The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60095-7
Abstract ( 1943 ) PDF (0 KB)( 237 )
Power allocation (PA) plays an important role in capacity improvement for cooperative multiple-input multiple- output (Co-MIMO) systems. Many contributions consider a total power constraint (TPC) on the sum of transmit power from all nodes in addressing PA problem. However, in practical implementations, each transmit node is equipped with its own power amplifier and is limited by individual power constraint (IPC). Hence these PA methods under TPC are not realizable in practical systems. Meanwhile, the PA problem under IPC is essential, but it has not been studied. This paper extends the traditional non-cooperative water-filling PA algorithm to IPC-based Co-MIMO systems. Moreover, the PA matrix is derived based on the compound channel matrix from all the cooperative nodes to the user. Therefore, the cooperative gain of the IPC-based Co-MIMO systems is fully exploited, and further the maximal instantaneous capacity is achieved. Numerical simulations validate that, under the same IPC conditions, the proposed PA scheme considerably outperforms the non-cooperative water-filling PA and uniform PA design in terms of ergodic capacity.
江帆 ,FAN Jiu-lun ,CHANG Zhi-xian
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60096-9
Abstract ( 1717 ) PDF (0 KB)( 182 )
A novel network protocol, enhanced cooperative medium access control (ECoop MAC), is present in this article. Its function is to guarantee the quality of service (QoS) in wireless local area networks. For the sake of supporting different application scenarios, two proposed schemes, namely E-scheme I for lower priority traffic and E-scheme II for higher priority traffic can be adopted independently or in combination. ECoop MAC takes into account request failure problems, and utilizes cooperative protocol information to boost the system performance as well as to effectively cut control packets overhead. Simulation results show that the proposed algorithm can not only improve network throughput, but also lead to reduced network delays for individual packets.
LU Yang , GUO Wen-bin, WANG Xing, WANG Wen-bo
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60097-0
Abstract ( 1599 ) PDF (0 KB)( 201 )
This paper presents a probabilistic greedy pursuit (PGP) algorithm for compressed wide-band spectrum sensing under cognitive radio (CR) scenario. PGP relies on streaming compressed sensing (CS) framework, which differs from traditional CS processing way that only focuses on fixed-length signal’s compressive sampling and reconstruction. It utilizes analog-to-information converter (AIC) to perform sub-Nyquist rate signal acquisition at the radio front-end (RF) of CR, the measurement process of which is carefully designed for streaming framework. Since the sparsity of wide-band spectrum is unavailable in practical situation, PGP introduces the probabilistic scheme by dynamically updating support confidence coefficient and utilizes greedy pursuit to perform streaming spectrum estimation, which gains sensing performance promotion progressively. The proposed algorithm enables robust spectrum estimation without the priori sparsity knowledge, and keeps low computational complexity simultaneously, which is more suitable for practical on-line applications. Various simulations and comparisons validate the effectiveness of our approach.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60098-2
Abstract ( 1656 ) PDF (0 KB)( 220 )
A hybrid system of cellular mode and device-to-device (D2D) mode is considered in this paper, where the cellular resource is reused by the D2D transmission. With the objective of capacity maximization, the power optimization of D2D sub-system is considered, taking into account quality of service (QoS) requirement. The power optimization problem is divided into two stages: The first stage is the admission control scheme design based on the QoS requirement of D2D users, and the second is power allocation to maximize aggregate throughput of admissible D2D users. For the D2D admission control problem, a heuristic sorting-based algorithm is proposed to index the admissible D2D links, where gain to Interference ratio (GIR) sorting criterion is used. Applying an approximate form of Shannon capacity, the power allocation problem can be solved by convex optimization and geometric programming tools efficiently. Based on the theoretical analysis, a practical algorithm is proposed. The precision can reach a trade-off between complexity and performance. Numerical simulation results confirm that combining with GIR sorting method, the proposed scheme can significantly improve the D2D system's capacity and fairness.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60099-4
Abstract ( 1463 ) PDF (0 KB)( 174 )
In this paper, a block mapping spatial modulation (BMSM) scheme is proposed to increase the transmit rate of multiple-input multiple-output (MIMO) wireless communication systems. In the BMSM scheme, the information to be transmitted is mapped into different combinations of transmit antenna indices and distinct constellation symbols at each time instant. Multiple transmit antennas are activated, which is different from spatial modulation (SM) and generalised spatial modulation (GSM) techniques, and also the information bits to be mapped to the digital constellation diagram exploits block mapping in the BMSM scheme. The multiplexing gain is obtained and the transmit rate is increased. The simulation results for some cases of channel states are presented which verifies the efficiency of the proposed BMSM scheme.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60100-8
Abstract ( 1671 ) PDF (0 KB)( 189 )
The performance of transmit diversity (TD) assisted amplify-and-forward (AF) relay system with partial relay selection, which experiences mixed Rayleigh and Rician fading channels, is investigated. We first investigate the closed-form expression of the cumulative distribution function for the end-to-end equivalent signal-to-noise ratio (SNR), and then the exact expressions of outage probability and average symbol error probability (SEP) are derived. The theoretical observations are verified by the Monte Carlo simulation results.
