Showing papers on "QAM published in 2018"

OTFS: A New Generation of Modulation Addressing the Challenges of 5G.

Abstract: In this paper, we introduce a new 2D modulation scheme referred to as OTFS (Orthogonal Time Frequency & Space) that multiplexes information QAM symbols over new class of carrier waveforms that correspond to localized pulses in a signal representation called the delay-Doppler representation. OTFS constitutes a far reaching generalization of conventional time and frequency modulations such as TDM and FDM and, from a broader perspective, it establishes a conceptual link between Radar and communication. The OTFS waveforms couple with the wireless channel in a way that directly captures the underlying physics, yielding a high-resolution delay-Doppler Radar image of the constituent reflectors. As a result, the time-frequency selective channel is converted into an invariant, separable and orthogonal interaction, where all received QAM symbols experience the same localized impairment and all the delay-Doppler diversity branches are coherently combined. The high resolution delay-Doppler separation of the reflectors enables OTFS to approach channel capacity with optimal performance-complexity tradeoff through linear scaling of spectral efficiency with the MIMO order and robustness to Doppler and multipath channel conditions. OTFS is an enabler for realizing the full promise of MUMIMO gains even in challenging 5G deployment settings where adaptation is unrealistic.

Design and Analysis of SCMA Codebook Based on Star-QAM Signaling Constellations

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.

Trans-Atlantic Field Trial Using High Spectral Efficiency Probabilistically Shaped 64-QAM and Single-Carrier Real-Time 250-Gb/s 16-QAM

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.

One-Bit Precoding and Constellation Range Design for Massive MIMO With QAM Signaling

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.

Quantized Constant Envelope Precoding With PSK and QAM Signaling

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.

A Distance and Bandwidth Dependent Adaptive Modulation Scheme for THz Communications

Abstract: In this paper, we provide a novel distance and frequency dependent adaptive modulation scheme, which is suitable for communication systems operating in the terahertz (THz) band After determining the transmission bandwidth, the proposed scheme evaluates the subcarrier bandwidth of the orthogonal frequency division modulated (OFDM) transmission signal, in order to countermeasure the frequency selectivity of the THz channel Next, the power is allocated to the OFDM subcarriers and the modulation order of the quadrature modulated (QAM) symbol loaded in each subcarrier is selected, based on the instantaneous channel conditions and a predetermined bit error rate (BER) requirement The proposed link adaptation algorithm has low computational complexity and can significantly increase the link's throughput

The Trade Off Between Different Modulation Schemes for Maximum Long Reach High Data Transmission Capacity Optical Orthogonal Frequency Division Multiplexing (OOFDM)

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.

A 28GHz 41%-PAE linear CMOS power amplifier using a transformer-based AM-PM distortion-correction technique for 5G phased arrays

Abstract: To fulfill the insatiable demand for high data-rates, the millimeter-wave (mmW) 5G communication standard will extensively use high-order complex-modulation schemes (e.g., QAM) with high peak-to-average power ratios (PAPRs) and large RF bandwidths. High-efficiency integrated CMOS power amplifiers (PA) are highly desirable for portable devices for improved battery life, reduced form factor, and low cost. To meet simultaneous requirements for high efficiency and reasonable linearity, PAs intended for use with complex modulation are often operated in Class-AB mode [1,2]. For small input amplitude in Class-AB, the device is turned-on and has an input capacitance (C gs ) of ∼(2/3)WLC ox . As the input amplitude becomes large, the device turns-off for part of the RF cycle, thus reducing its effective input capacitance. This input capacitance-modulation effect creates an input-amplitude-dependent phase shift in Class-AB mode resulting in an amplitude-modulation to phase-modulation (AM-PM) distortion [2]. Consequently, it degrades linearity metrics (e.g., error vector magnitude (EVM), adjacent channel power ratio (ACPR)) in complex-modulation systems. External linearization techniques (e.g., digital pre-distortion) are often used in transmitters to meet linearity requirements, but they are complex in nature and expensive to implement. Apart from these, few works at low-GHz frequencies are reported to improve the PA's intrinsic linearity using a varactor-or PMOS-based AM-PM correction methods [1,2]. These works reduce the design overhead of external linearization systems; however, the inclusion of additional capacitive element to correct AM-PM degrades gain and efficiency, which is not optimal for mmW frequencies [1,2].

Analysis of a Multibeam Optical Beamforming Network Based on Blass Matrix Architecture

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.

