the nonlinear signal spectrum. This transmission technique, combined with the appropriate distributed Raman amplification, can provide an effective eigenvalue division multiplexing with high spectral efficiency, thanks to highly suppressed channel cross talk. The proposed NIS approach can be integrated with any modulation formats. Here, we demonstrate numerically the feasibility of merging the NIS technique in a burst mode with high spectral efficiency methods, such as orthogonal frequency division multiplexing and Nyquist pulse shaping with advanced modulation formats (e.g., QPSK, 16QAM, and 64QAM), showing a performance improvement up to 4.5 dB, which is comparable to results achievable with multi-step per span digital back propagation.
119 citations
TL;DR: Two proposals to reduce the hardware complexity required by digital back-propagation are discussed, one confirms and extends published results for non-dispersion managed link, while the second introduces a novel method applicable to dispersion managed links, showing complexity reductions in the order of 50% and up to 85%, respectively.
Abstract: Next-generation optical communication systems will continue to push the ( bandwidth · distance) product towards its physical limit. To address this enormous demand, the usage of digital signal processing together with advanced modulation formats and coherent detection has been proposed to enable data-rates as high as 400 Gb/s per channel over distances in the order of 1000 km. These technological breakthroughs have been made possible by full compensation of linear fiber impairments using digital equalization algorithms. While linear equalization techniques have already matured over the last decade, the next logical focus is to explore solutions enabling the mitigation of the Kerr effect induced nonlinear channel impairments. One of the most promising methods to compensate for fiber nonlinearities is digital back-propagation (DBP), which has recently been acknowledged as a universal compensator for fiber propagation impairments, albeit with high computational requirements. In this paper, we discuss two proposals to reduce the hardware complexity required by DBP. The first confirms and extends published results for non-dispersion managed link, while the second introduces a novel method applicable to dispersion managed links, showing complexity reductions in the order of 50% and up to 85%, respectively. The proposed techniques are validated by comparing results obtained through post-processing of simulated and experimental data, employing single channel and WDM configurations, with advanced modulation formats, such as quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16-QAM). The considered net symbol rate for all cases is 25 GSymbol/s. Our post-processing results show that we can significantly reduce the hardware complexity without affecting the system performance. Finally, a detailed analysis of the obtained reduction is presented for the case of dispersion managed link in terms of number of required complex multiplications per transmitted bit.
116 citations
TL;DR: The approximate average symbol error rate of the considered beamforming and combining based hybrid AF cooperative scheme for M-ary phase shift keying constellation is derived; analytical diversity order of the hybrid system is obtained.
Abstract: In this paper, we consider the transmission of signals in a hybrid satellite-terrestrial cooperative system. In particular, we address the problem of beamforming and combining based amplify-and-forward (AF) relaying in a hybrid satellite-terrestrial cooperative system. In this set-up, a multiple antenna based relay node forwards the received satellite signals to the destination, by using a beamforming vector, and multiple antenna based destination node uses maximal ratio combining. The approximate average symbol error rate of the considered beamforming and combining based hybrid AF cooperative scheme for M-ary phase shift keying constellation is derived; analytical diversity order of the hybrid system is also obtained. Moreover, diversity calculations for some specific antenna configurations are shown for providing useful insight of the proposed scheme, at high signal-to-noise ratio.
115 citations
22 Dec 2014
TL;DR: An optical camera communication system utilizing the under-sampled phase shift ON-OFF keying modulation is proposed to support non-flickering visible light communication.
Abstract: In this paper, an optical camera communication system utilizing the under-sampled phase shift ON-OFF keying modulation is proposed to support non-flickering visible light communication. This system sends three types of light symbols through light emitting diode (LED) lamps, which are recorded by a camera. By employing a dual LED lamp with a designated mapping and framing method, the data rate can reach up to 3 times of the camera's frame rate. The experiment results show that the proposed camera communication system can achieve 150 bps error-free communications for a range up to 12 m.
