WANG Jian, YANG Xun, LI Dao-ben
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60192-2
Abstract ( 3168 ) PDF (277 KB)( 392 )
This article proposes a time/frequency synchronization algorithm in the multiple input multiple output (MIMO) systems, in which the perfect complete generalized complementary orthogonal loosely synchronous code groups are used as the synchronization sequence. The synchronization algorithm is divided into four stages: 1) synchronization in time domain by signal autocorrelation; 2) synchronization in frequency domain by fast Fourier transform (FFT); 3) multipath dissociation using coherent detection and fine time synchronization; 4) fine frequency offset estimation by phase rotation. As per the perfect complete generalized complementary orthogonal loosely synchronous code groups, the cross-correlation and out-of-phase auto-correlation for any relative shift between any two codes is always zero. This ideal property makes the time/frequency synchronization algorithm simple and efficient. The simulation results show that even in the multipath fast fading channel with low signal noise ratio (SNR), the MIMO system can get synchronized both in the time domain and frequency domain with high stability and reliability.
JIANG Hui, LI Dao-ben
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60193-4
Abstract ( 2857 ) PDF (330 KB)( 432 )
A technique named overlapped frequency-time division multiplexing (OVFTDM)) is proposed in this article. The technique is derived from Nyquist system and frequency-time division multiplexing system. When the signals are compactly overlapped without the orthogonality in time domain, the technique is named overlapped time division multiplexing (OVTDM), whereas when signals are compactly overlapped without the orthogonality in frequency domain, the technique is called overlapped frequency division multiplexing (OVFDM). To further improve spectral efficiency, the OVFTDM in which signals are overlapped both in frequency domain and in time domain is explored. OVFTDM does not depend on orthogonality whatever in time domain or in frequency domain like Nyquist system or OFDM system, but on the convolutional constraint relationship among signals. Therefore, not only the spectral efficiency but also the reliability is improved. The simulations verify the validity of this theory.
HUANG Jing, WANG Ying, WU Tong, YU Xin-min
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60194-6
Abstract ( 2233 ) PDF (317 KB)( 423 )
Cooperative relaying techniques can greatly improve the capacity of the multiple input and multiple output (MIMO) wireless system. The transmit power allocation (TPA) strategies for various relaying protocols have become very important for improving the energy efficiency. This article proposes novel TPA schemes in the MIMO cooperative relaying system. Two different scenarios are considered. One is the hybrid decode-and-forward (HDF) protocol in which the zero-forcing (ZF) process is operated on relays, and the other is the decode-and-forward (DF) protocol with relay node and antenna selection strategies. The simulation results indicate that the proposed schemes can bring about significant capacity gain by exploiting the nature of the relay link. Additionally, the proposed TPA scheme in the HDF system can achieve the same capacity as the equal TPA with fewer relay nodes used. Finally, the capacity gain with the proposed schemes increases when the distribution range of relay nodes expands.
DU Juan, KANG Gui-xia, ZHANG Ping
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60195-8
Abstract ( 3133 ) PDF (234 KB)( 391 )
This article investigates transmitter design in Rayleigh fading multiple input multiple output (MIMO) channels with spatial correlation when there are channel uncertainties caused by a combined effect of channel estimation error and limited feedback. To overcome the high computational complexity of the optimal transmit power allocation, a simple and suboptimal allocation is proposed by exploiting the transmission constraint and differentiating a bound based on Jensen inequality on the channel capacity. The simulation results show that the mutual information corresponding to the proposed power allocation closely approaches the channel capacity corresponding to the optimal one and meanwhile the computational complexity is greatly reduced.
YANG Rui-zhe, YUAN Chao-wei, TENG Ying-lei, ZHANG Yan-hua
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60196-X
Abstract ( 2887 ) PDF (202 KB)( 435 )
A threshold setting scheme is proposed based on the resource management and limited feedback theory in multiuser orthogonal frequency division multiplexing (OFDM) systems. In adaptive resource allocation, the factors denoting the quality of service (QoS) and fairness are both considered as the user weight. From the aspect of feedback outage probability, the proposed algorithm sets the threshold for each user related to its weight, which brings enough feedback to the user with greater weight. Analysis and simulation results show that, compared with the threshold ignoring weights, the proposed scheme has much lower feedback load while with better QoS.
YANG Cheng, ZHOU Zheng, WANG Shu-bin, ZOU Wei-xia
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60197-1
Abstract ( 2951 ) PDF (274 KB)( 374 )
To suppress the side-band interferences caused by multiband orthogonal frequency division multiplexing (MB-OFDM)-based cognitive radio systems, a mathematical expression of the side-band signal is derived. Based on this expression, the constraints among the transmitted symbols, which help to suppress the interferences, are obtained. Combined with the constraints, a type of block Turbo code modulation scheme is proposed. In the modulation scheme, the side-band interferences are attenuated quickly. Compared with other techniques, in this scheme, the interference suppression is implemented more easily and sufficiently. Simultaneously, the bit error rate (BER) performance can be improved. Theoretical analyses and simulation results show that it is highly applicable for MB-OFDM-based cognitive radio systems to suffer from Rayleigh fading.
