TDHQ Enabling Fine-Granularity Adaptive Loading for SSB-DMT Systems

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.

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.

In this paper, a rate adaptive geometric constellaion shaping (GCS) scheme which is fully backward-compatible with existing state of the art bit-interleaved coded modulation (BICM) systems is proposed and experimentally demonstrated. The system relies on optimization of the positions of the quadrature amplitude modulation (QAM) points on the I/Q plane for maximized achievable information rate, while maintaining quantization and fiber nonlinear noise robustness. Furthermore, ‘dummy’ bits are multiplexed with coded bits before mapping to symbols. Rate adaptivity is achieved by tuning the ratio of coded and ‘dummy’ bits, while maintaining a fixed forward error-correction block and a fixed modulation format size. The points' positions and their labeling are optimized using automatic differentiation in a many-to-one fashion such that the performance of the ‘dummy’ bits is sacrificed in favor of the performance of the data bits. The proposed GCS scheme is compared to a time-sharing hybrid (TH) QAM modulation and the now mainstream probabilistic amplitude shaping (PAS) scheme employing a Maxwell-Boltzmann probability mass function. The TH without shaping is outperformed for all studied data rates in a simulated linear channel by up to 0.7 dB. In a linear channel, PAS is shown to outperform the proposed GCS scheme, while similar performances are reported for PAS and the proposed GCS in a simulated nonlinear fiber channel. The GCS scheme is experimentally demonstrated in a multi-span recirculating loop coherent optical fiber transmission system with a total distance of up to 3000 km. Near-continuous zero-error flexible throughput is reported as a function of the transmission distance. Up to 1-2 spans of increased reach gains are achieved at the same net data rate w.r.t. conventional QAM. At a given distance, up to 0.79 bits/2D symbol of gain w.r.t. conventional QAM is achieved. In the experiment, similar performance to PAS is demonstrated.

We propose a single sideband three‐dimensional modulation technique for a passive optical network which has an insufficient signal‐to‐noise ratio (SNR). We demonstrated a SE improvement of 1.65 times with 3dB lower SNR compared to a conventional quadrature amplitude modulation (QAM) signal.

A high bit-rate acoustic link for underwater video transmission is examined. Currently, video encoding standards allow video transmission at bit rates on the order of 64 kbps. To provide an acoustic transmission capability that meets this bit-rate requirement, we focus on the use of high-level bandwidth-efficient modulation methods. We consider the use of 16-, 32-, and 64-differential amplitude and phase shift keying (DAPSK) with varying number of amplitude levels. DAPSK does not require explicit carrier phase synchronization at receiver, but instead relies on differentially coherent detection. It thus represents an alternative to conventional quadrature amplitude modulation (QAM) methods, whose high-level constellations are sensitive to phase distortion induced by the channel. System performance is demonstrated experimentally, using 25<th>000 symbols/s at a carrier frequency of 75 kHz over a short vertical path. Excellent results were obtained, thus achieving bit rates as high as 150 kbps, which are sufficient for real-time transmission of compressed video.

The ultra-dense wavelength division multiplexing (UDWDM)-based fiber-millimeter-wave integration network (FMWIN) is a key enabler for the 6G radio access network (RAN), providing high access density and large capacity. Due to the high density of wavelengths and bandwidth limitations, a modulation format of high spectral efficiency is required in the UDWDM FMWIN. In this article, we propose a spectrally efficient orthogonal odd-even staggered multi-band carrier-less amplitude and phase (OES-m-CAP) modulation. Each sub-band of OES-m-CAP transmits pulse amplitude modulation (PAM) symbols, which is different from the sub-bands of the conventional quadrature amplitude modulation (QAM)-based m-CAP. The center frequency spacing of adjacent sub-bands in OES-m-CAP is half of the baud rate of each sub-band, and the roll-off spectra of adjacent sub-bands can overlap each other. Even if the roll-off factor increases, the center frequency of each sub-band does not shift, and the consumed system bandwidth increases only slightly. Thus, high spectral efficiency and good performance of the pulse shaping filters in OES-m-CAP can both be achieved without compromise. Moreover, we prove the orthogonality of OES-m-CAP in this article. By using OES-m-CAP in a UDWDM FMWIN system of 92-GHz millimeter-wave, we achieve a total data rate of 416 Gbps allocated across 32 sub-bands on 8 wavelengths over a transmission distance of 10 km.

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.