Comparison of Laguerre-Gaussian and Donut modes for MDM-WDM in OFDM-Ro-FSO transmission system

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.

Chaotic Constellation Mapping for Physical-Layer Data Encryption in OFDM-PON

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.

Quantized Constant Envelope Precoding with PSK and QAM Signaling

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 (MUI) and the quantization distortions in a downlink Multi-User (MU) 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 the QCE constraint. The optimization is based on maximizing the safety margin to the decision thresholds of the receiver constellation modulation. Simulation results show a significant gain in terms of the uncoded Bit Error Ratio (BER) compared to the existing linear precoding techniques.

A Simple Nonlinearity-Tailored Probabilistic Shaping Distribution for Square QAM

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.

Digitally Linearized Radio-Over Fiber Transmitter Architecture for Cloud Radio Access Network’s Downlink

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.

Joint Modulation Classification and OSNR Estimation Enabled by Support Vector Machine

Abstract: By adopting the cumulative distribution function of the received signal’s amplitude as feature, a support vector machine-based algorithm is proposed to jointly classify the modulation format and estimate the optical signal-to-noise ratio (OSNR) in coherent optical communication systems. Three commonly-used quadrature-amplitude modulation (QAM) formats are considered. Numerical simulations have been carried out in the OSNR ranges from 5 to 30 dB, and results show that the proposed algorithm achieves a very good modulation classification (MC) performance, as well as high OSNR estimation accuracy with a maximum estimation error of 0.8 dB. Optical back-to-back experiments are also conducted in OSNR ranges of interest. A 99% average correct MC rate is observed, and mean OSNR estimation errors of 0.38, 0.68, and 0.62 dB are noticed for 4-QAM, 16-QAM, and 64-QAM, respectively. Furthermore, compared with the neural networks-based joint estimation algorithm, the proposed algorithm attains better performance with comparable complexity.

A 1.58 Gbps/W 0.40 Gbps/mm2 ASIC Implementation of MMSE Detection for $128\times 8~64$ -QAM Massive MIMO in 65 nm CMOS

Abstract: The minimum-mean-square error (MMSE) plays a significant role in the signal detection process of massive multiple-input-multiple-output (MIMO) systems Matrix inversion, which is the major part of calculating the MMSE, suffers from high computing loads and low parallelism, especially in massive MIMO systems; as such, hardware implementation is difficult This paper proposes a user-level parallelism-based fully pipelined very large-scale integration (VLSI) architecture of an MMSE detector for an uplink $128\times 8~64$ -QAM massive MIMO system First, a diagonal-based systolic array with single-sided input is adopted; this array eliminates the throughput limitation Second, a weighted Jacobi-iteration-based architecture is proposed to iteratively achieve matrix inversion, thereby reducing the computational load and exploiting the potential parallelism of the matrix inversion Third, an approximated architecture is proposed to compute the log-likelihood ratio This architecture is verified on an FPGA and fabricated onto a 257 mm2 silicon with TSMC 65 nm CMOS technology, thereby achieving a 102 Gbps data rate at 680 MHz while dissipating 646 mW The results indicate an energy efficiency of 158 Gbps/W and an area efficiency of 040 Gbps/mm2, which are $293\times $ and $286\times $ that of state-of-the-art similar designs with CMOS technology, respectively

A high-efficiency 28GHz outphasing PA with 23dBm output power using a triaxial balun combiner

Abstract: Gigabit-per-second millimeter-wave (mm-wave) access and backhaul networks at 28GHz demand high-order QAM, OFDM, and/or carrier-aggregated waveforms that force the PA to operate under high peak-to-average power ratio (PAPR) [1]. High PAPR requirements aggravate the design of mm-wave Si CMOS and SiGe BiCMOS PAs since a linear response and high efficiency are simultaneously desired. Recent work has demonstrated mm-wave PAs with peak efficiency exceeding 30% at 28GHz for output powers above 20dBm [1-5]. However, high average efficiency associated with high-PAPR waveforms remains elusive. To improve average efficiency, circuit techniques based on Doherty [3] and outphasing [6] have been demonstrated in mm-wave bands. Earlier work using these techniques showed average efficiency with QAM waveforms that is well under 20%.

Impact of Imperfect CSI on ASER of Hexagonal and Rectangular QAM for AF Relaying Network

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.

