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The diversity-multiplexing tradeoff (DMT) provides a fundamental performance metric for different multiple-input multiple-output (MIMO) schemes in wireless communications. In this paper, we explore the block fading optical wireless communication (OWC) channels and characterize the DMT in the presence of both optical peak- and average-power constraints. Three different fading distributions are considered, which reflect different channel conditions. In each channel condition, we obtain the optimal DMT when the block length is sufficiently large, and we also derive the lower and upper bounds of the DMT curve when the block length is small. These results are dramatically different from the existing DMT results in radio-frequency (RF) channels. These differences may be due to the fact that the optical input signal is real and bounded, while its RF counterpart is usually complex and unbounded.

The channel state information (CSI) needs to be fed back from the user equipment (UE) to the base station (BS) in frequency division duplexing (FDD) multiple-input multiple-output (MIMO) system. Recently, neural networks are widely applied to CSI compressed feedback since the original overhead is too large for the massive MIMO system. Notably, lightweight feedback networks attract special attention due to their practicality of deployment. However, the feedback accuracy is likely to be harmed by the network compression. In this paper, a cost free distillation technique named codeword mimic (CM) is proposed to train better feedback networks with the practical lightweight encoder. A mimic-explore training strategy with a special distillation scheduler is designed to enhance the CM learning. Experiments show that the proposed CM learning outperforms the previous state-of-the-art feedback distillation method, boosting the performance of the lightweight feedback network without any extra inference cost., 4 pages, 4 figures, 3 tables. This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice

Visible light communications (VLC) techniques are viewed as promising candidates for the upcoming B5G&6G mobile wireless networks. Due to the broadcast nature of VLC channel, physical layer security (PLS) techniques have been considered and explored to improve the confidentiality of VLC transmission. Nevertheless, almost all current designs focus on application scenarios including sufficient transmitters and fail to match the scenarios with limited, even just two transmitters. For addressing this challenge, in this article, multiple optical beam switching scheme is proposed. Unlike conventional Lambertian beam based technique paradigm, the given scheme tentatively utilize two asymmetry non-Lambertian beams to configure each VLC transmitter. Numerical results show that, for the typical center legitimate receiver, compared with about 0.92 bps/Hz average secrecy capacity (SC) of the conventional Lambertian beam configuration, up to 5.55 bps/Hz average SC gain is acquired through the proposed beam switching scheme. Moreover, this potential gain will be enhanced to about 5.86 bps/Hz when three candidate non-Lambertian beams are available for each transmitter.

Millimeter wave (mmWave) communications can support huge data rate growth and wide bandwidth in the new 5G era, and a hybrid precoding architecture can effectively handle the high hardware cost and energy consumption problems. A crucial goal is to optimize the system's spectral efficiency (SE) by effectively designing the digital precoder and the analog precoder. In this article, we review the conventional hybrid precoding schemes in mmWave systems, and then investigate several novel systems with index modulation (IM) techniques as well as their hybrid precoder designs. With the advantages of IM, higher SE can be achieved with limited radio frequency chains in mmWave systems. Simulation results demonstrate that two types of IM-aided systems both outperform conventional mmWave systems, which proves that IM is an enabling technique in practical SE-driven mmWave systems. Finally, we discuss the limiting factors and outlook of IM-aided mmWave systems in beyond-5G wireless communications.

Generalized spatial modulation (GenSM) aided millimeter wave (mmWave) multiple-input multiple-output (MIMO) system has been recently considered as a new efficient technique due to the combination of numerous antennas and reduced number of radio frequency (RF) chains. However, the present hybrid precoding schemes for GenSM-aided system are still troubled by high computational complexity and performance loss in spectral efficiency (SE). In this paper we propose low-complexity hybrid precoding schemes based on Martin's expansion for logarithmic determinant (log-det) form in analytical SE lower bound. Digital and analog precoders are herein optimized separately, which means complicated alternating minimization iteration is omitted. Besides, we can adjust algorithmic complexity adaptively corresponding to different demand levels for users. Finally the numerical simulations show that the proposed methods outperform other GenSM-aided mmWave MIMO schemes and can achieve a better tradeoff between complexity and SE.

