David Plets

Coverage prediction and optimization algorithms for indoor environments

A heuristic algorithm is developed for the prediction of indoor coverage. Measurements on one floor of an office building are performed to investigate propagation characteristics and validations with very limited additional tuning are performed on another floor of the same building and in three other buildings. The prediction method relies on the free-space loss model for every environment, this way intending to reduce the dependency of the model on the environment upon which the model is based, as is the case with many other models. The applicability of the algorithm to a wireless testbed network with fixed WiFi 802.11b/g nodes is discussed based on a site survey. The prediction algorithm can easily be implemented in network planning algorithms, as will be illustrated with a network reduction and a network optimization algorithm. We aim to provide an physically intuitive, yet accurate prediction of the path loss for different building types.

On the Methodology for Calculating SFN Gain in Digital Broadcast Systems

For broadcast networks, the Single-Frequency Network (SFN) mode is an alternative to the well-known Multi-Frequency Network (MFN) mode, where instead of transmitters operating at different frequencies, all base stations use the same frequency. Besides the optimal frequency reuse, it is usually expected that the more homogeneous distribution of received signal strength reception in an SFN will improve the quality of service. Nevertheless, it should be noted that not all the locations within the service area will benefit from the SFN configuration. Some areas will show a degraded quality caused by the SFN echoes. In this paper, the SFN gain is defined as a parameter describing potential gain or interference. An unambiguous methodology to obtain the actual SFN gain is presented and the variation of the gain is investigated for a DVB-H network as a function of the signal strength difference received from different transmitters. This SFN gain can be used for coverage planning of future broadcast networks.

Experimental Assessment of Specific Absorption Rate Using Room Electromagnetics

A closed room environment is viewed as a lossy cavity, characterized by possibly a line-of-sight component and diffuse scattering parts from walls and internal obstacles. A theory used in acoustics and reverberation chambers is applied for the electromagnetic case, and main issues related to measurement systems, antennas characteristics, diffuse energy properties, and human exposure are investigated. The goal of this paper aims first toward validation of the assessment of the reverberation time in an environment using a virtual multiple-input-multiple-output channel system. Second, the reverberation time in an adjacent room is investigated, and hence, a measurement-based method is readily developed to assess the absorption cross section and the whole-body specific absorption rate of humans at 2.3 GHz in a realistic closed environment.

Exposure Optimization in Indoor Wireless Networks by Heuristic Network Planning

Due to the increased use of indoor wireless networks and the concern about human exposure to radio-frequency sources, exposure awareness has increased during recent years. However, current-day network planners rarely take into account electric-fleld strengths when designing networks. Therefore, in this paper, a heuristic indoor network planner for exposure calculation and optimization of wireless networks is developed, jointly optimizing coverage and exposure, for homogeneous or heterogeneous networks. The implemented exposure models are validated by simulations and measurements. As a flrst novel optimization feature, networks are designed that do not exceed a user-deflned electric-fleld strength value in the building. The in∞uence of the maximally allowed fleld strength, based on norms in difierent countries, and the assumed minimal separation between the access point and the human are investigated for a typical o-ce building. As a second feature, a novel heuristic exposure minimization algorithm is presented and applied to a wireless homogeneous WiFi and a heterogeneous WiFi-LTE femtocell network, using a new metric that is simple but accurate. Field strength reductions of a factor 3 to 6 compared to traditional network deployments are achieved and a more homogeneous distribution of the observed fleld values on the building ∞oor is obtained. Also, the in∞uence of the throughput requirement on the fleld strength distribution on the building ∞oor is assessed. Moreover, it is shown that exposure minimization is more efiective for high than for low throughput requirements and that high fleld values are more reduced than low fleld values.

Simple Indoor Path Loss Prediction Algorithm and Validation in Living Lab Setting

A simple heuristic algorithm has been developed for an accurate prediction of indoor wireless coverage, aiming to improve existing models upon multiple aspects. Extensive measurements on several floors in four buildings are used as validation cases and show an excellent agreement with the predictions. As the prediction is based on the free-space loss model for every environment, it is generally applicable, while other propagation models are often too dependent on the environment upon which it is based. The applicability of the algorithm to a wireless testbed network in a living lab setting with WLAN 802.11b/g nodes is investigated by a site survey. The results can be extremely useful for the rollout of indoor wireless networks.

A novel method to assess human population exposure induced by a wireless cellular network

This paper presents a new metric to evaluate electromagnetic exposure induced by wireless cellular networks. This metric takes into account the exposure induced by base station antennas as well as exposure induced by wireless devices to evaluate average global exposure of the population in a specific geographical area. The paper first explains the concept and gives the formulation of the Exposure Index (EI). Then, the EI computation is illustrated through simple phone call scenarios (indoor office, in train) and a complete macro urban data long-term evolution scenario showing how, based on simulations, radio-planning predictions, realistic population statistics, user traffic data, and specific absorption rate calculations can be combined to assess the index. Bioelectromagnetics. 36:451-463, 2015.

