Performance of a spread spectrum infrared transmission system under ambient light interference

In order to carry out real-time 3D reconstruction of large components in the outdoor environment, this paper proposes a laser stripe centerline extraction algorithm that is resistant to ambient light interference. The median filter is used to preprocess the laser stripe to be extracted, and the Rosenfeld thinning and least square fitting algorithm are organically combined to extract the centerline of the laser stripe. Experimental results show that this method can effectively avoid strong light interference and accurately obtain the centerline of the laser stripe to be extracted.

Ambient light and optical interference can severely affect the performance of pulse oximeters. The deployment of a robust modulation technique to drive the pulse oximeter LEDs can reduce these unwanted effects and increases the resilient of the pulse oximeter against artificial ambient light. The time division modulation technique used in conventional pulse oximeters can not remove the effect of modulated light coming from surrounding environment and this may cause huge measurement error in pulse oximeter readings. This paper presents a novel cross-coupled sigma delta modulator which ensures that measurement accuracy will be more robust in comparison with conventional fixed-frequency oximeter modulation technique especially in the presence of pulsed artificial ambient light. Moreover, this novel modulator gives an extra control over the pulse oximeter power consumption leading to improved power management.

Imaging through scattering media is a fascinating subject in the computational imaging domain. The methods based on speckle correlation imaging have found tremendous versatility. However, a darkroom condition without any stray light is required because the speckle contrast is easily disturbed by ambient light, which can lead to the reduction in object reconstruction quality. Here, we report a plug-and-play (PnP) algorithm to restore the object through scattering media under the non-darkroom environment. Specifically, the PnPGAP-FPR method is established via the generalized alternating projection (GAP) optimization framework, Fienup phase retrieval (FPR) method, and FFDNeT. The proposed algorithm is demonstrated experimentally and shows significant effectiveness and flexible scalability, which describe the potential for its practical applications.

Due to a world wide surge in the intelligent vehicle highway system (IVHS), the field of automatic vehicle identification (AVI) has been rapidly growing. The use of spread spectrum communications has not yet pervaded the AVI market. However, in the already cramped electromagnetic environment, spread spectrum techniques have gained significant popularity in many growing areas of wireless communication. AVI is perfectly suited to benefit. The fundamental advantage of spread spectrum technology in AVI applications is its invulnerability to interference and its ability to operate alongside narrow band communication systems already in place. The second advantage is the ease of licensing for spread spectrum AVI, since it does not require a dedicated frequency spectrum. It is also possible for several spread spectrum AVI systems to operate simultaneously in the vicinity of each other, using different spreading codes. This article concentrates on architecture as well as applied key signal processing techniques for a proposed direct sequence spread spectrum (DSSS) AVI system. A functional block diagram that outlines the major components of the system is presented. The system consists of three major functional parts: interrogator, transponder, and trigger. Free flow of traffic can be maintained only if the interrogator can isolate each vehicle in a common interrogation zone. DSSS allows this through code division multiple access (CDMA). The triggering system is based on the principles of speed enforcement radar. The proposed digital modulation scheme is BPSK. The DSSS modulator applies a Gold pseudo-random (PN) code to spread the spectrum of the binary signal. Despreading is carried out through the use of a PN matched filter. The antenna is assumed to have a 60/spl deg/ half-power radiation field and is placed on an existing overpass approximately 6 meters above the roadway. With 50 mW antenna transmit power, link budget analysis indicates that sufficient bit energy-to-noise power spectral density ratio is available at the receiver to generate an excellent bit error rate without requiring error control coding.

Many techniques using polarizers, differential detectors, and electrical filters are used to overcome the penalty induced by artificial light interference and are analyzed. These techniques are used to reduce noise current or remove it by using an electrical filter or a polarizer or both of them together. We are going to display the effect of noise voltage, flicker voltage of a tungsten lamp, and signal-to-noise ratio (SNR) of the systems by changing each parameter to reach the best solution for reducing the effect of noise on free space optics. This paper will show that the best SNR is obtained with the differential detector with a two orthogonal polarizer system and that the worst one is with the system of a single photodetector.©TheAuthors.PublishedbySPIEunderaCreative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication,

Ambient light interference stands as the primary source of noise encountered by the light detection and ranging (LiDAR) systems based on single-photon avalanche diode (SPAD), which seriously restricts the detection range and accuracy of sensors. Multi-event mode and time-gating method are extensively employed due to their effective suppression ability of the ambient light interference with easily implemented circuit structure. However, the current research on these two operational modes is limited to qualitative description, lacking a comprehensive theoretical analysis. This paper investigates the impact of the multi-event mode and time-gating method on enhancing the imaging capabilities of the sensor, employing a probability distribution perspective. A behavioral model is established, enabling the simulation of the comprehensive functionality of a SPAD-based LiDAR system in either first-hit mode or multi-event mode, including the histogramming, coincident detection, time- gating functions. The model can serve as a substitute for the actual circuit in system function validation and parameter optimization, thereby significantly reducing the design and simulation cycle.

Troposcatter radio links may be a low cost alternative for long distance communications, or when the transmitter and the receiver are separated by difficult terrain that prevent from line-of-sight communications. These links permit one to preserve satellite resources in the case of civil applications, so as to overcome geographical barriers (oceans, mountains, desert, etc.). They also can easily and rapidly be installed for emergency situations in both civil and military cases. They represent a good solution in the case of single transhorizon hops of length limited to several hundreds of kilometers. The problem is that the transmission is based on the presence of multipath, whose dispersion is very varying on long periods. Wide-band transmission schemes can be then employed, like OFDM or spread spectrum techniques. The limitations of OFDM in presence of non-linearities of the amplifiers has often led one to prefer spread spectrum techniques in the case of troposcatter links: direct sequence (DS) or frequency hopping (FH). All the more so as other characteristics of spread spectrum are exploited for performance and also discretion purposes, as we are concerned with military tactical transmissions. The implementation of hybrid DS/FH spread spectrum receivers, which realize a maximal ratio combination of the paths (RAKE) is presented. After a description of the channel, we then describe the communication systems involved, and finally estimate the bit error rate.

