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A spatially polarized time-frequency distribution (SPTFD) based on dual-polarized double-fed antenna arrays is adapted to deal with polarization-unstable signals. A linear time-frequency (TF) representation was used for an instantaneous frequency (IF) estimate, primarily due to its simplicity and immunity to cross-interference. Using a set of linear TF transformations using Gaussian windows and Fourier oscillation kernels, the IF estimated window widths of multiple unstable signals are obtained. This paper introduces a new method for estimating the direction of arrival (DOA) of polarized waves using adaptive linear time-frequency transforms. In this paper, a narrowband far-field point source on the receiving array is analyzed. The source signal is split into two orthogonally polarized components. The optimal window is determined by the first derivative of the IF; for this purpose, we take a simple algorithm for solving the derivative and optimize it. In developing TF-adaptive and fully automatic TF display technology, the first method is to use the time-adaptive window for minimizing the IF estimate mean square error (MSE) sum at each moment, while the second procedure is to adjust according to time and frequency and minimize estimate MSE sum at each position in the TF region. Due to its combination with signal polarization, the spatial time-frequency distribution (STFD) gains more freedom and thus perfects the phonon space estimation of noise and signal. On the SPTFD platform, polarized time-frequency multiple signal classification (PTF-MUSIC) is used for the estimation of signal direction of arrival, which outperforms conventional time-frequency MUSIC. Using the example of a synthesized signal, this method outperforms conventional techniques in DOA estimation.

Bo Li,1 Weiqing Wu,1 Aijun Liu,1 Lifeng Feng,1 Bin Li,1 Yong Mei,1 Li Tan,1 Chaoyang Zhang,2 Yangtao Tian1 1Department of Pancreatic Surgery, Shangluo Center Hospital, Shangluo, Shaanxi, 726000, People’s Republic of China; 2Department of Ultrasound Medicine, Shangluo Center Hospital, Shangluo, Shaanxi, 726000, People’s Republic of ChinaCorrespondence: Yangtao Tian, Department of Pancreatic Surgery, Shangluo Center Hospital, 37 Shangyang, Shangzhou, Shangluo, Shaanxi, 726000, People’s Republic of China, Email 928763821@qq.comBackground: Severe acute pancreatitis (SAP) can progress to lung and kidney dysfunction, and blood clotting within 48 hours of its onset, and is associated with a high mortality rate. The aim of this study was to establish a reliable diagnostic prediction model for the early stage of severe pancreatitis.Methods: The clinical data of patients diagnosed with acute pancreatitis from October 2017 to June 2022 at the Shangluo Central Hospital were collected. The risk factors were screened by least absolute shrinkage and selection operator (LASSO) regression analysis. A novel nomogram model was then established by multivariable logistic regression analysis.Results: The data of 436 patients with acute pancreatitis, 45 (10.3%) patients had progressed to SAP. Through univariate and LASSO regression analyses, the neutrophils (P < 0.001), albumin (P < 0.001), blood glucose (P < 0.001), serum calcium (P < 0.001), serum creatinine (P < 0.001), blood urea nitrogen (P < 0.001) and procalcitonin (P = 0.005) were identified as independent predictive factors for SAP. The nomogram built on the basis of these factors predicted SAP with sensitivity of 0.733, specificity of 0.9, positive predictive value of 0.458 and negative predictive value of 0.967. Furthermore, the concordance index of the nomogram reached 0.889 (95% CI, 0.837– 0.941), and the area under the curve (AUC) in receiver operating characteristic curve (ROC) analysis was significantly higher than that of the APACHEII and ABISAP scoring systems. The established model was validated by plotting the clinical decision curve analysis (DCA) and clinical impact curve (CIC).Conclusion: We established a nomogram to predict the progression of early acute pancreatitis to SAP with high discrimination and accuracy.Keywords: acute pancreatitis, prediction model, risk factor, nomogram, decision curve analysis

