Distance Of Constellation Research Articles

Detection of Information Hiding at Physical Layer in Wireless Communications

This paper concerns the problem of detecting the use of information hiding at the physical layer in wireless communications. Prior schemes for detecting physical layer based information hiding are either heuristic based or machine learning based. Our insight is that embedding information on wireless signals at the physical layer will inevitably have negative impact on the decodability of the cover signals, such as the increase of the error probability at the receiver (as well as the monitor). In our approach, after the monitor demodulates and decodes the cover signals, it will re-encode and re-modulate the cover signals, and then compare the resulting recovered signals with the raw signals that it received from the sender. We further propose a new estimation scheme for calculating receiver noise variance and conducted theoretical analysis. Specifically, we propose two hidden information detection schemes, a noise grouping based detection scheme and a constellation distance based detection scheme, both taking estimation errors into consideration. Our experimental results show that when the received SNR is more than 20 dB, our approach with the new estimation scheme has the probability of detection more than 0.95, and our constellation distance based detection scheme can correctly pinpoint all embedded locations.

Optimal selection of spatial dimensions of signal subspace for relay constellation decoding

The dimension of the right null space is only one for traditional signal space alignment with the minimum configuration of antennas. Then, the direction of a pair of alignment signal space is fixed and cannot be flexibly adjusted. Although the different alignment directions are mutually independent to facilitate relay decoding, the minimum Euclidean distance between modulated signals code words is small, which affects the decoding accuracy. In this paper, we design a novel alignment signal transmission scheme using degrees of freedom of null space generated by redundant antennas. The scheme selects the mutually orthogonal space dimension in the redundant null space as the signal alignment direction. It optimizes the minimum Euclidean distance in the system by maximizing the minimum constellation point distance. Simulation results show that the distances between the constellation points of different code symbols become significantly larger. The larger constellation distance of different coded symbols can improve the decoding accuracy. By optimizing the distance between the minimum constellation points, the transmission performance of each link is balanced and the whole system performance is improved.

An enhanced MMSE detection with constellation distance correction for the Internet of things with multiple antennas

A feature of the Internet of Things (IoT) is that the data demanded users in the system need to be served with low energy consumption. To address this requirement, multi-input multi-output (MIMO) technology can be used in the communication modules. In this paper, a novel low-complexity parameter estimator combined with an MMSE detector and a constellation distance correction (CDC) structure is proposed for multiple antenna systems. A hard-output detector is proposed to enhance the reliability of the estimation output. By measuring the distance between constellation candidates and the MMSE estimated soft output, the proposed equalizer may avoid processing redundancy of candidates with decision distance. Simulation results show that the proposed MMSE-CDC technique may provide about the same BER performance as the other post detection processing (PDP) techniques but requires significant less computational complexity.

Signature Design of Sparsely Spread Code Division Multiple Access Based on Superposed Constellation Distance Analysis

Sparsely spread code division multiple access (SCDMA) is a non-orthogonal superposition coding scheme that allows concurrent communications between a base station and multiple users over a common channel. However, the detection performance of an SCDMA system is mainly determined by its signature matrix, which should be sparse to facilitate the belief propagation (BP) detection. On the other hand, to guarantee good maximum likelihood (ML) detection performance, the minimum Euclidean distance for the equivalent signal constellation after multi-user superposition should be maximized. In this paper, a code distance analysis is proposed for SCDMA systems with a finite number of users and spreading lengths. Based on this analysis, good signature matrices whose factor graphs have very few short cycles and possess large superposed signal constellation distances are designed. The proposed signature matrices have both good BP and ML detection performances. Moreover, their BP detection performances exactly converge to their ML detection performances with few iterations. It is worth pointing out that the proposed signature matrix design could be directly applied to the 5G non-orthogonal multiple access systems.

