Earticle

Mmillimeter-wave (mmWave) massive multiuser multiple-input multiple-output (MU-MIMO) system usually utilizes hybrid precoding to reduce complex hardware and high energy consumption. However, most hybrid precoding scheme consider the fully connected architecture, which may result in a significant loss of energy efficiency. In this paper, we propose a hybrid precoding scheme based on the overlapped subarray architecture (OSA), where the analog part of the MU-MIMO system is realized by a OSA network. Based on the OSA architecture, a modified generalized low rank approximation of matrices (GLRAM) based hybrid precoding scheme is designed to maximize the achievable sum-rate, where the analog precoding algorithm apply the phase alignment technology and GLRAM approach to obtain RF precoder/combiner with high array gain provided by massive MIMO system. Then, the block diagonalization (BD) technology is performed to obtain the digital precoding matrix for the multiplexing gain. Simulation results show that the modified GLRAM based hybrid precoding algorithm for OSA architecture can reduce the number of iterations. Compared with the existing hybrid precoding algorithm, it achieves higher spectral efficiency and lower complexity.

Most studies on symbol-level (SL) precoding have assumed that channel estimation is perfect. However, because interference signals or additive white Gaussian noise exist in the received signal for channel estimation, channel estimation errors always exist. In this paper, we propose an SL precoding scheme that is robust to channel estimation errors. First, using the characteristics of the channel estimation errors, we derive an equation for the worst-case mean squared error (MSE) which is the maximum of the MSE. Then by designing the SL precoding to minimize the worst-case MSE, it has robust characteristics against channel estimation errors.

The high peak-to-average power ratio (PAPR) is one of the major drawbacks of the orthogonal frequency division multiplexing (OFDM) systems that make non-linear distortion in practical implementation of high power amplifier (HPA). In this study, the performance of discrete Hartley matrix transform (DHMT) in precoding based OFDM system is analyzed to minimize the high PAPR. We demonstrate that the DHMT precoding method eliminates the multicarrier assumption in a special circumstance. The remarkable results are achieved and compared with conventional OFDM, Walsh?Hadamard matrix transform (WHMT), discrete cosine matrix transform (DCMT) and Vandermonde-like matrix transform (VLMT) in precoding based OFDM signals.

Peak signal reduction is a critical problem in orthogonal frequency-division multiplexing (OFDM) systems. Herein, we focus on Zadoff?Chu matrix (ZCM) precoding as a peak signal reduction method and analyze its integration using the discrete Fourier transform process. The analysis reveals that the integrated process can be substituted by a sparse matrix multiplication and the influence of ZCM parameters on the sparse matrix is mathematically clarified. The results also show that the ZCM precoding works to produce a single-carrier signal and explains how the ZCM precoding reduces the peak of the OFDM signal.

One of promising transmission technologies for beyond-5G wireless communication is cell-free massive MIMO where all the access nodes (ANs) cooperate to coherently serve all the user equipments (UEs). Based on the benefits from massive MIMO, the novel notion of cell-free network architecture is adequate to overcome the inter-cell interference limitation in ultra-dense network (UDN) environments, owing to the full cooperation among ANs. In this paper, we develop synergetic operations between the cell-free massive MIMO and mmWave ultra-wide frequency band, which is able to provide a genuine high-quality and robust wireless pervasive service by fully utilizing the basic three pillars for wireless capacity, such as bandwidth, spectral efficiency and network densification. For this goal, we study the impacts of analog precoding schemes to be combined with zero-forcing digital precoding on cell-free mmWave massive MIMO UDN systems. In addition, we investigate the effect of correlated shadowing and pilot assignment strategies on the average spectral efficiency performance for the proposed hybrid precoding schemes in both outdoor and indoor UDN environments.

In the non-orthogonal multiple access (NOMA) system, multiple user signals on the single carrier are superimposed in a non-orthogonal manner, which results in the interference between non-orthogonal users and noise interference in the channel. To solve this problem, an improved algorithm combining regularized zero-forcing (RZF) precoding with minimum mean square error-serial interference cancellation (MMSE-SIC) detection is proposed. The algorithm uses RZF precoding combined with successive over-relaxation (SOR) method at the base station to preprocess the source signal, which can balance the effects of non-orthogonal inter-user interference and noise interference, and generate a precoded signal suitable for transmission in the channel. At the receiver, the MMSE-SIC detection algorithm is used to further eliminate the interference in the signal for the received superimposed signal, and reduce the calculation complexity through the QR decomposition of the matrix. The simulation results show that the proposed joint detection algorithm has good applicability to eliminate the interference of non-orthogonal users, and it has low complexity and fast convergence speed. Compared with other traditional method, the improved method has lower error rate under different signal-to-interference and noise ratio (SINR).

