Table of Content

20 October 2011 Volume 38 Issue 5

  

Original Articles

Dynamic mode switch algorithm in multi-cell MU-MIMO systems

LI Jiandong;MA Yanjun;LIU Wei;SHI Chao

J4. 2011, 38(5):  1-6.  doi:10.3969/j.issn.1001-2400.2011.05.001

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Based on the interference alignment (IA) method, by cascading the inter-cell interference rejection matrix P before the intra-cell interference rejection matrix, the rates of cell edge users can be improved obviously. However, this method can only be designed for users at a fixed position| however, users are randomly distributed in real cellular systems. So, a dynamic mode switch (DMS) scheme is proposed. The users in a cell calculate a threshold according to its suffered interferences and choose the preferred mode accordingly (IA-MMSE or MF scheme), and opportunistic dispatch is performed at the base stations for two groups. Simulation shows that the DMS scheme can achieve the improved performance of the cell edge users without affecting the rates of the cell center users. At the same time, the rates of the cell edge users are further improved through the optimization of matrix P.

Precoding for MIMO downlinks with imperfect CSI

LI Xinmin;BAI Baoming;TONG Sheng

J4. 2011, 38(5):  7-12.  doi:10.3969/j.issn.1001-2400.2011.05.002

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When the base station knows imperfect channel state information (CSI) with limited estimation errors, the robust precoding scheme based on signal to interference plus noise ratio (SINR) constraints is less feasible. In this paper, a precoding scheme based on signal to leakage plus noise ratio (SLNR) is proposed for MIMO downlinks. By solving a series of semidefinite program (SDP) problems, the proposed design minimizes the total transmitted power under each user's SLNR constraint. At the same time, it can dynamically allocate each user's SLNR threshold according to their channel states, so it is more feasible than the similar SINR-based precoding scheme. In the case of having higher estimation errors for CSI, a channel modification matrix based on the minimum mean square error (MMSE) is used to increase feasibility of the proposed precoding method. Simulation results show that the proposed precoding scheme is robust to channel estimation errors, and can achieve optimal solutions with higher probability. Moreover, it has a better bit error rate performance than similar SINR-based precoding.

Novel method for digital modulation signal identification in the multipath fading channel

LI Yanling;LI Bingbing;YIN Changyi;LIU Mingqian

J4. 2011, 38(5):  13-19.  doi:10.3969/j.issn.1001-2400.2011.05.003

Abstract ( 1459 )   PDF (622KB) ( 1023 )   Save

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Two major drawbacks of digital modulation identification are its low probability of correct classification (Pcc) and difficulty in classifying a variety of digital signal types in the multipath fading channel. Thus, a new blind classification method using the wavelet transform and higher-order cyclostationary cumulants (W-HOCC) is presented, in which a new classification feature is extracted using the linearity property of WT and the Superposition property of HOCC. Through theoretical analysis, it is proved that the extracted feature parameter can eliminate the influence of the multipath channel parameter. Monte Carlo simulation results show that in identification of 2ASK, 2PSK and 4QAM signals the proposed method yields the Pcc of 100% in the multipath fading channel when the signal-to-noise ratio (SNR) is 0dB. Compared with the higher-order cumulants-based method, the W-HOCC method can lead to better identification performance. Also, the W-HOCC method can bring about highly accurate recognition even for a  low SNR.

Novel modulation identification scheme for subcarriers of OFDM signals in the multipath channel

LIU Mingqian;LI Bingbing;ZHAO Lei

J4. 2011, 38(5):  20-26.  doi:10.3969/j.issn.1001-2400.2011.05.004

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In view of modulation identification of subcarriers of orthogonal frequency division multiplexing(OFDM) signals with a pilot in a multipath channel is a difficult problem in the non-cooperation communications system, a novel method for recognition of the subcarriers modulation of OFDM signals is proposed. The method firstly removes the null carrier signals of the OFDM using the combination characteristic of fourth-order and second order cumulants, and then filters out the pure pilot subcarrier signals and some of the modulated subcarrier signals with a pilot by the combination feature of fourth-order and sixth-order cumulants. Finally, it recognizes the modulated subcarrier signals which are less affected by pilots with the improved subtractive cluster method. Simulation results show that the proposed method has robust recognition performance in the multipath channel.

