An apparatus and method for supporting diversity in a beamformed wireless communication system. A method for transmitting a signal in a transmit end includes determining Receive (Rx) beamforming capability information of a receive end, receiving channel information on at least one Transmit (Tx) beam pattern from the receive end, determining at least one Tx beam pattern for transmitting a signal to the receive end, in consideration of Rx beamforming support information of the receive end and the channel information on the at least one Tx beam pattern, and transmitting a signal to the receive end using the at least one Tx beam pattern for transmitting the signal to the receive end.

Apparatus and method for supporting multi-antenna transmission in beamformed wireless communication system

Large-scale multi-cell multiuser multiple-input multiple-output (LS-MIMO) systems can greatly increase the spectral efficiency. But the performance of these systems is deteriorated by pilot contamination. In this paper, first, a pilot design criterion is proposed by exploiting the orthogonality of channel vectors of LS-MIMO systems. Second, following this criterion, Chu sequences based pilots are designed. Because of the proposed pilots, the channel estimate of most terminals of a cell is only interfered by the partial cells rather than all the other cells, where the latter is caused by traditional pilots. As a result, pilot contamination is mitigated. Numerical results verify the effectiveness of the proposed pilots.

Pilot design for large-scale multi-cell multiuser MIMO systems

Channel estimation is an important issue for wireless communication systems. A channel estimation scheme using a Takagi-Sugeno (T-S) fuzzy-based Kalman filter under the time-varying velocity of the mobile station in a multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system is proposed in this paper. The fuzzy technique is used to interpolate several linear models to approximate the nonlinear estimation system. A MIMO system with the orthogonal space-time block coding (OSTBC) scheme is considered, where the radio channel is modeled as an autoregressive (AR) random process. The parameters of the AR process and the channel gain are simultaneously estimated by the proposed method. One-step-ahead prediction can be obtained during this estimation procedure. This is useful for the decision-directed channel-tracking design, particularly in the fast-fading channel. Furthermore, the robust minimum mean-square error (MMSE) equalization design can be achieved by considering the channel prediction error to improve the performance of symbol detection. To validate the performance of our proposed method, several simulation results are given and compared with those of other methods. When considering the time-varying velocity of the mobile station communication in the MIMO-OFDM system, the enhanced equalizer based on the T-S fuzzy-based Kalman filter performs better than those based on the conventional channel estimators in terms of symbol error rate.

Robust Fast Time-Varying Multipath Fading Channel Estimation and Equalization for MIMO-OFDM Systems via a Fuzzy Method

In this paper, optimal pilot sequence designs for MIMO-OFDM systems in multi-cell environments are provided. The proposed multi-cell optimality criterion is to minimize the worst-case MSE of an LS-based channel estimator. To satisfy the multi-cell optimality, it is found that the pilot sequence set, having the perfect auto-correlation property, should meet the Welch bound and the maximum magnitude of the cross-correlation function should be further minimized. Multi-cell optimal pilot sequence designs for various pilot types and their DFT representations are proposed by adopting Chu sequences and a tight upper-bound on the maximum size of the pilot sequence set is derived for a given pilot sequence length and the maximum allowed cross-correlation value. Simulation results show that the proposed pilot sequences can improve both the MSE performance and the system performance in multi-cell environments.

Optimal Pilot Sequence Design for Multi-Cell MIMO-OFDM Systems

Channel estimation in time division duplexing (TDD)-based massive multiple-input multiple-output (MIMO) systems is heavily hampered by the pilot contamination, which constitutes a major bottleneck on the overall system performance. This study considers the pilot contamination problem in multi-cell TDD-based massive MIMO systems, and analytical expressions are presented on the normalised mean square error (NMSE) of the minimum mean square error channel estimation algorithm. Based on the obtained NMSE, this study proposes an optimal pilot assignment strategy to minimise the effect of pilot contamination. In order to further improve the system performance, a pilot design-based channel estimation scheme is proposed, where Chu sequences with perfect auto-correlation property are employed to design the optimal pilot sequences aiming at acquiring the accurate channel state information. Simulation results show that the proposed pilot assignment strategy outperforms the random pilot assignment method, and approaches to the performance of the exhaustive search method which requires high computational complexity. Moreover, the performance gain of the pilot design-based channel estimation scheme is verified in massive MIMO systems.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-com.2018.5557

Pilot contamination reduction in TDD-based massive MIMO systems

In this letter, the design of pilots aiming at mitigating the inter-cell interference in MIMO OFDM systems is addressed. It is shown that if an ideal channel between interferer and receiver is assumed, pilots resulting in a variation coefficient of zero, and therefore best performance on system level, can be designed. The properties of these pilots are described, and numerical calculations as well as simulation results are presented to verify the theoretical analysis.

Pilot Design for Inter-Cell Interference Mitigation in MIMO OFDM Systems

The present invention discloses a method, a system and a transmitter, which are used for realizing transmission. The method comprises the following steps: processing the channel-related information from the transmission end so as to acquire the weighted vector of transmission; processing the input signals so as to acquire a plurality of channels of first signals; completing the beam formation of each channel of first signals so as to acquire a plurality of channels of forming signals with the parameters of the beam formation as the weighted vector of transmission; completing the OFDM of the channels of forming signals so as to acquire a plurality of channels of modulation signals. The method divides the input signals into a plurality of channels, so that different antennas can transmit different signals; the weighted vector of transmission is acquired according to the feedback channel-related information of the reception end; the weighted vector of transmission is used for the beam formation of a plurality of channels of signals to be transmitted; the transmission power is optimized according to the feedback information, thus the method improves the selection gain of the antenna used for signal transmission, and improves the signal-noise ratio of the received signals at the reception end.

Method and system for implementing transmission as well as transmitter

In this paper, we address the problem of the design of pilots aiming at mitigating the inter-cell interference in OFDM systems. Based on the conventional pilot design used in the intra-cell, we design the pilots which can make the power of inter-cell interference distribute in all paths of the channel uniformly, and result in a variation coefficient of zero, then the better performance on system level will be derived. The properties of these pilots are described, and the simulation results are presented.

Pilot Tone Design for Inter-Cell Interference Mitigation in OFDM Systems

In this paper, we first overview the least square (LS) space-time joint channel estimation in filtered multi-tone (FMT) system in multi-input multi-output (MIMO) system. Then the design of pilots aiming at mitigating the inter-cell interference in MIMO FMT systems is addressed. It is shown that if the pilots which result in a zero variation coefficient of the estimation error are used, the better performance on system level was obtained. The properties of these pilots are described, and the simulation results are presented.

Pilot Sequence Design for Inter-cell Interference Mitigation in MIMO FMT Systems

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Pilot Design for Inter-Cell Interference Mitigation in MIMO OFDM Systems

Method and system for implementing transmission as well as transmitter

Pilot Tone Design for Inter-Cell Interference Mitigation in OFDM Systems

Pilot Sequence Design for Inter-cell Interference Mitigation in MIMO FMT Systems