The millimeter-wave (mmWave) full-dimensional (FD) MIMO system employs planar arrays at both the base station and the user equipment and can simultaneously support both azimuth and elevation beamforming. In this paper, we propose atomic-norm-based methods for mm-wave FD-MIMO channel estimation under both uniform planar arrays (UPA) and non-uniform planar arrays (NUPA). Unlike existing algorithms, such as compressive sensing (CS) or subspace methods, the atomic-norm-based algorithms do not require to discretize the angle spaces of the angle of arrival and angle of departure into grids, thus provide much better accuracy in estimation. In the UPA case, to reduce the computational complexity, the original large-scale atomic norm minimization problem is approximately reformulated as a semi-definite program (SDP) containing two decoupled two-level Toeplitz matrices. The SDP is then solved via the alternating direction method of multipliers where each iteration involves only closed-form computations. In the NUPA case, the atomic-norm-based formulation for channel estimation becomes nonconvex and a gradient-decent-based algorithm is proposed to solve the problem. Simulation results show that the proposed algorithms achieve better performance than the CS-based and subspace-based algorithms.

In this paper, we propose a beamforming training method in Multiple-Input-Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) that aims to reduce the beamforming training time and interference between the mobile device and the base station. The proposed beam training scheme utilizes the directional beamforming codebook such as the discrete Fourier transform (DFT) beamforming codebook and the beamforming training sequences throughout the beam training phase. The orthogonal beam training sequence can assist the receiver to mitigate the neighbor transmission point's training beam interference so the receiver can obtain a better effective channel estimation. An estimated effective channel covariance matrix can be feedback to the basestation for the Direction of Departure (DoD) calculation thus it can be used for performing the finer beamforming thus enhancing beam training quality and shorten the beam training time. The performance of proposed algorithm is evaluated and compared with solutions in technical literature using simulation.

Frequency-dependent I/Q imbalance is one of the major impairments in the direct-conversion receivers (DCR) for high-speed wideband wireless systems. We propose two new blind methods for compensating frequency-dependent I/Q imbalance. The first one is a time-domain approach. Specifically we develop a blind identifiability condition based on which a cost function and a gradient descent search algorithm are proposed for blind I/Q imbalance compensation. The second blind method is a frequency-domain approach for OFDM systems. Here we provide blind estimators for the frequency-selective I/Q imbalance parameters, which once obtained, the I/Q imbalance can then be compensated by a simple single-tap matrix filter inversion. We provide extensive simulation results to demonstrate the performance of the proposed algorithms.

I/Q imbalance is one of the major concerns in the design of direct-conversion front-end receivers in high data rate wireless networks. To address the challenge, various I/Q imbalance estimation and compensation algorithms have been proposed in the literature. In this paper, we propose a blind cyclostationary based estimation and compensation of frequency-flat I/Q imbalance. The proposed blind estimation algorithm uses second-order statistics to compensate I/Q imbalance without estimating the mismatch parameters and is an unbiased estimator when a DC offset exists at the receiver. The performance of our approach is evaluated and compared to other existing blind I/Q imbalance estimation algorithms.

We propose a OFDM-CDMA system that employs polyphase codes to support variable spreading factors. A systematic approach for constructing the polyphase code sequences of variable spreading factors is developed. Polyphase codes exhibit better auto- and cross-correlation properties than Hadamard codes. When employed in OFDM-CDMA systems, polyphase codes result in certain structured multiple-access interference (MAI) caused by multipath. Analytical and numerical results show that OFDM-CDMA systems employing polyphase codes have better PAPR performance than those using Hadamard codes. The BER performance of the OFDM-CDMA system using polyphase codes is evaluated by numerical results and compared to that of the OFDM-CDMA system using Hadamard codes with and without clipping.

We study time and frequency synchronization for 3GPP long term evolution systems. A new method to generate repetitive synchronization signals is described, and a corresponding detection algorithm taking advantage of the proposed synchronization signal structure is provided. The described synchronization scheme combines the advantages of auto- and cross-correlation based detection algorithms. The performance of our approach is evaluated and compared to other existing algorithms.

A new repetitive synchronization signal structure is proposed for wireless communication systems. A corresponding successive maximum likelihood detection algorithm that uses the proposed synchronization signals is provided. The successive maximum likelihood detection algorithm uses reliably estimated frequency offset in a successive way to refine the estimated timing offset. The performance of our approach is evaluated and compared to other existing algorithms.

Novel orthogonal polyphase codes with constant envelope design for OFDM-CDMA system are proposed in the paper. The proposed codes can support large number of users and variable spreading factor like Hadamard codes. Proposed orthogonal polyphase codes not only have better periodic auto- and cross correlations than Hadamard codes but also have constant envelope properties which is preferred for uplink/reverse link transmission. New transmitter and receiver architecture and MMSE receiver are proposed for the OFDM-CDMA system using the proposed polyphase codes. Simulation results show that OFDM-CDMA system using proposed polyphase codes has better PAPR and BER performance than OFDM-CDMA system using Hadamard codes and OFDMA system