8-QAM Constellation Research Articles

Interleaved superposed-64QAM-constellation design for spatial multiplexing visible light communication systems

Superposed constellation combined with spatial multiplexing multiple-input multiple-output (MIMO) techniques have been increasingly utilized in visible light communication (VLC) systems, as multiplexing gains can be achieved regardless of the correlation extent of the VLC channel. Herein, we propose a novel superposed 64-quadrature amplitude modulation (QAM) constellation scheme for 2 × 2 MIMO VLC systems. Considering the nonlinearity of light-emitting diodes (LEDs), two geometrically shaped 8QAM constellations are introduced to reduce the peak-to-average power ratio at the transmitter. Because the two 8QAM constellations are superposed in an interleaved manner, the required power ratio between two transmitted signals is 1, which further reduces the risk of nonlinear distortion and avoids signal-to-noise ratio deterioration induced by power competition. The proposed superposed 64QAM constellation scheme is experimentally investigated comprehensively, where the system performance is evaluated under different transmitted powers, direct current bias currents, and driving peak-to-peak voltages (Vpps). The experimental results show that the proposed scheme achieves better bit error rate (BER) performance than the traditional superposed 64QAM constellation schemes. Below the 7% pre-forward error correction BER threshold of 3.8 × 10-3, the dynamic range of the driving Vpps of the two LEDs improves from 0.06 to 0.4 V and 0.23 to 0.4 V when the optimal power ratio is achieved.

Support vector machine based machine learning method for GS 8QAM constellation classification in seamless integrated fiber and visible light communication system

Visible light communication (VLC) network over optical fiber has become a potential candidate in ultra-high speed indoor wireless communication. To mitigate signal distortion accumulated in optical fiber and VLC channel, we present to utilize support vector machine (SVM) for constellation classification in two kinds of geometrically-shaped 8QAM (quadrature amplitude modulation) seamless integrated fiber and VLC system. We introduce 4 sub-bands to simulate multi-user. Experimental results show that system performance can be significantly improved, and transmission at −2.5 dBm input optical power under 7% forward error correction (FEC) threshold can be realized employing Circular (7, 1) geometrically-shaped 8QAM and SVM. At overall capacity of 960 Mbps, Q-factor increases by up to 11.5 dB.

8-QAM Division for Uplink Massive SIMO Systems

In this letter, we consider an ultra-reliable low-latency communication (URLLC) scheme for one uplink massive single-input multiple-output (SIMO) system with three users. In our design, to enable all the users to update status information to the base station (BS) concurrently with an extremely low latency, we specifically decompose a cross 8-QAM constellation into one additive uniquely decomposable constellation group (AUDCG), and then devise a new multiuser space-time modulation scheme at the transmitters accordingly. For the receiver side, to assure that the BS can detect all the transmitted signals of different users simultaneously with a high reliability and a low latency, we investigate a noncoherent maximum likelihood (ML) receiver in comparison to a minimum Riemannian distance (MRD) estimator and a minimum Euclidean distance (MED) detector when the antenna array size is scaled up. Finally, extensive computer simulations are carried out to validate the effectiveness of our proposed design when the antenna array size is large.

Superposed 32QAM Constellation Design for 2 × 2 Spatial Multiplexing MIMO VLC Systems

Spatial multiplexing multiple-input multiple-output (MIMO) visible light communication (VLC) has become a potential candidate for next-generation wireless communication networks. In this paper, a novel superposed odd-order 32QAM constellation scheme is proposed in 2 × 2 MIMO VLC systems. Two independent signals generated from two light emitting diode (LED)-based transmitters with a four-quadrature amplitude modulation (4QAM) and geometrically shaped square 8QAM, respectively, are transmitted over free space and spatially multiplexed in the receiver to obtain a distinctly square-shaped 32QAM signal. The high channel correlation causes failure of MIMO detection in traditional spatial multiplexing (SMP) systems owing to the rank defect of the channel matrix. However, MIMO detection can always be realized by a simple constellation de-mapping based on the concept of superposed constellations, regardless of the extent of channel correlation. Considering the non-linearity of an LED, the square-shaped 8QAM constellation is introduced to reduce the peak to average power ratio (PAPR) at the transmitter, which also benefits from its maximum minimum Euclidean distance (MED) at the receiver compared to those of traditional 8QAM constellations. Moreover, the equal-gain combining (EGC) algorithm is employed to gain the receive diversity. The proposed system is experimentally studied in detail, where the system performance is evaluated under the conditions of different driving peak-to-peak voltages (Vpps) and channel gains. The experimental demonstration also shows that the dynamic range of the driving Vpp can be improved from 0.3 V to 0.6 V when compared with that of the traditional non-geometrically-shaped 8QAM, clearly validating the superiority of the proposed system.

The phase estimation of geometric shaping 8-QAM modulations based on K-means clustering in underwater visible light communication

With more and more human underwater activities carrying out, underwater visible light communication has received increasing attention worldwide. To solve the problem of noise and nonlinearity in underwater visible light communication systems, we proposed a phase deviation correction algorithm based on K-means clustering to correct the phase deviation of special-shaped 8-QAM constellations. The experimental results indicate the performance of the circle has the maximum improvement after using the phase deviation correction algorithm. Before the use of the K-means phase correction algorithm, the highest data rate that circle can achieve is 1.3875 Gbps. The highest data rate increases to 1.4625 Gbps after applying the algorithm.