JIN Li-biao, LI Jian-zeng
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60198-3
Abstract ( 2870 ) PDF (358 KB)( 389 )
Double-correlated channels commonly occur due to insufficient scattering around both the transmitting and receiving antennas. In this article, the authors propose a linear precoding strategy with a modified system model over double-correlated channels. In this system model, an inner decorrelation strategy is added combined with precoding. First, a linear precoder that achieves minimum bit error rate (MBER) is proposed and analyzed based on the modified system model. The simulation results show that the bit error rate （BER） performance can be improved by decorrelation. Second, the influence of double correlation on multiple input and multiple output (MIMO) capacity is analyzed and simulated.
WANG Yang-zhi, XU Cheng-qian
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60199-5
Abstract ( 2882 ) PDF (109 KB)( 378 )
Zero correlation window (ZCW) or zero correlation zone (ZCZ) sequence can be used in quasi-synchronous code division multiple access (QS-CDMA) system to eliminate multiple access and multipath interferences. However, as the length of ZCW or ZCZ increases, fewer sequences are available. Recently, a new concept, sequence set with group-wise zero correlation window is introduced, which can increase the number of available sequences for a QS-CDMA system. In this article, a new method for generating sequence set with group-wise zero correlation window is presented. This method is based on a Hadamard matrix of size N×N and a pair of Hadamard matrices of size M×M. Compared with previous methods, the proposed sequence set has a group-wise zero correlation window for both periodic and aperiodic cross-correlation functions.
QI Yuan, PENG Tao, WANG Wen-bo, LUO Shi-feng
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60202-2
Abstract ( 2256 ) PDF (282 KB)( 367 )
Embedding specific signatures in transmitted signals for identifying common control channels of cognitive radio are addressed in research laboratories because availability of the spectrum occupied by the common control channel might change in time. A novel solution to embed a unique cyclostationary signature for the common control channel of cognitive radio is proposed in this article. Based on linear periodically time-variant transformation (LPTV) model, the cyclic autocorrelation expression of the proposed signature is derived, which characterizes its cyclostationarity. Analysis of the cyclostationary signature is presented considering effects of additive white Gaussian noise (AWGN) and multiplath channels. Simulation results illustrating the reliability of signatures are given.
LI Xi, JI Hong
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60200-9
Abstract ( 3228 ) PDF (318 KB)( 447 )
Peer-to-peer technologies have attracted increasing research attention with fruitful protocols and applications proposed for wired networks. As to mobile environments, there are currently no mature deployments. A novel resource managing and discovering protocol, Cheer, is proposed to realize scalable and effective peer-to-peer lookup in wireless self-organized networks. Cheer resolves the topologies mismatch problem between peer-to-peer overlay networks and actual nodes distribution, allowing for frequent nodes membership changes. With specially designed resource storage table, Cheer also supports multikey and fuzzy lookup. Its hybrid architecture and improved routing scheme based on small-world theory may realize effective lookup routing. Theoretical analysis and simulation results both prove that Cheer makes using peer-to-peer applications in large-scale self-organized mobile networks feasible and promising.
JIANG An-you, ZHU Jin-kang
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60201-0
Abstract ( 2123 ) PDF (146 KB)( 407 )
This article proposes a novel nonlinear network code in the GF(2m) finite field. Different from previous linear network codes that linearly mix multiple input flows, the proposed nonlinear network code mixes input flows through both multiplication and exponentiation in the GF(2m). Three relevant rules for selecting proper parameters for the proposed nonlinear network code are discussed, and the relationship between the power parameter and the coding coefficient K is explored. Further analysis shows that the proposed nonlinear network code is equivalent to a linear network code with deterministic coefficients.
LI Chun-xi, CHEN Chang-jia
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60203-4
Abstract ( 2213 ) PDF (288 KB)( 395 )
Conventionally, P2P video is regarded as CBR traffic. However, our measurements have shown that the rate reset cannot be neglected in a practical IPTV system because each rate reset often leads to performance degradation. Thus, addressing the problem of inferring playback rate and rate reset in a P2P video system is significant. In this article, an algorithm termed piecewise linear envelope approximation (PLEA) is proposed, in which a follow-up time is introduced to smooth rate fluctuations in a small time scale and to adapt rate jumps in a large time scale automatically. With the PLEA algorithm, discontinuity introduced by blind segmentations adopted by current methods is avoided. Furthermore, unlike existing algorithms in which both segmentation and combinations are performed in multiple runs, only a single computation path is involved in the PLEA algorithm. This makes PLEA algorithm amenable to implementation of low complexity by either software or hardware. Both theoretical analysis and experiment based on measured data show that the PLEA outperforms existing algorithms based on segmentation.
