Amplification effects of the send rate of TCP connection through an optical burst switching network

This paper investigates support for TCP RENO flows in an Optical Burst Switching (OBS) network. In particular we evaluate the TCP send-rate, i.e., the amount of data sent per time unit taking into account the burst assembly mechanism at the edge nodes of the OBS network and burst loss events inside the network. The analysis demonstrates an interesting phenomenon, that we call correlation benefit. This phenomenon is introduced by the aggregation mechanism and can give rise, in some conditions, to a significant increase in the TCP send-rate. These results are obtained by means of an analytical model, based on a Markovian approach, and have been validated via an intensive simulation campaign.     

Electrophilic additions to allenes—II : The reaction of benzeneselenenyl chloride with some 1,3-disubstituted allenes

Benzeneselenenyl chloride reacts with 1,3-dialkyl-substituted allenes in methylene chloride solution to give 1:1-adducts. Attack by selenium is found to occur exclusively at the central allenic carbon. In contrast to the analogous reaction of arenesulphenyl chlorides, the preferential formation of the Z-alkene is observed. A mechanism involving the preequilibrium formation of alkylideneseleniranium ions and/or alkylideneepiselenuranes which, in the product-determining step, collapse to products via an anti attack of chloride at the methine carbon of the ring is proposed to account for the preferential formation of the Z-isomers.     

A subarray-synthesis based 2D DOA estimation method

In some satellite communications, we need to perform Direction Of Arrival （DOA） angle estimation under the restriction that the number of receivers is less than that of the array elements in an array antenna. To solve the conundrum, a method named subarray-synthesis-based Two-Dimensional DOA （2D DOA） angle estimation is proposed. In the method, firstly, the array antenna is divided into a series of subarray antennas based on the total number of receivers; secondly, the subarray antennas＇ output covariance matrices are estimated; thirdly, an equivalent covariance matrix is synthesized based on the subarray output covariance matrices; then 2D DOA estimation is performed. Monte Carlo simulations showed that the estimation method is effective.     

Frequency-Time Block Code for frequency diversity in UWB-OFDM systems

The Ultra-WideBand Orthogonal Frequency Division Multiplexing （UWB-OFDM） approach is a promising physical-layer technique for short-range, high data-rate wireless networks. As the occupied bandwidth increases, however, its implementation becomes more and more difficult. In order to make it easier to achieve a UWB-OFDM system, a complexity-reduced Frequency diversity （F-diversity） scheme, Frequency-Time Block Code （FTBC）, is presented in this paper. The FTBC halves the sampling rate required by other F-diversity techniques so as to cut down the cost of UWB-OFDM systems with F-diversity to a certain extent.     

Ergodic capacity formula of MIMO-OFDM systems under correlated frequency selective Rayleigh fading channels

An explicit formula for the ergodic capacity of Orthogonal Frequency Division Multiplexing (OFDM)-based Multiple-Input Multiple-Output (MIMO) systems under correlated frequency selective Rayleigh channels is derived,by simplifying the channel response matrix in frequency domain into the so-called Kronecker model composed of three kinds of correlations,i.e.multipath tap gain correlation and spatial fading correlations at both transmitter and receiver.The derived formula is very simple and convenient for one to estimate the effects of all three kinds of correlations on MIMO-OFDM capacity.If taps are independent,there is a very simple expression for the ergodic capacity.In case of tap correlation,the capacity formula could be further given in an integral expression.The validity of the new formula is verified and the effects of correlations,delay spread as well as the number of subcarriers on the ergodic capacity are evaluated via Monte Carlo simulations.     

A dual reservation CDMA-based MAC protocol with power control for ad hoc networks

This paper proposes a new multi-channel Medium Access Control （MAC） protocol named as Dual Reservation Code Division Multiple Access （CDMA） based MAC protocol with Power Control （DRCPC）. The code channel is divided into common channel, broadcast channel and several data channels. And dynamic power control mechanism is implemented to reduce near-far interference. Compared with IEEE 802.11 Distributed Coordination Function （DCF） protocol, the results show that the proposed mechanism improves the average throughput and limits the transmission delay efficiently.     

Computer simulation of Rayleigh fading channels in MC-CDMA systems

For Multi-Carrier-Code Division Multiple Access (MC-CDMA) systems,it is usually as- sumed that the fading of the subcarriers is frequency non-selective and independent of each other. This paper shows that the two assumptions are incompatible.In fact,the MC-CDMA signals at each subcarrier undergo fading that are highly correlated.Based on this observation,this paper develops a simulation algorithm for Rayleigh fading channels via frequency-domain correlation function,which incorporates the Doppler effect simultaneously.Numerical examples are presented to demonstrate the effectiveness of the new algorithm,with the conclusion that the independence assumption of subcar- rier fading overrates the system performance.     

ITERATIVE "ONE-SHOT" DECORRELATION IN DS-CDMA SYSTEMS

In this paper, an iterative "one-shot" decorrelator for asynchronous code Division Multiple Access(CDMA) systems is proposed. This decorrelator feedbacks the decorrelated symbols of interfering users before decision to mitigate their interferences. As a result, this decorrelator is a linear detector and does not need any amplitude information of users as in decision-feedback detectors. Compared with existing "one-shot" decorrelator, it has reduced complexity and provided better performance while eliminating all Multiple Access Interference(MAI). The performance of this decorrelator is analyzed thoeritically, and analytical result is given. Numerical results show near-far resistant capability of this decorrelator in both AWGN and fading channel.     

Normal subgroups of are not finitely generated

As a generalization of Wedderburn's classic theorem, it is shown that the multiplicative group of a noncommutative finite dimensional division algebra cannot be finitely generated. Also, the following conjecture is investigated: An infinite non-central normal subgroup of cannot be finitely generated.

     

一种快速换频的小数分频频率合成器

本文提出一种新的频率合成器,它通过引入一种新的脉冲频率鉴频器和采用小数分频技术,使得其具有换频速度快,并不需要附加小数分频补偿电路等优点.文章给出了这种合成器的原理框图,分析了它的性能,并列出部分实验结果.