Quadrature Amplitude Modulation Signals Research Articles

Performance of decode-and-forward over Nakagami-m fading channel in cooperative wireless networks

In this paper, we analyse the performance of a decode-and-forward (DF) multi-relay system over Nakagami-m fading channels. First, the closed form expression for the symbol error rate (SER) for both M phase shift keying (MPSK) and M quadrature amplitude modulation (MQAM) signals is derived using the concept of moment generating function (MGF) in the high signal to noise ratio (SNR) and determining a tight SER lower bound that converges to the same limit as the theoretical upper bound. Next, by optimising SER, we can identify the optimal amount of power that should be allocated at the source and relay nodes to develop an optimal power allocation (OPA) technique to reduce the SER. The validation of the theoretical analysis is corroborated by the simulation results of the proposed model over Nakagami-m fading compared to the various schemes regarding the performance in terms of the model’s achievable SER and OPA.

Digital signal processing techniques in Nyquist-WDM transmission systems

In single-carrier wavelength-division-multiplexing (WDM) systems, the spectral efficiency can be increased by reducing the channel spacing through digital signal processing (DSP). Two major issues of using tight filtering are crosstalk between channels and inter-symbol interference (ISI) within a channel. By fulfilling the Nyquist criterion, Nyquist spectral shaped WDM systems can achieve a narrow channel spacing close to the symbol rate (Rs) with negligible crosstalk and ISI. In principle, DSP can generate any signals with arbitrary waveforms and spectrum shapes. However, the complexity of DSP is limited by its cost and power consumption. It is necessary to optimize the DSP to achieve the required performance at a minimum complexity. In this paper, we investigated the use of digital finite impulse response (FIR) filters to generate Nyquist-WDM 16-ary quadrature amplitude modulation (16QAM) signals with the raised-cosine (RC) and root-raised-cosine (RRC) shape spectrum. The system performance of both the RC and RRC spectra are also examined. Moreover, we explored the various methods to reduce digital-to-analog-converter (DAC) sampling speed, such as using super Gaussian electrical filters (E-filter), and spectral pre-emphasis.

Two Novel Blind Equalization Algorithms for Rectangular Quadrature Amplitude Modulation Constellations

Two novel blind equalization techniques for odd bit rectangular quadrature amplitude modulation (RQAM) signaling are proposed in this paper, namely, rectangular contour algorithm (R RECT CA) and improved rectangular contour algorithm (IRCA). The proposed R RECT CA algorithm minimizes the dispersion of constant with respect to a rectangular-shaped zero error contour. The algorithm exploits the geometry of the RQAM to correct phase error within 180°, thus enhancing the convergence rate while minimizing the equalizer mis-adjustments. On the other hand, the proposed IRCA algorithm employs the estimated output from the decision device into the cost function, thus guiding the equalizer output to reside on multiple zero error rectangular shaped moduli. This method of feeding back the slicer output further reduces the mis-adjustment between the transmitted constellation and the new cost function in an efficient manner, which leads to faster convergence and better intersymbol interference suppression. The proposed algorithms can also work for the square QAM by mere change of only two constellation dependent constants, thus facilitating the implementation in hardware to enable transmission of both even and odd number of bits per symbol based constellations. Steady-state error analysis, MSE, and residual ISI comparison through the simulation results confirm the good performance of the proposed algorithms. Furthermore, the convergence characteristics of the proposed IRCA scheme establish the supremacy of IRCA over R RECT CA, which is its parent algorithm.

Maximum entropy whitening algorithm with adaptive neuron slope for blind DFE

The addressed blind decision feedback equalizer (DFE) reverses the classical order of its feed-forward and feedback filters at the beginning of adaptation to achieve the best equalization of the minimum and maximum phase components of a channel transfer function. Although very effective, this blind equalization approach deals with the feedback filter mismatch at the time of its transformation from the front-end all-pole whitener of the received signal to the decision-directed feedback equalizer placed after the feedforward filter. To eliminate this weakness, the adaptive neuron slope is introduced instead of the fixed one into the stochastic gradient whitening algorithm based on the joint entropy maximization cost. The performance of the innovated algorithm is verified by simulating m-QAM (quadrature amplitude modulation) signals transmission over multipath channels. The algorithm with the adaptive neuron slope achieves a better whitening of the received signal spectrum, and, hence, increases the equalization successfulness.

