Browsing by Author "Cheffena, Michael"
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Item The Application of Lognormal Mixture Shadowing Model for B2B Channels(IEEE, 2018-09) Cheffena, Michael; Mohamed, MarshedIn this article, a Lognormal mixture shadowing model based on a cluster concept is utilized in the modeling of body-to-body (B2B) channels for different running and cycling activities. The mixture model addresses the inaccuracies observed using a unimodal distribution that may not accurately represent the measurement dataset. Parameters of the mixture model are estimated using the expectation-maximization (EM) algorithm. The accuracy of the proposed mixture model is compared to other commonly utilized unimodal distributions showing significant improvement in representing the empirical dataset. The measured data, as well as the developed model, can be used for accurate planning and deployments of wireless B2B networks for use in various sporting and other related activities.Item Buffer Delay Improvement in Gait-Cycle-Driven Transmission Power Control Scheme for WBAN(IEEE, 2020-10-08) Mohamed, Marshed; Cheffena, Michael; Ai, Yun; Al-Saman, AhmedDue to the dynamic nature of the wireless body area network (WBAN) channels, there is a need for dynamic transmission power control (TPC) to increase their energy efficiency. The existing gait-cycle-driven TPC (G-TPC) successfully achieves this objective, however, it introduces maximum buffer delay equal to the period of the gait cycle. In this study, we investigate the relationship between the potential power saved and the maximum buffer delay in the G-TPC approach. A new approach is proposed based on the transmission window (instead of currently used transmission point) to reduce the maximum buffer delay by studying the received signal strength indicator (RSSI) gait patterns collected from 20 subjects. The results indicated that with a slight modification of the protocol, the same power saving can be achieved for 1.2% of the time with less than half of the maximum buffer delay. The study also indicated that, with tolerant power saving requirements, at least half of the gait channels can reduce the maximum buffer delay by more than 38%.Item Characterization of dynamic wireless body area network channels during walking(Springer International Publishing, 2019-04-29) Mohamed, Marshed; Joseph, Wout; Vermeeren, Günter; Tanghe, Emmeric; Cheffena, MichaelIn this work, finite-difference time-domain was used for the investigation of dynamic wireless body area network channel characteristics during walking, thus accounting for dynamic aspects and body postures. This involves the study of on-body, off-body, and body-to-body communication in an empty environment, at the center frequency of 2.45 GHz. The channels were investigated in terms of fade variation and their corresponding amplitude distributions. For on-body channels, the fade variation was found to be periodic, with larger fade variations for the channels involving the nodes at the hand and thigh. For off-body and body-to-body channels, channels with the absence of line of sight experienced constructive and destructive interference as the distance between the end nodes changes, resulting in larger fade variations. For the amplitude distribution of the channels, a multivariate normal distribution was considered. The distribution has the capability of modeling channels jointly which makes it easier for network analysis and was considered because of the significant correlation between the channels. The resulting estimated multivariate distributions fit well with the simulated data, for on-body, off-body, and body-to-body channelsItem Characterization of the Body-to-Body Propagation Channel for Subjects during Sports Activities(IEEE, 2018-02-18) Mohamed, Marshed; Cheffena, Michael; Moldsvor, ArildBody-to-body wireless networks (BBWNs) have great potential to find applications in team sports activities among others. However, successful design of such systems requires great understanding of the communication channel as the movement of the body components causes time-varying shadowing and fading effects. In this study, we present results of the measurement campaign of BBWN during running and cycling activities. Among others, the results indicated the presence of good and bad states with each state following a specific distribution for the considered propagation scenarios. This motivated the development of two-state semi-Markov model, for simulation of the communication channels. The simulation model was validated using the available measurement data in terms of first and second order statistics and have shown good agreement. The first order statistics obtained from the simulation model as well as the measured results were then used to analyze the performance of the BBWNs channels under running and cycling activities in terms of capacity and outage probability. Cycling channels showed better performance than running, having higher channel capacity and