ZHANG Deng-yin, JIANG Juan, ANANI Adi, LI Hai-bo
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60204-6
Abstract ( 2097 ) PDF (248 KB)( 511 )
To guarantee the quality of service (QoS) of a wireless network, a new packet scheduling algorithm using cross-layer design technique is proposed in this article. First, the demand of packet scheduling for multimedia transmission in wireless networks and the deficiency of the existing packet scheduling algorithms are analyzed. Then the model of the QoS-guaranteed packet scheduling (QPS) algorithm of high speed downlink packet access (HSDPA) and the cost function of packet transmission are designed. The calculation method of packet delay time for wireless channels is expounded in detail, and complete steps to realize the QPS algorithm are also given. The simulation results show that the QPS algorithm that provides the scheduling sequence of packets with calculated values can effectively improve the performance of delay and throughput.
WANG Xiao-fen, DONG Qing-kuan, ZHOU Yu, XIAO Guo-zhen
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60205-8
Abstract ( 2161 ) PDF (125 KB)( 380 )
McCullagh-Barreto key agreement protocol and its variant achieve perfect forward security and key generation center (KGC) forward security, but provide no resistance to key compromise impersonation attack (KCI attack). In this paper, we give a formal treatment of key compromise impersonation (KCI) attack and define the security notion against it. Then an variant of McCullagh-Barreto protocol is presented with only one more Hash operation. The improved protocol preserves perfect forward security and KGC forward security, and furthermore is proved to be secure against KCI attack under k-Gap-BCAA1 assumption.
DAN Yong-ping, ZOU Xue-cheng, LIU Zheng-lin, HAN Yu, YI Li-hua
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60206-X
Abstract ( 2225 ) PDF (331 KB)( 466 )
In this article, a parallel hardware processor is presented to compute elliptic curve scalar multiplication in polynomial basis representation. The processor is applicable to the operations of scalar multiplication by using a modular arithmetic logic unit (MALU). The MALU consists of two multiplications, one addition, and one squaring. The two multiplications and the addition or squaring can be computed in parallel. The whole computations of scalar multiplication over GF(2163) can be performed in 3 064 cycles. The simulation results based on Xilinx Virtex2 XC2V6000 FPGAs show that the proposed design can compute random GF(2163) elliptic curve scalar multiplication operations in 31.17 μs, and the resource occupies 3 994 registers and 15 527 LUTs, which indicates that the crypto-processor is suitable for high-performance application.
CHEN Chun-ling, YU Han, LÜ Heng-shan, WANG Ru-chuan
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60207-1
Abstract ( 2058 ) PDF (128 KB)( 396 )
The modified version of Yahalom protocol improved by Burrows, Abradi, and Needham (BAN) still has security drawbacks. This study analyzed such flaws in a detailed way from the point of strand spaces, which is a novel method of analyzing protocol’s security. First, a mathematical model of BAN-Yahalom protocol is constructed. Second, penetrators’ abilities are restricted with a rigorous and formalized definition. Moreover, to increase the security of this protocol against potential attackers in practice, a further improvement is made to the protocol. Future application of this re-improved protocol is also discussed.
JIN Jin, WANG Hong-xiang, JI Yue-feng
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60208-3
Abstract ( 2991 ) PDF (144 KB)( 371 )
The article proposes a network parameter-awareness (NPA) method and applies it to routing discovery algorithms in autonomic optical Internet. This NPA method can perceive the main parameters of the network, such as delay, jitter and traffic, which can represent the current situation of the network. And these parameters enable network to determine the appropriate nodes for routing discovery. The simulation results of evaluating performance of a network with NPA method and its routing applications show that the method and its applications in routing improve the performance of the network significantly with quality of service (QoS) guaranteed.
TIAN Hong-da, YU Zhong-yuan, HAN Li-hong, LIU Yu-min
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60209-5
Abstract ( 2894 ) PDF (321 KB)( 489 )
Using a full-vector finite-difference time-domain (FDTD) method, this article explores the propagation characteristics of photonic crystal fiber (PCF) theoretically. The dependence of structural parameters on the effective index of the fundamental guided mode, effective index of the fundamental cladding mode, mode field diameter, confinement loss, effective mode area, and chromatic dispersion in PCF have been studied, respectively. The research presents a reference for designing of PCF with a specific purpose.
