Optical Wireless Transmission Research Articles

Performance Improvement of ACO-OFDM Indoor Optical Wireless Transmissions Using Partial Pre-Equalization

This paper analyzes the performances and presents the benets of partial pre-equalization for indoor optical wireless transmissions based on asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) with intensity modulation and direct detection (IM/DD). In particular, for diffuse indoor optical wireless channels, partial pre-equalization can reduce the optical transmit power over post-equalization at the same target bit error rate (BER) for point-to-point transmissions even with imperfect channel knowledge. To further im-prove its performance, bit loading is considered to minimize the optical transmit power of ACO-OFDM while maintaining a constant target BER. In addition, broadcast transmissions to multiple users with possibly dierent channel qualities are considered, where pre-equalization is not applicable. Finally, we specify an appropriate channel estimate at the transmitter for such broadcast transmissions.

High speed optical wireless data transmission system for particle sensors in high energy physics

High speed optical fiber or copper wire communication systems are frequently deployed for readout data links used in particle physics detectors. Future detector upgrades will need more bandwidth for data transfer, but routing requirements for new cables or optical fiber will be challenging due to space limitations. Optical wireless communication (OWC) can provide high bandwidth connectivity with an advantage of reduced material budget and complexity of cable installation and management. In a collaborative effort, Scuola Superiore Sant'Anna and INFN Pisa are pursuing the development of a free-space optical link that could be installed in a future particle physics detector or upgrade. We describe initial studies of an OWC link using the inner tracker of the Compact Muon Solenoid (CMS) detector as a reference architecture. The results of two experiments are described: the first to verify that the laser source transmission wavelength of 1550 nm will not introduce fake signals in silicon strip sensors while the second was to study the source beam diameter and its tolerance to misalignment. For data rates of 2.5 Gb/s and 10 Gb/s over a 10 cm working distance it was observed that a tolerance limit of ±0.25 mm to ±0.8 mm can be obtained for misaligned systems with source beam diameters of 0.38 mm to 3.5 mm, respectively.

A Novel Wireless Mobile Platform to Locate and Gather Data From Optical Fiber SensorsIntegrated Into a WSN

This paper presents a novel design for a wireless mobile platform to locate and gather data from different types of optical fiber sensors, thereby enabling the more effective integration of a number of such optical fiber sensors with an advanced mobile wireless sensor network (WSN). This then more readily permits potential applications, such as monitoring in remote and harsh environments and tracking, exploiting fully the combined advantages offered both by the mobile WSN and the advanced optical fiber sensing technologies. The platform which was designed and implemented consists of an optical fiber sensor module and a smart mobile WSN module, which shows important advantages for mobile sensing and tracking and mesh networking. In this paper, a fiber Bragg grating-based temperature sensor and an intrinsic pH optical fiber sensor were specially designed and integrated successfully into the optical fiber sensor module as an exemplar to investigate the performance of the integrated system based on the mobile WSN platform. The positive experimental results obtained have confirmed the functionality of the platform designed and demonstrated its capacity for real-time optical fiber sensor data monitoring, processing, and wireless transmission. The successful creation of this type of wireless mobile platform with optical fiber sensors can thus be expected to make an important impact on a number of sectors, where either conventional optical sensor designs or WSNs alone cannot meet the systems requirements.

Overlapping PPM for band-limited visible light communication and dimming

Abstract The synthesis of visible light communication (VLC) and lighting state control necessitates data-light modulation that can accommodate intensity control. A number of techniques that enable both optical wireless data transmission and intensity control of light-emitting diodes (LEDs) have been proposed as a response to this need. Relevant schemes leverage amplitude modulation (AM)/continuous current reduction (CCR) and/or pulse-width modulation (PWM) for dimming capability. Two-level schemes related to PWM, such as on-off keying with compensation time (OOK + CT), variable pulse position modulation (VPPM), and multiple pulse position modulation (MPPM), are most commonly investigated. In this paper, we survey and compare OOK + CT, VPPM and MPPM. Moreover, we propose a novel approach towards dimming and data transmission through the variation of codeword weights in overlapping pulse-position modulation (OPPM). The proposed approach has comparatively high spectral efficiency. Using realistic constraints of a practical VLC system, analysis reveals that OPPM can increase data rates by more than 20Mbps over expected performance of related, two-level schemes, when using LEDs suitable for lighting that have relatively low modulation bandwidths.

