FIXED-POINT BLIND ADAPTIVE MULTIUSER DETECTION ALGORITHM FOR IR UWB SYSTEMS IN MULTIPATH CHANNEL

Using the hypothesis that data transmitted by different users are statistically independent of each other,this paper proposes a fixed-point blind adaptive multiuser detection algorithm for Time-Hopping (TH) Impulse Radio (IR) Ultra Wide Band (UWB) systems in multipath channel,which is based on Independent Component Analysis (ICA) idea. The proposed algorithm employs maximizing negentropy criterion to separate the data packets of different users. Then the user characteristic se-quences are utilized to identify the data packet order of the desired user. This algorithm only needs the desired user’s characteristic sequence instead of channel information,power information and time-hoping code of any user. Due to using hypothesis of statistical independence among users,the proposed algorithm has the outstanding Bit Error Rate (BER) performance and the excellent ability of near-far resistance. Simulation results demonstrate that this algorithm has the performance close to that of Maximum-Likelihood (ML) algorithm and is a suboptimum blind adaptive multiuser detection algorithm of excellent near-far resistance and low complexity.

Physical-Layer Key Generation Based on Multipath Channel Diversity Using Dynamic Metasurface Antennas

Physical layer key generation(PKG)technology leverages the reciprocal channel randomness to generate the shared secret keys.The low secret key capacity of the existing PKG schemes is due to the reduction in degree-of-freedom from multipath fading channels to multipath combined channels.To improve the wireless key generation rate,we propose a multipath channel diversity-based PKG scheme.Assisted by dynamic metasurface antennas(DMA),a two-stage multipath channel parameter estimation algorithm is proposed to efficiently realize super-resolution multipath parameter estimation.The proposed algorithm first estimates the angle of arrival(AOA)based on the reconfigurable radiation pattern of DMA,and then utilizes the results to design the training beamforming and receive beamforming to improve the estimation accuracy of the path gain.After multipath separation and parameter estimation,multi-dimensional independent path gains are utilized for generating secret keys.Finally,we analyze the security and complexity of the proposed scheme and give an upper bound on the secret key capacity in the high signal-to-noise ratio(SNR)region.The simulation results demonstrate that the proposed scheme can greatly improve the secret key capacity compared with the existing schemes.

EFFECT OF MULTIPATH CHANNEL MODELS TO THE RECOVERY ALGORITHMS ON COMPRESSED SENSING IN UWB CHANNEL ESTIMATION

Multipath arrivals in an Ultra-WideBand (UWB) channel have a long time intervals between clusters and rays where the signal takes on zero or negligible values. It is precisely the signal sparsity of the impulse response of the UWB channel that is exploited in this work aiming at UWB channel estimation based on Compressed Sensing (CS). However, these multipath arrivals mainly depend on the channel environments that generate different sparse levels (low-sparse or high-sparse) of the UWB channels. According to this basis, we have analyzed the two most basic recovery algorithms, one based on linear programming Basis Pursuit (BP), another using greedy method Orthogonal Matching Pursuit (OMP), and chosen the best recovery algorithm which are suitable to the sparse level for each type of channel environment. Besides, the results of this work is an open topic for further research aimed at creating a optimal algorithm specially for application of CS based UWB systems.

Compressed sensing based channel estimation used in non-sample-spaced multipath channels of OFDM system

By virtue of an increase in spectral efficiency by reducing the transmitted pilot tones, the compressed sensing （CS） has been widely applied to pilot-aided sparse channel estimation in orthogonal frequency division multiplexing （OFDM） systems. The researches usually assume that the channel is strictly sparse and formulate the channel estimation as a standard compressed sensing problem. However, such strictly sparse assumption does not hold true in non-sample-spaced multiple channels. The authors in this article proposed a new method of compressed sensing based channel estimation in which an over-complete dictionary with a finer delay grid is applied to construct a sparse representation of the non-sample-spaced multipath channels. With the proposed, the channel estimation was formulated as the model-based CS problem and a modified model-based compressed sampling matching pursuit （CoSaMP） algorithm was applied to reconstruct the discrete-time channel impulse response （CIR）. Simulation indicates that the new method proposed here outperforms the traditional standard CS-based methods in terms of mean square error （MSE） and bit error rate （BER）.

BDS B1I multipath channel statistical model comparison between static and dynamic scenarios in dense urban canyon environment

Global Navigation Satellite System(GNSS)multipath channel models are fundamental and critical for signal simulation and receiver performance evaluation.They also aid the designing of suitable multipath error mitigation algorithms when the properties of multipath channel are available.However,there is insufficient existing research on BeiDou Navigation Satellite System(BDS)signal multipath channel models.In this study,multipath channel statistical models are established on the basis of extensive datasets of the BDS B1I signal.A multipath parameter estimation algorithm is designed to extract information of multipath rays from the intermediate frequency data.The delay,power loss,Doppler fading frequency,and lifetime distribution models for static and dynamic vehicle platforms are established and compared,and the effects of the satellite orbit type and platform speed on the models are analyzed.The results reveal the detailed distribution and variation characteristics of the multipath parameters and are valuable for the development of accurate urban navigation systems.