With LED-based lighting lamps now being utilized all over the world, the concept of the Internet of Lights (IoL) using existing LED illumination networks with information and communications technologies including visible light communications (VLC) was created. IoL improves the lighting efficiency and indoor lighting comfort level, and can support value-added information services by modulating the light intensity. However, further investigation of its impact on human beings is needed. This article first introduces the concept, the requirements, and the system structure of IoL using the Internet of Radio Light system as an example for information service. We investigate the feasibility of regulating human physiological rhythms, especially to alleviate degenerative neurological diseases. This would possibly bring light therapy treatments to patients in a non-intrusive way. From a preliminary set of experiments, it is seen that the hippocampus area of mice clearly reacts to the lighting at low frequency, showing the influence of light intensity variation on degenerative neurological diseases. This suggests that the future standardization of VLC needs to consider not only the system transmission performance but also its potential impact on human beings for indoor applications.

In this letter, a novel deep learning-based transmit antenna selection (TAS) scheme for the multiple-input multiple-output (MIMO) with spatial modulation (SM) system is proposed. We formulate the generalized TAS pipeline in both neural networks (NN) and gradient boosting decision trees (GBDT), in which the importance of different features reflecting the different elements from channel state information (CSI) is analyzed regarding to the empirical data as well. Furthermore, the bit error rate (BER) performance and the complexity comparison of two structures is investigated. Simulation results confirm that GBDT can be efficiently implemented for real-time application with near-optimal performance.

Ultrafast fiber lasers with a wide spectral range have huge demands for many applications. In this article, magnetron sputtering deposition (MSD) technique was utilized to prepare a new broadband microfiber based Sb thin film saturable absorber (SA), and ultrafast pulses in both 1.5 and 2 μm wavebands were generated with the integrated microfiber-based Sb thin film SA in erbium-doped fiber laser (EDFL) and thulium-doped fiber laser (TDFL), respectively. Pulse duration of 544 fs/972 fs and output power of 21.76 mW/36.1 mW centered at 1557 nm/1892 nm were respectively produced from stable mode-locked EDFL and TDFL. To the best our knowledge, this is the first time that ultrafast fiber lasers including both 1.5 μm and 2 μm wavebands were mode locked by a single microfiber-based Sb thin film SA.

In this work, a wireless broadcast network with a base station (BS) sending random time-sensitive information updates to multiple users with interference constraints is considered. The Age of Synchronization (AoS), namely the amount of time elapsed since the information stored at the network user becomes desynchronized, is adopted to measure data freshness from the perspective of network users. Compared with the more widely used metric---the Age of Information (AoI), AoS accounts for the freshness of the randomly changing content. The AoS minimization scheduling problem is formulated into a discrete time Markov decision process and the optimal solution is approximated through structural finite state policy iteration. An index based heuristic scheduling policy based on restless multi-arm bandit (RMAB) is provided to further reduce computational complexity. Simulation results show that the proposed index policy can achieve compatible performance with the MDP and close to the AoS lower bound. Moreover, theoretic analysis and simulations reveal the differences between AoS and AoI. AoI minimization scheduling policy cannot guarantee a good AoS performance., Comment: accepted and to appear, IEEE Transactions on Wireless Communications

The Fifth generation of mobile broadband (BB) networks, popularly known as 5G, aims to revolutionize different vertical industries, including media broadcasting. Although it remains to be seen the real impact and timescale of the 5G revolution, 5G may represent an opportunity rather than a threat for broadcast (BC), especially when considering new approaches for BC and BB evolving into new converged platforms inter-connecting terrestrial BC and cellular/wired BB systems together [item 1) in the Appendix]. Hybrid BC-BB platforms are already a success in several countries, based, e.g., on HbbTV in EU, hybridcast in Japan and Ginga in Brazil. But the increasing importance of fixed and mobile BB IP delivery for television services, well-illustrated by the new IP-based ATSC 3.0 standard [item 2) in the Appendix] and the on-going DVB-I (Internet) specification, and the fact that the 5G system will support and be interoperable with non-3GPP access technologies, potentially allowing multiple access technologies to be used simultaneously for one or more services, opens the door to new convergence scenarios.

