Hierarchical Modulation Scheme Research Articles

Distance-Enhanced Hybrid Hierarchical Modulation and QAM Modulation Schemes for UAV Terahertz Communications

Unmanned aerial vehicles (UAVs) are extensively employed in pursuit, rescue missions, and agricultural applications. These operations require substantial data and video transmission, demanding significant spectral resources. The ultra-broad bandwidth of 0.1–10 THz in the Terahertz (THz) frequency range is essential for future UAV-based wireless communications. However, the available bandwidth in the THz frequency spectrum varies with transmission distance. To enhance spectral efficiency over this variable bandwidth, we propose using hierarchical modulation (HM) in the overlapped spectrum and traditional quadrature amplitude modulation (QAM) in the non-overlapped spectrum for closer users. Furthermore, we analyze the single-user case and utilize the block-coordinated descent (BCD) method to jointly optimize the modulation order, subcarrier bandwidth, and sub-band power to improve the system sum rate. Finally, considering the mobility and randomness of UAV users, we design a modulation switching rule to dynamically adjust to changes in distance as users move, thereby enhancing data rates. Simulation results demonstrate superior performance in data rate and design complexity compared to existing methods such as hierarchical bandwidth modulation (HBM) and HM schemes.

SoftHM: A Software-Based Hierarchical Modulation Design for Wireless System

Hierarchical Modulation (HM) is quite efficient for multimedia broadcast in wireless networks. It exploits the wireless broadcast advantage and allows a transmission to reach different users with various qualities. However, existing HM related schemes are based on specially designed hardware, leading to extra hardware and deployment cost in practice. As a remedy for this, we design and implement a software-based HM scheme, named as SoftHM. By carefully tuning the Physical Layer input of a packet (a sequence of “0” or “1” bits, known as PHY payload), a transmitter simply broadcasts the packet with a single rate (e.g., 54Mbps, the highest rate in 802.11g WLAN), while diverse receivers can decode and extract different amount of information (with different reception rate, e.g., 12Mbps or 54Mbps) from it based on their link qualities. Reverse engineering techniques are adopted so that SoftHM works in a plug-in mode, offering it high potentials for wireless systems without any changes in existing modulation and coding modules. We implement SoftHM based on Universal Software Radio Peripheral (USRP) B210 and Commercial of the Shelf (COTS) Wi-Fi devices. Both rigorous analysis on its performance and comprehensive implementation-based experiments show that compared with the traditional time-sharing approach, to support low-quality users with the same bandwidth, high-quality users in SoftHM achieve 111.1% to 616.7% higher throughput. Likewise, to serve high-quality users with the same bandwidth, low quality users in softHM achieve 176.9% to 390.9% higher throughput.

Multi-Carrier $M$-ary DCSK System With Code Index Modulation: An Efficient Solution for Chaotic Communications

A new multi-carrier $M$ -ary differential chaos shift keying system with code index modulation, referred to as CIM-MC- $M$ -DCSK , is proposed in this paper. In the proposed CIM-MC- $M$ -DCSK system, the reference and information-bearing signals for each subcarrier can be transmitted simultaneously by using the orthogonal sinusoidal carriers, where the information-bearing signal adopts the $M$ -DCSK modulation to further increase the data rate. With an aim to making full use of the system energy resources, the reference signals in all subcarriers are coded by a Walsh code to carry additional information bits. The analytical bit-error-rate (BER) expressions of the proposed CIM-MC- $M$ -DCSK system are derived over additive white Gaussian noise as well as multipath Rayleigh fading channels. Furthermore, a noise-reduction scheme and a hierarchical-modulation scheme are designed for the proposed system. In particular, the former scheme can significantly improve the BER performance while the latter scheme can provide different quality of service for the transmitted bits according to their different levels of importance. Simulation results verify the accuracy of the analytical expressions and the superiority of the proposed systems.

