Kei Inage

White space vectors for channel selection in vehicular cognitive networks

In vehicular cognitive networks, a vehicle (secondary user) communicates with other vehicles or with the roadside units by borrowing licensed but unused frequency bands, a.k.a. white spaces, which are originally allocated to primary users. While doing so, secondary users make sure that the rights of the incumbent users are protected. In comparison to the cases with stationary secondary users, the probability that a primary user appears in the currently borrowed channel is much higher due to high mobility of vehicles. In order to avoid harmful interference to the primary users, a vehicle is required to vacate the currently borrowed channel and switch to another unused one. This vertical handover poses significant disruption to the ongoing communication due to the overhead induced by the channel handshaking. In this paper, we present a novel approach to reduce the number of vertical handovers. Specifically, we first introduce the White Space Vector (WSV) scheme which enables a simpler representation of the complex geographical white space information stored in spectrum usage databases. This new representation allows us to trim down the amount of data downloaded from the database required for adequately avoiding interference to the primary users. Furthermore, we present a new channel selection method leveraging the white space vector representation. We evaluate the number of vertical handovers from the point of view of accuracy and overhead, and show that WSV method can reduce the number of vertical handovers while also reducing the amount of data downloaded from the spectrum database without significant loss in accuracy.

Outlier detection methods of low SNR nodes for cooperative spectrum sensing

In this paper, we have studied methods of detecting low signal-to-noise ratio (SNR) nodes by outlier detection in cooperative spectrum sensing. In many studies in the field of cooperative sensing, it is assumed that an average received energy among sensing nodes is equal. However, in practical wireless environment, the performance of cooperative sensing with low SNR nodes located underground, indoor, and so on, is severely degraded. The goal of this research is to detect the low SNR nodes and minimizes the impacts caused by these low SNR nodes to the cooperative sensing performance. We propose an outlier detection algorithm to exclude low SNR nodes from cooperative sensing nodes by using past accumulated energy data. Several outlier detection methods are compared, and a suitable method for the low SNR node detection algorithm is selected. In addition, the required length of estimation period for the outlier detection is revealed. Simulation results show that the performance of cooperative sensing is improved even if the low SNR nodes exist in the cooperative nodes.

Short paper: Probing the spectrum with vehicles: Towards an advanced spectrum database

This paper proposes a concept of advanced spectrum database generated through the measurements of radio environment from sensors on vehicles. In the current design of TV white space spectrum databases, which is regulated by the United States Federal Communications Commission (FCC), a propagation model is utilized to decide on the availability of spectrum. To ensure protection of primary users (PUs) this approach requires a large margin for the PU coverage area. In the proposed database, the actual measurements of radio signals are used to generate the database. Since the sensors on moving vehicles gather large amount of data, an accurate propagation status can be obtained, including propagation loss and shadowing. In this paper we introduce the concept of advanced database and present initial results of experimental database generation using actual TV broadcast signals.

Capacity conservation ratio: a novel interference constraint for spectrum sharing

This paper presents an interference constraint and power control schemes based on the capacity conservation ratio (CCR). The CCR is the ratio of the decreased capacity in the spectrum sharing to the original capacity of a system. By utilising the CCR as a metric to protect the primary user, a secondary user can achieve sufficient performance, without a large degradation in the primary capacity. In this paper, we propose novel power control schemes under interference constraints based on the CCR, with consideration of the fading effect, by using theoretical analysis. There are two types of power control schemes, namely, an exact power control scheme (EPCS) and a simplified power control scheme (SPCS). The EPCS can control the outage probability; however, a numerical analytic approach is necessary to determine the transmit power. In contrast, the SPCS can be used to derive the transmit power from a closed form with an archiving requirement of the constraint. We analytically derive the average capacity of the primary user and secondary user and the complementary cumulative distribution function of the primary capacity. From these numerical results, we show that the interference constraint based on the CCR achieves better performance in underlay spectrum sharing than the other two interference constraints. Furthermore, the SPCS can achieve a performance equivalent to that of the EPCS, and the SPCS can protect both the low and the high primary capacities under the same constraint. Copyright

Power control schemes for spectrum sharing based on capacity conservation ratio in Rayleigh fading channel

In this paper, we propose novel criterion and novel power control schemes based on the capacity conservation ratio (CCR) by taking the Rayleigh fading effect into account using theoretical analysis. The CCR is defined as the ratio of the decreased capacity in the spectrum sharing to the original capacity of a system. We utilize the CCR as a novel metric for protecting a primary system (PS) from large capacity degradation. The proposed power control schemes based on CCR are divided into two kinds of power control scheme; an exact power control scheme and a simplified power control scheme. We analytically evaluate the performance of the simplified power control scheme and compare it with that of the other. We find that the simplified power control scheme offers sufficient PS protection performance without high computational cost.

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.

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.

Interference-adapted scheduling weight for small-cell in heterogeneous network

A Heterogeneous Network (HetNet) is the mixture network consisted of pico cell, femto cell and relay network in addition to macro cell. A home eNodeB (HeNB) overlays smaller coverage to the macro cell coverage in order to support the local high traffic of Macro eNodeB (MeNB) by off-loading the traffic to the HeNB. In the view point of the spectral efficiency, the frequency band of the HeNB is designed using the same band of the MeNB. However, the inter-cell interference between the MeNB and the HeNB gives harmful effects to both communication qualities of two cells. The performance degradation of the MeNB communication can be avoided by the transmit power control of the HeNB under the interference constraint at Macro User Equipments (MUEs). On the other hand, it is difficult to improve the communication quality of the Home User Equipment (HUE) by the transmit power control or the power allocation, since the transmit power of the HeNB is restricted according to the interference constraint. In addition, the HeNB and the HUE should communicate in the interference environment. Hence, HeNB has to achieve the efficient spectrum access by scheduling without the transmit power control. Therefore, we propose an adaptive interference scheduling for small cell in the HetNet without increasing the feedback information compared with the Proportional Fair Scheduling. Through the computer simulation, we show the effectiveness of the proposed scheduling.