Rician Channel Model Research Articles

Doppler frequency offset estimation and diversity reception scheme of high-speed railway with multiple antennas on separated carriage

The challenges of severe Doppler effects in high-speed railway are considered. By building a cooperative antenna system, an algorithm of joint channel estimation and Doppler frequency offset (DFO) estimation is proposed based on Ricean channel model. First, a maximum likelihood estimation (MLE) algorithm for DFO is designed, showing that the Doppler estimation can be obtained by estimating moving velocity of the train and the path loss with the exploitation of pilots that are placed inside the frame. Then a joint detection algorithm for the receiver is proposed to exploit multi-antenna diversity gains. Last, the theoretical Crammer Rao bound (CRB) for joint channel estimation and DFO estimation is derived. The steady performance of the system is confirmed by numerical simulations. In particular, when the Ricean fading channel parameter equals 5 and the velocities of train are 100 m/s and 150 m/s, the estimation variances of DFO are very close to the theoretical results obtained by using CRB. Meanwhile, the corresponding signal to noise ratio loss is less than 1.5 dB when the bit error rate is 10−5 for 16QAM signals.

Average Mutual Information Analysis of Multiple Input and Multiple Output System with Multihop Relaying in Wireless Communication System

Problem statement: Multiple Input and Multiple Output (MIMO) system with Multihop relaying techhnique is significant and active areas of wireless communication. In a rich scattering environment MIMO antenna system provides better channel capacity and data rates than single antenna systems. To provide high throughput, reliable transmission and broad coverage, wireless relaying techniques are essential in a variety of applications. In a cellular environment a relay can be used to overcome shadowing effect due to obstacles and multihop relaying can improve the throughput for mobiles suffering from poor signal to interference, noise ratio at the edge of a cell and reduce cell size to increase spectral efficiency. Approach: This study analyzes average mutual information of the Ricean channel for single hop Multiple Input Multiple Output (MIMO) system for different antenna configuation and dependence of capacity on the Rice factor for cellular system. The asymptotic capacity of multiuser two-hop MIMO system with Regularization Block Diagonalization (RBD) precoding techniques for Indepenent Identically Distributed (IID) channal and realistic Mobile to Mobile fading channel model was examined. In this realistic model, Non-Line-Sight (NLOS) propagation conditions are assumed from source mobile station to mobile relay and also from mobile relay to destination station. A non regenerative Amplify and Forward (AF) relay is used to optimize the capacity between the source and destination and also the evaluation was made for multiuser multi-hop relay system with correlated fading channel model using RBD precoding matrix. Results: The simulation results for average mutual information of single hop MIMO relay system for different antenna configuration with ricean channel model, ergodic sum mutual information for two hop relay system with RBD precoding technique and mutual information results for multiuser multihop relay system with correlated channel model was presented. Conclusion/Recommendations: Cellular systems generally operated at a fairly low SINR which can be increased on each hop by adding relays. Multiuser two hop relay system with RBD precoding for realistic mobile to mobile fading channel model is simulated and compared with IID channel model. Multiuser Multi-hop relay with optimal precoding and RBD precoding technique results were analyzed for correlated fading channel and found that capacity offered by RBD precoding scheme is better than other relaying systems.

Soft Metrics and EXIT Chart Analysis of Noncoherent MFSK with Diversity Reception in Rician Fading Channel

A convolutionally encoded noncoherent M-ary Frequency Shift Keying (MFSK) modulation scheme with diversity reception is considered. Soft metrics for Soft Decision Decoding (SDD) of noncoherent MFSK are derived assuming Rician channel model. Furthermore, the convergence behavior of the MFSK receiver is investigated using EXtrinsic Information Transfer (EXIT) charts. It has been demonstrated that the derived expressions for soft information are useful allowing SDD of the MFSK scheme exploiting diversity and the EXIT chart analysis provides useful insights into its iterative decoding behavior.

