Carrier-to-noise Ratio Research Articles

Frequency synchronization technique using replica created by mutual correlation value for classifying the weight in autocorrelation operation

AbstractIn an orthogonal frequency‐division multiplexing (OFDM) system, a method based on the autocorrelation of two consecutive known symbols is proposed in order to estimate the frequency offset. In this system, the autocorrelation is calculated for all samples in a symbol. When the products of samples are summed and averaged, the product of each sample is weighted by the absolute amplitude of the received sample. Consequently, a sample which exhibits large received absolute amplitude due to the effect of noise is given a large weight. Since the product of samples given a large weight has a large effect on the estimation, it may degrade the estimation accuracy. Based on this idea, this paper proposes a method of reducing the effect of noise in frequency offset estimation, in which a replica constructed on the basis of information concerning the arrival time, the power, and the phase rotation of each path contained in the cross‐correlation is used to determine the weights used in the calculation of the autocorrelation. It is shown by computer simulation that the proposed method can improve the accuracy of frequency offset estimation in the region where the carrier‐to‐noise ratio (CNR) is low. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(5): 28–40, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20243

A Study of Material Selection for Super-Resolution Readout of Optical Disk with PtOx Recording Layer

Zn33Sb67, Ge20Te80, and Au5Te95 (in at. %) are used in a super-resolution readout optical disk combined with a PtOx recording layer. A high carrier-to-noise ratio (CNR) (40–42 dB) was obtained at a 200 nm mark length, which is smaller than the resolution limit of the optics (265 nm) used. The compositions of the above materials are close to a eutectic point of the binary alloy system. The results indicate that it is a key for the material selection to obtain a high CNR in super-resolution readout.

A CATV Lightwave Transport System Based on Fabry-Perot Laser and External ASE Light Injection Technique

We propose a low cost WDM optical source using split band technology and external ASE light injection for CATV signals transmission. Good performance of carrier-to-noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) were observed over 30 km SMF transmission.

Analysis of the effect of transverse modes on free-space optical interconnect performance

Vertical-cavity surface-emitting lasers (VCSELs) and microlenses can be used toimplement free space optical interconnects (FSOIs) which do not suffer from thebandwidth limitations inherent in metallic interconnects. A comprehensive linkequation describing the effects of both optical and electrical noise is introduced.We have evaluated FSOI performance by examining the following metrics: thespace–bandwidth product (SBP), describing the density of channels and aggregatebandwidth that can be achieved, and the carrier-to-noise ratio (CNR), whichrepresents the relative strength of the carrier signal. The mode expansion method(MEM) was used to account for the primary cause of optical noise: laser beamdiffraction. While the literature commonly assumes an ideal single-mode laser beam,we consider the experimentally determined multimodal structure of a VCSELbeam in our calculations. It was found that maximum achievable interconnectlength and density for a given CNR was significantly reduced when the higherorder transverse modes were present in simulations. However, the simulationsdemonstrate that free-space optical interconnects are still a suitable solution for thecommunications bottleneck, despite the adverse effects introduced by transverse modes.

A CMOS TV tuner/demodulator IC with digital image rejection

Superheterodyne TV tuners have been implemented in discrete forms using tunable RF and SAW IF filters. Integrating TV tuners in CMOS technology without them is a challenging task to cope with technical issues such as harmonic mixing and image. The image rejection in low- or zero-IF systems has been limited to 30-40 dB by analog imperfections such as I/Q path gain and phase mismatches. A single-chip low-IF TV tuner solution is proposed so that the image can be suppressed digitally using an image cancellation technique based on a complex one-tap LMS signal decorrelation algorithm. Programmable digital filtering and video/sound demodulation make a multistandard TV tuner feasible in the 48-860 MHz VHF/UHF band. The chip has a maximum gain of 63 dB and an input automatic gain control (AGC) range from -15 to 25 dB with 0.85-dB steps. It achieves an image and IF rejection of 60 dB, a peak carrier-to-noise ratio (CNR) of 55 dB, and a peak sound signal-to-noise ratio (SNR) of 44 dB without frequency modulation (FM) de-emphasis. The prototype occupies 6/spl times/6 mm/sup 2/ in 0.25-/spl mu/m CMOS and consumes 1 W at 2.5 V.