lower outage probability, regardless of the speed of the subjects involved in the measurement campaign.Item A Dynamic Channel Model for Indoor Wireless Signals: Working Around Interference Caused by Moving Human Bodies(IEEE, 2018-02-16) Mohamed, Marshed; Cheffena, Michael; Fontán, Fernando Pérez; Moldsvor, ArildThe use of indoor wireless devices has substantially increased in recent years. This escalation is due to the expansion of traditional communication devices, such as mobile phones and laptop computers, to less traditional ones, such as wirelessly communicating sensor nodes present in smart homes, office buildings, and industrial environments. The placement of these nodes varies considerably from one application to the next, but, when the nodes are placed indoors and within the vicinity of human height, a body's movement can cause significant time-varying channel conditions. The movement is even more compelling in such networks because of the power constraints involved [1]. Thus, an accurate study on the impact of a moving body and the characteristics of indoor propagation channels is important.Item Empirical Path Loss Models for Wireless Sensor Network Deployment in Snowy Environments(IEEE, 2017-09-11) Cheffena, Michael; Mohamed, MarshedIn this letter, practical sensor nodes are utilized to study the path loss effects of wireless sensor networks (WSNs) at 2.425 GHz in a ground covered by snow at different heights from the ground. The measurement results are compared with the ground reflection (two-ray) path loss model and the ray-tracing model showing significant difference. New empirical path loss models for different heights from the ground based on the log-distance path loss model are presented. The developed models are compared with the existing path loss models to demonstrate their accuracy between sensor nodes deployed in snowy environments. The experimental data as well as the developed path loss models can be utilized for efficient planning and deployments of WSNs in snowy environments. They can support applications including rescue and monitoring of snow avalanche, environmental surveillance, or monitoring winter sporting activities.Item Hybrid automatic repeat request‐based intelligent reflecting surface‐assisted communication system(Institution of Engineering and Technology, 2021-01-20) Ai, Yun; Mohamed, Marshed; Kong, Long; Al‐Saman, Ahmed; Cheffena, MichaelThe intelligent reflecting surface (IRS) is an emerging technique to extend wireless coverage. In this letter, the performance of the hybrid automatic repeat request (hybrid ARQ) for an IRS‐assisted system is analysed. More specifically, the outage performance of the IRS‐aided system using hybrid ARQ protocol with chase combining is studied. The asymptotic analysis also shows that the outage performance is better and improves linearly by increasing the number of reflectors of the IRS‐aided system. The results also verify the potential of combining the ARQ scheme in the link layer of the IRS‐aided system and demonstrate that a very small change of path loss condition can impact the performance largely.Item Indoor Channel Estimation Using Single-Snapshot Wideband Measurement(IEEE, 2020-03-15) Ai, Yun; Cheffena, Michael; Mohamed, Marshed; Al-Saman, AhmedThe successful design of communication systems generally requires knowledge of various channel characteristic parameters. This paper utilizes the reverberation time extracted from single-snapshot wideband measurement to estimate different indoor propagation parameters based on the room electromagnetics theory. The indoor room environment is conceived as a lossy cavity that is characterized by the diffuse scattering components resulting from the surrounding walls and objects and possibly a line-of-sight (LoS) component. The main advantages of the room electromagnetics based approach are simplicity and good accuracy. The approach needs only one wideband measurement in order to extract the reverberation time in addition to some dimensional information on the investigated room to predict various important channel parameter of great importance. The measurements show good agreement with the theoretical predicted results.Item Performance of Full-Duplex Wireless Back-Haul Link under Rain Effects Using E-Band 73 GHz and 83 GHz in Tropical Area(MDPI, 2020-09-03) Al-Saman, Ahmed; Mohamed, Marshed; Cheffena, Michael; Azmi, Marwan Hadri; Rahman, TharekThis paper presents rain attenuation effects on the performance of the full-duplex link in a tropical region based on one-year measurement data at 73.5- and 83.5-GHz E-band for distances of 1.8 km (longer links) and 300 m (shorter links). The measured rain attenuations were analyzed for four links, and the throughput degradation due to rain was investigated. The findings from this work showed that the rain attenuation for both frequencies (73.5 and 83.5 GHz) of E-band links are the same. The rain rates above 108 and 193 mm/h caused an outage for the longer and shorter links, respectively. The 