FPGA implementation of a non-binary LDPC decoder using the EMS algorithm

HE Guanghua;BAI Baoming;LI Bo;LIN Wei

J4. 2011, 38(5):  27-33.  doi:10.3969/j.issn.1001-2400.2011.05.005

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Due to the high resources demand during the decoding process of non-binary LDPC codes, a non-binary LDPC decoder based on the EMS (Extended Min-Sum) algorithm is proposed. The messages are updated iteratively in the block unit, and the flooding schedule is utilized in this proposed decoder. To reduce the storage resources and logical resources, the messages are first contracted in length. Then, the resources are multiplexed between the process of check nodes updating and that of variable nodes updating by the time difference. An FPGA chip for decoding an irregular non-binary LDPC over GF(64) of length 1044bit has been developed based on the Xilinx XC4VLX60 FPGA device. Compared to the existing solutions, about 54% storage resources and logical resources can be saved. Meanwhile, the decoding speed and throughput can be greatly improved.

Distributed cooperative routing algorithm for mobile Ad Hoc networks

ZHANG Wansheng;LIU Kai;WANG Li

J4. 2011, 38(5):  34-39.  doi:10.3969/j.issn.1001-2400.2011.05.006

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A distributed throughput-optimized cooperative routing (TOCR) algorithm is proposed to improve network throughput in the mobile Ad Hoc network. Through theoretical analysis, by means of a cooperative relay, the received signal-to-noise ratio (SNR) at a recipient node can be increased, and then the probability of successful packet reception and link throughput are increased. Based on the adaptive forwarding cluster routing (AFCR) algorithm, the TOCR algorithm constructs cooperative links with maximum throughput on a route hop by hop, and finally establishes the route with the maximum throughput from the source node to the destination node. Simulation results show that compared with the noncooperative routing algorithm, the proposed algorithm can obviously improve network throughput, especially in the presence of low transmission power and a large number of nodes.

Research on a novel all IP integrated mobile communication system

HAN Qingmian

J4. 2011, 38(5):  40-45+114.  doi:10.3969/j.issn.1001-2400.2011.05.007

Abstract ( 1017 )   PDF (709KB) ( 997 )   Save

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To solve the problem of network converging and interworking of the traditional mobile communication technique and new developed mobile communication technique based on all IP networks, an IMS-based all-IP integrated mobile telecommunication system is designed, which integrates the digital cluster subsystem, broadband wireless access subsystem and telephony endpoints, and achieves the convergence of multiple access technologies by the uniform mobile switch platform. Besides offering voice and other services on IP, it also supports the development of IP-based new services. This system can satisfy the requirements of normal and emergency telecommunication at the same time. Finally, the feasibility of the system is validated by united tests.

Cooperative spectrum sensing over the constrained control channel in cognitive radio networks

SONG Zhaoxia;ZHOU Zheng;SUN Xuan

J4. 2011, 38(5):  46-51.  doi:10.3969/j.issn.1001-2400.2011.05.008

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This paper presents a multiband joint cooperative spectrum sensing scheme. For the local detection of each frequency band, two thresholds can be calculated according to noise uncertainty and a secondary user can decide whether there are primary users who utilize multiband joint detection. For the uncertain frequency band with its test statistic falling into the two local detection thresholds, the multi-point cooperative spectrum sensing is performed. In this scheme, secondary users transfer the sensing information by utilizing the idle frequency bands, rather than only depending on the common control channel. Analytical and simulation results show that the new scheme can decrease the communication overhead of the common control channel and obtain a smaller miss alarm probability for the uncertain spectrum bands compared to traditional cooperative sensing schemes.