Atherosclerosis (AS) is one of the main causes of cardiovascular diseases (CVDs). Trimethylamine N-oxide (TMAO) exacerbates the development of AS. This study aimed to investigate the roles of TMAO in AS. In this study, mice were fed with high fat food (HF) and/or injected with TMAO. Oil red O staining was applied for histological analysis. ELISA, qRT-PCR, and Western blot were conducted to determine the TMAO, serum, mRNA, and protein levels. CCK-8, colony formation assay, and flow cytometry assays were performed to detect the functions of human aortic endothelial cells (HUVECs). The results showed that TMAO induced thick internal and external walls and intimal plaques in vivo, and HUVEC dysfunction in vitro. TMAO and lncRNA enriched abundant transcript 1 (NEAT1) were increased in AS clinical samples and TMAO-HUVECs. Downregulated NEAT1 inhibited proliferation and promoted the apoptosis of HUVECs. NEAT1 regulated the expression of signal transducer and activator of transcription 3 (STAT3) via sponging miR-370-3p. Overexpression of miR-370-3p facilitated the effects of NEAT1 on the cellular functions of HUVECs, while STAT3 exerted opposing effects. The activation of STAT3 promoted the expression of flavin-containing monooxygenase-3 (FMO3). Taken together, our results show that TMAO-NEAT1/miR-370-3p/STAT3/FMO3 forms a positive feedback loop to exacerbate the development of AS. This novel feedback loop may be a promising therapeutic target for AS.

This paper examines the direction of arrival (DOA) estimation for polarized signals impinging on a sparse vector sensor array which is based on the maximum interelement spacing constraint (MISC). The vector array effectively utilizes the polarization domain information of incident signals, and the quaternion model is adopted for signals polarization characteristic maintenance and computational burden reduction. The features of MISC arrays are crucial to the mutual coupling effects reduction and higher degrees of freedom (DOFs). The quaternion data model based on vector MISC arrays is established, which extends the scalar MISC array into the vector MISC array. Based on the model, a quaternion multiple signal classification (MUSIC) algorithm based on vector MISC arrays is proposed for DOA estimation. The algorithm combines the advantages of the quaternion model and the vector MISC array to enhance the DOA estimation performance. Analytical simulations are performed to certify the capability of the algorithm.

Satellite and unmanned aerial vehicle (UAV) net-works have been introduced as enhanced approach to providedynamic control, massive connections and global coverage forfuture wireless communication systems. This paper considersa coordinated satellite-UAV communication system, where theUAV performs the environmental reconnaissance task with theassistance of satellite in a hostile jamming environment. To fulfillthis task, the UAV needs to realize autonomous trajectory controland upload the collected data to the satellite. With the aid ofthe uploading data, the satellite builds the environment situationmap integrating the beam quality, jamming status, and trafficdistribution. Accordingly, we propose a closed-loop anti-jammingdynamic trajectory optimization approach, which is divided intothree stages. Firstly, a coarse trajectory planning is made accord-ing to the limited prior information and preset points. Secondly,the flight control between two adjacent preset points is formulatedas a Markov decision process, and reinforcement learning (RL)based automatic flying control algorithms are proposed to explorethe unknown hostile environment and realize autonomous andprecise trajectory control. Thirdly, based on the collected dataduring the UAV’s flight, the satellite utilizes an environmentsituation estimating algorithm to build an environment situationmap, which is used to reselect the preset points for the first stageand provide better initialization for the RL process in the secondstage. Simulation results verify the validity and superiority of theproposed approach.

Supplemental material, sj-docx-1-tct-10.1177_15330338221094422 for The Association Between Low T3 Syndrome and Survival in Patients With Newly Diagnosed Multiple Myeloma: A Retrospective Study by Qingrong Pan, Yuan Jian, Yeqing Zhang, Wenkai Zhang, Zhe Chen, Yanna Yang, Aijun Liu and Guang Wang in Technology in Cancer Research & Treatment

Additional file 1: Supplementary Figure S1. Full-length blots from different gels showing the expression levels of c-myc, FosB, JunD, and GAPDH.

