175 research outputs found
Impact of power control and lognormal shadowing on the mean transmit power of Bluetooth devices
This letter analyzes Bluetooth's power-control algorithm with a goal to study the mean transmit power required in the presence of lognormal shadowing. The following results are found. 1) A smaller power-control step size yields a lower mean transmit power. 2) When the standard deviations of lognormal shadowing are 3 and 6 dB, respectively, a Bluetooth device needs to consume 11.1 dB and 15.0 dB more in the transmit energy than the minimum one required in the absence of shadowing. 3) The transmit energy consumption varies by around 6 dB among Bluetooth devices as a result of the ±6 dB tolerance in the Golden Receive Power Range, which has a nominal size of 20 dB.published_or_final_versio
Modelling and characterisation of antennas and propagation for body-centric wireless communication
PhDBody-Centric Wireless Communication (BCWC) is a central point in the development
of fourth generation mobile communications. The continuous miniaturisation of sensors,
in addition to the advancement in wearable electronics, embedded software, digital
signal processing and biomedical technologies, have led to a new concept of usercentric
networks, where devices can be carried in the userâs pockets, attached to the
userâs body or even implanted.
Body-centric wireless networks take their place within the personal area networks,
body area networks and body sensor networks which are all emerging technologies
that have a broad range of applications such as healthcare and personal entertainment.
The major difference between BCWC and conventional wireless systems is the
radio channel over which the communication takes place. The human body is a hostile
environment from radio propagation perspective and it is therefore important to understand
and characterise the effect of the human body on the antenna elements, the
radio channel parameters and hence the system performance. This is presented and
highlighted in the thesis through a combination of experimental and electromagnetic
numerical investigations, with a particular emphasis to the numerical analysis based
on the finite-difference time-domain technique.
The presented research work encapsulates the characteristics of the narrowband
(2.4 GHz) and ultra wide-band (3-10 GHz) on-body radio channels with respect to
different digital phantoms, body postures, and antenna types hence highlighting the
effect of subject-specific modelling, static and dynamic environments and antenna performance
on the overall body-centric network. The investigations covered extend further
to include in-body communications where the radio channel for telemetry with
medical implants is also analysed by considering the effect of different digital phantoms
on the radio channel characteristics. The study supports the significance of developing
powerful and reliable numerical modelling to be used in conjunction with measurement campaigns for a comprehensive understanding of the radio channel in
body-centric wireless communication. It also emphasises the importance of considering
subject-specific electromagnetic modelling to provide a reliable prediction of the
network performance
ENABLING SMART CITY SERVICES FOR HETEROGENEOUS WIRELESS NETWORKS
A city can be transformed into a smart city if there is a resource-rich and reliable communication infrastructure available. A smart city in effect improves the quality of life of citizens by providing the means to convert the existing solutions to smart ones. Thus, there is a need for finding a suitable network structure that is capable of providing sufficient capacity and satisfactory quality-of-service in terms of latency and reliability. In this thesis, we propose a wireless network structure for smart cities. Our proposed network provides two wireless interfaces for each smart city node. One is supposed to connect to a public WiFi network, while the other is connected to a cellular network (such as LTE). Indeed, Multi-homing helps different applications to use the two interfaces simultaneously as well as providing the necessary redundancy in case the connection of one interface is lost. The performance of our proposed network structure is investigated using comprehensive ns-2 computer simulations. In this study, high data rate real-time and low data rate non-real-time applications are considered. The effect of a wide range of network parameters is tested such as the WiFi transmission rate, LTE transmission rate, the number of real-time and non-real-time nodes, application traffic rate, and different wireless propagation models. We focus on critical quality-of-service (QoS) parameters such as packet delivery delay and packet loss. We also measured the energy consumed in packet transmission. Compared with a single-interface WiFi-based or an LTE-based network, our simulation results show the superiority of the proposed network structure in satisfying QoS with lower latency and lower packet loss. We found also that the proposed multihoming structure enables the smart city sensors and other applications to realize a greener communication by consuming a lesser amount of transmission power rather than single interface-based networks
Experimental Characterisation of Body-Centric Radio Channels Using Wireless Sensors
PhDWireless sensors and their applications have become increasingly attractive for industry, building automation and energy control, paving the way for new applications of sensor networks which go well beyond traditional sensor applications. In recent years, there has been a rapid growth in the number of wireless devices operating in close proximity to the human body. Wearable sensor nodes are growing popular not only in our normal living lifestyle, but also within healthcare and military applications, where different radio units operating in/on/off body communicate pervasively. Expectations go beyond the research visions, towards deployment in real-world applications that would empower business processes and future business cases.
