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• 351.
Effect of Oscillator Phase Noise on Uplink Performance of Large MU-MIMO Systems2012Ingår i: Proceedings of the 50th Annual Allerton Conference on Communication, Control, and Computing,, IEEE , 2012, s. 1190-1197Konferensbidrag (Refereegranskat)

The effect of oscillator phase noise on the sumrate performance of a frequency selective multi-user multipleinputmultiple-output (MU-MIMO) uplink channel is studiedunder imperfect channel state information. A maximum ratiocombining detection strategy is employed by the base station(BS) (having a large antenna array of M elements), and ananalytical expression of a lower bound on the sum capacity ofthe system is derived. It is shown that an array power gainof O(pM) is achievable. It is also observed that phase noiseeffectively limits the fraction of the time used for informationtransmission and the number of users in the system. Finally itis concluded that, phase noise degrades the performance butdoes not eliminate the fundamental gains of a Large ScaleAntenna System (LSAS), i.e., power efficiency and high sumrate performance with low complexity receiver processing.

• 352.
On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems2012Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 1, nr 4, s. 276-279Artikel i tidskrift (Övrigt vetenskapligt)

A single carrier transmission scheme is presentedfor the frequency selective multi-user (MU) multiple-input singleoutput(MISO) Gaussian Broadcast Channel (GBC) with a basestation (BS) having M antennas and K single antenna users.The proposed transmission scheme has low complexity andfor M ≫ K it is shown to achieve near optimal sum-rateperformance at low transmit power to receiver noise power ratio.Additionally, the proposed transmission scheme results in anequalization-free receiver and does not require any MU resourceallocation and associated control signaling overhead. Also, thesum-rate achieved by the proposed transmission scheme is shownto be independent of the channel power delay profile (PDP). Interms of power efficiency, the proposed transmission scheme alsoexhibits an O(M) array power gain. Simulations are used toconfirm analytical observations.

• 353.
Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise2015Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, s. 711-723Artikel i tidskrift (Refereegranskat)

Multi-user multiple-input multiple-output (MU-MIMO) cellular systems with an excess of base station (BS) antennas (Massive MIMO) offer unprecedented multiplexing gains and radiated energy efficiency. Oscillator phase noise is introduced in the transmitter and receiver radio frequency chains and severely degrades the performance of communication systems. We study the effect of oscillator phase noise in frequency-selective Massive MIMO systems with imperfect channel state information (CSI) and M BS antennas. In particular, we consider two distinct operation modes, namely when the phase noise processes at the BS antennas are identical (synchronous operation) and when they are independent (non-synchronous operation). We analyze a linear and low-complexity time-reversal maximum-ratio combining (TR-MRC) reception strategy. For both operation modes we derive a lower bound on the sum-capacity and we compare the performance of the two modes. Based on the derived achievable sum-rate, we show that with the proposed receive processing an O($\sqrt{M}$) array gain is achievable. Due to the phase noise drift the estimated effective channel becomes progressively outdated. Therefore, phase noise effectively limits the length of the interval used for data transmission and the number of scheduled users. The derived achievable rates provide insights into the optimum choice of the data interval length and the number of scheduled users.

• 354.
University of Pisa, Italy.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten. University of Pisa, Italy. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
Network Deployment for Maximal Energy Efficiency in Uplink with Multislope Path Loss2018Ingår i: IEEE Transactions on Green Communications and Networking, E-ISSN 2473-2400, Vol. 2, nr 3, s. 735-750Artikel i tidskrift (Refereegranskat)

This work aims to design the uplink (UL) of a cellular network for maximal energy efficiency (EE). Each base station (BS) is randomly deployed within a given area and is equipped with M antennas to serve K user equipments (UEs). A multislope (distance-dependent) path loss model is considered and linear processing is used, under the assumption that channel state information is acquired by using pilot sequences (reused across the network). Within this setting, a lower bound on the UL spectral efficiency and a realistic circuit power consumption model are used to evaluate the network EE. Numerical results are first used to compute the optimal BS density and pilot reuse factor for a Massive MIMO network with three different detection schemes, namely, maximum ratio combining, zero-forcing (ZF) and multicell minimum mean-squared error. The numerical analysis shows that the EE is a unimodal function of BS density and achieves its maximum for a relatively small density of BS, irrespective of the employed detection scheme. This is in contrast to the single-slope (distance-independent) path loss model, for which the EE is a monotonic non-decreasing function of BS density. Then, we concentrate on ZF and use stochastic geometry to compute a new lower bound on the spectral efficiency, which is then used to optimize, for a given BS density, the pilot reuse factor, number of BS antennas and UEs. Closed-form expressions are computed from which valuable insights into the interplay between optimization variables, hardware characteristics, and propagation environment are obtained.