Supplemental material, sj-docx-1-tct-10.1177_15330338221094422 for The Association Between Low T3 Syndrome and Survival in Patients With Newly Diagnosed Multiple Myeloma: A Retrospective Study by Qingrong Pan, Yuan Jian, Yeqing Zhang, Wenkai Zhang, Zhe Chen, Yanna Yang, Aijun Liu and Guang Wang in Technology in Cancer Research & Treatment

In addition to target echoes, high frequency surface wave radar (HFSWR) receives sea and ionospheric clutter. Among these clutters, the ionospheric clutter is dominant and significantly affects the detection performance of HFSWR, particularly when the targets are located 100 kilometers away from the radar, rendering it an unsolved problem for HFSWR. Existing studies concerning HFSWR ionospheric clutter lack empirical research on the nonlinear dynamical characteristics of the ionosphere of HFSWR as existing ionospheric suppression methods are still insufficient to adapt the project application. Therefore, the present study utilized the threshold segmentation method to eliminate the sea clutter in HFSWR Range-Doppler spectrum and extracted ionospheric signals from this spectrum by edge feature extraction. Subsequently, the chaotic invariants, such as correlation dimension and the largest Lyapunov exponent of HFSWR ionospheric clutter, were calculated by phase space reconstruction, whilst the chaotic dynamical characteristics of HFSWR ionospheric clutter were determined by the 0-1 test for chaos and other algorithms. Furthermore, the present study demonstrated, for the first time, the chaotic dynamics of the ionospheric clutter of HFSWR with a low-dimensional attractor by processing and analyzing the experimental data from the Weihai High Frequency Radar Station. The conclusion redefines HFSWR ionospheric clutter based on chaotic dynamics rather than regarding it as a stochastic process, which is conducive to efforts to explore the formation mechanism of ionospheric clutter in essence, which can ultimately improve the detection capability of HFSWR, particularly for long-distance targets.

Additional file 1: Supplementary materials and methods. Fig. S1. Downregulated SMAD1 reduced migratory and invasive abilities of MM cells in vitro (A) Representative images of soft agar colony formation assays with the different cell models. Bar graphs indicate the colony count expressed in different microscopic fields. (B) Migration ability toward serum of 8226R5 and OPM2 vel/R cell lines were assessed using Transwell filter. Cells were pre-treated with DM 5uM for 24 h prior to the assay. (C) Migration ability toward serum of 8226R5 and OPM2 vel/R cell lines were assessed using Transwell filter. Cells were pre-treated with siSMAD1 50 nM and/or TGF-β 24 h Data were presented as mean ± s.d. from at least separate experiment. *: p

Based on the MODIS NDVI product data source of Xilingol from 2010 to 2019, we use the pixel dichotomous model to retrieve the vegetation coverage in our study. The spatiotemporal changes of the vegetation cover were analyzed in the model by using the meteorological data from researched sites or the vicinal meteorological stations for evaluating the meteorological influence on the vegetation cover changes. Based on this, an evaluation method was established to estimate the relative influences of the climate changes and anthropogenic activities. The main conclusions are as follows: (1) Fractional vegetation cover in Xilingol was decreased from the northeast to the southwest. (2) The overall trend in Xilingol fractional vegetation cover in the 10-year period shows a fluctuating increasing trend. (3) An opposite distribution pattern was detected between mean precipitation and mean temperature in the study site. (4) Compared with temperature, annual precipitation has a higher correlation with fractional vegetation cover in the study site and is the main climatic factor that affects vegetation growth in the study site. (5) During the 10-year period in the study site, anthropogenic human activities have slightly greater inhibitory effects on vegetation growth than promoting effects. (6) Climate change is a major factor to accelerate grassland degradation from 2010 to 2019 in vegetation degradation regions. The promotion effect of precipitation on vegetation coverage is obviously higher than the limitation of human activities, which leads to the increase of vegetation coverage in 2010–2019.