Channels estimation in OFDM system over Rician fading channel based on comb-type pilots arrangement

Orthogonal frequency-division multiplexing (OFDM) is a transmission technique that is based on many orthogonal carriers that are transmitted simultaneously. Channel estimation techniques for OFDM systems, based on comb-type pilot arrangement, over frequency-selective Rician and time-varying fading channel are investigated. The advantage of comb-type pilot arrangement, in channel estimation, is the ability to track the variation in the channel, which is the main reason for inter-carrier interference modelled as an additive white Gaussian noise, leading to an increase in the noise level. The estimation of the channel at the pilot frequencies is based on least-square (LS) method. Several interpolation methods have been used to estimate the channel response at the data frequency. In this study, simulation results for Rician channel model were examined and bit error rate/signal-to-noise ratio performance, for various conditions, were considered, and the pilot arrangement was used with the LS estimation and low-pass interpolation techniques, leading to a reduction in the effect of Doppler frequency.

Performance Improvement in Estimation of Spatially Correlated Rician Fading MIMO Channels Using a New LMMSE Estimator

In most of the previous researches on the multiple-input multiple-output (MIMO) channel estimation, the fading model has been assumed to be Rayleigh distributed. However, the Rician fading model is suitable for microcellular mobile systems or line of sight mode of WiMAX. In this paper, the training based channel es-timation (TBCE) scheme in the spatially correlated Rician flat fading MIMO channels is investigated. First, the least squares (LS) channel estimator is probed. Simulation results show that the Rice factor has no effect on the performance of this estimator. Then, a new linear minimum mean square error (LMMSE) technique, appropriate for Rician fading channels, is proposed. The optimal choice of training sequences with mean square error (MSE) criteria is investigated for these estimators. Analytical and numerical results show that the performance of proposed estimator in the Rician channel model compared with Rayleigh one is much better. It is illustrated that when the channel Rice factor and/or the correlation coefficient increase, the per-formance of the proposed estimator significantly improves.

Weak Solar Scintillation Effects on Deep Space Communication

摘要: 行星聚合和太阳闪烁是影响深空通信的重要因素. 分析了行星聚合和太阳闪烁的物理特性, 建立了弱太阳闪烁条件下深空通信信道的Rician 模型, 并得出了当Rician 因子大于10 dB 时近似为高斯信道的结论. 对弱太阳闪烁下X 波段和Ka 波段的通信性能进行了仿真, 这对建立可靠的深空通信链路具有十分重要的意义. 关键词: 太阳闪烁 / 行星聚合 / 深空通信

Optimal Design of Uniform Rectangular Antenna Arrays for Strong Line-of-Sight MIMO Channels

We investigate the optimal design of uniform rectangular arrays (URAs) employed in multiple-input multiple-output communications, where a strong line-of-sight (LOS) component is present. A general geometrical model is introduced to model the LOS component, which allows for any orientation of the transmit and receive arrays, and incorporates the uniform linear array as a special case of the URA. A spherical wave propagation model is used. Based on this model, we derive the optimal array design equations with respect to mutual information, resulting in orthogonal LOS subchannels. The equations reveal that it is the distance between the antennas projected onto the plane perpendicular to the transmission direction that is of importance with respect to design. Further, we investigate the influence of nonoptimal design, and derive analytical expressions for the singular values of the LOS matrix as a function of the quality of the array design. To evaluate a more realistic channel, the LOS channel matrix is employed in a Ricean channel model. Performance results show that even with some deviation from the optimal design, we get better performance than in the case of uncorrelated Rayleigh subchannels.

Ultrawideband Channel Modeling on the Basis of Information-Theoretic Criteria

We present results of two indoor ultrawideband channel measurement campaigns in the 2-5 GHz frequency band. In measurement campaign I (MC I), the channel is static and we sample it spatially, while in MCII the transmitting and receiving antennas are fixed and channel variation is induced by people moving in the environment. Transmitter and receiver are separated by up to 27 m in MC I and up to 20 m in MC II. To determine suitable small-scale fading distributions for the tap amplitudes of the discrete-time baseband-equivalent channel impulse response, we use Akaike's information criterion (AIC). Despite the large bandwidth, AIC supports the Rayleigh (MCI) or the Rice distribution (MC II). For data from MC II, we estimate the covariance matrix of the random channel impulse response and demonstrate that the number of corresponding significant eigenvalues, and hence the diversity order of the channel, scales approximately linearly with bandwidth. Contrary to the uncorrected scattering assumption, we find that the channel taps are weakly correlated. The ergodic capacity predicted by the Ricean channel model with parameters estimated from MC II shows good agreement with the ergodic capacity obtained by direct evaluation of the measurement results, while the corresponding outage capacities show a worse fit for low outage probabilities because of shadowing.