A MATCHED FILTER BANK BASED DOA ESTIMATION FOR ASYNCHRONOUS MULTIPATH CDMA CHANNELS

In this paper, a Direction Of Arrival (DOA) estimation algorithm is proposed for multiuser signals through uplink asynchronous multipath Code Division Multiple Access (CDMA) channels. The algorithm is based directly on the correlation matrices of matched filter bank outputs of desired user’s multipath signals and it does not require that the elements of base station antenna array outnumber the multipath signals, which is necessary for the conventional sub-space based direction-finding algorithm. Simulation results show that the proposed algorithm estimates the DOA of multipath signals effectively and acceptably. The proposed algorithm has the prominent advantages of low complexity, simpleness and practicality, which make it much more suitable for practical application.

Response of adaptive matched filter to multipath channel

Response of adaptive matched filter, also called adaptive correlator, to multipath channel is discussed in this paper. It has been proved that the new type processor can better match with multipath chan -nel. The results of experiment carried out on lake and in laboratory are presented. It shows that the processor has good detecting performance in time domain.

Multipath Fading Channel Simulation for Mobile Satellite Communication System

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PERFORMANCE ANALYSIS OF CHANNEL ESTIMATION FOR LDPC-CODED OFDM SYSTEM IN MULTIPATH FADING CHANNEL

In this paper, the channel estimation techniques for Orthogonal Frequency Division Multiplexing （OFDM） systems based on pilot arrangement are studied and we apply Low Density Parity Check （LDPC） codes to the system of IEEE 802.16a with OFDM modulation. First investigated is the influence of channel cstimation schemes on LDPC-code based OFDM system in static and multipath fading channels. According to the different propagation environments in 802.16a system, a dynamic channel estimation scheme is proposed. A good irregular LDPC code is designed with code rate of 1/2 and code length of 1200. Simulation results show that the performance of LDPC coded OFDM system proposed in this paper is better than that of the convolution Turbo coded OFDM system proposed in IEEE standard 802.16a.

Optimal Spacing Design for Pilots in OFDM Systems over Multipath Fading Channels

In wireless orthogonal frequency division multiplexing (OFDM) systems, the time-varying channel is often estimated by algorithms based on pilot symbols. Such an estimator, however, requires statistical prior knowledge that is not easily obtained. Therefore, the pilot tones have to be close enough to fulfill the sampling theorem. In this case the statistical knowledge of the channel is not required to reconstruct correctly the channel impulse response (CIR). This paper explores the optimal placement and number of pilot symbols, we investigate optimal training sequences in OFDM systems and we analyze the number of pilot symbols required to fulfill the sampling theorem. Using a general model for a multipath slowly fading channel, the approach is based on the LS as a criterion of channel estimation while the channel interpolation is done using the piecewise-constant interpolation compromising between complexity and performance. Simulation results demonstrate the good performance of our approach.

Performance Prediction of Packet Mobile Communication through Wireless Multipath Fading Channel Modeling

This paper presents a software simulator applicable to multipath fading channels in urban environments of mobile communication networks. The simulator is constructed by a two-state Markov model and several statistical models for simulating the characterizations of different environments. A core idea of the simulator is to construct a Rice distribution-based multipath fading module produced by a modified Gans Doppler power spectrum, and in combination with a Markov model to predict the time-dependent characteristics of packet in different radio circumstances. It can simply predict the packet performance of the future channel and evaluate the relations between the radio channel and the modulation schemes, error control protocols and channel coding. Simulation results demonstrate that it is a reliable and efficient method.

An enhanced iterative joint channel estimation and symbol detection algorithm for OFDM systems

For orthogonal frequency division multiplexing (OFDM) wireless communication, the system throughput and data rate are usually limited by pilots, especially in a high mobility environment. In this paper, an enhanced iterative joint channel estimation and symbol detection algorithm is proposed to enhance the system throughput and data rate. With lower pilot power, the proposed scheme increases system throughput firstly, and then the channel estimation and symbol detection proceed iteratively within one OFDM symbol to improve the BER performance. In the proposed algorithm, the original channel estimate of each OFDM symbol is based on the channel estimate of the previous OFDM symbol, thus the variation of the mobile channel is traced efficiently, so the number of pilots in the time domain can be reduced greatly. Besides reducing the system overhead, the proposed algorithm is also shown by simulation to give much better BER performance than the conventional iterative algorithm does.

Adversarial Training-Aided Time-Varying Channel Prediction for TDD/FDD Systems

In this paper, a time-varying channel prediction method based on conditional generative adversarial network(CPcGAN) is proposed for time division duplexing/frequency division duplexing(TDD/FDD) systems. CPc GAN utilizes a discriminator to calculate the divergence between the predicted downlink channel state information(CSI) and the real sample distributions under a conditional constraint that is previous uplink CSI. The generator of CPcGAN learns the function relationship between the conditional constraint and the predicted downlink CSI and reduces the divergence between predicted CSI and real CSI.The capability of CPcGAN fitting data distribution can capture the time-varying and multipath characteristics of the channel well. Considering the propagation characteristics of real channel, we further develop a channel prediction error indicator to determine whether the generator reaches the best state. Simulations show that the CPcGAN can obtain higher prediction accuracy and lower system bit error rate than the existing methods under the same user speeds.