A SiGe BiCMOS Power Amplifier Using a Lumped Element-Based Impedance Tuner

A dual-path multi-band power amplifier (PA) with a tunable output matching network is presented for long-term- evolution (LTE) handset applications. To optimize output load impedances for various power regions with various frequency bands, an impedance tuner implemented using lumped elements is used. The dual-path multi-band PA fabricated using $0.35{\mathchar702D}\mu{\rm m}$ SiGe BiCMOS process is evaluated for the evolved UMTS terrestrial radio access (E-UTRA) bands 1, 2, 3, 5, and 8 with a 10 MHz bandwidth (BW) LTE 16 quadrature amplitude modulation signal having a peak-to-average ratio of 6.4 dB.

Crosstalk Reduction With Bidirectional Signal Assignment on Square Lattice Structure 16-Core Fiber Over WDM Transmission for Gradual Upgrade of SMF-Based Lines

C-band and L-band wavelength division multiplexing (WDM) transmission performance was improved by using bidirectional signal assignment (BSA) to reduce crosstalk (XT) in square lattice structure 16-core fiber. Transmission of 16 WDM channels with 256-Gb/s polarization multiplexed-16 quadrature amplitude modulation signals on a 50-GHz grid with a net spectral efficiency of 4 b/s/Hz over 55-km of 16-core fiber spans was achieved. Use of BSA to reduce XT extended the transmission distance to 880 km in both types of transmission. Furthermore, transmission was achieved over eight mixed spans consisting of 16-core fiber and conventional single-mode fiber (SMF), demonstrating the possibility of gradually upgrading standard SMF-based lines to multicore fiber-based lines. With BSA, six 16-core fiber spans can be acceptable if the Q penalty from XT is below 0.5 dB.

All-optical multi-channel wavelength conversion of Nyquist 16 QAM signal using a silicon waveguide.

We experimentally demonstrate on-chip all-optical multi-channel wavelength conversion of Nyquist 16 ary quadrature amplitude modulation (16 QAM) signal in a silicon waveguide. The measured optical signal-to-noise ratio (OSNR) penalties of wavelength conversion are ∼2 dB. The observed constellations of converted idlers indicate favorable performance of silicon-waveguide-based multi-channel wavelength conversion. We also experimentally study and compare the phase-conjugated wavelength conversion by degenerate four-wave mixing (FWM) and transparent wavelength conversion by non-degenerate FWM in the silicon waveguide.

Simultaneous demultiplexing and steering of multiple orbital angular momentum modes

We present a simple scheme to perform simultaneous demultiplexing and steering of multiple orbital angular momentum (OAM) modes using a single complex phase mask. By designing the phase mask, the propagation directions of demultiplexed beams can be arbitrarily steered. System experiments using orthogonal frequency-division multiplexing 32-ary quadrature amplitude modulation (OFDM-32QAM) signals over two OAM modes are carried out by using a two-mode complex phase mask. Moreover, demultiplexing of sixteen OAM modes and arbitrary demultiplexed beam steering are also demonstrated in the experiment.

Transmission and reception of PDM dual-subcarrier coherent 16QAM-OFDM signals

In this paper, 16-Gbaud polarization-division-multiplexed (PDM) dual-subcarrier coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission and reception are successfully demonstrated without overhead. The in-phase and quadrature (I/Q) components of dual-subcarrier 16-ary quadrature amplitude modulation (QAM) OFDM signal are both seven-level signals in time domain, and thus can be equalized like a 49 QAM signal in time domain with cascaded multi-modulus algorithm (CMMA) equalization method. The experimental results show that there is no power penalty observed between optical back to back (OBTB) and after 80-km single-mode fiber-28 (SMF-28) with time domain CMMA equalization method. A 0.4dB optical signal to noise ratio (OSNR) penalty in OBTB is observed when the bandwidth of channel is set at 26GHz at the BER of 2.0×10−2.