Tolerance of the frequency deviation of LO sources at a MIMO system

We analyze and simulate the tolerance of frequency offset at a W-band optical-wireless transmission system. The transmission system adopts optical polarization division multiplexing (PDM), and multiple-input multiple-output (MIMO) reception. The transmission signal adopts optical quadrature phase shift keying (QPSK) modulation, and the generation of millimeter-wave is based on the optical heterodyning technique. After 20-km single-mode fiber-28 (SMF-28) transmission, tens of Gb/s millimeter-wave signal is delivered. At the receiver, two millimeter-wave signals are down-converted into electrical intermediate-frequency (IF) signals in the analog domain by mixing with two electrical local oscillators (LOs) with different frequencies. We investigate the different frequency LO effect on the 2×2 MIMO system performance for the first time, finding that the process during DSP of implementing frequency offset estimation (FOE) before cascaded multi-modulus-algorithm (CMMA) equalization can get rid of the inter-channel interference (ICI) and improve system bit-error-ratio (BER) performance in this type of transmission system.

Layered ACO-OFDM for intensity-modulated direct-detection optical wireless transmission.

Layered asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) with high spectral efficiency is proposed in this paper for optical wireless transmission employing intensity modulation with direct detection. In contrast to the conventional ACO-OFDM, which only utilizes odd subcarriers for modulation, leading to an obvious spectral efficiency loss, in layered ACO-OFDM, the subcarriers are divided into different layers and modulated by different kinds of ACO-OFDM, which are combined for simultaneous transmission. In this way, more subcarriers are used for data transmission and the spectral efficiency is improved. An iterative receiver is also proposed for layered ACO-OFDM, where the negative clipping distortion of each layer is subtracted once it is detected so that the signals from different layers can be recovered. Theoretical analysis shows that the proposed scheme can improve the spectral efficiency by up to 2 times compared with conventional ACO-OFDM approaches with the same modulation order. Meanwhile, simulation results confirm a considerable signal-to-noise ratio gain over ACO-OFDM at the same spectral efficiency.

60-GHz optical/wireless MIMO system integrated with optical subcarrier multiplexing and 2x2 wireless communication.

This paper proposes a 2x2 MIMO OFDM Radio-over-Fiber scheme based on optical subcarrier multiplexing and 60-GHz MIMO wireless transmission. We also schematically investigated the principle of optical subcarrier multiplexing, which is based on a dual-parallel Mach-Zehnder modulator (DP-MZM). In our simulation result, combining two MIMO OFDM signals to drive DP-MZM gives rise to the PAPR augmentation of less than 0.4 dB, which mitigates nonlinear distortion. Moreover, we applied a Levin-Campello bit-loading algorithm to compensate for the uneven frequency responses in the V-band. The resulting system achieves OFDM signal rates of 61.5-Gbits/s with BER of 10(-3) over 25-km SMF transmission followed by 3-m wireless transmission.

Experimental outdoor visible light data communication system using differential decision threshold with optical and color filters

An experimental outdoor optical wireless data communication system with a differential decision threshold (DDT) using filtering techniques in the presence of sunlight or artificial light is presented. In the proposed system, an optical filter is employed for reducing ambient light noise and sunlight, and a red color filter is also applied for detecting a specific wavelength only at the receiver with DDT. Unlike previously reported methods, such as spread spectrum techniques, combining methods, and preamble methods, the proposed method is very practical and efficient in that it uses filters on the top of the photodiode to occlude obliquely incident unwanted light under the realistic assumption that the light noise does not come directly into the photodiode. The proposed outdoor visible light communication can thus facilitate a practical free space outdoor optical wireless data transmission system.

