1,721,101 research outputs found
A METADATA-BASED VIDEO-ON-DEMAND TRAFFIC CONTROL OVER THE NETWORK SUPPORTING BANDWIDTH RENEGOTIATIONS
No full textIn this paper, we study an effective video-on-demand traffic control algorithm using the metadata over the network supporting bandwidth-renegotiations. The proposed algorithm includes bandwidth smoothing. bandwidth-burstiness estimation and rate adaptation algorithms. The proposed video-on-demand server has not only video database but also metadata database that includes coding information of the compressed video in video database and the traffic burst characteristics with respect to control parameters of the bandwidth smoothing algorithm. Thus, we can predict the traffic properties accurately with a low computational complexity by using the stored metadata, and then determine the efficient bandwidth renegotiating variables such as the renegotiating instants and the required bandwidth in terms of network utilization and video-on-demand service quality. In addition, we present a rate adaptation algorithm that pursues an effective trade-off between spatial and temporal qualities of the decoded video to improve the perceptual video quality when the bandwidth request is rejected.open112sciescopu
Simultaneous Frequency Conversion Technique utilizing an SOA-MZI for Full-Duplex WDM Radio over Fiber Applications
No full textSimultaneous all-optical frequency up/downconversion technique utilizing a single semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) for full-duplex WDM radio over fiber (RoF) applications is presented. Using this technique, error-free simultaneous up-conversion and downconversion of RoF signals with a finite-length single mode fiber were experimentally demonstrated. The results show the potential of the proposed scheme for use in a cost-effective full-duplex WDM RoF link.1137sciescopu
Simultaneous All-optical frequency downconversion technique utilizing an SOA-MZI for WDM radio over fiber (RoF) applications
No full textSimultaneous all-optical frequency-downconversion technique utilizing a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) is experimentally demonstrated, and its application to a wavelength-division-multiplexing (WDM) radio over fiber (RoF) uplink is proposed. The conversion efficiencies from 22.5 (f(RF)) to 2.5 GHz (f(IF) = f(RF) - 2f(LO)) are in the range from 1.5 to 3 dB for the optical RF wavelength between 1548 and 1558 nm. Error-free simultaneous all-optical frequency downconversion of the two WDM RoF upstream channels that carry 155-Mb/s differential phase-shift keying data at 22.5 GHz to an optical intermediate frequency signal having the frequency of 2.5 GHz with,the power penalty less than 0.1 dB at the bit error rate of 10(-8) is achieved.112026sciescopu
On-Wafer Noise Figure Measurement at 300 GHz Using UTC-PD As Noise Source
No full textWe demonstrate on-wafer noise measurement based on the Y-factor technique at 300 GHz utilizing a uni-traveling-carrier photodiode (UTC-PD) as a noise source. Since the UTC-PD can provide high and scalable noise power for the hot state and has a waveguide output port, easy and reliable measurement is available even at terahertz frequencies, where the loss from the experiment setup is not ignorable. We describe the experimental procedure with the UTC-PD as a noise source and a diode mixer as a noise receiver and present a noise figure measurement for a 300 GHz amplifier MMIC in an on-wafer environment. In addition, we discuss the uncertainty due to using the UTC-PD.1111sciescopu
Present and Future of Terahertz Communications
No full textRecent changes in how people consume multimedia services are causing an explosive increase in mobile traffic. With more and more people using wireless networks, the demand for the ultra-fast wireless communications systems is increasing. To date, this demand has been accommodated with advanced modulation schemes and signal-processing technologies at microwave frequencies. However, without increasing the carrier frequencies for more spectral resources, it may be quite difficult to keep up with the needs of users. Although there are several alternative bands, recent advances in terahertz-wave (THz-wave) technologies have attracted attention due to the huge bandwidth of THz waves and its potential for use in wireless communications. The frequency band of 275 similar to 3000 GHz, which has not been allocated for specific uses yet, is especially of interest for future wireless systems with data rates of 10 Gb/s or higher. Although THz communications is still in a very early stage of development, there have been lots of reports that show its potential. In this review, we will examine the current progress of THz-wave technologies related to communications applications and discuss some issues that need to be considered for the future of THz communications.11392390Nsciescopu