113 citations
TL;DR: This paper examines the performance of several modulation formats in more than four dimensions for coherent optical communications systems and compares two high-dimensional modulation design methodologies based on spherical cutting of lattices and block coding of a 'base constellation' of binary phase shift keying on each dimension.
Abstract: In this paper, we examine the performance of several modulation formats in more than four dimensions for coherent optical communications systems. We compare two high-dimensional modulation design methodologies based on spherical cutting of lattices and block coding of a ‘base constellation’ of binary phase shift keying (BPSK) on each dimension. The performances of modulation formats generated with these methodologies is analyzed in the asymptotic signal-to-noise ratio regime and for an additive white Gaussian noise (AWGN) channel. We then study the application of both types of high-dimensional modulation formats to standard single-mode fiber (SSMF) transmission systems. For modulation with spectral efficiencies comparable to dual-polarization (DP-) BPSK, polarization-switched quaternary phase shift keying (PS-QPSK) and DP-QPSK, we demonstrate SNR gains of up to 3 dB, 0.9 dB and 1 dB respectively, at a BER of 10−3.
111 citations
TL;DR: In this paper, the authors demonstrate direct quadrature modulator and demodulator monolithic microwave integrated circuits for future terahertz communications at 300 GHz based on the Quadrature Phase-Shift keying (QPSK) modulation format.
Abstract: We demonstrate direct quadrature modulator and demodulator monolithic microwave integrated circuits for future terahertz communications at 300 GHz based on the quadrature phase-shift keying (QPSK) modulation format. For the modulating and demodulating signal, we employed half-Gilbert cell mixers, which provide balanced signaling and moderate performance in conversion efficiency with a simple circuit configuration. In order to maintain the balance performance of the modulator and demodulator, passive baluns and couplers are implemented with thin-film microstrip lines, which exhibit less insertion loss than inverted microstrip lines (IMSLs), while the active mixers are based on IMSLs for short interconnections. The half-Gilbert-cell mixers have a wide enough operation bandwidth for high-throughput communications of more than 10% at 300 GHz. According to the static constellation of the modulator, imbalance is expected to be less than approximately ±0.6 dB ∠4°. A nonchip back-to-back experiment was conducted at up to 60 Gb/s, and 50-Gb/s operation was verified with a low bit error rate on the order of 10-8 or less. The results demonstrate that the QPSK modulation scheme can be applied to double the data rate at terahertz frequencies.
TL;DR: In this article, a W-band seamlessly integrated fiber-wireless-fiber transmission system enabled by photonic millimeter-wave generation and demodulation techniques is proposed and experimentally demonstrated.
Abstract: We propose and experimentally demonstrate a W-band seamlessly integrated fiber-wireless-fiber transmission system enabled by photonic millimeter-wave generation and demodulation techniques, in which up to 128-Gb/s (16-Gbd) polarization division multiplexing 16-ary quadrature amplitude modulation (16QAM) signal can be first transmitted over 50-km single-mode fiber-28 (SMF-28), then delivered over 1-m × 2 multiple-input multiple-output wireless link at 100 GHz and finally transmitted over another 50-km SMF-28 with a bit-error ratio less than the third-generation soft-decision forward-error-correction threshold of 2 × 10
-2
. The proposed system can be well compatible with high-level QAM and is suited to large-capacity high-spectral-efficiency fiber-wireless integration communication.
TL;DR: DB-NGH can be regarded the first third-generation broadcasting system because it allows for the possibility of using multiple input-multiple output antenna schemes to overcome the Shannon limit of single antenna wireless communications.
