Abstract: System (100) and methods (1100) for improving packet loss due to fast optical power fades in an FSO communication link (136). The methods involve: obtaining Channel Fade Statistics (“CFSs”) for the FSO communication link; and analyzing CFSs to determine if Redundant Packet Transmission (“RPT”) is required to mitigate fast optical power fading. If RPT is required, then first operations are performed at a data link layer (408) of a protocol stack (400) to generate first packets (600). Each packet has a sequence number (602) disposed between a data link layer header (502) and a network layer header (504). If RPT is not required, then second operations are performed at the data link layer to generate a second packet absent of the sequence number or alternatively having a sequence number equal to zero. Thereafter, the packet(s) is transmitted over the FSO communication link one or more times.

Abstract: A communications device includes a transmitter device having first and second optical sources and generating respective first and second modulated optical carrier signals at first and second optical carrier frequencies based upon an input signal. The communications device also includes an optical waveguide coupled to the transmitter device, and a receiver device coupled to the optical waveguide and including an FM-PM discriminator having a transfer function with a positive slope portion and a negative slope portion so that the first optical carrier frequency is positioned on the positive slope portion and the second optical carrier frequency is positioned on the negative slope portion.

Abstract: A free space optical communication system (10) including first and second mono-static transceivers (20a, 20b). Each transceiver (20a, 20b) includes a reflective assembly (40) defining a reflective surface (44) about a receiving end of a respective optical fiber (32) and configured to reflect optical signals (26) within a field of view of the transceiver (20a, 20b) as a modulated retro-reflective signal (28). Each mono-static transceiver (20a, 20b) includes an acquisition system (60) configured to detect a modulated retro-reflective signal (28) and adjust the alignment of the respective transceiver (20a, 20b) in response to a detected modulated retro-reflective signal (28). A mono-static transceiver and a method of aligning a mono-static transceiver are also provided.

Abstract: System (100) and methods (1100) for improving packet loss due to fast optical power fades in an FSO communication link (136). The methods involve: obtaining Channel Fade Statistics (“CFSs”) for the FSO communication link; and analyzing CFSs to determine if Redundant Packet Transmission (“RPT”) is required to mitigate fast optical power fading. If RPT is required, then first operations are performed at a data link layer (408) of a protocol stack (400) to generate first packets (600). Each packet has a sequence number (602) disposed between a data link layer header (502) and a network layer header (504). If RPT is not required, then second operations are performed at the data link layer to generate a second packet absent of the sequence number or alternatively having a sequence number equal to zero. Thereafter, the packet(s) is transmitted over the FSO communication link one or more times.

Abstract: A communications device includes a transmitter device including first and second optical sources, a first optical coupler coupled to the first and second optical sources, and a first modulator coupled to the first optical coupler and to modulate a combined carrier signal including the first and second optical carrier signals with an RF input signal. The communications device includes a receiver device having a second modulator to further modulate the modulated combined carrier signal with an LO signal, a FM-PM discriminator coupled to the second modulator and to convert the modulated combined carrier signal to an intensity modulated combined carrier signal based upon the LO signal, a second optical coupler coupled to the FM-PM discriminator and to generate first and second intensity modulated carrier signals, and an optical-to-electrical converter coupled to the second optical coupler and to generate an IF signal.

Abstract: A communications device includes a transmitter device having an optical source to generate an optical carrier signal, and a first modulator coupled to the optical source and to modulate the optical carrier signal with a radio frequency (RF) input signal, and an optical waveguide coupled to the transmitter device. The communications device includes a receiver device coupled to the optical waveguide and including a second modulator to further modulate the modulated optical carrier signal with a local oscillator (LO) signal, a frequency modulation-phase modulation (FM-PM) discriminator coupled to the second modulator and to convert the modulated optical carrier signal to an intensity modulated optical carrier signal based upon the LO signal, and an optical-to-electrical converter coupled to the FM-PM discriminator and to generate an intermediate frequency (IF) signal based upon the intensity modulated optical carrier signal.

Abstract: A communications device includes a transmitter device having an optical source to generate an optical carrier signal, and a first modulator coupled to the optical source and to modulate the optical carrier signal with a radio frequency (RF) input signal, and an optical waveguide coupled to the transmitter device. The communications device includes a receiver device coupled to the optical waveguide and including a second modulator to further modulate the modulated optical carrier signal with a local oscillator (LO) signal, a frequency modulation-phase modulation (FM-PM) discriminator coupled to the second modulator and to convert the modulated optical carrier signal to an intensity modulated optical carrier signal based upon the LO signal, and an optical-to-electrical converter coupled to the FM-PM discriminator and to generate an intermediate frequency (IF) signal based upon the intensity modulated optical carrier signal.

