Abstract:Detailed survey and discussion on several potential key technologies are provided for the future wireless communication systems, such as heterogeneous wireless networks, massive multiple-input multiple-output (MIMO) communications, green communications and millimeter wave communications. First, the appearance of complicated interference signals and the increase of energy consumption resulted from the change of the heterogeneous structure in the future wireless communication networks are introduced. Second, the advantages, the state-of-the-art technologies and the difficulties of the massive MIMO are respectively analyzed. Then, the mathematical problems of maximizing spectrum efficiency, energy efficiency and resource efficiency are thoroughly described. Finally, the hybrid beamforming scheme of the millimeter-wave wireless communication system is given to deal with the lack of spectrum resource.

Abstract:The secure transmission of distributed two-way relay systems is studied. To maximize the secrecy sum rate subject to the aggregate power constraint, an artificial-noise-aided beamforming (ANBF) scheme is proposed. The major difficulty in the ANBF scheme is a non-convex optimization problem. Therefore, a sequential parametric convex approximation (SPCA) algorithm is proposed, together with a New ton iteration method, to optimize the beamforming vector, artificial noise covariance matrix as well as the transmission power in an alternating iterative way. The ANBF scheme is proved to be a generalization of the existing beamforming (BF) scheme without AN and the null space beamforming (NSBF) scheme, and the system design is more universal. Simulation results and performance analysis verify t he efficiency of the proposed ANBF scheme, and reveal that it achieves the highest secrecy sum rate.

Abstract:In massive MIMO systems, the matched filter (MF) beamformer is an attractive technique due to its extremely low complexity compared with the high-complexity decomposition-based beamforming techniques， such as zero forcing and minimum mean square error. An approximate formula is derived for probability density function (PDF) of the signal-to-interference-and-noise ratio (SINR) at user terminal when multiple antennas and the MF beamformer are used at the base station. The formula is important in calculating or analyzing system performance such as sum-rate and outage probability. Simulations exhibit that the difference between the derived approximate formula for PDF and the simulated PDF approaches zero while the number of antennas at the base station tends to large-scale.

Abstract:Traditional compression algorithms of OFDM signals with low compression ratio and signal to quantization-error ratio(SQR) come along with a high error rate, which fail to meet the requirements of OFDM systems. To achieve the high compression ratio and the low e rror rate, a new algorithm is proposed based on a combination of clipping with tail plug (CTP), geometric series companding (GSC) and partial sample calibration (PSC). The new algorithm can achieve the nearly loss-less compression and the compression ratio can be as high as 1.86∶1 with a error rate less than 10-7, while SQR corresponding to the quantization error is 70 dB in 4096-QAM OFDM signal modulation schemes meeting the requirements of the FTTdp+GDSL systems well.

Abstract:According to communication requirements of the smart grid, WMN and the power line-based communication framework for smart grid communications is proposed. Based on the framework, a genetic algorithm and a heuristic algorithm are proposed to establish virtual networks for various types of services respectively, and are embedded in the heterogeneous substrate network.Finally, the simulation experiment shows that the reliability of real time services is achieved by increasing transmission diversity enhancement, while throughput of the best-effort service is maximized.

Abstract:In a cloud data center network, virtual machines (VMs) can be dynamically created and terminated, causing the fact that fragmented resources cannot be further utilized. To solve the problem, the server consolidation is proposed to minimize the number of active servers. Although the approach can reduce resource fragmentation at particular time, it may be over aggressive at the price of too frequent VM migration. Therefore, a novel provident resource defragmentation algorithm is proposed to reduce the unnecessary VM migration and maxmize the profit by re-consolidating fragments into available continuous resources. An optimization problem is formulated, and a heuristic method for obtaining near-optimal results is developed. Extensive numerical results confirm that the framework provides the highest profit and significantly reduces the VM migration cost.

Abstract:A generalized three-dimensional (3-D) geometric model is proposed with the 3-D scattering hollow-hemispheroid at the mobile station (MS) considering macrocellular mobile systems such as crowded square and large shopping malls. Closed-form expressions for joint and marginal probability density functions (PDFs) of the angle of arrival (AOA) seen at the MS and base station (BS) in the azimuth plane and elevation plane are derived respectively. Moreover, closed-form expressions for propagation path delays and trivariate joint PDFs of the time of arrival (TOA) seen at the MS are investigated. The observed theoretical results are compared with some presented 2-D and 3-D scattering models to validate the generalization of the proposed model. The proposed theoretical results provide effective support and development for a practical 3-D scattering environment.

