In this study, the most recent topics related to the precise global navigation satellite system (GNSS) positioning technology are discussed. Precise positioning here means that the position can be estimated with centimeter-level accuracy. Technologies supporting precise GNSS positioning include an increase in the number of positioning satellites and the availability of correction data. Smartphones are now capable of centimeter-level positioning. For correction data, real-time kinematic positioning (RTK)-GNSS, which has primarily been used in surveying, and the new precise point positioning-real-time kinematic (PPP-RTK) and PPP, are garnering attention. The Japanese Quasi-Zenith Satellite System was among the first to broadcast PPP-RTK and PPP correction data free of charge. RTKLIB has long been popular for both real-time and post-processing precise positioning. Here, I briefly present a method for improving this software. Precise positioning technology remains crucial as the use of GNSS in highly reliable applications, such as advanced driver-assistance systems, autonomous drones, and robots, is increasing. To ensure precise positioning, improving multipath mitigation techniques is essential; therefore, key factors related to these techniques are discussed. I also introduce my efforts to develop software GNSS receivers for young researchers and engineers as a basis for this purpose. This study is aimed at introducing these technologies in light of the most recent trends.

In this paper, we study the problem of high stability code tracking for band-limited direct sequence spread spectrum (DSSS) systems. In band-limited DSSS systems carrying critical applications, high stability is required in addition to low error variance for code tracking. Therefore, we propose a high stability code tracking method for band-limited DSSS systems, which constructs frequency domain vectors from the received signal, reduces the dimension of the vectors by frequency domain integration and dump, and estimates the time-delay error by the subspace method. We also give a closed-form expression for the steady-state time-delay error variance of the proposed method, which can be used to analyze the error variance performance theoretically and design proper band-limited DSSS systems. The theoretical analysis and simulation results show that the proposed method is able to enhance both the maximum and linear code tracking ranges, thus realizing high stability code tracking, and has constant error variance performance and appropriate computational complexity.

In Information-Centric Networking (ICN), different routing and caching schemes have been proposed to efficiently utilize in-network caches and reduce network traffic. Most of them assume that the popularity distribution of user-requested content is homogeneous. However, the actual popularity distribution measured on the Internet is reported to possess spatial and temporal localities, which can heavily affect caching performance in ICN. Breadcrumbs (BC) routing is a key solution to mitigate performance degradation due to spatial locality because of its ability to flexibly discover cached contents in the off-path. In this paper, we deeply investigate the spatial effects of BC by revealing where utilized cached contents are located, how BC discovers these contents, what kind of contents are found, and how BC fill in the locality gap of content popularity. We also focus on another time-dimension perspective, i.e., the temporal locality of content popularity, and conduct a comprehensive study of how BC routing can be adapted to the spatiotemporal locality of content popularity in ICN.

This paper proposes an anomaly-detection method using the Fast xFlow Proxy, which enables fine-grained measurement of communication traffic. When a fault occurs in services or networks, communication traffic changes from its normal behavior. Therefore, anomalies can be detected by analyzing their autocorrelations. However, in large-scale carrier networks, packets are generally encapsulated and observed as aggregate values, making it difficult to detect minute changes in individual communication flows. Therefore, we developed the Fast xFlow Proxy, which analyzes encapsulated packets in real time and enables flows to be measured at an arbitrary granularity. In this paper, we propose an algorithm that utilizes the Fast xFlow Proxy to detect not only the anomaly occurrence but also its cause, that is, the location of the fault at the end-to-end. The idea is not only to analyze the autocorrelation of a specific flow but also to apply spatial analysis to estimate the fault location by comparing the behavior of multiple flows. Through extensive simulations, we demonstrate that base station, network, and service faults can be detected without any false negative detections.