Multicarrier faster-than-Nyquist signaling (MFT-N) is a promising transmission scheme for future communication, since its high spectral efficiency. However, same as other Multicarrier modulations, MFTN exhibits a high peak-to-average power ratio (PAPR). Therefore, the PAPR problem in MFTN signaling system is a meaningful topic. In this paper, we propose a new PAPR reduction method for MFTN based on selective mapping (SLM). The proposed SLM method reserves multiple phase rotation vectors in each stage, and choose the signal with lowest PAPR for transmission. The new SLM method shows better proformance while almost without computational complexity increase.

The detection performance of high-frequency surface wave radar (HFSWR) is significantly impacted by ionospheric clutter and sea clutter. In order to suppress the ionospheric clutter, a new method based on the largest Lyapunov exponent prediction algorithm is proposed in this Letter. Firstly, it is demonstrated, for the first time, that the ionospheric clutter from HFSWR is a chaotic dynamical process, and then the largest Lyapunov exponent is estimated using the Wolf algorithm. After verifying the actual data, this suppression algorithm can decrease the amplitude of the ionospheric clutter by at least 30 dB.

A new cyclic redundancy check (CRC) concatenation with polar codes based on partial protection is proposed, where only the crucial bits chosen from the total information bits are protected with the CRC. The index set of crucial bits is determined by the row weight of generator matrix of polar codes and the indexes with minimum row weight make up this crucial set. Using this new concatenation, the number of polar codewords with minimum Hamming weight can be efficiently decreased. Simulation results show that the performance of the proposed partial protection scheme owns a lower error floor than that of the classical blind protection.

High Frequency Surface Wave Radar (HFSWR) has been shown to provide enhanced performance in over the horizon detection of targets and sea states remote sensing by the returns of targets and ocean surface. Meanwhile, HFSWR can also receive ionospheric echoes reflected by the ionosphere, which severely affect the radar detection performance. In this paper, the radar cross section (RCS) of ionosphere for HFSWR is estimated, which would help quantify the impact of the ionosphere to radar system and the performance of clutter mitigation techniques. Simulations are provided to illustrate the effect of parameters including radar operating frequency, scale size of irregularities, aspect angle and detection range on the RCS of ionosphere.

Inevitable perturbations have a significant impact on collaborative production (CP) cause that the complexity are greatly increased. In order to assess the impact accurately enterprises to make precise decisions, it is prerequisite to master the dynamic behaviour of CP when changes occur. Accordingly, in this paper, an evolution model for simulating CP task state to perturbations is proposed. Regard CP tasks as a directed weighted complex network (DWCPTN) firstly, and statistical properties of DWCPTN are analysed. Two perturbation cases and two modifications policies are defined followed. Based on above mentioned, evolution model based on cellular automaton (CA) and SIS (Susceptible-Infected-Susceptible) is presented to reveal the varying process by three indices (friction of resolved nodes, convergence time and economic behaviour). Finally, analytic results from a case of a chemical product CP network (CPNCP) are used to illustrate the model and method proposed in this paper. Simulation results shows that unplanned perturbations promote a negative role to CP but the improvements of self-healing can decrease the negative effects efficiently. With the analysis, it can provide insight into ways of improving the strategic and operational decision making for enterprises.

Wireless sensor network is one of the most important supporting technologies in the Internet of things, this paper studies the low power hierarchical routing protocol in the water environment. Energy is a vital problem in water environment. Wireless sensor network is composed of many wireless sensor nodes, which is a flexible and adaptive network. This paper studies the problem of low power consumption in wireless sensor networks, so as to prolong the lifetime of wireless sensor networks. In this paper, we analyze the advantages and disadvantages of LEACH protocol and related protocols, and find out the best low power hierarchical routing protocol. In the water environment, has practical value in the water environment.

