Risto Vuohtoniemi

On the Measurement of Duty Cycle and Channel Occupancy Rate

Duty cycle (DC) and channel occupancy rate (COR) measurements are important to characterize the availability of white space for cognitive radio systems (CRSs). The COR is related to the real occupancy of channels considered by a CRS but despite its importance it has not yet been widely considered for spectrum use measurements. Spectrum use measurements have typically used detection with a single threshold. In order to improve sensitivity, we utilize the localization algorithm based on double-thresholding (LAD) with the adjacent cluster combining (ACC) to spectrum use measurements and propose a modified version of it. We theoretically analyze the probability of false alarm after the LAD processing in a realistic case with correlation among samples and theoretically analyze the probability of detection after the LAD ACC processing. We propose COR estimation algorithm based on hard decision fusion of the frequency domain decisions. Measurement and theoretical results confirm the accurate DC and COR estimation and the significant sensitivity gains with the proposed algorithms.

Measurement-based on-body path loss modelling for UWB WBAN communications

This paper presents a path loss model for an ultra wideband (UWB) wireless body area network (WBAN) on-body communication. The modelling is based on the static frequency domain measurements in an anechoic chamber. The studies are done for several on-body radio channels and with two different UWB antennas (dipole and double loop) for the frequency range of 2-8 GHz. A linear least squares (LS) polynomial data fitting is applied to the post processed measurement data resulting parameters for a path loss model. It is shown that the loop antenna outperforms the dipole antenna in respect to the slope of the attenuation. However, the path loss at the reference distance is higher for the loop. It is also shown that the signal propagation delay in the antenna structures causes error in distance measurement and unless the error is compensated significant differences in the parameters of the path loss model may occur in a WBAN case. Finally, it is observed that by using energy detection notable benefit can be obtained if all propagation paths are considered instead of the first arriving path.

Adaptive FCME-based threshold setting for energy detectors

The detection threshold setting and noise uncertainty are known to be critical aspects for energy detectors. Adaptive methods for threshold setting outperform non-adaptive methods due to flexibility and robustness. There exists several adaptive threshold setting methods of which the forward consecutive mean excision (FCME) algorithm is among the most attractive ones since it is blind, computationally simple and efficient. However, in some situations, it may give a too large threshold. We propose to apply median filtering with the FCME. Real-life real-time measurement results show that proposal enables more stable thresholds even in the situations when there are no signal-free reference samples for the initial threshold computing.

Measurement studies of a spectrum sensing algorithm based on double thresholding

Welch spectrum estimator may be used for spectrum monitoring and sensing. Conventionally, the detection threshold is set assuming that the noise power is estimated from noise-only samples. The forward consecutive mean excision (FCME) algorithm is a method for automatically making decisions based on the decision variables, without estimation of the noise power a priori. In this paper, we propose the utilization of the FCME algorithm with the Welch spectrum estimator. Additionally, theoretical analysis about asymptotic threshold setting for the FCME algorithm with the Welch spectrum estimator is presented. The localization algorithm based on double-thresholding (LAD) with adjacent cluster combining (ACC) utilizes the FCME algorithm and is very suitable for signal detection. Laboratory and field measurement results with the LAD ACC method are included to study the detectability of different signal types, including a real wireless microphone signal.

IoT Connectivity in Radar Bands: A Shared Access Model Based on Spectrum Measurements

To address the challenge of more spectrum for IoT connectivity, this article proposes an SA framework with rotating radars. The proposed framework is based on the results of our measurement campaign in which we measured spectrum usage patterns and signal characteristics of three different ground-based fixed rotating radar systems near Oulu, Finland. In our work, we review different IoT protocols and their use of licensed or unlicensed spectrum. We make the case that IoT systems generate much data that cannot be accommodated with licensed/unlicensed spectrum, which already suffer from congestion. We identify the suitability of shared access between different rotating radars and IoT networks. We then present a zone-based SA framework in rotating radar spectrum for the operators providing IoT services, highlight its benefits, and also specify challenges in its implementation. To fully develop the considered zone-based SA method that ensures coexistence of IoT devices with no harmful interference to the rotating radars, we propose an REM-enabled architecture for the SA. The proposed architecture provides principles and rules for using the SA for the IoT, and it does not require modifications in the incumbent radar systems.

Detection of broadcast signals in cognitive radio based PLC using the FCME algorithm

Today, and especially in the future, there is an increasing need for complementary techniques to meet the growing capacity requirements of wireless communications. A high data rate connection with power line communication (PLC) is one attractive solution to achieve this need. One way to improve the data rates obtained in PLC networks is to increase the used bandwidth and operate at higher frequencies. At the same time, however, it should be kept in mind that the power lines, unfortunately, act as quite good antennas which can detect strong near-by FM and TV signals. In the future, the PLC frequency range can overlap with the broadcasting frequency bands resulting in interference for these transmissions and vice versa. With the static notching the whole FM-frequency band is notched during the PLC communication. This may result in inefficient spectrum utilization as in a given place and at a given time only a part of the FM-frequency band may be occupied. In this paper, a blind spectrum sensing algorithm based on forward consecutive mean excision (FCME) algorithm is proposed to locate the free frequency bands inside the broadcasting frequency range in PLC-network. The performance of this sensing algorithm is analyzed using spectrum analyzer measurement results and calculations in the broadcasting frequency range. The results verify that the proposed method performs well when detecting free frequency bands in broadcasting frequency band providing means for better spectrum utilization in PLC-network.

