We address a design of high-capacity and low-peak-to-average power ratio (PAPR) orthogonal frequency-division multiplexing (OFDM) systems based on bit-interleaved coded modulation (BICM) utilizing non-equiprobable and non-uniform (NENU) constellations as well as clipping and filtering (CAF). The proposed constellations are generated using a truncated Gaussian distribution and the merging of constellation points, where the former creates a non-uniform constellation (NUC), and the latter adjusts the number of signal points for further improving the total bitwise mutual information (BMI). Unlike other exhaustive search-based approaches, the proposed constellations are uniquely determined by only two parameters associated with NUC and cardinality. Due to this property of limited degrees of freedom, the complexity required for the numerical optimization process can be significantly low. We focus on the constellation design based on one dimension, i.e., pulse amplitude modulation (PAM), which facilitates the reduction of demapping complexity for the BICM receiver. The use of CAF at the transmitter can efficiently reduce the PAPR of OFDM signals; however, it introduces clipping noise that may degrade error rate performance, making the application of clipping noise cancellation (CNC) at the receiver essential. Therefore, we optimize the NENU constellations in the presence of CAF and CNC. Simulation results demonstrate that the combination of constellation shaping with CAF and CNC enables BICM-OFDM systems to simultaneously achieve low PAPR and high spectral efficiency over additive white Gaussian noise (AWGN) as well as frequency-selective fading channels. Furthermore, comparative studies confirm that the proposed system significantly outperforms the single-carrier counterpart (i.e., DFT-precoded BICM-OFDM) in terms of PAPR and bit error rate (BER) performance over fading channels.

In this work, we propose a systematic shaping design based on nonuniform quadrature amplitude modulation (NU-QAM) constellations for rate-adaptive bit-interleaved coded modulation (BICM) systems. Since our main interest lies in low-complexity signal design and high bandwidth efficiency, we focus on one-dimensional nonuniform constellations (1-D NUCs). In the proposed approach, the constellation points are first generated according to a truncated Gaussian distribution specified by a single parameter, and then a novel Gray labeling strategy with many-to-one mapping is applied. This scheme enables a systematic and flexible constellation design in terms of the number of constellation points and its geometrical distribution. Simulation results using turbo codes show that the proposed constellation achieves noticeable shaping gains over the conventional uniformly-spaced QAM across a wide range of SNRs and is almost comparable to the 1-D NUCs adopted by the ATSC 3.0 standard. The major practical advantage of the proposed shaping scheme is its lower demapping complexity due to the reduced number of constellation points. Our numerical analysis indicates that, compared to the equivalent NUC of ATSC 3.0, the proposed constellation with 1024 bit labels successfully reduces the complexity associated with the demapping process by 69% and 41% for code rates of 2/5 and 3/5, respectively, at the cost of a slight loss in shaping gain.

The majority of modern communication systems adopt quadrature amplitude modulation (QAM) constellations. However, they suffer from a high peak-to-average power ratio (PAPR) as the modulation order grows, which severely reduces the efficiency of the power amplifier. This issue becomes even more critical when the signal points are non-uniformly spaced to improve the achievable information rate (AIR) along with bit-interleaved coded modulation (BICM). On the other hand, amplitude phase shift keying (APSK) constellations provide important benefits compared to QAM due to their circular shape, helping to increase the AIR and reduce the PAPR. In this work, we propose a systematic design approach for a class of APSK constellations composed of multiple concentric rings, each containing the same number of points. In the proposed method, all the radii of the rings are determined by a single parameter, making it easier to identify the best constellation that increases the AIR while keeping the PAPR within limits. Simulation results indicate that in a single-carrier system with pulse shaping, the proposed 1024-APSK constellation increases the AIR by 0.25 bits per symbol compared to the regular 1024QAM with the same signal PAPR, or it can reduce the PAPR by 1.0 dB while maintaining the same spectral efficiency.

We investigate the application of geometric constellation shaping for standard bit-interleaved coded modulation (BICM) systems employing Gray labeling and high-order quadrature amplitude modulation (QAM). We focus on the non-uniform Gaussian-like distributions, and analyze their performance in terms of the mutual information as well as more practical bit-wise mutual information (BMI). We also propose a new systematic constellation design approach based on truncated Gaussian distribution, where a single parameter balances the two extreme constellations represented by uniform and Gaussian distributions. We also evaluate the peak-to-average power ratio (PAPR) of the resulting constellations, where a good trade-off between the BMI and PAPR can be achieved by optimizing the associated parameter. Simulation results based on the conventional Gray-labeled BICM with binary turbo codes show that a noticeable shaping gain can be achieved by the proposed constellation design.

A novel amplification and phase optimization method for distributed reconfigurable repeater-assisted multiple-input multiple-output (MIMO) systems is proposed in this paper. Although distributed multiple-input multiple-output (D-MIMO) architectures such as cell-free multiple-input multiple-output (CF-MIMO) has shown in the literature to be a promising alternative to the current central multiple-input multiple-output (C-MIMO) deployed in real networks, there remain several challenges to be concured when it comes to real-world deployment. This paper intends to elucidate potential performance of repeater-assisted MIMO systems so as to highlight its capability to be a great successor to C-MIMO in a scenario where/when D-MIMO deployment is arduous. Simulation results are offered to illustrate the effectiveness of the proposed approach compared to other possible MIMO architectures.