Abstract: The present invention relates to a time-division radio transmission technique which uses a modified full-duplex arrangement where two channels are assigned to each two-way link. Simultaneous two-way transmission includes sequential digital symbol bursts between two remote transceivers which alternate between a first and a second channel centered on a first and a second radio frequency, respectively, with each transceiver using a different one of the channels at any instant of time.

Abstract: The present invention relates to a nonlinear optical time-division multiplexer and demultiplexer formed from a cascaded plurality of triggerable optical switching elements. In accordance with the present invention, an exemplary triggerable optical switching element comprises a nonlinear optical material disposed in, for example, a ring resonator arrangement. The nonlinear optical material exhibits an index of refraction which is a function of the intensity of the light passing therethrough. An exemplary switching element is responsive to two separate optical pulse streams, where neither pulse stream comprises a sufficient intensity to cause the element to switch. A trigger pulse is utilized which comprises a sufficient intensity to stimulate switching the output from a first optical pulse stream to a second optical pulse stream.

Abstract: The present invention relates to a channel port module (16) capable of being bridged with a plurality of similar channel port modules onto a single first data rate communication line existing between a hub office (10) and a satellite earth station (12). Each channel port module is in communication with a separate sub-rate user and functions to extract the portion, or channel set, of the first data rate communication signal from the hub office destined for its associated user. Each channel port module also functions to insert a sub-rate return message onto its allocated portion of the return first data rate communication signal which is transmitted back to the hub office. The channel port modules are bridged in parallel onto the communication line, thereby achieving simultaneous reception of the first data rate signal by the plurality of channel port modules sharing the same communication line.

Abstract: An anti-Stokes Raman up-converter is disclosed which is capable of up-converting a variety of conventional laser sources. A metal-halide, for example, thallium chloride or thallium iodide, is employed as a lasing medium, and is photodissociated to create a population inversion in a metastable state of the metal ion. An excimer laser, for example, and ArF* or KrF* excimer laser, may be employed to photodissociate the metal-halide in accordance with the present invention. Alternatively, an excimer flashlamp, for example a ArF* or KrF* flashlamp, may be employed to photodissociate the metal-halide in accordance with the present invention. A conventional laser source, for example a CO.sub.2 laser or any harmonic of a Nd:YAG laser, is subsequently employed to pump the population inversion from the metastable state to a virtual level near an intermediate state. Anti-Stokes Raman lasing occurs from this virtual state, where the lasing frequency is greater than the frequency of the conventional laser pump source.

Abstract: The present invention relates to a multibeam antenna arrangement having minimal aberration of astigmatism and coma over a wide area of the focal surface of the antenna. The present antenna comprises a plurality of N reflectors arranged confocally in a sequence along a feed axis of the antenna and at least one feed disposed in the vicinity of a focal point on the focal surface. The reflectors and the at least one feed are further arranged to provide an equivalent centered antenna arrangement with the longitudinal axis of the feed corresponding to an equivalent axis of the centered arrangement for eliminating astigmatism. Coma is then eliminated by deforming two of the N reflectors in a predetermined manner.

Abstract: An anti-Stokes Raman laser which uses a metastable level of bromine is provided. A medium of molecules each of which contains at least one bromine atom is provided. Means are provided for dissociating the bromine atom from the molecules so that a majority of dissociated bromine atoms go into at least one excited metastable state. Means are provided for jumping the bromine atoms in the metastable state with pump photons in order to provide anti-Stokes Raman output photons by transition from the metastable state to a final state. The output photons have energy equal to the pump photon energy plus an energy gain given by the energy difference between the metastable state and the final state.

Abstract: The present invention relates to a technique using interpolative coders and decoders to permit an analog input message signal to be sampled at the Nyquist rate, each sample is then encoded into a corresponding level of an X-bit code and the encoded corresponding level is then encoded into a unique corresponding digital number pair. Each digital number pair includes two separate digital signals comprising Y bits each for transmission over two separate channels or paths to a remote receiver for inverse decoding. In accordance with the present technique either half of the transmitted signal can be used to reproduce the original signal to a fair degree of accuracy and both halves can provide high-quality reproduction of the original signal.

