Hierarchical Quadrature Amplitude Modulation Research Articles

Modern types of signal manipulation analysis of wireless communication systems

This paper presents an overview of modern types of signal manipulation such as hierarchical quadrature amplitude modulation (HQAM), circular quadrature amplitude modulation (CQAM) and parametric quadrature amplitude modulation (θ-QAM). Then follows the modeling of the above-mentioned types of modulations and quadrature amplitude modulation (QAM) using the MATLAB programming language. To compare the four selected types of modulation two types of modulation order are used: 16 and 64. To evaluate the effectiveness of using one or another type of modulation a communication channel was modeled to which additive white Gaussian noise (AWGN), Doppler frequency distortion and inaccurate frame synchronization were added.

An adaptive 3-Dimensional hierarchical QAM scheme for elastic optical network

In this paper, a novel 3-Dimensional adaptive hierarchical Quadrature Amplitude Modulation (QAM) scheme for elastic optical networks has been introduced. The scheme can adjust the spacing between constellation points and control bit-mapping to provide different degrees of protection according to channel conditions or Quality of Service (QoS) requirements. The simulation results indicate that the multi-dimensional hierarchical constellation effectively improves the receiver sensitivity and reduces the bit error rate of the system. The 3D-AH-8/64QAM modulation scheme can obtain a maximum of 3.3 dB and 5.7 dB SNR gains respectively compared with 2D-8QAM and 2D-64QAM. The proposed scheme has a huge potential in the future high-speed elastic optical network.

Unequal error protection technique for video streaming over MIMO-OFDM systems.

In this paper, a novel unequal error protection (UEP) technique is proposed for video streaming over multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. Based on the concept of hierarchical quadrature amplitude modulation (HQAM) UEP and multi-antenna UEP, the proposed technique combines the relative protection levels (PLs) of constellation symbols and the differentiated PLs of the transmit antennas. In the proposed technique, standard square quadrature amplitude modulation (QAM) constellations are used instead of HQAM so that the QAM mapper at the transmitter side and the soft decision calculation at the receiver side remain unchanged, but the UEP benefit of HQAM is retained. The superior performance of the proposed technique is explained by the improved connections between data with various priorities and data paths with various PLs. The assumed video compression method is H.264/AVC, which is known to be commercially successful. The IEEE802.16m system is adopted as a data transmission system. With the aid of realistic simulations in strict accordance with the standards of IEEE802.16m systems and H.264/AVC video compression systems, the proposed technique HQAM-multi-antenna UEP is shown to improve the video quality significantly for a given average bit error rate when compared with previous techniques.

BER performance of an MRT‐HQAM system over Rayleigh fading channels with channel estimation errors and feedback delay

In this study, the bit error rate (BER) performance of multiple-input-multiple-output (MIMO) hierarchical quadrature amplitude modulation systems employing maximum ratio transmission (MRT-HQAM) is investigated under the effects of imperfect channel state information (ICSI) due to the channel estimation error and feedback delay. Theoretical expressions for the BER performance of the MRT-HQAM systems are derived using the two common ICSI models that exist in the current literature, specifically when studying the MIMO beam-forming systems with ICSI, where the error term due to the ICSI is assumed to contribute to either the noise component or to the signal component. The BER results for the two ICSI models are presented and then compared. In addition, various antenna configurations are studied to illustrate the performance gains achievable with additional antennas, and to identify the ideal antenna configuration for a given number of antennas. Moreover, the hierarchical modulation parameter is varied to determine the varying levels of sensitivity of the hierarchical layers in the presence of ICSI. The theoretical BER expressions provided for both ICSI models are verified by simulation results.