Recently, the open radio access network (O-RAN) architecture has been expected to enhance both the openness of network components and the intelligence of control functions as a promising RAN architecture for Beyond 5G (B5G)/6G networks. Meanwhile, the power consumption of base stations (BSs) in RAN is a serious problem that needs to be addressed owing to the recent increase in service types such as 4G-LTE, 5G, and local 5G, and it will be more remarkable in the future B5G era. However, a conventional RAN experiences energy wastage because it turns on the power of all BSs at all times, even in coverage areas that accommodate a small number of mobile terminals and low traffic. The O-RAN Alliance discusses the energy savings of BSs, but its standard specification lacks sufficient discussions on concrete models and protocols to realize highly energy-efficient power-on/off management of BSs. On the other hand, terrestrial network (TN) and non-terrestrial network (NTN) convergence has recently been considered in both academic research and standardization as an emerging technology for B5G networks. However, utilizing NTN capacities for BS power-on/off control of TN in the standard O-RAN architecture remains uninvestigated, although it has the potential to achieve higher energy efficiency. This study proposes a novel energy-efficient power management architecture for O-RAN BSs. The proposed power management architecture extends the traditional standard O-RAN architecture such that the pedestrian flow analytics results and NTN capacities can be effectively utilized to obtain a higher energy-saving effect for O-RAN BSs. Consequently, the proposed power-on/off control reduces the power consumption of O-RAN BSs while maintaining the continuity of communications, bitrate, and other metrics. We performed numerical calculations using real datasets of pedestrian flows in regional mesh areas. As a result, we proved that the proposed architecture reduces power consumption by up to 40% when the NTN can accommodate UEs’ traffic of approximately 400 Mbps. In addition, we implemented pedestrian flow analytics and power control functions in the controllers. We verified the feasibility of the functions by demonstrating the power-on/-off of an O-RAN BS using a mobile network testbed.

Phased-array technology is primarily employed in atmospheric and wind profiling radars for meteorological remote sensing. As a novel avenue of advancement in phased-array technology, the Multiple-Input Multiple-Output (MIMO) technique, originally developed for communication systems, has been applied to radar systems. A MIMO radar system can be used to create a virtual receive antenna aperture plane with transmission freedom. The MIMO technique requires orthogonal waveforms on each transmitter to identify the transmit signals using multiple receivers; various methods have been developed to realize the orthogonality. In this study, we focus on the Doppler Division Multiple Access (DDMA) MIMO technique by using slightly different frequencies for the transmit waveforms, which can be separated by different receivers in the Doppler frequency domain. The Middle and Upper atmosphere (MU) radar is a VHF-band phased array atmospheric radar with multi-channel receivers. Additional configurations are necessary, requiring the inclusion of multi-channel transmitters to enable its operation as a MIMO radar. In this study, a comparison between the brightness distribution of the beamformer, utilizing echoes reflected from the moon, and the antenna pattern obtained through calculations revealed a high degree of consistency, which means that the MU radar functions effectively as a MIMO radar. Furthermore, it is demonstrated that the simultaneous application of MIMO and Capon techniques has a mutually enhancing effect.

Intelligent reflecting surface (IRS) is an effective technology to improve the energy and spectral efficiency of wireless powered communication network (WPCN). Under user cooperation, we propose an IRS-assisted WPCN system where the wireless devices (WDs) collect wireless energy in the downlink (DL) and then share data. The adjacent single-antenna WDs cooperate to form a virtual antenna array so that their information can be simultaneously transmitted to the multi-antenna common hybrid access point (HAP) through the uplink (UL) using multiple-input multiple-output (MIMO) technology. By jointly optimizing the passive beamforming at the IRS, the active beamforming in the DL and the UL, the energy consumed by data sharing, and the time allocation of each phase, we formulate an UL throughput maximization problem. However, this optimization problem is non-convex since the optimization variables are highly coupled. In this study, we apply the alternating optimization (AO) technology to decouple the optimization variables and propose an efficient algorithm to avoid the difficulty of directly solving the problem. Numerical results indicate that the joint optimization method significantly improves the UL throughput performance in multi-user WPCN compared with various baseline methods.

Analytical expression of transmission for the orbital angular momentum (OAM) communication using loop antenna arrays and paraboloids is derived to achieve a communication distance of 100 m. With the field distribution of the single “transformed OAM mode” radiated by a loop antenna, the collimated field by the transmitting paraboloid and its diffracted field are analytically derived. Effects of frequencies, sizes of paraboloids, and shifts of transmitting and receiving arrays from the focal planes are included. With the diffracted field distribution on the focal plane of the receiving paraboloid, transmission between the transmitting and receiving loop antennas is analytically estimated. It is shown that the transmission between the antennas with different OAM modes is null, but the transmission between the antennas with the same mode can be reduced. To clarify the mechanism of the reduction, factors of the reduction are quantitatively defined, and the explicit formulae are derived. Based on the analytical results, numerical estimation for a communication distance of 100 m is demonstrated, where the frequency, the focal length, and the size of the paraboloid are 150 GHz, 50 cm and 100 cm, respectively. Where both arrays are located on each focal plane, the transmission for the signal is more than -7.78 dB for eight kinds of OAM modes. The transmission is the least for the highest-order mode. The transmission loss is shown to be mitigated by optimizing the shifts of transmitting and receiving arrays from their focal planes. The loss is made almost even by exploiting the tradeoff of the improvement for the mode orders. The transmission is improved by 5.98 dB, to be more than -1.80 dB, by optimizing the shifts of the arrays.