In this paper, a cooperation system suitable for networks with multiple users is proposed. In the first phase of the cooperation, the user who has correctly decoded the source signal and has the best channel condition is selected as the relay. Given that the best relay selected by one source–destination (s-d) pair may also be selected by other pairs, complex field network coding (CFNC) is adopted by the relay in the second phase, to provide diversity gains for the s-d pairs simultaneously. The number of channels used is reduced, thus increasing the network throughput. Additionally, this system makes up for the performance loss of the traditional CFNC cooperation in large-scale networks by achieving more diversity gains. Especially, a closed-form expression of the average signal error probability (SEP) is derived for small-scale networks, while an upper-bound estimation is given for larger networks. It is demonstrated that the system achieves full diversity and is robust. To improve the SEP performance of the system, the receiver is modified, and the results demonstrate desirable average SEP performance. Finally, the analytical results are validated by numerical simulations. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

In this paper a hybrid Network Coding Cooperation (hybrid-NCC) system is proposed to achieve both reliable transmission and high throughput in wireless networks. To balance the transmission reliability with throughput, the users are divided into cooperative sub-networks based on the geographical information, and the cooperation is implemented in each sub-network. After receiving signals from the cooperative partners, each user encodes them by exploiting hybrid network coding and then forwards the recoded symbols via the Link-Adaptive Regenerative (LAR) relaying. First, the Diversity-Multiplexing Tradeoff (DMT) is analyzed to demonstrate that the proposed system is bandwidth-efficient. Second, the Symbol Error Probability (SEP) is also derived, which shows that the proposed system achieves a higher reliability as compared to the traditional Complex Field Network Coding Cooperation (CFNCC). Moreover, because dedicated relays are not required, our proposed system can both reduce the costs and enhance the flexibility of the implementation. Finally, the analytical results are supported and validated by numerical simulations.

This paper describes a technique related to the design of a trellis encoder, combined with the continuous phase modulation (CPM). Based on the idea of decomposing CPM into continuous phase encoder (CPE) and memoryless modulator (MM), superior trellis encoders are designed following Ungerboeck's set partitioning rules. Combinations are optimized with the squared minimum Euclidean distance based on the super trellis structure constructed by the trellis structure of trellis coded modulation (TCM) and CPE. Simulation results show that this new coding scheme consistently obtains better performance than previous schemes. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

In this paper, we investigate the noncoherent iterative demodulation of coded continuous phase modulation (CPM) in frequency hopped (FH) systems. In this field, one important problem is that the complexity of the optimal demodulator is prohibitive unless the number of symbols per hop duration is very small. To solve this problem, we propose a novel demodulator, which reduces the complexity by applying phase quantization and exploiting the phase rotational invariance property of CPM signals. As shown by computational complexity analysis and numerical results, the proposed demodulator approaches the performance of the optimal demodulator, and provides considerable performance improvement over the existing solutions with the same computational complexity.

Continuous phase modulation (CPM) is a widely used modulation scheme in communication systems. However, difficulties arise with the design of CPM receivers, due to the nonlinear nature of CPM. One popular solution is to linearize CPM with pulse amplitude modulation (PAM) representation. In this paper, a reduced-complexity non-data-aided (NDA) timing recovery method for PAM-based M-ary CPM receivers is proposed. The proposed method is based on the PAM representation and maximum likelihood principle. The merits of the proposed method are twofold. On one hand, the proposed method is reduced-complexity in nature for PAM-based CPM receivers, i.e., it shares the match filter bank with PAM-based detectors. On the other hand, it is shown that the performance of the proposed method is better than the existing method with some modulation schemes. Therefore, the proposed method provides an important synchronization component for PAM-based M-ary CPM receivers.

This paper introduces the theoretical basis of spatial time-frequency distributions in direction-of-arrival (DOA) estimation, and then proposes a new method through analysis to non-stationary signals' time-frequency distributions and extraction of their cross terms. The work done by the previous researchers almost based on paying attention to the auto terms information and suppressing of cross terms, and this paper examines the signal cross terms from a new perspective. Study found that cross terms between signals do contain rich information, and using cross terms information alone can calculate out the direction of the source signals. In particular, when the strength between the signals is different, the auto terms information of the weak signal have a certain possibility can not be detected. Therefore, extraction of cross terms information to estimate the DOA of signals is much easier. Simulation experiments verified these characteristics.

