Quadrature Amplitude Modulation Modulation Research Articles

Hexagonal QAM-Based Four-Dimensional AMO-OFDM for Spectrally Efficient Optical Access Network Transmission

A novel spectrally efficient optical transmission in a passive optical network (PON) with hexagonal quadrature amplitude modulation (QAM)-based adaptive modulated optical (AMO) orthogonal frequency division multiplexing (OFDM) is proposed and experimentally demonstrated. With the help of hexagonal QAM and 4-dimensional (4D) modulation, adaptive bit loading is effectively processed to enhance the total data rate. In this approach, some subcarriers are aggregated to transmit integer bits. To employ hexagonal QAM-based 4D AMO-OFDM, the signal to noise (SNR) ratio is calculated using the measured error vector magnitude of the training signal. In our experiment, hexagonal QAM-based 4D AMO-OFDM transmission with a total data rate of 21 Gbps is demonstrated over a 20 km standard single mode fiber for two optical network units (ONUs). The experimental results show that the total data rate obtained using the proposed method is increased by 14% compared to the conventional square QAM-based AMO-OFDM.

Downlink Precoding for Massive MIMO Systems Exploiting Virtual Channel Model Sparsity

In this paper, the problem of designing a forward link linear precoder for massive multiple-input multiple-output (MIMO) systems in conjunction with quadrature amplitude modulation (QAM) is addressed. A challenge in such system design is to consider finite alphabet inputs, especially with larger constellation sizes, such as $M\geq 16$ . First, we employ a novel and efficient methodology that allows for an orthogonal, sparse representation of multiple users and groups in a fashion similar to joint spatial division and multiplexing (JSDM), thus offering an extension of JSDM to finite alphabet data symbols. We term the new approach JSDM for finite alphabets (JSDM-FA). JSDM-FA employs virtual channel model beams in order to explore the orthogonality between different groups. Then, we present a natural generalization of JSDM-FA to the frequency-selective case with orthogonal frequency-division multiplexing (OFDM) and also enhance OFDM with combined frequency and spatial division and multiplexing. This configuration offers high flexibility in Massive MIMO systems, as it is capable of offering separate decoding of each user data within a group or increase the spectral efficiency of spatially overlapping groups without sacrificing the overall cell spectral efficiency. The proposed methodology is next applied jointly with the complexity-reducing Per-Group Processing within groups technique, on a per user group basis, in conjunction with QAM modulation and in simulations, for constellation size up to $M=64$ . We show by numerical results that the precoders developed offer significantly better performance than the configuration with no precoder or the plain beamformer and with $M\geq 16$ .

High Power Efficient Quadrature Amplitude Modulation Soft Decision Algorithm

The quadrature amplitude modulation (QAM) is the basic technology on high speed broadband communication physical level symbol mapping. Systems requiring lower signal to noise ratio to achieve the same error probability are more power-efficient. The usage of high order modulation is limited due to its low power efficiency compared to lower order modulation. This paper combines the characteristics of Gray code symbol mapping for QAM constellation to design a soft decision algorithm based on signal diversity (div-log-MAP). The bottle-neck of the low power efficiency is overcome and highest power efficiency can be realized. The performance of div-log-MAP can beyond the performance of log maximum a posteriori probability algorithm. At the same time, the proposed algorithm is a more effective method to utilize high order QAM modulation on high speed broadband communication.

Increasing the symbol rate in QAM system using a new set of orthonormal basics functions

This paper proposes a new technique to increase the symbol rate in Quadrature Amplitude Modulation (QAM) using a new set of orthonormal functions. The proposed technique increases the rate of QAM symbols without increasing the bandwidth of the modulated signal or increasing the modulation order of the QAM symbol. The set of orthonormal functions consists of four shaped-sinusoidal functions. The shaping functions are Hilbert-Transform pair. The proposed QAM modulator modulates two independent complex symbols in the same time. Each modulated symbol uses two different functions from the proposed set. The paper shows the structure of the modulator and demodulator of the proposed system. The paper presents different shaping pulses, which can be used with the proposed system.

Performance of M ‐ary quadrature amplitude modulation ‐based orthogonal frequency division multiplexing for free space optical transmission

In this study, the authors analyse the performance of the free space optical (FSO) transmission link using orthogonal frequency division multiplexing (OFDM) modulation with M -ary quadrature amplitude modulation (QAM) encoder. For strong and weak atmospheric attenuation, the analysis of channel distribution in FSO is carried out using gamma–gamma model. In this analysis, the expressions for probability density function and cumulative density function of OFDM-based FSO channel have been derived in terms of Meijer's G-function. Also, the bit error rate and outage probability of M -ary QAM-based OFDM for an FSO transmission link has been derived. The feasibility of the system and the derived expressions are verified using Opti-system and MATLAB. From the analysis, it is observed that the performance of OFDM using M -ary QAM modulation is feasible for 7000 m, owning to its simplicity and good performance.