ZHANG Cai-hong ，GUO Li
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60101-X
Abstract ( 1772 ) PDF (0 KB)( 205 )
In this paper, we consider the downlink channel of multi-user multi-input single-output (MU-MISO) system in cognitive radio network, where the cognitive base station (CBS) resort to beamforming scheme to relief co-channel interference. The design criterion is to minimize the transmit power at CBS, subject to the signal-to-interference-plus-noise-ratio (SINR) constraints of cognitive users (CUs) and the interference constraints at primary users (PUs). Standard conic optimization packages can handle the problem, however, the complexity is very high and optimization packages are not always available. Basing on the karush–kuhn–tucker (KKT) conditions of the converted optimization problem, we proposed an iteration algorithm. Simulation results reveal that the proposed algorithm can converge to the optimal beamforming vectors that lead to minimum transmit power with all constraints satisfied.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60102-1
Abstract ( 1587 ) PDF (0 KB)( 203 )
This paper investigates the performance of a two-way amplify-and-forward (AF) relay system with adaptive modulation over independent and non-identical Nakagami-m fading channels. The tight closed-form cumulative distribution function (CDF) expression of the instantaneous end-to-end signal-to-noise ratio (SNR) is provided. Further, approximate closed-form expression for the average spectral efficiency of the two-way AF system with adaptive modulation is obtained. Then, a tight lower bound of outage probability is derived. Finally, we use numerical simulations to verify the tightness of our analytical results.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60103-3
Abstract ( 1576 ) PDF (0 KB)( 154 )
A new quasi-orthogonal space-time block code (QO-STBC) scheme, based on eigen value decomposition (EVD), is explored in this paper. The new scheme can significantly reduce the QO-STBC decoding complexity at receiver and achieves better bit-error rate (BER) performance as well. With EVD manipulations, the detection matrix and the channel matrix can be redefined to remove all interference terms which come from other antennas, and therefore the conventional maximum likelihood (ML) decoding method with less complexity can be applied. Moreover the new scheme improves the BER performance significantly. Theoretical analysis and simulation results are presented in this paper to show the validation of this new scheme.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60104-5
Abstract ( 1609 ) PDF (0 KB)( 166 )
Non-line-of-sight (NLOS) propagation is a major source of error for accurate time-of-arrival (TOA) location estimation. The two-step least square (LS) method, which does not need any information about the distribution of the NLOS error, has been studied in related researches to provide efficient location estimation of the mobile terminal (MT). By observing the estimation of the error covariance matrix in the two-step LS method, this paper finds that the measured distances are more suitable than the initial estimated distances by maximum likelihood (ML) algorithm in NLOS environments. Moreover, by making use of the geometry relations among fixed terminals (FTs), some measured distances which are corrupted by big NLOS errors may be reduced. Further, an iteration method can be adopted to further improve the performance of the algorithm. Accordingly, an improved algorithm based on the two-step LS method is proposed. Simulation results demonstrate that the improved algorithm has better performance than the two-step LS method and converges more quickly. Meanwhile, it is robust in different NLOS environments
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60105-7
Abstract ( 1648 ) PDF (0 KB)( 164 )
To improve the scalability and reduce the implementation complexity of Mesh and Mesh-like networks, the semi-diagonal Torus (SD-Torus) network, a regular and symmetrical interconnection network is proposed. The SD-Torus network is a combination of a typical 2D-Torus network with two extra diagonal links from northwest to southeast direction for each node. The topological properties of SD-Torus networks are discussed, and a load balanced routing algorithm for SD-Torus is presented. System-C based simulation result shows that, compared with diagonal Mesh (DMesh), diagonal Torus (DTorus) and XMesh networks, the SD-Torus network can achieve high performance with a lower network cost. It makes the SD-Torus network a powerful candidate for the high performance interconnection networks.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60106-9
Abstract ( 1706 ) PDF (0 KB)( 177 )
