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BackgroundPrevious researches have implicated a vital association between gut microbiota (GM) and diabetic retinopathy (DR) based on the association of the “gut-retina” axis. But their causal relationship has not been elucidated.MethodsInstrumental variables of 211 GM taxa were obtained from genome wide association study (GWAS), and Mendelian randomization study was carried out to estimate their effects on DR risk from FinnGen GWAS (14,584 DR cases and 202,082 controls). Inverse variance weighted (IVW) is the main method to analyze causality, and MR results are verified by several sensitive analyses.ResultsAs for 211 GM taxa, IVW results confirmed that family-Christensenellaceae (P = 1.36×10-2) and family-Peptococcaceae (P = 3.13×10-2) were protective factors for DR. Genus-Ruminococcaceae_UCG_011 (P = 4.83×10-3), genus-Eubacterium_rectale_group (P = 3.44×10-2) and genus-Adlercreutzia (P = 4.82×10-2) were correlated with the risk of DR. At the phylum, class and order levels, we found no GM taxa that were causally related to DR (P>0.05). Heterogeneity (P>0.05) and pleiotropy (P>0.05) analysis confirmed the robustness of MR results.ConclusionWe confirmed that there was a potential causal relationship between some GM taxa and DR, which highlights the association of the “gut-retina” axis and offered new insights into the GM-mediated mechanism of DR. Further explorations of their association are required and will lead to find new biomarkers for targeted prevention strategies of DR.

This paper considers transmit beamforming optimization problem for a multi-cell downlink channel with multiple transmit antennas at the base-station. In contrast to the conventional sum-power constraint on the transmit antennas, this paper adopts a per-cell power constraint, which is more realistic in practical implementations. Assuming that the second-order statistics of the channel coefficients are available, this paper investigates the optimization problem of minimizing the total transmission power with individual signal-to-interference-plus-noise ratio (SINR) constraint and per-cell transmission power constraint using Lagrangian duality theory. It is shown that with the approach of Lagrangian duality, the downlink beamforming problem with per-cell power constraint can be transformed into a dual uplink minimax problem with an uncertain noise, and the uplink-downlink duality gives rise to efficient numerical algorithm for solving the downlink per-cell beamforming problem.

Taking into consideration that perfect channel state information (CSI) is prohibitive in practice and imperfect CSI degrades system performance remarkable, we extends the joint transceiver design for multiuser multiple-input multiple-output (MIMO) downlink with perfect CSI to imperfect CSI where each user equipped with multiple antennas. We discussed the correlated case and uncorrelated case respectively. The proposed robust joint design aims to minimize all the users' sum mean-squared-error (MSE) under the constraint of total transmit power. By utilizing the channel error covariance information and moreover the correlation information in spatial correlated channel during the design process, the proposed transceiver design incorporates the impact of the imperfect CSI and spatial correlation, thus it is rather robust to channel errors and spatial correlation. Simulation results also indicate that the robustness of the proposed joint transceiver designs with imperfect CSI in independent channels as well as spatial correlated channels.

This paper investigates low complexity user selection in multiuser multiple-input multiple-output (MU-MIMO) downlink assuming perfect channel state information. Various capacity-based user selection algorithms have been proposed, most of which usually based on null multiuser interference. There is always a performance gap between channel capacity theory and real transmission rate. We study the user selection based on minimum-sum-mean-squared-error (MSMSE) criterion which can reflects the system's performance more properly. We then propose a low-complexity user selection algorithm that doesn't eliminate the multiuser interference completely and considers power allocation during the selection procedure. Simulations show that the proposed algorithm can achieve a much lower BER, and attain the sum rate close to the brute-force search.

This paper presents a novel Bayesian solution to the difficult problem of joint active users' identification, timing estimation and multiuser detection in an asynchronous DS-CDMA system. The observation vectors are considered as a compound Poisson process vitiated by the colored noise, the number of active users is subjected to Poisson distribution and active users' timing information followed the conditional distribution of arriving time in Poisson process. We show the conditional posterior probability density function by introducing subspace algorithm and Bayesian inference, then use RJMCMC algorithm and particle filter to parameters estimation and multiuser detection jointly. Simulation results support the effectiveness of methods.

