Shota Yamashita

Stochastic Geometry Analysis of Spatial Grid-Based Spectrum Database

In database-driven spectrum sharing for 5G mobile networks, a primary user (PU) can experience harmful interference due to unexpected propagation paths, even when the secondary user (SU) follows the spectrum sharing policy stored in a database, during operations. A framework for deriving the optimal radius of a circular primary exclusive region (PER) has been proposed. However, a practical PER can be non-circular and should be designed on the basis of the geographical information and directivity of the PU antenna. To design a non-circular PER, in this paper, we introduce a spatial grid-based spectrum database; the database permits or forbids SU transmissions for each annular sector divided by a spatial grid. Considering the random locations of the SUs on each annular sector as an inhomogeneous Poisson point process, we analytically derive the PUs outage probability (OP) using stochastic geometry, where the PUs OP is defined as the probability that the aggregate interference power at a PU, from the SUs, exceeds a threshold. Numerical results show that a non- circular PER results in a lower PU OP compared to a circular PER.

Experiment of microwave power and data transmission scheduling for IEEE 802.11-based sensor networks

In wireless sensor networks, individual nodes must be batteryless to make them maintenance-free, which is particularly important for networks that have an enormous number of nodes. When these wireless batteryless nodes are microwave-powered devices, they would necessitate scheduling of power and data transmission. In addition, to ensure network sustainability, a constant amount of energy should be stored in the capacitors of the batteryless nodes. In the experiment conducted in this study, we confirm the necessity of scheduling. In addition, sleep periods are scheduled to ensure that a constant amount of energy remains in the capacitor.

Optimization of primary exclusive region in spatial grid-based spectrum database using stochastic Geometry

In database-driven spectrum sharing for 5G mobile networks, a primary user (PU) may experience harmful interference caused by unpredictable propagation paths, even when secondary users (SUs) follow a spectrum sharing policy established on the basis of a database. A framework for determining the optimal radius of a circular primary exclusive region (PER) on the basis of SUs information has been proposed. However, a practical PER can be complex-shaped and should be designed on the basis of the directivity of the PU antenna, and the SU information in each region. In this paper, we present a stochastic geometry analysis in a spatial grid-based spectrum database, and propose a design for an optimal complex-shaped PER. The database determines the transmission probability of the SUs on each divided annular sector. By regarding the SUs locations on each annular sector as an inhomogeneous Poisson point process, we analytically derive a PUs outage probability (OP), where the PUs OP is defined as the probability that the aggregate interference power at a PU from the SUs exceeds a threshold. Using the derived expression, we formulate an optimization problem to maximize the number of transmitting SUs, which optimizes the SUs transmission probability on each annular sector. Then, we numerically evaluate the solution of the optimization problem in various scenarios. The results show that the accuracy of the PER improves as the grid size decreases. In addition, we successfully design a complex-shaped PER with holes in which the SUs are permitted to transmit.

Experiment of Power Supply Method for WLAN Sensor Using Both Energy Harvesting and Microwave Power Transmission

This paper proposes to improve effectiveness of supplying a sensor with energy using microwave power transmission (MPT) and energy harvesting (EH). The MPT duration should be as short as possible to avoid serious interference between the MPT and wireless local area network data transmission when co-channel operation of both microwave power transmission (MPT) and wireless data transmissions is performed. To shorten the MPT duration, we use multiple power sources such as an MPT source and an EH source to supply a sensor with power. Here, an overcharge or an energy shortage could occur at the sensor if the power supplied by both the MPT and EH sources is not adjusted appropriately. To solve this problem, the power supplied by multiple sources should be estimated precisely. In this paper, we propose a scheme for estimating the power supplied by multiple sources on the basis of an existing MPT scheduling system and then conducted an experiment using the scheme. From the experimental results, it is confirmed to estimate the power supplied by multiple sources successfully. In addition, the required MPT duration when the EH source is used is reduced compared to that when it is not used. Moreover, it is confirmed that the sensor station successfully estimates the power supplied by an MPT source and that by an EH source and adequately configures the MPT duration.

Co-channel operation of microwave power and IEEE 802.11-based data transmissions: A feasibility study

This paper reports a feasibility study including experimental implementation of a battery-less wireless sensor whose power is supplied by a microwave power transmitter. In particular, both microwave power transmissions (MPTs) and wireless communications using wireless local area networks (WLANs) are performed on the same frequency band, 2.4 GHz, to achieve high spectral efficiency. In this case, time scheduling of MPT and wireless communication is necessary to avoid interference. In addition, for stable operation, the duty ratio, which is defined as the ratio of the active duration to the whole period, is set depending on the charge remaining in the capacitor of the sensor. In the initial experimental setup, a single battery-less wireless sensor is successfully operated, and then the feasible transmission range of the designed time scheduling system is discussed.