Experimental Investigation on Fiber-Wireless MIMO System With Different LO at W Band

We experimentally demonstrate an optical-wireless transmission system at W band, which can support long-distance wireless transmission and tolerate some frequency difference of the local oscillators (LOs) at the receiver. The generation of millimeter-wave signal is based on the photonic technique by heterodyne mixing of an optical polarization division multiplexing quadrature phase shift keying (PDM-QPSK) signal and an optical LO signal. After 20-km fiber transmission, tens of gigabit-per-second millimeter-wave signals are delivered over multiple-input–multiple-output (MIMO) wireless links by different polarization antennas. Then, analog downconversion is performed before the received signal is demodulated by coherent detection and advanced digital signal processing. Using this system, we experimentally demonstrate the transmission of 18.7-, 29.9-, and 37.4-Gb/s PDM-QPSK wireless signals at W band over 80-, 40-, and 20-m wireless links, respectively, with bit error rate less than the forward error correction threshold of $3.8\times 10^{-3}$ . In addition, we investigate the effect of different frequency LOs on the MIMO system performance, finding that the system can tolerate about 1.25-GHz frequency difference for a 10-Gbaud signal. The proposed system can be suitable for the building-to-building broadband connection, in-building hybrid fiber-wireless access networks, and some scenarios that bridge natural obstacles and difficult-to-access terrain.

40-Gb/s PDM-QPSK signal transmission over 160-m wireless distance at W-band.

We experimentally demonstrate a W-band optical-wireless transmission system over 160-m wireless distance with a bit rate up to 40Gb/s. The optical-wireless transmission system adopts optical polarization-division-multiplexing (PDM), multiple-input multiple-output (MIMO) reception and antenna polarization diversity. Using this system, we experimentally demonstrate the 2×2 MIMO wireless delivery of 20- and 40-Gb/s PDM quadrature-phase-shift-keying (PDM-QPSK) signals over 640- and 160-m wireless links, respectively. The bit-error ratios (BERs) of these transmission systems are both less than the forward-error-correction (FEC) threshold of 3.8×10-3.

Optical wireless transmission of 405 nm, 1.45 Gbit/s optical IM/DD-OFDM signals through a 4.8 m underwater channel.

In this paper, we experimentally demonstrate wireless transmission of optical intensity modulation/direct detection-orthogonal frequency division multiplexing (IM/DD-OFDM) signals in an underwater channel using a field programmable gate array based real-time transmitter. The real-time transmission of a 405 nm 1.45 Gbit/s optical OFDM signal through a 4.8 m underwater channel with an error vector magnitude of approximately 10% was successfully achieved.

Wireless data transmission using visual codes

In this paper, a new approach for wireless data transmission within an aircraft cabin is presented. The proposed application enables the transmission of data to a passenger’s user device. As wireless in-flight applications are subject to strict frequency and electromagnetic compatibility (EMC) regulations, the data is transferred by optical wireless transmission, specifically by two-dimensional visual codes. To this end, black-and-white or colored visual code sequences are displayed on the in-flight entertainment screen. These visual codes are captured by the built-in camera of the passenger’s mobile device and are decoded to reconstruct the transmitted data. In order to compensate for frame losses caused by effects like occlusion and motion blur, a temporal forward error correction coding scheme is applied. Transmission experiments within an Airbus A330 cabin mock-up demonstrate the functionality of the implemented system under realistic conditions such as ambient illumination and geometric configuration. Representative user devices are used for evaluation; specifically, a low-cost and a high-end smartphone are employed as receivers. Performance evaluations show that the proposed transmission system achieves data rates of up to 120 kbit/s per individual passenger seat with these user devices. As the user device has no physical connection to the sensitive on-board system, the proposed transmission system provides an intrinsic safety feature.