Abstract: This paper reviews the main technical solutions adopted by the next-generation mobile broadcasting standard DVB-NGH, the handheld evolution of the second-generation digital terrestrial TV standard DVB-T2. The main new technical elements introduced with respect to DVB-T2 are: layered video coding with multiple physical layer pipes, time-frequency slicing, full support of an IP transport layer with a dedicated protocol stack, header compression mechanisms for both IP and MPEG-2 TS packets, new low-density parity check coding rates for the data path (down to 1/5), nonuniform constellations for 64 Quadrature Amplitude Modulation (QAM) and 256QAM, 4-D rotated constellations for Quadrature Phase Shift Keying (QPSK), improved time interleaving in terms of zapping time, end-to-end latency and memory consumption, improved physical layer signaling in terms of robustness, capacity and overhead, a novel distributed multiple input-single output transmit diversity scheme for single-frequency networks (SFNs), and efficient provisioning of local content in SFNs. All these technological solutions, together with the high performance of DVB-T2, make DVB-NGH a real next-generation mobile multimedia broadcasting technology. In fact, DVB-NGH can be regarded the first third-generation broadcasting system because it allows for the possibility of using multiple input-multiple output antenna schemes to overcome the Shannon limit of single antenna wireless communications. Furthermore, DVB-NGH also allows the deployment of an optional satellite component forming a hybrid terrestrial-satellite network topology to improve the coverage in rural areas where the installation of terrestrial networks could be uneconomical.
TL;DR: A simple digital preemphasis (DPE) algorithm to compensate for DAC-induced signal distortions is proposed, and performance improvements are established across various DAC hardware requirements and channel baud rates, for m-state quadrature amplitude modulation (QAM) formats.
Abstract: Next-generation coherent optical systems are geared to employ high-speed digital-to-analog converters (DAC), allowing for digital preprocessing of the signal and flexible optical transport networks. However, one of the major obstacles in such architectures is the limited resolution (less than 5.5 effective bits) and –3 dB bandwidth of commercial DACs, typically limited to half of the currently commercial baud rates, and even relatively reduced in case of higher baud rate transponders (400 Gb/s and 1 Tb/s). In this paper, we propose a simple digital preemphasis (DPE) algorithm to compensate for DAC-induced signal distortions, and exhaustively investigate the impact of DAC specifications on system performance, both with and without DPE. As an outcome, performance improvements are established across various DAC hardware requirements (effective number of bits and bandwidth) and channel baud rates, for m-state quadrature amplitude modulation (QAM) formats. In particular, we show that lower order modulation formats are least affected by DAC limitations, however, they benefit the most from DPE in extremely challenging hardware conditions. On the contrary, higher order formats are severely limited by DAC distortions, and moderately benefit from DPE across a wide range of DAC specifications. Moreover, effective number of bit requirements are established for m-state QAM, assuming low and high baud rate transmission regimes. Finally, we discuss the application scenarios for the proposed DPE in next-generation terabit transmission systems, and establish maximum transportable baud rates, which are shown to be used toward increasing channel baud rates to reduce terabit subcarrier count or toward increasing forward error correction (FEC) overheads to reduce the pre-FEC bit error rate threshold. Maximum baud rates after DPE are summarized here for polarization multiplexed BPSK, QPSK, 8QAM, and 16QAM, assuming two DACs: Current commercial DACs (5.5 effective bits, 16 GHz bandwidth) 57, 54, 51, and 48 Gbaud, respectively. Next-generation DACs (7 effective bits, 22 GHz bandwidth): 62, 61, 60, and 58 Gbaud, respectively.
20 Nov 2014
TL;DR: Ultra-broadband mm-wave wireless data transmission at 240 GHz carrier frequency is demonstrated successfully over a distance of 40m using a direct conversion MMIC-based RF front end.
Abstract: Ultra-broadband mm-wave wireless data transmission at 240 GHz carrier frequency is demonstrated successfully over a distance of 40m using a direct conversion MMIC-based RF front end. A new generation 64GS/s Fujitsu DAC evaluation board provides 64Gbit/s and 96Gbit/s data rates for QPSK and 8-PSK modulated baseband signals. The overall link performance is evaluated in terms of error vector magnitude (EVM) measurement. For the QPSK and 8-PSK data transmission EVM measurement shows values of 23.7% and 21.6%, respectively.