The research about deep learning application for physical layer has been received much attention in recent years. In this paper, we propose a Deep Learning (DL) based channel estimator under time varying Rayleigh fading channel. We build up, train and test the channel estimator using Neural Network (NN). The proposed DL-based estimator can dynamically track the channel status without any prior knowledge about the channel model and statistic characteristics. The simulation results show the proposed NN estimator has better Mean Square Error (MSE) performance compared with the traditional algorithms and some other DL-based architectures. Furthermore, the proposed DL-based estimator also shows its robustness with the different pilot densities.

Usually, multiple secondary users (SUs) utilize the opportunistic spectrum access (OSA) in cognitive radio networks to communicate with the secondary base station (sBS). In uplink transmission, each SU can only select one channel from ${C}$ primary channels to sense, access, and transmit data packets with the constraints of hardware and energy. Distributed non-orthogonal multiple access-based multi-armed bandit (D-NOMA-MAB) approach is proposed to solve the problem of the channel selection and the power level selection, which alleviates the impact of the collision in the same channel. D-NOMA-MAB approach improves the energy efficiency of the system and the successful transmission probability obviously by introducing 2-D selection for the arms and the factor of energy efficiency in the policy index of the restless MAB problem.

Digital terrestrial television multimedia broadcasting-advanced (DTMB-A), the new digital terrestrial television broadcasting (DTTB) system proposed by China, has been accepted by International Telecommunications Union as the international DTTB standard in July, 2015. By adopting several advanced technologies, such as near-capacity channel coding and modulation as well as improved frame structure, DTMB-A can provide faster system synchronization, higher receiving sensitivity, better performance against multipath effect, higher spectrum efficiency, and the flexibility for future extension, compared with its previous generation, DTMB system. This paper provides the technical analyses on the physical layer specifications of DTMB-A system in detail, together with the discussion on the key technologies adopted. Laboratory test and field trial results are also given which demonstrate that DTMB-A can offer excellent overall system performance for both fixed and mobile receptions under complicated terrestrial broadcasting conditions, and is capable of supporting multiple services with different quality of service requirements.

In this letter, we study the outage achievable rate region of non-orthogonal multiple access (NOMA), which is defined as the achievable rate region when all users are required to satisfy their outage probability constraints. First, we formally define the outage achievable rate region of NOMA assuming a slow fading channel model. Then, we introduce a successive interference cancelation (SIC) order under the assumption of statistical channel information. Under this assumption, we find that the outage capacity region of broadcast channel (BC) is also ${\epsilon }$ -achievable by NOMA, which requires the use of SIC, though the definition of outage in NOMA is different from that in BC. Combining the converse result, we get a full characterization of the outage achievable rate region of NOMA, which also shows the optimality of the SIC order used here. Then, we give some discussions about power allocation and the practical insights derived from the characterization. Finally, numerical simulations are provided.

In this paper, we introduce spatial modulation (SM) in the layered division multiplexing (LDM) system for digital TV scenarios. To analyze the achievable spectral efficiency (SE) performance of the proposed SM-LDM system, we calculate its mutual information (MI) through the Monte Carlo method. Considering both Gaussian and finite alphabet inputs, we derive the MI’s computational-efficient lower bounds as well as their asymptotic values. Simulation results confirm both the advantages and our SE analysis of the proposed SM-LDM system.

