Spectral Efficiency Analysis for Spatial Modulation Aided Layered Division Multiplexing Systems With Gaussian and Finite Alphabet Inputs

As the conventional spatial modulation (SM) system lacks an efficient downlink multiple access scheme, this paper proposes a novel downlink nonorthogonal multiple access aided multiple-input multiple-output SM system with unite alphabet inputs. Mutual information (MI) is used to characterize the system's achievable spectral efficiency (SE). Because the MI lacks a closed-form formulation, in this paper we propose a computational-efficient lower bound to provide an approximation to the simulated MI. Besides, preprocessing is also designed at the receiver to mitigate the detrimental effect of channel correlation, which leads to striking a higher SE performance. Simulation results not only confirm the accuracy of our SE analysis, but also substantiate the superior SE performance achieved by the proposed preprocessing.

Based on the assumption of finite alphabet inputs, the precoding design for MIMO interference channels (MIMO-IC) is proposed by exploiting statistical channel state information (SCSI) at the transmitter. Most of the related precoding design relies on Gaussian input assumption instead of discrete constellation symbols. However, the input data consist of discrete constellation symbols in practice, which would inevitably lead to performance loss. Under the finite alphabet inputs, the upper bound of the sum average mutual information is firstly derived. Then, by maximizing this upper bound, the optimal precoding matrices are achieved. Simulation results demonstrate that the proposed precoding design could obtain higher mutual information than the existing schemes (such as the Max-SGINR scheme, D-SVD scheme and BM scheme).

In this paper, we present performance evaluation of multiple physical layer pipe (PLP) based layered division multiplexing (LDM) systems for the next generation terrestrial broadcasting. In addition to a conventional multiple-PLP configuration, which is based on time division multiplexing (TDM), a variety of LDM configurations, which includes combinations of TDM and two-layer LDM, and three-layer LDM, are considered. Given three different broadcasting contents are delivered by three PLPs, performance comparison and analysis are provided when four different multiple-PLP configurations including TDM, two-layer LDM, and three-layer LDM are used.

Existing research on a simultaneous wireless information and power transfer (SWIPT) system is based on the assumption of Gaussian inputs. However, the optimal design on Gaussian inputs may lead to dramatic performance loss for practical systems with finite-alphabet inputs. This paper focuses on the precoder design for a SWIPT system with finite-alphabet inputs and instantaneous channel state information over a multiple-input multiple-output channel. We formulate the optimal precoder design as an optimization problem, in which the objective is to maximize the mutual information over the channel from the transmitter to the information receiver under the constraints of transmit power and harvested energy threshold. The formulated problem is NP-hard, so a global optimal solution cannot be found within the polynomial time. The main contributions of this paper are as follows: 1) By using its structure, the NP-hard problem is relaxed to a semidefinite programming problem. Then, a general solving framework for both co-located and separated receiver cases, based on the semidefinite relaxation (SDR) technique, is developed to achieve a near optimal precoder. 2) For the case of co-located receivers, we show that the optimal precoder design is a concave problem with respect to power allocation; then, a specific algorithm for co-located receivers is proposed. Compared with the general SDR-based method, the specific algorithm for co-located receivers exhibits almost the same performance but much lower complexity. 3) The performance of several practical co-located receiver designs is analyzed in SWIPT systems with finite-alphabet inputs. Finally, we provide simulation results to show the efficacy of the proposed algorithms.

This paper investigates the linear precoder design for multiple-input multiple-output (MIMO) K-user interference channels with finite alphabet inputs. We first obtain the general explicit expressions of the achievable rate of each user in MIMO interference channel systems. We study optimal transmission strategies in both high signal-to-noise ratio (SNR) and low SNR regions. We show that given finite alphabet inputs, a simple power allocation design can achieve optimal performance. In contrast, the well-known interference alignment technique for Gaussian input scenarios, only utilizes a partial interference-free signal space for transmission and leads to a constant performance loss when it is applied to finite-alphabet input scenarios. We determine this constant rate loss at high SNR. Moreover, we establish necessary conditions for the linear precoder design of the weighted sum-rate maximization. We also develop an efficient iterative algorithm for determining precoding matrices of all the users. Our numerical results show that for the practical digital modulated signals from discrete constellations, the proposed iterative algorithm achieves considerably higher sum-rate than the existing methods.