As research continues for the commercialization of 5G and 6G communications, the study of MU-MIMO systems in the mm-Wave band is one of the most key research areas in the field of communication algorithm research. MU-MIMO systems utilize a very wide bandwidth in the tens to hundreds of GHz frequency band, which has a significant disadvantage that the power consumption of the RF at the Rx end is very high. In this paper, a hybrid precoding algorithm in a hybrid beamforming and combining system is studied to solve these drawbacks. The proposed hybrid precoding algorithm defines a problem formulation that can eliminate interference by setting constraint conditions and designing an unconstrained precoder, and then derives a hybrid precoder by projecting a square circle into the null space. The proposed algorithm reduces the computational complexity by about 40% or more by reducing the size and number of SVDs compared to existing works.

In this paper, we study precoding techniques for co-channel interference suppression in multiuser MIMO systems. DPC is optimal techniques to achieve the system capacity of multiuser MIMO downlink channels. DPC is not proper in practical wireless systems because complexity is very high. So block diagonal precoding for multiuser MIMO downlink channel is studied. The block diagonal precoding is used to suppress co-channel interference between multiuser. Block diagonal precoding method, whose complexity is reduced by modified null space operation, change multiuser MIMO channel to multiple single-user MIMO channel. We also use V-BLAST decoder in receiver. V-BLAST decoder can achieve increased system capacity in proportion to the number of users. We show improved system performance by using computer simulation.

Power line carrier communication, with the widespread application, broadband multi-input multi-output system will have a co-channel interference, the interference is in addition to asynchronous pulse noise and pulse cycle factors influencing the multi-input multi-output (MIMO) system's largest broadband power line carrier. Aiming at this problem, this paper, by using multiple input multiple output channel state information, the sender with the method of block diagonalization, eliminate the interference between the channel, so as to improve the capacity of broadband power line carrier system, at the same time reduce the bit error rate of the system. Through the simulation results and analysis can show that the proposed block diagonalization pre-coding method effectively eliminates the common channel interference, improve the drying ratio, thus improve the maximum mutual information of the system and reduce the bit error performance of the system.

In this work, we develop on average relationship between the Per-Antenna Signal to Interference plus Noise Ratio (PA-SINR) and the Per-Antenna Signal to Leakage plus Noise Ratio (PA-SLNR) performance metrics. Simulation results confirm the equivalence between the two metrics which opens up the door to use PA-SLNR instead of PA-SINR to construct simple Multi-user Multiple Input Multiple Output (MU-MIMO) precoding algorithm.

In this paper, we propose a limited feedback transmission based on precoding mechanism for multiple-input multiple-output (MIMO) systems, referred as to supermode transmission. With a fixed data-rate, it allows different degree-of-freedom (DoF) depending on the current channel state information (CSI) and different transmission scheme with the same DoF. Through numerical examples, we show that the pairwise error probability (PEP)-based criterion outperforms the conventional criterion based on minimum eigenvalue (ME) of the received signal matrices, and the supermode transmission improves performance over both multimode MIMO (MM-MIMO) and multimode space-time block coding (MM-STBC), in particular, at low SNR regime.

Out-of-band (OOB) power emission is a conventional issue in orthogonal frequency division multiplexing (OFDM) system. The spectral leakage results in interference to licensed users (LU) in OFDM-based cognitive radio (CR) system. In this article, an adaptive precoding scheme based on the adaptive orthogonal projection matrix is proposed for OOB power suppression. Low complexity is the main feature of this preceding scheme. Simulation and analysis show that this method reduces the out-of-band power significantly by forcing the power spectrum density (PSD) of several frequency points in OOB to be zero. An advanced precoding scheme proposed later achieves a tradeoff between performance of OOB power suppression and bit error rate (BER) in the receiver. With those schemes, an adaptive precoder is proposed, which has three ways to adaptively adjust precoding matrix to achieve a balance among the complexity of system, the performance of out-of-band power reduction and BER in the receiver.

