Abstract:Under the assumption of noncircular signals, the conventional linear beamforming technique only utilizes the covariance matrix of the observation vector from the antenna array. However, in the area of modern communication, many artificial modulation signals have noncircularity property, i.e., the observation vector not only has the covariance matrix but also has the conjugated covariance matrix. The WL beamforming technique is proposed as a new technique under the scenario of noncircular signals, which is achieved by defining an extended observation vector consisted by the observation vector and its conjugated version, and obtaining a extend weight vector after constructing an objective function and constraints. In contrast with the conventional beamforming technique, the WL beamforming technique for the reception of noncircular signal has an obvious improvement. In recent years, the WL beamforming technique has been the focus of research at home and abroad. In this paper the definitions of circular and noncircular are introduced, the array model, the minimum variance distortionless response beamformer and various WL beamforming algorithms are presented. Finally, the future research directions are prospected.

Abstract:With the rapid increase of wireless devices and the openness of wireless communication, the security problem becomes more and more serious and challenging. Different from traditional key-based cryptography schemes, physical layer security has been proposed to realize unconditional security from the information theory perspective. This paper provides a review of the model of physical layer security built by Shannon and tracks the evolution of security schemes without key leaded by Wyner and secret key-based secrecy schemes leaded by Maurer. Among them, the former aims at widening the channel quality gap between the authorized user and the eavesdropper; while the latter using the wireless channel as a nature random source exploiting the channel characteristics. In the coming fifth generation mobile communication scheme, physical layer security can match it with a lightweight security technology which avoids the long delay in the traditional cryptography. Although the theoretical studies of physical layer security have become maturity, they still face many practical problems to be solved in practical.

Abstract:Both digital fountain codes and network coding are efficient technologies for improving transmission efficiency of the networks. Network fountain codes, which are the combination of these two technologies, are of great importance in both theories and applications. In this paper, the development of digital fountain codes and network fountain codes are overviewed. Firstly, the recent research progress of digital fountain codes is surveyed, and the researches of some typical types of digital fountain codes are introduced. Secondly, the current researches on network fountain codes are summarized. The related theories and the latest research achievements of homogeneous network fountain codes, heterogeneous network fountain codes and wireless network fountain codes are introduced, while the existing problems of current researches are discussed. Finally, the development trend of network fountain codes concerning both theories and applications are analyzed and expected.

Abstract:The problem of joint collaborative relay beamforming and linear receiver design is addressed for uplink multi-user relay network where each user transmits independent data streams to a multi-antenna basestation through a decentralized relay network. Two dfferent but related design approaches are proposed with different dsign criteria. In the first approach, the total transmit power of al the relay nodes is minimized under individual SINR constraint. In the second approach,the minimal SINR is maximized subject to the aggegate power constraint on the relay nodes. The optimal linear receivers are derived for each collaborative relay beamforming vector, and the collaborative bemforming vectors are explicitly obtained. We show that both joint optimization problems can be reformulated into a standard semi-definite programming problem by performing relaxation on the feasible region. The resulting problem can be solved optimally by using the interior-point method.

Abstract:The problem of joint collaborative relay beamforming and linear receiver design is addressed for uplink multi-user relay network where each user transmits independent data streams to a multi-antenna basestation through a decentralized relay network. Two dfferent but related design approaches are proposed with different dsign criteria. In the first approach, the total transmit power of al the relay nodes is minimized under individual SINR constraint. In the second approach,the minimal SINR is maximized subject to the aggegate power constraint on the relay nodes. The optimal linear receivers are derived for each collaborative relay beamforming vector, and the collaborative bemforming vectors are explicitly obtained. We show that both joint optimization problems can be reformulated into a standard semi-definite programming problem by performing relaxation on the feasible region. The resulting problem can be solved optimally by using the interior-point method.

