- EI核心期刊
In order to construct nonbinary low density parity check (LDPC) codes with good waterfall and error floor properties, a method to improve the minimum Hamming distance of a class of nonbinary quasi cyclic (QC) LDPC codes is presented. Two upper bounds on the minimum Hamming distance are derived for the nonbinary QC LDPC codes whose paritycheck matrices consist of weight 2 columns. A special base matrix design allowing linear encoding in a parallel manner is also proposed. In addition, the design principals are given, according to which, the parallel and efficiently encodable codes reaching the upper bound on the minimum Hamming distance can be developed. Simulation shows that the proposed codes have both good waterfall and error floor properties.
Considering pure rolling condition and track stand motion’s characteristics of front bar being vertical to frame，nonholonomic constraints between front wheel’s driving angle velocity and frame’s yaw angle rotational rate are derived，from which dynamic model is built by Lagrange formulation．With partial feedback linearization method，a track stand motion controller is designed，in which the under actuated frame rolling angle is linearized and the whole dynamics are taken as output．Simulation of the controller indicates that，under proper parameters，the track stand motion within ±10° rolling angle can be achieved quickly with a small driving torque．Experiment also validates that，with the proposed controller，the frontwheel drive bicycle robot can realized a small rolling angle range of track stand motion only by front wheel driving torque input．
System performance is studied when employing random vector quantization (RVQ) to qualify limited feedback beam forming for multiple input single output （MISO）system under Nakagami m fading channel, and the closed form of bit error rate and outage probability are derived. The closed form is expanded to the multiple input multiple output （MIMO） system based on receiving antenna selection mechanism. Simulation shows that the results from proposed closed form are consistent with the results of actual system. It verifies that the closed form is correct.
When using ISO standard of perceptual noise substitution (PNS) algorithm in advanced audio coding(AAC), it seems to cause misjudgment when detecting the noise, and results in quality deterioration of coded audio. A new noise detection algorithm is proposed to solve the problem. It employs the characteristic of noise spectrum that is more flat than tone spectrum, and sets the dual threshold for the frames and scaling factor bands to detect the noise accurately. In addition, precoding module is added into the PNS module to further improve the coding efficiency of PNS. Experiments show that, compared with standard algorithm, the proposed greatly did improve the accuracy of noise detection, and obtain higher coding efficiency without any increase in coding complexity.
Using virtual multiple-input single output (MISO) technologies, the performance for cooperative transmission in clustered wireless sensor networks
(WSNs) is studied. The symbol-error-rate (SER) formulas are derived for the phases of intra-cluster broadcasting and inter-cluster cooperative transmission as well as for end-to-end, respectively. Moreover, an effective low bound on the end-to-end SER is proposed. Besides, an optimal power allocation model using the end-to-end SER as constraints is proposed. An efficient method for solving the optimal solution of the model is proposed. Simulation shows that the model has energy-saving advantages under different SER requirements.
In multiplein multipleout (MIMO) broadcast systems with limited feedback, when receivers are equipped with multiple antennas, the socalled quantization error of channel direction matrix will be unavoidably introduced. This quantization error results in the reduction of system capacity since it is referenced in the Precoding design. A robust Precoding method based on minimum mean square error（MMSE） is proposed, which considers the statistical characteristics of the quantization error for channel direction matrix. Simulation shows that the proposed method effectively enhanced system capacity, reduced bit error rate (BER), as well as mitigated the plateau effect.
In order to truly analyze the multipath angle error of the microwave landing system（MLS） receiver, an error research method based on the equivalent replacement of the scanning beaming main lobe is presented. Through the equivalent Gauss replacement of the beam mainlobe of “From” and “To” pulse, the leading and trailing edge error of 3 dB scanning pulses threshold and the anglemeasuring model of microwave landing system are derived. The method is used to calculate the anglemeasuring performance error of the receiver for the special multipath environment. The results of replacement method computation are compared with the computed results of classical model. The new method can overcome the limitation and deficiency of classical model in the exact error calculation. Moreover, the accuracy of results is more improved than the classical model.
