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We investigate performance characteristics of a timing recovery circuit for high density 4096 QAM signal reception in cable TV channels. Also, we precisely evaluate the convergence and jitter characteristics. The circuit is designed using software to demodulate IF signal data stored in PC memory. Experimental and simulation results show that the implementation loss of the timing recovery circuit is sufficiently small enough for a 4096 QAM receiver. The convergence time is within a period of 4000 symbols at a CN ratio of 40 dB, which is sufficiently short to permit practical demodulation signal processing.

We present a high density single carrier 1024 QAM transmission scheme for digital cable TV systems. A transmission of approximately 50 Mbps within a single 6 MHz channel and with a higher spectrum efficiency than a conventional digital cable modem, is achieved. For evaluating an equalizer performance in a cable TV channel, we carry out computer simulations before hardware implementation of a 1024 QAM receiver. The BER result of a prototype 1024 QAM modem without forward error correction is 10-4at a CN ratio of 37 dB with Gaussian noise. The implementation loss is less than 1 dB. In addition, we experimentally investigate robustness against interference and the influence of nonlinear amplification of a 1024 QAM signal.

In a hybrid analog (AM VSB) /digital (QAM) sub carrier multiplexed (SCM) optical cable TV system, clipping induced impulsive distortion occurs when the SCM signal's amplitude drops below the laser diode (LD) threshold This distortion may induce bursts of bit errors in digital channels We have investigated the duration of clipping induced distortion and its effect on the BER performance of QAM signals As a result, we found that the frequency accuracy of the analog sub carriers is one of the main factors that characterize the clipping induced impulsive distortion which affects the performance of the digital channel The more accurately the frequencies of the analog sub carriers are set, the longer the duration of the clipping induced distortions becomes If the duration exceeds the ability of the forward error correction (FEC) system, the FEC system will not work well because of the error bursts This factor has not been considered in previous approaches

In multi-channel cable transmission systems, the non-linearity of a laser diode or an amplifier causes a number of intermodulation (IM) distortions (CSO, CTB, etc). IM distortions and thermal noise impair the digital signal in cable transmission and degrade the BER of digital channels. In order to find out the relationship between the IM distortions and the BER, the authors measured the interference's amplitude distribution in a channel. Experimental results show that the amplitude distribution of interference, including the IM distortion and thermal noise, differs from a Gaussian distribution. The distributions depend not only on its power but also on the kind of IM (CSO or CTB), the number of components, and the CN ratio. We performed a computer simulation of the experimental setup. The results of the simulation matched well with the measured results from the experiment.

High speed transmission for UHDTV cable broadcasting is achieved by adopting MPEG-2 TS basis channel bonding technology. A newly designed TDM frame format based on ITU-T J.183 is proposed. A 181.2 Mbps signal transmitted by a 64 QAM and four 256 QAM channels is received error-free at our prototype set-top box.

The 1024-QAM demodulator we developed for cable television networks uses a modified symbol-decision region to reduce the effects of phase noise due to set-top-box tuners. The symbol-decision region is optimized by analysis of phase noise distribution. Simulation results show that good demodulation characteristics of a 1024-QAM signal are achieved under typical phase-noise conditions. The results are verified in a field trial with a prototype demodulator and an off-the-shelf tuner.

A blind demodulator for 1024 quadrature amplitude modulation (QAM) is described. It uses a method that combines carrier recovery without decision-directed operation and decision feedback equalization by using a modified constant modulus algorithm (MCMA) to improve equalization. A prototype shows good 1024-QAM demodulation under multipath and frequency offset conditions. The demodulator also operates well in commercial hybrid-fiber-and-coaxial cable systems.

We studied the colonial morphology and some characteristics of phase variants of Actinomyces viscosus, in order to clarify factors of its virulence.All of A. viscosus examined spontaneously presented three types (P1-P3) of colonies on TYC agar, which contained 5% sucrose. These morphological differences of colonies seemed to be due to the difference of their ability to produce extracellular polysaccharide. The strain which produced the largest amount of extracellular polysaccharide was designated P1, the strain which was designated P3 lacked or had little ability to produce it, and P2 possessed an intermediate.Although both P1 and P3 strains showed similar characteristics in many biochemical tests, P1 adhered well to the glass wall when cultivated in sucrose-containing medium, whereas adherence of P3 was negligible. Electron microscopic examination of cell walls revealed longer fibrils on P1 cell walls than on P3 cell walls. P1 was virulent for infected golden hamsters, causing periodontal disease, bone loss and root surface caries, but P3 was avirulent.These data suggest that the ability to produce extracellular polysaccharide and the presence of fibrils on cell surfaces are important factors in making A. viscosus successful members of plaque community and oral pathogens. The phase variation which occurred spontaneously during sub-culturing of A. viscosus should be given attention because it might influence the pathogenicity of the organism.

