Large Number Of Receive Antennas Research Articles

Oversampling Based Analog Beamforming for Initial Access With a Large Number of Receive Antennas

Beamforming can provide huge array gains in large-scale antenna systems under the condition that the channel state information (CSI) has been obtained by training signals. During the initial access, no CSI is available at the receiver because the communication link between the transmitter and the receiver has not been established. This paper considers the problem of obtaining the beamforming gain for receivers with the analog beamforming architecture in the initial access, assuming that a fixed beam pattern is employed. We present the necessary and sufficient condition to obtain the receive beamforming gain in the absence of CSI, and then derive the upper bound of the receive beamforming gain for different antenna spacings. It is shown that oversampling in space is needed at the receiver to obtain a non-trivial beamforming gain without CSI, since the total received signal power is proportional to the number of receive antennas. We also design the beamformer that can achieve the upper bound. Numerical results demonstrate the effectiveness of the proposed beamformer in the scenarios of downlink synchronization and random access in millimeter-wave systems.

Scattered Pilots-Based Frequency Synchronization for Multiuser OFDM Systems With Large Number of Receive Antennas

Large-scale multi-input multi-output (MIMO) technique has drawn considerable research interest recently. However, multiuser transmissions in large-scale MIMO systems would face challenging estimation and compensation for multiple carrier frequency offsets (CFOs) that co-exist at the receiver. In this paper, we design a new frequency synchronization scheme in multiuser orthogonal frequency division multiplexing uplink with the aid of scattered pilot symbols. We specifically consider a base station with a large number of antennas and propose to assign a number of scattered pilot subcarriers to each user. With sufficient spatial dimensions offered by the large number of antennas, the designed scheme could estimate CFO for each user individually and eliminate the necessity of the multidimensional search. Moreover, after the CFO estimation, the receive beamforming matrix is further designed for inter-user interference cancelation, which yields an equivalent single user transmission model. The conventional single user channel estimation and data detection can then be performed. Finally, the numerical results are provided to verify the proposed studies.

Blind Frequency Synchronization for Multiuser OFDM Uplink With Large Number of Receive Antennas

In this paper, we propose a new blind frequency synchronization scheme for multiuser orthogonal-frequency-division multiplexing (OFDM) uplink transmissions. The spatial multiplexing is supported in the considered model that allows the subcarriers to be simultaneously occupied by multiple users, while the orthogonal frequency division multiple access (OFDMA) can serve as a special case of our discussion. We propose to assign different null subcarriers to different users and design algorithm that can perform blind carrier frequency offset (CFO) estimation for each individual user with the aid of large number of receive antennas, which then removes the necessity of multidimensional searching. After estimating CFO for one user, the orthogonal complement space of the other users can be obtained which could be further utilized for multiuser interference cancelation. Hence, the multiuser OFDM uplink model reduces to an equivalent single user signal model, where the blind channel estimation with scalar ambiguity can be designed and the conventional single-user data detection can be peformed. To make the proposed study complete, the closed-form performance analysis for mean square error (MSE) of the CFO estimation is derived, based on which the discussion about optimal null subcarrier assignment scheme is further provided. Finally, the Cramer–Rao bound (CRB) is derived, and the numerical results are provided to corroborate the proposed studies.

SAGE Based Data Detection for Multiuser Spatial Modulation With Large Number of Receive Antennas

In this letter, we propose to exploit the concept of space-alternating generalized expectation maximization (SAGE) to resolve the data detection for multiuser spatial modulation (SM) systems with a large number of receive antennas. The proposed SAGE based detector recursively perform data detection for each user with multiuser interference (MUI) cancellation from the other users. The standard SAGE detector may converge to a local extremum point which results in observable performance degradation under the high signal-to-noise (SNR) region. To further improve the performance, we propose a new list recursive SAGE based detector, where at each cycle during the iteration procedure, the redundant MUI terms are removed and a very small list of detection candidates are reserved for each user. The simulation results are provided which show that the proposed list recursive detector can closely approach the single-user performance benchmark, and can substantially outperform the existing competitor especially with QAM constellations.

Low-Complexity Detector for Spatial Modulation Multiple Access Channels With a Large Number of Receive Antennas

In this letter, a low-complexity detector, called ordered nearest neighbor search (NNS) minimum mean square error (MMSE) detector, is proposed for the spatial modulation multiple-access channel with a large number of receive antennas. In the proposed detector, the antenna index is first determined based on the channel direction information, and then, the modulation signal is recovered by the MMSE detector. Furthermore, to improve the separable detection performance, an ordered candidate list of the antenna index is acquired through NNS. Simulation results show that the proposed detector approaches the interference-free performance with very low complexity.