Koya Sato

Kriging-Based Interference Power Constraint: Integrated Design of the Radio Environment Map and Transmission Power

This paper proposes a probabilistic interference constraint method with a radio environment map (REM) for spatial spectrum sharing. The REM stores the spatial distribution of the average received signal power. We can optimize the accuracy of the measurement-based REM using the Kriging interpolation. Although several researchers have maintained a continuous interest in improving the accuracy of the REM, sufficient study has not been done to actually explore the interference constraint considering the estimation error. The proposed method uses ordinary Kriging interpolation for the spectrum cartography. According to the predicted distribution of the estimation error, the allowable interference power to the primary user is approximately formulated. Numerical results show that the proposed method can achieve the probabilistic interference constraint asymptotically. Additionally, we compare the performance of the proposed technique with three methods: the perfect estimation, the path loss-based method, and the Kriging-based method without the error prediction. The comparison results show that the proposed method has a higher spectrum sharing opportunity than the path loss-based method, even if only a small amount of measurement data is available. It is also shown that the proposed method dramatically improves the outage probability of the interference power compared to the conventional Kriging-based method.

Kriging-Based Interference Power Constraint for Spectrum Sharing Based on Radio Environment Map

This paper proposes a probabilistic interference constraint method with radio environment map (REM) for spectrum sharing. Kriging interpolation is a well-known technique that can optimize the REM accuracy. However, although many researchers have maintained continuous interests in the accuracy of the REM, little study has been done to actually explore the interference constraint considering the estimation error. The proposed method uses ordinary kriging interpolation for the spectrum cartography. According to the predicted distribution of the estimation error, the allowed interference power to the primary user (PU) is approximately formulated. Numerical results show that the proposed method can achieve the probabilistic interference constraint asymptotically. Additionally, we compare the performance of the proposed technique with two methods: limit of the path loss-based method and perfect estimation. From the comparison results, it is shown that the kriging-based method has higher spectrum sharing opportunity than the path loss-based method, even if there are few measurement data.

Spectrum database-assisted radio propagation prediction for wireless distributed networks: A geostatistical approach

The concern over wireless distributed networks (WDNs) such as Machine-to-Machine (M2M) systems and Internet of Things (IoT) has risen. In massive WDNs, it is important to strictly manage the interference power among wireless links: radio propagation prediction between distributed terminals is a critical issue for highly efficient spectrum use. In this paper, we propose a novel radio propagation estimation using spectrum database which collects communication results from mobile terminals. The proposed method focuses on the spatial-correlation of radio propagation characteristics between different wireless links. Using maximum likelihood-based pathloss estimation and Kriging-based shadowing estimation, the radio propagation of the wireless link that has arbitrary location relationship can be predicted. From numerical results, it is shown that the proposed method achieves higher estimation accuracy than the conventional pathloss-based estimation methods. Furthermore, we show that the proposed technique can predict the probability density function (PDF) of the estimation error.

Average interference power constraint with measurement-based spectrum database

In this paper, we propose an interference power constraint method using measurement-based spectrum database for high efficient spectrum sharing. The spectrum database is constructed from measurement radio environment information measured by secondary users (SUs) with mobility, and stores radio environment maps (REMs). This paper focuses on a database-aided communication parameter adaption method which can constraint harmful interference at an edge of communication coverage of a primary user (PU). The proposed method estimates a lower confidence limit of the average received power by using non-parametric bootstrap method. The estimated lower confidence limit is treated as the average value, and the allowed interference power is estimated with cumulative distribution function (CDF) of instantaneous signal-to-interference power ratio (SIR). Simulation results show that the probabilistic protection can be achieved by using the proposed method under the situation with no impact of shadowing in each separated grid. Moreover, the impact of correlated shadowing on the protection ability is evaluated.