TL;DR: In this paper, the performance of a wireless optical communication system is analyzed using different modulation formats such as, binary phase shift keying-subcarrier intensity modulation (BPSK-SIM), differential phase shifter keying (DPSK) and differential phase shift-keyboard (DSK-SLC) and M-ary pulse position modulation (M-PPM) for strong atmospheric turbulences.
TL;DR: In this paper, the authors demonstrate high speed optical transmission systems using digital coherent detection at all-electronically multiplexed symbol rates of 80 and 107 Gbaud using two optical subcarriers.
Abstract: We demonstrate high speed optical transmission systems using digital coherent detection at all-electronically multiplexed symbol rates of 80 and 107 Gbaud. At 107 Gbaud, we demonstrate a single-carrier polarization division multiplexed quadrature phase shift keyed (PDM-QPSK) line rate of 428 Gb/s. At 80 Gbaud, we achieve a single-carrier line rate of 640 Gb/s using PDM 16-ary quadrature amplitude modulation (16-QAM). Using two optical subcarriers, we demonstrate a 1-Tb/s optical interface and conduct long-haul wavelength-division multiplexed (WDM) transmission on a 200-GHz grid over 3200 km of ultra-large effective area fiber.
TL;DR: Besides EVM-like and bit error rate (BER) metrics, secrecy rate as used in information theory community is also derived for the purpose of this QPSK DM system evaluation.
Abstract: In this paper, metrics for assessing the performance of directional modulation (DM) physical-layer secure wireless systems are discussed. In the paper DM systems are shown to be categorized as static or dynamic. The behavior of each type of system is discussed for QPSK modulation. Besides EVM-like and bit error rate (BER) metrics, secrecy rate as used in information theory community is also derived for the purpose of this QPSK DM system evaluation.
TL;DR: It is shown that the optimized constellations are much more robust with respect to the changes in the phase noise characteristics than the phase shift keying (PSK) modulation and quadrature amplitude modulation (QAM).
Abstract: In this paper, we optimize the constellation sets to be used in communication systems affected by phase noise. The main objective is to find the constellation which maximizes the channel mutual information under given power constraints. For any given constellation, the average mutual information (AMI) and the pragmatic average mutual information (PAMI) of the channel are calculated approximately, assuming that both the additive noise and phase noise are memoryless. Then, a simulated annealing algorithm is used to optimize the constellation. When the objective function is the PAMI, the proposed algorithm jointly optimizes the constellation and the binary labeling. We focus on constellations with 8, 16, 64 and 256 signals. The performances of the optimized constellations are compared with conventional constellations showing considerable gains in all system scenarios. In particular, it is shown that the optimized constellations are much more robust with respect to the changes in the phase noise characteristics than the phase shift keying (PSK) modulation and quadrature amplitude modulation (QAM).
TL;DR: This work theoretically and experimentally investigates a time-domain digital pre-equalization (DPEQ) scheme for bandwidth-limited optical coherent communication systems, which is based on feedback of channel characteristics from the receiver-side blind and adaptive equalizers, such as least-mean-squares (LMS) algorithm and constant or multi- modulus algorithms (CMA, MMA).
Abstract: We theoretically and experimentally investigate a time-domain digital pre-equalization (DPEQ) scheme for bandwidth-limited optical coherent communication systems, which is based on feedback of channel characteristics from the receiver-side blind and adaptive equalizers, such as least-mean-squares (LMS) algorithm and constant or multi- modulus algorithms (CMA, MMA). Based on the proposed DPEQ scheme, we theoretically and experimentally study its performance in terms of various channel conditions as well as resolutions for channel estimation, such as filtering bandwidth, taps length, and OSNR. Using a high speed 64-GSa/s DAC in cooperation with the proposed DPEQ technique, we successfully synthesized band-limited 40-Gbaud signals in modulation formats of polarization-diversion multiplexed (PDM) quadrature phase shift keying (QPSK), 8-quadrature amplitude modulation (QAM) and 16-QAM, and significant improvement in both back-to-back and transmission BER performances are also demonstrated.
