Bidirectional Communication System Research Articles

Bi-directional multimedia satellite communication system using ultrasmall user terminals

NTT started development of a multimedia satellite communication system to provide a medium for Internet access in 1995. This system, which entered commercial service in 1998, uses a hybrid network consisting of a high-speed satellite forward link and terrestrial access links. To meet the increasing demand for low-cost and ubiquitous access links, a second-generation system equipped with satellite transmitting functions is now being developed. The user terminal design calls for a DTH-sized receiver antenna and a transmission power of less than 0.1 W, which will make it suitable for use in homes and small offices. The access link signals from the user terminals are superimposed onto the high-speed TDM forward link signal for efficient use of the frequency band. The transmission power from the user terminal is significantly low compared to that of the forward link signal, a novel interference cancellation technique is introduced. A channel assignment scheme called “channel reservation with rapid release” is introduced for both efficient use of the channels and higher transmission throughput. The forward link signal is completely compatible with the first-generation system, and the data rate is about 30 Mb/s. The paper describes the system's configuration, the central earth station's configuration, and the key technologies of the radio system and access control system.

Irritable bowel syndrome.

The irritable bowel syndrome (IBS) is a functional gastrointestinal disorder whose hallmark is abdominal pain or discomfort associated with a change in the consistency or frequency of stools. In the western world, 8% to 23% of adults have IBS and its socioeconomic cost is substantial. Research-generated insights have led to the understanding of IBS as a disorder of brain-gut regulation. The experience of symptoms derives from dysregulation of the bidirectional communication system between the gastrointestinal tract and the brain, mediated by neuroendocrine and immunological factors and modulated by psychosocial factors. The biopsychosocial model integrates the various physical and psychosocial factors that contribute to the patient's illness. This model and the recently revised symptom-based criteria (i.e. the "Rome II criteria") form the basis for establishing a comprehensive and effective approach for the diagnosis and management of the disorder.

Fiber Optical CATV Addressable System

In this paper, we propose and demonstrate a bidirectional interactive fiber optical CATV addressable system. We use the relative-poor linearity of Fabry-Perot (FP) laser diode, wavelength division multiplexing (WDM) and CATV addressable techniques. The measured values of carrier-to-noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) can satisfy the fiber optical CATV system requirements in our proposed system. This proposed bidirectional communication system is new, simple, economic and suitable for fiber optical CATV architecture.

High Speed Digital Circuits for Medical Communication; the MINCS-UH Project

In Japan, a high speed, bidirectional digital satellite communication system called Medical Information Network by Communications Satellite for University Hospitals is currently available in 30 national universities, and many programs, including clinical conferences, lectures and tutorials, have been broadcasted. Its characteristics are: (1) a state-of-the-art digital high-definition television system, (2) excellent security protection using digital encryption (3) bidirectional communications using two satellite circuits simultaneously, and (4) easy operability. High-quality motion images, and security protection mechanisms are essential for use in clinical medicine.

A CDMA based bidirectional communication system for hybrid fiber-coax CATV networks

Hybrid fiber-coax CATV networks are considered a promising infrastructure for the implementation of future interactive services. Efficient utilization of the available CATV spectrum requires a communication system which is dedicated to the specific properties of these networks. This paper presents the physical layer of a bidirectional communication system for HFC CATV networks which is based on CDMA, a technique that has a certain robustness to the ingress noise found in the CATV bandwidth. Because the application of asynchronous CDMA results in a poor spectral efficiency, a transmission scheme based on synchronous CDMA is adopted. Using synchronous CDMA and QPSK modulation, a capacity of 64 channels of 64 kbit/s each can be achieved in a bandwidth of 6 MHz. It is found that small synchronization errors can be tolerated without significant performance degradation. Next, a description is given of the cable modems responsible for the communication between subscribers and a CATV headend. The design exploits the typical CATV network configuration to enable a cost-effective hardware realization. Sensitivity of system performance to linear distortion is investigated by computer simulation. Especially linearly varying group delay and uneven amplitude response are shown to be potential causes of performance degradation.

Rayleigh backscattering of four-wave mixing in bidirectional optical communication systems

The Rayleigh backscatter properties of four-wave-mix light (FWM) are theoretically and experimentally investigated for the first time. The experimental results agree well with the theoretical predictions. It was found that the Rayleigh backscattering of FWM light may cause severe crosstalk problems in bidirectional multichannel systems.