Performance of MC-CDMA Systems with Orthogonal Transmit Diversity over Rayleigh Fading Channel

Transmit diversity has been recently proposed to reduce the effects of fading channels in various wireless applications. Orthogonal transmit diersity (OTD) is one of the standardized techniques in 3G systems. In this paper, we apply orthogonal transmit diversity technique to multicarrier CDMA systems. Andlysis and simulation results show that performance benefits can be achieved compared with conventioal MC-CDMA systems in multipath fading channels.

AN IMPROVED DOA ESTIMATION ALGORITHM FOR ASYNCHRONOUS MULTIPATH CDMA SYSTEM

This paper proposes an improved Direction Of Arrival（DOA） estimation algorithm for asynchronous multipath Code Division Multiple Access（CDMA） system. The algorithm is based on the correlation matrices of outputs of decorrelator, which is a Multi-User Detection（MUD） approach, one of the key techniques for CDMA system. Through decorrelating processing, the desired user＇s mulipath signals can be resolved and all the other resolved multipath signal interference is eliminated. So the proposed algorithm is expected to perforln much better than algorithm such as that based directly on the Matched Filter（MF） bank outputs. Simulation results confirm this. While the improved algorithm performs better and better as Signal-to-Noise Ratio（SNR） increases, the performance of algorithm based directly on the MF bank outputs can not be improved.

Clustering in the Wireless Channel with a Power Weighted Statistical Mixture Model in Indoor Scenario

Cluster-based channel model is the main stream of fifth generation mobile communications, thus the accuracy of clustering algorithm is important. Traditional Gaussian mixture model (GMM) does not consider the power information which is important for the channel multipath clustering. In this paper, a normalized power weighted GMM (PGMM) is introduced to model the channel multipath components (MPCs). With MPC power as a weighted factor, the PGMM can fit the MPCs in accordance with the cluster-based channel models. Firstly, expectation maximization (EM) algorithm is employed to optimize the PGMM parameters. Then, to further increase the searching ability of EM and choose the optimal number of components without resort to cross-validation, the variational Bayesian (VB) inference is employed. Finally, 28 GHz indoor channel measurement data is used to demonstrate the effectiveness of the PGMM clustering algorithm.

The influence of PRF on BER performance of THSS UWB radio systemwith PPM in dense multipath fading environments

The influence of pulse repetition frequency(PRF) on performance of wireless digital time hopping spread spectrum(THSS) ultrawide bandwidth(UWB) radio systems with PPM in dense multipath fading environments is firstly investigated. The receiver used in this UWB system is a hybrid selection/maximal-ratio combining(H-S/MRC) diversity receiver in which L strongest multipath components out of N multipath diversity branches are selected and combined using maximal-ratio combining. The exact expressions for the bit error rate(BER) of this UWB system are firstly derived by using the virtual branch technique in term of PRF, the number of multipath components selected and combined L, and multipath spread of the channel and then this BER performance is evaluated. With the computer simulation for impulses having different pulse shapes, numerical results show that PRF, as well as pulse shape and the number of multipath diversity branches selected and combined L, has much effect on the BER performance of this UWB system in dense multipath fading environments. As PRF increases, the BER performance of this UWB system is much degraded under the conditions of fixed L and pulse shape.

Performance Study of DS-SFH/SSMA Communication with Multipath Diversity

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On Time-of-Arrival Statistic of Gaussian Channel Model

A model of an angle-spread source, termed the “Gaussian Channel Model” is considered. The cumulative distribution function of the Time-of-Arrival of the multipath components is derived for an arbitrary angle spread. The simple approximate expressions for the Time-of-Arrival cumulative distribution function and probability density function are proposed. Numerical results obtained with the help of the derived expressions show the good coincidence with the experimental data and other known results.

Simulation Model of Wireless Channel

The change of channel is caused by Doppler effect, and the degree of change is related to relative velocity in the condition of the certain carrier frequency. The multipath fading channel is independent of each other, whose amplitude obeys Rayleigh distribution and the phase obeys uniform distribution. The model of multipath time-varying transmission channel is built. Through the pro-cess of channel model building, the simulation results produced by the channel model verify the effect of the proposed model in the aspect of reducing test data. In a communication system, signal passing through the channel is involved with the process of digital modulation and demodulation. Binary sequence signal is modulated into a complex sequence in the process of modulation before the transmission in the channel, in order to accommodate the wireless channel transmission. With the increase of SNR, BER is overall slightly drops. However there exists violent fluctuation and it presents the random variation of details in the multipath channel. I employ the mathematical model of multipath time-varying channel, i.e. Jakes model to be simulated so as to compare with the AGWN channel in the same situation. Jakes model has the characteristics of the reference chan-nel compared with the AGWN. BER does not change with the increase of SNR significantly and coincides with multipath time-varying channel. The BER considerably decreases with the increase of SNR in the AGWN channel.