Abstract: A communications device includes a transmitter device including first and second optical sources, a first optical coupler coupled to the first and second optical sources, and a first modulator coupled to the first optical coupler and to modulate a combined carrier signal including the first and second optical carrier signals with an RF input signal. The communications device includes a receiver device having a second modulator to further modulate the modulated combined carrier signal with an LO signal, a FM-PM discriminator coupled to the second modulator and to convert the modulated combined carrier signal to an intensity modulated combined carrier signal based upon the LO signal, a second optical coupler coupled to the FM-PM discriminator and to generate first and second intensity modulated carrier signals, and an optical-to-electrical converter coupled to the second optical coupler and to generate an IF signal.

Abstract: A communications device includes a transmitter device having first and second optical sources and generating respective first and second modulated optical carrier signals at first and second optical carrier frequencies based upon an input signal. The communications device also includes an optical waveguide coupled to the transmitter device, and a receiver device coupled to the optical waveguide and including an FM-PM discriminator having a transfer function with a positive slope portion and a negative slope portion so that the first optical carrier frequency is positioned on the positive slope portion and the second optical carrier frequency is positioned on the negative slope portion.

Abstract: A system and method of detecting Automatic Identification System (AIS) signals in space and decoding these signals. In one aspect, a system for performing this function is described which includes a receiver configured to receive the plurality of AIS signals and pre-process the plurality of AIS signals to produce digital input data, and a processor configured to process the digital input data to identify one or more candidate AIS message signals based on Doppler offsets associated with the digital input data, determine corresponding Doppler offset estimates and time estimates of the one or more candidate AIS message signals, decollide and decode the one or more candidate AIS message signals to obtain corresponding message segments and validate the decoded message segments for proper AIS formatting.

Abstract: An interdigital transducer for use in a surface acoustic wave filter has two busbars of an irregular shape to reduce the effect of internally reflected surface waves. The busbars will usually have an identical shape to one another and have stepped outer and inner edges. The distance between a portion of the outer edge and a corresponding portion of the inner edge can be constant for a particular busbar or that distance can vary. With previous busbars, the outer and inner edges are linear and each busbar has a rectangular shape.

Abstract: A filterbank using surface acoustic wave technology and having a plurality of filters. Each filter has an input transducer and an output transducer. The input transducers are connected in parallel to a single matching circuit. The output transducers each have a separate matching circuit. The transducers are formed by a thin film of aluminum pattern on a piezoelectric substrate. The input transducers all have the same structure and the output transducers all have the same structure, though that structure is different from the input transducers. The only difference between the transducers of each filter is the location of electrode breaks for each electrode. A weighting function of the transducers is scaled and biased to provide a constant impedance across the bandwidth of the filterbank and to equalize the output amplitudes and capacitances of the output transducers. This produces a continuous level response across the bandwidth of the filterbank.

Abstract: A surface acoustic wave filter comprising; a first bidirectional ID transducer (5) of symmetrical form; a second ID transducer (1) acoustically coupled with the first transducer and comprising two parts (1A, 1B) each of which parts is in the form of one half of a respective bidirectional ID transducer (9 or 11) of symmetrical form, the two parts being positioned with respect to one another and the first transducer so that when respectively excited by corresponding signals of different phases they co-operate to produce a unidirectional acoustic signal propagating towards the first transducer from one side thereof; and a third transducer (3) acoustically coupled with the first transducer and comprising two parts (3A, 3B ), each of which parts is electrically connected in parallel with a respective one of the two parts of said second transducer, and each of which parts of the third transducer is effectively in the form of the mirror image about the center line (7) of the first transducer of the other half of the

Abstract: A spectrum analyzer incorporates a 36.degree. Y cut lithium niobate Bragg cell provided on one face with an interdigital transducer. The 36.degree. Y cut maximizes the ratio of quasi-longitudinal to quasi-shear wave piezoelectric coupling with the interdigital transducer and thereby minimizes the output of spurious signals from the analyzer. In a preferred embodiment the Bragg cell comprises two lithium niobate crystals bonded by a metal (preferably gold) film, the crystal attached to the transducer being 36.degree. Y cut and the other crystal being cut so as to maximize acousto-optic coupling.