A Wireless Optical Gate and IMU System for Agility Assessment: Architecture, Synchronization and Validation

Amidst revolutionary communication technologies of recent decades such as optical fiber and wireless systems other forms of communication technologies are popping up in order to complete or complement the ever-increasing and insatiable need for communications links in today's society. Among many such niche technologies optical wireless communication technology, in particular, is begining to enjoy a wide range of applications and attention from many industries for short-range interchip applications to interplanetary space applications. Furthermore, optical wireless systems have attracted even further considerable growth in research and development since they can be appropriate alternatives for wireless or fiber-optic communication systems in some specific applications. Indoor wireless LANs, atmospheric optical links, and submarine optical wireless systems have grown in importance where lightwave communications is preferred to radio communications. This preference in various applications can be originated from security requirements, radio interference avoidance, no need for reserving frequency bands and cost of development [1]–[9].

In this paper, we have analyzed different precoding based Peak-to-Average-Power (PAPR) reduction techniques for asymmetrically-clipped Orthogonal Frequency Division Multiplexing (OFDM) optical wireless communication systems. Intensity Modulated Direct Detection (IM/DD) technique is among the popular techniques for optical wireless communication systems. OFDM cannot be directly applied to IM systems because of the bipolar nature of the output signal. Therefore some variants of OFDM systems have been proposed for (IM/DD) optical wireless systems. Among them are DC-biased-OFDM, Asymmetrically-Clipped Optical OFDM (ACO-OFDM) [2] and Pulse Amplitude Modulated Discrete Multitone (PAM-DMT) [3]. Both ACO-OFDM and PAM-DMT require low average power and thus are very attractive for optical wireless systems. OFDM systems suffer from high PAPR problem that can limit its performance due to non-linear characteristics of LED. Therefore PAPR reduction techniques have to be employed. This paper analyzes precoding based PAPR reduction methods for ACO-OFDM and PAM-DMT. We have used Discrete Fourier Transform (DFT) coding, Zadoff-Chu Transform (ZCT) [8] and Discrete Cosine Transform (DCT) for ACOOFDM and only DCT for PAM-DMT since the modulating symbols are real. We have compared the performance of these precoding techniques using different QAM modulation schemes. Simulation results have shown that both DFT and ZCT offer more PAPR reduction than DCT in ACO-OFDM. For PAM-DMT, DCT precoding yields significant PAPR reduction compared to conventional PAM-DMT signal. These precoding schemes also offer the advantage of zero signaling overhead.

Underwater optical wireless communication applications include robot communication, data monitoring and collection and control applications (SCADA). Underwater optical wireless communication using visible light is used because of the high data rate compared to acoustic technology and low path attenuation compared to radio frequency (RF) technology. The blue-green wavelength has minimum attenuation for absorption and scattering. One application for optical wireless communications is real time swimmers feedback. This system requires short range communication over 1 m between sensors mounted at the swimmer's wrist and a receiver on his/her goggles. The link was sometimes line of sight (LOS) and sometimes non line of sight (NLOS). Air bubbles generated from a swimmer causes additional link attenuation. Pool lighting may cause interference both above and below the water. The final unit should be low cost, have low power consumption and small size to reduce drag. This paper reviews technology used to give real time feedback to a swimmer during swimming. This new technology should help swimmers improve their performance during training. Different optical wireless systems using LEDs as a light source are presented. The authors investigated in the previous work the effect of air bubbles and they designed, implemented and tested an optical wireless communication system based on light emitting diode (LED) and integrated detector preamplifier (IDP). Both the position and the orientation of the transmitter and the receiver change during the swimmer's actions. Simulation results for the line of sight (LOS) communication link and the non line of sight (NLOS) with the effect of air bubbles were used to evaluate the effect on the underwater optical signal. Link budgets were calculated for different light sources. This paper reviews research in underwater optical wireless communication system using LEDs as a light source. The applications to swimming monitoring is presented.

This paper reviews the research effort to date into optical wireless communication systems, both in academic and industrial contexts. The idea of using the optical medium for wireless communications is not new, having been proposed as a means for indoor communications almost two decades ago. However, the last few years have seen an explosive interest in the potential for free space optical systems to provide portable data communications. One of the prime motivators for reconsidering the use of an optical carrier in the wireless context is the demand for greater transmission bandwidths. The radio frequency spectrum is already exceedingly congested and frequency allocations of sufficient bandwidths are extremely hard to obtain. Further, for the high bandwidth services envisaged, the use of microwave or mm-wave systems will be required, where device technology is currently either expensive or immature. Proponents of optical wireless systems argue that the optical medium is the only cost-effective way to provide high bit-rate mobile services to volume markets. This paper identifies the technical obstacles and limitations of indoor optical wireless delivery in addition to techniques for mitigating these effects and shows that infrared is a viable alternative to radio for certain applications.

