Applied Mechanics and Materials Vols. 519-520

Abstract: We present a nonuniform method sampling to form the 1 105 points of GPS signal for real-time implementation of prime factor Fourier transform (PFFT) processor, which uses less resource with more utilization rate, and is more efficient and computationally faster than fast Fourier transform (FFT). The high-speed capturing method by irregular sampling for GPS quick positioning is developed to obtain the specified number of sampled data to suit the requirement of fast pipelined PFFT implementation. Simulation results show that the irregular sampling method is efficient in terms of computational complexity and achieves minimum operations of sampling for 1 105 samples based PFFT processing.

Abstract: In the modulation recognition of MQAM signals cluster points of traditional clustering algorithm were not accurate, iterations of the algorithm are multiple and the curve of square error function was not smooth. To solve these problems, this paper presents a theory of modulation recognition method for reconstruction of MQAM signal constellation diagram based on semi supervised clustering, using labeled samples to guide the membership degree and the clustering center update. Analysis the receiving constellation and extracting the characteristic parameters R of constellation compared with parameter Rs of standard constellation, to realize modulation recognition of the different order of MQAM signal. The results show that the method to identify the MQAM signal at rate of 90. Convergence of iterative process is reduced from 40 to 8 times. The algorithm has low computation complexity and the square error function curve is smooth.

Abstract: On the basis of current Charge Detail Record (CDR) collecting process in one communication operator, the paper analyzed processing bottleneck of this module. It easily caused system untimely collecting CDR and was unable to response promptly to fault. This paper added a Disaster Recovery System with collecting procedures to ensure collecting CDR promptly. And it analyzed and monitored abnormal situation such as CDR collecting with delay or processing with abnormity in the billing system, CDR generating with delay or abnormity in the device or platform and so on. Then it would alarm by sending alarm short messages and displaying alarm hints. The results show that this scheme can effectively collects CDR and discovers abnormity promptly in the billing system, device and platform. And it is much better than the old one in processing timeliness, system safety and stability.

Abstract: In this paper, the bipartite graphical structure of LDPC codes is studied, some methodology for designing shorten LDPC Codes are presented. The performance evaluation of shorten LDPC codes presented provides easy and effective strategy in selecting appropriate shorten scheme, avoiding the complex encoding and iterative decoding steps. The shorten LDPC codes whose minimum code weight greater and length 4-cycle free have better performance.

Abstract: This paper studies the Peak-to-Average Power Ratio (PAPR) distribution in orthogonal frequency division multiplexing (OFDM) signal of visible light communication (VLC) systems with intensity modulation direct detection (IM/DD). In this paper, a closed form expression of PAPR distribution in OFDM-VLC signals is derived, with unequal power allocation to subcarriers is considered. Simulation with different number of subcarriers is conducted. The numerical results show the proposed distribution expression matches well with the result obtained by simulation.

Abstract: To further improve the performance of traditional dual-threshold cooperative spectrum sensing, the article proposed a dynamic-dual-threshold cooperative spectrum sensing algorithm based on D-S evidence theory (DDDS). The article is applied the D-S evidence theory in dual-threshold sensing algorithm and set threshold value depending on the channel gain. If the received signal is outside of dual-threshold, the cognitive user will send the judgment result to the base station; otherwise the cognitive user will calculate trust information based on D-S evidence theory, and then transmit them to the cognitive base station. Cognitive base station makes the final decision.

Abstract: In this paper, a low-complexity LDPC decoder structure was proposed by optimizing the confidence propagation algorithm based on the deep space standard LDPC codes developed by the Consultative Committee for Space Data Systems (CCSDS). With the improved decoding algorithm, the structure made full use of the quasi-cyclic structure to reduce the variables in the decoder and the storage unit use for the index position of the check nodes, which saves the hardware resources greatly. Furthermore, the updating of the check nodes takes advantages of the information iterative structure of the JPL-LDPC decoder, which can reduce the computational complexity. By improving the searching methods, the computational complexity and the difficulty in FPGA implementation were reduced. The decoding performance of the decoder is close to that of the floating-point BP algorithm, which can be widely used in deep space communication with low signal-to-noise ratio.performance close to a floating-point the BP algorithm performance, can be widely used in deep space communications suitable for low signal-to-noise ratio transmission.

Abstract: Parameter estimation is essential to receive a linear frequency modulation (LFM) signal precisely, so in this paper an improved parameter estimation algorithm based on FFT is proposed. Compared to the traditional one-dimension search procedure, the algorithm just needs two FFT steps plus one correlation step only. Without searching process and low computational complexity, the algorithm is easy for project application. The simulations verify feasibility of the algorithm, when SNR is above-3 dB, the algorithm can work well.

Abstract: Fractionated Spacecraft is a concept which transforms a traditional monolithic spacecraft into a network of elements where a free-flying payload module is supported by nearby free-flying infrastructure modules. In this paper, we propose a novel concept named as Payload-Distributed GEO Communication Satellite System (PD-GEO) which divides the traditional GEO communication satellite into several modules. Those modules can be reconfigured, added, or exchanged independently from the others, and be reused over several missions. Then, for the purpose of reliable and high-efficient data transmission in this system, an opportunistic network coding based cooperative information exchange (ONC²IE) scheme was presented. Qualitative analysis and extensive simulations demonstrate the effectiveness and efficiency of ONC²IE.

Abstract: In this paper, optimal time-frequency-angle (TFA) resource distribution is proposed. It is achieved by fractional Fourier transform (FrFT) angle division multiple access (ADMA), and multiple data streams can be transmitted in the same frequency and time slot. Comparing with conventional time-frequency (TF) resource based orthogonal frequency division multiplexing (OFDM) system, the exponential base at each sub-channel is replaced by a set of chirp bases, which keep mutually approximately orthogonal. Each base station (BS) can support more move stations (MSs) or cell throughput. Simulations show the essential advantages in TFA resource distribution and system spectrum efficiency.