Nyquist four-level pulse amplitude modulation scheme (PAM-4) based on hierarchical modulation in IM/DD-TDM PON with hybrid equalization

In order to achieve higher power margin in the intensity-modulation and direct detection (IM/DD) based time division multiplexed passive optical network (TDM-PON) system, at the optical line terminal (OLT) side, we propose to use a Nyquist pulse shaped four-level pulse amplitude modulation (PAM-4) by using the electric low pass filter(LPF). In addition, we apply the hierarchical modulation (HM) scheme by assigning of most-significant bits (MSBs) and the less-significant bits (LSBs) of the PAM-4 symbol to optical network units (ONUs) located at different link positions. In addition, an overlap frequency domain equalizer (OFDE) and a vestigial-side band (VSB) filter are used to mitigate the linear inter symbol interference (ISI) and power fading (both of which are incurred by chromatic dispersion (CD)), respectively. The system performance, i.e., bit error rate (BER) and receiver sensitivity for both MSB and LSB, are analyzed by varying different system configurations. Simulation results show that increasing the hierarchical power ratio, which determines the significance difference between the points in the Nyquist pulse shaped HM PAM-4 constellation diagram, can increase the MSB’s receiver sensitivity and reduce the LSB’s receiver sensitivity. Furthermore, it has been demonstrated that the electric low pass filter can reduce the system ISI. In addition, the effect of linear ISI and power fading can be migrated by utilizing OFDE and VSB filter, respectively.

Joint Vehicular and Static Users Multiplexing Transmission With Hierarchical Modulation for Throughput Maximization in Vehicular Networks

With the rapid development of intelligent transportation system (ITS), increasing the throughput of all kinds of users in the mobile communication network is a pressing problem. We consider there are two types of users, i.e. vehicular users (VUs) and static users (SUs), in a vehicular communication network. Since the channel characteristics of VUs and SUs are different, designing a multi-user multiplexing transmission strategy to provide an efficient and reliable transmission for two types of users is quite challenging. We propose a dynamic cross-layer transmission strategy with joint admission control, user association and resource allocation to increase the total throughput of VUs and SUs while satisfying the different quality of service (QoS) requirements. First, we formulate a throughput utility maximization problem subject to the QoS and maximum transmit power constraints. Second, with the help of Lyapunov optimization theory, the problem can be decomposed into three subproblems including traffic admission control, user association and resource allocation. Third, a novel robust resource allocation scheme with discrete-rate hierarchical modulation (HM) is designed for the reliable multiplexing transmission of two types of users. In addition, an optimal algorithm and a low complexity suboptimal algorithm are presented to solve the user association subproblem. For two types of users, comparing with uniform modulation schemes, the proposed transmission strategy with HM scheme can improve the throughput by more than 15%.

A Hierarchical Modulation Coherent Communication Scheme for Simultaneous Four-State Continuous-Variable Quantum Key Distribution and Classical Communication

We present a hierarchical modulation coherent communication protocol, which simultaneously achieves classical optical communication and continuous-variable quantum key distribution. Our hierarchical modulation scheme consists of a quadrature phase-shifting keying modulation for classical communication and a four-state discrete modulation for continuous-variable quantum key distribution. The simulation results based on practical parameters show that it is feasible to transmit both quantum information and classical information on a single carrier. We obtained a secure key rate of $10^{-3}$ bits/pulse to $10^{-1}$ bits/pulse within 40 kilometers, and in the meantime the maximum bit error rate for classical information is about $10^{-7}$ . Because continuous-variable quantum key distribution protocol is compatible with standard telecommunication technology, we think our hierarchical modulation scheme can be used to upgrade the digital communication systems to extend system function in the future.

Performance of duo‐binary turbo codes with optimized hierarchical modulation

Non‐binary turbo codes (TCs) have become an important class of TCs following the adoption of duo‐binary TCs (DBTCs) in the digital video broadcasting with return channel via satellite (DVB‐RCS) standard. Several hierarchical modulation (HM) schemes for binary TCs have been proposed with a view to enhancing their performance. However, the existing techniques make use of fixed parameters throughout the Eb/N0 range and have not been applied to non‐binary TCs. In this paper, optimum parameters have been derived from exhaustive simulations for performing HM with 8‐PSK integrated with DBTCs. To validate the improved error performances obtained with the optimized parameters for HM, EXIT charts have been generated. Moreover, a model that could predict the optimized parameters at each Eb/N0 using K‐nearest neighbor (K‐NN)‐based binary classification has been derived from the results of exhaustive simulations. Significant improvement in error performances have been observed with the proposed scheme. For example, with a couple length of 48, code rate of 1/3 or 1/2, and 8‐PSK modulation, a significant average gain of 0.5 dB is obtained over conventional DBTCs without HM.