Random codekey selection using codebook without pre-shared keys for anti-jamming in WBAN

Lateral distance measurement system for AVCS (advanced vehicle control systems) has been developed in the various countries. This paper describes a lateral distance measurement system using spread spectrum (SS) technique. Our method does not require significant infrastructure investment because it is based on the reflected signal from the guardrails currently installed on many roads. The range resolution of SS radar is generally equal to the length of one chip because it is based on the correlation using chip synchronization. We propose a short range measurement system utilizing the slope of the correlation function of m-sequence as an application of SS technique and indicate the results of the experiment.

Due to the weak signal energy of the backscatter link, traditional RFID communication is easily affected by noises, interferences, and interceptions from the environment. To solve the problem, a novel passive UHF RFID tag baseband processor enhanced with spread spectrum technique is presented in this paper. In addition, power-saving strategies are proposed to reduce the power consumption of the tag. Simulated results show that spread spectrum approach largely reduces the Bit Error Rate and improves system's reliability and security. Finally, a complete RFID tag with the proposed baseband processor was designed and fabricated using 0.18um 1P6M CMOS technology. From the measurement result, the overall power consumption of the baseband processor is about 8.8uW at the minimum voltage of 1.04V.

After a watermarked image is printed, copied several times and scanned, the watermark usually cannot be extracted rightly, as well as distorted by noise. In this paper, a spread spectrum technique was introduced to image watermarking which can be applied to print and generation copy. The watermarking message is modulated by the key-dependent pseudo-random sequences to produce a spread spectrum signal. The watermark is embedded into the cover image by modifying the gray value of each pixel. The cover image is not needed when the watermark is detected. The watermark is estimated exploiting the properties of HVS(Human Visual System) and extracted through the same key-dependent 2D sequences. Experimental results show that the scheme can resist print, generation copy and scan process.

There is able to be critical performance impairment because satellite digital broadcasting system such as DVB-S2 is sensitive to heavy rain environment. This feature of the satellite channel does not only make users be able to give inconvenient broadcasting service but they cannot see the service. Spread spectrum technique is the new proposal which can overcome those problems that are generated due to rain attenuation. Applying spread spectrum to DVB-S2 system, we examine how effective the technique is in the broadcast system. Assuming that signal power and channel bandwidth are same in the proposed system and the original system, the reason why spread spectrum technique is effective in heavy rain environment will be demonstrated. And using computer simulation, the performance improvement is shown.

In this paper, we address the admission control issue for the TDMA/SS (time division multiple access with spread spectrum) system for multimedia services. In the TDMA/SS system, time is divided into frames and each frame is further divided into slots. Only one user is allowed to transmit in a slot and thus the spread spectrum technique is adopted to combat inter-cell interference. A packet can occupy more than one slot, depending on the user's data rate and quality of service requirement. We derive a necessary and sufficient condition for a group of users to be admissible for the TDMA/SS system and prove that its admission region contains that of the TDMA/CDMA system. In the TDMA/CDMA system, time is also divided into frames and each frame consists of several slots. The difference is that every packet occupies exactly one slot and multiple users can transmit their packets in the same slot. Numerical results show that the admission region of the TDMA/SS system can be significantly larger than that of the TDMA/CDMA system. To further increase bandwidth utilization and guarantee delay bound requirements, several access control schemes are proposed. Simulation results are obtained for these access control schemes.

High dynamic range 3-D shape measurement is a challenge. In this work, we propose a novel method to solve the 3-D shape reconstruction of high-reflection and colored surfaces. First, we propose a method to establish a fast pixel-level mapping between the projected image and the captured image. Secondly, we propose a color texture extraction method using a black-and-white (B/W) camera and a pixel-level projection color adjustment method. Third, we give an optimal projection fringe modulation/background intensity ratio. Fourth, we propose a method for estimating the reflectivity of the object surface and ambient light interference, and a method for adjusting the projection intensity at the pixel level and a method for estimating the optimal exposure time. Experiments show that, compared with the existing methods, the proposed method not only can obtain high-quality captured images, but also has higher measurement efficiency and wider application range.

This paper proposes a closed-loop nonlinear scheme for precisely controlling the luminosity and correlated color temperature (CCT) of a bicolor adjustable light-emitting diode (LED) lamp. The main objective is to achieve a precise and fully independent dimming and CCT control of the light mixture emitted from a two-string LED lamp comprising warm-white and cool-white color LEDs, regardless of the operating conditions and throughout the long operating lifetime of the LED lamp. The proposed control method is formulated using the nonlinear empirical LED model of the bicolor white LED system. Experimental results show that with the proposed closed-loop nonlinear approach, both CCT and dimming control of the bicolor lamp is significantly more accurate and robust to ambient temperature variations, ambient light interference, and LED aging than the conventional linear approach used in existing products. The maximum error in luminous flux employing the proposed closed-loop nonlinear approach is 3%, compared with 20% using the closed-loop linear approach. The maximum deviation in CCT is only 1.78%, compared with 27.5% with its linear counterpart.