Gengxin Zhang

A novel waveform for FQPSK modulation

Feher Quadrature Phase Shift Keying (FQPSK) is a quasi constant envelope modulation and it can be used to improve the power efficiency of high power amplifier (HPA). However, the envelope of FQPSK still has a least fluctuation of 0.18 dB and can be further improved. New waveforms for FQPSK modulation are presented in this paper. The performance of the FQPSK adopting new waveform is justified by analysis and simulation. The signal of new FQPSK has the strictly constant envelope. It improves the power efficiency of the amplifiers to the utmost, and outperforms over conventional FQPSK in both the bandwidth efficiency and the end to end performance of bit error probability. At last, the impact of frequency selective multi-path fading on the bit error rate performance of new FQPSK is derived and analyzed.

Constant envelope enhanced FQPSK and its performance analysis

Its a challenging task to design a high performance modulation for satellite and space communications due to the limited power and bandwidth resource. Constant envelope modulation is an attractive scheme to be used in such cases for their needlessness of input power back-off about 2~3 dB for avoidance of nonlinear distortion induced by high power amplifier. The envelope of Feher quadrature phase shift keying (FQPSK) has a least fluctuation of 0.18 dB (quasi constant envelope) and can be further improved. This paper improves FQPSK by defining a set of new waveform functions, which changes FQPSK to be a strictly constant envelope modulation. The performance of the FQPSK adopting new wave- form is justified by analysis and simulation. The study results show that the novel FQPSK is immune to the impact of HPA and outperforms conventional FQPSK on bit error rate (BER) performance. The BER performance of this novel modulation is better than that of FQPSK by more than 0.5 dB at least and 2 dB at most.

A novel space information network architecture based on autonomous system

Space Information Network (SIN) has recently become prevalent as a promising approach to solve the collaboration difficulty among current space programs. However, due to large scale, high component complexity and dynamic characteristics of the SIN, the task of proper SIN architecture design is challenging. We propose a novel architecture of SIN, which composed of Geostationary Earth Orbit (GEO) satellites as backbone network nodes, Low Earth Orbit (LEO) or Incline Geosynchronous Orbit (IGSO) satellites as enhanced coverage nodes, and high altitude platforms to meet the service requirements of emergency or hot-spot applications. Compared with most existing studies, the proposed architecture is autonomous system (AS) based. The complex and dynamic SIN is decoupled into semi-static subnetworks constituted by similar nodes which are easier to control.

Capacity Model and Constraints Analysis for Integrated Remote Wireless Sensor and Satellite Network in Emergency Scenarios

This article investigates the capacity problem of an integrated remote wireless sensor and satellite network (IWSSN) in emergency scenarios. We formulate a general model to evaluate the remote sensor and satellite network capacity. Compared to most existing works for ground networks, the proposed model is time varying and space oriented. To capture the characteristics of a practical network, we sift through major capacity-impacting constraints and analyze the influence of these constraints. Specifically, we combine the geometric satellite orbit model and satellite tool kit (STK) engineering software to quantify the trends of the capacity constraints. Our objective in analyzing these trends is to provide insights and design guidelines for optimizing the integrated remote wireless sensor and satellite network schedules. Simulation results validate the theoretical analysis of capacity trends and show the optimization opportunities of the IWSSN.

A concatenated coded modulation scheme and its iterative receiving for deep space communications

Due to the long propagation distance between spacecraft and Earth station the high power efficiency is more important for deep space communication than others communication systems. One novel coded modulation scheme based on AR4JA code and FQPSK (Fehers QPSK) is proposed out in this paper, which can alleviate the challenge of huge loss in space communications. The novel approach utilizes the property that AR4JA code enables communication at very low signal noise rate and constant envelope property of FQPSK to overcome the nonlinear impact of high power amplifier. At receiver, large gain can be attained by iterative demodulation and decoding. The paper presents the system model of coded modulation and proposes out iterative receive algorithm. Finally, the bit error rate performance of new scheme is confirmed by computer simulation.

An efficient algorithm for TDOA/FDOA estimation based on approximate coherent accumulative of short-time CAF

Considering the huge calculation in estimation of TDOA/FDOA using conventional CAF algorithmic, a fast algorithm based on coherent accumulative of a approximate calculation of short-time CAF is proposed. Feasibility and performance of the fast algorithm is analyzed. Simulation analysis of conventional and fast CAF algorithmic under the same condition is performed. The simulation results show the effectiveness of the new algorithmic, and it can cut down time consumption around 90%.

Efficient distributed storage strategy based on compressed sensing for space information network

This article investigates the distributed data storage problem with compressed sensing in the space information network. Since there exists a performance-energy trade-off, most existing strategies focus only on improving the compressed sensing construction performance or reducing the energy consumption, respectively. In order to achieve a better balance, a novel and efficient strategy, referred to as distributed storage strategy based on compressed sensing, is proposed in this article. Unlike other strategies which require source packets visiting the entire network, the proposed strategy is a “one-hop” method since information exchange is only performed between neighbors. Therefore, the compressed sensing measurement matrix depends heavily on the degree of each space node. We prove that the proposed strategy guarantees the compressed sensing reconstruction performance under both sparse orthonormal basis and dense orthonormal basis. Simulation results validate that, compared with the representative CStorage strategy and compressive data persistence strategy, the proposed strategy consumes the least energy and computational overheads, while almost without sacrificing the compressed sensing reconstruction performance.

Channel Estimation in DCT-Based OFDM

This paper derives the channel estimation of a discrete cosine transform- (DCT-) based orthogonal frequency-division multiplexing (OFDM) system over a frequency-selective multipath fading channel. Channel estimation has been proved to improve system throughput and performance by allowing for coherent demodulation. Pilot-aided methods are traditionally used to learn the channel response. Least square (LS) and mean square error estimators (MMSE) are investigated. We also study a compressed sensing (CS) based channel estimation, which takes the sparse property of wireless channel into account. Simulation results have shown that the CS based channel estimation is expected to have better performance than LS. However MMSE can achieve optimal performance because of prior knowledge of the channel statistic.

A Multiple Frequency Channels Reserved Timeslots Assignment Algorithm for Real-Time Traffic in MF-TDMA Satellite System

Timeslots assignment can have a great impact on the bandwidth allocation efficiency in multi-frequency time division multiple access (MF-TDMA) satellite system. In this paper a multiple frequency channels reserved timeslots assignment algorithm is proposed for MF-TDMA user terminals (UTs) with real-time traffic. The scheme can reserve several frequency channels simultaneously for one UT and realize fast timeslots block searching within a MF-TDMA frame. Computational complexity analysis demonstrates the performance of the proposed method on computational efficiency. What’s more, simulation results show that both channel utility and connection rejection ratio can be improved compared with existing algorithm.

A novel hybrid distributed storage strategy for Space Information Network

Hierarchical autonomous system (AS) network model makes the control of the entire Space Information Network (SIN) easier. In this paper, we investigate the distributed data storage problem in the SIN, a novel hybrid distributed storage (HDS) strategy is proposed to improve the data reliability based on the AS network model. After a data object is optimal encoded using maximum distance separable (MDS) codes, the storage process is divided into two phases: the inter-AS storage phase and intra-AS storage phase, respectively. The inter-AS storage is modeled as an optimal storage allocation problem for a heterogeneous network under multiple constraints, where different AS networks have different capacities and availabilities. Then, we deduce the distributed storage within each AS network to a data persistence problem. As a result, the data object is disseminated over the SIN and it can be recovered by collecting a few encoded packets. The proposed strategy utilizes the advantage of AS network model of SIN, while aiming to improve data reliability and energy efficiency.