Robust adaptive multi-service transmission with hierarchical modulation for OFDM systems in high mobility scenarios

Wireless communications play a key role in intelligent transportation systems for bearing multiple application services with different quality of service (QoS) requirements. Hierarchical modulation (HM) is an effective technique to increase the spectral efficiency (SE) of differentiated services multiplexing transmissions. In high mobility scenario, due to the impact of the feedback delay and channel estimation error, only the imperfect channel state information is available at the transmitter. Thus, the performance of the existing HM schemes degrades severely. In this paper, we propose a robust adaptive HM scheme to increase the overall SE in the mobile orthogonal frequency division multiplexing system. The bit error rate of the HM symbol is derived for the reliable QoS-aware multi-service transmission, and the strategies of bit assignment and modulation parameters selection for different services are designed. Finally, comparing with the traditional uniform modulation scheme, the proposed robust adaptive HM scheme increases the overall SE of multiplexing transmissions by $$15\%$$ at $$300\,\hbox { km}/\hbox {h}$$ .

Design and Analysis of Hierarchically Modulated BICM-ID Receivers With Low Inter-Layer Interferences

In this article, we present a novel methodology to optimize Hierarchically Modulated Bit-Interleaved Coded Modulation with Iterative Decoding (HM-BICM-ID). This methodology allows designing a receiver which supports several configurations. Each configuration is able to decode the same transmitted signal over the air with different fidelity. This concept permits using radios with varying processing capabilities, e.g. handheld radios, vehicular based radios etc. However, earlier simulation results have shown that HM-BICM-ID loses, if compared to non-hierarchical schemes, in Bit Error Rate (BER) performance due to Inter-Layer Interferences and design restrictions. Our proposed iterative tunable procedure optimizes hierarchical modulation schemes considering two criteria, the Harmonic Mean of the minimum squared Euclidean Distance and the bit error probability. The optimization is done by moving critical constellation points towards the optimal direction. A novel modulation scheme has been found and simulation results show an improved asymptotic BER performance in a wide range of channel conditions for an exemplary two-layered HM-BICM-ID. Finally, we present an analysis of HM-BICM-ID in context of Extrinsic Information Transfer Charts.

성상회전 변조기법을 이용한 새로운 계층변조 기법

In this paper, we propose a new hierarchical modulation scheme for DVB-NGH to improve the performance of LP (Low-Parity) signals by applying a conventional constellation-rotation method to the LP signals without virtually a loss of performance of a HP (High-Parity) signals. The improvement of the LP signals is mainly due to the increased divesity gain caused by the constellation-rotation method which barely affect the performance of the HP signals. For the new scheme, we also propose a hardware-efficient ML (Maximum-Likelihood) detection algorithm that first decodes the HP signals by using a conventional HP receiver, and then simply decodes the precoded LP signals based on the pre-detected HP signals.

Discrete‐input continuous‐output memoryless channel capacity of cooperative hierarchical modulation

Hierarchical modulation (HM) is a layered modulation scheme, which is widely employed by the telecommunication industry. The higher flexibility and lower complexity of the HM scheme has its dramatic benefits for wireless communications, hence the achievable performance of cooperation-aided coded HM has drawn substantial research interests. In this study, a triple-layer HM-aided four-node cooperative communication system is proposed, and its discrete-input continuous-output memoryless channel capacity is derived, which is used for finding the optimal position of the relay nodes as well as to design appropriate HM constellations. The authors’ simulation results show that if a rate-1/2 ‘perfect’ channel code is assumed, the four-node network becomes capable of conveying a coded HM-64QAM signal in three time slots at an average signal-to-noise ratio of ?0.71 dB.

Decode-and-Forward Cooperation-Aided Triple-Layer Turbo-Trellis-Coded Hierarchical Modulation

Hierarchical modulation (HM) is widely employed across the telecommunication industry. The potential application of the coded HM scheme in cooperative communications has drawn much interest. In this paper, a twin-relay-aided triple-layer cooperative communication system is proposed. The system amalgamates rate-1/2 TTCM, triple-layer HM-64QAM, and twin-layer SPM-16QAM schemes in the context of cooperative communications. We have optimized the entire system based on the HM ratio pair $(R_{1}, R_{2} )$ , the superposition modulation (SPM) weighting pair $(\alpha,\beta) $ , and the positions of the two relays. The simulation results show that our optimized system is capable of reliably transmitting a triple-layer HM-64QAM signal with the aid of two time slots at an average signal-to-noise ratio of 6.94 dB per time slot.