In this paper, we analyzed the structure of wireless optical access system, and established a wireless optical access system, which is compatible with actual communication networks, to explore the criterion of wireless optical access system. We simulated the voice in this wireless optical access system based on MATLAB, the emulational results indicated that the communication capability was credible, and the communication index can achieve the desire.

Optical wireless systems have attracted much attention, because they allow high speed transmission without electromagnetic interference. Orthogonal frequency division multiplexing (OFDM) can send multiple high speed signals by using orthogonal carrier frequencies. Recently, studies have focused on the optimal OFDM technique for optical wireless systems. When using OFDM, one important issue is the determination of the cyclic prefix and its removal from the frame before the receiver detects signals. In this paper, we propose a new auto synchronization technique for OFDM systems. This technique enables the removal of the cyclic prefix in any sample of the OFDM frame and valid only for unipolar MPAM signals. It is a candidate for 2 or 4-PAM OFDM. The results of mathematical analysis and simulations show that it can be used for optical wireless systems.

Optical wireless systems have attracted attention, because they allow high-speed transmission without electromagnetic interference. Orthogonal frequency division multiplexing (OFDM) can send multiple high speed signals by using orthogonal carrier frequencies. Recently, studies have been focused on the optimal OFDM technique for optical wireless systems. When using OFDM, one important issue is determining the cyclic prefix and removing it from the frame before the receiver detects signals. In this paper, we propose a new auto synchronization technique of unipolar MPAM signals. It can remove the cyclic prefix in any sample of the OFDM frame using unipolar MPAM. It is a candidate for wideband systems and using 2-PAM or 4-PAM. The results of mathematical analysis and simulations show that it can be used for optical wireless systems.

Pulse-based communication systems are a promising candidate in the deployment of future wireless networks, thanks to the potential robustness and capacity guaranteed by the transmission of pulses of very short duration. In the framework of pulse-based communication systems, the Impulse Radio-Ultra Wide Band (IR-UWB) technique recently received particular attention. In the past, most of the UWB research focused on hardware and physical layer aspects in order to solve the technological challenges posed by IR-UWB. UWB peculiar characteristics may, however, also stimulate innovative higher layers' design. This work addresses Medium Access Control (MAC) issues for IR-UWB communication systems and extends the discussion to wireless optical communication systems. Typical characteristics of an IR-UWB system are presented, and solutions proposed for such systems at the MAC layer are reviewed. The applicability of such solutions to an optical wireless communications system is then discussed, highlighting analogies and differences between IR-UWB and wireless optical systems.

Wireless indoor infrared transmission systems are affected by noise and interference induced by natural and artificial ambient light. While the shot noise induced on the receiver photodiode by steady ambient light has been extensively described and included in system models, the interference produced by artificial light has only been mentioned as a source of degradation and quite simple descriptions have been presented. This paper presents a characterisation (through extensive measurements) of the interference produced by artificial light and proposes a simple model to describe it. These measurements show that artificial light can introduce significant in-band components for systems operating at bit rates up to several Mbit/s. Therefore it is essential to include it as part of the optical wireless indoor channel. The measurements show that fluorescent lamps driven by solid state ballasts produce the wider band interfering signals, and are then expected to be the more important source of degradation in optical wireless systems.

Imperfect focusing of the receiver can be an important impairment in MIMO optical wireless systems using imaging receivers. This paper investigates the effect of defocus blur on an optical wireless system using spatial orthogonal frequency division multiplexing (OFDM). It is shown that when defocus blur is the only impairment, and when transmitter and receiver are perfectly aligned, the defocus blur causes the received constellation points to be attenuated. Simulation results show that the signal-to-noise ratio (SNR) penalty caused by defocus blur is less for a system using spatial asymmetrically clipped optical OFDM than for one using spatial DC biased optical OFDM.

We propose Low Density Parity Check (LDPC) coded optical wireless communication systems with multiple subcarrier modulation (BPSK and QPSK). Upper bounds on the bit-error rate (BER) for maximum likelihood (ML) decoding of LDPC coded systems have been obtained on atmospheric optical channels where the effects of the scintillation exist. We also show that LDPC coded atmospheric optical systems have better BER than Turbo coded atmospheric optical systems.