Abstract:In this paper, we consider computationally efficient direction of arrival (DOA) estimation for monistatic multiple-input multiple-output (MIMO) array. The computational loads of the propagator method (PM) can be significantly smaller since the PM does not require any eigen-value decomposition of the cross correlation matrix and singular value decomposition of the received data. DOA estimation for the MIMO array using PM and reduced-dimension transformation is proposed, and the proposed algorithm has less computational complexity than PM. The proposed algorithm works well without spectrum searching. Furthermore, the proposed algorithm still has slightly angle estimation performance than PM. The variance of the estimation error and Cramér-Rao Bound (CRB) of DOA estimation are derived. Simulation results verify the usefulness of the proposed algorithm.

Abstract:A low computational complexity blind channel identification algorithm based on FFT was proposed for short burst signal. This algorithm was expoliting the property of the MCR algorithm only requiring minimum redundancy information to obtain the channel vector,then made the linear equations established by MCR algorithm through FFT to get the channel vector, a fast order estimation algorithm was proposed by expoliting the rank information of matrix .The simulation proved that the proposed algorithm could overcome the shortcoming of the traditional identification algorithms in condition of small observed data and reduce the computational complexity of the original FFT-based algorithm with improved robustness to order.

Abstract:This paper studies a codebook based limited feedback transmission scheme for downlink multiuser massive MIMO system. We propose a 3D MIMO codebook design method based on Kronecker product of codewords in both the horizontal and vertical domains with focusing on two vertical codebook design. We make simulation analysis for our proposed 3D MIMO codebook with reasonable scheduling scheme. Simulation shows that our proposed 3D MIMO codebook significantly improves the system spectral efficiency and throughput performance compared with 2D codebook and traditional 3D MIMO DFT codebook.

Abstract:Co-channel interference must be suppressed in Uplink multiuser MIMO system. In this paper, an algorithm based on the criterion of maximizing signal to interference and noise ratio was proposed to suppress multiuser interference, and the improved algorithm in the presence of channel estimation error was also provided. In comparison with BD algorithm, The algorithm taked into account the influence of noise, and the performance had greatly improved. Then a method of reconstructing signals was proposed to employ Alamouti space-time coding in uplink multiuser MIMO system for the reason of further improving the detection performance. Finally aimed at limitations of algorithms with the near-far effect, an optimization algorithm of grouping users was proposed to ensure that each user can achieve the acceptable capacity. Simulation shows that the proposed algorithms achieve good performance.

Abstract:In this paper a new algorithm is proposed for detecting and mitigating NLOS error in a TOA based wireless positioning system. Received signal strength (RSS) is employed to detect whether a TOA value contains NLOS error and mitigate it. When the relationship between TOA and RSS in LOS situation is known, a possibility of NLOS can be calculated using the TOA RSS measurement results which are provided by a base station. Then the TOA measurement results can be trimmed using the possibility mentioned above. Finally, the algorithm is implemented in a wireless positioning system. Experiment results show that the algorithm can mitigate the effect of NLOS.

Abstract:For the issue of resource opportunistic scheduling in Orthogonal Frequency Division Multiple Access (OFDMA) systems with multimedia services supported，a resource scheduling algorithm of Minimum Performance Guarantee (MPG) based on Quality of Service (QoS) constraints was proposed. On the Basement of the opportunistic scheduling idea which was used to maximize the total throughput of the system, this paper realized the fair subcarrieres allocation among the services and guaranteed the QoS constraints of the services by designning the parameter of subcarrieres scheduling acording to the QoS constraints of services, and by using the method which solve the maximal weighted bipartite matching problem in graph theory. The simulation results show that the proposed algorithm can availably increase the total throughput of the system under guaranteeing a minimum rate constraints of every services.

