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Optics-Radio Hybrid Single Frequency Network for Digital Television Terrestrial Broadcasting
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In this paper, three hybrid modulation schemes for visible light communication based on orthogonal frequency division multiplexing (OFDM) are compared, which are asymmetrically clipped DC biased optical OFDM, hybrid asymmetrically clipped optical OFDM, and layered asymmetrically clipped optical OFDM (LACO-OFDM). The following aspects are analyzed and compared, such as the probability distribution functions, the peak-to-average power ratio, and the bit error ratio performance in terms of optical bit energy to noise power under different conditions. Furthermore, the optimal proportion of the optical power on different layers for LACO-OFDM is also investigated. Simulation results show that LACO-OFDM has better performance than other hybrid schemes in high signal-tonoise ratio (SNR) scenario, and the improvement is slight when more than four layers signals are utilized, while in low SNR condition, LACO-OFDM with two layers performs better than that with more layers.
In this letter, we present a novel hybrid intensity modulation and direct detection communication system, which integrates asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and on-off keying (OOK) modulation schemes. First, the negative ACO-OFDM is proposed based on the conventional ACO-OFDM system to accommodate the on case with direct current in the OOK modulation, while the ACO-OFDM can match the off case in the OOK modulation. Therefore, the novel hybrid system combines the ACO-OFDM and OOK modulation schemes, while the signals can be recovered at the receiver to support the different qualities of service with high spectral efficiency and can be adapted to various receivers with different complexities. Simulation results are reported for the visible light channel and show that both the ACO-OFDM and OOK signals can be well recovered.
In December 2011, Colombia updated its national Digital Terrestrial Television (DTT) standard from DVB-T to DVB-T2, the second generation of the DVB (Digital Video Broadcasting) project. DVB-T2 is the current state-of-the art DTT system in the world, and it brings very significant improvements in terms of capacity, robustness and flexibility compared with its predecessor. The case of Colombia is very special because it was the first country to deploy DVB-T2 with 6 MHz channelization and because the DVB-T2 networks were deployed from scratch without any constraint imposed by existing DVB-T infrastructure. This paper analyzes potential DVB-T2 transmission modes to optimize existing DTT network designs of Colombia, originally made for DVB-T, analyzing the trade-offs between capacity, coverage level and Single Frequency Network (SFN) size. Network planning results has been performed with a professional DTT network-planning tool based on the three first deployment phases of the DTT network of the public national TV broadcaster RTVC. Results obtained fully justify the decision of adopting DVB-T2. Compared with the initial DVB-T design, DVB-T2 can increase the national covered population up to 7.3% or offer 70.2% more of capacity transmission, or increase the SFN size up to 135% keeping the total power transmission and the geographic distribution of the transmitters
Visible light communication (VLC) using the light-emitting diode (LED) will become an appealing alternative to the radio frequency communication technology for indoor wireless broadband broadcasting. However, the LED lamps should access to the backbone information network and this requirement is not easily satisfied. Power line communication (PLC) systems utilize the ubiquitous power line network to power the LED lamps while serving as the backbone network for the VLC systems naturally. In this paper, we propose a novel and cost-effective indoor broadband broadcasting system based on the deep integration of PLC and VLC. The proposed scheme significantly reduces the complexity of the VLC network protocol, and requires much less modification to the current infrastructure, while providing better signal coverage. A two-lamp network demo is implemented and the performance evaluation for the proposed scheme is carried out in the laboratory. The proposed scheme is an appealing solution for the indoor family broadcasting, and could be well extended to the scenarios including the hospitals, shopping malls, stadiums, music halls, and etc.
Modern hospitals are beginning to adopt E-HEALTH as efficient complements to the traditional healthcare services. To support the E-HEALTH services, a locatable, radiation-free and high-capacity communication system is urgently needed in hospitals. Power line communication (PLC) systems can use the ubiquitous power line network to power the light-emitting diode (LED) lamps while serving as the backbone network for the indoor visible light communication (VLC) systems naturally. In this article, a hybrid broadband power line and visible light communication system with orthogonal frequency division multiplexing modulation is proposed for the indoor hospital applications, which gives a brand-new solution to replace the conventional wireless communication systems in hospitals. A general-purpose system model is provided and some basic techniques to enhance system performance are also investigated. Moreover, a feasible demonstration which supports over 48 Mbps data rate within a bandwidth of 8 MHz is implemented in the laboratory.
This letter proposes a time-frequency joint sparse channel estimation for multiple input multiple output orthogonal frequency division multiplexing (MIMO-OFDM) systems under the framework of structured compressive sensing (CS). The proposed scheme firstly relies on a pseudo random preamble which is identical for all transmit antennas to acquire the partial common support by utilizing the sparse common support property of the MIMO channels. And then a very small amount of frequencydomain orthogonal pilots are used for the accurate channel recovery. Simulation results show that the proposed scheme demonstrates better performance and higher spectral efficiency than the conventional MIMO-OFDM schemes. Moreover, the obtained partial common support can be further utilized to reduce the complexity of the CS algorithm as well as improve the signal recovery probability under low signal to noise ratio conditions.