The terrestrial return channel provides interactive services in digital television terrestrial broadcasting systems to meet various consumers’ demands around the world. The extension of non-orthogonal multiple access and generalized spatial modulation multiple-input multiple-output to the terrestrial return channel improves both the spectral and energy efficiencies of the system, but it puts forward detection challenges. In this paper, a joint user activity and signal detection scheme based on the block-sparse compressive sensing (BS-CS) method in the terrestrial return channel is proposed, in which the generalized spatial modulation technology is used. By exploiting the structure and sparsity of the multi-user generalized spatial modulation signal, we formulate the detection problem into a block-sparse recovery problem. Then a BS-CS-based detection algorithm, enhanced structured block-sparse compressive sampling matching pursuit (ESB-CoSaMP), is proposed to detect the active users and transmitted data efficiently. Moreover, the information of active antennas at each user is exploited in ESB-CoSaMP to further improve the accuracy. Simulations show that the proposed detection scheme outperforms the conventional CS and BS-CS-based schemes.

Recently the combination of massive multiple-input multiple-output (MIMO) and spatial modulation (SM), has been considered as a promising concept for uplink transmission, in which each user equipment (UE) uses SM for uplink transmission and base station (BS) is equipped with massive antennas. In this paper, we evaluate a massive single-carrier (SC) SM-MIMO system with frequency domain equalization, where SC transmission is combined with SM (SC-SM) to combat the negative impact of broadband frequency-selective fading, and frequency domain equalization is utilized to mitigate the intersymbol-interference with a low complexity. With frequency domain processing, a framework is proposed to analyze the achievable uplink spectral efficiency (SE) of single-cell massive SC-SM MIMO systems. Based on this framework, the closed-form SE lower bound of frequency domain maximum ratio combining is derived, and both the derivation of framework and SE lower bound are much more complicated than those of systems with time domain combining. Monte Carlo simulations verify the tightness of proposed SE lower bound, and show that massive SC-SM MIMO systems can outperform the SE of conventional single transmit antenna (TA) massive MIMO systems. The systems can even have a better SE performance than massive MIMO systems with spatial multiplexing UEs in a low signal-to-noise ratio. Finally, the SE gain is found to be mainly dependent on the specific number of UE's TAs, which facilitates an SE maximization via optimizing the number of TAs.

We report the usage of chemical vapor deposition-grown monolayer WSe2 as a saturable absorber (SA) for a mode-locked thulium-doped fiber laser. The monolayer WSe2 was transferred onto a microfiber and then incorporated into a typical all-fiber-integrated ring cavity configuration. Stable soliton pulses emitting at 1863.96 nm were obtained with pulse duration of 1.16 ps, repetition rate of 11.36 MHz, and an average power of 32.5 mW. This is, to the best of our knowledge, the first demonstration of WSe2-based SA in fiber lasers at 2 μ m regime.

Conventional non-orthogonal multiple access (NOMA) schemes assume perfect channel state information (CSI) at the transmitter side, which is nearly impractical for many communication scenarios. Instead, this letter considers a practical downlink NOMA system in the Nakagami- ${m}$ fading channels, of which the transmitter only knows the statistical CSI associated with each user. We analyze the outage performance of the proposed system and derive a closed-form formulation of each user’s outage probability. Moreover, based on statistical CSI, the transmitter can optimize the system’s sum throughput over power allocation for different users. The accuracy of our outage analysis and the efficacy of the proposed optimization algorithm are both confirmed by simulation results.

The combination of massive multiple-input multiple-output (MIMO) and single-carrier (SC) aided spatial modulation (SM), is recently proposed for uplink multi-user transmission over dispersive channels, which has also attracted plenty of research interest. In this letter, first the spectral efficiency (SE) lower bound with non-uniform power allocation for uplink single-cell massive SC-SM MIMO systems is proposed, in which, the base station (BS) applies maximum ratio combining and many non-ideal factors of the wireless channels are all considered. Then, a barrier function-based gradient projection method is proposed to allocate power of each transmit antenna (TA) in terms of SE maximization. The SE lower bound is shown to be tight via simulation results, and simulation results also show that the SE gain introduced by our proposed PA algorithm is mainly dependent on the TA correlation and number of TAs.