Abstract:The performance of the adaptive beamforming is vulnerable to the DOA mismatch, especially in the case that the power of the desired signal is large enough compared with the interference. This phenomenon is called “self-nulling”. In addition, the desired signa l is mitigated and the beamformer catches the interference whose power is larger when the blind beamforming algorithm is employed based on the constant module property. A new beamforming algorithm is presented so that beamformer could work well even if the dynamic range of the interest signal is considerably large. In the new deployment, the DOA information and constant module property of the desired signal are both used. The implementation of the proposed algorithm is presented and the array gain is analyzed. Simulation results show that the main lobe of the array antenna is steered to the desired signal and the interferences are suppressed in the the assumed condition.

Abstract:With the rapid development of wireless communications and the popularization of smartphones, higher data rate of the service is required. The demand can be efficiently and conveniently satisfied by increasing the number of antennas at base station (BS), thus resulting in a massive MIMO system. The massive MIMO system can exploit the spatial degree of freedom, and therefore BS is enabled to simultaneously serve several user equipments (UE) with the same temporal and frequency resource. Three key techniques are presented in the massive MIMO system, including the pilot contamination issue and the corresponding solutions, the theoretical and practical channel model that fits for the massive MIMO system, and the low complexity transmission and implement methods. Compared with the existing MIMO system, the massive MIMO system can distinctively increase the spectral efficiency, the energy efficiency, and the system robustness. As one of the most promising topics on the fifth generation (5G) of wireless communication systems, the massive MIMO system has attracted the extensive attention worldwide. Nevertheless, the research of massive MIMO systems is still at its early stage, with a lot of technical problems to be solved.

Abstract:To solve the user selection and channel estimation problem in multi-user MISO system, a new data transmission frame structure combined with the decentralized user self-selecting strategy in TDD mode is designed. Then, the base station receiving uplink random pilot sequence signatured with the user identity is built as a block sparse linear model based on the natural signal sparsity from users′ low active degree and the channel impulse response sparsity in delay-spread domain. In addtion, to resolve such an objective optimization problem, an efficient block-sparse signal recovery algorithm is proposed based on l2/l1 reconstruction model. In the novel algorithm, the objective function is transformed through variable splitting and four variables are alternately updated in the framework of alternating direction method (ADM) until the prespecified convergence criterion is satisfied. During the alternate updating procedure, Aiming at unobtainable closed form solution of the signal variable item, the block coordinate descent (BCD) method is utilized to acquire an iterative solution. Simulation results demonstrate that the proposed method can achieve higher computational efficiency and the better estimation accuracy compared with two state-of-art fast algorithms, such as block orthogonal matching pursuit (Block OMP) and block compressive sampling matching pursuit (Block CoSaMP).

Abstract:In order to improve the tracking precision, real time performance, and reduce communication costs, distributed particle filter is applied to binary wireless sensor network tracking. The node with the biggest signal strength is selected as cluster, and the dynamic clustering is composed of the cluster and all nodes within one hop communication range of the cluster. State estimation are achieved in cluster heads, particles and their weight are transmitted between cluster heads. Therefore the distributed particle filter tracking algorithm for binary wireless sensor is given. Effect on tracking precision caused by number of particle and node is investigated. Simulation results indicate that the number of particle has greater impact on tracking precision than that of the node number. Meanwhile the distributed particle filter has better real-time performance and lower energy consumption than centralized particle filter.

Abstract:An adaptive transmit power allocation (TPA) scheme to minimize bit error rate (BER) is investigated in a vertical bell labs layered space-time (V-BLAST) system with channel correlation and estimation error. The closed expression for average BER can be derived according to the instantaneous signal-to-interference-plus-noise ratio (SINR) of each sub-stream by system modeling and performance analysis. At the transmitter, with the total TPA constraint condition, TPA matrix is calculated through the Lagrange multiplier method. Numerical results demonstrate that the correlation structure and channel estimation error have a profound effect on the performance of V-BLAST system. The proposed TPA scheme can improve the BER performance effectively and be practical for the actual communication system.