Although theoretical and simulation models give initial results of the antenna behaviour and the radio channel performance of wireless body area network (WBAN) devices, empirical data from different set of measurements still form an essential part of the radio propagation models. Usually, measurements are performed in laboratory facilities which are equipped with bulky and expensive RF instrumentation within calibrated and controllable environments; thus, the acquired data has the highest possible reliability. However, there are still measurement uncertainties due to cables and connections and significant variations when designs are deployed and measured in real scenarios, such as hospitals wards, commercial buildings or even the battle field.
Consequently, more flexible and less expensive measurement tools are required. In this sense, wireless sensor nodes offer not only easiness to deploy or flexibility, but also adaptability to different environments. In this thesis, custom-built wireless sensor nodes are used to characterise different on-body radio channels operating in the IEEE 802.15.4 communication standard at the 2.45 GHz ISM band. Measurement results are also compared with those from the conventional technique using a Vector Network Analyser. The wireless sensor nodes not only diminished the effect of semi-rigid or flexible coaxial cables (scattering or radiation) used with the Vector Network Analyser (VNA), but also provided a more realistic response of the radio link channel. The performance of the wireless sensors is presented over each of the 16 different channels present at the 2.45 GHz band.
Additionally, custom-built wireless sensors are used to characterise and model the performance of different on-body radio links in dynamic environments, such as jogging, rowing, and cycling. The use of wireless sensors proves to be less obstructive and more flexible than traditional measurements using coaxial cables, VNA or signal generators. The statistical analysis of different WBAN channels highlighted important radio propagation features which can be used as sport classifiers models and motion detection.
Moreover, specific on-body radio propagation channels are further explored, with the aim to recognize physiological features such as motion pattern, breathing activity and heartbeat. The time domain sample data is transformed to the frequency domain using a non-parametric FFT defined by the Welchâs periodogram. The Appendix-Section D explores other digital signal processing techniques which include spectrograms (STFT) and wavelet transforms (WT). Although a simple analysis is presented, strong DSP techniques proved to be good for signal de-noising and multi-resolution analysis.
Finally, preliminary results are presented for indoor tracking using the RSS recorded by multiple wireless sensor nodes deployed in an indoor scenario. In contrast to outdoor environments, indoor scenarios are subject to a high level of multipath signals which are dependent on the indoor clutter. The presented algorithm is based on path loss analysis combined with spatial knowledge of each wireless sensor
Performance Evaluation of Class A LoRa Communications
Recently, Low Power Wide Area Networks (LPWANs) have attracted a great interest
due to the need of connecting more and more devices to the so-called Internet of Things
(IoT). This thesis explores LoRaâs suitability and performance within this paradigm,
through a theoretical approach as well as through practical data acquired in multiple field
campaigns. First, a performance evaluation model of LoRa class A devices is proposed. The
model is meant to characterize the performance of LoRaâs Uplink communications where
both physical layer (PHY) and medium access control (MAC) are taken into account. By
admitting a uniform spatial distribution of the devices, the performance characterization of
the PHY-layer is studied through the derivation of the probability of successfully decoding
multiple frames that were transmitted with the same spreading factor and at the same time.
