This paper proposes a joint access point (AP) clustering and beamforming design method for network-assisted full-duplex cell-free massive multiple-input multiple-output (NAFD CF-mMIMO) systems that maximizes energy efficiency (EE) while maintaining high spectral efficiency (SE). The proposed method improves energy efficiency (EE) by reducing power consumption of APs with low contributions to performance. Numerical results demonstrate that the proposed approach achieves SE performance comparable to that of conventional methods designed to maximize SE.

This paper investigates the beamforming design for an upper mid-band multi-user multiple-input single-output (MUMISO) system, aiming to mitigate interference from terrestrial base stations to satellites. The upper mid-band (7-24 GHz) is already utilized by several satellite services, necessitating the coexistence of emerging cellular systems with these existing satellite systems. As such, we propose a beamforming design with an angular radiated power constraint directed towards the sky angle region, effectively mitigating interference without requiring prior information about the satellites. Numerical results validate the efficacy of the proposed method in reducing interference. Moreover, we demonstrate that the proposed method can achieve sum spectral efficiency performance comparable to sum rate maximization approaches without such constraints.

In this paper, we propose a new transmission scheme for grant-free non-orthogonal multiple access (GF-NOMA) based on orthogonal frequency division multiplexing (OFDM) in the presence of timing offsets. The proposed method utilizes differential phase-shift keying (DPSK) between subcarriers, eliminating the need for channel estimation and mitigating the degradation of data detection caused by timing offsets. Furthermore, the proposed method conducts active user detection based on the coordinate descent method, which offers a lower computational complexity compared to the conventional method based on the structured generalized approximate message passing (S-GAMP). Computer simulations demonstrate that the proposed method achieves a lower miss detection probability compared to S-GAMP and a lower bit error rate than the method using PSK.

This paper studies an uplink grant-free non-orthogonal multiple access (GF-NOMA) system using low-density signature orthogonal frequency division multiplexing (LDS-OFDM), where each user transmits non-orthogonal pilots and data symbols that are mapped onto a small number of subcarriers determined by the LDS sequence. After an initial estimation based on pilot symbols, our proposed receiver utilizes the low-density signal structure to improve active user detection, channel estimation, and multi-user detection accuracy. To achieve this, a birth-death drift process is applied to model the information exchange between two estimation modules for pilot and data symbols, and a corresponding side information (SI) calculation and denoiser design are proposed for SI-aided multiple measurement vector approximate message passing (MMV-AMP). Moreover, the asymptotic performance of the proposed SI-aided MMV-AMP is analyzed based on state evolution. Numerical results confirm that the proposed method outperforms state-of-the-art methods and that it can perform predictions using the derived state evolution.

Detecting structural changes in time-series data is crucial in many applications. However, the changes in the data may appear as global structural changes that cannot be detected by conventional methods. In recent years, Topological Data Analysis (TDA) has been used to detect such global structural changes. In TDA, information on connected components or holes of data is encoded into a two-dimensional plot called a persistence diagram (PD), which can be used to detect global changes in time-series. However, only a few studies on TDA conducted change detection assuming probabilistic structure on PDs. In this paper, we introduce probability structures into PD, with which we conduct change detection on the basis of the minimum description length principle. We propose the following two methods: (1) A parametric method: We employ the Gaussian mixture model for PD modeling and then detect global changes by tracking the changes in the optimal number of mixture components. (2) A non-parametric method: We employ kernel densities for PD modeling and then detect changes by tracking changes in their global complexity. These methods not only improve the detection accuracy of global structural changes but also provide the explainability of global changes. We showcase the effectiveness of the proposed methods using synthetic data and real-world financial time-series data.

Grant-free non-orthogonal multiple access (GF-NOMA) systems suffer from the performance degradation of active user detection (AUD) due to carrier frequency offsets (CFOs) caused by imperfect frequency synchronization among users and a base station. Although a conventional method efficiently performs CFO estimation, AUD, and channel estimation (CE) by introducing extended pilot sequences based on discrete grids of the CFOs, the inevitable estimation error caused by off-grid CFOs significantly degrades the quality of the CE. This paper proposes a more accurate joint AUD and CE method by performing AUD and CFO estimation independently and iteratively. Computer simulations demonstrate that our proposed scheme can estimate the active users and the corresponding channel coefficients as accurately as the case with the perfect knowledge of the CFOs.

Emergency Rescue Information Sharing System supports rescue operations in early stage by gathering information about victims in need of help at the time of disaster. In this system, in-vehicle relays are used to gather extensive information. In-vehicle relays transmit information sent by mobile terminals to a database server via gateway switches. There are several wireless connections between relays and gateway switches to make the transmission redundant. However, information loss occurs when all links are disconnected. In addition, mobile terminals cannot send information without available wireless connections. In this paper, we propose a disaster information gathering mechanism that adopts Web-based offline operation and OpenFlow-based routing control. Offline operation of the system is realized by information caching and synchronization. Wireless links between in-vehicle relays and gateway switches are controlled by OpenFlow. Our mechanism selects a link for transmission dynamically in response to the status and priority changes of the wireless links. In order to prevent information loss while relays isolated from networks, information from mobile terminals is temporarily stored in in-vehicle servers. Prototype demonstration shows that the proposed mechanism can achieve high information gathering rate at the database server.