Design of bidirectional communication systems with optical amplifiers

The performances of four different configurations implementing bidirectional communication systems with erbium-doped fiber optical amplifiers in a 622-Mb/s IM/DD system are compared. The transmission span and the tolerance to variation in link attenuations (attenuation margin) are studied as a function of the amplifiers' position in the link. Operating the amplifiers slightly into saturation (0.4 dB) turns the configurations robust with respect to changes in link attenuations (4.0-dB improvement in the tolerable increase of attenuation, for a span of 76.9 dB).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Stress-induced immune changes, and brain-immune interaction

It is commonly known that psychosocial stress influences the immune system. Recent progress in neuroscience and immunology has elucidated the mechanism of stress induced immune changes, as well as brain-immune interactions. Numerous studies suggest that psychosocial stress increases the susceptibility to bacterial and viral infections. Stressful life events, inappropriate coping behavior and disturbed emotional states are associated with decreased phagocytosis, reduced lymphocyte response to mitogen, diminished natural killer cell activity, and with the risk of developing neoplasm. There is increasing evidence for a bidirectional communication system between the immune system and the brain through common receptors and biologically active substances such as cytokines and neuropeptides. Research has demonstrated the direct regulatory effect of the autonomic nervous system on the immune system, as well as the hypothalamic-pituitary-adrenal axis. It has also been shown that immune and allergic reactions can be classically conditioned, cytokines have an effect on the central nervous system, and that lymphocytes can produce neuropeptides. In this article, stress induced immune changes and brain-immune interactions are reviewed and discussed using pertinent literature, including studies by the authors.

Crosstalk penalities due to coherent Rayleigh noise in bidirectional optical communication systems

The statistical properties, i.e. power spectral densities and probability density functions, of the noise due to Rayleigh backscattered light and due to interference of backscattered and reflected light are derived from the autocorrelation function of the optical source field. The crosstalk penalties due to Rayleigh backscattering in single- and double-source bidirectional systems are calculated. It is shown that it is possible to realize a bidirectional system with commercially available connectors in which Rayleigh backscattering is the dominant crosstalk contribution. The measured crosstalk penalties and bit-error probabilities in a double-source bidirectional system confirm the theoretical results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Meander coupler, a novel wavelength division multiplexer/demultiplexer

We have realized a novel wavelength division multiplexer/demultiplexer based on rib waveguides in GaInAsP/InP. The device is a strongly asymmetric codirectional coupler with periodic variation of the coupling constant and has sinc2-type characteristics. Our devices have center wavelengths around 1.3 μm, filter half-widths 10–15 nm, and far end isolation down to −17 dB. The structure is suited for integration into optoelectronic integrated circuits for applications in bidirectional optical communication systems.

Neuropeptides: Conductors of the immune orchestra

There is increasing evidence for a bidirectional communications system between the immune system and the brain. Many of the substances involved in this communication appear to be neuropeptides. These findings have given biochemical validity to the clinical and epidemiological studies that have suggested that psychosocial factors can modulate the response to infections and neoplasms.

Multiple quantum well reflection modulator

We demonstrated a quantum-confined Stark effect electroabsorption modulator consisting of quantum wells of AlGaAs and GaAs on an epitaxial multilayer dielectric mirror, all grown by molecular beam epitaxy. The resulting reflection modulator avoids problems of substrate absorption, and has relatively high contrast ratio (up to ∼8:1 with peak reflectivity of 25% at 853 nm) because the light passes twice through the quantum wells. Reflection modulators are of interest for bidirectional communication systems, in parallel arrays of optical switching and processing devices and for optical interconnects. For the latter there exists the possibility of this device grown on the same substrate alongside a GaAs integrated circuit or even on Si substrates.

A Transistorized Directional Coupler

In previous papers an active directional coupler using a triode, [1],[2] and its use in a bidirectional broad-band amplifier, [3] has been described. It is obvious that it is important to investigate how such a device can be realized using semiconductor techniques. The use of transistors in directional couplers creates new problems due to the variability of transistor parameters. In this paper a transistorized directional coupler that exhibits high directivity over a broad band and a tight coupling coefficient is described. The problems of stability and nonlinear distortion are discussed and overcome by using feedback. Noise problems are also treated. The use of such a coupler in bidirectional amplifiers is also proposed. For this use, the problem of the long-term stabilization of the directivity of the active coupler has been overcome by means of a control system using a reference signal. Experimental results concerning directivity and bandwidth confirm the possibility of a practical use of the proposed amplifier in bidirectional broad-band communication systems.