Comparison between balanced and unbalanced precoding technique in high-order QAM vector mm-wave signal generation based on intensity modulator with photonic frequency doubling.

We experimentally investigate high-order quadrature-amplitude-modulation (QAM) vector millimeter-wave (mm-wave) signal generation based on intensity modulator (IM) with photonic frequcney doubling and precoding in this paper. In order to obtain an ordinary QAM modulated radio-frequency (RF) signal after the square-law detection of the photodiode, amplitude and phase precoding technique should be employed. In this paper, we experimentally investigate the generation of 1~4 Gbaud vector mm-wave signal with the modulation formats of 8QAM and 16QAM at the carrier frequency of 40 GHz, and study the bit-error-rate (BER) performance of both balanced precoding scheme and unbalanced precoding scheme adopting high-order QAM modulation.

BER Performance of QAM and QPSK Modulation Technique for DCT Based Channel Estimation of STBC MIMO OFDM

Consumer demand for high speed data communication system is increasing day by day. However the major challenges for wireless communication system are Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) that occur during data transmission. This interference will distort signal and increase error rate in the system. Combination of Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input Multiple Output (MIMO) give a reliable high data rate. Discrete Cosine Transform (DCT)-based channel estimation is used in STBC MIMO-OFDM and simulated using MATLAB software. The system performance is compared with multiple antenna configuration and different modulation technique. Multiple antenna configurations that involve during simulation are 2x2, 4x4 and 6x6 while modulation techniques are Quadrature Amplitude Modulation (QAM) and Quadrature Phase Shift Keying (QPSK). This simulation will prove that the higher number of transmit and receive antenna, the lower BER for the system.

QAM Vector Signal Generation by Optical Carrier Suppression and Precoding Techniques

We numerically and experimentally investigate and compare photonic constant- and multi-amplitude quadrature-amplitude-modulation (QAM) vector signal generation at radio frequency (RF) bands enabled by a Mach-Zehnder modulator (MZM)-based optical carrier suppression (OCS) modulation. In order to attain an electrical vector RF signal displaying multi-amplitude QAM modulation, such as 8 QAM and 16 QAM, after square-law photodiode detection, the driving RF signal carrying multiamplitude QAM transmitter data, should be both amplitude- and phase-precoded before used to drive the MZM. However, for constant-amplitude QAM modulation, such as quadrature-phase-shift-keying (QPSK), only phase precoding is needed. We experimentally demonstrate 1-GBd vector signal generation at 12 GHz enabled by an MZM-based OSC modulation, adopting QPSK, 8 QAM, and 16 QAM modulation, respectively. We also experimentally compare the bit error rate performance of the three different vector signals, and the QPSK case is the best, while the 16 QAM case is the worst.

Performance Analysis of Scheduled STBC Over Non-Identically Distributed Arbitrary Nakagami Fading Channels

In this letter, we study the performance analysis of combining space-time block coding (STBC) and user scheduling over arbitrary Nakagami fading channels. Especially, we mainly focus on the independent and non-identically distributed (i.ni.d.) user terminals. This letter derives the exact cumulative distribution function (CDF) of the scheduled STBC over i.ni.d. arbitrary Nakagami fading channels. Using CDF and the Lauricella hypergeometric function, this letter derives the closed-form expressions of the scheduled STBC for the symbol error rate (SER) and the outage probability with phase shift keying (PSK) and quadrature amplitude modulation (QAM) over i.ni.d. arbitrary Nakagami fading channels. This letter also quantifies the diversity order and the signal to noise ratio (SNR) gain for the SER and the outage probability. From the analysis, we show that the diversity order of the scheduled STBC is $\sum_{k=1} ^Km_kLN_k$ for QAM and PSK modulations including the outage probability over i.ni.d. Nakagami fading channels.

W-Band 8QAM Vector Signal Generation by MZM-Based Photonic Frequency Octupling

We propose a novel scheme for photonic multiamplitude quadrature-amplitude-modulation (QAM) vector signal generation at microwave/millimeter-wave bands enabled by Mach-Zehnder modulator (MZM)-based adaptive photonic frequency multiplication. In order to attain an electrical millimeter-wave vector signal displaying multiamplitude QAM modulation, such as 8QAM, after square-law photodiode detection, the driving radio-frequency (RF) signal, carrying multiamplitude QAM transmitter data, should be both amplitude- and phase-precoded before used to drive the MZM. We experimentally demonstrate 8QAM vector signal generation at W-band adopting photonic frequency octupling (x8) enabled by our proposed scheme. The MZM is driven by a 12-GHz precoded RF signal carrying 1-GBaud 8QAM transmitter data. The generated 1-GBaud 8QAM vector signal at W-band is air transmitted over 2-m distance. To the best of our knowledge, it is the first time to realize the generation and reception of multiamplitude QAM vector signal by one external modulator at W-band.