BER performance of an MRT‐HQAM system over Rayleigh fading channels

Hierarchical quadrature amplitude modulation (HQAM) allows for transmission of multiple classes of data (such as voice, video and file transfer), provides flexibility in terms of coverage area and allows for network upgrades while maintaining backwards compatibility. However, the addition of hierarchical layers leads to higher-order modulation schemes which make the system increasingly susceptible to noise and fading. To mitigate fading while maintaining backwards compatibility, maximum ratio transmission (MRT) is incorporated into the HQAM system to maximise signal-to-noise ratio for a given number of diversity branches. This study presents a theoretical bit error rate (BER) performance analysis of an MRT enhanced HQAM (MRT-HQAM) system in Rayleigh fading. The BER performance gains of the proposed system over single-input–single-output and single-input–multiple-output HQAM systems are shown. The HQAM hierarchical modulation parameter is varied and the effects are presented. Furthermore, the authors present the effects of varying the number of antennas on the transmitting and receiving ends and discuss the optimal antenna configuration. The theoretical BER expressions used in the performance analysis are verified using simulation results.

Improving the Channel Utilization of Basic Safety Message in VANETs with Superposition Coded Modulation

In this paper, we propose a broadcast scheme to effectively utilize the scarce and shared wireless medium for vehicular ad-hoc networks (VANETs). By using superposition coded modulation (SCM), information elements that comprise basic safety messages (BSMs) were delivered with different service qualities determined by real-time traffic situations. The optimal power allocation strategy and achievable performance gain of the proposed method were first theoretically analyzed. To apply the proposed method into practice, the hierarchical quadrature amplitude modulation technology was then employed to implement the proposed SCM-based broadcast scheme for VANETs. To evaluate the performance of the proposed method in real-time traffic environments, a joint traffic-communication simulation was further conducted. Results agree that the proposed method extends the coverage of the BSM broadcast while maintaining an acceptable communication reliability to meet the requirement of driving safety.

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.

Multimedia Transmission Over Cognitive Radio Channels Under Sensing Uncertainty

This paper studies the performance of hierarchical modulation-based multimedia transmission in cognitive radio (CR) systems with imperfect channel sensing results under constraints on both transmit and interference power levels. Unequal error protection (UEP) of data transmission using hierarchical quadrature amplitude modulation (HQAM) is considered in which high priority (HP) data is protected more than low priority (LP) data. In this setting, closed-form bit error rate (BER) expressions for HP data and LP data are derived in Nakagami-$m$ fading channels in the presence of sensing errors. Subsequently, the optimal power control that minimizes weighted sum of average BERs of HP bits and LP bits or its upper bound subject to peak/average transmit power and average interference power constraints is derived and a low-complexity power control algorithm is proposed. Power levels are determined in three different scenarios, depending on the availability of perfect channel side information (CSI) of the transmission and interference links, statistical CSI of both links, or perfect CSI of the transmission link and imperfect CSI of the interference link. The impact of imperfect channel sensing decisions on the error rate performance of cognitive transmissions is also evaluated. In addition, tradeoffs between the number of retransmissions, the severity of fading, and peak signal-to-noise ratio (PSNR) quality are analyzed numerically. Moreover, performance comparisons of multimedia transmission with conventional quadrature amplitude modulation (QAM) and HQAM, and the proposed power control strategies are carried out in terms of the received data quality and number of retransmissions.

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.

Analytical Performance Evaluation of Hierarchical 16 QAM for Multicast/Broadcast Transmission

An information theoretical approach is applied to analyze the performance of hierarchical 16 quadrature amplitude modulation (QAM). Using the approach, it is quantitatively evaluated how much the hierarchical 16 QAM outperforms non-hierarchical, conventional 16 QAM. More specifically, two kinds of performance comparisons are examined. First, the performance of the hierarchical QAM combined with layered source encoding (such as scalable video coding) is compared to that of the non-hierarchical QAM without layered source encoding. Second, the former is compared to the performance of the non-hierarchical QAM, also with layered source encoding.