Quality of service (QoS) routing algorithms have been hardly discussed in the scientific community, most previous work on QoS routing concentrates on the performance of the single route. Cognitive packet network (CPN) has been designed for providing QoS routing. In this paper, to balance the loads among networks, we present a multi-path routing algorithm based on load-balance (MPRLB), which is carried out in two steps. The algorithm with low computational complexity is firstly applied to establish multi path routing for each source and destination node pairs (SD-pair) nodes in the network. Then, we propose the hopfield neural network algorithm, which is applied to improve the efficiency of the flow deviation method for fast flow allocation among the links of the network based on load balance. Extensive simulation results demonstrate that the proposed scheme significantly improves the performance compared with the existing scheme that ignores load balancing.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60107-0
Abstract ( 1600 ) PDF (0 KB)( 190 )
In peer-to-peer (P2P) video on demand (VoD) system, once the P2P downloading rate cannot satisfy the need of playback, server is quickly referred to for help in providing enough bandwidth. Thus the switch of downloading from other peers (P2P) and server (HTTP) exists. This paper uses the proportion of P2P downloading amount (PPDA) during the video watching process to measure server load. This article is interested in finding a better strategy or switch rule between P2P and HTTP downloading for saving server bandwidth. The authors suggest and model a kind of switch rule based on local buffer amount, using mathematical theory of Brownian motion. It can effectively alleviate the impact of P2P rate fluctuation, reduce the switch times and improve the PPDA by at least 3%–5% on the basis of the former switch rule, which means substantial cost can be saved. Particularly the PPDA is related with the ratio of playback bit rate to the HTTP downloading rate which means the PPDA can be restricted by controlling the ratio in the real-world system. Though the result comes from constant bit rate (CBR) video supposition, it provides perspective and method for variable bit rate (VBR) application, and valuable insights for the future development of P2P VoD system.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60108-2
Abstract ( 1616 ) PDF (0 KB)( 158 )
Network virtualization is considered as a powerful way to deploy different network architectures and protocols over a shared physical infrastructure. Virtual network (VN) embedding plays an important role in the network virtualization environment. Virtual network embedding is mainly about mapping virtual nodes and virtual links onto the physical network resources efficiently. However, load balancing of substrate network has not received much consideration. This paper proposes an adaptive virtual network mapping algorithm based on status feedback. The main contribution is to embed the virtual network requests according to the current load distribution of substrate network. This adaptive algorithm differentiates the residual bandwidth of substrate links and takes full advantage of the multi-path to improve the load balancing of the substrate network. Simulation experiments show that the proposed algorithm improves the load distribution of substrate network distinctly while reducing the average substrate link stress significantly.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60109-4
Abstract ( 1693 ) PDF (0 KB)( 180 )
Cascading failures are common in most of the networks, where traffic is rerouted to bypass malfunctioning routers, eventually leading to an avalanche of overloads on other routers that are not equipped to handle extra traffic, which can result in a congestion regime with degradation in the network performance. In order to investigate how a small shock can trigger avalanches mechanisms affecting a considerable fraction of the network, lots of failure models have been constructed, but they have focused only on the static properties of the network that can not reflect the performance affected by the avalanche exactly. In this paper, we proposed a simple model for cascading failures in the network to explore how the failures can have a great impact on the network performance, and we allocated every node a capacity by tolerance parameter based on the node importance , which is determined by node degree, the number of the shortest paths through a node, and the number of the shortest paths through the neighbors of a node, then we fixed every element a weight to compute the node importance by analytic hierarchy process (AHP) theory. Based on our model, we analyzed the influence of different types of attacks to the network performance, and also tabled some proposals for reducing the damage that the networks suffered from the cascading failures.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60110-0