Meckel-Gruber syndrome (MKS) is a lethal autosomal recessive condition characterized by renal cysts and variably associated features, including developmental anomalies of the central nervous system (typically encephalocele), hepatic ductal dysplasia and cysts, and polydactyly. Genetic heterogeneity has been demonstrated at eleven loci, MKS1-11. Here, we present the clinical and molecular characteristics of a Chinese MKS3 family with occipital encephalocele and kidney enlargement. DNA sequencing of affected fetuses revealed a homozygous c.1645C>T substitution in exon 16 of TMEM67, leading to a p.R549C substitution in meckelin. The R549 residue is highly conserved across human, rat, mouse, zebrafish, chicken, wolf and platypus genomes. Hha I restriction analysis demonstrated that the c.1645C>T mutation was absent in 200 unrelated control chromosomes of Chinese background, supporting the hypothesis that it represents causative mutation, not rare polymorphism. Our data provide additional molecular and clinical information for establishing a better genotype-phenotype understanding of MKS.

Channels of mobile satellite communications are affected by multipath fading and shadowing attenuation. At the same time, diversity gains are believed to improve the transmission reliability in fading channels. Considering that the traditional Space-Time Coding (STC) is not suitable for the cooperative mobile satellite communication, in this paper, a new cooperative mobile satellite communication system is proposed based on the Dynamic Space-Time Coding (D-STC). The transmitting energy of the proposed scheme is saved by avoiding forwarding erroneous signals in cooperative users. Meanwhile, this system benefits from diversity gains and the transmission is robust. Additionally, a closed-form expression of the outage probability for the proposed scheme is derived, and then it is demonstrated that this scheme is much better than the existing noncooperative scheme and schemes with traditional STCs in the outage performance. Finally, the analytical result is supported and validated by numerical simulations.

Recently, the quaternion-valued feedforward neural network (QFNN) has been developed to process three dimensional (3-D) and 4-D signals in quaternion domain, and the weight matrices and bias vectors of the QFNN were obtained based on the quaternion backward propagation (QBP) method. However, it should be noted that the QBP is a first-order quaternion gradient descent algorithm. The convergence speed of the QBP is usually slow and may not be very suitable to process nonstationary quaternion-valued signals. To address this problem, a widely linear quaternion unscented Kalman filter (WLQUKF) algorithm is proposed to train the QFNN. This is derived by utilizing some recent studies in the augmented quaternion statistics and the $\mathbb {HR}$ -calculus. With the augmented quaternion statistics, the WLQUKF is able to process general quaternion-valued noncircular, nonlinear, and nonstationary signals, effectively. Simulations on both benchmark circular and noncircular quaternion-valued signals, and on real-world quaternion-valued signals support the analysis.

In this paper, we investigate a cooperative communication system which consists of a source, a destination and NR relays. The differential modulation and relay selection (DM-RS) are combined in the system, where the best relay is selected to assist the source node with detect-and-forward (DetF) protocol. We consider general fading scenarios where the channel variances of different links are not equal, the average bit error rate (ABER) performance and power allocation strategy are investigated. Firstly, a theoretical ABER expression of the scheme with differential M-ary phase shift keying (DMPSK) modulation is derived. Then, to gain more insightful understanding, we look into the high signal-to-noise ratio (SNR) regime and provide a simple and informative asymptotic ABER expression, which reveals that the scheme can achieve a full diversity order. Furthermore, based on the simple asymptotic ABER expression, the optimum power allocation strategy is determined to improve the system ABER performance. Simulation and numerical results show that the optimum power allocation strategy yields significant performance improvement over the equal power allocation strategy.