Rician K-Factor Distribution in Broadband Fixed Wireless Access Channels under Rain Fades

The performance of broadband fixed wireless access (BFWA) systems operating at frequencies above 10 GHz is adversely influenced by rainfall, which introduces severe attenuation and a short-term variation to the received signal. In this letter, the fading channel of a BFWA link is modeled as Rician with a strong Rician K-factor. A novel analytical model relating the Rician K-factor with the rain fading effects is presented based on which, an analytical prediction model for the cumulative distribution of the Rician K-factor is derived. Experimental data is necessary to validate the proposed models. The presented methodology provides an efficient way to incorporate the mathematically intractable physical input of rain fading into the easy-to-simulate Rician channel model. The proposed models can be applied on a global scale and incorporate the impact of various crucial operational and geometrical parameters of a BFWA system on the wideband multipath behavior of the channel. Useful numerical results regarding the validity of the presented models are also provided

Approximate closed-form expression for the ergodic capacity of polarisation-diversity MIMO systems

MIMO systems using single dual-polarised antennas at transmitter and receiver can be a simple, cheap and compact alternative to conventional multi-antenna MIMO configurations. Recently, approximate expressions and bounds for the ergodic capacity of such systems have been proposed assuming Rayleigh or Ricean channel models. Atight closed-form approximation for the ergodic capacity of such systems in arbitrary multipath fading channels is derived.

Performance of Space-Time Modulation for a Generalized Time-Varying Rician Channel Model

We analyze the performance of trained and differential space-time modulation for channels with a constant specular component and time-varying diffuse fading. We examine the case where the channel varies from sample to sample within a space-time symbol matrix according to a first-order time-varying model. We show that the effect of the time-varying diffuse channel can be described by an effective signal-to-noise ratio (SNR) that decreases with time. We derive pairwise probability of error expressions based on these effective SNR values that accurately describe performance for unitary modulation. We quantify the significant advantage that differential modulation provides at high SNR where the effect of the time-varying channel dominates. At low SNR where additive noise dominates, we note that trained modulation with perfect channel state information provides a 3-dB advantage over differential modulation, but decoding based on a maximum likelihood channel estimate yields worse performance than differential modulation at all SNR values. Simulation results are provided to support our analysis.

GENERAL PACKET RADIO SERVICE PHYSICAL-LAYER PERFORMANCE SIMULATION

In this paper, we present some results on GPRS physical- layer performance based on a GPRS simulator. The simulator strictly abides by the GSM standards implementing the detailed transmission chain. We analyze the results of a comprehensive simulation of the GPRS traffic channels. We evaluate the GPRS performance under various environment and service rates. The reference channel model used for the simulations is entirely based on the Ricean channel model and provides a reasonable scenario for radio propagation. The results shown here provide an insight into how to assess the actual GPRS data channels performance under various service rates.

Worst-case partial-band noise jamming of Rician fading channels

Analyses of worst-case partial-band noise jamming of binary digital modulation are presented. Both noncoherent detection and differentially coherent detection over slowly varying, frequency-nonselective Rician fading channels are considered. The analysis bridges the gap between earlier works by Viterbi and Jacobs (1975) and by Omura (1981) for the limiting cases of Gaussian and Rayleigh channels, respectively. The results complement those by Crepeau (1990) for noncoherent binary transmission over the Nakagami fading channel. However, the Rician channel model has more physical significance since the parameter k is the ratio of scattered and specular powers. It is shown that a partial-band (partial-time) jamming strategy is optimum for all Rician channels with k<1 if the signal-to-jamming power ratio is sufficiently high. On the other hand, a full-band jamming strategy is the optimal strategy for k/spl ges/1. Results for the Gaussian and Rayleigh channels can be derived from the present analysis in the limit as k=0 and k/spl rarr//spl infin/, respectively.