Classification and recognition algorithm for the halftone image

KONG Yueping;ZENG Ping;ZHANG Yuepeng

J4. 2011, 38(5):  52-58+183.  doi:10.3969/j.issn.1001-2400.2011.05.009

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After analyzing the influences of quality on inverse halftoning, the research on how to classify the halftone has gone into our view. Using the Self-correlation Function of one-dimension, the Grey Level Co-ocurrence Matrices(GLCM) and the Grey Run-length Matrices(GLRM) the periodic and texture features of the halftoning image are discovered. Based on these properties a new classification algorithm for usual halftones is proposed. Experimental results indicate that the average rate of correct recognition has reached 99%. The new algorithm not only solves the application problem for Estimated-Inverse-Halftoning, but also makes a basic of design and optimization for inverse halftoning.

Algorithm for extraction of the local region common vector for defect classification

J4. 2011, 38(5):  59-64.  doi:10.3969/j.issn.1001-2400.2011.05.010

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The large differences in texture and shape of the same type cloth and certain similarities between heterogeneous types result in the difficult classification of fabric defects. In this paper, it is proposed to select the fabric defect local region features and use the common vector method to extract features and to do classification. The defect local region features refer to the fabric defect local region gray histogram and geometrical features. First, we detect the fabric defect region by the optimal multiple-channels 2D Gabor wavelet| then select the features of the fabric defect local region gray histogram and geometrical feature (the rate of defect length and width, and the direction feature), and extract the common vector by the common vector algorithm| and finally, use the minimum distance method for defect classification. The algorithm is of small-sample learning, less computational load and high recognition rate.

Novel algorithm for automated detection of fabric defect images

CUI Lingling;LU Zhaoyang;LI Jing;LI Yihong

J4. 2011, 38(5):  65-72.  doi:10.3969/j.issn.1001-2400.2011.05.011

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Considering the advantages that decomposition coefficients in the non subsampled Contourlet of fabric images can describe the contour characteristics in a better way, and that they have shift-invariant and multidirection, a novel algorithm for automated detection of fabric defect images is presented. Firstly, the nonsubsampled Contourlet transform (NSCT) is used to perform the sparse representations in multi-scales and multi-directions. On this basis, the optimal sub-bands of NSCT are selected by the cost function, and then the robust descriptions are obtained. Finally, the parameters of defect and nondefect images are timely estimated separately by the Mixture Gaussian Model(MGM), which effectively avoids estimating each defect and reduces the computational complexity evidently. Experimental results show that the proposed algorithm can lead to a better performance than the traditional algorithms in subjective effects and objective evaluation.

Depth characteristic of the edge pixels based depth estimation method

LIU Xiaoxian;CHANG Yilin;LI Zhibin;YUAN Hui

J4. 2011, 38(5):  73-78.  doi:10.3969/j.issn.1001-2400.2011.05.012

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To improve the depth estimation precision at the object edges, a novel depth characteristic of the edge pixels based depth estimation method(DCE-SADE) is proposed . In the proposed method, based on the depth characteristics of the object edges, the pixels in the image are firstly divided into three categories, and then the corresponding smoothing terms of the matching cost function are derived. Experimental results have shown that compared with the existing edge information based semi-automatic depth estimation method(E-SADE) in the free-viewpoint television (FTV) system, the proposed method can greatly improve the depth estimation precision at the object edges, and that the PSNR of the synthesized virtual view based on the proposed method can be improved to a certain extent with an average of 0.32dB in the receiver of the FTV system.

Optimal credibility spectrum sensing algorithm in cognitive radio networks

XIAO Lin;LIU Kai

J4. 2011, 38(5):  79-84.  doi:10.3969/j.issn.1001-2400.2011.05.013

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The current cooperative spectrum sensing algorithm with typical hard decisions in cognitive radio networks can not improve sensing capability efficiently due to allocating the same weight to secondary users' decisions in data fusion. To solve the problem, this paper proposes a cooperative spectrum sensing algorithm based on sensing credibility (SC-CSS). It gets secondary users' sensing credibility from their average received SNRs, integrates both their independent decisions and sensing credibility to fuse data, and makes a final sensing decision to improve sensing capability. Simulation results show that compared to the cooperative spectrum sensing algorithm with typical hard decisions, SC-CSS has a better receiver characteristic curve (ROC) and can achieve a lower detection error probability by suitably selecting the detecting threshold for secondary users for a low SNR.

