Comparison of direct and heterodyne detection optical intersatellite communication links

The performance of direct and heterodyne detection optical intersatellite communication links are evaluated and compared. It is shown that the performance of optical links is very sensitive to the pointing and tracking errors at the transmitter and receiver. In the presence of random pointing and tracking errors, optimal antenna gains exist that will minimize the required transmitter power. In addition to limiting the antenna gains, random pointing and tracking errors also impose a power penalty in the link budget. This power penalty is between 1.6 to 3 dB for a direct detection QPPM link, and 3 to 5 dB for a heterodyne QFSK system. For the heterodyne systems, the carrier phase noise presents another major factor of performance degradation that must be considered. In contrast, the loss due to synchronization error is small. The link budgets for direct and heterodyne detection systems are evaluated. It is shown that, for systems with large pointing and tracking errors, the link budget is dominated by the spatial tracking error, and the direct detection system shows a superior performance because it is less sensitive to the spatial tracking error. On the other hand, for systems with small pointing and tracking jitters, the antenna gains are in general limited by the launch cost, and suboptimal antenna gains are often used in practice. In which case, the heterodyne system has a slightly higher power margin because of higher receiver sensitivity

Phase error statistics of a phase-locked loop synchronized direct detection optical PPM communication system

Receiver timing synchronization of an optical Pulse-Position Modulation (PPM) communication system can be achieved using a phased-locked loop (PLL), provided the photodetector output is suitably processed. The magnitude of the PLL phase error is a good indicator of the timing error at the receiver decoder. The statistics of the phase error are investigated while varying several key system parameters such as PPM order, signal and background strengths, and PPL bandwidth. A practical optical communication system utilizing a laser diode transmitter and an avalanche photodiode in the receiver is described, and the sampled phase error data are presented. A linear regression analysis is applied to the data to obtain estimates of the relational constants involving the phase error variance and incident signal power

Integration of an LED/SPAD optical wireless transceiver with CubeSat on-board systems

We demonstrate the integration of Cube-Sat on-board equipment with a field programmable array gate-based light-emitting diode/single-photon avalanche photodiode transceiver using an inter-integrated circuit protocol

A review of communication-oriented optical wireless systems

This article presents an overview of optical wireless (OW) communication systems that operate both in the short- (personal and indoor systems) and the long-range (outdoor and hybrid) regimes. Each of these areas is discussed in terms of (a) key requirements, (b) their application framework, (c) major impairments and applicable mitigation techniques, and (d) current and/or future trends. Personal communication systems are discussed within the context of point-to-point ultra-high speed data transfer. The most relevant application framework and related standards are presented, including the next generation Giga-IR standard that extends personal communication speeds to over 1 Gb/s. As far as indoor systems are concerned, emphasis is given on modeling the dispersive nature of indoor OW channels, on the limitations that dispersion imposes on user mobility and dispersion mitigation techniques. Visible light communication systems, which provide both illumination and communication over visible or hybrid visible/ infrared LEDs, are presented as the most important representative of future indoor OW systems. The discussion on outdoor systems focuses on the impact of atmospheric effects on the optical channel and associated mitigation techniques that extend the realizable link lengths and transfer rates. Currently, outdoor OW is commercially available at 10 Gb/s Ethernet speeds for Metro networks and Local-Area-Network interconnections and speeds are expected to increase as faster and more reliable optical components become available. This article concludes with hybrid optical wireless/radio-frequency (OW/RF) systems that employ an additional RF link to improve the overall system reliability. Emphasis is given on cooperation techniques between the reliable RF subsystem and the broadband OW system

Noise Detection And Estimation In Free Space Optical Communication

Free Space Optical Communication (FSOC) has become a popular wireless communications technique for providing and supporting optical high-speed bandwidth data transmission for telecommunication and computer networking. FSOC is expected to supplement traditional Radio Frequency (RF) technologies and successfully aid in removing congestion from the overly crowded RF spectrum, and its optical fiber communications. FSO system performance is highly dependent on channel conditions, wherein background noise poses a significant problem, even in the absence of weather and/or atmospheric turbulence. Transmitted signals are significantly affected by background noise (e.g., thermal, shot noise, dark currents) primarily on the receiver side, which leads to system performance deterioration. Such effects are often described by Additive White Gaussian Noise (AWGN). This phenomenon affects the communication link and can hinder the accurate detection of information. The work reported in this thesis investigated the addition of generated AWGN to single FSOC links, as well as the extraction of noise signals at the receiver end via a subtraction method. Test results demonstrated that AWGN can be extracted from an FSOC signal when standard deviation and noise signal mean are estimated using a Gaussian Mixture Model (GMM). Outcomes show there is approximately 80% cross-correlation when compared with an original Pseudorandom Binary Sequence (PRBS) signal