Abstract:To solve the continuous phase modulation signal synchronization problem, a signal acquisition and frequency offset estimation lgorithm is proposed based on a set of pilot symbols. First, the pilot signal composed of the spread spectrum codeword is complex-matching-filtered, then the output modulus value is obtained. The signal is captured by searching the peak to sync signal. Then the frequency offset and initialization phase are estimated based on the least squares method of argument of correlation results. The range of the frequency offset estimation and the estimation accuracy are deduced in a lower SNR ratio. Simulation results show that the range of the frequency offset estimation is ±0.25Rb and the estimated accuracy is close to the Cramer-Rao lower bound when SNR is 3.3 dB.

Abstract:To improve the reliability and security of underwater acoustic (UWA) FH system, a method producing frequency hopping (FH) pattern is presented based on bit error rates (BER) mapping and the quantification of pseudo random numbers. BER of all FH channels are ma pped into the probability density function (PDF), a quantitative vector can therefore be obtained. Furthermore, the pseudo random numbers, produced by the pseudo random number generator, generate FH patterns according to the specific statistical rule and quantitative criteria, which are used for FH communications. A specific adaptive FH communication simulation system based on probabilities is further established. Experimental simulation demonstrates that the proposed method has a lower BER compared with the traditional FH or adaptive FH. Moreover, it features better security performance.

Abstract:In several applications such as multimedia transmission and deep space communications, some data may need more protection than the rest because of the different importance of the data. Such applications raise the need for fountain codes with unequal error protection (UEP).The operation mechanism of the unequal error protected fountain codes based on block duplication is analyzed, and an improved selection strategy of information symbols is proposed to improve the protection of more important bits (MIB) in local area. Degree 1 encoded symbols are selected from MIB and a certain number of degree 2 encoded symbols are chosen from MIB and less important bits(LIB), respectively. Simulation results show that compared with the existing method， the proposed scheme perform better on decoding MIB without reducing the decoding of LIB while reserving a better unequal recovery time (URT) property.

Abstract:The derivation and the performance analysis of a kind of high-rate low density parity check （LDPC）codes algorithm are proposed to the application of impulse radio ultra-wideband (IR-UWB) communication system. The PEG algorithm is combined with block quasi-cyclic manner to construct the parity check matrix and the two different algorithms performance are compared by using the matrix I and matrix Q as the sub-block cyclic matrix. The performance analysis is conducted with bit-error curve from Matlab simulation. Moreover, the minimum sum (MS) decoding algorithm based on a variable factor of the design is proposed and the final low complexity low density parity-check code (LDPC) decoder incurs only about 3.2dB signal-to-noise ratio (SNR) loss with the error rate of 10-6 bit in standard UWB fading channels.

Abstract:Key words: impulse radio ultra-wideband (IR-UWB); progressive edge-growth algorithm (PEG); quasi-cyclic (QC); low-density parity check code (LDPC)

Abstract:To overcome the drawbacks of phase difference of arrival （PDOA）dual-frequency comparison ranging method, i.e. large frequency selection random and low measuring distance accuracy, the phase difference of arrival in frequency domain (FD-PDOA) dual-frequency comparison ranging method is proposed. Combining with the least square method and linear regression, a mathematic model is built to measure the distance. Simulation results show that the measurement error of PDOA dual-frequency comparison ranging method floats at 50% and 30% at distance 0.5 m and 1.0 m respectively, while the measurement error of FD-PDOA dual-frequency comparison ranging method is reduced to 10% through an overall analysis of the phase difference change characteristics, and the method considerably improve the measuring distance accuracy.

Abstract:How to achieve high-resolution ADCs from low-resolutionones by filtering quantization noise is the key problem of signal processing researchers. Considering IF bandpass signals in communication, a method is proposed to reduce the quantization noise and improve the resolution of A/D conversion by adding a post-bandpass filter. Then the method is analyzed and tested by numerical simulations with a common IF bandpass signal as an example. Results show that the quantization noise is observably reduced,through bandpass filtering for quantized signals. Therefore, the A/D conversion performance are improved obviously. In addition, in the aspect of theory, this paper revises certain traditional views on the statistic model of quantization noise and loosens the assumption condition that the quantization noise is a white one.

Abstract:An algorithm for blind recognition of (n,k,m) non-systematic convolutional code with high BER is proposed in information interception. Firstly, an alterable matrix model is constructed to deal with the received data in advance. Then, statistical analysis of the preprocessed data matrixes is carried out to recognize parameters of the convolutional code and extract check-sequences of the each data matrix. Linear equation set using check-sequences is built to figure out the generator polynomial matrix group. Through setting condition of selecting the generator polynomial matrix of the non-systematic convolutional code, the non-systematic convolutional code is recognized. Finally simulation results show that the algorithm can recognize (n,k,m) non-systematic convolutional code effectively in the high BER condition.