The valley-to-peak difference in power consumption is a crucial problem in load regulation and control for a power grid. By allowing electric vehicles (EVs) to charge during off-peak hours and feed power back into the grid during peak hours, Vehicle-to-Grid (V2G) technology can help to shave the power peak. Long-distance communication is essential for data exchange between dispersed EVs and charging stations for the realization of V2G systems. However, because of the high mobility of EVs, the highvolume data transmission required and the limitations of the third-party infrastructure, it is challenging to achieve efficient and effective communication. To address these challenges, we propose a new V2G network architecture based on software-defined networking (SDN) technology. (1) We use an IEEE 802.11 WiFibased long-distance (WiLD) network with the TDMA scheme as the backhaul network, and (2) we partially replace the road side units (RSUs) with some of the WiLD nodes to provide access for, and to rapidly broadcast data to, EVs. In addition, we propose: (3) a two-stage flow table mechanism and a double roaming mechanism to address the mobility demands of V2G network terminals; and (4) a rapid data transmission scheme for communication from charging stations to EVs. A testbed was built to validate the proposed network architecture. Experimental results show that the communication time delay is in the order of milliseconds and that the reliability is higher than 99.9%.

The concept of generalized spatial modulation (GenSM) aided millimeter wave (mm-wave) multiple-input multiple-output (MIMO) has recently attracted substantial research interest, as it benefits from the large bandwidth of mm-wave MIMO, while maintaining a reduced number of radio frequency (RF) chains. However, due to the lack of precoding design, the preceding GenSM-aided mm-wave MIMO schemes suffered from severe performance loss. Inspired by the reduced-RF-chain structure making implementation cost low while maintaining the benefit of GenSM, in this paper, we incorporate the technique of hybrid precoding into GenSM-aided mm-wave MIMO, where a hybrid digital and analog precoding regime is proposed to enhance the system’s achievable rate. Moreover, a closed-form expression is proposed to provide an accurate approximation to the spectral efficiency (SE) achieved by the proposed scheme. The proposed expression is further simplified in the region of high signal-to-noise ratio (SNR). By exploiting the proposed SE expressions as low-complexity cost functions, two algorithms, i.e. the gradient ascent algorithm and the high-SNR approximation algorithm, are exploited to optimize the hybrid precoders in terms of SE maximization. Finally, numerical simulations are provided to substantiate the superior SE performance achieved by the proposed scheme over other GenSM-aided mm-wave MIMO schemes as well as the state-of-the-art mm-wave MIMO systems.

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 finite 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.

In this paper, we investigate the issue of multiuser detection (MUD) in a massive spatial modulation (SM) multiple-input multiple-output (MIMO) system, where the base station is equipped with a large number of antennas and each user equipment uses single-carrier SM (SC-SM) for uplink transmission. Unlike the conventional MUD for massive SM-MIMO systems, the application of forward error correction (FEC) coding is explored in our design, which is utilized to combat the impact of multiuser interference (MUI). More specifically, we propose to utilize the soft information from the FEC decoder to iteratively improve the MUI rejection procedure and provide more accurate estimation of the transmitted signals. The soft information is exchanged between the decoder and the MUI cancellation unit, which constitutes a turbo structure and leads to simultaneous improvement of the mean square error and the bit error ratio performance. The performance gain is substantiated by theoretical analysis as well as numerical simulations.

This paper proposes a new iterative receiver for single-carrier multiple-input–multiple-output (SC-MIMO) underwater acoustic (UWA) communications, which utilizes frequency-domain turbo equalization (FDTE) and iterative channel estimation. Soft-decision symbols are not only fed back to the equalizer to cancel the intersymbol interference (ISI) and cochannel interference (CCI), but also used as training signals in the channel estimator to update the estimated channel state information (CSI) after each turbo iteration. This iterative channel estimation scheme helps to combat the problem commonly suffered by block-processing receivers in fast time-varying channels. Compared with time-domain turbo equalization, FDTE achieves comparable performance with significantly reduced computational complexity. Using soft-decision symbols to reestimate the time-varying channels, iterative channel estimation further improves the accuracy of the estimated CSI. The proposed iterative receiver has been verified through undersea experimental data collected in the Surface Processes and Acoustic Communications Experiment 2008 (SPACE08).