Time-domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) has advantages in spectral efficiency and synchronization. However, its iterative interference cancellation algorithm will suffer from performance loss especially under severely fading channels with long delays and has difficulty supporting high-order modulations like 256 QAM, which may not accommodate the emerging ultra-high definition television service. To solve this problem, a channel estimation method for OFDM under the framework of compressive sensing (CS) is proposed in this paper. Firstly, by exploiting the signal structure of recently proposed time-frequency training OFDM scheme, the auxiliary channel information is obtained. Secondly, we propose the auxiliary information based subspace pursuit (A-SP) algorithm to utilize a very small amount of frequency-domain pilots embedded in the OFDM block for the exact channel estimation. Moreover, the obtained auxiliary channel information is adopted to reduce the complexity of the classical SP algorithm. Simulation results demonstrate that the CS-based OFDM outperforms the conventional dual pseudo noise padded OFDM and CS-based TDS-OFDM schemes in both static and mobile environments, especially when the channel length is close to or even larger than the guard interval length, where the conventional schemes fail to work completely.
Single frequency network (SFN) is an attractive scheme for the digital television terrestrial broadcasting (DTTB) coverage with efficient utilization of the spectral resources. In this paper, a method featuring low complexity and low workload is proposed to estimate the reception quality under the SFN environment with the maximum delay spread of the artificial multipath no longer than the guard interval. Based on the analysis of error probability and channel capacity, this method supports an unambiguous prediction of the signal-to-noise ratio (SNR) threshold according to the parameters of received signals, which is thus meaningful for system evaluation. We applied this method to the digital television/terrestrial multimedia broadcasting (DTMB) systems, and carried out the laboratory measurements for performance verification. The predicted results show a satisfactory match with the measured results, validating the accuracy and effectiveness of the proposed method.
In this paper we describe the implementation of a prototype of an optical wireless system based on visible white LED lamps, which allows a video broadcasting to reach a bit rate of 2 Mbps. This technology is usually called VLC or Visible Light Communications and presents several advantages as the robustness against EM interference, safety for human eye and security against undesired network access. These conditions make this system suitable for co-existing with commercial RF networks -WiFi, Bluetooth, etc.-, especially for in-house applications. For the uplink channel we have also included in the prototype an infrared 115 kbps transceiver. This VLC system could be used for supporting data transmission applied to low-speed sensor network connections as well. The electronic structure of a low-cost VLC transceiver, based on commercial off-the-shelf components and LED lamps is presented too. The modulation process and the Ethernet interface implemented in each access point are also described. Finally, some conclusions and application scenarios are drawn.
This special issue of the proceedings of the IEEE presents a systematical and complete tutorial on digital television (DTV), produced by a team of DTV experts worldwide. This introductory paper puts the current DTV systems into perspective and explains the historical background and different evolution paths that each system took. The main focus is on terrestrial DTV systems, but satellite and cable DTV are also covered,as well as several other emerging services.
This book focuses on optical wireless communications (OWC), an emerging technology with huge potential for the provision of pervasive and reliable next-generation communications networks. It shows how the development of novel and efficient wireless technologies can contribute to a range of transmission links essential for the heterogeneous networks of the future to support various communications services and traffic patterns with ever-increasing demands for higher data-transfer rates.
The book starts with a chapter reviewing the OWC field, which explains different sub-technologies (visible-light, ultraviolet (UV) and infrared (IR) communications) and introduces the spectrum of application areas (indoor, vehicular, terrestrial, underwater, intersatellite, deep space, etc.). This provides readers with the necessary background information to understand the specialist material in the main body of the book, which is in four parts.
The first of these deals with propagation modelling and channel characterization of OWC channels at different spectral bands and with different applications. The second starts by providing a unified information-theoretic treatment of OWC and then discusses advanced physical-layer methodologies (including, but not limited to: advanced coding, modulation diversity, cooperation and multi-carrier techniques) and the ultimate limitations imposed by practical constraints. On top of the physical layer come the upper-layer protocols and cross-layer designs that are the subject of the third part of the book. The last part of the book features a chapter-by-chapter assessment of selected OWC applications.
Optical Wireless Communications is a valuable reference guide for academic researchers and practitioners concerned with the future development of the world’s communication networks. It succinctly but comprehensively presents the latest advances in the field.
The idea of visible light communication (VLC) is presented in this paper. In VLC, from the electromagnetic (EM) frequency spectrum the visible light portion is used for information interchange which is analogous to conventional forms of wireless communication such as Bluetooth and Wireless-Fidelity (Wi-Fi), in which data or information is transmitted over the wireless medium using radio frequency (RF) signals. By modulating the intensity of light sources like LED is used as a transmitter and a photosensitive detector like Photodiodes (PD) is used for demodulation of the light signals to convert back into electrical form as a receiver. The intensity of light sources is modulated in such a way that which is unnoticeable to the human eyes. There is a crucial need of VLC technology, to overcome the problem faced by the conventional wireless communication system. In this paper wide overview of need of VLC, applications of VLC, design challenges for VLC and recent development in VLC are provided.
