Rongtao Xu

Approximation to the Capacity of Rician Fading MIMO Channels

In this paper, the capacity of multiple-input multiple-output (MIMO) systems over a Rician fading channel is evaluated. We show that the capacity of MIMO Rician channels can be well approximated by that of correlated MIMO Rayleigh channels. We take the Rician channel with rank-1 mean matrices as an example, the asymptotic capacities at low and high signal- to-noise ratio (SNR) regions are analyzed. Finally, the asymptotic capacity loss of Rician channels relative to Rayleigh channels is derived.

Bivariate gamma distribution from complex inverse wishart matrix

In this letter, a new form of bivariate gamma distribution is proposed from the complex inverse Wishart matrix. We have derived the closed-form expressions for the probability density function and the joint central moments of this bivariate gamma distribution. Finally, the analytical results are used to obtain the outage probability for a multiple-input multiple-output wireless communication systems with two transmit antennas.

Performance Evaluation of MIMO Systems with Transmit Antenna Selection over Correlated Rayleigh Fading Channels

In this paper, we investigate MIMO systems with transmit antenna selection over an intra-class correlated Rayleigh fading channel. In our study, one single transmit antenna with an aim to maximizing the total received signal-to-noise ratio (SNR) is selected for transmission, while it is assumed that the receive side use all the available antennas. Using binary-phase-shift-keying (BPSK) modulation as an illustration, we derive the exact bit error rates (BERs) of two diversity schemes, namely transmit antenna selection and full complexity schemes. Moreover, we compare the asymptotic performance of the two diversity schemes analytically. The effect of correlation among the sub-channels on the SNR degradation is also determined in terms of the correlation coefficient and the number of transmit/receive antennas. Finally, results show that the transmit antenna selection scheme can achieve better performance than the full complexity scheme at the expense of a small amount of feedback information from the receiver.

Time-Selective and Frequency-Selective Relay-Based Channel Capacity for Wireless Communication Systems in High-Speed Railway Environment

One open problem for wireless communication in the high-speed railway environment is channel capacity. In this paper, we study the problem of ergodic capacity for the time-selective and frequency-selective wireless channels in the high-speed railway environment. Firstly, we build up the channel model for the wireless communication between mobile users on the high-speed train and the base station along the railway via the train antennas. Next both the upper bound and the lower bound for the ergodic channel capacity are derived on the basis of this model. Furthermore, the closed-form expression for the ergodic channel capacity is obtained at high SNR. Finally, simulation results are provided to corroborate our proposed studies.

A Novel Algorithm to Control Contents Selectively for Vehicular Communication Networks

With the development of recent vehicular communication technologies, distributing multimedia contents in the vehicular communication networks (VCNs) has become more and more popular, to provide conveniences and entertainment services during the time of driving. However, as multimedia contents are changed and updated dynamically, how to keep the consistency between the original and these replicas in VCNs is very important. Therefore, this paper designs a novel algorithm to control the consistency for the VCNs. In our proposal, after the analyses of the status of road-side units, on-board units and local geographical information, we divide all replicas into two groups, where one is necessary for update and the other are not. Then, we compare the cost to update replicas by using wireless and wired connection, and propose a method to make selection between them. The performance of our proposal is tested by simulation experiments. And the results show that our method can reduce the delay successfully.

Robust Time-Domain OFDM Timing Offset Estimation Based on PN Sequence under Multipath Channels

A novel timing offset estimation scheme for orthogonal frequency division multiplex (OFDM) systems is proposed in this paper, which can eliminate the ambiguity of the first arriving path estimation in multipath channels. The timing of the first arriving path is determined by detecting the first falling edge of the sliding window of the correlation result. A predefined threshold is adopted to validate the presence of the first path. Simulation results show that the proposed scheme can provide more precise timing offset estimation than existing approaches.

Analytical Results for the Performance of MIMO Systems in Frequency Selective Fading Channels

The performance of spatial multiplexing-based multiple-input multiple output (MIMO) systems using zero forcing (ZF) detector in frequency selective fading channels is analyzed in this paper. The approximation of a linear combination of Wishart matrices is used to derive the probability density function (p.d.f.) of output signal-to-noise ratio (SNR) expression. Analytical error rate expressions for the system are obtained with the assumption that inter-path interference is omitted. Simulations are carried out to evaluate the analytical results. We relate the diversity order of frequency selective fading channels with the multipath power delay profile.

Application of Rough Sets and Grey Clustering in Frequency of Wireless Railway Systems

Frequency planning of wireless system is the ubiquitous and urgent key problem due to limited frequency spectrum. This paper presents a frequency planning method according to the characteristics of GSM-R. Rough Sets (RS) theory and Grey Clustering (GC) theory are applied in frequency planning and the factors that affect on frequency planning and their proper thresholds are discussed. Then, the optimal plan is given by means of the GC assessment. Moreover, we compare different frequency planning methods by simulations. Finally, the derivation and simulation results show that the frequency planning based on RS and GC theory is more precise than other algorithms.

Design of Cells for High Speed Railway System

In this paper, the design of cells for high speed railway cellular system based on the bit error rate (BER) is proposed. The BER contours are presented by extending the results in the literature up to 360km/h. Both physical channel modeling and system reliability are considered to study the high speed railway cellular system. The cluster size, reuse distance and overlapping areas are determined by BER which is generated by co-channel interference, delayed signals Doppler affect and additive noise. The simulation results show that the cluster smaller than 5 is not available if maximum BER requirement is 10^(-3) and the cluster should be larger than 4 with BER requirement 10^(-2). Therefore, it is a powerful tool to design and evaluate the performance of high speed railway cellular system.

Analytical Results of V-BLAST MIMO Systems with Two Transmit Antennas over Correlated Rayleigh Channels

In this paper, the performance of vertical Bell Labs Space-Time (V-BLAST) algorithms for the MIMO systems with two transmit antennas is analyzed over correlated-Rayleigh channel. We derive the analytical bit error rates (BERs) of the first and second detection steps for both optimal and fixed detection ordering schemes. We also investigate the signal-to-noise ratio (SNR) degradation of the detection steps for correlated-Rayleigh channels over an independent and identically distributed (i.i.d.) Rayleigh channel. Afterwards, the effect of optimal ordering on the SNR improvement over fixed detection ordering has been discussed. Results have shown that the correlation reduces the SNR improvement of optimal ordering in the first step, whereas the correlation has no effect on the performance of the second step.