Practical Web-oriented fair non-repudiation protocol

SU Ruidan;DING Zhenguo;ZHOU Lihua

J4. 2011, 38(5):  85-89.  doi:10.3969/j.issn.1001-2400.2011.05.014

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Since more and more transaction systems are built using Web technology, users generally work on thin nodes with the browser where users only can access the internet actively and can not be accessed passively. The non-repudiation service implemented currently mostly does not consider the requirement of fairness and the fair non-repudiation protocols to date can not be suitably applied in real environment due to its complexity of interaction. This paper proposes a practical and fair online-TTP non-repudiation protocol which simplifies protocol interaction with the aid of TTP and can be embedded in one round exchange for HTTP request and response. Evidence chaining is introduced to make TTP process centrally simplify evidence verification and management and decrease the cost of certificate revocation checking and time-stamp generation for signatures on the client-side. The protocol owns properties of strong fairness and timeliness.

Novel frequency estimation of MPSK signals in low SNR environment

CUI Yanpeng;HU Jianwei;YANG Shaoquan;WANG Wei

J4. 2011, 38(5):  90-94.  doi:10.3969/j.issn.1001-2400.2011.05.015

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A novel frequency estimation method of MPSK signals in the low SNR condition is proposed, which solves the problem of requiring a high signal-to-noise ratio. First, the AR models are created by using the modern spectrum estimation method, and the small residual frequency offset signal is obtained through rough carrier frequency estimation values of the MPSK signal. Then after the M-th nonlinear transformation, the higher accuracy of the residual frequency offset value is estimated based on the maximum likelihood criterion. Simulation results show that the algorithm can lead to a higher accuracy under the low-SNR condition and that it is stable and reliable.

Fast contour tracking algorithm for human body in infrared images

GAO Jing;XU Jianjun;BI Duyan

J4. 2011, 38(5):  95-100.  doi:10.3969/j.issn.1001-2400.2011.05.016

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A novel algorithm based on the level set is proposed for tracking the precise contour of the human body in infrared videos. The algorithm first adopts the nearest neighbor decision method to construct the velocity expression for the fast level set only in the target region and its neighbor background region but not in the whole image plane, then contour tracking is realized by evolving the zero level set curve using the dynamic neighbor region fast level set algorithm proposed in this paper. Experiments show that this algorithm can adapt to the scale change of the target and the split or mergence of the target, and lead to the exact contour of the human body.

Research on the adaptive load balancing routing algorithm

ZHU Bin;ZENG Xiaoping;CHEN Li;LIAO Hongyun;YAN Fang

J4. 2011, 38(5):  101-107.  doi:10.3969/j.issn.1001-2400.2011.05.017

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The traditional routing algorithms for Ad hoc networks use the minimum hop count as the routing metric, so some central nodes are overloaded and the performance of the networks is degraded. Therefore, an adaptive load balancing routing algorithm based on a gossip mechanism is proposed. This routing algorithm combines the gossip routing mechanism and the load balancing of the network. In the phase of routing discovery, it adjusts the transmission probability in gossip adaptively according to the distributing situation of the nodes and the relative degree of the load in the local area, and lets the nodes with a smaller load join the foundation of the routing preferentially. Simulation demonstrates that this algorithm reduces the routing control overhead remarkably, increases the average packet delivery ratio, and decreases the average end-to-end delay of the data packets, so it is of high practicability.