Layered Offset Hierarchical QAM Modulation for Intersymbol Interference Reduction

Layered offset hierarchical QAM modulation scheme is proposed to enhance the high priority stream error performance by reducing the intersymbol interference from the superimposed symbols of the low priority stream. The proposed scheme shifts the symbols of the two priority layers by half the symbol duration, whereas the detector performs multi-stage maximum-likelihood detection with interference cancellation. The simulations demonstrate the performance and design options offered by the proposed scheme compared to conventional hierarchical schemes where no time offset exists between the superimposed symbols.

Optimization of Hierarchical Modulation for Decode-and-Forward Wireless Relay Networks

This paper presents two designs of optimal nonuniformed constellations for decode-and-forward wireless relay networks with an orthogonal space-time block code (STBC). The first design is concerned with the unequal error protection issue, in which two data streams to be transmitted from a source to a destination are protected at two different levels. The design is to minimize the bit error rate (BER) of one stream while maintaining the BER of the other stream to be no larger than a given threshold. Based on a simple approximation of the average BER, a design parameter is obtained in closed form. The second design focuses on minimizing the average BER of the combined data stream at the destination. Developed are two near-optimal designs for 4/16-quadrature amplitude modulation (QAM) and 4/64-QAM hierarchical modulation (HM) schemes. The designs are also extended to two-way relay networks where both the source and the destination have data to transmit to each other. Simulation results confirm the superiority of the proposed designs and the advantages of relay-assisted transmission employing HM over conventional point-to-point transmission. A comparison with the existing relay-assisted transmission model is also discussed.

Power margin improvement for OFDMA-PON using hierarchical modulation

We propose and experimentally demonstrate a hierarchical modulation scheme to improve power margin for orthogonal frequency division multiple access-passive optical networks (OFDMA-PONs). In a PON system, under the same launched optical power, optical network units (ONUs) have different power margins due to unequal distribution fiber lengths. The power margin of the PON system is determined by the ONU with the lowest power margin. In our proposed scheme, ONUs with long and short distribution fibers are grouped together, and downstream signals for the paired ONUs are mapped onto the same OFDM subcarriers using hierarchical modulation. In a pair of ONUs, part of the power margin of the ONU with short distribution fiber is re-allocated to the ONU with long distribution fiber. Therefore, the power margin of the ONU with the longest distribution fiber can be increased, leading to the power margin improvement of the PON system. Experimental results show that the hierarchical modulation scheme improves the power margin by 2.7 dB for an OFDMA-PON system, which can be used to support more users or extend transmission distance.

Multi-hop transmission and routing with hierarchical modulation

Hierarchical modulation multiplexes layers of different robustness into one stream. Usually being exploited in broadcast systems such as digital video broadcasting, hierarchical modulation can also be applied to unicast communications in a cooperative manner. This article deals with novel multi-hop cooperative transmission and routing strategies with hierarchical modulation. In multi-hop networks, when intermediate nodes receive different sets of streams, they cooperatively forward streams toward the final destination. We first show how hierarchical modulation reduces the total number of transmissions in tandem networks. We then model an optimization problem that determines proper modulation schemes and routing strategies as a stationary infinite-horizon Markov decision process (MDP). The MDP problem requires exponential computations forcing us to delve for heuristic solutions. We simplify the optimization problem by restricting hierarchical modulation consisting of only two fixed constellations. Even with this approximation, the routing problem with hierarchical modulation is still too complex because we must consider all possible paths and hierarchical modulation schemes at the same time. We introduce an approximation scheme that determines the most efficient hierarchical modulation scheme for each three node subgraph assuming subgraphs are isolated each other. Based on the three node subgraph approximation, we map original graphs to virtual graphs. We then apply one of shortest path algorithm to the virtual graphs to find the best route with hierarchical modulation. We perform simulations with various network topologies to evaluate the efficiency of hierarchical modulation in multi-hop unicast communication. Our results show that hierarchical modulation enhances the throughput about 25–30% compared to non-hierarchical modulation. However, optimal solution derived by solving the MDP is also 5% better than heuristic solutions suggesting the necessity to develop better heuristics in future.