In the literature, optimal power allocation assuming Gaussian input has been evaluated in OFDM based Cognitive Radio (CR) systems to maximize the capacity of the secondary user while keeping the interference introduced to the primary user band within tolerable range. However, the Gaussian input assumption is not practical and Finite Symbol Alphabet (FSA) input distributions, i.e., M-QAM are used in practical systems. In this paper, we consider the power optimization problem under the condition of FSA inputs as used in practical systems, and derive an optimal power allocation strategy by capitalizing on the relationship between mutual information and minimum mean square error. The proposed scheme is shown to save transmit power in a CR system compared to its conventional counterpart, that assumes Gaussian input. In addition to extra allocated power, i.e., power wastage, the conventional power allocation scheme also causes nulling of more subcarriers, leading to reduced transmission rate, compared to the proposed scheme. The proposed optimal power algorithm is evaluated and compared with the conventional algorithm assuming Gaussian input through simulations. Numerical results reveal that for interference threshold values ranging between 1mW to 3mW, the transmit power saving with the proposed algorithm is in the range between 55-75%, 42-62% and 12-28%, whereas the rate gain is in the range between 16.8-12.4%, 13-11.8% and 3-5.8% for BPSK, QPSK and 16-QAM inputs, respectively.

This paper investigates linear precoding scheme that maximizes mutual information for multiple-input multiple-output (MIMO) channels with finite-alphabet inputs. In contrast with recent studies, optimizing mutual information directly with extensive computational burden, this work proposes a low-complexity and high-performance design. It derives a lower bound that demands low computational effort and approximates, with a constant shift, the mutual information for various settings. Based on this bound, the precoding problem is solved efficiently. Numerical examples show the efficacy of this method for constant and fading MIMO channels. Compared to its conventional counterparts, the proposed method reduces the computational complexity without performance loss.

Recent broadcast standards support Layered Division Multiplexing (LDM) to achieve graceful degradation as signal quality degrades at the receiver. LDM is accomplished by using different constellations within the same Radio Frequency (RF) spectrum. LDM thus enables delivering multiple service tiers in a single broadcast channel. LDM when used in conjunction with scalable source coding codecs such as the Scalable extension of High Efficiency Video Coding (SHVC), further helps improve overall spectrum utilization and efficiency. In this paper we investigate a 2-tier broadcast LDM based service with one service tier aimed at lower video resolution such as 540p, 720p, 1080p for a mobile receiver (smaller/indoor antenna) and the other service tier targeting twice the video resolution of the lower tier, for stationary receivers (larger/outdoor antenna). The primary contribution of this paper is to identify 2-tier transmission configurations of interest to broadcasters and compare the spectrum and bitrate coding efficiency gains of an SHVC-based multi-tier service versus a simulcast (single layer) based multi-tier service for an Advanced Television Systems Committee (ATSC) 3.0 transmission system. Bitrate savings ranging from 38% and 57% is observed for the SHVC based layered system. For large coverage and pedestrian with a receiver test scenarios, channel utilization savings ranging from 23% to 46% is observed. For mobile and tablet in bedroom scenarios a smaller broadcast bandwidth savings ranging from 6% to 9% is observed.

In this paper, we present an efficient transmission method of multiple broadcasting services using layered division multiplexing (LDM) and scalable high efficiency video coding (SHVC) based on the next generation terrestrial digital broadcasting standard, advanced television systems committee 3.0. In a two-layer LDM system, each layer forms a physical layer pipe that carries base layer and enhancement layer video streams of SHVC, respectively. This combination of physical and presentation layers technologies can maximize channel utilization when multiple broadcasting services are delivered in a single radio frequency channel with different robustness and reception conditions. An intensive performance analysis is provided when the proposed combination of LDM and SHVC is compared with other approaches, such as time division multiplexing and/or high efficiency video coding simulcast broadcasting. Several performance measurements are also introduced, such as constant data rate measurement and constant quality measurement, which are used to evaluate the performance of video codecs in conjunction with different physical layer system parameters. A prototype hardware system with LDM and SHVC capable of selecting different parameter combinations is tested in the laboratory and in real field environments to verify the performance and feasibility of the proposed LDM and SHVC combination. Results show that the proposed LDM and SHVC combination provides significant gains on video service quality as well as reception robustness.

Achievable rate regions in broadcast channels are usually determined for infinite Gaussian input alphabets. Since these alphabets are not used for practical systems, we investigate the influence of finite signal constellations in the two user AWGN broadcast channel. We show that results derived with Gaussian inputs are not transferable to the finite case. For scenarios where the rate of one user should be maximized whilst a required rate for the other user is delivered we establish design rules.

A novel Layered Division Multiplexing (LDM) With Index Modulation (LDM-IM) system is proposed in this paper. It employs the Index Modulation (OFDM-IM) technology to enhance the transmission performance of the original LDM system by transmitting extra bits through the Orthogonal Frequency Division Multiplexing (OFDM) subcarriers indices. The proposed system is based on a two-layer, Upper Layer (UL) and Lower Layer (LL), LDM system that serves two independent data services for at least two User Equipment(s) (UE) simultaneously. Besides this, by exploiting the Index Modulation (IM), each UE can receive the extra bits by decoding the subcarriers activation patterns. To map the extra bits to the subcarriers, a simple random codebook is designed in the proposed system based on the concept of OFDM-IM. To proof the availability and reliability of the proposed system, two metrics are chosen to evaluate the system performance, the average Symbol Error Rate (SER) and the transmission rate. In this paper, the architecture of the proposed system is introduced firstly. After that, the average SER of it is analyzed and verified by the Monte Carlo simulation. Finally, the transmission rate of the proposed system and the original LDM system is compared and evaluated.

