Masayuki Ariyoshi

A Novel Spectrum-Sensing Method Based on Maximum Cyclic Autocorrelation Selection for Cognitive Radio System

In the dynamic spectrum access (DSA) type of cognitive radios, secondary users need to detect the signals from the primary system prior to communicating in the sharing band. Hence, spectrum sensing is an important function for DSA. Key requirements for spectrum sensing in realistic radio environments are stable performance in detecting the primary signals as well as robustness against noise uncertainty at the secondary device or interference signals from other secondary systems. This paper proposes a novel spectrum-sensing method based on maximum cyclic autocorrelation selection (MCAS), which exhibits good detection performance and robustness against noise uncertainty and interference with low computational complexity. Our MCAS-based spectrum-sensing method is used to detect whether the primary signal is present or not, by comparing the peak and non-peak values of the cyclic autocorrelation function (CAF). Our MCAS-based spectrum-sensing method does not require noise variance estimation. Furthermore, it is robust against noise uncertainty and interference signals. Through computer simulations, we found that our method performs as well as or better than conventional sensing methods and is robust against noise uncertainty and interference signals. Therefore, it could be a practical candidate in realistic radio environments.

IEEE dynamic spectrum access networks standards committee

This article presents the latest status and achievements of the IEEE Communication Society Standards for Dynamic Spectrum Access Networks, formerly IEEE Standards Coordinating Committee 41, which develops standards in the areas of dynamic spectrum access, cognitive radio, interference management, coordination of wireless systems, advanced spectrum management, and policy languages for next generation radio systems under the sponsorship of the IEEE Communications Society. The article also envisions future directions for the DYSPAN Committee.

Monitoring-based spectrum management for expanding opportunities of white space utilization

Spectrum management is one of the key functions needed for opportunistic spectrum access (OSA) to utilize white space without causing harmful interference to incumbent receivers. Geo-location database approaches using radio propagation estimation have been regarded as practical spectrum management methods. However, propagation models inevitably include an estimation error of path loss in actual radio environments, resulting in estimation error of carrier to interference ratio (CIR) of the incumbent receivers. Consequently, an allowable transmit power of the opportunistic system has to be limited to keep the CIR at a required level. This could prevent white space from being efficiently utilized. To improve the accuracy of CIR estimation, we propose monitoring-based spectrum management. In the proposed technology, referred to as Interference Monitoring, a monitoring node located near the incumbent receivers actually measures both the interference signals and the incumbent signals. Using the measurement results, the CIR estimates are compensated based on minimum mean square error (MMSE) criterion. The proposed Interference Monitoring can be extended cooperatively to utilize spatial diversity. Analytical evaluations assuming a simple cellular system model show that the Interference Monitoring can more accurately estimate CIR, and thus it can significantly increase the allowable transmit power. For an urban macro cell, the Interference Monitoring with a single node achieved more than a 4 dB increase of the transmit power; the Cooperative Interference Monitoring with 4 nodes achieved more than a 7 dB increase. Thus, the Interference Monitoring can expand opportunities for white space utilization without increasing the interference to the incumbent system.

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.

Realization of 4-by-4 MIMO channel using one composite leaky coaxial cable

Leaky coaxial cable (LCX) is widely used for wireless communication systems as an antenna for a linear-cell, which covers long and shallow areas. Since one LCX is usually utilized as one antenna, more than one LCX is required to configure a multi-input multi-output (MIMO) system. It means it is costly and space-consuming. To resolve these problems, we proposed a novel MIMO method for LCX. In this paper, we propose the method to utilize one composite cable, which consists of a pair of LCXs with different radiation characteristics, to configure a 4 × 4 MIMO channel. The measurement results confirmed that the proposed composite cable can realize a good channel condition for 4 × 4 MIMO transmission even if it is put in an anechoic chamber where no reflection path exists. On the other hand, the results also confirmed that it has good channel condition even if the spacing between a pair of LCX is as small as 2cm for the 5GHz band. Therefore the proposed system can reduce the space requirement for MIMO deployment for wireless application over linear-cell environments to cope with the high rapid increase of consumer electronics devices.

An experimental evaluation of 2 × 2 MIMO system using closely-spaced leaky coaxial cables

This paper introduces a two by two multiple-input multiple-output (MIMO) system using two closely-spaced leaky coaxial cables (LCXs). In this LCX-MIMO system, two different types of LCXs are placed in parallel with a narrow spacing, and different RF signals are fed to each of the LCXs from the same side. We show with our experimental results that the proposed LCX-MIMO set up works as well as MIMO transmission specified by the IEEE802.11n standard in the 2.4 GHz ISM band.

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

Directional propagation measurements and modeling in an urban environment at 3.7 GHz

In order to realistically model urban micro-cell environments with low base station heights, a measurement campaign has been conducted in the 3.5–3.8 GHz frequency band. The two scenarios of interest are the Urban Micro (UMi) Campus and Open Square scenarios. The findings of this campaign led to a parameter set for the quasi deterministic radio channel generator (QuaDRiGa) channel model and shall be used to improve accuracy in small-cell network design and evaluation towards 5G. This report includes details about the measurement array antenna as well as the approach of data analysis and postprocessing.

Comparative Analysis on Interference Suppressive Transmission Schemes for White Space Radio Access

With opening up of the TV white spaces for opportunistic access, designing a flexible physical layer (PHY) scheme has become an important focus for cognitive radio (CR) systems. Two possible PHY design solutions proposed are: generalized frequency division multiplexing (GFDM) and interference avoidance by partitioned frequency and time domain transmission (IA-PFT). Both of these methods extend the orthogonal frequency division multiplexing (OFDM) scheme to be applicable as a flexible CR PHY solution in a fragmented spectrum. In GFDM, introduction of pulse shaping filters reduces the out-of-band radiation of the opportunistic signals into the frequency band of the incumbent users; while in IA-PFT, simultaneous cancellation carrier insertion and time windowing technique suppress spectral leakage into the incumbent band of operation. In this paper, these two different approaches are compared in terms of interference suppression, transmission performance and processing complexity.

Interference Avoidance Transmission by Partitioned Frequency- and Time-Domain Processing

This paper presents an interference avoidance transmission technique for dynamic spectrum access (DSA). Generally, OFDM transmission induces high out-of-band emission due to the side-lobes of the transmitted sub-carriers. For a DSA based OFDM system, it is thus important to reduce the out-of-band emission. Aiming at providing high suppression effect for an interference avoidance notch, an interference avoidance transmission by partitioned frequency- and time-domain processing (IA-PFT) is proposed. IA-PFT is configured by a partitioned combination of the CC processing in the frequency domain and windowing processing in the time domain. Computer simulations show that IA-PFT reduces the interference power spectrum density under the condition of a highly prioritized wireless microphone in white space. Moreover, it is shown that IA-PFT realizes transmission performance and PAPR performance as much as those attained by conventional interference avoidance methods.