Advanced real-time indoor tracking based on the Viterbi algorithm and semantic data

A real-time indoor tracking system based on the Viterbi algorithm is developed. This Viterbi principle is used in combination with semantic data to improve the accuracy, that is, the environment of the object that is being tracked and a motion model. The starting point is a fingerprinting technique for which an advanced network planner is used to automatically construct the radio map, avoiding a time consuming measurement campaign. The developed algorithm was verified with simulations and with experiments in a building-wide testbed for sensor experiments, where a median accuracy below 2 m was obtained. Compared to a reference algorithm without Viterbi or semantic data, the results indicated a significant improvement: the mean accuracy and standard deviation improved by, respectively, 26.1% and 65.3%. Thereafter a sensitivity analysis was conducted to estimate the influence of node density, grid size, memory usage, and semantic data on the performance.

Joint Minimization of Uplink and Downlink Whole-Body Exposure Dose in Indoor Wireless Networks

The total whole-body exposure dose in indoor wireless networks is minimized. For the first time, indoor wireless networks are designed and simulated for a minimal exposure dose, where both uplink and downlink are considered. The impact of the minimization is numerically assessed for four scenarios: two WiFi configurations with different throughputs, a Universal Mobile Telecommunications System (UMTS) configuration for phone call traffic, and a Long-Term Evolution (LTE) configuration with a high data rate. Also, the influence of the uplink usage on the total absorbed dose is characterized. Downlink dose reductions of at least 75% are observed when adding more base stations with a lower transmit power. Total dose reductions decrease with increasing uplink usage for WiFi due to the lack of uplink power control but are maintained for LTE and UMTS. Uplink doses become dominant over downlink doses for usages of only a few seconds for WiFi. For UMTS and LTE, an almost continuous uplink usage is required to have a significant effect on the total dose, thanks to the power control mechanism.

Characterization of the On-Body Path Loss at 2.45 GHz and Energy Efficient WBAN Design for Dairy Cows

Wireless body area networks (WBANs) provide promising applications in the healthcare monitoring of dairy cows. The characterization of the path loss (PL) between on-body nodes constitutes an important step in the deployment of a WBAN. In this paper, the PL between nodes placed on the body of a dairy cow was determined at 2.45 GHz. Finite-difference time domain simulations with two half-wavelength dipoles placed 20 mm above a cow model were performed using a 3-D electromagnetic solver. Measurements were conducted on a live cow to validate the simulation results. Excellent agreement between measurements and simulations was achieved and the obtained PL values as a function of the transmitter-receiver separation were well fitted by a lognormal PL model with a PL exponent of 3.1 and a PL at reference distance (10 cm) of 44 dB. As an application, the packet error rate (PER) and the energy efficiency of different WBAN topologies for dairy cows (i.e., single-hop, multihop, and cooperative networks) were investigated. The analysis results revealed that exploiting multihop and cooperative communication schemes decrease the PER and increase the optimal payload packet size. The analysis results revealed that exploiting multihop and cooperative communication schemes increase the optimal payload packet size and improve the energy efficiency by 30%.

Experimental characterisation of the off-body wireless channel at 2.4GHz for dairy cows in barns and pastures

Off-body path loss in indoor (barn) and outdoor (pasture) environments.Path loss was well fitted by a one-slope log-normal model.Cow body shadowing presented maximum value of 7dB.Temporal fading can be described by a Ricean distribution in the considered environments. Wireless Sensor Networks (WSNs) provide promising applications in healthcare monitoring of dairy cows. After sensors measure the data in or on the cows body (temperature, position, leg movement), this information needs to be transmitted to the farm manager, enabling the evaluation of the health state of the cow. In this work, the off-body wireless channel between a node placed on the cows body and an access point positioned in the surroundings of the cows is characterised at 2.4GHz. This characterisation is of critical importance in the design of reliable WSNs operating in the industrial, scientific and medical (ISM) band (e.g., Wi-Fi, ZigBee, and Bluetooth). Two propagation environments were investigated: indoor (inside three barns) and outdoor (pasture). Large-scale fading, cow body shadowing, and temporal fading measurements were determined using ZigBee motes and spectrum analysis measurement. The path loss was well fitted by a one-slope log-normal model, the cow body shadowing values increased when the height of the transmitter and/or the receiver decreased, with a maximum value of 7dB, and the temporal fading due to the cow movement was well described by a Rician distribution in the considered environments. As an application, a network planning tool was used to optimise the number of access points, their locations, and their power inside the investigated barns based on the obtained off-body wireless channel characteristics. Power consumption analysis of the on-cow node was performed to estimate its battery lifetime, which is a key factor for successful WSN deployment.