광필터를 이용한 실험적 실외 가시광 통신 시스템

본 논문은 태양광 혹은 인공광이 존재하는 외부 환경에서 광필터를 적용한 실험적 실외 광무선 데이터 통신 시스템을 제안한다. 광잡음의 효과적인 차단을 위해 마이크로루버 필름을 사용한 광필터를 광다이오드에 직접 적용하였으며 잡음광이 광다이오드에 정면으로 입사하지 않는다는 가정하에 입사각 30도를 초과하는 잡음광을 차단하도록 설계하였다. 제안하는 시스템을 낮시간 실외에서 데이터 전송을 통해 검증하였는데 지정한 입사각 혹은 그 이상의 입사 잡음광에 대해 거의 완벽하게 차단할 수 있었으며 전송된 패킷데이터의 90%이상을 성공적으로 수신하였다. 본 제안 시스템은 향후 실외 자유공간 광무선 데이터 전송에 효과적으로 사용될 수 있을 것이다. An experimental outdoor optical wireless data communication system with an optical filter in the presence of sunlight or artificial light is presented. For the efficient blocking of light noise outdoors, we employ an optical filter made of microlouver film on the top of the photo diode. This filter is designed to block any light noise incident from an angle higher than <TEX>$30^{\circ}$</TEX> on the assumption that light noise does not face the photo diode horizontally. Outdoor experiments daytime with the optical filtering have been conducted. The experimental results demonstrate that the optical filter effectively blocks nearly all light noise incident from the specified angle or higher and more than 90% of the transmitted data packets are successfully received. The proposed outdoor visible light data communication can thus facilitate a practical free space outdoor optical wireless data transmission.

A Perimeter Intrusion Detection System (PIDS) Based on Sensor Network

A perimeter intrusion detection system (PIDS) based on sensor network is proposed and designed for safeguarding important area from illegal intrusion. The PIDS consists of a front-end detection sub-system, a control center sub-system, anassociated sub-system, a network transmission sub-system and a power supply sub-system. The front-end detection sub-system is a sensor network containing a large number of smart sensors, which are of different types and functions. The control center sub-system is an integrated control platform based on the special analysis software, which can accurately identify the type of intrusion, locate the intrusion target, and reduce false alarms caused by environmental interference. The other four sub-systems provide the associated video monitoring, acoustic or optical alarm, wired or wireless transmission and AC or DC power supply. The development of sensor network technology has been and will continue to promote the PIDS technology.

Analog Joint Source Channel Coding for Wireless Optical Communications and Image Transmission

An analog joint source channel coding (JSCC) system is developed for wireless optical communications. Source symbols are mapped directly onto channel symbols using space filling curves and then a non-linear stretching function is used to reduce distortion. Different from digital systems, the proposed scheme does not require long block lengths to achieve good performance reducing the complexity of the decoder significantly. This paper focuses on intensity-modulated direct-detection (IM/DD) optical wireless systems. First, a theoretical analysis of the IM/DD wireless optical channel is presented and the prototype communication system designed to transmit data using analog JSCC is introduced. The nonlinearities of the real channel are studied and characterized. A novel technique to mitigate the channel nonlinearities is presented. The performance of the real system follows the simulations and closely approximates the theoretical limits. The proposed system is then used for image transmission by first taking samples of a set of images using compressive sensing and then encoding the measurements using analog JSCC. Both simulation and experimental results are shown.