Asynchronous Layered Modulation for High Spectral Efficiency Transmission with Lower Sensitivity to Phase Errors

In this paper, an asynchronous double layered modulation scheme is proposed to achieve high spectral efficiency transmission but has lower sensitivity to phase errors. By intentionally introducing a delay offset to the transmitted signals at each layer, the asynchronous double layered format can use lower level quadrature amplitude modulation (QAM) to achieve the same spectral efficiency as the conventional high level QAM modulation. The error probability performance of the asynchronous double layered format is analyzed in the presence of phase errors and the symbol error rate and the bit error rate are derived in the closed-form expression. Both the theoretical analysis and the simulation results show that the asynchronous layered format can achieve the same spectral efficiency as the conventional high level QAM modulation while has lower sensitivity to the phase errors.

Full-duplex fiber-wireless link with 40 Gbit/s 16-QAM signals for alternative wired and wireless accesses based on homodyne/heterodyne coherent detection

A novel full-duplex fiber-wireless link with 40Gbit/s 16-ary quadrature amplitude modulation (QAM) signals is proposed to provide alternative wired and wireless accesses for the user terminals. In the central station (CS), the downstream signal for wired and wireless accesses is beared onto the CW laser source via an optical I/Q modulator to realize the QAM modulation. At the hybrid optical network unit (HONU), a tunable laser is used to provide coherent optical local oscillator for homo-/heterodyne beating to coherently down-convert the baseband optical signal to the baseband electrical one for wired access or to the mm-wave one for wireless access according to the requirement of the user terminals. Simultaneously, the lightwave from the tunable laser is also used as the uplink optical carrier for either wired or wireless access, and is modulated colorlessly by the baseband or mm-wave signal of the uplink alternatively. After filtering, only one tone carrying the uplink signal is transmitted back to the CS even for the wireless access. The theoretical analysis and simulation results show that our proposed full-duplex link for the alternative wired and wireless accesses maintains good performance even when the transmission link with standard single mode fiber (SSMF) is extended to 30km.

Intercarrier Interference Immune Single Carrier OFDM via Magnitude-Keyed Modulation for High Speed Aerial Vehicle Communication

Orthogonal Frequency Division Multiplexing (OFDM) has been considered as a strong candidate for next generation wireless communication systems. Compared to traditional OFDM, Single Carrier OFDM (SC-OFDM) has demonstrated excellent bit error rate (BER) performance, as well as low peak to average power ratio (PAPR). Similar to other multi-carrier transmission technologies, SC-OFDM suffers significant performance degradation resulting from intercarrier interference (ICI) in high mobility environments. Existing techniques for OFDM can be directly adopted in SC-OFDM to improve performance, however, this improved performance comes at costs such as decreased throughput. In this paper, we analyze the effect of ICI on an SC-OFDM system and propose a novel modulation scheme. The proposed Magnitude-Keyed Modulation (MKM) modulation provides SC-OFDM system immunity to ICI and with an easy implementation it significantly outperforms OFDM, SC-OFDM and MC-CDMA systems with Phase Shift Keying (PSK) modulation and Quadrature Amplitude Modulation (QAM) in severe ICI environment. Analysis also illustrates the proposed SC-OFDM system with MKM modulation maintains low PAPR compared to traditional OFDM and SC-OFDM systems with PSK and QAM modulations. Simulation results for different modulation schemes in various ICI environments confirm the effectiveness of the proposed system.

64QAM Modulator With a Hybrid Configuration of Silica PLCs and LiNbO$_{3}$ Phase Modulators

Quadrature amplitude modulation (QAM) is a promising approach for increasing the spectral efficiency of wavelength-division-multiplexing transmission, but its optical implementation is challenging. We demonstrate a 64-level QAM (64QAM) modulator, which uses a signal synthesis in the optical domain. We achieved an integration of low-loss asymmetric couplers and three quadrature-phase-shift-keying modulation circuits using a hybrid configuration of silica-based planar lightwave circuits and an array of LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> phase modulators. The modulator successfully operated at 60 Gb/s (10 Gbaud).