Spectral function modulation based on nonlinear frequency division multiplexing

A combination of phase and amplitude modulation in nonlinear discrete spectrum is proposed based on nonlinear frequency division multiplexing. Here the integrable nonlinear Schrodinger equation is used as the channel model. We propose the transmission system with designed transmitting signals and implement our scheme with simulation. We use 8QAM constellation and 2 eigenvalues to generate 5 bit signals, which greatly improve spectral efficiency. This method can be expanded for higher order modulation and further improve transmission capacity in limited bandwidth.

Performance Analysis of Circular 8-QAM Constellation with MMSE Equalizer for OFDM System Using USRP

Bandwidth is very important in communication system, and it is a limited resource. In order to save the limited bandwidth resource, high order M-ary modulation is widely employed in modern communication and broadcasting systems. In Orthogonal Frequency Division Multiplexing (OFDM), fading environment lead to a loss of orthogonality between the subcarriers. In this paper, we present the performance analysis of circular 8-Quadrature Ampilutude Modulation (QAM) constellation for Orthogonal Frequency Division Multiplexing (OFDM) system. We also combine the system with Minimum Mean Square Error (MMSE) equalizer to mitigate the effect of Inter Symbol Interference (ISI). Then, all of this system is implemented practically using Universal Software Radio Peripheral (USRP). The performance of circular 8-QAM and MMSE equalizer is evaluated by comparing with other 8-QAM modulation models such as circular-Zero Forcing (ZF), star-ZF, Square-ZF, Star-MMSE, and Square-MMSE. The performance of circular 8-QAM with MMSE equalizer is better than the other combinations. Bit Error Rate (BER) graph shows that the performance of circular-MMSE is better than star-MMSE. The performance improvement using circular-MMSE is about 1.6%. The performance will decrease when the distance is increased. The performance of this system is greatly affected by the distance between transmitter and receiver.

Investigation on performance of special-shaped 8-quadrature amplitude modulation constellations applied in visible light communication

Light-emitting diode (LED)-based visible light communication (VLC) has become a potential candidate for next-generation ultra-high-speed indoor wireless communication. In this paper, four special-shaped 8-quadrature amplitude modulation (QAM) constellations are investigated in a single-carrier VLC system. It is numerically verified and experimentally demonstrated that circular (7,1) shows obvious superiority in the performance of the dynamic range of signal voltage peak-to-peak (vpp) value and bit error rate (BER). Next best is rectangular, followed by triangular; circular (4,4) has the worst performance. A data rate of 1.515 Gbit/s is successfully achieved by circular (7,1) employing a red chip LED over 0.5 m indoor free space transmission below a BER threshold of 3.8×10−3. Compared with circular (4,4), the traditional 8-QAM constellation, circular (7,1) provides a wider dynamic range of signal vpp, a higher data rate, and a longer transmission distance. To the best of our knowledge, this is the first investigation into the performance differences of special-shaped 8-QAM constellations in a high-speed, single-carrier VLC system, and the results comprehensively demonstrate that circular (7,1) is the optimal option.

Experimental Analysis of 8-QAM Constellations for Adaptive Optical OFDM Systems

In this letter, we numerically and experimentally evaluate the influence of adopting different 8-QAM constellations. The performance of flexible/adaptive direct detection optical orthogonal frequency division multiplexing transmission systems has been evaluated in the back-to-back configuration. Metro/regional network scenario is also considered using the four-node photonic mesh network of the ADRENALINE testbed. In general, different optical paths of the network ranging from 50 to 185 km are analyzed to asses the optimal 8-QAM format, which maximizes the system performance. In addition, single side band modulation is implemented in order to enhance the robustness against the chromatic dispersion (CD). The effect of CD on the format selection is investigated targeting different data rates using the implemented loading algorithm.

Design, implementation and measurement of a 120 GHz 10 Gb/s phase-modulating transmitter in 65 nm LP CMOS

A novel mm-wave phase modulating transmit architecture, capable of achieving data rates as high as 10 Gb/s is presented at 120 GHz. The circuit operates at a frequency of 120 GHz. The modulator consists of a differential branchline coupler and a high speed 4-to-1 analog multiplexer with direct digital input. Both a QPSK as well as a 8QAM constellation are supported. To achieve high output power, a 9-stage power amplifier is designed and connected to the multiplexer output. The complete chip is integrated in a 65 nm low power CMOS technology. Capacitive neutralization is used to achieve high gain and good stability for the MOS devices. Also, various differential transmission line topologies are investigated to achieve high performance in terms of loss and area consumption.

A general method to decode ABBA quasi-orthogonal space-time block codes

ABBA codes, a class of quasi-orthogonal space-time block codes (STBC) proposed by Tirkkonen et al., allow low complexity pair-wise complex-symbol decoding. A refined version of ABBA codes with special signal mapping leads to pair-wise real-symbol decoding, i.e. with minimum decoding complexity (MDC) achievable by non-orthogonal STBC. Despite these advantages, a general simple closed-form method to decode ABBA and MDC-ABBA codes for an arbitrary number of transmit/receive antennas is not available. We thus derive an equivalent channel representation to address this issue. The maximum mutual information of ABBA/MDC-ABBA codes is also derived. We found that MDC-ABBA codes perform better than ABBA codes when using two 8QAM constellations.