For satisfying the diverse needs of nextgeneration networks to access multiclass services, an intelligence call admission control (ICAC) algorithm for uplink multiclass services based on cell systems was proposed. The traffic load is estimated through the traffic statistics and the bandwidth is allocated for the next period by this method; for date services, fuzzy logic is used by this method to allocate bandwidth to date traffic; simulation results show that for dynamical traffic load, the method has better performance in reducing call drop rate and block rate of voice traffic, and decreasing accessing waiting time of date traffic.
By analyzing the multi-hop cooperative cognitive diversity network in underlay sharing(US) mode, an approximate outage probability formulation and diversity order is derived for decode-and-forward(DF) protocol in high signal-to-noise ratio to get theory equations of cognitive transport performance. A good outage performance of cognitive system with the increase of hop number in high signal-to-noise ratio is obtained. Simulation shows that multi-hop DF cooperative cognitive diversity system achieves no more space diversity gain.
Forwarding tendency based fixed path ferry routing algorithm (FTFPF) is proposed for delay tolerant network (DTN) without focusing on how to design reasonable ferry routes. This algorithm can maintain DTN good performance even when ferry nodes move on arbitrary ferry routes. According to different performance requirements of DTN applications (delay sensitive or loss sensitive), FTFPF can adjust its parameters to satisfy these different types of requirements. Simulations show that FTFPF outperforms optimized waypoints (OPWP) algorithm in many aspects, such as the message deliver ratio, the average delay and the average buffer time of messages etc.
The existing trust models for wireless sensor networks seems imprecise when the node credibility presents periodic changes which are affected by nodes’ performance and environment. For that, a subjective trust model based on mixed Gaussian distribution (MGSRM) is proposed. This model builds multiple Gaussian distributions corresponding to different “state”, improves dynamic adaptability of trust values. Current trust value and integrated trust value are separately used to reflect the node credibility under long-term and short-term behavior. A better focus and practicability is obtained. Simulation shows that, compared to existing trust models, MGSRM model has obvious advantages in accuracy, dynamic adaptability and learning ability.
To prolong the lifetime of wireless sensor networks (WSNs), a cross-layer algorithm in terms of physical layer and network layer is proposed. Based on power control in the physical layer, the preliminary candidate sensor nodes for potential transmission are decided. Subsequently, considering the access probability of each sensor node, the per-hop transmission success probability, and the energy efficiency of end-to-end transmission links, an equilibrium routing of network layer is accomplished. Thus the end-to-end communication can be achieved in WSNs. Simulation
result show that the crosslayer strategy can prolong the system lifetime of WSNs with energy efficiency.
A distributed coordination control algorithm is proposed for multi-robot formation with limited communication. The algorithm is inspired by the flocking of animals and the consensus theory. Based on the formation graph and the matrix representation of formation graph, the stability of the formation system is analyzed via the frequency domain method combined with the stable theory. The sufficient and necessary condition is obtained. The multi-robot formation is obtained to get the desired geometry formation and velocity. The relations between the maximum tolerable delay, the parameters, and the eigenvalues of the Laplacian matrix are also investigated through simulations of fourrobot formation verify the effectiveness of formation control strategy and the correctness of the conclusions.
When artificial immune system (AIS) is used in electromagnetism signal monitoring, the monitoring performance is infected because the fluctuation of input parameters is not in the same extent and the extent is changed as the monitoring environment. By introducing variable weight theory, an adaptive variable weighting immune network (AVWIN) algorithm for electromagnetism signal monitoring is presented. The algorithm can adaptively modulate the weight of input parameters according to monitoring environment in order to maximize the signal separating degree. The algorithm has been tested by real wireless signal monitoring data. It is shown that the definition of signal separating degree is reasonable and the algorithm can improve the monitoring performance apparently.