SAR interference suppression algorithm for narrow band interference via wavelets

ZHANG Shuangxi;ZHANG Lei;GUO Rui;ZHOU Peng;XING Mengdao

J4. 2011, 38(5):  108-114.  doi:10.3969/j.issn.1001-2400.2011.05.018

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The presentation of Narrow-band interference (NBI) usually degrades the imaging quality dramatically. Based on the time-frequency feature analysis of NBI, a new NBI suppression algorithm is proposed by Wavelets transform in this paper. In this algorithm, spectrum of echo corrupted by NBI is transformed into multi-resolution wavelet domain. Then the NBI components can be identified and subsequently filtered out while preserving useful signal as much as possible by constant-false-alarm-rate. In the following, the data after NBI suppression is transformed into the original echo domain. Finally, well-focused SAR imagery can be obtained from the echoes without NBI by traditional SAR imaging algorithm. The loss of the effective data during the operation is smaller than other NBI suppression algorithm. In addition, this algorithm is robust to time-varying NBI. Imaging results of both simulation data and measured data have proved the validity of this algorithm.

Fast algorithm for low-angle direction-of-arrival estimation in VHF radar

LIU Jun;LIU Zheng;XIE Rong;ZHANG Fangfang

J4. 2011, 38(5):  115-120.  doi:10.3969/j.issn.1001-2400.2011.05.019

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Aimed at the problem of low elevation estimation in VHF multipath environment, a fast temporal-spatial sequential algorithm is proposed. The information in both the time domain and frequency domain is applied to improve the direction-of-arrival estimation performance. First, by utilizing the information on range and velocity, which has been achieved in tracking environment, the received data are integrated to form a single sample of the array signal vector. Then, a matrix pencil is constructed by the vector. Finally, the generalized eigen-decomposition is employed to estimate the direction-of-arrival directly. While overcoming the multipath effect, this method avoids the spectrum peak searching and reduces the computational burden. Theoretical analysis and computer simulation results demonstrate the effectiveness of the proposed method.

Research on the geometric correction algorithm for the remote sensing image by a support vector machine

SHE Xiangyang;LI Chonggui;YAO Wanqiang

J4. 2011, 38(5):  121-128+146.  doi:10.3969/j.issn.1001-2400.2011.05.020

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Facing the disadvantages of geometric correction algorithm for the remote sensing image at present,a new algorithm is studied and we put forward the geometric correction algorithm and solving steps for the remote sensing image based on SVM, introduce the SVM theory and approach and adopt the essence theory of the remote sensing image approximate geometric correction. One testing region is selected, the ground control points coordinates and altitudes are surveyed by differential GPS, and the coordinates of the ground control points in the remote sensing image are measured with image processing software. We select a varying number of control points to correct the remote sensing image in the geometrical plain, and use other control points as testing points by the cluster algorithm in all the ground control points. We carry out remote sensing image geometric correction by the approximate geometric correction , the neural network model and the SVM algorithms, analyze and compare correction precision. Algorithm testing show that the algorithm for the SVM has good correction precision and generalizing ability. The algorithm for the SVM supports remote sensing application to develop the quantitative and accurate technique, and enlarges the geometric correction approach.

Integral imaging characteristics based on the virtually curved lens-array

SHEN Xin;WANG Xiaorui;XU Yin;GUO Qiang;CHEN Yujiao

J4. 2011, 38(5):  129-134.  doi:10.3969/j.issn.1001-2400.2011.05.021

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The virtually curved lens-array has become an effective way to improve the image quality of Integral Imaging (II). Based on the principle of the pick-up and reconstruction processes of a typical Virtually Curved Integral Imaging (VCII) system, the optical ABCD matrix theory is utilized to derive the mapping relationship between the three-dimensional object and 3D integral image, and the VCII computational reconstructed image is realized. Then a theoretical model of the elemental image sampling rate is introduced to analyze the relation between the sampling rate and the reconstructed image quality at various depths. Finally, by using the correlation image metric factor, a comparison between the VCII and the conventional II reconstructed image quality is performed, which confirms the advantage of the virtually curved lens-array in improving the integral image quality.

