Tang Youxi

A new access method used in beyond 3G mobile system using MC-CDMA

A new access method that can be used in a post 3G mobile system is proposed. In the future mobile communication systems, OFDM technology probably become the main technology. On account of multi-traffic demands in the future, we should design the access method in OFDM system to accord with those demands. With this method, the system resources utilization can be optimized.

A Suboptimal Multiuser-Pairing Algorithm With Low Complexity for Virtual MIMO Systems

In virtual multiple-input-multiple-output (V-MIMO) systems, employing a user-pairing algorithm can significantly improve system capacity and spectral efficiency using multiuser diversity. The optimal pairing algorithm can achieve optimal system performance, but it is not feasible to implement in practice due to its huge complexity. To solve the problem, an efficient suboptimal pairing algorithm with lower complexity is proposed, which maximizes the system throughput by selecting users one by one. Furthermore, to achieve a good balance between throughput and user fairness, a novel pairing algorithm is derived, which combines the advantages of the suboptimal pairing algorithm and proportional fair (PF) criteria. Simulation results show that the proposed algorithm achieves better fairness and higher system throughput than the double PF (D-PF) algorithm, and has much lower complexity than the optimal pairing algorithm.

Performance and optimization of multistage partial parallel interference cancellation for wideband CDMA systems in multipath fading channels

In this paper, a closed-form bit error rate (BER) of hard-decision multistage partial parallel interference cancellation (PPIC) having perfect and imperfect channel estimation for complex spreading code-division multiple access (CDMA) over multipath Rayleigh channels was derived. The effects of receiving BER, power ratio of pilot to data channels, multiple-access interference (MAI) and multipath interference, additive white Gaussian noise, and other factors affecting channel estimation error are analyzed. The expression determining the optimal interference cancellation weight at path level for PPIC is first derived. Then, the oscillatory behavior of user-level-optimized PIC and the convergence of perfect channel estimation PIC and path-level-optimized PIC are validated. Results indicate that all factors determining the optimal weight certainly affect the BER performance of PPIC and that the lower BER limit of multistage PPIC depends on the adjustable factors, which include power ratio, observation length, and signal-to-noise ratio, and an unchangeable factor, i.e., number of users. In addition, the variance of MAI for complex spreading sequence is obtained, and the analytical expression can also be employed to predict the performance of multicode CDMA

A Novel Method to Design Phase Factor for PTS Based on Pseudo-Random Sub-Block Partition in OFDM System

Partial transmit sequence (PTS) with pseudo-random sub-block partition can achieve lower Peak-to-Average Power Ratio (PAPR) performance. Based on the correlation of the candidate signals, we can prove that the performance is uncorrelated with the input signal. In general, the correlation of the candidate signals will increase with the number of candidate signals. As a result, the performance improvement will decrease evidently. In this paper, we provide a novel method to design the phase factor for PTS scheme, so as to achieve quasi orthogonal candidates to get better PAPR reduction performance. Simulation results prove it is more efficient than the traditional one.

Performance of time and frequency domain chip-level differential detection in two-dimension spread spectrum system

This paper is concerned with the design and performance evaluation of a time and frequency domain chip-level differential detection (TF-CLDD) technique for two-dimension spread spectrum system. Unlike the conventional chip-level differential encoding/detection performed either time domain or frequency domain, such a technique envisages differential detection of the time domain and frequency domain spreading code chips to counteract both the time-selective and frequency-selective fading at the same time. The bit error rate performance of the receiver is analytically evaluated as a function of the relevant system parameters.

Effect of correlations on the symbol error rate of orthogonal space-time block codes in keyhole MIMO channels

Keyhole channels generally characterize rank-efficient MIMO channels, which were predicted theoretically and also observed experimentally. In this paper, we present error rate performance analysis of orthogonal space-time block codes (STBCs) in correlated keyhole multiple-input multiple-output (MIMO) channels, which is not only suitable for exponential correlation models, but also for constant correlation models. Using a moment-generation-function (MGF) based approach, we provide the exact expressions of the average symbol error rate (SER). Simulation results are provided to validate our analytical results.