A new scheduling and user pairing algorithm is proposed for the time division high speed uplink packet access (TD-HSUPA) system to address the indoor multi-user in multiple-input multiple-output (MU-MIMO) scenario. The impacts of multi-stream interferences between different receiving antennas and co-channel interference within the same antenna are considered. By admitting different users into different antennas‘ serving user lists, the proposed algorithm can significantly improve average system throughput while maintaining good user fairness. It is suitable to deploy the proposed scheme in practical indoor systems due to its low computational complexity and little additional signaling costs.
A new coded modulation scheme is proposed using fewer constellation points than normal quadrature amplitude modulation (QAM). With properly designed code rate and labeling strategy, it is not necessary to map one to one from bit vectors to channel symbols. Iterative decoding and demodulation of the new scheme could obtain earlier turbo cliff compared with the coded modulation system with normal QAM constellation. As an example, a new constellation is constructed to replace the commonly used 64QAM based on the design rules of such systems. Experiments show the effectiveness of the new scheme.
To analyze the influence of the dynamics of download speed on performance of peer to peer (P2P) video on demand (VoD) streaming systems, a playback interruption model is presented. The model shows that the dynamics of download speed is the main reason of the playback interruption. Both increasing the prefetched content and the download speed can reduce the number of interruptions. However, the former delays the interruption, the latter brings forward the interruption. The interruption may happen frequently in the whole playback process, though with low probability. Through network measurement towards PPLive VoD system, the behavior of the interruption can be verified.
Considering the poor imaging caused by limited inverse synthetic aperture radar (ISAR) echo data of real target, a new super-resolution algorithm based on improved contourlet transform （CT） is proposed to achieve ISAR super-resolution imaging. It is realized by nonsubsampled contourlet decomposition to extract high-frequency information from ISAR echo data in different directions based on scale invariant feature. Then decomposition levels of CT are constructed with the high-frequency information in different directions and raw echoed data. Contourlet reconstruction is used to expand ISAR echo signal in scale. It shows that ISAR image using this method will be with great advantages of reflecting YAK42 airplane information in detail and improving imaging quality over that using interpolation method, which validates the validity of this method.
To reduce the impact of the multi-rate sharing problem on multi-hop wireless networks, combining with the message of the routing process, a cross-layer design method of the channel assignment is proposed based on the rate and the network traffic. It proposes a capacity cost function, and designs an optimized channel assignment model. It reduces the impact of new access service on existing service, while ensuring that the bandwidth requirement of the new service, and then achieves the optimization of the rate and the channel with the routing process at one time. Simulations show that the method greatly improves the network throughput, and saves a lot of protocol overhead.
A dynamic resource allocation scheme is designed to implement user equipment(UE)-centric coordinated multi-point transmission (CoMP) in
long term evolution advanced (LTE-A) system. The decomposition of cooperate resources is used to decouple the resource among the cooperation transmission points, and the random resource allocation is used to reduce the negotiation among the cooperation transmission points. Also，a simplex local scheduling can be implemented with less resource conflict. It is proved by simulation that the scheme can effectively outperforms on both the average sector spectrum efficiency and celledge UEs’ spectrum efficiency.
A cognitive radio (CR) learning and decision making method based on least squares support vector machine (LSSVM) is proposed by the demand of CR intelligent learning research. Genetic algorithm is adopted to search the hyper-parameters of LSSVM, and the CR learning model based on LSSVM is established. Through LSSVM offline learning on historical instances, the CR system gets the knowledge and uses it to guide future decisions. Simulation shows that GA-LSSVM algorithm can find out appropriate hyper-parameters within small generations and the LSSVM learning and decision making method can improve CR system’s performances effectively.
In Rayleigh two-way relay channel, the power allocation problem aiming at minimizing the outage probability for bidirectional communication is investigated under the total power budget constraint. The closed-form solution for the optimal power allocation is developed. It shows that the optimal power allocation scheme always allocates half of the total power for the relay node. Furthermore, the best location for relay node is discussed. It indicates that the best relay location is at the right middle of the two end nodes. It is shown that two-way relay transmission with the optimal power allocation is superior to direct transmission in terms of outage probability.