There are many strict constraints in the design of WSN such as small size, light weight, ultra-low energy efficiency and low cost. Among these energy efficiency should be considered as one of the most critical issues since it is impractical to replace batteries on thousands of microsensors. Furthermore, in some cases the microsensors may not be accessible for battery replacement. Therefore designing energy-efficiency protocols is crucial for prolonging the lifetime of WSN. This paper presents a probability matrix H to average power consumption of every sensor. Then a circuit routing protocol is proposed. The essence of this protocol is that electric circuit is equivalent to the sensor network, and the transmission information content is equivalent to the electric current; the path loss is equivalent to the resistance. Finally, the performance of the proposed protocol is evaluated and simulation results show that it can enhance the energy efficient of wireless sensor network.

In order to suppress mass low power jamming and some high power jamming in GPS receiver; GPS planar array combined sidelobe constraints and quadratic null constraints is designed; sidelobe constraints can suppress low power jamming, quadratic null constraints can suppress high power jamming; computer simulation results show that this design can restrain concealed jamming from sidelobe at controlled level and generate larger and deeper null than simple null at strong jamming direction; this design is very suit for array design of the GPS anti-jamming receiver.

The concept of cooperative diversity promises to offer the benefits of spatial diversity gains to handheld wireless devices with single antennas. So far the research has focused on special modulation or space-time coding in order to allow the cooperating terminals transmit simultaneously during the relay phase. In this paper, we proposed a joint relay selection and ARQ scheme in the cooperative diversity wireless networks. The simulation comparison of the direct transmission scheme, decode- and-forward scheme (DF) and joint relay selection and ARQ scheme showed that the proposed scheme can always achieve the highest throughput.

A chirp frequency-translated reference ultra-wideband system is proposed based on the time-domain and code-domain transmitted-reference impulse radio UWB systems. Mathematic derivation and simulation results show that while this system has similar performance to pulse-based UWB system without losing the merits, it has the advantages of chirp communication system as well. Meanwhile, this system not only offers a solution of simple structure and low-power consumption for low rate and short distance wireless data transmission and location, but performs well in medium and long distance wireless data transmission and location.

Relaying techniques can extend the communication range and coverage, and reduce the transmission power required to reach the users far from the base station. These benefits make MIMO relaying techniques a powerful candidate for implementation in the next generation of wireless networks. The conventional non-regenerative approach is the amplify and forward (AF) approach, where the signal received at the relay is simply amplified and retransmitted. In this paper, we have proposed a optimal relaying and power allocation scheme for a non-regenerative MIMO relay system, which maximizes the capacity for non-regenerative cooperative transmission, when the total transmit power for the source and the relay is restricted. We compare the performance so obtained with the performance for the conventional AF approach, the regenerative relaying scheme and a suboptimal relaying scheme.

The code-orthogonalized transmitted-reference (COTR) impulse-based ultra-wideband wireless communication system has been recently proposed based on the standard transmitted-reference (TR) and frequency-shifted reference (FSR) impulse-based ultra-wideband system by the authors. This paper studies timing acquisition for the COTR-UWB system. The mathematical expressions of synchronization output function in additive white Gaussian noise and multi-path fading environments are deduced first, followed by a simulation on the synchronization algorithm. The outcome of simulation demonstrates that the COTR-UWB system is capable of quick and simple synchronization, without sacrificing the complexity of the receiver.

In this paper, the problem of joint Bayesian active users' identification and multiuser detection in an uncoded cell DS-CDMA system with unknown colored noise is considered. The number of active users follows the Poisson distribution and the observation vectors are considered as the compound Poisson process vitiated by the colored noise. According to the actual condition of users' calling and being called in cells, it defines five kinds of active users' state parameter space movements. We show the conditional posterior probability density function and the equation of conditional posterior likelihood ratio of multiuser detector by introducing subspace algorithm and Bayesian inference. Two-layer nesting iteration Markov Chain Monte Carlo (MCMC) method of Reversible Jump MCMC (RJMCMC) and Gibbs Sampler is used parameters estimation and multiuser detection jointly. Simulation results support the effectiveness of nesting iteration methods.

The estimation of the number of users and detection of the signatures in the unknown colored noise is considered. We exploit the Reversible Jump Markov Chain Monte Carlo (RJMCMC) method to solve the problem. Through introducing subspace algorithm and converting condition state spaces of the posterior distribution, the method based on Bayesian inference achieves the joint posterior probability density function of desired parameters by integrating out the nuisance. Simulation results support the effectiveness of the algorithm.

This paper deals with frequency estimation for burst- mode transmissions in AWGN channel. A semi-data-aided (SDA) maximum likelihood frequency estimation algorithm is derived. According to the algorithm, known pilot symbols and unknown data symbols are used together in order that both estimation accuracy and spectral efficiency can be satisfied. The simulations show that the good performance reaching the CRLB of a large number of pilot symbols can be obtained at moderately high signal-to-noise ratios even when fewer pilot symbols are used.