Abstract:Mainlobe of regular beamforming changes with frequency and spatial direction. In order to achieve constant mainlobe in both frequency and steering domain, a wideband Frequency-Steering Invariant Beamforming (FSIB) algorithm based on constrained optimization is proposed. Firstly steering invariant constraints on reference frequency are realized, and then frequency invariant constraints on different mainlobe directions are realized. Finally constraints are transformed to standard Second-Order Cone Programming (SOCP) forms and solved with SeDuMi. A wideband DOA estimation method using FSIB is also proposed. Simulations show the proposed FSIB algorithm can realize constant mainlobe on different frequencies and directions. Compared with method using Frequency Invariant beamforming (FIB), DOA estimation using FSIB has better performance in resolution and accuracy.

Abstract:In this paper, a multi-objective particle swarm optimization (MOPSO) with an initial non-inferior solution from maximizing directivities of conformal antenna array is proposed to get Pareto optimal solutions for desired multi-beam and low sidelobes. The proposed algorithm first uses multi-objective decomposition strategy to get a non-inferior solution by the weighted linear combination of multiple single-beam optimal solution. Then, the local search strategy based on the particle space and target space constraints at the same time in MOPSO is designed to achieve optimization of multi-beam and sidelobes. Results indicate that the approach can effectively get Pareto optimal solutions for multi-beam forming with low sidelobes of the satellite conformal array antenna.

Abstract:In this paper, the estimation of hybrid position for mixing GMSK signals is researched，and a iterative algorithm base on parameter estimation and hybrid position estimation is proposed. Considering the differences of mixed and non-mixed part in frequency and amplitude, the frequency and amplitude can be estimated by zero-crossing and extreme points estimation, and then, each sampling point is mixed or not can be judged. The hybrid origin is correspond to relative time delay, when the delay is large , the parameter estimation will be better when using the non-mixed part data. The CRLB(Cramer-Rao lower bound) for onset estimation of the mixing signals is also researched, the simulation shows that, the proposed algorithm has high precision but less data, can be use in burst mode ,and it shows good robustness to different parameters.

Abstract:Recently, multidimensional scaling (MDS) algorithms have been verified to be robust for the mobile localization. However, they have not attained Cram?r-Rao lower bound (CRLB), even though the measurement noise is small. In this paper, a novel complex MDS method is proposed for time-of-arrival based mobile location. Unlike the existing MDS algorithms depending on the eigendecomposition of the scalar product matrix, the proposed method relies on the complex matrix and contains more information. We decompose a complex distance matrix using eigenvalue factorization and get a better performance. Computer simulations are included to contrast the estimator performance with several kinds of position methods.

Abstract:Nowadays, communication service under low SNR is developing. To achieve lower computing expense and better precision of the carrier synchronization system under low SNR, a new frequency and phase estimation algorithm is suggested. The received signal is firstly processed by FFT operation; carrier estimation model based on maximized trigonometric interpolating result of FFT spectrum is built. Precise estimating results of frequency and phase are achieved by resolving the model. Implement of the algorithm is also proved to reduce computing expense. Simulations indicate that the algorithm not only has high precision which approaches CRB bound closer, but also has low SNR threshold. Compared with Rife and Quinn Algorithm, the algorithm requires almost equal computing expenses but has much higher precision. Compared with three-spectrum technique, the algorithm has slight higher precision but requires only half computing expense. When compared with iterative carrier estimation algorithms, the algorithm has approximate precision but requires much fewer computing expense and processing delay.

Abstract:The algebra algorithm solving the linear combination characteristic of delayed m-sequence is discussed. Based on analysis of linear relationship between status of the central m-sequence and the delayed sequence, a new algorithm, which solves the multiplex problem of delayed m-sequence is given by taking advantage of linear equations over binary finite field. Application of this algorithm in the design of the mask of the N-CDMA mobile communication system is discussed. This algorithm provides a convenient way in solving the multiplex problem of long m-sequence in engineering calculation.