Performance analysis of a family of adaptive blind equalization algorithms for square-QAM

Multimodulus algorithms (MMA) based adaptive blind equalizers mitigate inter-symbol interference and recover carrier-phase in communication systems by minimizing dispersion in the in-phase and quadrature components of the received signal using the respective components of the equalized sequence in a decoupled manner. These equalizers are mostly incorporated in bandwidth-efficient digital receivers which rely on quadrature amplitude modulation (QAM) signaling. The nonlinearities in the update equations of these equalizers tend to lead to difficulties in the study of their steady-state performance. This paper presents originally the steady-state excess mean-square-error (EMSE) analysis of different members of multimodulus equalizers MMAp–q in a non-stationary environment using energy conservation arguments, and thus bypassing the need for working directly with the weight error covariance matrix. In doing so, the exact and approximate expressions for the steady-state mean-square-error of several MMA based blind equalization algorithms are derived, including MMA2–2, MMA2–1, MMA1–2, and MMA1–1. The accuracy of the derived analytical results is validated using Monte–Carlo experiments and found to be in close agreement.

Performance Analysis of Best Relay Selection in Cooperative Wireless Networks

Cooperative communication has been proposed recently in wireless communication systems because of its producing high network reliability and considerable error rate decrease with an extension in the coverage area in wireless networks without need for an increase in the infrastructure. The most challenging problem in implementing cooperation protocols in cooperative wireless networks is the relay selection. This paper proposes a relay selection technique based on Decode-and-Forward (DF) relaying protocol, using the available channel state information (CSI) at the source and the relays. We first establish a closed form symbol error rate (SER) by using the concept of moment generating function (MGF) for both M phase shift keying (MPSK) and M quadrature amplitude modulation (MQAM) signals. By finding the cumulative density function (CDF) and the probability density function (PDF); this facilitated the derivation of a new SER and can propose an optimal power method with relay selection (RS) technique where only the best relay is selected that maximizes the signal-to-noise ratio (SNR) to achieve the transmission process and develop the performance of the system. Finally, simulation results provided good confirmation of the theoretical analysis.

Linear Vector Physical-Layer Network Coding for MIMO Two-Way Relay Channels: Design and Performance Analysis

In this paper, we propose a new linear vector physical-layer network coding (NC) scheme for spatial multiplexing multiple-input multiple-output (MIMO) two-way relay channel (TWRC) where the channel state information (CSI) is not available at the transmitters. In this scheme, each user transmits $M$ independent quadrature amplitude modulation signal streams respectively from its $M$ antennas to the relay. Based on the receiver-side CSI, the relay determines a NC generator matrix for linear vector network coding, and reconstructs the associated $M$ linear combinations of all messages. We present an explicit solution for the generator matrix that minimizes the error probability at a high SNR, as well as an efficient algorithm to find the optimized solution. We propose a novel typical error event analysis that exploits a new characterization of the deep fade events for the TWRC. We derive a new closed-form expression for the average error probability of the proposed scheme over a Rayleigh fading MIMO TWRC. Our analysis shows that the proposed scheme achieves the optimal error rate performance at a high SNR. Numerical results show that the proposed scheme significantly outperforms existing schemes, and match well with our analytical results.

A Fast Converge Momentum Dual-Mode Modified Constant Modulus Blind Equalization Algorithm for High-Order QAM Signals

A dual-mode blind channel equalization algorithm for high-order quadrature amplitude modulation (QAM) signals is proposed. The proposed algorithm, named momentum constellation matching error modified constant modulus algorithm (MCME---MCMA), firstly starts the equalization by momentum MCMA algorithm, and then introduces a constellation matching error term when it beginning to converge, which significantly reduces the steady-state mean square error (MSE). An optimized switching-point is provided and confirmed by simulations. Simulations demonstrate that MCME---MCMA improves the convergence rate and decreases the MSE by 5---7 dB for 64-QAM and 256-QAM compared with that of MCMA.