An efficient hierarchical 16‐QAM dynamic constellation to obtain high PSNR reconstructed images under varying channel conditions

Startling growth in multimedia services over wireless channels emphasizes the need for bandwidth and power efficient modulation techniques. This study investigates the suitability of hierarchical quadrature amplitude modulation (HQAM) for image transmission over erroneous wireless Gaussian channels. HQAM provides unequal error protection, to compressed and coded image data, transmitted without increasing the required bandwidth, unlike channel coding. A discrete cosine transform based image coder is used to divide the image data bit stream into high-priority (HP) and low-priority (LP) sub-streams for significant and non-significant data respectively. The ratios between the constellation distances are then dynamically adjusted with the objective to achieve an acceptable bit-error rate (BER) for HP sub-stream over varying channel conditions at the cost of increased BER for LP sub-stream. The work highlights HQAM implementation using conventional quadrature amplitude modulation (QAM) demodulator at the receiver which does not require the knowledge of varying constellation distance ratios at the transmitter. An analysis of 16-HQAM transmission for different values of distance ratios is presented to obtain high peak signal-to-noise ratio (PSNR) values of reconstructed images under poor as well as good channel conditions and the performance is compared qualitatively and quantitatively with 16-QAM.

Priority-based Unequal Error Protection Scheme of Data partitioned H.264 video with Hierarchical QAM

In this paper, we propose a priority-based unequal error protection scheme of data partitioned H.264/AVC video with hierarchical quadrature amplitude modulation. In order to map data with higher priority onto the most significant bits of QAM constellation points, a priority sorting method categorizes different data partitions according to the unequal importance factor of encoded video data in one group of pictures by evaluated the average distortion. Then we propose a hierarchical quadrature amplitude modulation arrangement with adaptive constellation distances, which takes into account the unequal importance of encoded video data and the channel status. Simulation results show that the proposed scheme improves the received video quality by about 2 dB in PSNR comparing with the state-of-the-art unequal error protection scheme, and outperforms EEP scheme by up to 5 dB when the average channel SNR is low.

Universal Bounds on the Derivatives of the Symbol Error Rate for Arbitrary Constellations

The symbol error rate (SER) of the minimum distance detector under additive white Gaussian noise is studied in terms of generic bounds and higher order derivatives for arbitrary constellations. A general approach is adopted so that the recent results on the convexity/concavity and complete monotonicity properties of the SER can be obtained as special cases. Novel universal bounds on the SER, which depend only on the constellation dimensionality, minimum and maximum constellation distances are obtained. It is shown that the sphere hardening argument in the channel coding theorem can be derived using the proposed bounds. Sufficient conditions based on the positive real roots (with odd multiplicity) of an explicitly-specified polynomial are presented to determine the signs of the SER derivatives of all orders in signal-to-noise ratio. Furthermore, universal bounds are given for the SER derivatives of all orders. As an example, it is shown that the proposed bounds yield a better characterization of the SER for arbitrary two-dimensional constellations over the complete monotonicity property derived recently.

An Adaptive Hierarchical QAM Scheme for Enhanced Bandwidth and Power Utilization

Hierarchical quadrature amplitude modulation (HQAM) enables unequal priority transmission through the use of non-uniformly spaced constellations. In this paper, we propose an adaptive HQAM (A-HQAM) scheme where the ratios between the constellation distances are regularly adjusted based on the channel condition with the objective of maximizing the transmission efficiency. The source bit stream is divided into multiple sub-streams which are simultaneously transmitted, each on a different priority level. When using A-HQAM, the high priority sub-stream maintains an acceptable bit error rate performance over all channel conditions. As the channel condition improves, the required protection for the high priority sub-stream is reduced allowing for increasing the protection level of lower priority sub-streams. Hence, the number of sub-streams with acceptable BER performances is incrementally increased as the channel condition improves. Analysis and simulation results show that the proposed A-HQAM not only enhances the transmission efficiency but also provides reduced peak to average power ratio (PAPR). The proposed scheme offers reduced complexity by using one constellation size, unlike conventional adaptive schemes which require the use of several constellation sizes. Moreover, a practical A-HQAM implementation is presented which enables the receiver to successfully demodulate the received signal without knowing the varying transmission parameters.

Prioritized transmission of data partitioned H.264 video with hierarchical QAM

In this letter, hierarchical quadrature amplitude modulation (HQAM) is used to provide unequal error protection (UEP) for layered (data partitioned) H.264 coded video. In a conventional HQAM system, the high-priority (HP) and low-priority (LP) capacities have a constant ratio, whereas in H.264 data partitioning, the corresponding parts do not necessarily have this constant ratio. This letter proposes a multilevel HQAM arrangement with adaptive constellation distances that provides a graceful degradation in the quality of the decoded video without requiring feedback from the receiver. The arrangement improves the quality relative to nonhierarchical transmission through poor signal-to-noise ratio (SNR) channels at the price of a modest quality reduction through good SNR channels.