Analysis of CNR penalty of radio-over-fiber systems including the effects of phase noise from laser and RF oscillator

The effect of phase noises from a laser and an oscillator on radio-over-fiber (RoF) systems is analyzed and discussed with a power spectral density (PSD) function. A Mach-Zehnder modulator (MZM) and a phase shifter are employed to externally generate an optical single sideband (OSSB) signal since the OSSB signal is tolerable for power degradation due to a chromatic fiber-dispersion effect. It is shown that a carrier-to-noise ratio (CNR) penalty is deeply related to the bandwidth of a receiver filter and the phase noise from a radio frequency (RF) signal oscillator rather than that from a laser in a small differential-delay environment and a direct detection scheme. The CNR penalty due to the increment of the laser linewidth from 10 to 624 MHz is almost 1.1 dB, while the increase of the RF-oscillator linewidth from 1 to 100 Hz results in about a 20-dB penalty at a 30-GHz 10-km transmission in a standard single-mode fiber (SSMF) with a fiber chromatic dispersion of 17 ps/km/spl middot/nm.

CATV/radio-on-fiber transport system based on direct modulation

A directly modulated CATV/radio-on-fiber (ROF) transport system based on external light injection technique, optical single sideband (SSB) filter, and RF amplifier predistorter is proposed and demonstrated. To the best of my knowledge, it is the first time to transmit CATV and ROF signals simultaneously in a directly modulated form. Good performances of carrier-to-noise ratio (CNR), composite second order (CSO) and composite triple beat (CTB) were obtained for CATV band; and low third order intermodulation distortion to carrier ratio (IMD3/C), and bit error rate (BER) values were achieved for ROF application.

Noise and distortions limitations in the design of HFC CATV systems

The paper deals with HFC CATV systems. System parameters determinative in obtaining the desired carrier-to-noise ratio (CNR) and acceptable nonlinear distortions are considered. Formulae for the gain and the maximum number of RF amplifiers in the longest coaxial trunk line are developed. A mathematical model of the optical channel is suggested that makes it possible for the signal minimum level at the optical receiver input to be calculated if the value of CNR and the number of TV channels transmitted are known. Analytical expressions to determine the RF signal voltage in the input and output of the optical line are given that take into consideration the nonlinear distortions in the laser transmitter, the number of TV channels and the losses within the optical fiber and passive elements. Experimental results are given to illustrate the application of the formulae in the design of a HFS system section.

A robust fiber-radio architecture for wavelength-division-multiplexing ring-access networks

In this paper, we propose a dynamic wavelength-allocation scheme for wavelength-division multiplexing (WDM) fiber-radio ring-access networks. This scheme can be used to improve the use efficiency of wavelengths at the burst traffic load on the fiber-radio networks. Moreover, a novel bidirectional wavelength add-drop multiplexer (B-WADM) is designed on the backboned ring, which can connect the working and standby sub-rings. It can provide the self-protected function that uses just a few optical devices under link failures. Furthermore, we carry out this study through the simulation and analysis for carrier-to-noise ratio (CNR), channel capacity, and spurious free dynamic range (SFDR) of the fiber-radio network. Finally, we set up an experimental network to demonstrate its performance. The experimental results illustrate that this fiber-radio architecture can provide the robust, flexible, and reliable characteristics for large radio terminals.

New Write-Once Medium with NiOx Film Using Blue Laser

Both a new write-once medium with a sputtered NiOx film and a write-once optical disk using a blue laser has been fabricated. The optical constant of sputtered NiOx films for different ratios of O2/Ar was determined, and showed little dependence on sputtering ratios of O2/Ar and wavelength. The X-ray photoelectron spectra (XPS) data indicated those films have two major components, NiO and Ni2O3. Most NiOx films released oxygen gradually below 300°C. Over 300°C, there was an apparent transition due to the decomposition of the Ni2O3. At a writing power of 12 mW and a reading power of 0.5 mW under conditions of a numerical aperature (NA) of 0.65 and a wavelength of 405 nm, the carrier to noise ratio (CNR) was more than 47 dB and jitter was less than 13%. The recording principle depends primarily on the explosive pressure of the O2 released due to laser heating of the NiOx film.