Photonic-aided pre-coding QAM signal transmission in multi-antenna radio over fiber system

A novel method has been proposed and experimentally demonstrated to provide photonic-aided pre-coding quadrature amplitude modulation (QAM) signal transmission in multi-antenna radio over fiber system to increase the throughput. For downlink, two different multi-level amplitude-shift-keying (M-ASK) modulated signals, such as 4-ASK signals, are applied on two uncorrelated optical Mach–Zehnder modulators at central office. After photonic-aided pre-coding module and photo-detection process, the received M-ASK mm-waves from two remote access units (RAUs) can be synthesized to a M2-QAM signal in the proposed system. Regardless of forward error correction (FEC) coding overhead, the 4-Gb/s and 8-Gb/s 16-QAM mm-wave signals are obtained from two independent 2-Gb/s and 4-Gb/s 4-ASK 40-GHz channels, respectively. The experimental results show that a doubled bit rate of the original 4-ASK one can be achieved without additional digital signal processing (DSP) in small cell RAUs and mobile users.

High-Speed Signal Transmission at W-Band Over Dielectric-Coated Metallic Hollow Fiber

We demonstrate, for the first time, over 100-Gb/s signal transmission at W-band over the dielectric-coated metallic hollow fiber (DMHF). We have experimentally demonstrated the transmission of both up to a 48-Gb/s single polarization quadrature phase shift keying signal and up to an 80-Gb/s single polarization 16-ary quadrature amplitude modulation signal at W-band over 1.5-m DMHF with bit error ratios (BERs) less than 3.8 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . We have also experimentally demonstrated the transmission of up to a 128-Gb/s dual-polarization 16-ary quadrature amplitude modulation (DP-16QAM) signal at W-band over two parallel spans of 1.5-m DMHF based on space division multiplexing with a BER less than 3.8 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . The experimental results establish a transmission record for radio frequency at W-band carrying such a high data rate over the DMHF and demonstrate the potentiality of a new high-speed transmission medium for W-band.

Adaptive power-controllable orbital angular momentum (OAM) multicasting.

We report feedback-assisted adaptive multicasting from a single Gaussian mode to multiple orbital angular momentum (OAM) modes using a single phase-only spatial light modulator loaded with a complex phase pattern. By designing and optimizing the complex phase pattern through the adaptive correction of feedback coefficients, the power of each multicast OAM channel can be arbitrarily controlled. We experimentally demonstrate power-controllable multicasting from a single Gaussian mode to two and six OAM modes with different target power distributions. Equalized power multicasting, “up-down” power multicasting and “ladder” power multicasting are realized in the experiment. The difference between measured power distributions and target power distributions is assessed to be less than 1 dB. Moreover, we demonstrate data-carrying OAM multicasting by employing orthogonal frequency-division multiplexing 64-ary quadrature amplitude modulation (OFDM 64-QAM) signal. The measured bit-error rate curves and observed optical signal-to-noise ratio penalties show favorable operation performance of the proposed adaptive power-controllable OAM multicasting.

SEP of Decode-and-Forward Cooperative Systems With Relay Selection in Nakagami- &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$m$&lt;/tex-math&gt;&lt;/inline-formula&gt; Fading Channels

The exact average bit error probability (BEP) of decode-and-forward (DF) cooperative systems with relay selection for binary phase-shift keying (BPSK) signals in Nakagami-m fading channels is derived. Two types of relay selection schemes, i.e., signal-to-noise ratio (SNR)-based relay selection and log-likelihood-ratio-based relay selection, are investigated, assuming that there are no feedback channels from the destination to the relays. Two types of receivers, i.e., a λ-maximal ratio combining receiver and a piecewise linear receiver, are examined. The BEP analysis for DF cooperative systems employing BPSK signals is used to derive symbol error probability upper bounds of DF cooperative systems with SNR-based relay selection for quadrature phase-shift keying and 16-quadrature amplitude modulation (16-QAM) signals.

Demonstration of terabit-scale data transmission in silicon vertical slot waveguides.