In this paper, a novel Enhanced Spatial Modulation-based Orthogonal Time Frequency Space (ESM-OTFS) is proposed to maximize the benefits of enhanced spatial modulation (ESM) and orthogonal time frequency space (OTFS) transmission. The primary objective of this novel modulation is to enhance transmission reliability, meeting the demanding requirements of high transmission rates and rapid data transfer in future wireless communication systems. The paper initially outlines the system model and specific signal processing techniques employed in ESM-OTFS. Furthermore, a novel detector based on sparse signal estimation is presented specifically for ESM-OTFS. The sparse signal estimation is performed using a fully factorized posterior approximation using Variational Bayesian Inference that leads to a low complexity solution without any matrix inversions. Simulation results indicate that ESM-OTFS surpasses traditional spatial modulation-based OTFS, and the newly introduced detection algorithm outperforms other linear detection methods.

This paper studies the secrecy outage probability of transmit antenna selection (TAS) with hybrid generalized selection combining (GSC)/selection combining (SC) in amplify and forward (AF)-multiple input multiple output (MIMO) relay system. This paper derives the exact cumulative distribution (CDF) expression of the received signal to noise ratio (SNR) for TAS with hybrid GSC/SC system. Using derived CDF, this work derives the lower bound and asymptotic forms for the hybrid combining system for the secrecy outage probability. Asymptotic results shows that the proposed hybrid system provides the secrecy diversity of product of the number of antennas in the relay node and the number with the smaller number of antennas among the source node and user node. An interesting result is that the secrecy diversity order is independent of the number of combining signals and the number of eavesdroppers.

In modern radar systems, the Generalized compound distribution model is more suitable for describing the amplitude distribution characteristics of radar sea clutter. Accurately and efficiently simulating sea clutter has important practical significance for radar signal processing and sea surface target detection. However, in traditional zero memory nonlinearity (ZMNL) method, the correlated Generalized compound distribution model cannot deal with non-integral or non-semi-integral parameter. In order to overcome this shortcoming, a new method of generating correlated Generalized compound distributed clutter is proposed, which changes the generation method of Generalized Gamma distributed random sequences in traditional Generalized compound distribution models. Firstly, by combining with the Gamma distribution and using the additivity of the Gamma distribution, the Probability Density Function (PDF) of Gamma function is transformed into a second-order nonlinear ordinary differential equation, and the Gamma distributed sequence under arbitrary parameter is solved. Then the Generalized Gamma distributed sequence with arbitrary parameter can be obtained through the nonlinear transformation relationship between the Generalized Gamma distribution and the Gamma distribution, so that the shape parameters of the Generalized compound distributed sea clutter are extended to general real numbers. Simulation results show that the proposed method is not only suitable for clutter simulation with non-integral or non-semi-integral shape parameter values, but also further improves the fitting degree.

In satellite positioning, both the reception of ranging signals and the acquisition of navigation messages are necessary. In general, the acquisition of navigation messages does not always require the reception of radiowaves; however, when radiowaves are used for acquisition, a period of continuous reception significantly longer than one second is required. The European satellite positioning system, Galileo, started broadcasting new navigation messages from August 2022. The improvement is based on a secondary synchronization pattern, secondary forward error correction, and reduced ephemeris to aid in the rapid recovery from interruptions in message acquisition caused by temporary deterioration in radio reception. This paper evaluates the recovery characteristics from interruptions in navigation message acquisition by moving reception of this improved I/NAV navigation message.

Adaptive bitrate (ABR) video streaming is an important application on the Internet. To ensure that users enjoy high-quality services, ABR control mechanisms need to be designed that select chunks wisely on the basis of the available network throughput. To address the chunk selection problem, this paper describes an adaptive bitrate control mechanism that leverages long-term throughput information in the chunk selection process. While previous work has considered how quality should be requested on a per-chunk basis, the proposed method increases the timeframe of the analysis and allows higher quality of experience (QoE) to be reached. This is done by appropriately selecting a sequence of consecutive chunks’ quality values instead of a single chunk’s value. Simulation results are reported on a large variety of real-world network conditions and various throughput prediction algorithms and show the benefit of the proposed method over conventional ABR control mechanisms.