73.5 and 83.5 GHz bands can support the full-duplex wireless back-haul link under rainy conditions with outage probability of 2.9×10−4 and 6×10−5 for the longer and shorter links, respectively. This work also finds that the heavy rain with rain rates above 80 mm/h for long link and 110 mm/h for short link causes about 94% and 0.90% degradation of maximum throughput. The application of these findings would help improve the architecture and service of full-duplex wireless E-band links that are established at other sites and in other tropical areas.Item Physical-Statistical Channel Model for Off-body Area Network(IEEE, 2017-01-02) Mohamed, Marshed; Cheffena, Michael; Moldsvor, Arild; Fontán, Fernando PérezIn this letter, a physical-statistical-based channel model for off-body wireless communications is presented. The model utilizes a dynamic human walking model, which provides detailed description of the movement of the different body parts. The received signal is composed of a direct component, which might be subject to shadowing by the body parts, and a multipath component due to reflections from the environmental scatterers. The uniform theory of diffraction (UTD) is utilized to accurately calculate the time-varying shadowing and scattering effects of the direct signal due to the moving of body parts. A Rayleigh distribution is used to represent the multipath fading effects by the scatterers around the human body. The model is validated in terms of first- and second-order statistics using 2.36 GHz measurement data, showing good agreement.Item Radio Propagation Measurements in the Indoor Stairwell Environment at 3.5 and 28 GHz for 5G Wireless Networks(Hindawi, 2020-12-28) Al-Saman, Ahmed; Mohamed, Marshed; Cheffena, MichaelTo cover the high demand for wireless data services for different applications in the wireless networks, different frequency bands below 6 GHz and in millimeter-wave (mm-Wave) above 24 GHz are proposed for the fifth generation (5G) of communication. The communication network is supposed to handle, among others, indoor traffic in normal situations as well as during emergencies. The stairway is one of those areas which has less network traffic during normal conditions but increases significantly during emergencies. This paper presents the radio propagation in an indoor stairway environment based on wideband measurements in the line of sight (LOS) at two candidate frequencies for 5G wireless networks, namely, 3.5 GHz and 28 GHz. The path loss, root mean square (RMS) delay spread, K-factor results, and analysis are provided. The close-in free-space reference distance (CI), floating intercept (FI), and the close-in free-space reference distance with frequency weighting (CIF) path loss models are provided. The channel parameters such as the number of clusters, the ray and cluster arrival rates, and the ray and cluster decay factors are also obtained for both frequencies. The findings of the path loss show that the CI, FI, and CIF models fit the measured data well in both frequencies with the path loss exponent identical to the free-space path loss. Based on clustering results, it is found that the cluster decay rates are identical at both bands. The results from this and previous measurements indicate that at least one access point is required for every two sections of the stairway to support good coverage along the stairwell area in 5G wireless networks. Moreover, for 5G systems utilizing mm-Wave frequency bands, one access point for each stair section might be necessary for increased reliability of the 5G network in stairwell environments.Item Rain Attenuation Measurements and Analysis at 73 GHz E-Band Link in Tropical Region(IEEE, 2020-03-25) Al-saman, Ahmed; Mohamed, Marshed; Ai, Yun; Cheffena, Michael; Azmi, Marwan Hadri; Rahman, TharekThis letter presents the rainfall intensity and rain attenuation analysis in tropical region based on a one-year measurement using the 73.5 GHz E-band link of 1.8 km with three rain gauges installed along the path. The measured rain rate and rain attenuation were analysed and bench-marked with previous measurements and prediction models. The findings from this work showed that Malaysia agrees with the ITU-R rain prediction model of Zone P by 99.99% of time. The maximum measured rain attenuation exceeding 0.03% of the year is around 40.1 dB at the maximum rain rate of 108 mm/h.Item Received Signal Strength Based Gait Authentication(IEEE, 2018-08-15) Mohamed, Marshed; Cheffena, MichaelExpansion of wireless body area networks applications, such as health-care, m-banking, and others has lead to vulnerability of privacy and personal data. An effective and unobtrusive natural method of authentication is therefore a necessity in such applications. Accelerometer-based gait recognition has become an attractive solution, however, continuous sampling of accelerometer data reduces the battery life of wearables. This paper investigates the usage of received signal strength indicator (RSSI) as a source of gait