We design and fabricate silicon vertical slot waveguides for terabit-scale data transmission. The designed silicon photonic device is composed of apodized grating couplers, strip waveguides, strip-to-slot/slot-to-strip mode converters, and slot waveguide. Tight light confinement in the nano-scale air slot region is achieved in the silicon vertical slot waveguide which features relatively lower nonlinearity compared to silicon strip waveguide. Using the fabricated silicon photonic devices, we first demonstrate ultra-wide bandwidth 1.8-Tbit/s data transmission through a 2-mm-long silicon vertical slot waveguide using 161 wavelength-division multiplexing (WDM) channels each carrying 11.2-Gbit/s orthogonal frequency-division multiplexing (OFDM) 16-ary quadrature amplitude modulation (16-QAM) signal. All 161 WDM channels achieve bit-error rate (BER) less than 1e-3 after on-chip data transmission. We further demonstrate terabit-scale data transmission through four silicon vertical slot waveguides with different lengths (1 mm, 2 mm, 3.1 mm, 12.2 mm). The optical signal-to-noise ratio (OSNR) penalties of data transmission through four silicon vertical slot waveguides are 1, 2, 3.2 and 4.5 dB at a BER of 1e-3, respectively. The obtained results indicate that the presented silicon vertical slot waveguide might be an alternative promising candidate facilitating chip-scale high-speed optical interconnections.

오차 스케일링에 의해 블라인드 수렴 특성을 개선한 새로운 판정의거 등화

The Decision-directed (DD) algorithm is known to be not effective to initialize a blind equalizer in the channel conditions when the eye diagram of received signals is completely closed because it can not open the eye diagram enough. In this paper, we propose a new error to replace the error of the conventional DD algorithm. The new DD error is the conventional DD error scaled by the modulus of symbol decision, new DD algorithm using this error is effective to open the closed eye diagram in early stage of equalization unlike the conventional DD. The new DD algorithm appling the new error is showed excellent convergence characteristics as compared to the CMA widely used in blind initialization, particularly, is useful for equalization of signals having multimodulus. The performance of the new DD algorithm is verified through the simulation for the higher-order QAM signals. ※ 이 연구는 2014년도 광주대학교 대학 연구비의 지원을 받아 수행되었음. First Author : Dept. of Optical Commun. Eng., Gwangju Univ., knoh@gwangju.ac.kr, 종신회원 논문번호:KICS2015-01-008, Received January 12, 2015; Revised March 11, 2015; Accepted March 11, 2015 I. 서 론 고차 QAM(quadrature amplitude modulation) 신 호에 대한 블라인드 등화 시, 블라인드 초기화에 널리 사용되는 CMA(constant modulus algorithm)는 원 신호점 대신 일정 모듈러스(constant modulus)를 기준 신호(reference signal)로 사용하여 등화기의 수렴을 달성한다. 그러나 그 대가로 CMA는 정상상태 성능이 The Journal of Korean Institute of Communications and Information Sciences '15-03 Vol.40 No.03 420 k h n s n y + n ν

Feed-forward carrier phase recovery for offset-QAM Nyquist WDM transmission.

Due to the half symbol delay between in-phase and quadrature components for offset quadrature amplitude modulation (OQAM) signal, phase noise cannot only lead to constellation rotation but also introduce additional crosstalk. Therefore, OQAM signal has very poor tolerance to the laser linewidth. Here, we carry out a semi-analytical investigation of phase noise induced crosstalk during OQAM Nyquist WDM transmission, and find that the carrier phase recovery (CPR) has to be implemented prior to the inter-symbol-interference (ISI) equalization. Then, after a function separation of polarization de-multiplexing and ISI equalization, we propose a new DSP flow with a linewidth-tolerant blind feed-forward CPR scheme for OQAM signal. Its effectiveness is verified under the scenario of 5-channel 28-Gbaud polarization multiplexing (PM) OQAM Nyquist WDM systems. A tolerance of linewidth and symbol duration products of 6.5×10(-4) and 1.1×10(-4) is secured for 4-OQAM and 16-OQAM, respectively, given 1-dB required-OSNR penalty at BER = 10(-3).