TL;DR: SOH integration combines highly efficient electro-optic organic materials with conventional silicon-on-insulator (SOI) slot waveguides, and allows to overcome the intrinsic limitations of silicon as an optical integration platform with high signal quality and record-low energy consumption.
Abstract: We demonstrate silicon-organic hybrid (SOH) electro-optic modulators that enable quadrature phase-shift keying (QPSK) and 16-state quadrature amplitude modulation (16QAM) with high signal quality and record-low energy consumption. SOH integration combines highly efficient electro-optic organic materials with conventional silicon-on-insulator (SOI) slot waveguides, and allows to overcome the intrinsic limitations of silicon as an optical integration platform. We demonstrate QPSK and 16QAM signaling at symbol rates of 28 GBd with peak-to-peak drive voltages of 0.6 Vpp. For the 16QAM experiment at 112 Gbit/s, we measure a bit-error ratio of 5.1 × 10˗5 and a record-low energy consumption of only 19 fJ/bit.
TL;DR: It is shown that the correlation functions of the received signals for certain modulation formats exhibit peaks at a particular set of time lags, a result which can be exploited as a discriminating feature.
Abstract: This letter proposes a blind modulation classification (MC) algorithm applicable to single and multiple-antenna systems operating over frequency-selective channels. We show that the correlation functions of the received signals for certain modulation formats exhibit peaks at a particular set of time lags, a result which can be exploited as a discriminating feature. We also develop a new hypothesis test in order to detect the correlation-induced peaks. The proposed algorithm is general in the sense that it accommodates any number of transmit- and receive-antennas, without prior information about channel statistics. The classification performance of the proposed algorithm is assessed through Monte Carlo simulations.
TL;DR: The average bit error rate (BER) for binary phase-shift keying modulation in free-space optical links over turbulence atmosphere modeled by the exponentiated Weibull (EW) distribution is investigated and the analytical results deduced by the generalized Gauss-Laguerre quadrature rule are verified by the Monte Carlo simulation.
Abstract: The average bit error rate (BER) for binary phase-shift keying (BPSK) modulation in free-space optical (FSO) links over turbulence atmosphere modeled by the exponentiated Weibull (EW) distribution is investigated in detail. The effects of aperture averaging on the average BERs for BPSK modulation under weak-to-strong turbulence conditions are studied. The average BERs of EW distribution are compared with Lognormal (LN) and Gamma-Gamma (GG) distributions in weak and strong turbulence atmosphere, respectively. The outage probability is also obtained for different turbulence strengths and receiver aperture sizes. The analytical results deduced by the generalized Gauss-Laguerre quadrature rule are verified by the Monte Carlo simulation. This work is helpful for the design of receivers for FSO communication systems.
TL;DR: It is shown that, at any transmission rate, there exists an optimal APM dimension in which the symbol error rate (SER) performance is minimized and a trade-off between the number of transmit antennas and the transmit power is introduced.
Abstract: Spatial modulation (SM) is a new transmission technique for multi-antenna systems in which the transmit antennas are used to modulate the signal. In this paper, the symbol error rate (SER) performance of SM is investigated. In SM, a signal domain modulation (i.e. amplitude-phase modulation) and an antenna domain modulation (i.e. space shift keying) are combined together to achieve a certain transmission rate while exploiting the properties of two independent modulation domains. A key question is the fine balance between the constellation sizes in the two domains when a constant rate is targeted. For a fixed rate, there are many ways to assign constellation vectors to the spatial and signal domains. In this paper, we investigate optimal constellation breakdown between space and signal domains. The analysis is based on the union bound of the error probability of SM with two typical APM schemes, i.e. phase-shift keying (PSK) and square quadrature amplitude modulation (S-QAM). It is shown that, at any transmission rate, there exists an optimal APM dimension in which the SER is minimized. Furthermore, a trade-off between the number of transmit antennas and the transmit power is introduced.