Optical recording characteristics of WO3 films grown by pulsed laser deposition method

W O 3 films were deposited on the glass substrate (Corning No. 7059 with an area of 26×38mm) by the pulsed laser deposition method using an ArF excimer laser. It was found that after annealing at 500°C for 10min, the film thickness became 1.8 times compared with that (approximately 40nm) in the as deposited state. At this time, the difference in the transmittance, ΔT, between the annealed state and the as deposited state was about 40% at the wavelength of 400nm. From x-ray diffraction spectra and x-ray photoelectron spectroscopy spectra, it was considered that the ratio of the peak values of W6+ 4f5∕2 (tungsten oxide) versus W 4f5∕2 (metal tungsten) increased steeply after the annealing process. From this, it was considered that oxygen was absorbed into the WO3 films through the annealing process. From the revolution test for the sample without the protection layer in which the WO3 films were deposited upon the digital versatile disk disk substrate, a write peak-power dependence of carrier to noise ratio (CNR) (at λ=406nm, NA=0.65) of 3T signal (58.5MHz) was measured at a linear velocity of 5m∕s and a read power of 0.6mW. It was confirmed that the values of CNR obtained at the write peak-power 5–6mW were near 50dB (the region A) and the ones obtained at the write power 7–10mW were more than 60dB (the region B). From scanning electron microscopy observation, it was recognized that bits with 0.16–0.25μm size, having the fine-shaped dots with clear-cut edge, were made in the region A. This corresponded to the maximal storage capacity of 25GB in the “Blu-ray disk” specification. However, it was also identified that holes were formed in the region B and the film materials were scattered by receiving a train of high write power impulses. Next, it was found that the write power corresponding to region A for the structures with the WO3 layer sandwiched between a Al2O3 or ZnS–SiO2 protection layer increased or decreased, respectively. Larger values of the CNR will be obtained if the film thickness of each layer including the active layer were optimized.

Read-only memory disk with <inline-formula><math display="inline" overflow="scroll"><msub><mi>AgO</mi><mrow><mi>x</mi></mrow></msub></math></inline-formula> and AgInSbTe superresolution mask layer

Two novel read-only memory (ROM) disks, one with an AgOx mask layer and the other with an AgInSbTe mask layer, are proposed and studied. The AgOx and the AgInSbTe films sputtered on the premastered substrates with pit depths of 50 nm and pit lengths (space) of 380 nm are studied by atomic force microscopy. Disk readout measurement is carried out using a dynamic setup with a laser wavelength of 632.8 nm and an object lens numerical aperture (NA) of 0.40. Results show that the superresolution effect happens only at a suitable oxygen flow ratio for the AgOx ROM disk. The best superresolution readout effect is achieved at an oxygen flow ratio of 0.5 with the smoothest film surface. Compared with the AgOx ROM disk, the AgInSbTe ROM disk has a much smoother film surface and better superresolution effect. A carrier-to-noise ratio (CNR) of above 40 dB can be obtained at an appropriate readout power and readout velocity. The readout CNR of both the AgOx and AgInSbTe ROM disks have a nonlinear dependence on the readout power. The superresolution readout mechanisms for these ROM disks are analyzed and compared as well.

Super-RENS Disk for Blue Laser System Retrieving Signals from Polycarbonate Substrate Side

Super-resolution near-field structure (super-RENS) technology was applied to the high definition digital versatile disk (HD DVD) based system that retrieves signals from the polycarbonate substrate side using a blue laser. We used an optics with a laser wavelength (λ) of 405 nm and a numerical aperture (NA) of 0.65, and have obtained high carrier-to-noise ratios (CNRs) of 45 dB at a 100 nm mark length and 40 dB at 60 nm, which are smaller than the resolution limit (λ/4NA=156 nm). The results demonstrate that the technology can also be used in the HD DVD-based system. We discussed how well the CNR is obtained below the resolution limit when this technology is used in the DVD-, Blu-ray Disc- and HD DVD-based systems. Comparison of the best results to date strongly suggests that the difference between these systems simply comes from their λ and NA.

Signal Enhancement of Super Resolution Enhanced Near-Field Structure Disc by Silver Nano-Particles

We propose a carrier-to-noise ratio (CNR) increment method for a super resolution enhanced near-field structure (super-RENS) with silver nanoparticles. The silver nanoparticles were fabricated by the RF magnetron sputtering method. The mean diameters of the particles under as-deposited and 600°C annealed conditions were evaluated as 5 nm and 15 nm, respectively. The light absorption peak of the silver nanoparticles was adjusted to a laser wavelength of 405 nm for an optical disc system. The silver nanoparticles showed a higher absorption characteristic when they were annealed at above 500°C. In the case of a recording mark size of 50 nm, the CNR enhancement of the super-RENS with the silver nanoparticles was evaluated as 11 dB. This method using the silver nanoparticles provided a higher CNR increment in recording marks below the optical resolution limit.

