Wanzhi Ma

Performance Analysis of TDD Reciprocity Calibration for Massive MU-MIMO Systems With ZF Beamforming

This study analyzes a two-way signaling method for time division duplex reciprocity calibration (RC) in multiuser beamforming systems. The system model of RC is established, and the estimation error of the RC coefficient is derived. The effect of this error is examined in terms of the user signal-to-interference-plus-noise ratio (SINR) and capacity. Results reveal the relationship between the user SINR and RC errors as well as the number of antennas and users. Moreover, the findings show that the colocated antenna array is less sensitive to calibration errors than the case of distributed antennas even if the calibration signal-to-noise ratio (SNR) is identical. The interference resulting from imperfect calibration becomes the determinant that constrains the performance, particularly when a high user SNR is required.

Performance of an M-QAM full-duplex wireless system with a nonlinear amplifier

The effect of amplifier nonlinearity is analyzed for M-QAM full-duplex communications in additive white Gaussian noise channels. Two classical memoryless nonlinear amplifier models, i.e., a traveling-wave tube amplifier and a solid-state power amplifier, are considered. An analytical expression for the bit error ratio is derived using a characteristic function and numerical integration. Theoretical results show perfect agreement with those obtained by simulation. The analytical results could be used to evaluate the degradation in performance of an M-QAM full-duplex system caused by amplifier nonlinearity, and will be helpful in finding the optimal static operating point of an amplifier.摘要创新点本文分析了非线性功放对M-QAM全双工无线通信性能的影响; 采用行波管功放(TWTA)模型和固态功放(SSPA)模型, 并通过特征函数和数值积分的方法求出M-QAM全双工无线通信误码率的表达式, 最终用仿真验证了理论分析的正确性。本文结论可用于估算M-QAM全双工无线通信中非线性功放带来的信噪比损失, 以及为非线性功放选择最佳的静态工作点。

Adaptive Step Size for OFDM CFR with Cognitive Clipping

In this paper, an adaptive step size algorithm is proposed to reduce peak-to-average power ratio (PAR) of OFDM signals. The error vector magnitude (EVM) and spectral mask constraints are considered. Unlike the existing cognitive clipping method, the proposed scheme adjusts the EVM threshold with adaptive step size, which is proportionate to the ratio between PAR of each OFDM symbol and that required by system. Compared with the original method, the new algorithm offers more than 0.2dB PAR reduction at 10e-4 complementary cumulative distribution function (CCDF) level and 20% iteration reduction for 256 subcarriers QPSK WiMAX signal.

Layered space-time codes over Ricean fading channels by reducing the correlation of spatial shaping pulses

In this paper, an asynchronous layered space-time architecture is proposed to realize the spatial multiplexing over the Ricean multiple-input multiple-output (MIMO) channels. Based on reducing the correlation of spatial shaping pulses between the multiplexed streams, this approach can be used to solve the problem of detection in the ill-conditioned channel matrix. It is shown that at the receiver, the reduction of the correlation enables the requirement on the number of the receive antennas to be removed by the zero forcing (ZF) detector compared with the conventional synchronous layered space-time architecture. First, this paper presents how to exploit the correlation of spatial shaping pulses between the multiplexed streams. Then deriving the exact closed-form expression of error rate for the proposed scheme, this paper finds that the maximum possible diversity gain can be achieved based on the independent layered architecture by the ZF detector at the cost of limited multiplexing gain.

Layered Space-Time codes Over Ricean Fading Channels by Reducing the Correlation of Spatial Shaping Pulses

In this paper, an asynchronous layered space-time architecture is proposed to realize the spatial multiplexing over the Ricean multiple-input multiple-output (MIMO) channels. Based on reducing the correlation of spatial shaping pulses between the multiplexed streams, this approach can be used to solve the problem of detection in the ill-conditioned channel matrix. It is shown that at the receiver, the reduction of the correlation enables the requirement on the number of the receive antennas to be removed by the zero forcing (ZF) detector compared with the conventional synchronous layered space-time architecture. First, this paper presents how to exploit the correlation of spatial shaping pulses between the multiplexed streams. Then deriving the exact closed-form expression of error rate for the proposed scheme, this paper finds that the maximum possible diversity gain can be achieved based on the independent layered architecture by the ZF detector at the cost of limited multiplexing gain.