Using fuzzy clustering and TTSAS algorithm for modulation classification based on constellation diagram

The automatic recognition of the modulation format of a detected signal, the intermediate step between signal detection and demodulation, is a major task of an intelligent receiver, with various civilian and military applications. Obviously, with no knowledge of the transmitted data and many unknown parameters at the receiver, such as the signal power, carrier frequency and phase offsets, timing information, etc., blind identification of the modulation is a difficult task. This becomes even more challenging in real world.In this paper I develop a novel algorithm using Two Threshold Sequential Algorithmic Scheme (TTSAS) algorithm and pattern recognition to identify the modulation types of the communication signals automatically. I have proposed and implemented a technique that casts modulation recognition into shape recognition. Constellation diagram is a traditional and powerful tool for design and evaluation of digital modulations. In this paper, modulation classification is performed using constellation of the received signal by fuzzy clustering and consequently hierarchical clustering algorithms are used for classification of Quadrature–Amplitude Modulation (QAM) and Phase Shift Keying (PSK) modulations and also modulated signal symbols constellation utilizing TTSAS clustering algorithm, and matching with standard templates, is used for classification of QAM modulation. TTSAS algorithm used here is implemented by the Hamming neural network. The simulation results show the capability of this method for modulation classification with high accuracy and appropriate convergence in the presence of noise.

An improved and efficient detection scheme for V-BLAST systems with QAM modulation

The paper proposed an improved Ordered Successive Interference Cancellation (OSIC) detection scheme for V-BLAST systems with square/rectangular Quadrature Amplitude Modulation (QAM) modulation. It utilizes an equivalent real-valued vector expression of relationship between transmit signals and received signals, exploits the constellation’s product-form structure and can eventually make the order, in which components of the transmit signals vector are extracted, more “optimal” in some sense. Thereby, it can offer an improved error probability as compared to the conventional OSIC detection scheme. In addition, the paper also proposes an efficient projection algorithm to calculate nulling vectors in a simple recursive fashion in order to avoid the vast increase of complexity, which is due to the fact that the original complex N-dimensional data vector and M × N channel matrix are transformed into a real 2N-dimensional data vector and a real 2M × 2N channel matrix respectively. A scrutinous complexity analysis shows that the complexity increases by only 33% as compared to the conventional scheme.

Turbo equalization receivers for evolved GSM/EDGE radio access network using QAM modulation

For evolution of the GSM/EDGE radio access network (RAN), the use of higher order modulation like 16- and 32-ary quadrature amplitude modulation (QAM) is considered in standardization for increased peak data rates and reduced transmission delays. In this paper, an optimized receiver design for different packet data transmission schemes is proposed. Turbo coding and turbo equalization is discussed for improved power efficiency and interference robustness. An efficient complexity reduction of the equalizer enables the usage of turbo equalization at a complexity comparable to that of separate equalization and decoding for turbo-coded transmission.

Design of Broadband Highly Linear IQ Modulator Using a 0.5$\mu$m E/D-PHEMT Process for Millimeter-Wave Applications

A broadband highly linear IQ modulator using a 0.5-mum enhancement/depletion-pseudomorphic high-electron mobility transistor process is presented in this letter. An innovative broadside/edge coupler is proposed to apply to the IQ modulator. The chip size is only 1times1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , including radio frequency and baseband PADs. The sideband and local oscillation suppressions of the modulator are better than -33 and -15 dBc, respectively. At a carrier frequency of 60 GHz with a 64 quadrature amplitude modulation (QAM) modulation, the modulator demonstrates an error vector magnitude of within 3%, and an adjacent channel power ratio of better than -40 dBc. To the best of the authors' knowledge, this work demonstrates the best modulation quality with a 64 QAM modulation up to 60 GHz among all the reported reflection-type IQ modulators.

Direct 16 QAM six-port modulator

A direct 16 quadrature amplitude modulation (QAM) modulator based on the six-port technique is proposed. It uses a six-port passive microwave network to implement the modulation scheme with suitable terminations. A microwave prototype was built to validate the 16 QAM modulation up to 200 Mbit/s data rate at 4.2 GHz carrier frequency. The error vector magnitude and local oscillator (LO) power testing show that this six-port 16 QAM modulator has wide dynamic range capability to overcome the LO power variation. It has potentially low cost and low power consumption for RF communications applications.

Unified models for adaptive OFDM systems when QAM or PSK modulation is applied

AbstractIn this paper, the solutions of the major bit‐loading problems that are found in the literature, are unified into simple equations (models). These equations give an insight of the affection of the channel over a multicarrier system. Moreover, the models allow the transition from the solution of one loading problem to the solution of the others. The models are dependent on the modulation type that is used. We examine the quadrature amplitude modulation (QAM) modulated orthogonal frequency division multiplexing (OFDM), and the phase shift keying (PSK)‐modulated OFDM systems. For each modulation type, the continuous throughput model is extracted. The continuous throughput model refers to a system that its subcarriers can be loaded with non‐integer number of bits. The non‐integer bit distribution can then be rounded to integers, using a rounding method. The models except from the calculation of the optimised quantities (total data rate, total power and symbol error rate) without the need of running a loading algorithm to its extent, provide a means to manipulate a whole multicarrier system in a way similar to single‐carrier system. Copyright © 2007 John Wiley &amp; Sons, Ltd.