RATE CONTROL FOR LOW-BIT-RATE VIDEO VIA VARIABLE-ENCODING FRAME RATES
No full textA novel rate-control algorithm with a variable-encoding frame-rate method is proposed in this work for low-bit-rate video coding. Most existing rate-control algorithms for low-bit-rate video focus on bit allocation at the macroblock level under a constant frame-rate assumption. The proposed rate-control algorithm is able to adjust the encoding frame rate at the expense of tolerable time-delay, The new rate-control algorithm attempts to achieve a good balance between spatial quality and temporal quality to enhance the overall human perceptual quality at low bit rates. It is demonstrated that the rate-control algorithm achieves higher coding efficiency at low bit rates, with a low additional computational cost. The proposed variable-encoding frame-rate method is compatible with the bit-stream structure of H.263(+).X1173sciescopu
EFFECTIVE QUALITY-OF-SERVICE RENEGOTIATING SCHEMES FOR STREAMING VIDEO
No full textEffective quality-of-service renegotiating schemes for streaming video is presented. The conventional network supporting quality of service generally allows a negotiation at a call setup. However, it is not efficient for the video application since the compressed video traffic is statistically nonstationary. Thus, we consider the network supporting quality-of-service renegotiations during the data transmission and study effective quality-of-service renegotiating schemes for streaming video. The token bucket model, whose parameters are token filling rate and token bucket size, is adopted for the video traffic model. The renegotiating time instants and the parameters are determined by analyzing the statistical information of compressed video traffic. In this paper, two renegotiating approaches, that is, fixed renegotiating interval case and variable renegotiating interval case, are examined. Finally, the experimental results are provided to show the performance of the proposed schemes.open11sciescopu
A REGION-BASED H.263+CODEC AND ITS RATE CONTROL FOR LOW VBR VIDEO
No full textThis paper presents a region-based video codee, which is compatible with the H.263+ standard, and its associated rate control algorithm for low variable-bit-rate (VBR) video. The proposed region-based coding scheme is a hybrid method that incorporates traditional block DCT coding as well as object-based coding. To achieve this, we adopt H.263+ as the platform, and develop a fast macroblock-based segmentation method to implement the new region-based codec. The associated rate control solution includes rate control in three levels: encoding frame selection, frame-layer rate control and macroblock-layer rate control. The goal is to improve human visual perceptual quality at low bit rates. The efficiency of the proposed rate control algorithm applied to the region-based H.263+ codec is demonstrated via several typical test sequences.X1133sciescopu
Compact THz LTCC Receiver Module for 300-GHz Wireless Communications
No full textA compact, low-cost, fully-integrated package solution has been developed for 300 GHz short-range communication systems. Using low-temperature co-fired ceramic (LTCC) technology, an integrated reflector for the on-chip antenna and high-data-rate signal interconnections including a flip-chip and via transition are embedded in a package. A reduced-size silicon lens antenna is placed in a package cavity together with a flip-chip bonded receiver IC with an on-chip antenna. The overall size of the front-end receiver is only 10 x 10 x 4mm(3), including the 6 mm diameter silicon lens. This compact terahertz receiver, mounted on an evaluation board, demonstrated wireless links with data rates up to 27Gb/s.1198sciescopu
Laminated metamaterials flat lens at millimeter-wave frequencies
No full textA flat and thin shape is obviously advantageous not only in terms of reducing the volume of a device, but also in handling and using it. Particularly, laminating or stacking flat devices is an intuitive and straightforward way of tailoring performance and functions. Here, we experimentally demonstrated a laminated flat lens for millimeter-wave frequencies that is based on split-ring resonators (SRRs) composed of multiple layers with different and/or identical index profiles and that exhibits characteristics that are linear combinations of those of the individual lenses. Since the characteristics of the lenses of each layer are preserved regardless of the neighbouring layers, the desired functionalities can be easily implemented simply by laminating elementary lenses designed already. When we laminated two lenses designed for bending or focusing incoming waves at 120 GHz, we clearly observed that the outgoing waves collimated and bended as desired. (C) 2015 Optical Society of America112Nsciescopu
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