Optimized Unequal Error Protection Using Multiplexed Hierarchical Modulation

With progressive image or scalable video encoders, as more bits are received, the source can be reconstructed with progressively better quality. These progressive codes have gradual differences of importance in their bitstreams, which necessitates multiple levels of unequal error protection (UEP). One practical method of achieving UEP is based on a constellation of nonuniformly spaced signal points, or hierarchical constellations. However, hierarchical modulation can achieve only a limited number of UEP levels for a given constellation size. Though hierarchical modulation has been intensively studied for digital broadcasting or multimedia transmission, most work has considered only two layered source coding, and methods of achieving a large number of UEP levels for progressive transmission have rarely been studied. In this paper, we propose a multilevel UEP system using multiplexed hierarchical quadrature amplitude modulation (QAM). We show that multiple levels of UEP are achieved by the proposed multiplexing method. When the BER is dominated by the minimum Euclidian distance, we derive an optimal multiplexing approach which minimizes both the average and peak powers. We next propose an asymmetric hierarchical QAM which reduces the peak-to-average power ratio (PAPR) of the proposed UEP system without any performance loss. Numerical results show that the performance of progressive transmission over Rayleigh fading channels is significantly enhanced by the proposed methods.

Unequal error protection scheme based hierarchical 16-QAM for 3-D video transmission

In this paper, an unequal error protection (UEP) scheme based on hierarchical quadrature amplitude modulation (HQAM) for three-dimensional (3-D) video transmission is proposed. The proposed scheme exploits unique characteristics of the color plus depth map stereoscopic video, where the color sequence has a more significant impact on the reconstructed video quality. The UEP scheme assigns more protection to the color sequence than the depth map so as to achieve high quality 3-D video. Different levels of protection are assigned through hierarchical 16-QAM. The color data with high priority (HP) are mapped onto the most significant bits (MSBs) of the 16- QAM constellation points and the depth map with low priority (LP) are mapped onto the less significant bits (LSBs). Simulation results demonstrate that the proposed UEP scheme outperforms the conventional equal error protection (EEP) schemes by up to 5 dB in terms of the received left and right views quality.

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.

Hierarchical Quadrature Amplitude Modulation for Image Transmission over Erroneous Wireless Channels

Hierarchical Quadrature Amplitude Modulation for Image Transmission over Erroneous Wireless Channels

A novel hierarchical QAM-based unequal error protection scheme for H.264/AVC video over frequency-selective fading channels

A novel unequal error protection (UEP) scheme based on the hierarchical quadrature amplitude modulation (QAM) is proposed for H.264/AVC video transmission over frequency selective fading channels. In order to avoid the situation that data with higher priority in the H.264/AVC video streams to be mapped onto subcarriers in deep fading, an OFDM subcarrier classification strategy with two signal-to-noise ratio (SNR) thresholds is presented. Simulation results show that the proposed UEP scheme outperforms the state-of-the-art UEP method by up to 1.6 dB in terms of the quality of the reconstructed video.

Reliable transmission of wavelet-based scalable video over wireless networks using cross-layer approach

The conventional network layers are mainly designed for fixed networks and are not suitable to cope the challenges offered by the modern wireless networks. Moreover, certain functionalities can be implemented simultaneously in more than one layer. For example, unequal error protection (UEP) can be performed at the application layer, using forward error correction (FEC), but it is bandwidth inefficient. On the other hand, UEP can also be performed at the physical layer using hierarchical modulation to protect higher priority bits more strongly without any additional bandwidth, but at the cost of increased errors in the lower priority bits. The authors propose a cross-layer UEP approach to enhance reliability of scalable video by combining adaptive FEC at the application layer and hierarchical quadrature amplitude modulation (HQAM) at the physical layer. The idea is to slightly reduce the FEC protection of higher priority bits and increase the FEC protection of low-priority bits in such a fashion that the overall data rate at the application layer remains unchanged. The higher priority bits are additionally protected using HQAM at the physical layer. Simulation results show significant improvements in performance when the proposed scheme is used.