Effects of Solvent and Ambient Humidity on Nanodot Structures for Near-Field Optical Data Storage Using Self-Assembled Diblock Copolymer

We present the formation of nanodot structures on a glass substrate by the self-assembly of a diblock copolymer. The structures can be used as nanopatterned media for near-field optical data storage with high data density. Improvements in the carrier-to-noise ratio (CNR) and in the uniformity of the recorded bit marks are expected with these structures. It is found that the structure of nanodots depends strongly on the ambient humidity during dripping and subsequent spin-casting and also on the solvent used. Nanodots of uniform size can be formed on a glass substrate with benzene, toluene, or toluene blended with acetone as a solvent when the ambient humidity is in the range of 60% to 70%. The size of the individual nanodots as well as the distance between two consecutive nanodots can be controlled, and the nanodots may be aligned like regular hexagonal close-packed structures by adjusting the volume ratio of acetone to toluene.

Signal Characteristics of Super-Resolution Near-Field Structure Disks with 100 GB Capacity

We report the basic characteristics of super resolution near-field structure (Super-RENS) media at a blue laser optical system (laser wavelength 405 nm, numerical aperture 0.85). Using a novel write once read many (WORM) structure for a blue laser system, we obtained a carrier-to-noise ratio (CNR) above 33 dB from the signal of the 37.5 nm mark length, which is equivalent to a 100 GB capacity with a 0.32 micrometer track pitch, and an eye pattern for 50 GB (2T: 75 nm) capacity using a patterned signal. Using a novel super-resolution material (tellurium, Te) with low super-resolution readout power, we also improved the read stability.

Fiber Optical CATV System Performance Improvement by Using Push-Pull Modulated DFB Laser Diodes

A directly modulated AM-VSB CATV erbium-doped fiber amplifier (EDFA)-repeated system that uses push-pull modulated distributed feedback (DFB) laser diodes and half-split-band technique is proposed and demonstrated. Push-pull modulation scheme enhances the frequency response of the laser diode, and thus improves the overall performance of the fiber optical CATV systems. Good performances of carrier-to-noise ratio (CNR), composite second order (CSO), and composite triple beat (CTB) were achieved for the full channel band over a 100-km single-mode fiber (SMF) transport.

Analysis on a new type magneto-optical disk for blue lasers

The conventional TbFeCo magneto-optical (MO) medium has a relatively smaller Kerr rotation angle in the blue region than in the red. With the recording wavelength gradually moving to the short wavelength, if TbFeCo is still used as recording medium, the conventional MO disk structure must be optimized to get a larger carrier to noise ratio (CNR). Sabi et al. have found that adding a metal layer attached to the TbFeCo film as thermal control layer is a useful way to get a high CNR. In this paper, we proved this through calculation, and carried out optimization of the new type of disk. Calculation results showed that the new structure is useful in preventing an excessive temperature increase, and has a better thermal response.

Performance of Multiple High Altitude Platforms using Directive HAP and User Antennas

This paper examines the behaviour of system capacity in High Altitude Platform (HAP) communications systems as a function of antenna directivity and HAP positioning. Antenna models for the user and the HAP are discussed, and it is shown that a flat sidelobe antenna pattern is suitable for modelling multiple HAP constellations when HAPs are located outside the coverage area. Using a single HAP scenario it is shown how narrowing the HAP antenna beamwidth may give better downlink Carrier-to-Noise Ratio (CNR) over the most of the coverage area. The roles of the HAP antenna beamwidth, HAP antenna pointing and HAP spacing radius are investigated. An equation is derived to determine the location of the peak CNR combined with these three parameters. A more complex multiple HAP scenario where all HAP's operate on the same channel and interfere with each other is also assessed in terms of the Carrier to Interference plus Noise Ratio (CINR) and spectral efficiency. It is shown that locating HAPs at a specific spacing radius that is outside the coverage area can improve performance. Using these techniques the combined bandwidth efficiency is shown to increase almost pro-rata when the number of HAPs is increased up to 16.

Improved Performance of Fabry-Perot Laser Diode Transport System with External Light Injection Technique

We use external light injection technique to improve the performance of Fabry-Perot laser diodes. The external light injection technique progresses the performance of carrier-to-noise ratio (CNR), composite second order (CSO), and composite triple beat (CTB) of fiber optical cable television (CATV) system.