Abstract: In a radio communication system, an adaptive transmitter power control system is described wherein the signal level at each receiver is monitored and a control signal, which is a function of the signal level, is transmitted back to the transmitting station to adjust the transmitter output power, as required. By transmitting the lowest power level consistent with system objectives, the repeater circuits operate in a highly linear mode, and cochannel interference is significantly reduced.

Abstract: The present invention relates to a means for achieving simultaneous transmission of data and speech with only a minimal expansion of the bandwidth of the speech signal. A Fourier transform (14) is performed on the speech signal and a predetermined number of phase components are replaced with data (d(n)) in an appropriate form. The number of phase components replaced with data is determined by approximately classifying the speech (16) as either "silence", no data inserted; "unvoiced" speech, M phase components convey data; and "voiced" speech, J phase components convey data; where J is less than M, and M is not greater than the number of phase components in the message band of the speech signal. An inverse Fourier transform (22) is subsequently performed on the combined data and speech signal. The combined message signal (G(t)) will comprise approximately the same bandwidth as the original speech signal, by virtue of the frequency domain insertion of the data into the speech.

Abstract: The present invention relates to transmitters and receivers in a digital time division multiple access (TDMA) communication system wherein the resource sharing concept is generalized by fully exploiting the available clear air carrier-to-noise ratio (CNR) of a transmission link to achieve very high transmission capacity while maintaining low rain outage. Transmission is accomplished by using a first predetermined redundancy code and a first predetermined signal constellation for quadrature amplitude modulation during clear air conditions to permit a high rate of information transfer. When the fade depth exceeds the built-in fade margin, a second predetermined redundancy code and a second predetermined signal constellation is used while using time slots borrowed from a resource sharing reserved time slot pool to maintain the data rate at the fade site. Either one of the first redundancy code or signal constellation can equal either one of the second redundancy code or signal constellation.

Abstract: The present invention relates to an antenna arrangement which uses a large offset spherical main reflector to communicate with several, spaced-apart, remote locations. Large aberrations caused by the main reflector are corrected by a first subreflector forming a small image of the main reflector at a conjugate image surface and a second subreflector which is disposed at the image location and is shaped to correct for the aberrations caused by the main reflector. Such correction is, to a good approximation, frequency independent and provides aberration free operation at feeds adjacent each other and associated with remote locations having small differential angles of incidence on the center of the main reflector.

Abstract: An anti-Stokes Raman laser is disclosed which is tunable over a range of 10-70 cm.sup.-1. An alkali halide is used as the lasing medium and a metastable halide population inversion is created with respect to the ground state of the halide by selective photodissociation of the alkali halide. A pump laser is then employed to move the population from the metastable state to a region near an intermediate state of the halide. The population subsequently falls back to the initial ground state, thereby creating the anti-Stokes Raman emission. Since the intensity of the photodissociation is directly proportional to the amount of population inversion achieved, and hence, to the region the population may be pumped to, the tuning of the output anti-Stokes Raman lasing is a function of the intensity of the initial photodissociation.

Abstract: The present invention relates to a multibeam antenna arrangement having minimal primary aberration of astigmatism and coma over a wide area of the focal surface of the antenna. The present antenna comprises a plurality of N reflectors arranged confocally in a sequence along a feed axis of the antenna and at least one feed disposed in the vicinity of a focal point on the focal surface. The reflectors and the at least one feed are further arranged to provide an equivalent centered antenna arrangement with the longitudinal axis of the feed substantially parallel to an equivalent axis of the centered arrangement for eliminating astigmatism. Primary coma is then eliminated by deforming two of the N reflectors in a predetermined manner.

Abstract: The present invention relates to hybrid mode feeds which are capable of handling very wide bandwidths. In the present feed arrangements, a dominant TE.sub.11 mode is converted to the HE.sub.11 hybrid mode which is then launched. The TE.sub.11 to HE.sub.11 mode conversion is achieved by inserting a circular dielectric rod (12) into a flared end (11) of a smooth-walled cylindrical feedhorn until a small cylindrical section of the dielectric rod engages with the inner wall (15) of the unflared portion of the feedhorn. In one feed arrangement, the other end of the dielectric rod is similarly inserted into a flared end (21) of a corrugated cylindrical feedhorn section (22) until a short longitudinal section of the cylindrical portion of the rod is concentric with the corrugations of an unflared section of the feedhorn to provide a transition for the HE.sub.11 mode into the corrugated waveguide for subsequent launch.