LI Bin, LEE Kuei-jen, CHOU Hsi-tseng, HUANG Shan-guo, GU Wan-yi
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60210-1
Abstract ( 2244 ) PDF (390 KB)( 408 )
Circular-polarization discrimination appears in many antennas’ applications. A compensation approach based on multilayer film structure is proposed to improve the axial ratio of the magnitude of the two perpendicular modes of the lump ports. The goal is to widen the beamwidth of radiation that has an axial ratio less than 3 dB and thus reducing the complexity at the receiver. A transfer matrix method was developed to represent the multilayer film and characterize its performance. Simulation using high frequency structure simulator shows that a crossed dipole, as an example, can achieve a beamwidth of more than at the frequency of 12.45 GHz after compensation. Finally, conclusions and future work about this compensation method are presented.
LIU Xin, GUO Shu-xu, CHANG Yu-chun, ZHU Shun-dong, WANG Shuai
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60211-3
Abstract ( 2312 ) PDF (284 KB)( 503 )
This article presents a control strategy based on simple digital pulse-width modulation (DPWM) and pulse-skip modulation (PSM) for a DC-DC boost converter, to drive a luminance-regulated white light emitting diodes (WLEDs). The presented control strategy not only retains most of the advantages and flexibilities of traditional digital PWM, but also reduces complexity and cost. Based on analyzing the principle of the presented control strategy, the white light emitting diode (WLED) driver is designed and simulated using the 0.6 m CMOS process. Simulation results of the boost converter show that the power efficiency is above 76% for a full load, with a peak efficiency of 88% when supply voltage varies from 2.7 V to 5.5 V. The control strategy overcomes low efficiency for PWM mode with light load.
LI Zhi-cheng, LIU Tao, ZHANG Yong-jun, GU Wan-yi
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60212-5
Abstract ( 2868 ) PDF (236 KB)( 390 )
This article presents an efficient rate control scheme for H.264/AVC video coding in low bit rate environment. In the proposed scheme, an improved rate-distortion (RD) model by both analytical and empirical approaches is developed. It involves an enhanced mean absolute difference estimating method and a more rate-robust distortion model. Based on this RD model, an efficient macroblock-layer rate control scheme for H.264/AVC video coding is proposed. Experimental results show that this model encodes video sequences with higher peak signal-to-noise ratio gains and generates bit stream closer to the target rate.
XIAO Peng, HU Zhi-gang
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60213-7
Abstract ( 2248 ) PDF (290 KB)( 411 )
The advance reservation technique has been widely applied in many grid systems to provide end-to-end quality of service (QoS). However, it will result in low resource utilization rate and high rejection rate when the reservation rate is high. To mitigate these negative effects brought about by advance reservation, a relaxed advance reservation policy is proposed, which allows accepting new reservation requests that overlap the existing reservations under certain conditions. Both the benefits and the risks of the proposed policy are presented theoretically. The experimental results show that the policy can achieve a higher resource utilization rate and lower rejection rate compared to the conventional reservation policy and backfilling technique. In addition, the policy shows better adaptation when the grid systems are in the presence of a high reservation rate.
REN Hong, ZHENG Yan, WU Ye-rong
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60214-9
Abstract ( 2293 ) PDF (128 KB)( 432 )
In this article, a clustering method based on genetic algorithm (GA) for telecommunication customer subdivision is presented. First, the features of telecommunication customers (such as the calling behavior and consuming behavior) are extracted. Second, the similarities between the multidimensional feature vectors of telecommunication customers are computed and mapped as the distance between samples on a two-dimensional plane. Finally, the distances are adjusted to approximate the similarities gradually by GA. One advantage of this method is the independent distribution of the sample space. The experiments demonstrate the feasibility of the proposed method.
LU Jian-guo, CAI An-ni
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60215-0
Abstract ( 2194 ) PDF (436 KB)( 398 )
This article presents a novel people-tracking approach to cope with partial occlusions caused by scene objects. Instead of predicting when and where the occlusions will occur, a part-based model is used to model the pixel distribution of the target body under occlusion. The subdivided patches corresponding to a template image will be tracked independently using Markov chain Monte Carlo (MCMC) method. A set of voting-based rules is established for the patch-tracking result to verify if the target is indeed located at the estimated position. Experiments show the effectiveness of the proposed method.
ZHANG Ya-jun, WANG Cui-ping, WANG Guang-yi, XU Ning, WANG Zhong-lin
The Journal of China Universities of Posts and Telecommunications, 2009, 16 (2). doi： 10.1016/S1005-8885(08)60216-2
Abstract ( 2152 ) PDF (1110 KB)( 490 )
To generate complex pseudo-noise (PN) sequences for chaos-based communications, this article presents a novel switched hyperchaotic model, which is constructed based on a modified Chen system by introducing a dynamical controller. The system consists of two different hyperchaotic subsystems and can change its behavior randomly via a switching function. Basic dynamical behaviors of the hyperchaotic system are further investigated. Furthermore, the switched system is confirmed by its positive Lyapunov exponents and laboratory measurements by an electronic circuit.