The MAC performance is evaluated by admitting that the inter-arrival time of the frames
generated by each LoRa device is exponentially distributed. A typical LoRaWAN operating
scenario is considered, where the transmissions of LoRa Class A devices suffer path-loss,
shadowing and Rayleigh fading. Numerical results obtained with the modeling methodology
are compared with simulation results, and the validation of the proposed model is discussed
for different levels of traffic load and PHY-layer conditions. Due to the possibility of
capturing multiple frames simultaneously, the maximum achievable performance of the
PHY/MAC LoRa scheme according to the signal-to-interference-plus-noise ratio (SINR)
is considered. The contribution of this model is primarily focused on studying the average
number of successfully received LoRa frames, which establishes a performance upper bound
due to the optimal capture condition considered in the PHY-layer. In the second stage
of this work a practical LoRa point-to-point network was deployed to characterize LoRaâs
performance in a practical way. Performance was assessed through data collected in
the course of several experiments, positioning the transmitter in diverse locations and
environments. This work reports statistics of the received packets and different metrics
gathered from the physical-layer
SNR-based evaluation of coexistence in wireless system of hospital
Abstract. The wireless system (IEEE Std. 802.11) of North Karelian Central Hospital (NKCH) has been studied in the newly opened J2 building of the hospital. The measurements have been carried out using Ekahau Sidekick spectrum analyser and Ekahau Pro software. Signal propagation has been modelled in the control ward of the Emergency department because many coexisting systems are used with critical requirements of data communication over there. The analytical models have been developed to understand the radio-frequency (RF) signal propagation in the entire building. Measurements have also been carried out on the entire first floor, in the Department of the Abdominal Diseases on the ground floor and in the Childrenâs wards on the third floor.
The multi-slope path-loss propagation models with shadowing have been generated based on the Received Signal Strength Indicator (RSSI) measurements for typical hospital environment at the 2.4 GHz and 5 GHz Industrial, Scientific, and Medical (ISM) band. The measurements have been carried out within the two predefined routes. The models have also been compared to the empirically derived path-loss models. The probability of signal outage has been calculated for both measured routes.
The aggregate interference has been measured within the routes that cover the area where remarkable signal variations and the high level of interference has been indicated based on the heatmaps of Ekahau. The use of Ekahau Sidekick and Ekahau Pro software in the coexistence study has been described. The noise floor has been determined based on the averaged values of the six measurement campaigns. The local changes in signal strength of the desired signal and aggregated power of interference have been studied. The Signal-to-Interference Ratio (SIR) models have been generated within the measured routes.
The rapid decreases of Signal-to-Noise Ratio (SNR) have been indicated on all measured floors of building J2. They have been studied and their effect on the network performance has been evaluated. The evaluation has been done by comparing the measured values of RSSI, SNR and SIR to the requirements of the respective Modulation and Coding Scheme (MCS). The link margins have been calculated based on the chosen bit error probability and the given SNR requirement of the respective MCS. The comparison between the measured RSSI readings and the required threshold of the respective MCS has been done using the defined shadowing as a link margin.
It has been shown that the measured difference between the signal strength of the 2.4 GHz and 5 GHz bands has been caused by the reduced transmit power at the 2.4 GHz band. Based on the SIR measurements, it has been shown that the access points of the neighbouring building have contributed locally to the measured aggregate interference in the Control ward. However, the primary reason for the decrease of SIR at the 2.4 GHz band has been the decrease of desired signal power that has been contributed by the above mentioned reduced transmit power. The strong SNR drops have been indicated on every measured floor before the roaming has occurred.Sairaalan langattoman jÀrjestelmÀn arviointi signaali-kohina-suhteen avulla. TiivistelmÀ. TÀssÀ diplomityössÀ on tutkittu Pohjois-Karjalan keskussairaalan (PKKS) langatonta verkkoa (IEEE Std. 802.11) ÀskettÀin avatussa sairaalan laajennusosassa (J2-rakennus). Mittaukset on toteutettu kÀyttÀen Ekahau Sidekick spektrianalysaattoria ja Ekahau Pro -ohjelmaa. PÀivystyksen valvontaosasto on valittu tutkimuskohteeksi, koska siellÀ kÀytetÀÀn paljon eri teknologioihin perustuvia jÀrjestelmiÀ, joiden vÀlinen tiedonsiirto on luonteeltaan kriittistÀ. Luotujen mallien avulla rakennuksen langatonta toimintaympÀristöÀ tutkitaan RF-jÀrjestelmÀn (Radio-Frequency) nÀkökulmasta myös muissa mittausten kohteina olleissa tiloissa. Mittauksia on tehty myös valvontaosaston ulkopuolella 1. kerroksessa sekÀ 3. kerroksen lastenosastoilla ja Vatsakeskuksen tiloissa pohjakerroksessa.