A low complexity hierarchical QAM symbol bits allocation algorithm for unequal error protection of wireless video transmission

A low complexity hierarchical quadrature amplitude modulation (QAM) symbol bits allocation algorithm for unequal error protection of video transmission over wireless channels is proposed in this paper. An unequal error protection (UEP) scheme using hierarchical QAM, which takes into consideration the non-uniformly distributed importance of intracoded frame (I-frame) and predictive coded frame (P-frame) in a group of pictures (GOP), is first proposed. In order to optimally allocate the hierarchical QAM's high priority (HP), medium priority (MP) and low priority (LP) symbol bits to the H.264/AVC video, a generic solution for optimal allocation of hierarchical QAM's high priority (HP), medium priority (MP) and low priority (LP) symbol bits to the H.264/AVC video is then proposed. Finally, a low complexity symbol bits allocation algorithm, namely ranking search algorithm, which reduces the computational complexity of the proposed optimal symbol bits allocation algorithm, is proposed. Simulation results show that our proposed UEP scheme outperforms the classical equal error protection (EEP) scheme and also the previous UEP scheme.

On the BER Performance of Hierarchical <formula formulatype="inline"><tex>$M$</tex></formula>-QAM Constellations With Diversity and Imperfect Channel Estimation

The analytical bit error rate of hierarchical quadrature amplitude modulation formats, which include uniform and nonuniform constellations, over flat Rayleigh fading environments is studied in this paper. The analysis takes into account the effect of imperfect channel estimation and considers diversity reception with both independent identically and nonidentically distributed channels, employing maximal ratio combining.

Transmitter/Receiver Method for Supporting Hierarchical Modulations in MBMS Transmissions

In this paper we consider the use of hierarchical Quadrature Amplitude Modulation (QAM) constellations for Multimedia Broadcast/Multicast Service (MBMS) within Wideband Code Division Multiple Access (WCDMA) based systems. These constellations are employed so as to increase the transmission efficiency, since they are able to provide unequal error protection to different information bit streams. With this strategy, the most important information can be received by all users while the less relevant information will only be extracted by users with good propagation conditions. However, these constellations are very sensitive to inter-symbolic interference introduced by multipath propagation, especially for large constellations. Moreover, large hierarchical constellations have also high channel estimation requirements. For these reasons, we propose an iterative receiver for joint detection and channel estimation. The proposed receiver takes advantage of the turbo-code present in the transmission system and uses feedback information from the turbo-decoder to estimate and suppress the interference, as well as to provide enhanced channel estimates.

Rate Adaptive Hierarchical Modulation-Assisted Two-User Opportunistic Scheduling

We propose and study a two-best user opportunistic scheduling scheme using fixed power discrete rate adaptive hierarchical constellations (known also as embedded, multi- resolution, or asymmetrical constellations). According to the classical opportunistic scheduling, the scheduler transmits information to the selected first best user in each transmission slot in order to maximize the spectral efficiency. Our newly proposed scheme transmits information not only to the first best user but also to the second best user if the channel qualities of the selected two users support. As such the frequency of channel access of the users is increased without any degradation of overall spectral efficiency compared to the classical single best user scheduling. The key idea is to rely on hierarchical constellations to transmit information to two best users simultaneously. Specifically, according to the channel quality of the first best user, the alphabet size of the square quadrature amplitude modulation (QAM) is selected in order to maximize the spectral efficiency. However, if the first best user's channel quality is good enough to decode the information transmitted in the second hierarchy of the selected size hierarchical QAM constellation while the second best user's channel quality is capable of decoding the information transmitted in the first hierarchy, information is transmitted to both the selected first and second best users using the hierarchical QAM constellation. Otherwise, information is transmitted only to the first best user using the selected size uniform QAM constellation. We present expressions for the information transmission probability and the overall average spectral efficiency [bits/sec/Hz] defined as the overall average transmitted data rate per unit bandwidth for a specified number of users, a specified average carrier-to-noise ratio (CNR), and bit error rate (BER). Numerical results for a fading environment where the channel variation among the users is identically and independently distributed (i.i.d.) are presented. These results show that, in such i.i.d. fading environment, our newly proposed fixed power discrete rate adaptive hierarchical modulation- assisted two-best user scheduling provides more frequent access to the information (almost double) without any average spectral efficiency degradation compared to the classical single best user opportunistic scheduling.