Header Length Research Articles

Improved Subset Difference Method with Ternary Tree

This paper proposes a ternary subset difference method (SD method) that is resistant to coalition attacks. In order to realize a secure ternary SD method, we design a new cover-finding algorithm, label assignment algorithm and encryption algorithm. These algorithms are required to revoke one or two subtrees simultaneously while maintaining resistance against coalition attacks. We realize this two-way revocation mechanism by creatively using labels and hashed labels. Then, we evaluate the efficiency and security of the ternary SD method. We show that the number of labels on each client device can be reduced by about 20.4 percent. The simulation results show that the proposed scheme reduces the average header length by up to 15.0 percent in case where the total number of devices is 65, 536. On the other hand, the computational cost imposed on a client device stays within O(log n). Finally, we prove that the ternary SD method is secure against coalition attacks.

CFD modeling of shell-and-tube heat exchanger header for uniform distribution among tubes

Several different designs for a header type were numerically studied to achieve uniform distribution of gas phase flow in the header of a shell-and-tube heat exchanger. The different geometries included the position and shape of the inlet nozzle, number of outlet tubes, and length. In numerical calculations, the k-epsilon realizable turbulent model was employed. Standard deviation was used to evaluate the uniformity of the velocity distribution among the whole outlets of the header. As a result, flow patterns in the header could be visualized by using post-processing of numerical results. The uniformity of flow distribution increased with header length, whereas it decreased with gas flow rate. Furthermore, the optimum position and shape of the inlet nozzle could be proposed for a uniform distribution of a 1.3 m-length header, the very same used for the heat exchange of the commercially viable allyl chloride process.

Optical header recognition using time stretch preprocessing

We propose and demonstrate the time stretch optical header recognition technique where a high speed header is extracted and slowed down by more than an order of magnitude, in optical domain, to facilitate the capture and processing in electronic domain. The technique can be implemented in continuous time or discrete time. Both implementations are experimentally demonstrated for stretching a 10 Gb/s header by a factor of 20. Eye diagrams and Q values are generated to evaluate the quality of stretched headers. While both implementations are capable of slowing down the header bit rate, each method has its own advantages and disadvantages in terms of bandwidth, maximum header length, latency, and sensitivity to the sampling clock jitter.

Does header length affect performance in optical burst switched networks?

Feature Issue on Next-Generation WDM Network Design and Routing (WDMN). We investigate the effect of nonnegligible header length (HL) in optical burst switching on blocking probability. The HL is the total delay of a control packet at the controller. We first develop a model that explicitly presents the distribution of offset times as a function of the HL. Next we argue that the variance of this distribution (and not the mean) affects the blocking probability. In particular, the total blocking probability of a burst is dominated by the blocking on its last link, where its offset is shortest. We derive a lower bound for a HL threshold value below which blocking is not sensitive to the reservation algorithm. This threshold depends on network connectivity, number of channels per fiber, and burst length. The blocking probabilities of both the just enough time and the horizon reservation algorithms were empirically found not to be very sensitive to the distribution of burst sizes.

The effect of low SNR in phase estimation in wideband CDMA

In wideband code-division multiple-access (CDMA) systems, where large diversity gains are used to mitigate the effects of multipath fading, system performance is increasingly limited by channel estimation error. In a packet-based system, the estimation error can be reduced by increasing the header length; however this, for a fixed bandwidth, reduces the amount of transmit energy available to the data symbols and reduces the processing gain of the system. To determine the allocation of the transmit energy between the data and estimation symbols in order to minimize the probability of bit error, we use an approximate upper bound on the probability of bit error for a RAKE receiver operating with imperfect phase estimates.

Multiple-bit-rate clock recovery circuit: theory

The multiple-bit-rate clock recovery circuit has been recently proposed as a part of the communications packet switch. All packets must be the same length and be preceded by the frequency header, which is a number of consecutive ones (return-to-zero mode). The header is compared with the internal clock, and the result is used to set output clock frequency. The clock rate is defined by a number of fluxons propagating in ring oscillator, which is a close circular Josephson transmission line. The theory gives a bit rate bandwidth as a function of internal clock frequency, header length and silence time (maximum number of consecutive zeros in the packet).

The HIPERLAN equalizer ASIC complexity and its relationship with the training header

In this document, an attempt is made to estimate the size of the HIPERLAN equalizer ASIC by extrapolating from existing adaptive equalizer ASICs and making certain assumptions regarding the process and methodology used to design the HIPERLAN equalizer. Two scenarios are considered, first, an equalizer using the LMS algorithm every baud to update the tap coefficients and second, an equalizer using an RLS algorithm performing a set of updates every ten baud intervals. It was discovered that the computational complexity of both approaches are within the same order of magnitude, however, the LMS ASIC will occupy at most half the size of its RLS counterpart. The smaller IC will reduce the overall system cost at the expense of the longer convergence time required by the LMS algorithm. The paper also demonstrates that when the overall packet processing delay is taken into account, the slower-converging and cheaper LMS type equalizer will actually produce faster turn-around times for short packets than its RLS counter part. Thus, a new training header length is suggested that would allow vendors some flexibility in choosing the structure that best suites their product.

Artificial-lung design: sheet-membrane units.

An overall design analysis is presented for oxygenators with sheet-membrane blood channels. Those types considered are clear channels without and with transverse mixing and woven-mesh filled channels with thick and thin membranes. The analysis accounts for oxygen-transfer rates and increased flow resistance produced by the screens and for such fabrication variables as blood header length, header-thickness-to-channel-height ratio, and blood-screen void volume. For reasonable priming volumes, practical channel lengths and total widths, oxygenators having screen-filled channels with thick membranes or clear channels without mixing are only suitable for partial adult or neonatal support. Adult total bypass is feasible with screen-filled channel designs using thin or highly permeable membranes. Since the configuration of existing clear channel devices with secondary mixing (e.g. Couette or Taylor-vortex types) usually involves a single and relatively thick channel, they are restricted to neonatal or partial bypass applications despite their inherent high transfer efficiencies.

Artificial lung design: tubular membrane units.

The overall design of tubular membrane oxygenators is considered for three blood conditions: that of a normal adult, haemodiluted adult and new-born. Variations in blood viscosity and oxygen transfer due to the Fahraeus-Lindquist effect are taken into account as well as fabrication variables, including blood header length, potted tube length and packing density of the tubes. For a laminar rectilinear flow, 50 mm Hg≤pressure drop≤200 mm Hg, and practical fabrication parameters, there exists a range of tube diameters from 150 μm to 200 μm which give a minimum priming volume and small blood distribution (header) area. The analysis indicates that, with current construction techniques, low-pressure loss oxygenators are not feasible for adult total-bypass requirements. Such units can be practicable if transfer rates are increased with secondary mixing of the blood. For example, a threefold increase in the transfet rate reduces priming volume and header area by 50% of the unmixed flow values.