Scalable Modulation for Video Transmission in Wireless Networks

In conventional wireless systems with layered architectures, the physical (PHY) layer equally treats all data streams from the upper layers and applies the same modulation and coding schemes to them. Newer systems such as Digital Video Broadcast start to introduce hierarchical modulation schemes with SuperPosition Coding (SPC) and support data streams of different priorities. However, SPC requires specialized hardware and has high complexity, which is not desirable for handheld devices. In this paper, we propose scalable modulation (s-mod) by reusing the current mainstream modulation schemes with software-based bit remapping. The performance evaluation has shown that s-mod can achieve the same and, in some cases, even better performance than SPC with much lower complexity. We further propose how to optimize the configuration of the PHY-layer s-mod and coding schemes to maximize the utility of video streaming with scalable video coding (SVC). Simulation results demonstrate substantial performance gains using s-mod and cross-layer optimization, indicating that s-mod and SVC are a good combination for video transmission in wireless networks.

Hierarchical cooperative relay based heterogeneous networks

This article presents a hierarchical cooperative relay-based heterogeneous network (HCRHeNet) to support both unicast and multicast services, where hierarchical cooperative relay nodes are deployed to provide a cost-effective coverage extension based on the convergence of heterogeneous radio networks. The underlined HCR-HeNet divides its coverage into three layers: hierarchical cooperative basic layer, homogeneous cooperative enhanced layer, and heterogeneous cooperative extended layer. In the hierarchical cooperative basic layer, highspeed data transmission is enabled using highorder modulation and coding schemes for unicast services, and hierarchical modulation schemes for multicast services. In the homogeneous cooperative enhanced layer, where users may be located near a cell boundary and thus need the help of relay nodes, cooperative homogeneous diversity gain can be achieved. In the heterogeneous cooperative extended layer, heterogeneous cooperative diversity gain guarantees the convergence and interworking of multiradio access networks. The key techniques in the physical and MAC layers are identified. Issues in the application of cognitive radio and self-organized networking techniques in HCR-HeNet are also discussed. Finally, a physical layer testbed for the proposed HCR-HeNet with multicast services is introduced.

Design of AT-DMB Baseband Receiver SoC

This paper presents the design of an advanced terrestrial digital multimedia broadcasting (AT-DMB) baseband receiver SoC. The AT-DMB baseband is incorporated into a hierarchical modulation scheme consisting of high priority (HP) and low priority (LP) stream decoders. The advantages of the hierarchical modulation scheme are backward compatibility and an enhanced data rate. The structure of the HP stream is the same as that of the conventional T-DMB system; therefore, a conventional T-DMB service is possible by decoding multimedia data in an HP stream. An enhanced data rate can be achieved by using both HP and LP streams. In this paper, we also discuss a time deinterleaver that can deinterleave data for a time duration of 384 ms or 768 ms. The interleaving time duration is chosen using the LP symbol mapping scheme. Furthermore, instead of a Viterbi decoder, a turbo decoder is adopted as an inner error correction system to mitigate the performance degradation due to a smaller symbol distance in a hierarchically modulated LP symbol. The AT-DMB baseband receiver SoC is fabricated using 0.13 µm technology and shows successful operation with a 50 mW power dissipation.

A Hierarchical Modulation for Upgrading Digital Broadcast Systems

A hierarchical modulation scheme is proposed to upgrade an existing digital broadcast system, such as satellite TV, or satellite radio, by adding more data in its transmission. The hierarchical modulation consists of a basic constellation, which is the same as in the original system, and a secondary constellation, which carries the additional data for the upgraded system. The upgraded system with the hierarchical modulation is backward compatible in the sense that receivers that have been deployed in the original system can continue receiving data in the basic constellation. New receivers can be designed to receive data carried in the secondary constellation, as well as those in the basic constellation. Analysis will be performed to show the tradeoff between bit rate of the data in secondary constellation and the penalty to the performance of receiving the basic constellation.