UHD Video Transmission Over Bidirectional Underwater Wireless Optical Communication

Abstract: In this paper, we experimentally demonstrate for the first time a bidirectional underwater wireless optical communication system that is capable of transmitting an ultrahigh definition real-time video using a downlink channel while simultaneously receiving the feedback messages on the uplink channel. The links extend up to 4.5 m using QPSK, 16-QAM, and 64-QAM modulations. The system is built using software defined platforms connected to TO-9 packaged pigtailed 520 nm directly modulated green laser diode (LD) with 1.2 GHz bandwidth as the optical transmitter for video streaming on the downlink, and an avalanche photodiode (APD) module as the downlink receiver. The uplink channel is connected to another pigtailed 450 nm directly modulated blue LD with 1.2 GHz bandwidth as the optical uplink transmitter for the feedback channel, and to a second APD as the uplink receiver. We perform laboratory experiments on different water types. The measured throughput is 15 Mb/s for QPSK, and 30 Mb/s for both 16 QAM and 64 QAM. We evaluate the quality of the received live video streams using peak signal-to-noise ratio and achieve values up to 16 dB for 64 QAM when streaming UHD video in harbor II water and 22 dB in clear ocean.

10.72Gb/s Visible Light Communication System Based On Single Packaged RGBYC LED Utilizing QAM-DMT Modulation With Hardware Pre-Equalization

Abstract: In this paper, we experimentally demonstrated a 10.72Gb/s wavelengths multiplexing visible light communication system over 1-m indoor free space transmission using a single packaged RGBCY LED with hardware pre-equalization and post equalizer with the bit error rate below 3.8×10−3.

Improved Performance of high-order QAM OFDM Based on Probabilistically Shaping in the Datacom

Abstract: We experimentally demonstrated a PS-256-QAM OFDM fiber transmission in a low-cost IM-DD system. Compared with uniform 128-QAM, the proposed PS-256-QAM obtains the same entropy of 7 bits/QAM symbol, but higher achievable-information-rate performance and stronger nonlinearity robustness.

Spectrally efficient digitized radio-over-fiber system with k-means clustering-based multidimensional quantization.

Abstract: We propose a spectrally efficient digitized radio-over-fiber (D-RoF) system by grouping highly correlated neighboring samples of the analog signals into multidimensional vectors, where the k-means clustering algorithm is adopted for adaptive quantization. A 30 Gbit/s D-RoF system is experimentally demonstrated to validate the proposed scheme, reporting a carrier aggregation of up to 40 100 MHz orthogonal frequency division multiplexing (OFDM) channels with quadrate amplitude modulation (QAM) order of 4 and an aggregation of 10 100 MHz OFDM channels with a QAM order of 16384. The equivalent common public radio interface rates from 37 to 150 Gbit/s are supported. Besides, the error vector magnitude (EVM) of 8% is achieved with the number of quantization bits of 4, and the EVM can be further reduced to 1% by increasing the number of quantization bits to 7. Compared with conventional pulse coding modulation-based D-RoF systems, the proposed D-RoF system improves the signal-to-noise-ratio up to ∼9 dB and greatly reduces the EVM, given the same number of quantization bits.

Paraunitary-Based Boolean Generator for QAM Complementary Sequences of Length $2^{K}$

Abstract: A Boolean generator for a large number of standard complementary QAM sequences of length $2^{K}$ is proposed. This Boolean generator is derived from the authors’ earlier paraunitary generator, which is based on matrix multiplications. Both generators are based on unitary matrices. In contrast to previous Boolean QAM algorithms which represent complementary sequences as a weighted sum, our algorithm has a multiplicative form. Any element of a sequence can be generated efficiently by indexing the entries of unitary matrices with the binary representation of the discrete time index (which is easily implemented as a binary counter). Our 1Qum (based on one QAM unitary matrix) and 2Qum (based on two QAM unitary matrices) algorithms generate generalized Case I – III sequences and generalized Case IV and V sequences, respectively, as specified by Liu et al. in 2013, in addition to many new 2Qum sequences. The ratio of the numbers of sequences that are generated by our new construction and the previous construction increases with the constellation size. For example, for a 1024-QAM sequence of length 1024, this ratio is 4.4. However, if we compare only 2Qum sequences to Case IV and V sequences, this ratio is 267.

On line rates, information rates, and spectral efficiencies in probabilistically shaped QAM systems.

Abstract: We carefully revisit the definitions of line rates, information rates, and spectral efficiencies in probabilistically shaped optical transmission systems. Generally accepted definitions for uniform quadrature amplitude modulation (QAM) systems are extended to more generally apply to systems with probabilistically shaped QAM, as well as to systems using pilot symbols of different QAM order than the information symbols. Based on the proper definitions, we correct erroneous claims in a recently reported work.