A new steganalysis algorithm on model-based (MB) steganography is proposed after researching the high order statistics of images. The difference, imported by MB steganography is described by the co-occurrence discrete cosine transform(DCT) matrix, the boundary gradient energy in airspace and the imaginary eigenvalue decomposition. The MB steganography is detected using all of the features and support vector machine. Experiments show that this algorithm has a high accuracy rate of detection with a low false detection rate.
A time-varying channel coefficients of data-directed equalization algorithm (VCC-DDEA) is proposed for single tone narrow-band high frequency communication. The channel coefficient is estimated at each symbol sampling time based on adaptive tracking algorithm. The inter-symbol interface caused by training sequences is eliminated，then the user data is estimated as well based on least sum square error(LSSE) criterion. The demand that the channel coefficients being constant for DDEA in the frame is broken through VCC-DDEA and a conspicuous performance improvement is obtained.
To improve spectral efficiency in cooperative relay system, a cross-layer optimization scheme is proposed, that combines adaptive modulation and coding (AMC) at physical layer with hybrid automatic repeat request (HARQ) at data link layer based on Nakagami-m fading channel. A state transition model is used to analyze and calculate the average packet error rate (PER) of cooperative relay system. To maximize the average spectral efficiency under the constraints of PER and transmission delay, the crosslayer optimization model by using iteration algorithm is solved, and the average PER and spectral efficiency of three types of HARQ protocol is compared. It is shown that the system performance of cooperative relay system is much better than that of non-cooperative relay system. In addition, the cross-layer design scheme combining type-III HARQ can achieve higher spectral efficiency and lower PER than type-I,II HARQ.
An extensive set of full elastohydrodynamic lubrication(EHL) simulation is studied based on shear-thinning rheological model. The correction factor formulae to predict EHL film thickness for space liquid lubricants are developed to account for the effect of shear-thinning behavior. The film thickness is obtained with the correction factor formulae and compared to the published experimental measurements with good agreement under a wide range of operating conditions. It proves that the correction formulae can predict EHL film thickness accurately. Multiplied the corresponding Newtonian film thickness by the correction factor, the EHL film thickness can be easily obtained in practical engineering applications.
Aiming at the Non-preemptive task, the task schedule conditions are derived. Based on the task re-execute-time, the fixed priority and dynamic priority two kinds scheduling algorithm is designed. The performance of non-preemptive earliest-deadline-first fault-tolerant (NP-EDF-FT) non-preemptive rate-monotonic fault-tolerant (NP-RM-FT), non-preemptive fix priority fault tolerant (NP-FP-FT)and non-preemptive dynamic priority fault tolerant (NP-DP-FT)are analyzed as well. It is shown that the NP-FP-FT scheduling tasks have the lowest average invalidation rate.
Hybrid leader based protocol (HLBP) is a media access control layer multicast error control protocol in WLANs. And HLBP can improve multicast performance，but some receivers with bad channel can affect all the other receivers. In allusion to the bottleneck problem, a cooperative hybrid leader based protocol (CHLBP) based on HLBP is proposed. CHLBP send a package in two phases, the base station sends a package in the first phase, and in the second phase some receivers from the receivers which receive the package in the first phase. Therefore, it can reduce the effect of the bottleneck problem and enhance the throughput of the network. Theoretical analysis and simulation results show that cooperative HLBP is reliable for multicast in WLANs. It can reduce the average number of retransmissions per package and improve the throughput of the network.
When measuring network performance characteristics in network topology inference, the time synchronization is needed. Meanwhile, the time network topology inference suffers the limits of network load, so there are more limits when applying network topology inference. In order to conquer the limits, a 4-tuple packets measurement method is put forward that could measure the end to end loss and jitter. An algorithm of computing the correlation between nodes is proposed which combining jitter and end to end loss. The 4-tuple packets measurement and the algorithm of computing correlation are suited for the network of lightly loaded, moderately loaded and highly loaded. The measurement method and topology inference algorithm have less limits than other algorithms.