BICM-Compatible Rate Adaptive Geometric Constellation Shaping Using Optimized Many-to-One Labeling

A multicarrier quadrature amplitude modulation (QAM) modulator has been developed and implemented with programmable logic devices. The multicarrier QAM modulator contains four CORDIC-based QAM modulators. A conventional QAM modulator needs two multipliers, one adder, and sine/cosine ROM's. The designed CORDIC-based QAM modulator has about the same logic complexity as the two multipliers and the adder with the same word sizes. Each QAM modulator accepts 13-bit in-phase and quadrature data streams, interpolates them by 16, and upconverts the baseband signal to a selected center frequency. The frequencies of the four carriers can be independently adjusted. The proposed multicarrier QAM modulator does not use an analog I/Q modulator, and therefore, the difficulties of adjusting the dc offset, phasing, and the amplitude levels between the in-phase and quadrature-phase signal paths are avoided. The multicarrier QAM modulator is designed to fulfil the spectrum and error vector magnitude (EVM) specifications of the wideband code-division multiple-access (WCDMA) system. The simulated EVM is 1.06% root mean square (rms), well below the specified 12.5% rms for WCDMA. The measured ratio of the integrated first/second/third adjacent channel power (4.096-MHz bandwidth) to the integrated channel power (4.096-MHz bandwidth) is -68.16/-68.24/-66.17 dB versus the specified -45/-55/-55 dB.

Coherent optical fiber transmission systems, which allow the development of advanced communication systems with superior performance by using high-performance constituent subsystems, such as optical transmitters, fibers and receivers, are discussed. Essential technologies for developing the coherent optical fiber transmission systems are reviewed and system advantages are discussed. The state of the art in transmission experiments is also described, and future areas of concern essential to further development are outlined. >

A brief overview of recent experimental research on coherent optical fiber transmission systems at Queen’s University is presented. Exemplary results are described that exploit real-time signal processing to assess the impact of cascaded optical filtering.

This study investigates the effects of polarization mode dispersion (PMD) on high-speed multimode fiber (MMF) optical communication systems, focusing on how differential group delay (DGD) and environmental conditions such as temperature and humidity influence signal quality. The research was conducted in Abuja, Nigeria, using two modulation formats—non-return-to-zero (NRZ) and quadrature amplitude modulation (QAM). Experimental measurements were carried out over fiber lengths ranging from 1 km to 38 km, and data rates from 15 Gbps to 240 Gbps. Key performance metrics such as bit error rate (BER), jitter, and signal-to-noise ratio (SNR) were analyzed in relation to DGD under varying environmental conditions. Results showed that DGD increased from 0.136 ps to 2.78 ps for NRZ and from 0.058 ps to 2.24 ps for QAM across the tested fiber lengths. Corresponding BER values for NRZ ranged from 1.18 × 10-7 to 1.35 × 10-7, while QAM showed slightly better performance with BER values between 1.18 × 10-7 and 1.29 × 10-7. Jitter rose from 4.26 ps to 31.20 ps in NRZ and from 4 ps to 33.54 ps in QAM. SNR values declined as DGD increased, with NRZ dropping from 34.59 dB to 54.56 dB and QAM from 34.83 dB to 52.90 dB. Environmental factors also played a role; temperature increases from 28.34°C to 29.90°C and humidity from 53.1% to 59.5% led to significant increases in DGD. The findings confirm that PMD, though less dominant in MMF than modal dispersion, still significantly affects signal quality in long-distance and high-speed MMF systems. QAM demonstrated greater resilience to PMD compared to NRZ. This study highlights the need for effective dispersion management and modulation format optimization in designing robust optical networks for environmentally dynamic regions like Abuja.

In this study, the performance analysis of the recently proposed Hexagonal Square Amplitude Modulation Spatial Modulation (HQAM-SM) system on Nakagami-m fading channels is presented. Performance analysis was performed considering the most general state of the Nakagami-m channel distribution phase for the phase without uniform-distribution. HQAM optimizes the assignment of code words to points in the form of a hexagonal constellation to minimize the average Hamming distance. This arrangement always uses energy more effectively than conventional quadrature amplitude modulation (QAM) and performs almost the same performance as QAM at higher SNRs. In this study, a more energy-efficient system was proposed for Nakagami-m fading channels compared to conventional SM, where SM will carry data with HQAM instead of carrying data with conventional modulated symbols in addition to the antenna index. Performance analysis of the proposed system was carried out in Nakagami-m fading channels.

Odd-bit quadrature amplitude modulations (QAMs) can achieve higher data rates than even-bit QAMs in some signal-to-noise (SNR) regions but they have not been used in wireless communication standards due to its high demapping complexity. In this paper, we propose a novel constellation for odd-bit QAM, called dual square-QAM (DSQAM). It consists of two regular even-bit square-QAMs spaced apart by a shift value in the diagonal direction. We also propose a two-layer coding which effectively exploits the structural property of the constellation and a successive demapping to use the decoding result of the first layer for the second layer. The proposed DSQAM is enhanced by the two-layer coding and successive demapping, which consists of multi-level coding and bit-interleaved coded modulation (BICM). The asymptotic information rate (AIR) under the coding scheme is maximized for a given channel state by adjusting the shift value. The AIR analysis shows that the DSQAM with the two-layer coding and the successive demapping is the best among conventional QAMs with the BICM for a wide range of SNR values. Based on the structure of the constellation, we propose a low-complexity implementation of the max-log approximation to calculate the log-likelihood ratio for practical use. It is shown via simulations over the additive white Gaussian channel that the proposed DSQAMs with the coding scheme have significant block error rate gains over the conventional odd-bit non-square-QAM (NSQAM) and cross-QAM (XQAM) with bit-interleaved coded modulation. The computational complexity for demapping is reduced by up to 10% and 59% compared to NSQAM and XQAM, respectively.