In this study, we investigate the performance of optical orthogonal frequency division multiplexing (O-OFDM) based visible light broadcasting. Although indoor spaces usually have more than one light source, most of the existing works on visible light communication (VLC) in the current literature consider point-to-point communication and few efforts have been made on the scenarios with multiple transmitters. In this work, we consider a broadcasting scenario in which multiple transmitters (light sources) simultaneously emit the same information. Since this network structure constitutes a similar network topology to single frequency networks (SFN) in OFDM-based digital audio/video broadcasting, we coin the term 'single color network (SCN)' to refer these visible light broadcasting systems. Based on extensive Monte Carlo simulations, we present the error rate performance of SCNs as well as discuss their lighting performance.
This paper proposes Kalman-filter drift removal (DR) and Heron-bilateration location estimation (LE) to significantly reduce the received signal strength index (RSSI) drift, localization error, computational complexity, and deployment cost of conventional radio frequency identification (RFID) indoor positioning systems without any sacrifice of localization granularity and accuracy. By means of only one portable RFID reader as the targeted device and only one pair of active RFID tags as the border-deployed landmarks, this paper develops a real-time portable RFID indoor positioning device and cost-effective scalable RFID indoor positioning infrastructure, based on Kalman-filter DR, Heron-bilateration LE, and four novel preprocessing/postprocessing techniques. Experimental results reveal that the proposed Kalman-filter DR method is faster and better to converge the distance measurement (DM) error than conventional probability/statistics in terms of various relative distances under certain RSSI drift effect condition, and the proposed Heron-bilateration LE method is also faster and better to converge the LE error than conventional proximity pattern matching and trilateration in terms of three or more landmarks under certain DM error condition. On the other hand, a portable RFID indoor positioning device is smoothly implemented on an Android smartphone platform attached with a portable Bluetooth-based RFID reader.
In this letter, we present a scheme generating OFDM signals in optical domain instead of electrical domain by transmitting subcarrier signals with multiple LEDs. According to the simulation, this scheme can effectively eliminate signal degradation caused by the high peak-to-average power ratio of OFDM signals in traditional transmitter. Computational complexity in digital part of the transmitter can be reduced by using look-up table. Receiver will stay unchanged.
Interest in mobile broadband and ubiquitous usage of mobile phones in all areas, especially in closed venues requires a new approach in designing radio access mobile networks. A new approach that requires planning from “indoor to outdoor” has been proposed and appropriate examples have been given to demonstrate the difference to standard planning of indoor coverage.
In this paper, three forms of orthogonal frequency division multiplexing (OFDM) designed for intensity modulated/direct detection (IM/DD) optical systems are compared. These are asymmetrically clipped optical OFDM (ACO-OFDM), DC biased optical OFDM (DCO-OFDM) and asymmetrically clipped DC biased optical OFDM (ADO-OFDM). ADO-OFDM is a new technique that combines aspects of ACO-OFDM and DCO-OFDM by simultaneously transmitting ACO-OFDM on the odd subcarriers and DCO-OFDM on the even subcarriers. The odd subcarriers are demodulated as in a conventional ACO-OFDM receiver and the even subcarriers are demodulated using a form of interference cancellation. ADO-OFDM is shown to be more optically power efficient than conventional ACO-OFDM and DCO-OFDM, for some bit rate/normalized bandwidths. It is also shown that by varying the proportion of optical power on the ACO-OFDM component, the DC bias level of DCO-OFDM and the constellations sent on the odd and even subcarriers, the optical power efficiency of ADO-OFDM can be changed.
In this letter, we present indoor multipath dispersion characteristics for visible light communications (VLC). Since the VLC uses a wide spectrum between 380 nm and 780 nm, the conventional narrowband model for infrared may not apply. We generalize the Barry's model by including wavelength-dependent white LED characteristics and spectral reflectance of indoor reflectors. We perform a computer simulation to compare the power delay profile of the VLC with that of infrared communications. From our studies, we show that the VLC provides a larger transmission bandwidth than infrared communications.
In this paper, we analyze the performance of different diversity combining techniques over fading channels with impulsive noise. We use Middleton's Class A model for the noise distribution and adopt two noise models, which assume dependent and independent noise components on each branch. We systematically analyze the performance of maximum ratio combing (MRC), equal gain combining (EGC), selection combining (SC), and post-detection combining (PDC) under these impulsive noise models, and derive insightful lower and upper bounds. We show that even under impulsive noise, the diversity order is retained for each combining scheme. However, we also show that under both models, there is a fundamental tradeoff between diversity gain and coding gain. Under the independent noise model, PDC is shown to combat impulsive noise more effectively than MRC, EGC, and SC. Our simulation results also corroborate our analysis.