Keying

About: Keying is a research topic. Over the lifetime, 6598 publications have been published within this topic receiving 82943 citations.

Multi-rate DPSK optical transceivers for free-space applications

Abstract: We describe a flexible high-sensitivity laser communication transceiver design that can significantly benefit performance and cost of NASA's satellite-based Laser Communications Relay Demonstration Optical communications using differential phase shift keying, widely deployed for use in long-haul fiber-optic networks, is well known for its superior sensitivity and link performance over on-off keying, while maintaining a relatively straightforward design However, unlike fiber-optic links, free-space applications often require operation over a wide dynamic range of power due to variations in link distance and channel conditions, which can include rapid kHz-class fading when operating through the turbulent atmosphere Here we discuss the implementation of a robust, near-quantum-limited multi-rate DPSK transceiver, co-located transmitter and receiver subsystems that can operate efficiently over the highly-variable free-space channel Key performance features will be presented on the master oscillator power amplifier (MOPA) based TX, including a wavelength-stabilized master laser, high-extinction-ratio burst-mode modulator, and 05 W single polarization power amplifier, as well as low-noise optically preamplified DSPK receiver and built-in test capabilities

Performance evaluation of multilevel polarisation shift keying modulation schemes

Abstract: The performance of coherent optical transmission systems using multilevel polarisation modulation is derived in terms of the symbol error probability. Four new multilevel modulation schemes based on equipower signal constellations at the vertices of regular polyhedra inscribed into the Poincare sphere are proposed. For an increasing number of signals in the constellation, the shot noise performance of these systems show a remarkably less rapid degradation with respect to standard multilevel schemes with an equal number of signals.

Compressed-Sensing-Aided Space-Time Frequency Index Modulation

Abstract: In space-time shift keying (STSK), the information is conveyed by both the spatial and time dimensions, which can be used to strike a tradeoff between the diversity and multiplexing gains. On the other hand, orthogonal frequency-division multiplexing (OFDM) relying on index modulation (IM) conveys information not only by the conventional signal constellations as in classical OFDM, but also by the indices of the subcarriers. In this paper, we combine the benefits of STSK and IM in order to strike a flexible tradeoff between the throughput and bit-error performance by transmitting extra information bits in each subcarrier block, while increasing the diversity order. In order to further improve this tradeoff, as well as to decrease the complexity of the detector, compressed sensing is combined with the proposed STSK-aided IM system. We first present the maximum likelihood (ML) detection, which forms the best-case bound on the proposed system's performance. Then, we propose a pair of reduced-complexity detection algorithms capable of approaching the ML detector's performance. Furthermore, in order to attain a near capacity performance, we propose a soft-input soft-output decoder that is capable of exchanging soft information with a channel decoder through iterative decoding.

Same frequency repeater for a multiple repeater system

Abstract: This invention is directed to a same frequency repeater (SFR) for use in a multiple SFR system in which only one SFR at a given time is allowed to retransmit a received signal thereby preventing simulcast distortion which could occur due to multiple SFR retransmissions. The SFR includes a receiver for receiving a signal carrying information at a given frequency and a transmitter for rebroadcasting the received signal at the given frequency. A mechanism is provided for keying the transmitter upon the reception of a received signal. A detector senses if a predetermined pilot tone is carried by the received signal. A mechanism responsive to the detection of the pilot tone inhibits the keying of the transmitter if the pilot tone is detected before the transmitter is keyed. A tone generator encodes the output signal of the transmitter with the pilot tone. The keying mechanism preferably delays the keying of the transmitter for a time period having a duration inversely proportional to the magnitude of the received signal in response to a mechanism which senses the magnitude of the received signal. The present invention further contemplates a method for the operation of such an SFR.

Connector keying system

Abstract: The connector keying system has a first connector housing (4) with a mating surface and a second connector housing (2) with a mating surface. The second housing (2) is movable relative to the first housing (4). In this system a programming of the keying shall occur automatically as the connector housings (2, 4) are mated together. This achieved as follows: A keying means receiving recess (23) is provided on the mating surface of the first connector housing (4) proximate an end thereof. A keying means is provided in the recess (23). The keying means has a first (22) and a second keying member (24). The first keying member (22) is secured to the first connector housing (4) by first securing means (50, 52). The second keying member (24) is frictionally maintained in corporation with the first keying member (22). The second keying member (24) has second securing means which are provided to cooperate with the second connector housing when the connector housings (2, 4) are mated together.