In this letter, we introduce time domain hybrid quadrature amplitude modulation (TDHQ) for the single sideband discrete multi-tone systems. The experimental results reveal that with a single precoding set and the proposed adaptive loading algorithm, the TDHQ scheme can achieve finer granularity and therefore smoother continuous growth of data rate than that with the conventional quadrature amplitude modulation. Besides, thanks to the frame construction and the tailored mapping rule, the scheme with TDHQ has an obviously better peak to an average power ratio.

In wireless communications, the design of digital constellations and the associated bit labeling methods have a large impact on the robustness of transmissions. With the aid of increased minimum Euclidean distance (MED), high-dimension constellations have shown notable performance improvements against their conventional two-dimensional (2-D) counterparts, such as conventional quadrature amplitude modulation (QAM). In this paper, we propose a new method that exploits genetic algorithm (GA) to construct multi-dimensional constellations with optimized MED and bit labeling. More specifically, the GA-based design method is capable of producing both new constellations that have greater MED values and near-optimum labeling that yields improved performance, when compared with conventional schemes. A few design examples and simulation results are provided to demonstrate the benefits of the proposed constellation and labeling design method.

MIMO technology not only offers diversity and capacity gains, but also provides higher spectral efficiency and significant link reliability over SISO systems. Many methods are developed to exploit the diversity offered by multi-antenna systems such as Alamouti code and spatial multiplexing that do not require transmitter-side channel status information (Tx-CSI). Other power allocation optimization techniques, also known as precoding, require a full or partial Tx-CSI. These techniques aim to transform the signal before transmission according to different criteria, among which the minimal Euclidean distance seems to be very effective and continues to interest the researchers. Given perfect channel state information at both sides of the communication, we propose in this paper a novel design of wireless transmission schemes that joint the minimal Euclidean distance precoder and error correction coding based on the non-binary low-density parity-check code (NB-LDPC), to finally determine a power allocation optimization solution that adapts a linear precoding block to an NB-LDPC encoded MIMO transmission. In this paper we use a quadrature amplitude modulation (QAM), over a Rayleigh fading channel with a maximum likelihood detection. Simulations results in term of bit error rate confirmed that NB-LDPC codes are particularly well suited to be jointly used with precoding schemes based on the maximization of the minimum Euclidean distance criterion.

Chapter 5 - The interplay between modulation and channel coding

Preservation of a polarization state in single-mode fibers is essential in coherent optical fiber transmission systems.1 Uniaxially stressed single-polarization fibers2 have been developed to maintain a linear polarization state. An alternative is to transmit circular polarization in a twisted single-mode fiber.3 This paper presents a long span twisted fiber having a high degree of polarization.

A tutorial review of techniques for coherent optical fiber transmission systems

In this paper, we propose a promising nonlinear noise power estimation method based on correlation functions using artificial neural networks (ANN), which is robust against both amplifier spontaneous emission noise and the symbol patterns. Error vector correlation (EVC), together with the amplitude noise correlation (ANC) and the phase noise correlation (PNC), is used as the input of ANN in the proposed method. 378 cases of 224 Gb/s polarization-multiplexed 16-quadrature amplitude modulated (PM-16-QAM) signal transmitted over a wide range of conditions by varying launch power, OSNR and transmission distance are used to train and test the ANN. With the launch power varying from 0 to 8 dBm and the transmission distance as long as 2400 km, the results of tested samples demonstrate that the maximum absolute deviation (MAD), mean absolute error (MAE) and root mean square error (RMSE) of the estimated nonlinear noise power are 0.65 dB, 0.20 dB and 0.27 dB, respectively. In order to verify the independence of symbol patterns, 150 new cases with 30 pseudo-random binary sequence (PRBS) seeds are used to test the trained ANN. The results show that the MAE, MAD and RMSE of estimated nonlinear noise power are 0.86 dB, 0.25 dB and 0.33 dB respectively, meaning that the trained ANN is valid even if the test samples are not covered by the trained process. The results in this work verified that the ANN with EVC, ANC and PNC as input can make the trained model feasible to accurately estimate the nonlinear noise power in high speed optical coherent communication systems.

Independent component analysis based digital signal processing in coherent optical fiber communication systems

A low-loss, wide band, compact, polarization preserving, fiber optic directional coupler (PPFDC) is developed for use in future coherent optical fiber transmission systems or gyroscopes. The PPFDC is made of two 200 μm diameter sapphire ball lenses, a half-mirror and four conical alumina-ceramic ferrules with flat reference plane to preserve polarization at the connection of the fibers. Built-in thermal stress change in the fiber is minimized, because the fiber is polished only for the short length within the straight ferrule. The optical and mechanical axes are tilted, so cross-talk light from the fiber endfaces or lens surfaces is avoided. The optical directivity of the PPFDC is over 50 dB and return loss is over 40 dB in the 1.3 μm wavelength range. The excess loss is under 1 dB in the 1.2 to 1.4 μm wavelength range. The extinction ratio is over 25 dB. The length of the coupling region of the PPFDC is about 1 mm including the two ball lenses and half mirror. Spectral line widths of a fiber interfaced DFB laser diode are measured by a self delayed homodyne detection scheme, using the PPFDC. Experimental results of a novel polarization preserving fiber-optic gyroscope using a phase modulating PPFDC showed reasonable sensitivity and stability. These experimental results verified the above mentioned characteristics of the PPFDC.