: Calculating the amount of information about a random function contained in another random function has important uses in communication theory. An expression for the mutual information for continuous time random processes has been given by Gelfand and Yaglom, Chiang, and Perez by generalizing Shannon's result in a natural way. Under a condition of absolute continuity of measures the continuous time expression has the same form as Shannon's result. For two Gaussian processes Gelfand and Yaglom express the mutual information in terms of a mean square estimation error. We generalize this result to diffusion processes and express the solution in a different form which is more naturally related to a corresponding filtering problem. We also use these results to calculate some information rates.

In multi-user multiple input multiple output (MIMO) systems, the non-orthogonal multiple access (NOMA) method based spatial modulation (SM) and generalized spatial modulation (GSM) can mitigate inter-user interference. However, the spectral efficiency of these methods is restricted because of antenna configuration. In this paper, a combination of the variable active antenna spatial modulation (VASM) scheme with the downlink power domain NOMA system, so-called NOMA-VASM, is proposed to improve spectral efficiency while main-taining mitigation of inter-user interference. In the novel NOMA-VASM, the antenna configuration is arbitrary and the number of enabled transmitting antennas (TAs) can be altered, so it is easier to increase spectral efficiency compared to NOMA-SM and NOMA-GSM. Monte Carlo simulations were performed under various scenarios, and the results showed that NOMA-VASM outperformed conventional NOMA-SM and NOMA-GSM in terms of spectral efficiency, average bit-error-rate (ABER) performance, and required number of TAs.

In this paper, we study the potential of interference exploitation symbol-level precoding (SLP), focusing on maximizing mutual information (MI) in multiple-input multiple-output (MIMO) systems with finite-alphabet inputs. As traditional MI expressions based on Gaussian signalling do not apply to SLP, we firstly derive the expression of the MI for SLP based on finite alphabet inputs, which is shown to be a nonlinear and non-concave function of the precoder. Subsequently, we formulate an optimization problem aimed at maximizing the MI without investing additional transmit signal power. Due to the original problem being non-convex, we design an iterative gradient-projection (GP)-based algorithm by deriving the gradient of the MI with respect to the SLP signal matrix. To alleviate the heavy reliance on Monte Carlo evaluations, we further propose an effective variant that employs the channel cut-off rate (CR) as a tractable optimizaiton metric within the GP framework. Moreover, we develop a low-complexity algorithm by deriving a closed-form approximation of the MI and addressing the resulting problem through successive convex approximation (SCA), thereby obtaining a near-optimal solution to the original formulation. Numerical results verify that the proposed MI-optimization SLP (MIO-SLP) exhibits a noticeable gain over traditional SLP schemes in terms of MI, and achieves close-to-optimal MI performance, while ensuring satisfactory error rate.

We address the problem of analyzing and classifying into groups the downlink channel environment in a dense millimeter-wavelength cell, accounting for path loss, multipath fading, and User Equipment (UE) blocking, by employing a hybrid propagation and multipath fading model, thus using accurate inter-group interference modeling. The base station (BS) employs a large Uniform Planar Array (UPA) to facilitate massive Multiple-Input, Multiple-Output (MIMO) communications with high efficiency. UEs are equipped with a single antenna and are distributed uniformly within the cell. The key problem is analyzing and defining groups toward efficient precoding. Because balanced throughput is desired between groups, up to four separate frequency sub-carriers are employed in an Orthogonal Frequency Division Multiple Access (OFDMA) system. We show that by employing three or four OFDMA subcarriers, depending on the number of UEs in the cell and the cell range, the UEs can be efficiently separated into <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">high-throughput</i> groups, with each group employing Virtual Channel Model Beams (VCMB) based inner precoding, followed by efficient Multi-User Multiple-Input Multiple-Output (MU-MIMO) outer precoders. For each group, we study two different sub-grouping methods offering different advantages. We show that the improvement offered by Zero-Forcing Per-Group Precoding (ZF-PGP) over Matched Filter Precoding (MFP) and Zero-Forcing Precoding (ZFP) is very high when finite-alphabet inputs are used. We also show ZF-PGP with finite-alphabet inputs significantly outperforms MFP with Gaussian inputs in certain realistic setups. Finally, a new technique for power allocation among different UEs is proposed, called Optimized Per-Group Power Allocation (OPGPA), which achieves much higher power efficiency jointly with equal throughput among all UEs in each group.