Generalized spatial modulation (GSM) is an extended architecture to the spatial modulation multiple antenna system. The GSM system uses multiple activated transmit antennas to further exploit the system transmission capacity. In this paper, we consider the GSM systems with channel diagonalization (CD-) transmitter pre-coder (TPC), channel inversion TPC, and without TPC. For each TPC scheme, the pairwise activated antenna detection discriminant and closed-form antenna detection pairwise error probability (PEP) of the GSM system are derived. We use the antenna detection PEP to calculate the analytical antenna detection symbol error rate union bound and the mutual information lower bound. We use asymptotic methods to analyze antenna detection diversity and coding gains of GSM system with or without TPC when the signal-to-noise ratio is high. Together with complexity analysis on the pre-coders and antenna detectors, we discover the CD-TPC trades the antenna detection performance for complexity reduction, while the CD-TPC scheme achieves a balance between the performance and complexity. This paper introduces methods to the performance evaluation of the GSM system, and provides a guideline for the GSM system design such as antenna configuration and TPC schemes selection.

The concept of massive spatial modulation aided multiple-input multiple-output (SM-MIMO) systems, where the base station (BS) is equipped with a large number of antennas and simultaneously serves several multi-antenna users that employ SM for their uplink transmission, has recently attracted substantial research interest. In this paper, we investigate the uplink bandwidth efficiency (BE) of single-cell massive SM-MIMO systems, and derive a new BE lower bound when the BS employs maximum ratio combining for uplink user detection. The proposed BE bound takes into account the impact of spatial correlations at the transmitter, of imperfect channel estimation, and of non-uniform power allocation among each user's antennas (i.e., different antennas are allocated with different levels of transmit power). These bounds are shown to be tight even when a moderate number of antennas is used by the BS. Based on this bound, a gradient ascent method-based optimization is carried out to find the optimal power allocation among the transmit antennas (TAs) of each user, so that the uplink BE can be maximized. More specifically, the optimal power allocation is found to be typically dependent both on the TAs' spatial correlation and on the large-scale attenuation of each user. Aided by this new power allocation scheme, a substantial BE gain can be achieved over the conventional uniform power allocation schemes, which is substantiated by our simulation results.

Time-varying channels destroy the orthogonality among subcarriers in orthogonal frequency division multiplexing (OFDM) systems, and introduce intercarrier interference (ICI). Lots of efforts have been devoted to mitigate ICI in OFDM systems, with different frame structures and channel models, but the computational complexity of the methods is usually very high. In multiple-input multiple-output (MIMO) systems, the complexity is even higher. In this paper, a low-complexity ICI mitigation method is proposed for MIMO-OFDM systems under the assumption of linear time-varying channels. It reduces the complexity of ICI compensation from $ {O(K^{3}(N^{3}+MN^{2}+MN)+NK\log (K))}$ to $ {O(K(N^{3}+2MN^{2}+2MN+2M^{2}+N\log (K)))}$ , where ${K}$ is the number of subcarriers, ${M}$ the number of transmitters, and ${N}$ the number of receivers. It requires channel estimation based on the linear time-varying channel model, and no transmission overhead is needed. The proposed algorithm applies to all OFDM systems as long as linear time-varying channel estimation is applicable. Time-domain synchronous-OFDM naturally suits for the proposed ICI mitigation algorithm because its receiver is able to easily estimate linear time-varying channels. Simulation with QPSK and 16QAM modulation demonstrates the performance of the proposed method, in comparison with no ICI mitigation case. It shows that 2 dB signal to noise gain is achieved when the uncoded bit error rate is $ {10^{-3}}$ and the normalized Doppler frequency is 0.1.