IEEE 802.11p defines an international standard for wireless access in vehicular environments. It is normally designed for operating at high user mobility. Thus, decreasing the signal bandwidth to 10 MHz in IEEE 802.11p makes the communication more efficient for the vehicular channel. Furthermore, the Orthogonal Frequency Division Multiplexing (OFDM) methodology is commonly used to mitigate the Inter-Symbol Interference (ISI) occurred over a wireless channel. However, the OFDM suffers from certain drawbacks including higher system complexity due to the generation of the peak to average ratio (PAPR). The objective of this study is to reduce the high PAPR resulted from adapting the OFDM system to vehicular networks. In this paper, we propose a novel precoding Zadoff-Chu Sequence (ZCS) combined with the Clipping technique for PAPR reduction in OFDM based on the Discrete Cosine Transform (DCT). The proposed technique which is based on precoding the constellation symbols of the vehicular channels with DCT succeeds to decrease the PAPR ratio up to 4dB for 64 subcarriers.

If there is a certain distance between the primary users and the second, there are asynchronous interferences because of existing nonsynchronous signals. And the interferences do not influence only the primary user system, but they could also affect second user system and increase interference. To solve this problem and to eliminate interference to primary and secondary asynchronous users among which there are influences in wireless communication system, a novel kind of precoding method based on the minimum mean square error is put forward in this paper. In this method, asynchronous interferences are eliminated in the precoding process and this process also satisfies users’ server quality. Analysis and simulation show that the proposed scheme effectively ,under the condition of the limitation of interferences in main user system, enhance the second user system capacity and improve the reliability of the transmission system of second users system.

본 논문에서는 개선된 AF(Amplify-and-Forward)와 DF(Decode-and-Forward) Relay 프로토콜을 결합한 다중 사용자 MIMO (Multiple Input Multiple Output) Relay 네트워크에서 간섭 제거 기술을 논의 한다. 간섭 제거 기술은 Relay 노드가 적용된 전체 전송 시스템의 오류 성능을 향상시키기 위해 eNB(evolved NodeB), Relay 노드(RN: Relay Node)와 UE(User Equipment)에 의해 이루어진다. 간섭 제거를 수행하기 위해 ZF(Zero Forcing), MMSE(Minimum Mean Square Error), SIC(Successive Interference Cancellation)와 OSIC(Ordered Successive Interference Cancellation)가 적용된 DPC(Dirty Paper Coding)와 THP(Thomilson Harashima Precoding)를 사용하였다. 이러한 기본적인 기술이 적용된 Relay 노드 기능들이 연구되고 개선된다. 협력 Relay 노드에서 두 계층 간의 간섭 제거를 강화한 DF는 성능을 향상시킨다. eNB와 RN간의 가중치 벡터를 사용하여 간섭 제거가 수행된다. 연구 최종 결과, 기존의 알고리즘과 비교하여 제안된 알고리즘이 낮은 SNR에서 더 좋은 성능을 나타냈다. 모의실험 결과 LTE-Advanced 시스템에서 제안된 기법이 오류 성능 면에서 상당한 향상을 나타냈다.

In this paper, we perform interference cancellation in multiuser MIMO (Multiple Input Multiple Output) relay network with improved Amplify-and-Forward (AF) and Decode-and-Forward (DF) relay protocols. The work of interference cancellation is followed by evolved NodeB (eNB), Relay Node (RN) and User Equipment (UE) to improve the error performance of whole transmission system with the explicit use of relay node. In order to perform interference cancellation, we use Dirty Paper Coding (DPC) and Thomilson Harashima Precoding (THP) allied with detection techniques Zero Forcing (ZF), Minimum Mean Square Error (MMSE), Successive Interference Cancellation (SIC) and Ordered Successive Interference Cancellation (OSIC). These basic techniques are studied and improved in the proposal by using the functions of relay node. The performance is improved by Decode-and-Forward which enhance the cancellation of interference in two layers at the cooperative relay node. The interference cancellation using weighted vectors is performed between eNB and RN. In the final results of the research, we conclude that in contrast with the conventional algorithms, the proposed algorithm shows better performance in lower SNR regime. The simulation results show the considerable improvement in the bit error performance by the proposed scheme in the LTE-Advanced system.