Abstract ( 1612 ) PDF (0 KB)( 144 )
This paper demonstrates the limitation of the traditional multi-fractal wavelet model (MWM). Through analyzing the multi-resolution behaviors of the real video traffic, we propose an improved MWM model. It synthesizes the traffic traces using another wavelet basis, and can adjust wavelet coefficients and multiplicative coefficients at each time scale, based on the network measurement. Subsequently, multifractal spectra and queue performances of the new model have been analyzed. The simulation proves it can capture the multifractal behaviors of network traces.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60111-2
Abstract ( 1625 ) PDF (0 KB)( 251 )
A point stabilization scheme of a wheeled mobile robot (WMR) which moves on uneven surface is presented by using fuzzy control. Taking the kinematics and dynamics of the vehicle into account, the fuzzy controller is employed to regulate the robot based on a kinematic nonlinear state feedback control law. Herein, the fuzzy strategy is composed of two velocity control laws which are used to adjust the speed and angular velocity, respectively. Subsequently, genetic algorithm (GA) is applied to optimize the controller parameters. Through the self-optimization, a group of optimum parameters is gotten. Simulation results are presented to show the effectiveness of the control strategy.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60112-4
Abstract ( 1653 ) PDF (0 KB)( 199 )
The long time-delay often exists in industrial process. In order to overcome the big overshoot and long regulating time of the long time-delay system control, a new fuzzy self-adaptive PI-Smith control method is proposed. This method combines the Smith predictive control with fuzzy self-adaptive proportional-integral (PI) control. The traditional proportional-integral-derivative (PID) controller in Smith predictive control is replaced by fuzzy PI controller which utilizes the principle of fuzzy control to tune parameters of PI controller on-line. The results of simulation for electric furnace show that the method has the advantages of shortening regulating time, no overshoot, no steady-state error, excellent control accuracy, and good adaptive ability to the change of system model.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60113-6
Abstract ( 1795 ) PDF (0 KB)( 168 )
Power analysis has been a powerful and thoroughly studied threat for implementations of block ciphers and public key algorithms but not yet for stream ciphers. Based on the consumed power differences between two neighboring clock cycles, this paper presents a correlation power analysis (CPA) attack on the synchronous stream cipher DECIMv2 (the tweaked version of the original submission DECIM). This attack resynchronizes the cryptographic device ceaselessly with many different initialization values (IVs) to obtain enough power traces. Then by modeling the statistical properties of the differential power traces with the correlation coefficients, the proposed attack algorithm can completely reveal the secret key of DECIMv2. Furthermore, a simulation attack is mounted to confirm the validity of the algorithm. The results show that the entire secret key of DECIMv2 can be restored within several minutes by performing 12 CPA attacks. It seems that there are still some defects in the design of DECIMv2 and thus some further improvements should be made to resist the proposed attack.
The Journal of China Universities of Posts and Telecommunications, 2011, 18 (5). doi： 10.1016/S1005-8885(10)60114-8
Abstract ( 1851 ) PDF (0 KB)( 180 )
In this paper, a novel four-way radial waveguide power divider with low insertion loss and high power-handling capacity is proposed. This power divider consists of an input coaxial waveguide, a central probe, a radial waveguide, four equispaced identical coupling probes, four equispaced identical adjusting posts and four output coaxial waveguides. The novel coupling probes and the adjusting posts are used to realize favorable uniform power division. A power divider with the center frequency of 4.1 GHz is designed, fabricated and measured. Good agreement between simulation and experiment is noted. The measured 15 dB return-loss bandwidth of the power divider is about 600 MHz. The measured 0.5 dB insertion loss bandwidth is wider than 700 MHz. The differences and isolations between the output ports are also discussed. The power-handling capacity of the power divider is analyzed through simulation, and the result proves its usability in high power applications.