Demo: A field test of measurement-based spectrum database using probing vehicles

Spectrum sharing with cognitive radio (CR) has attracted attention to solve the shortage of spectrum resources. In a spectrum sharing environment, secondary users (SUs) can utilize spectrum bands which are licensed to primary users (PUs) under interference constraint at PUs. In order to gain the spectrum sharing efficient by setting suitable communication parameters of SUs such as frequency and transmission power, it is important to accurately recognize the radio environment.

Parameter estimation method of primary user using measurement-based spectrum database

This paper proposes a parameter estimation method of primary user using geographical spectrum database consisting of measurement results gathered by secondary nodes. Compared to Model-based database such as FCCs database, the proposed method may enable higher accuracy spectrum sharing between secondary and primary users. Through the measurement experiment, results of the estimation accuracy are confirmed by changing the number of valid spatial data meshes.

Crowdsourcing-Assisted Radio Environment Database for V2V Communication

In order to realize reliable Vehicle-to-Vehicle (V2V) communication systems for autonomous driving, the recognition of radio propagation becomes an important technology. However, in the current wireless distributed network systems, it is difficult to accurately estimate the radio propagation characteristics because of the locality of the radio propagation caused by surrounding buildings and geographical features. In this paper, we propose a measurement-based radio environment database for improving the accuracy of the radio environment estimation in the V2V communication systems. The database first gathers measurement datasets of the received signal strength indicator (RSSI) related to the transmission/reception locations from V2V systems. By using the datasets, the average received power maps linked with transmitter and receiver locations are generated. We have performed measurement campaigns of V2V communications in the real environment to observe RSSI for the database construction. Our results show that the proposed method has higher accuracy of the radio propagation estimation than the conventional path loss model-based estimation.

Radio Environment Aware Computation Offloading with Multiple Mobile Edge Computing Servers

In this paper, we discuss a computation offloading in mobile edge computing (MEC) systems. We especially focus on the case where a mobile node sends calculation requests to surrounding access points (APs) that have the computational capability. Unlike wired distributed computing systems, MEC systems suffer from the unstable connectivity due to wireless channel fluctuations such as multipath fading and shadowing effect; there is a possibility that the calculation results disappear by loss of wireless connectivity. In order to maximize the offloading effect in the wireless environment, we propose radio environment aware task allocation methods with predicting wireless connectivity between the mobile node and APs. Especially, we discuss two methods: radio environment map (REM)-based connectivity prediction and distance-based one. Numerical results show that the proposed method can effectively offload the computation tasks compared with conventional methods that ignore the wireless connectivity.

Poster: A scheduling method for V2V networks using successive interference cancellation

In this paper, we propose a scheduling method with successive interference cancellation (SIC) for vehicle to vehicle (V2V) networks to improve the reliability and the capacity. SIC is a multi-user detection technique that repeatedly decodes the multiple signals by cancelling the strongest signal by using the detected signal in the previous step. In the proposed distributed scheduling method, the time slots are allocated by using the location information of the vehicles and the estimated signal to interference plus noise ratio (SINR) at multiple receivers for effectively working SIC. The location information can be known by the iterative beacon signal transmitted from each vehicles. The proposed method enables simultaneous detection by SIC. We compare the performance of the proposed scheduling method with random allocation method under multiple peer to peer unicast communication. In addition, we set SINR margin to slot allocation for improving robustness of SIC.

Directivity control of a compact circular loudspeaker array based on selected orders of circular harmonic expansion

We investigated directivity control of a compact circular loudspeaker array that can be attached to the arm. The loudspeaker array can be used for various wearable systems, such as personal audio reproduction systems. A personal audio system often requires that sound leakage outside the listening area in three-dimensional space be minimized. Digital filters that control directivity are usually designed using the multi-point control method. However, the multi-point method causes large filter gains at low frequencies, owing to unstable inverse matrix calculation, which results in sound distortion during practical use. Many methods that use a regularization parameter to overcome the unstable inverse matrix have been proposed; however, they are difficult to apply directly. Thus, after studying the relationship between orders of circular harmonic expansion and filter gain, we propose a stable digital filter design based on appropriately selected orders of circular harmonic expansion for each frequency band. Di...