Generation and Intradyne Detection of Single-Wavelength 1.61-Tb/s Using an All-Electronic Digital Band Interleaved Transmitter

Abstract: We generate 100-GHz wide in-phase and quadrature electrical signals via two synchronized digital band interleaved digital-to-analog converters and demonstrate single-wavelength digital band multiplexed QAM with an aggregate all-electronically generated line rate of 1.61 Tb/s.

Universal Hybrid Probabilistic-geometric Shaping Based on Two-dimensional Distribution Matchers

Abstract: We propose universal distribution matchers applicable to any two-dimensional signal constellation. We experimentally demonstrate that the performance of 32-ary QAM, based on hybrid probabilistic-geometric shaping, is superior to probabilistically shaped 32QAM and regular 32QAM.

Rate-Energy Region in Wireless Information and Power Transfer: New Receiver Architecture and Practical Modulation

Abstract: When simultaneous wireless information and power transfer is carried out, a fundamental tradeoff between achievable rate and harvested energy exists because the received power is used for two different purposes. The tradeoff is well characterized by the rate-energy region, and several techniques have been proposed to improve the achievable rate-energy region. However, the existing techniques still have a considerable loss in either energy or rate and thus the known achievable rate-energy regions are far from the ideal one. Deriving tight upper and lower bounds on the rate-energy region of our proposed scheme, we prove that the rate-energy region can be expanded almost to the ideal upper bound. Contrary to the existing techniques, in the proposed scheme, the information decoding circuit not only extracts amplitude and phase information but also combines the extracted information with the amplitude information obtained from the rectified signal. Consequently, the required energy for decoding can be minimized, and thus the proposed scheme achieves a near-optimal rate-energy region, which implies that the fundamental tradeoff in the achievable rate-energy region is nearly eliminated. To practically account for the theoretically achievable rate-energy region, we also present practical examples with an $M$ -ary multi-level circular QAM with Gaussian maximum likelihood detection.

Linewidth-tolerant and multi-format carrier phase estimation schemes for coherent optical m-QAM flexible transmission systems.

Abstract: Multi-format and linewidth-tolerant carrier phase estimation (CPE) is a vital part of digital signal processing (DSP) units for future elastic optical transmissions to relax the laser linewidth limitation. In this paper, an innovative CPE scheme outperforming existing CPEs in both universality and performance is presented and verified for multiple quadrature amplitude modulation (QAM) formats. Based on the technique of extended QPSK partitioning and quasi-linear approximation, accurate phase estimation is determined by calculating the intersection of two symmetric straight lines with very low complexity. Comprehensive simulation results of square 4/16/32/64-QAM not only demonstrate that the scheme can be applied to different modulation formats with a universal structure, i.e., indicate its flexibility in the format-adaptive elastic optical networks (EONs), but also show that the linewidth tolerance is greatly enhanced even in comparison with traditional BPS schemes. In addition, taking 64-QAM as an example, the computational efforts can be significantly reduced by a factor of 15.7 (or 10.3) in the form of multipliers (or adders). The slightly better OSNR performance is experimentally validated in polarization multiplexing 16GBaud 4/16-QAM systems respectively, which shows the potential application for flexible receiver-side DSP unit in EONs.

Single-RF Index Shift Keying Aided Differential Space–Time Block Coding

Abstract: We propose a new single-RF differential space–time block coding using index shift keying (DSTBC-ISK), which is the first differential space–time modulation (DSTM) scheme that can simultaneously achieve the following three imperative objectives: First, forming a finite-cardinality transmit-signals set; second, retaining a single-stream maximum-likelihood (ML) detection complexity; and third, offering a beneficial transmit diversity gain. In order to make a fair comparison, we also conceive a low-complexity single-stream detector for DSM. Furthermore, in order to improve the performance of finite-cardinality DSTM schemes at higher throughputs, we propose to generalize both differential amplitude shift keying (DASK) and amplitude shift keying (ASK), which subsume the existing two-/four-level-ring star quadratic–amplitude modulation (QAM) solutions as special cases. As a result of using star QAM signaling, the power of the DSTM's signal matrix becomes variable. Against this background, we further develop bespoke ML, minimum mean squared error, and least-square detectors for DSTM using DASK/ASK. Our simulation results demonstrate that the proposed DSTBC-ISK is capable of achieving substantial diversity gains over DSM without eroding its low transceiver complexity.