Analysis of the Performance of Iterative Estimation and Cancellation of Clipping Non-linear Distortion in OFDM

Clipping is usually applied to decrease the high peak-to-average power ratio (PAPR) caused by orthogonal- frequency-division-multiplex (OFDM) with interference. To resolve this problem, an iterative estimation and cancellation of clipping non-linear distortion scheme is proposed. This paper presents that the performance of iterative estimation and cancellation of clipping non-linear distortion is better than that of clipping noise. The method of iterative estimation and cancellation of clipping non-linear distortion can recover the signal before clipping perfectly with the ideal feedback data. However, if receiver only estimate and cancel the clipping noise the signal will still be influenced by the attenuation caused by clipping. Analysis and simulation results prove the conclusion. And it is shown by numerical simulation results that system performance can be improved evidently. When the clipping threshold is 1.2, the performance is improved about 2 dB with only one iterative estimation and cancellation.

ESTIMATION OF CARRIER FREQUENCY OFFSETS FOR MIMO SYSTEMS WITH DISTRIBUTED TRANSMIT ANTENNAS

The problem of estimating the carrier frequency offsets in Multiple-Input Multiple-Output (MIMO) systems with distributed transmit antennas is addressed. It is supposed that the transmit antennas are distributed while the receive antennas are still centralized, and the general case where both the time delays and the frequency offsets are possibly different for each transmit antenna is considered. The channel is supposed to be frequency flat, and the macroscopic fading is also taken into consideration. A carrier frequency offset estimator based on Maximum Likelihood (ML) is proposed, which can separately estimate the frequency offset for each transmit antenna and exploit the spatial diversity. The Cramer-Rao Bound (CRB) for synchronous MIMO (i.e., the time delays for each transmit antenna are all equal) is also derived. Simulation results are given to illustrate the performance of the estimator and compare it with the CRB. It is shown that the estimator can provide satisfactory frequency offset estimates and its performance is close to the CRB for the Signal-to-Noise Ratio (SNR) below 20dB.

A soft interference cancellation detection scheme for distributed antenna MIMO systems

We propose an iterative soft interference cancellation (SIC) detection scheme for distributed antenna multiple-input multiple-output (DA-MIMO) systems. The received signal is pre-processed via a matched filter before SIC is applied, then, the proposed SIC treats the intersymbol interference (ISI) as Gaussian noise with matched mean and covariance. The probability associated with each transmit symbol can be iteratively updated by the probabilistic data association (PDA) filter until the desired bit error rate (BER) performance is obtained. Simulation results show that the proposed SIC in DTA-MIMO (distributed transmit antenna MIMO) systems can achieve almost the same performance as maximum likelihood detection (MLD) with reduced complexity.

Performance analysis of TDD OFDM systems with phase and amplitude and phase pre-equalization

In this paper, the performance of time division duplex (TDD) orthogonal frequency division multiplexing (OFDM) systems over slow Rayleigh channels with phase and amplitude and phase pre-equalization are analyzed. The hit error rate (BER) formulas of binary phase-shift keying (BPSK) modulated TDD OFDM systems using ideal and nonideal pre-equalization are provided. Computer simulations are performed and the results verify corresponding formulas. The system performance of phase pre-equalization is decided by E/sub b//N/sub 0/ and channel estimation(CE) error. With the diminishing of CE error, system performance will reach towards the theoretical performance of a BPSK system in Rayleigh channels. In amplitude and phase pre-equalization systems, appropriate pre-equalization factor should he selected carefully to avoid the boost effect of transmission power and CE error on those subcarriers suffering deep fading. The corresponding BER formulas are presented, which base upon the E/sub b//N/sub 0/, mean square error (MSE) and pre-equalization factor.