It has been shown that the multiple trellis code can perform better than the conventional trellis code over AWGN channels, at the cost of additional computations per trellis branch. Multiple trellis coded multi-h CPM schemes have been shown in the literature to have attractive power-bandwidth performance at the expense of increased receiver complexity. In this method, the multi-h format is made to be associated with the specific pattern and repeated rather than cyclically changed in time for successive symbol intervals, resulting in a longer effective length of the error event with better performance. It is well known that the rate (n-1)/n multiple trellis codes combined with 2^n-level CPM have good power-bandwidth performance. In this paper, a scheme combining rate 1/2 and 2/3 multiple trellis codes with 4- and 8-level multi-h CPM is shown to have better power-bandwidth performance over the upper bound than the scheme with single-h.

By considering the frequency transition as a coding process, a new state diagram based distance property analysis algorithm for frequency transition function (FTF) is derived in this paper. In this new algorithm the distance property can be quickly obtained by solving the state equations derived from the transition process of the state diagram. It is confirmed that the BER performances of DFH systems which are decided by the distance properties of FTFs can be easily and effectively acquired. The new algorithm provides an efficient distance property analysis tool for the construction of FTF, it can help to optimize the design of a DFH system. Numerical simulation results support the theoretical analysis result of our algorithm.

Signal to noise ratio (SNR) estimators are required for many radio engineering applications. In this paper, a SNR estimator based on the first and second order moments is derived and examined for constant envelop modulations over additive white Gaussian noise (AWGN) channel. In the first, a modification method is proposed to reduce the bias of conventional first and second order moments based SNR estimator. Then, in order to reduce hardware implementation complicity, multi segments of cubic polynomial are adopted to approximate the expression of the proposed SNR estimator which doesn’t have a close form solution. The approximate expression is very precise in the SNR range -10dB ~ 20 dB as illustrated by numerical simulation. Besides, practical hardware circuit is proposed for FPGA implementation. Simulation results show that the proposed SNR estimator has the lowest normalized bias and variance when compared with two other classic estimators.

In GEO satellite communication with multi-beam antenna coverage, the decline of uplink performance will appear when the earth terminal near to the junction area of beams coverage. A method to solve the problem by beam diversity technique is studied in this paper. After presenting a new generation method of Nakagami-m fading channel simulation model, we build up a system model for the analysis of multi-beam diversity. In this model, terminal position, beam gain and channel fading level are taken into account. A number of results of simulation show that using beam diversity reception technique can effectively improve uplink performance of GEO satellite communication.

Two contradictory requirements of the on-board switch scheme are the Quality of Service (QoS) performance and the complexity limitation. Therefore, in order to achieve a better trade-off between the performance and the resource utilization, a new onboard switch scheme based on Differentiated Service (DiffServ) is proposed. Under the scheme, a QoS mapping module adopting the concept of the (m,k) model, which implements mapping between the terrestrial and satellite network traffic, is added to the terrestrial satellite terminal (ST). Additionally, according to the mapping results the on-board switch applying a double-Leak Bucket (LB) model controls the on-board traffic efficiently. In the end, Comparisons are made between the proposed scheme and the conventional one by simulation.

Based on the concept of DiffServ (Differentiated Service), an on-board switch framework is proposed, which satisfies QoS performance requirements and maintains a fairly low complexity. It applies the (m, k) model to the mapping between the terrestrial and satellite network traffic and uses the double-LB (Leak Bucket) model to control the traffic efficiently. Simulation results show that the scheme significantly improves the QoS performance, smoothes the burst traffic and saves the on-board buffer reservation.

An improved method for estimating the frequency of a single complex sinusoid in complex additive white Gaussian noise is proposed. The method uses a modified version of the iterative interpolation strategies of Aboutanios and Mulgrew which are asymptotically unbiased and normally distributed with a variance that is very close to the Cramer–Rao bound (CRB). The A&M algorithms require the calculation of four additional discrete Fourier transform (DFT) coefficients with two iterations, whereas the new algorithm only needs two additional coefficients by exploiting the standard DFT coefficients at the first iteration. It is shown by simulation results that the new algorithm maintains the same performance as the A&M estimators.