The concepts of cooperative diversity promise to offer the benefits of spatial diversity gains to handheld wireless devices with single antennas. So far the research has focused on the situation where perfect channel state information is available and coherent detection is employed at the destination receiver. This paper proposes a differential super-orthogonal space-time trellis code modulation scheme for a two-user cooperative diversity system, which does not require channel state information at either users or destination while providing a performance about 1. 5 dB better than DSTBC and 3 dB worse than the corresponding coherent scheme.

A novel PF (Polynomial Fitting) method with great complexity degradation is proposed to get refined channel estimation for the PSAM (Pilot symbol assisted modulation) communication systems in this paper. Different from the classical channel estimator based on the linear interpolation of the received pilot signals, the PF-based channel estimator is developed to avoid the repetitious process of the pilot signals. The impact of the polynomial order and fitting length on the channel estimation errors are studied. The Monte- Carlo simulations are also utilized to evaluate the proposed algorithm, and the results show that it is very simple and can achieve good performance over wide range of SNRs (Signalto- Noise Ratios) and velocities.

A novel collaborative strategy employing two relays is developed for the multihop inter-vehicle communication (IVC) systems in this paper, which has great complexity degradation. Instead of the traditional terminal collaboration or relay tier space-time coding (STC), a relay tier interaction is proposed. Considering time division multiple access (TDMA) scheme, two spatial adjacent vehicles are conjoined by an interaction radio link to create a virtual antenna array (VAA). Then the collaborative two-relay is integrated into a multihop IVC network mentioned above, which enables a single-antenna terminal to share its antenna with other terminals easily, and avoids the synchronization or other complicated requirements in terminal collaboration or STC systems. Furthermore, except the low complexity in hardware implementation, the proposed method also can enhance the performance of the IVC systems over both the quasi-static fading channel and time varying Rayleigh fading relay channel, which is verified through the Monte-Carlo simulations.

In this paper, we propose a novel stopping criteria that based on the mean of the magnitude of the extrinsic information in the iterative decoder of parallel concatenated LDPC (low- density parity-check) codes. The proposed criterion has low computation complexity and few storage requirements. Simulations results proved that the MEM (mean of extrinsic information magnitude) rules outperforms the other existing criterions in terms of BER and average number of super iterations.

In this paper, a LE (logarithmic envelope) algorithm is proposed to estimate one of the most important channel parameters, maximum Doppler frequency. The algorithm uses LE autocorrelation of received pilot signals, which is strongly related with the maximum Doppler frequency in a fading environment. The computer simulation is utilized to evaluate the proposed algorithm, and the results show that the proposed algorithm is very simple and of good performance over wide Doppler frequency range.

In this paper, in order to degrade the computation complexity and storage of the iterative decoder of parallel concatenated LDPC (Low-Density Parity-Check) codes, we propose a novel stopping criteria by using of the mean of the magnitude of the extrinsic information. We verify our algorithms with Monte Carlo simulation, and the results proved that the proposed rules outperforms the other existing criterions in terms of BER and average number of super iterations.

A method based on the combination of the periodogram and the ARMA modeling-total least squares (TLS) algorithm, is proposed for frequency estimation of differential frequency hopping (DFH) signals in Gaussian noise. The spectrum of the signal is first evaluated using the periodogram method. The frequency estimation can be directly obtained by peak-value-searching of the spectrum, if the frequency points are spaced far apart. When they are closely spaced, the singular value decomposition (SVD)-TLS algorithm is then employed for accurate estimation. Based on the above principles, this method enjoys the advantages of both, i.e., low computational complexity, simple implementation and high accuracy. This scheme can also avoid false frequency point estimation which might appear when only the SVD-TLS algorithm is employed. Simulation results verify the feasibility and effectiveness of the method.

This paper introduces an improved parallel interference cancellation algorithm in a DS/CDMA communication system. Because of the lack of the energy information of interfering signal in the conventional parallel interference cancellation (PIC) algorithm, the detection performance of the weak signals is not improved. The algorithm introduced in this paper takes advantage of the virtue of successive interference cancellation (SIC) algorithm and improves greatly the detection performance of weak signals by reducing the error of multi-access interference estimation through classifying the signals. Bit error rate of this improved algorithm has theoretically been analyzed in detail. Simulation results have been given for a multitude of different situations. Finally, it is concluded that the performance of this new algorithm is more desirable than that of the conventional one