Adaptive Photonics-Aided Coordinated Multipoint Transmissions for Next-Generation Mobile Fronthaul

We propose and demonstrate a concept of photonics-aided coordination for multi-cell downlink transmissions. The concept targets reliable high-throughput applications for future-proof millimeter-wave small cells based on radio-over-fiber fronthaul. Based on the physical properties of millimeter waves and the phase and magnitude relationship during optoelectrical conversion, a photonics-aided coordination module is proposed, which adjusts the overall channel matrix of optical wireless transmissions in order to achieve a distortion-free reception. Exploiting the multitude and density of remote access units, we specifically propose three methods of coordination, namely, photonics-aided amplification, synthesis, and interference cancellation, which directly enhance the signal-to-noise ratio, increase the throughput, and mitigate the interference of cell-edge users, respectively. These methods are realized at the physical layer and can be transparent to data, which reduces the coordination overhead. Prototypes, involving end-to-end downlink transmissions, are established, which demonstrate the feasibility and effectiveness of the proposed methods for both scalar and vector signals.

Low‐density parity‐check and fountain code performance over mobile wireless optical channels

ABSTRACTBy considering error control in different layers, the efficiency of several mechanisms is discussed in the context of wireless optical transmission of mobile health care application data. In this respect, we assume an emitter placed on a monitored patient and a fixed receiver. Because of patient mobility and health care data rate, the wireless optical channel is fading slowly. To ensure reliable communication, we study in the physical layer the low‐density parity‐check code performance by analysing the results in terms of outage probability. Concerning the application layer, we explore fountain codes, which are also known as Luby transform codes, together with an automatic repeat request mechanism by determining the related outage capacity. Taking into account the performance of both layers, we show that it is possible to design the physical layer code rate in that we maximise the effective data rate in the application layer. Moreover, we point out that Luby transform and low‐density parity‐check codes constitute an efficient and robust mechanism to reduce optical emitted power, which is of main concern for health care application. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Spatial Filtering in a Broadband In-Home OFDM Radio-Over-Fiber Network

The spatial filtering in an orthogonal frequency division multiplexing (OFDM) radio-over-fiber network is proposed to boost its capacity using broadband optical true time delay enabled microwave beam steering. The observed suppression ratio of the spatial filtering is 19.4 dB. The optical delivery and directional wireless transmission of 3.975 Gb/s OFDM data on a 19-GHz microwave carrier is studied. The observed beam directing-induced bit error ratio improvement is more than four orders of magnitude.

On the Benefits of Pre-Equalization for ACO-OFDM and Flip-OFDM Indoor Wireless Optical Transmissions Over Dispersive Channels

This paper analyzes the performances of indoor optical wireless data transmissions based on unipolar orthogonal frequency division multiplexing (OFDM). In particular, it is shown that using frequency-domain pre-equalization can provide benefits in terms of the reduction in the required optical transmit power for a given desired bit error rate (BER) from uncoded transmissions. Known for its power efficiency, asymmetrically clipped optical OFDM (ACO-OFDM) is considered as a unipolar modulation scheme for intensity modulation with direct detection (IM/DD). In addition, flip-OFDM is also considered as an alternative unipolar modulation scheme which is known to be as power efficient as ACO-OFDM. For both ACO-OFDM and flip-OFDM, analytical and simulation results show that using pre-equalization can save up to 2 dB of transmit optical power for a typical indoor optical wireless transmission scenario with the bit rate of 10 Mbps and the BER target of 10-5.

200 Mb/s visible optical wireless transmission based on NRZ–OOK modulation of phosphorescent white LED and a pre-emphasis circuit

We present a high-speed visible light communication (VLC) link that uses a commercially available phosphorescent white light-emitting diode (LED). Such devices have few megahertz bandwidth due to the slow response of phosphorescent component, which severely limit the transmission data rate of VLC system. We propose a simple pre-emphasis circuit. With blue-filtering and the pre-emphasis circuit, the bandwidth of VLC system can be enhanced from 3 to 77.6 MHz, which allows non-return-to-zero on-off-keying (NRZ–OOK) data transmission up to 200 Mb/s with the bit error ratio of 5.3 × 10-7 which is below 10-6. The VLC link operates at the room illumination level of ~1000 lx at 1.1 m range using a single 1 W white LED.