Fast hybrid algorithm for the analysis of transient scattering by 2-D conducting cylinders

QIN Santuan;GONG Shuxi

J4. 2011, 38(5):  135-141.  doi:10.3969/j.issn.1001-2400.2011.05.022

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Transverse Electric(TE) transient scattering by two-dimensional combinative conducting cylinders is investigated by the combination of the time domain integral equation (TDIE) method and the time domain physical optics (TDPO) method. Based on the electric field integral equation (EFIE), the explicit solution of Marching-On-in-Time (MOT) is developed. In this method, the TDPO is applied to the electrically large but smooth cylinder while the TDIE is applied to the electrically small but complicated one. To take account of the interactions between combinative cylinders, the mixed iteration of TDIE/TDPO is introduced. In numerical examples, the induced currents on the surface of conducting cylinders are presented. Numerical results show that in the case of similar accuracy, this hybrid method improves computational efficiency greatly.

Fast iterative method for the synthesis of the base-station antenna's shaped beam

DENG Jingya;ZHANG Xiaomiao;YIN Yingzeng;LIU Qizhong

J4. 2011, 38(5):  142-146.  doi:10.3969/j.issn.1001-2400.2011.05.023

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For the requirements of upper sidelobes suppression and lower null-fills of the base-station antennas' shaped beam, a fast iterative method for the synthesis of a pattern with specified levels of upper sidelobes and lower nulls is studied. Brent's method is used to iterate the extrema's positions with the specified levels of sidelobes and nulls of the power pattern's expression, the factorized expression of the pattern can be obtained according to final positions of zeros, and the coefficient of each term is the excitation coefficient with phase information. This method is much more efficient and consumes much less time than optimization methods which are normally used presently. A 10 unit array's pattern is synthesized using an element, and the pattern is confirmed by the result of HFSS simulation. The performances of upper sidelobes suppression and lower null-fills are good, showing that the iterative method presented in this paper is a fast and useful pattern synthesis method for base station antennas.

Multiple sub-bands analytical model of 2DEG properties in the Al_xGa_1-xN/GaN heterostructure

LIU Hongxia;LU Fengming;WANG Yonghuai;SONG Dajian;WU Yi

J4. 2011, 38(5):  147-151.  doi:10.3969/j.issn.1001-2400.2011.05.024

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To analyze a nitride heterostructure using a simple method, an analytic model is developed for the AlGaN/GaN heterostructure to study two-dimensional electron gas (2DEG) properties. The model is analytical for the energy band, sub-band level and wave function of 2DEG. A comparison of analytical results with complex self-consistent results of the Poisson-Schrodinger equation shows that the complicated numerical calculation and the disadvantage of time-consuming are avoided. We can obtain the variety of 2DEG distribution and sheet density and the shape of the potential well with Al content and thickness of the AlGaN barrier layer using the analytic model.

Low-power BLF genarator for the UHF RFID tag

TANG Longfei;ZHUANG Yiqi;LIU Weifeng;JIN Zhao

J4. 2011, 38(5):  152-158+164.  doi:10.3969/j.issn.1001-2400.2011.05.025

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A novel backscatter link frequency (BLF) generator for UHF RFID transponders which meet the EPC^TM Class1 Generation2 protocol is presented. A control signal is generated when the reader sends the Query command. Then this signal controls an integrator generating a reference voltage which makes a relaxation oscillator output a BLF. This BLF can meet the requirements of the Gen2 protocol. The BLF generator is implemented by the TSMC 0.18μm CMOS process. At the end of this paper, measuremental results show that the circuit power consumption is 0.52μW at the 1V operating voltage. As a result, the tag with the proposed circuit can acquire a longer read range and higher read rates.

Capacitive coupling connector and its signal integrity analysis

QU Yongzhe;LI Yushan;YAN Xu;DING Tonghao

J4. 2011, 38(5):  159-164.  doi:10.3969/j.issn.1001-2400.2011.05.026

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The traditional connectors of the Press-fit style need to plug in each connection, so the insertion force will make pins subjected to wear and kink. To avoid this problem, a novel capacitive coupling connector is presented based on the AC coupling principle in this paper. Two overlapping transmission lines generate coupling capacitance which will make the signal transport from the transmitter to the receiver. The phenomenon of the pins wear and kink are eliminated based on the contact-less of the signal transmission interfaces and zero insertion force. By analyzing the effect of the physical structure of the capacitive coupling connector on the pulse waveform at the receiving end, a strategy for selection of the size of the connector and an equalization method is proposed to reduce the inter-symbol interference and improve the signal transmission rate. Simulation results show that the signal transmission data rates of the capacitive coupling connector is up to 16Gb/s.