recognition. Unlike the accelerometer-based method, the RSSI approach does not require additional sensors (hardware) or sampling of them, but uses the RSSI values already available in all radio devices. Three radio channel features namely, the time series, auto-correlation function, and level crossing rate were extracted from unique signature of the RSSI in relation to the corresponding subject. The extracted features were then used together with four different classification learners, namely decision tree, support vector machine, k-nearest neighbors, and artificial neural network, to evaluate the method. The best performance was achieved utilizing artificial neural network with 95% accuracy when the features were extracted from one on-body radio channel (right wrist to waist), and 98% when the features were extracted from two on-body radio channels (right wrist to waist, and left wrist to waist). The developed RSSI-based gait authentication approach can complement high-level authentication methods for increased privacy and security, without additional hardware, or high energy consumption existing in accelerometer-based solutions.Item Statistical Analysis of Rain at Millimeter Waves in Tropical Area(IEEE, 202-03-09) Al-saman, Ahmed; Cheffena, Michael; Mohamed, Marshed; Azmi, Marwan Hadri; Ai, YunThe high frequencies of millimeter wave (mm-wave) bands have been recognized for the fifth generation (5G) and beyond wireless communication networks. However, the radio propagation channel at high frequencies can be largely influenced by rain attenuation, especially in tropical regions with high rainfall intensity. In this paper, we present the results of rainfall intensity and rain attenuation in tropical regions based on one-year measurement campaign. The measurements were conducted from September 2018 until September 2019 at 21.8 GHz (K-band) and 73.5 GHz (E-band) in Malaysia. The rainfall intensity was collected using three rain gauges installed along a 1.8 km link. The rain attenuation is computed from the difference between the measured minimum received signal level (RSL) during clear sky and rain conditions. The measured rain rate and rain attenuation distributions are then analysed and benchmarked with several previous measurements and well-known prediction models such as the ITU-R P. 530-17. The rainfall rate results showed that the best agreement between the measured rainfall rate in Malaysia and the ITU-R PN.837-1 prediction value for Zone P is up to 0.01% of time (99.99% of time agrees well and only disagrees for 0.01% of time). For the E-band, the maximum measured rain attenuation exceeding 0.03% of the year is around 40.1 and 20 dB for 1.8 and 0.3 km links, respectively, at the maximum rain rate of 108 mm/h. For the K-band, the maximum rain attenuation exceeding 0.01% of the year is around 31 dB for the 1.8 km link. Finally, the rain rates exceeding 108 and 180 mm/h at 73.5 and 21.8 GHz, respectively, along the 1.8 km path caused an outage on our measurement setup. The rain rate of 193 mm/h and above caused an outage for the 0.3 km E-band link. The experimental data as well as the presented data analysis can be utilized for efficient planning and deployments of mm-wave wireless communication systems in tropical regions.Item Wideband Channel Characterization for 6G Networks in Industrial Environments(MDPI, 2021-03-12) Al-Saman, Ahmed; Mohamed, Marshed; Cheffena, Michael; Moldsvor, ArildWireless data traffic has increased significantly due to the rapid growth of smart terminals and evolving real-time technologies. With the dramatic growth of data traffic, the existing cellular networks including Fifth-Generation (5G) networks cannot fully meet the increasingly rising data rate requirements. The Sixth-Generation (6G) mobile network is expected to achieve the high data rate requirements of new transmission technologies and spectrum. This paper presents the radio channel measurements to study the channel characteristics of 6G networks in the 107–109 GHz band in three different industrial environments. The path loss, K-factor, and time dispersion parameters are investigated. Two popular path loss models for indoor environments, the close-in free space reference distance (CI) and floating intercept (FI), are used to examine the path loss. The mean excess delay (MED) and root mean squared delay spread (RMSDS) are used to investigate the time dispersion of the channel. The path loss results show that the CI and FI models fit the measured data well in all industrial settings with a path loss exponent (PLE) of 1.6–2. The results of the K-factor show that the high value in industrial environments at the sub-6 GHz band still holds well in our measured environments at a high frequency band above 100 GHz. For the time dispersion parameters, it is found that most of the received signal energy falls in the early delay bins. This work represents a first step to establish the feasibility of using 6G networks operating above 100 GHz for industrial applications.