RSSI-mittausten perusteella on luotu radiotiehÀviöihin perustuvat etenemismallit molemmilla kÀytössÀ olevilla ISM-taajuuskaistoilla (Industrial, Scientific and Medical bands). Varjostuminen ja etenemishÀviökertoimen muutokset on otettu huomioon etenemismalleissa. Mittaukset on suoritettu ennalta mÀÀritellyillÀ reiteillÀ. Luotuja malleja on verrattu myös tutkimuskirjallisuudessa esitettyihin, empiirisesti johdettuihin etenemishÀviömalleihin. Signaalikatkoksen todennÀköisyys on laskettu molemmille reiteille 2.4 GHz:n taajuuskaistalla.
Vastaanotetun hÀiriötehon summa on mitattu koko mallinnettavan tilan alueelle ulottuvien mittausreittien pohjalta. Mittausreitit on mÀÀritelty Ekahau Pron tuottamien kuuluvuus- ja hÀiriökarttojen avulla ottaen huomioon havaitut signaalitason vaihtelut. Ekahau Sidekick -spektrianalysaattorin ja Ekahau Pro -ohjelman kÀyttöÀ on kuvattu tÀmÀn tutkimuksen kontekstissa. Kohinataso on mÀÀritelty kaikissa kuudessa mittauskampanjassa mitattujen kohina-tehoarvojen keskiarvona. Paikallisten hyötysignaalinvoimakkuus- ja hÀiriötehovaihteluiden vaikutusta verkon suorituskykyyn on tutkittu ja molemmat mittausreitit kattavat SIR-mallit (Signal-to-Interference Ratio) on luotu.
Kaikissa tutkituissa kerroksissa havaittuja ÀkillisiÀ signaali-kohinasuhteen vaihteluita on tutkittu ja niiden vaikutusta jÀrjestelmÀn suorituskykyyn on arvioitu. Mitattujen hyöty- ja hÀiriösignaalivaihteluiden arviointi on toteutettu vertaamalla mittaamalla saatuja SNR- (Signal-to-Noise ratio), SIR- ja RSSI-arvoja (Received Signal Strength Indicator) eri tiedonsiirtonopeuksia kÀyttÀvien MCS-indeksien vaatimiin signaalinvoimakkuus- ja signaali-kohina-suhteen arvoihin. Kynnysarvoille on laskettu linkkimarginaalit kÀyttÀen mitoitusvaatimuksena valittua bittivirhetodennÀköisyyden arvoa. Mitattuja RSSI-arvoja on verrattu kÀyttÀen linkkimarginaalina etenemismallinnuksessa mÀÀritettyjÀ varjostumisvaikutuksen arvoja.
2.4 ja 5 GHz:n taajuusalueiden vÀlillÀ mitatun signaalinvoimakkuuseron on tutkimuksessa saatujen tulosten perusteella osoitettu olevan seurausta alennetusta lÀhetystehosta 2.4 GHz:n kaistalla. SIR-mittausten perusteella on todettu viereisen rakennuksen tukiasemien kasvattaneen vastaanotettua hÀiriötehosummaa valvontaosastolla paikallisesti. Ensisijainen syy mitattuihin SIR-arvojen vaihteluihin ovat kuitenkin alhainen signaalinvoimakkuus 2.4 GHz:n kaistalla, mikÀ osittain johtuu edellÀ kuvatusta alennetusta lÀhetystehosta. Voimakkaita SNR-vaihteluita on mitattu kaikissa kerroksissa ennen kuin pÀÀtelaite kytkeytyy uuteen tukiasemaan
Experimental optimization of exposure index and quality of service in WLAN networks
This paper presents the first real-life optimization of the Exposure Index (EI). A genetic optimization algorithm is developed and applied to three real-life Wireless Local Area Network scenarios in an experimental testbed. The optimization accounts for downlink, uplink and uplink of other users, for realistic duty cycles, and ensures a sufficient Quality of Service to all users. EI reductions up to 97.5% compared to a reference configuration can be achieved in a downlink-only scenario, in combination with an improved Quality of Service. Due to the dominance of uplink exposure and the lack of WiFi power control, no optimizations are possible in scenarios that also consider uplink traffic. However, future deployments that do implement WiFi power control can be successfully optimized, with EI reductions up to 86% compared to a reference configuration and an EI that is 278 times lower than optimized configurations under the absence of power control
From Radio Channel Modeling to a System Level Perspective in Body-Centric Communications
Body-centric communications are emerging as a new paradigm in the panorama of personal communications. Being concerned with human behaviour, they are suitable for a wide variety of applications. The advances in the miniaturization of portable devices to be placed on or around the body, foster the diffusion of these systems, where the human body is the key element defining communication characteristics.