Doppler centroid estimation without ambiguity in DBS

ZUO Lei;LI Ming;ZHANG Xiaowei

J4. 2011, 38(5):  165-171.  doi:10.3969/j.issn.1001-2400.2011.05.027

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Doppler centroid, a foundational parameter of Doppler Beam Sharpening (DBS), needs to be estimated from echoes. Traditional estimated methods have a shortcoming of the ambiguity to pulse repetition frequency (PRF). The inaccuracy of Doppler centroid resulting from inertial navigation units measurement errors when resolving the ambiguity declines the quality of an image. A novel method has been proposed in this paper to estimate the Doppler centroid without ambiguity. According to the constant speed rotation of the antenna, from the expression for the coherent echoes, two parameters can be estimated, i.e., initial azimuth angle of the first echo in the coherent echoes, and the product of the velocity of plane and the cosine of elevation angle. Then Doppler centroid of the coherent echoes will be calculated from them without ambiguity. The results of computer simulation and the processing results of real DBS data prove the effectiveness of the processing procedure.

Influences of double-Rayleigh fading on transmission system performance

LI Zhaoxun;HU Hanying;REN Xiukun;CAO Wenkui

J4. 2011, 38(5):  172-177.  doi:10.3969/j.issn.1001-2400.2011.05.028

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Based on statistical properties of the receiving signal-to-noise ratio (SNR), the paper investigates error performance of the transmission system in double-Rayleigh fading. It analyses the outage probability and diversity gains of the system. A generalized formula for the average symbol error rate (ASER) of various M-ary modulations is derived by the moment generating function based approach and closed-form expressions for ASER for binary modulations are obtained. Simulation results show that, compared to Rayleigh fading, the outage performance and ASER in double-Rayleigh fading become worse than those in Rayleigh fading and the information rate is further limited consequently. The full diversity gain of unity in achievable SNR regions is difficult to acquire at the receiver under double-Rayleigh fading conditions. About 3dB SNR losses on system performance are induced by differentially coherent M-DPSK compared to coherent M-PSK.

BEB algorithm model of the probability distribution for the terminal in different backoff stages

XIE Honggang;XIAO Jinsheng;YI Benshun

J4. 2011, 38(5):  178-183.  doi:10.3969/j.issn.1001-2400.2011.05.029

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In the CSMA/CA protocol using the binary exponential backoff algorithm, an effective analytical model of the network collision is proposed for the characteristics of transmission performance with the scale of networks changing. The mechanism for the retry limit of backoff and delay detection is considered, and the whole pattern of queueing networks service for terminals is established in the network, on the basis of which the media access mechanism of the terminal contending for transmission time slot is analyzed after the backoff counter reset, and the expression rate of the network conflict is derived. The model demonstrates the steady state of network transmission, and the probability distributions for the terminal in different backoff stages. Simulation results indicate that the model and the analysis are very effective.

Improved cross-layer AQM algorithm in the mobile WiMAX

SONG Jianfeng;LI Jiandong;LI Hongyan

J4. 2011, 38(5):  184-188.  doi:10.3969/j.issn.1001-2400.2011.05.030

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A cross-layer active queue management scheme in the mobile WiMAX is proposed, in which an active queue algorithm, CHOKe-CRL, is designed. The merits of the traditional CHOKe algorithm and the utilization at the link layer of TCP window variations are both used to enhance the packet drop property of the uplink nodes, which gives a smooth throughput and a good QoS assurance. Experiments show that the CHOKe-CRL algorithm can improve the performance of the uplink nodes under a certain condition.