The purpose of this study was to investigate the effect of immunization with the cell surface antigen extracted from Actinomyces viscosus on periodontal disease of hamsters, which was induced by inoculation with A. viscosus K-TL +.Cell surface substances were released from A. viscosus K-TL+ cells by stirring them in 0.05M Tris-HCl buffer, pH 7.4, containing 1M NaCl. These were purified by ammonium sulfate precipitations, gel filtration and ion-exchange chromatography, and fibril-rich substance was obtained. This prepaation was used as an immunogen.Golden hamsters were divided into three groups, immunized, shamimmunized and diet-control groups, and they were immunized in their pouches at 4 and 5 weeks of age. At six weeks of age, they were infected with A. viscosus K-TL+, and the establishment of the strain was examined during the experiment. At the end of the experiment, 8 weeks after the last immunization, the hamsters were killed after sampling their saliva and sera, and the mandibulars were evaluated for their alveoral bone loss and root surface caries.In the immunized group, the mean recovery of A. viscosus K-TL+ was less, and the occurrence of alveolar bone loss and root surface caries considerbly decreased comparing with the sham-immunized group. Both saliva and sera obtained from hamsters in the immunized group also showed more elevated levels of antibody against cell surface antigens than in the sham-immunized group.The results suggested that immunization with the cell surface antigen might be effective in prevening periodontal diseases induced by A. viscosus.

A live measles virus vaccine was prepared with a virus strain attenuated by passage in the primary sheep kidney cell culture. All of 209 initially seronegative children showed seroconversion after subcutaneous inoculation of one dose of the vaccine. The geometric mean of neutralizing antibody titers following vaccination was 26.6. Axillary temperature of 37.5 C or higher was recorded in 23.6% of 199 vaccinees with adequate clinical records, but only 4% had fever over 39.0 C. The average maximal temperature in feverish children was 38.3 C. Fever usually lasted for only one or two days. Neither febrile convulsion nor other toxic reactions was observed.

In the 21st century, broadcasting systems are going digital . The Hybrid opticalFiber and Coaxial (HFC) is typically used in the physical layer of the cabletelevision system. The research works in this thesis are motivated by the hope ofimproving the transmission quality of cable television systems by replacingcoaxial trunk lines with optical fiber. It will enhance the transmission capacityof cable television systems and provide high-speed access networks for bothdigital broadcasters and Internet service providers.First , a high density single carrier 1024 QAM transmission scheme for digitalcable TV systems is presented as successful results of feasibility study. About50 Mbps transmission within a single 6 MHz channel , higher spectrumefficiency, is achieved. The BER performance without forward error correction(FEC) of a prototype 1024 QAM modem is 10-4 at the CN ratio of 37 dB. Theimplementat ion loss is less than 1 dB. Also, a 4096 QAM transmission, 60 Mbpsin a conventional cable TV facility is achieved. Robustness against interferenceon the QAM signal is experimentally investigated.Secondly, the statistical behavior of the amplitude probability distribut ion ofintermodulation ( IM) distortion in FDM systems is experimentally investigated.In FDM systems, the non- l inearity of a laser diode or an ampl fier causes anumber of IM, i .e. CSO (composite second order ) , CTB (composite triple beat ) ,and etc. The IM disto t ions impair the digital signal and degrade the BERper formance. In order to f ind out the relationship between the IM distortionsand the BER, the amplitude probability distribut ion is measured. Experimentalresults show that the amplitude distribut ion of interference, including the IMdistor t ion and thermal noise, differsf roma Gaussian distribution. Thedistributions depend not only on i ts power but also on the kind of IM sources(digital modulated or carrier waves) , the number of IM components, and the CNratio. The BER performance varies with IM of both CW and digital QAMcarriers even when the carrier to inter ference noise ratio is the same. Thesimulation results are matched well with the measurement results.Finally, the approximation of probability dist r ibut ion function of CTB fromOFDM signals in the presence of nonlinear devices is demonstrated. In order toclarify the validity of an approximation formula, the amplitude distribution ofCTB distortion and the BER of QAM channel are measured. They are in goodagreement with the formula. On the whole, these research results and findings inthis thesis are applicable for design and implementation of conventional cable TV systems to provide high speed digital video services., 2007