An error transfer chart is introduced to trace the iterative process of the decision feedback equalizer for the single-carrier modulation. In the investigated iterative MF-DFE structure, the forward filter is set to the matched filter to maximize the signal power, while the feedback filter is used to cancel the inter-symbol interference. MMSE detection is applied to minimize the decision error power. The trajectory of iterations is shown in the error transfer chart, in which MF-DFE maps a decision error power to an SINR and MMSE detection further converts the SINR to a new decision error power. The final state of iterations is shown to be the intersection of the MMSE curve and error power transfer curve corresponding to the MF-DFE algorithm. It is shown by simulation that the error transfer chart is a useful tool to analyze the convergence of non-linear iterative equalizers.

An iterative design of minimum mean square error decision feedback equalizer (MMSE-DFE) to suppress the intercarrier interference (ICI) of orthogonal frequency division multiplexing systems in the time-variant channels is analyzed in this paper. The channel is assumed to vary in a linear fashion within a frame. The error power transfer is investigated in parallel with the equalizing process, showing the gain in iterations and aiding the MMSE decision. Iteratively, the ICI components are estimated and canceled from the receive symbol, providing an MMSE estimate of the source symbol with an increasing reliability. It is shown that based on the error power transfer analyzed in this paper, ICI components can be significantly removed via the iterative MMSE-DFE, leaving the error composed of noise and negligible residue of ICI. Simulations have verified the accuracy of the error power estimation.

WirelessHART, as a robust and reliable wireless protocol, has been widely-used in industrial wireless sensoractuator networks. Its real-time performance has been extensively studied, but limited to the single criticality case. Many advanced applications have mixed-criticality communications, where different data flows come with different levels of importance or criticality. Hence, in this paper, we study the real-time mixedcriticality communication using WirelessHART protocol, and propose an end-to-end delay analysis approach based on fixed priority scheduling. To the best of our knowledge, this is the first work that introduces the concept of mixed-criticality into wireless sensor-actuator networks. Evaluation results show the effectiveness and efficacy of our approach.

Generalized space shift keying (GSSK), as one simplified version of spatial modulation (SM), has attracted plenty of interest in the study of large-scale multiple-input multiple-output (MIMO). In this letter, we propose a low-complexity symbol detector for GSSK based on $\ell_\infty$ minimization. Via a bijective transformation, the symbol detection for GSSK can be converted into the reconstruction of a binary symbol, of which the entries are selected from $\{-1, 1\}$ . The reconstruction is done by solving an $\ell_\infty$ minimization problem, which is convex and can be solved by many off-the-shelf optimization tools. The new detection scheme is capable of detecting GSSK symbols under overdetermined and underdetermined MIMO systems and only requires a polynomial complexity. Numerical simulations are further performed to substantiate the performance of the proposed detector.

Various factors contribute to the intercarrier interference (ICI) in orthogonal frequency-division multiplexing (OFDM), which violates the orthogonality among subcarriers and greatly degrades the performance. Traditional ICI compensation methods incorporate iterative estimation and cancelation for pilot subcarriers, bearing too much complexity and reducing the spectral efficiency. In this paper, a novel channel equalization method is proposed for time domain synchronous-orthogonal frequency-division multiplexing (TDS-OFDM), where fast and accurate channel estimation is achieved by utilizing the padded pseudo-noise sequence in consecutive blocks. The new equalizer refers to fast suboptimal-minimum mean square error structure, other than traditional overlap-add structure, inspired by the fact that linear convolution structure is better preserved than circular convolution structure in TDS-OFDM under time-varying channels. With the approximation of linear time-varying channel, the proposed equalizer achieves considerable performance with low complexity (linear) and no additional spectral overhead.

Spatial modulation (SM) is a recently proposed multiple-input multiple-output (MIMO) architecture that exploits the space domain for information transmission. In this paper, SM systems with continuous amplitude-phase modulation (APM) and the corresponding maximum likelihood (ML) active transmit antenna detector are considered. We introduced a method to compute the theoretical transition probability matrix and the mutual information of the ML antenna detector. For SM multiple-input single-output (MISO) system, we derive the error probability and the mutual information of the antenna detector in closed-form. For multiple receive antenna SM system, the union bound of error probability and the lower bound of antenna detection mutual information are proposed. The analytical results are verified by numerical simulation over Rayleigh fading channels. We investigate systems with different number of antennas and APM symbol input distributions to evaluate the performance of SM. The joint APM and antenna detection mutual information of SM systems is compared to the capacity of vertical Bell Labs layered space-time (V-BLAST) spatial multiplexing MIMO scheme. Our research gives achievable transmission rates of SM-MISO/MIMO systems and can be a guideline for suitable application scenarios.

