Measuring the service level in the 2.4 GHz ISM band

In this report we provide the findings of the 2.4 GHz service level research. Here service level means the following: can all devices in the 2.4 GHz band fulfill their communication needs. In other words this corresponds to the overall Quality of Service (QoS). The project is a short research exploratory project of about 400 hours in collaboration with Agentschap Telecom, the Dutch Radiocommunications Agency. First of all a survey has been made to investigate which measurement methods can be used to assess the service level in the 2.4 GHz. Here the focus is on IEEE 802.11b/g/n (WiFi) systems. The service level can be measured at several levels of the OSI model: spectrum sensing (physical layer) and packet sniffers (datalink layer). Power level measurements are used to assess the utilization of the 2.4 GHz ISM band. On the other hand packet sniffers are an appropriate method to measure congestion and to pinpoint problems. Secondly, in this project the interferer mechanisms of several sources (microwave, wireless A/V transmitter, Bluetooth, second WiFi network) have been measured in a controlled environment. It turns out that interferers not only increase retry rate, but also trigger unwanted WiFi mechanisms; especially the hidden node mechanism (Request To Send (RTS)/Clear To Send (CTS) packets). So this means that the CTS/RTS control packets, but also the retry rate can be used to identify congestion. The spectrum measurement results allow to identify which interferer source causes congestion. Finally, also a measurement setup is presented that allows to measure the service level. In addition, initial measurements are provided of live environments (college room, office room, city centre). The results show inefficient use of the wireless medium in certain scenarios, due to a large frame rate of management and control packets compared to the data frame rate. In a busy WiFi environment (college room) only 20% of all frames are data frames. Of these data frames only 1/10 are actual data frames as most data frames are so-called null frames; used to keep a WiFi connection alive in power save mode. From all frames about 70% are control frames of which most are ACK frames and in less extend CTS/RTS frames. More research is required to identify the reasons for the high number of control frames. It is likely that there is significant interference, probably due to the many WiFi devices. This is also depicted by the retry frame rate (7%). Combining spectrum sensing with packet sniffing seems to be a good method to assess the service level in the 2.4 GHz ISM band. However, the interferer mechanisms that occur between WiFi networks, WiFi devices and other technologies are complex. More research is needed to enhance the developed proof-of-concept demonstrator and to have a better understanding of the interferer mechanisms in WiFi systems

Coexistence and Spectrum Sensing of IEEE 802.11 Systems for Cognitive Radio Applications

Nowadays, a vast majority of the Wi-Fi systems operates in the 2.4 GHz ISM band that becomes more and more crowded due to the growing usage of Wi-Fi. On top of that, a growing number of non Wi-Fi technologies become active in this band as well. In this thesis the focus is on spectrum sensing and detection techniques to enhance the coexistence with Wi-Fi systems.First, we investigate spectrum sensing for monitoring short-range wireless technologies. We show the value of using mobile spectrum monitoring equipment and results are presented concordantly. Additionally the impact of Automatic Gain Control (AGC), an essential building block in spectrum monitoring receivers, is investigated in order to enhance spectrum sensing performance. By doing so, techniques are developed to remove the AGC influences from the monitoring spectrum data. The results show that interference due to the AGC could lead to an overestimation of the actual spectrum usage by 60% in the ISM band.Secondly, the influence of interference on Wi-Fi systems has been investigated. This entails respectively interference due to non Wi-Fi technologies and interference due to overlapping Wi-Fi networks. For this purpose a methodology has been developed to assess spectrum utilization and to measure the congestion simultaneously. The obtained results show the inefficient use of the wireless medium due to a large amount of transmission overhead which may lead to only 21% of actual data in highly congested areas.Thirdly, the alternative use of Wi-Fi communication in the licensed TV-bands has been investigated to alleviate the congestion and interference issues in the ISM band. The operation of Wi-Fi systems in these bands is considered to be allowed under the condition of secondary use, i.e. avoiding interference to users with the primary rights (e.g. TV-broadcasting stations). For this purpose a novel collaborative sensing scheme with geolocation access to a central white-space database is presented

An eigenvalue approach to enhance energy detection in a mobile spectrum monitoring network

For fulfilling new tasks of the regulator, we propose a novel mobile spectrum monitoring network. The huge amount of measurement data contains besides thermal noise also noise induced by the Automatic Gain Control (AGC). As a result the occupancy results based on normal energy detection are significantly biased. In order to assess the spectrum occupancy more accurately, we employ an eigenvalue based technique to eliminate AGC noise components. This technique, using singular value decomposition, enables signal space analysis based on the received spectral data by finding an optimal threshold. In addition, this technique allows to eliminate non-linear noise induced by the AGC. In this paper we apply this method to the UMTS downlink band using collected data of a mobile measurement system. The results indicate that spectrum occupancy can be assessed 21% more accurate compared to an ITU-based method

Patient Activation for Self-Management in Patients with Idiopathic Pulmonary Fibrosis or Sarcoidosis

BACKGROUND: Self-management is considered important in the management of patients with idiopathic pulmonary fibrosis (IPF) or sarcoidosis. However, data about the degree of activation for self-management is lacking. OBJECTIVES: The aim of the study was to determine the degree of activation for self-management in patients with IPF or sarcoidosis using the Patient Activation Measure (PAM) and to evaluate the association between PAM scores, clinical characteristics, and health-related outcomes. STUDY DESIGN AND METHODS: This cross-sectional prospective study assessed besides the PAM also demographics, lung function, dyspnea (modified Medical Research Council [mMRC]), fatigue (Checklist Individual Strength-Fatigue [CIS-Fatigue]), anxiety/depression (Hospital Anxiety and Depression Scale [HADS-A/HADS-D]), and generic health status (EuroQol five-dimensional-five-level [EQ-5D-5L]). RESULTS: Mean PAM was 55.0 (9.1) points in patients with IPF (n = 59) and low levels of patient activation for self-management (PAM ≤55.1 points) were present in 56% of the patients. PAM Scores correlated significantly (p < 0.05) with mMRC (ρ = -0.476), HADS-A (ρ = -0.326), HADS-D (ρ = -0.459), and EQ-5D-5L (ρ = 0.393). In patients with sarcoidosis (n = 59), the mean PAM score was 55.7 (11.0) points, and 46% of the patients reported low PAM levels. Significant correlations were found with mMRC (ρ = -0.356), HADS-A (ρ = -0.394), HADS-D (ρ = -0.478), and EQ-5D-5L (ρ = 0.313). CONCLUSION: About half of the outpatients with IPF or sarcoidosis have a low degree of activation for self-management, and these patients generally report more dyspnea, anxiety, depression, and a lower health status. Whether patients with a low degree of activation can be successful in self-managing their disease remains to be determined