Optical wireless communication network is gaining acceptance in an increasing number of sectors of science and industry, owing to its unique combination of features: Extremely high bandwidth, rapid deployment time, license and tariff-free bandwidth allocation, and low power consumption, weight, and size. The demand of high signal bandwidth in optical wireless communication networks is growing exponentially day by day, as the numbers of users have been increased drastically over the span of last five years. The next generation wireless communication systems therefore need to be of higher standards, so as to support various broadband wireless services such as, video conferencing, videophones, high-speed internet access, etc. The existing wireless systems can hardly provide transmission capacity of the order of few Mbps. However, wireless optical fiber technology has the potential of providing data capacity of the order of Mbit/sec and Tbit/sec, respectively. Therefore the requirements of optical broadband wireless system can be met through the integration of optical communication fiber and millimeter wave optical wireless systems. Terrestrial optical wireless communication network is emerging as a promising technology, which makes connectivity possible between high rise buildings and metropolitan and intercity communication infrastructures. We have developed a light beam carrying the audio and video information, which facilitates extremely ultra high transmission data rates for ultra long transmission distances within Shannon propagation technique. Key words: Wireless communication networks, transmission technique, point to point link, indoor and outdoor broadband wireless networks, audio signal, video signal

본 논문에서는 무선광 인식 장치를 새로이 제안하고 실험하였다. 무선광 인식 장치는 리더와 트랜스폰더로 구성되며, 이들은 동일한 구조로서 조명용 LED의 빛을 전송 매체로 사용하고 솔라 셀로 수신하여 서로 정보를 교환한다. 솔라 셀은 수광 표면이 넓고 평면이어서 렌즈를 사용한 광학적 정렬이 필요하지 않기 때문에 구조가 간단하고 사용이 편리하며, 관리 대상 물체의 표면에 부착하기가 용이하다. 또한 무선광 인식 장치는 빛을 전송 매체로 사용하기 때문에 RF 주파수와의 간섭이 없어 안정하다. 실험에서는 솔라 셀을 사용하여 거리가 약 1 m에서 트랜스폰더의 정보를 자동으로 인식하는 무선광 인식 장치를 구현하였다. In this paper, we newly propose a wireless optical identification system and carried out experiments. A wireless optical identification system consists of a reader and a transponder. The configuration of a reader is the same as that of a transponder, which uses LED light as transmission media and detects the signal light with a solar cell. Optical alignment with a lens is not required because the absorption area of a solar cell is wide and flat, and it is very easy to attach a solar cell on the surface of an object. As the light wavelength does not interfere with radio frequency, a wireless optical identification system shows stable operation. In experiments, we realized a wireless optical identification system that automatically identifies the transponder data at a distance of 1 m using solar cells.

User mobility in a diffuse optical wireless (OW) system is of particular interest as it can induce link performance degradations. While much attention has been given in the literature to the conventional indoor diffuse optical wireless system, little has been done in terms of evaluating the impact of user mobility in such an environment. Furthermore, there is a clear need for methods that can be used to reduce the link performance degradations attributed to user mobility. The paper considers a mobile OW system under the constraints of ambient light noise and multipath distortion. Moreover, the authors propose an original beam-clustering method (BCM) that utilises a spot diffusing technique and evaluate the associated channel characteristics. The performance of a mobile OW BCM system is analysed and compared with that of the conventional diffuse system (CDS) in a middle-sized room at 14 receiver locations. Our results indicate that, at the worst communication link, BCM can reduce the signal delay spread by nearly a factor of six and increase the SNR by >30 dB over the CDS SNR, while resulting in improved performance over all links.

In this paper, we use the percentage blockage as a metric when an opaque disc obstructs the Line-of-Sight link from the access point to the receiver in an optical wireless indoor communication system. The effect of the different parameters of the obstructing object are studied, these are the radius, the height, and the horizontal distance from the receiver in the positive y direction. The percentage of blocked room locations to the total number of room locations when varying the disc parameters is studied assuming a single serving link. It was found that depending on the dimensions of the obstructing object and the distance from the receiver in addition to which access point is serving the user, that blockage can vary between 0% up to 100%. Furthermore, the service received by a user, in terms of beam blockage depends on the access point they are connected to. The resulting fairness challenges will be addressed in resource allocation optimization in future work.