On opportunistic spectrum access in radar bands: Lessons learned from measurement of weather radar signals

The need for extra spectrum and the fact that a large amount of spectrum below 6 GHz is allocated to radar systems has motivated regulatory bodies and researchers to investigate the feasibility of dynamic spectrum access in radar bands. To design efficient wireless communication schemes that coexist with radar systems, it is essential that the wireless community thoroughly understand the operations of these systems in different bands. This article studies incumbent operations and usage patterns in the 5 GHz band, where weather radar systems dominate, dynamic frequency selection is employed as a sharing mechanism, and recent works have explored the possibility to temporally share the spectrum with such radar systems. We present a measurement-based study of spectrum usage by a weather radar in Finland. Our measurement results show that the weather radars scan patterns are quasi-periodic, and that use of sensing may not reliably detect radar signals due to its quasi-periodic scanning patterns and different vertical scanning angles. Finally, we present a framework for a database-assisted temporal sharing coexistence mechanism that takes into account the real occupancy behavior of the radar.

Threshold setting for the evaluation of the aggregate interference in ISM band in hospital environments

Estimation of the aggregate interference is required in order to predict the performance of a wireless system in its working environment. Body Area Networks (BANs) for healthcare applications are becoming a reality, allowing patients to be monitored continuously without forcing them to stay in bed or in hospital. The increasing number of wireless medical devices makes the ISM (Industrial, Scientific and Medical) band particularly crowded. If new smart BANs have to correctly operate in hospital, coexistence with the existing wireless devices must be accurately investigated, starting with studying the interference in the operating frequency band. The intensity of the interference is strongly related to the chosen threshold, which defines if a received sample has to be categorized as interference or noise. Adaptive threshold methods outperform the non-adaptive ones, due to flexibility and robustness. Among the adaptive threshold methods, the forward consecutive mean excision (FCME) is one of the most attractive, since it is blind, computationally simple and efficient. When applied to large data set, it may require too long time to be computed, thus median filtering has been proposed (med-FCME). In this paper we compare the performance of fixed vs adaptive threshold methods. The two methods are applied to a set of real measurements taken in a modern city hospital over one week.

Exploring radio environment map architectures for spectrum sharing in the radar bands

The need for extra spectrum to support future 5G networks and the fact that a large amount of spectrum below 6 GHz is allocated for different radar systems have motivated regulatory bodies and wireless researchers to investigate the feasibility of Dynamic Spectrum Access (DSA) in radar bands. Moreover, the next generation of infrastructures and devices will need to be more flexible to support a much wider range of application services, operate over much wider bandwidths, and exploit multiple radio access technologies. Radio Environment Maps (REMs) can be utilized to enhance the awareness of network entities of their operational radio environment. In the context of potential spectrum sharing in radar bands, REMs can be used to determine spectrum usage and propagation patterns of different incumbent radar systems operating in a given area. This information in turn can be utilized to establish different radar systems protection requirements in a particular band, and can also help to mitigate any interference between incumbent radar systems and Secondary Users (SUs). In this paper, based on spectrum measurement campaigns in Finland and Ireland, we explore the functional architecture of REMs for potential spectrum sharing in radar bands. We argue that the unique operating principle and signal characteristics of this type of incumbent needs to be considered in implementation of the sensor network, REM communication protocol, and REM architecture. We also discuss the potential of REM to facilitate the use of more advanced interference cancellation or avoidance technologies such as temporal sharing that can significantly reduce exclusion zones.

Stochastic spectral occupancy modeling: A body area network perspective in ISM band

Medical ICT is one of the most interesting and challenging research areas for both industry and academia. Wireless body area network (WBAN) applications for health-care systems are rapidly being developed and deployed. In an unlicensed frequency band like industrial, scientific and medical (ISM) band, WBANs will encounter tough competition for resources because several other wireless technologies share the band. Spectrum occupancy evaluations (SOEs) provide a statistical insight into the resource utilization patterns. This research work is focused on stochastic modeling of such spectrum occupancies in order to statistically describe the possible interference a WBAN may face. Modeling is based upon the measurement data acquired from accident and emergency ward, Oulu University hospital. Stochastic models for channel occupancies and spectrum resource occupancy are provided. The consistency of model produced data with actual data is validated through exact and asymptotic statistical hypothesis tests.