Modelling and simulation of a Ka‐band DBPSK/DQPSK mobile satellite channel

AbstractFor the prospective personal satellite communications in the early 21st century, this paper presents a general exploration of a Ka‐band DBPSK/DQPSK land‐mobile satellite channel model and its BER performance from system design, modelling and simulation. A forward‐link (i.e. outbound from the hub) channel design is introduced in brief. A complete model of channel multipath fading and shadowing is proposed for the first time, including a basic model and various derivative submodels corresponding to different actual propagation environments. Computer simulation results are given for a Rician channel model, a shadowed channel model and different combinational‐fading channel models by complete curve sets of BER performance, which coincide with the results of the analysis, and could be used as valuable references in further research and implementation.

Reed-Solomon codes for land mobile satellite channels

The performance of Reed-Solomon codes is determined for land mobile satellite communications where a shadowed Rician channel model is used. An effective coding/interleaving scheme is proposed which uses the multipath fading and shadowing statistics of the channel.

On the Utility of Chirp Modulation for Digital Signaling

The issue of signal selection in binary data transmission is presented. The question of the relative utility of linear frequency sweeping (LFS or chirp), compared to PSK and FSK, in terms of error probability and spectrum usage, is discussed. The transmission media considered are the coherent, partially coherent, Rayleigh, and Rician channel models. Theoretically, LFS has unconditionally superior characteristics in the partially coherent and fading cases, for certain ranges of channel conditions. This is due to the more negative values of cross-coherence parameters possible with the LFS signal set over the FSK signal set. For the fading channel, theoretical supremacy of LFS over FSK depends upon the specular-to-Rayleigh signal power ratio and the adjustability of in-phase cross coherence, with a constraint upon quadrature phase cross coherence. From a practical standpoint, coherent reception of the LFS signal set has severe limitations. These are manifested primarily in two aspects: the need for phase synchronization of a chirp signal set, and the fact that the optimum value of cross coherence is highly sensitive to synchronization channel signal-to-noise ratio (SNR), and/or spectral-to-Rayleigh signal power ratio. The latter would require that modulation characteristics track the channel conditions in order to achieve the supremacy in performance theoretically predicted by optimization of the cross-coherence parameter in LFS.

On the Analysis of Reed-Solomon Codes for OFDM Systems over Rician Fading Channels

The relative strength between the direct and the scattered paths of the received signal in wireless communication as described by the Rician factor K specifies the quality of the transmission link. Fading in Rician channel models influence the performance of Orthogonal Frequency Division Multiplexing (OFDM) systems. Accordingly, channel estimation together with different Forward Error Correction (FEC) schemes are used to provide significant performance gain for OFDM systems over fading channels. In most literature, the performance of FEC schemes such as Turbo and LDPC codes have been analysed for OFDM systems over frequency-selective Rician fading channels. This paper evaluates the performance of Reed-Solomon (RS) codes over frequency-selective Rician fading channels. The performance of RS codes is firstly studied for different Rician K factors and Doppler frequencies. Secondly, the performance of RS codes is reviewed assuming different code rates (n k ) for both hard-decision and soft-decision decoding algorithms. The Euclidean algorithm (EA) is used as the RS hard-decision decoding algorithm while the Parity-check Transformation Algorithm (PTA) is deployed as the RS soft-decision decoding algorithm. The results for the various channel and coding conditions are documented through computer simulations. The simulation results validate the importance of a high Rician K factor. Interestingly, the simulation results verify that adopting a low-rate code do not necessarily improve the error rate irrespective of the Rician K factor. This analysis is relevant in order to establish the performance of combined RS codes with OFDM systems over frequency-selective Rician fading channels.