TL;DR: The proposed system enhances the capacity of high-speed THz wireless transmission by using spectrally efficient modulated subcarriers spaced at the baud rate, which increases the overall transmission capacity and reduces the bandwidth requirement for electronic devices.
Abstract: We experimentally demonstrate photonic generation of a multichannel THz wireless signal at carrier frequency 200 GHz, with data rate up to 75 Gbps in QPSK modulation format, using an optical heterodyne technique and digital coherent detection. BER measurements were carried out for three subcarriers each modulated with 5 Gbaud QPSK or for two subcarriers modulated with 10 Gbaud QPSK, giving a total speed of 30 Gbps or 40 Gbps, respectively. The system evaluation was also performed with three subcarriers modulated with 12.5 Gbaud QPSK (75 Gbps total) without and with 40 km fibre transmission. The proposed system enhances the capacity of high-speed THz wireless transmission by using spectrally efficient modulated subcarriers spaced at the baud rate. This approach increases the overall transmission capacity and reduces the bandwidth requirement for electronic devices.
TL;DR: This paper investigates the performance of the Spatial Modulation (SM) transmission scheme over real-world 4×4 Multi-Input Multi-Output (MIMO) channels measured in typical indoor scenarios and proves that both the Independently and Identically Distribute channel model are oversimplified.
Abstract: The Spatial Modulation (SM) transmission scheme boosts the spectral efficiency and achieves the multiplexing gain by activating a single transmit antenna in each time slot. Radio wave propagation characteristics determined by the environment is a decisive factor for the SM system. In this paper, we investigate the performance of the SM scheme over real-world 4×4 Multi-Input Multi-Output (MIMO) channels measured in typical indoor scenarios. Firstly, a MIMO channel sounder is established. Based on the sounder, 15150 complex 4×4 MIMO channel matrices are measured inside a typical teaching building under both Line of Sight (LOS) and None Line of Sight (NLOS) scenarios. Secondly, by comparing the SM system over the measured channel and commonly-used channel models, we prove that both the Independently and Identically Distribute (i.i.d.) Rayleigh and the Spatial Correlation (SC) channel model are oversimplified, and that only practical experiences can yield definitive answers to the achievable real-world system performance. Thirdly, the Average Bit Error Probability (ABEP) performance of the SM system is studied based on the measured data under a variety of system configurations. The study of different receive antenna array settings (4×4, 4×2 and 4×1 MIMO setups) approves the significance of combining scheme at the receiver. SM systems employing different signal constellations (Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and 16 Quadrature Amplitude Modulation (16QAM)) are also investigated and some interesting results are revealed. Lastly, performance assessment of SM against State-Of-The-Art (SOTA) MIMO schemes (Space-Time Block Code (STBC) and Vertical Bell Labs Layered Space-Time (V-BLAST) code) is conducted. Results show that for a 4×4 MIMO, the low-complexity SM scheme outperforms both STBC and V-BLAST.
TL;DR: A low-complexity universal soft demapper is conceived, which reduces the demapper's complexity considerably for the binary-reflected Gray-labeled pulse amplitude modulation, phase shift keying (PSK), quadrature amplitude modulation (QAM, and amplitude phase-shift keying) relying on product constellation labeling (product-APSK).
Abstract: High-order constellations are commonly used for achieving high bandwidth efficiency in most communication systems. However, the complexity of the multiplication operations associated with the standard max-sum approximation of the maximum a posteriori probability in the log-domain (Max-Log-MAP) symbol-to-bit demapper is very high. In this contribution, we conceive a low-complexity universal soft demapper, which reduces the demapper's complexity considerably for the binary-reflected Gray-labeled pulse amplitude modulation (PAM), phase shift keying (PSK), quadrature amplitude modulation (QAM), and amplitude phase-shift keying (APSK) relying on product constellation labeling (product-APSK). Our theoretical analysis demonstrates that the proposed demapper has exactly the same performance as the Max-Log-MAP demapper for the Gray-labeled PAM, PSK, and QAM. Our theoretical analysis and simulation results also demonstrate that for the Gray-labeled product-APSK, the performance degradation of the proposed simplified soft demapper is negligible for both 64-ary and 256-ary constellations compared with the Max-Log-MAP demapper.