The interference levels that may be expected for a range of conventional cellular and microcellular clusters used in personal communication networks (PCNs) and personal communication systems (PCSs) are discussed. Simulation results show that for conventional size cells, 32- and 64-level quadrature amplitude modulation (QAM) schemes are preferred for bit error rates (BER) above 1*10/sup -2/, while 4PSK or variable-rate QAM schemes are better for lower BER. For microcells with communications at both 900 MHz and 1.8 GHz, four- or six-cell clusters are advocated, depending on the SNR expected. Based on the expected signal-to-noise ratio (SNR) and interference levels, it is argued that variable-rate QAM schemes are superior to the other modulation schemes considered. For low BERs 4PSK may often provide the best performance, whereas for high BERs, particularly when the SNR is high, 32- and 64-level star QAM are the most suitable.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Orthogonal space-time block codes (OSTBCs) have recently attracted considerable attention due to their properties of full diversity and low implementation complexity. However, most works in this area simply employ classic phase-shift keying (PSK) or quadrature amplitude modulation (QAM) constellations, which are not necessarily optimal for OSTBCs. In this paper, we consider the problem of designing signal constellations for communication systems using OSTBCs, where the channel state information (CSI) available at the receiver is an estimate of the time variant channel gains with a specific estimation error. We perform an asymptotic symbol error probability (SEP) analysis and derive a criteria to design constellations that match well with the level of the channel estimation error. New signal constellations are found by means of a gradient search over a continuous alphabet. Simulation results show that the obtained constellations outperform not only the conventional QAM constellation, but also other well-known constellations used for efficient data communications.

In wireless communications, fixed-point complex independent component analysis (ICA) algorithms have been applied to perform separation of complex signals. Presented is a novel complex adaptive ICA algorithm which employs individual convergence factors for the real and imaginary components of the weight vector. For wireless receivers operating on quadrature amplitude modulation, the adaptive algorithm performs better than the existing complex fast-ICA algorithm in terms of accuracy. Computer simulations confirm the effectiveness of the proposed algorithm.

A coding scheme that can provide different levels of error protection for different sets of bits in a transmitted symbol using trellis-coded modulation is presented. The scheme uses simple trellis code with 4-16 stages that are coupled with quadrature amplitude modulated (QAM) and asymmetrical QAM constellations. It has been found that the scheme can provide various levels of error protection for different sets of bits against channel impairments without much added complexity compared to the conventional trellis-coded modulation. The scheme also provides a design flexibility so that it is easily modified to accommodate different needs for error protection in various data transmission systems. A detailed design procedure and the performances of several unequal error protection codes are presented. >

Amplifier-free coherent systems are promising for short-reach links, but these systems are constrained by signal peak power instead of average power. In this paper, we propose a novel, to the best of our knowledge, quadrant-partitioning uniformly distributed modulation (QP-UDM) scheme for peak-power-constrained amplifier-free systems. The proposed scheme achieves finer modulation orders than conventional UDM schemes. It also avoids the problem in conventional amplitude-division irregular quadrature amplitude modulation, where the order of check bit sequence would be disrupted when there are errors, resulting in the failure of forward error correction decoding. When compared to probabilistic shaping (PS), the proposed QP-UDM has a lower peak-to-average-power ratio. Experiments of a 28 Gbaud amplifier-free system with the modulation order varying from 36 to 104 show that the proposed QP-UDM scheme solves the problem of conventional UDM schemes and outperforms PS-QAM at the same entropy.

OFDM is a special case of multicarrier transmission, where a single data stream is transmitted over a number of lower rate subcarriers. The main reason to use OFDM is to increase the robustness against the selective fading or narrowband interference. A large number of closely spaced orthogonal sub-carrier signals are used to carry data on several parallel data streams or channels. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth. Keywords: FFT, IFFT, OFDM, QAM, VHDL

In this paper, we studies the asymptotic analysis of space-time block codes (STBC) over spatially correlated Nakagami fading channels for the multiple-input multiple-output (MIMO) systems. Using asymptotic analysis, this paper quantifies the diversity order and signal to noise ratio (SNR) gain of the outage probability and symbol error rate (SER) with the M-ary quadrature amplitude modulation (QAM) and phase shift keying (PSK) modulation for STBC-based MIMO systems over spatially correlated Nakagami fading channels. From the analytical results, we know that the diversity order of STBC in spatially correlated Nakagami fading channels is one for both outage probability and SER regardless of modulation types while the diversity order of STBC over spatially uncorrelated Nakagami fading channels is the full diversity order.

The effect of the phase noise on the performance of bandwidth-efficient coded modulation is studied. To this end, the average mutual information (AMI) for specific constellations such as 8-phase-shift keying and 16-quadrature amplitude modulation is calculated in the presence of carrier phase error caused by imperfect carrier tracking over an additive white Gaussian noise channel. The AMI not only quantifies the effect of the phase noise from an information-theoretic viewpoint, but also serves as an estimate for a permissible amount of the phase noise for a given signal-to-noise ratio. The bit-error rate (BER) performance of a near-optimal turbo trellis-coded modulation scheme is then investigated over such a channel. For this purpose, an optimal branch metric which best fits the channel characteristics is derived. Furthermore, simple branch metrics (referred to as suboptimal, simplified, and Gaussian metrics) are derived, which may offer the tradeoff between BER performance and computational complexity. Numerical analysis shows that a near-optimal coded-modulation scheme renders a transmission system more robust against phase noise than is the case with a conventional trellis-coded modulation scheme.