Abstract:A concatenated scheme combining short length Luby Transform(LT) codes with traditional error correcting codes is proposed for the requirement of short erasure correcting codes in real-time communication. Considering the complexity and overhead of the scheme, Reed Solomon-Convolution coding(RS-CC) is used for the construction of equivalent erasure channels, and the short LT codes are concatenated for the correction of erasure errors. A decoding algorithm is proposed for the short LT codes, and the degree distribution selection method is shown for small message length. Simulation results demonstrate that, comparing with the existing codes, less overhead is needed and the reliability of the concatenated scheme is enhanced.

Abstract:In the multiple-input multiple-output(MIMO) system with limited feedback, traditional multiuser scheduling algorithm only takes account of the sum rate, and the requirement for quality of service(QOS) is always neglected, especially the strain rate. In this paper, we propose an improved scheme, with both the sum rate and the strain rate taken into consideration. Users which don’t meet strain rate temporarily stop communicating. Simulation results show that the sum rate decreases, the difference between traditional and improved algorithm is small in lower SNR and tends to be stable with increased SNR. At the same time, bit error rate performance of communicating users could be improved greatly because users which don’t meet the strain rate don’t disturb system any more. Therefore, the new scheme behaves favorably at both system sum rate and performance.

Abstract:The parameters estimation of time-frequency overlapped signals is a new subject of communication signals process, it is the base of subsequent processes, such as separation,modulation recognition and signal demodulation of co-channels signals. It shows that signals reflect cyclostationary character after modulation, pulse formation and sampling. This paper presents a method which based on cyclostationary of time-frequency signals, after calculating the cyclic spectrum and making use of mathematic morphology to pick up discrect spectrum-line and estimate modulation parameters, including carrier frequency and chip rate. This algorithm solves the problem of parameter pairs,and make use of mathematic morphology can reduce the background noise effectively. At the same time doing some research about accuracy in the multipath fading

Abstract:A range-free localization algorithm using received signal strength compare is proposed to balance the accuracy of the localization result with the complex technologies for the distance estimate. The algorithm’s name is received signal strength compare (RSSC). According to the non-cooperative characteristic of primary users (PUs) in cognitive radio networks, RSSC does not need the cooperation between PUs and secondary users (SUs). RSSC localization algorithm counts the PUs’ area based on comparing the received signal strength (RSS) of SUs, and estimates the centroid of the area as the location of the PUs. RSSC performance analysis in terms of its localization error parameterized by SU density, node density and SNR presents at the end of this paper. Experiments demonstrate that the localization accuracy is enhanced a lot with RSSC as compared to other range-free localization algorithms.

Abstract:Cooperative spectrum sensing can solve the problems such as channel fading or hidden terminal in local spectrum sensing of cognitive radio network effectively. This paper researched the weighted cooperative spectrum sensing technology and proposed a reliability-based cooperative spectrum sensing algorithm. In the algorithm, the local spectrum decision is obtained with the maximum-eigenvalue-based detection scheme in each sensing user. Then it is compared with the global decision and the reliability of each sensing user is estimated in fusion center. The fusion center reckons the credibility threshold using of the Trimmed Mean and selects the users which reliabilities are larger than the credibility threshold to participate in the cooperative spectrum sensing. This algorithm reduces the complexity of the system, improves the performance of the spectrum sensing, and is robust to the noise uncertainty. Simulation results showed that the proposed algorithm outperforms other weighted algorithms 1~3 dB in signal to noise ratio and save the communication overhead 43.75% or so.

Abstract:The paper presents a novel semi-blind equalization method for time-varying channel. The complex exponential basis expansion model is introduced to describe the time-varying channel taps. The new method adopts the iterative-Newton based equalization algorithm which combines the independent component analysis criterion with soft-decision directed criterion to remove the inter-symbol interference. What’s more, the method reduces the iterative computation burden by making use of the complex exponential basis expansion model structure. A small number of training symbols are utilized to provide a rough initial estimate of the equalizer’s weight vector and decide if the iteration should go on. Compared with existing ones, the proposed algorithm leads to better equalization result and appears more robust to noise. Simulation results prove the efficiency of it.