This thesis investigates the human impact on body-centric communications under its distinctive aspects. First of all, the unique propagation environment defined by the body is described through a scenario-based channel modeling approach, according to the communication scenario considered, i.e., on- or on- to off-body. The novelty introduced pertains to the description of radio channel features accounting for multiple sources of variability at the same time. Secondly, the importance of a proper channel characterisation is shown integrating the on-body channel model in a system level simulator, allowing a more realistic comparison of different Physical and Medium Access Control layer solutions. Finally, the structure of a comprehensive simulation framework for system performance evaluation is proposed. It aims at merging in one tool, mobility and social features typical of the human being, together with the propagation aspects, in a scenario where multiple users interact sharing space and resources
Perfomance Comparison of Genetic and Greedy Algorithms in Underlay Device-to-Device Communication
The number of cellular users (CU) continues to increase in Indonesia. This impacts a large network load for the number of devices connected to the main network so it will have an impact on the quality of service. Device-to-Device (D2D) communication as components for LTE-A technology enabling a direct wireless link between the CUs without routing the data via the evolved Node B (eNB) signal or the core network. The need for algorithm and power control used to allocate radio resources so it can get a good quality of service because of communications technology D2D. In this study, we analyze and compare the performance parameters of D2D communication systems, including system interference, system sum-rate, system spectral efficiency, total energy system, and system energy efficiency based on Genetic and Greedy Algorithms in allocating radio resources and controlling the power of users. The genetic algorithm works with three operators in allocating resource block (RB), including proportional selection, crossover, and mutation. This process is repeated many times to produce several generations so that the best allocation can be got. The genetic algorithm has a flexible number of D2D and cellular communications in several RBs, minimum signal to interference plus noise ratio (SINR) also considered for mobile communication in ensuring the quality of its services. Numerical evaluations demonstrate the superior performance of the Genetic Algorithm in terms of system power, energy efïŹciency, and interference mitigation. As repetition gets larger, the Genetic algorithm results in better spectral efficiency
Contribution to the Rapid Acquisition of Signals for UWB Communication Systems
Ultra Wide-band is a promising technology for future short-range wireless communications with high data rate. In generally, one of the biggest difficult tasks for researchers today is the acquisition task of signals, where they are looking through different tools for getting a good quality of transmission; the phenomenon of multipath always stands up in the front as the first problem to be faced. When we talk about the Ultra Wide Band (UWB) signals, the problem becomes more complicated due to ultrashort impulses duration used by this kind of signals that causes the generation of paths by huge numbers.
In this thesis, to address the task mentioned above, the study is subdivided into two aspects. The first one is the UWB channel estimation that we have done to have information about the amplitudes and the delays of the paths. For this purpose, a maximum likelihood method is used to find the amplitudes and the delays estimate using two estimation contexts: Data Aided (DA) and Non-Data-Aided (NDA). In the second aspect, various parameters affecting the acquisition of signals are evaluated. Furthermore, several contributions in the framework of a new strategy based on an Intelligent Controlling System (ICS) are done and detailed in this thesis for the first once.
This system is characterised by its flexibility through two techniques, one that allows to users to communicate even with different M-ary PPM levels at the same time. Another technique that gives the flexibility for dealing with the phenomenon of multipath, where this latter is combated through manipulating the modulationâs levels via the ICS to achieve a rapid acquisition of UWB signals
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