Evaluation of the aggregate interference in 2.4 GHz ISM band in home, office and hospital environments

Abstract. In the last years, the wireless body area network (WBAN) research has grown considerably and the idea to apply WBAN to the medical and healthcare issues could materialize. A possible WBAN could exploit the ISM (industrial, scientific and medical) band, clustered around 2.4 GHz. The ISM band is just used by other communication systems and non-communication systems. These systems transmit signals, defined aggregate interference, that could hinder the WBAN communications. In this thesis, the ISM band is investigated in order to understand if the amount of interference is too high to allow implementation of a new WBAN or if the coexistence between WBAN and the other systems is still possible. The ISM band analyses are carried out using data collected in real-life measurements, in environments where a patient monitored by a WBAN could usually stay. Data was collected in an office and a home environments, situated in Florence, Italy, in “San Giuseppe” hospital located in Empoli, Italy and in Oulu University Hospital, situated in Oulu, Finland. In each location, data are collected during a week using a spectrum analyzer (SA). The information measured by the SA is the power, expressed in dBm. In this work, a spectrum occupancy evaluation (SOE) has been developed to analyze the occupancy percentage of every frequency channel of the ISM band. The occupancy value is determined by a threshold, which divides the interference samples from the noise samples. In this work, the occupancy is evaluated using both a fixed threshold and a dynamic threshold, which value directly depends on the samples’ values. The results achieved using fixed and dynamic thresholds are discussed and compared. In addition, a time domain analysis has been carried out in order to know the amplitude, the time distribution and the size of the interference contributions. The time domain results allow to predict the interference behavior, making possible the extraction of a statistical interference modelling. The final results of the analyses depend strongly on the measurement location, the time and the measurement equipment. However, in most cases, the occupancy value is below 10%. Hence, the amount of interference is not so high as to prevent the implementation of a new WBAN or to determine an added smartness to the WBAN