Time domain synchronous orthogonal frequency division multiplexing OFDM (TDS-OFDM) has a higher spectral efficiency and faster synchronization than standard cyclic prefix OFDM, but suffers from the performance loss over multipath fading channels due to severe interblock-interference. Recently, compressive sensing (CS) is explored to solve those problems, but it heavily relies on the sparsity level of the channel, which is unknown in practice. In this paper, a signal-to-noise ratio-based sparsity estimation method is proposed to detect the sparsity level of the channel. Then we propose the priori aided subspace pursuit algorithm if the channel sparsity meets the theoretical CS model, otherwise we use an improved iterative channel estimation method with the help of the channel sparsity. Simulation results demonstrate that the proposed scheme could improve the robustness and performance of TDS-OFDM systems compared with the conventional iterative methods or recently proposed CS based methods.

The articles in this special section focus on point-to-multipoint communications and broadcasting. In the last few years, since the Internet, streaming video, and mobile devices such as tablets and smartphones have come to play prominent roles in modern daily life, the communication industry has started working on new, more effective digital broadcast systems that can simultaneously deliver signals to both fixed and mobile devices. Digital broadcast systems are suitable for large-volume broadband information delivery, especially for multimedia communications. In fact, the rapid global growth of mobile data traffi c is primarily driven by the massive deployment of mobile video services on modern large-screen devices.

Time domain synchronous OFDM (TDS-OFDM) has a higher spectrum and energy efficiency than standard cyclic prefix OFDM (CP-OFDM) by replacing the unknown CP with a known pseudorandom noise (PN) sequence. However, due to mutual interference between the PN sequence and the OFDM data block, TDS-OFDM cannot support high-order modulation schemes such as 256QAM in realistic static channels with large delay spread or high-definition television (HDTV) delivery in fast fading channels. To solve these problems, we propose the idea of using multiple inter-block-interference (IBI)-free regions of small size to realize simultaneous multi-channel reconstruction under the framework of structured compressive sensing (SCS). This is enabled by jointly exploiting the sparsity of wireless channels as well as the characteristic that path delays vary much slower than path gains. In this way, the mutually conditional time-domain channel estimation and frequency-domain data demodulation in TDS-OFDM can be decoupled without the use of iterative interference removal. The Cramer-Rao lower bound (CRLB) of the proposed estimation scheme is also derived. Moreover, the guard interval amplitude in TDS-OFDM can be reduced to improve the energy efficiency, which is infeasible for CP-OFDM. Simulation results demonstrate that the proposed SCS-aided TDS-OFDM scheme has a higher spectrum and energy efficiency than CP-OFDM by more than 10% and 20% respectively in typical applications.

Frequency domain equalization (FDE), as a linear equalizing method, is widely adopted in many applications with either OFDM or single carrier (SC) modulation. This paper analyzes the the noise transfer effect, a case for noise colorization, after FDE. This process is investigated for CP-OFDM, ZP-OFDM and SC systems where SC is treated as a multi-carrier modulation with the number of subcarriers equal to 1. Based on this analysis and by assuming the de-mapping independence among subcarriers, the average channel capacity for the systems is derived. We have proved that the capacity of the CP-OFDM system is at least equal to that of ZP-OFDM in both low and high SNR scenarios and that the capacity of the SC system is no greater than that of either ZP-OFDM or CP-OFDM systems. In a multi-path channel, if the IDFT size of the OFDM symbol is not equal to the DFT size of the equalizer, the leakage of the enhanced noise in a deeply faded sub-channel will cause the loss of capacity in adjacent sub-channels and the overall average capacity is thus reduced.