Abstract:The nonlinear characteristics of light emitting diode (LED) is an important factor in visible light communication (VLC) system based on the orthogonal frequency division multiplexing (OFDM). To decrease the effect of LED nonlinear characteristics, a transmission system based on amplitude-phase shift keying (APSK) modulation combined with OFDM technology is introduced in the VLC system. The schemes and the applications of APSK in VLC system based on OFDM are also introduced. The VLC system model based on APSK-OFDM modulation is compared with the system based on quadrature amplitude modulation (QAM). The simulation result shows that in OFDM system, the performance of QAM system is better than that of APSK system in the ideal channel, but the result is reversed when considering the nonlinear characteristics of LED.

Abstract:A new radar pulse signal clustering algorithm based on inner-pulse modulation characteristic is studied. The number of clusters in original data and the cluster that data vector belongs to is determined by clustering algorithm using the minimum description length (MDL)， thus obtaining the number of radar emitters in the electromagnetic environment. The radar pulse data collected by the interception system front-end is treated as vectors and is sorted after the necessary pre-processing. Pulse signals from different radars form different vector clusters after deinterleaving by using the algorithm based on MDL criterion， because of their different inner-pulse modulation characteristic. The largest advantage of the algorithm is that it is unnecessory for quantitative analysis, extraction and description of the inner-pulse modulation characteristic. Simulation proves its effective.

Abstract:Considering the long pseudo-code used by BD2 navigation system with the shortcoming of large resource occupation when employing the traditional matched filter acquisition method, a kind of folded-structure matched filter combined with fast Fourier transform (FFT) is proposed to reduce acquisition time and resource consumption. Firstly, the mathematical model of the algorithm is deduced and the c ore module among sinc interpolation unit is analyzed. The folded-structure and the FFT unit are realized on field-programmable gate array (FPGA). The experiment result show that the design realized rapid acquisition and low resource consumption. The method can be effectively applied to the signal acquiring of BeiDou navigation system as well as that of the other systems.

Abstract:Cross-correlation interference is caused by C/A code correlation properties. It is an inevitable problem for GPS systems. And it has been one of the problems affecting the sensitivity of GPS receivers. To solve the problem, a novel auto-correlation detection method based on multi-groups data comparison (MDC) is presented. In this method, the Doppler frequency and code phase within several groups of data are compared to find the auto-correlation peak. In contrast to the mean square ratio method and peak difference method, the proposed method can improve the detection probability of weak signals effectively in the presence of cross-correlation interference. The simulation results show that in the presence of one strong signal with -124　dBm power level, the method can achieve an 83% detection probability for the weak signal with -145 dBm power level. Therefore, it is useful for the acquisition of weak GPS signal.

Abstract:Most of the previous research on community detection are mainly based on the undirected graph structures. However, in actual complex networks, the links relation usually shows the asymmetric characteristic or directionality, such as citation network of scientific papers, the one-way follow relationship on Twitter, and hyperlinks between web pages. Therefore, based on the propagation of informat ion and the direction of information transmission, a k-Path conception and calculation method for measuring the similarity of co-community neighboring is presented to weigh possibility of nodes in the same community. Furthermore, the method of transferring directed graphs into undirected graphs with similarity of weight is presented. Then the local extension algorithm of detecting overlapping community based on weighted undirected graphs is proposed. Several experiments on the real data sets are conducted and analyzed. Experimental results demonstrate that the k-Path conception can achieve the reasonable conversion for directed graph and improve the effectiveness of the community gathering nodes. Finally, the results show that the algorithm can detect the overlapping community effectively.

Abstract:Analyzed the channel structure, it is found that there is an inherent signal feature on the plaintext in N-CDMA system. A new ciphertext-only attack method is proposed to solve the initial phase of the key sequence by eavesdropping 20 ms ciphertext frame. By exploiting the linear relations between the key sequence and the state of the long code generator, an algorithm for decoding the private mask is proposed. It is proved that the voice encryption of N-CDMA system is unsecure while attacked by ciphertext-only attack. Aiming at the safety defect of IS-95 system and possible attack methods, a new enhancement scheme is proposed to improve the security framework of IS-95 system.