TL;DR: A family of modulation formats referred to as core-coding is investigated, one of which has the same power and spectral efficiency as polarization switched quaternary phase shift keying but with half of the optical power, potentially improving non-linear tolerance for long distance transmission, albeit at the cost of implementation challenges.
Abstract: ©2014 Optical Society of America We investigate high dimensional modulation formats for multi-core fibers (MCFs) and spatial superchannels. We show that the low skew variations between MCF cores maybe exploited to generate 'multi-core' formats that offer significant advantages over independently transmitting conventional 4-dimensional formats in each core. We describe how pulse position modulation formats may be transposed to the spatial domain and then investigate a family of modulation formats referred to as core-coding, one of which has the same power and spectral efficiency as polarization switched quaternary phase shift keying but with half of the optical power, potentially improving non-linear tolerance for long distance transmission, albeit at the cost of implementation challenges. Finally, we investigate the application of set-partitioning to multi-core formats using a single-parity check bit transmitted in one quadrature of one polarization in one of the cores and polarization-division multiplexing quadrature phase shift keying data in all remaining cores. We observe that for high core counts, an advantage of almost 3 dB in asymptotic power efficiency may be obtained with negligible impact on spectral efficiency, which translates into experimentally measured reduction in the required optical signal-to-noise ratio of up to 1.8 dB at a bit-error-rate of 10-5 and the same data-rate, and additional transmission reach of up to 20%.
TL;DR: A novel method of in-band estimation of optical signal-to-noise ratio (OSNR) using a digital coherent receiver, where OSNR is determined from second- and fourth-order statistical moments of equalized signals in any modulation format is proposed.
Abstract: We propose a novel method of in-band estimation of optical signal-to-noise ratio (OSNR) using a digital coherent receiver, where OSNR is determined from second- and fourth-order statistical moments of equalized signals in any modulation format. Our proposed method is especially important in recently-developed Nyquist wavelength-division multiplexed (WDM) systems and/or reconfigurable optical-add/drop-multiplexed (ROADM) networks, because in these systems and networks, we cannot apply the conventional OSNR estimation method based on optical-spectrum measurements of the in-band signal and the out-of-band noise. Effectiveness of the proposed method is validated with computer simulations of Nyquist-WDM systems and ROADM networks using 25-Gbaud quadrature phase-shift keying (QPSK) and 16 quadrature-amplitude modulation (16-QAM) formats.
TL;DR: The BER performance of a multi-hop RoFSO system which is using an orthogonal frequency division multiplexing (OFDM) scheme, with either quadrature amplitude modulation (QAM) or phase shift keying format (PSK), over atmospheric turbulence channels modeled with the gamma gamma or the negative exponential distribution is studied.
Abstract: The optical wireless and in particular the radio-on-free-space-optical (RoFSO) communication systems are gaining popularity due to their high date rates, license free spectrum and adequate reliability at installation and operational costs which are much lower than comparable technologies. One significant disadvantage of these systems concerns the randomly time varying characteristics of the propagation path mainly caused by the atmospheric turbulence. In this work, we study the BER performance of a multi-hop RoFSO system which is using an orthogonal frequency division multiplexing (OFDM) scheme, with either quadrature amplitude modulation (QAM) or phase shift keying format (PSK), over atmospheric turbulence channels modeled with the gamma gamma or the negative exponential distribution. The individual RoFSO parts of the whole optical link are connected to each other by using regenerators relay nodes. The dominant impairments which are the most significant and have been taken into account are the atmospheric turbulence, the path losses, the nonlinear responsivity of the laser diode and the inter-modulation distortion effect. For this setup, we derive closed form mathematical expressions for the estimation of the BER performance for each individual OFDM RoFSO link and for the whole relayed optical communication system, as well. Finally, the corresponding numerical results, for common link׳s parameters, are presented.