Abstract: The present invention relates to antennas with a segmented reflecting surface for providing fully or partially overlapping beams from separate feeds associated with each segment without incurring cross-coupling between feeds and power loss. More particularly, a main reflector or a subreflector reflecting surface is segmented to provide separate images of the far field area of the antenna on separate focal surfaces in the vicinity of an original focal surface of a corresponding non-segmented antenna. Feeds disposed at essentially corresponding locations on each of the far field area images produced by each of the segments provide separate beam footprints which overlap each other in the far field area by a predetermined amount.

Abstract: The present invention relates to an antenna feed arrangement for correcting for astigmatism caused by an offset main reflector. The feed arrangement comprises at least one feed element, a first and a second cylindrical reflector disposed along the feed axis of the antenna with corresponding axes across the reflecting surfaces thereof oriented orthogonal to each other, and a pair of plates comprising a conductive material which are disposed parallel to, and on either side of, the feed axis of the antenna to enclose the area between the at least one feed element and the first reflector while forming an aperture thereof within a predetermined distance from the second reflector.

Abstract: The present invention relates to a frequency-hopped single sideband (SSB) mobile radio system implemented by hopping the carrier frequency of an input signal (s(t)) every .tau. seconds. The hopping is controlled by a carrier-frequency-hopped sequence (f.sub.i (t)) generated by a carrier-frequency-hopping generator (16,24). When employed in a frequency-hopped SSB transmitter (10), the carrier sequence functions to modulate the input signal, "hopping" it to a different carrier frequency every .tau. seconds. The carrier-frequency-hopped SSB receiver (20) employs the identical carrier sequence as used by the transmitter to demodulate the transmitted carrier-frequency-hopped SSB signal, thereby recovering the original single sideband signal (s(t)). By frequency hopping the carrier signal of an SSB signal, the present invention mitigates the effects of co-channel interference and frequency selective fading inherent in prior art SSB cellular mobile radio systems.

Abstract: The present invention relates to a decoder (10) for convolutional self-orthogonal codes which includes a multistage syndrome register (16) and is responsive to two separate threshold levels. The first threshold level, as in prior art arrangements, includes a first majority logic circuit (24) connected to selected stages of the syndrome register and functions to correct the information bits (X.sub.1 -X.sub.7) currently being processed. Instead of also using this majority logic circuit to correct the syndrome register, as in the prior art, the present invention includes a second majority logic circuit (28), which operates at a different threshold level than the first and functions to correct the selected stages of the multistage syndrome register.

Abstract: The present invention relates to a compatible high-definition television (CHDTV) color picture signal which is capable of conversion by simple and inexpensive means into either a HDTV composite color picture signal for use by a HDTV receiver or an associated conventional television system (ACTS) color picture signal for use by an ACTS receiver. The present CHDTV color picture signal comprises (a) a first line scan rate which is the same as that of the ACTS signal, (b) a first line signal of a HDTV camera signal produced at a second line scan rate which is time stretched and transmitted as is at the first line scan rate in a first portion of the CHDTV signal bandwidth, and (c) a second line signal of the HDTV camera signal which is time streched and transmitted as a line differential signal on a vestigial sideband carrier signal in a second portion of the HDTV signal bandwidth.

Abstract: The present invention relates to hybrid mode feeds which are capable of handling very wide bandwidths. In the present feed arrangements, a dominant TE.sub.11 mode is converted to the HE.sub.11 hybrid mode which is then launched. The TE.sub.11 to HE.sub.11 mode conversion is achieved by inserting a circular dielectric rod (12) into a flared end (11) of a smooth-walled cylindrical feedhorn until a small cylindrical section of the dielectric rod engages with the inner wall (15) of the unflared portion of the feedhorn. In one feed arrangement, the other end of the dielectric rod is similarly inserted into a flared end (21) of a corrugated cylindrical feedhorn section (22) until a short longitudinal section of the cylindrical portion of the rod is concentric with the corrugations of an unflared section of the feedhorn to provide a transition for the HE.sub.11 mode into the corrugated waveguide for subsequent launch.