• 355.
Fdn Research and Technology Hellas FORTH, Greece.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten. University of Crete, Greece; Fdn Research and Technology Hellas FORTH, Greece.
Flow Allocation for Maximum Throughput and Bounded Delay on Multiple Disjoint Paths for Random Access Wireless Multihop Networks2017Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 66, nr 1, s. 720-733Artikel i tidskrift (Refereegranskat)

In this paper, we consider random-access wireless networks, withmultipacket reception capabilities, where multiple flows are forwarded to the gateways through node disjoint paths. We explore the issue of allocating flow on multiple paths, exhibiting both intra-and interpath interference, in order to maximize average aggregate flow throughput (AAT) and provide bounded packet delay. A distributed flow allocation scheme is proposed where allocation of flow on paths is formulated as an optimization problem. Through an illustrative topology, it is shown that the corresponding problem is nonconvex. Furthermore, a simple but accurate model is employed for the AAT achieved by all flows, which captures both intra-and interpath interference through the signal-to-interference-plus-noise ratio (SINR) model. The proposed scheme is evaluated through Ns2 simulations of several random wireless scenarios. Simulation results reveal that the model employed accurately captures the AAT observed in the simulated scenarios, even when the assumption of saturated queues is removed. Simulation results also show that the proposed scheme achieves significantly higher AAT for the vast majority of the wireless scenarios explored than for the following flow allocation schemes: one that assigns flows on paths on a round-robin fashion, one that optimally utilizes the best path (BP) only, and another one that assigns the maximum possible flow on each path. Finally, a variant of the proposed scheme is explored, where interference for each link is approximated by considering its dominant interfering nodes only.

• 356.
Institute of Computer Science, Foundation for Research and Technology - Hellas (FORTH), Greece.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Institute of Computer Science, Foundation for Research and Technology - Hellas (FORTH), Greece .
On the delay of a throughput optimal flow allocation scheme for random access WMNs2014Ingår i: 2014 IEEE 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), IEEE, 2014, s. 218-223Konferensbidrag (Refereegranskat)

In this paper we consider random access wireless mesh networks with multi-packet reception capabilities where multiple flows are forwarded to the gateways through node disjoint paths. We address the issue of aggregate throughput optimal flow rate allocation with bounded delay guarantees for flows exhibiting both intra- and inter-path interference. In our prior work we have suggested a distributed flow allocation scheme that maximizes the average aggregate throughput of all flows also providing bounded delay guarantees. In this work we evaluate this scheme in terms of delay and compare its performance with the following schemes: a scheme that utilizes paths on a round-robin fashion, one that optimally utilizes the best path only and another one that assigns the maximum possible flow on each path. For the evaluation process Ns2 simulations of several random wireless scenarios are employed.

• 357.
Institute of Computer Science Foundation for Research and Technology, Hellas (FORTH), Greece.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten. Institute of Computer Science Foundation for Research and Technology, Hellas (FORTH), Greece.
Performance of Flow Allocation with Successive Interference Cancelation for Random Access WMNs2015Ingår i: 2015 IEEE Globecom Workshops (GC Wkshps), Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 1-7Konferensbidrag (Refereegranskat)

In this study we explore the gain that can be achieved by jointly allocating flow on multiple paths and employing successive interference cancelation (SIC), for random access wireless mesh networks with multi-packet reception capabilities. More precisely, we explore a distributed flow allocation scheme aimed at maximizing average aggregate flow throughput, while also providing bounded delay, when SIC is employed. Simulation results derived from three illustrative topologies show that the gain over treating interference as noise (IAN) for this scheme can be up to 15.2%, for an SINR threshold value equal to 0.5. For SINR threshold values as high as 2.0 however, SIC does not always result in higher throughput. In some scenarios explored, the gain of SIC over IAN is insignificant, while in some others treating interference as noise proves better. The reason is that, although SIC improves the throughput on a specific link, it also increases the interference imposed on neighbouring receivers. We also show that, the gain of applying SIC is more profound in cases of a large degree of asymmetry among interfering links.

• 358.
University of Oulu, Finland.
Vrije University of Brussel, Belgium. University of Oxford, England. Linköpings universitet, Institutionen för datavetenskap, Databas och informationsteknik. Linköpings universitet, Tekniska fakulteten. University of Oulu, Finland.
CHIP: Collaborative Host Identity Protocol with Efficient Key Establishment for Constrained Devices in Internet of Things2017Ingår i: Wireless personal communications, ISSN 0929-6212, E-ISSN 1572-834X, Vol. 96, nr 1, s. 421-440Artikel i tidskrift (Refereegranskat)

The Internet of Things (IoT) is the next evolutionary paradigm of networking technologies that interconnects almost all the smart objects and intelligent sensors related to human activities, machineries, and environment. IoT technologies and Internet Protocol connectivity enable wide ranges of network devices to communicate irrespective of their resource capabilities and local networks. In order to provide seamless connectivity and interoperability, it is notable to maintain secure end-to-end (E2E) communication links in IoT. However, device constraints and the dynamic link creations make it challenging to use pre-shared keys for every secure E2E communication scenario in IoT. Variants of Host Identity Protocol (HIP) are adopted for constructing dynamic and secure E2E connections among the heterogeneous network devices with imbalanced resource profiles and less or no previous knowledge about each other. We propose a solution called collaborative HIP (CHIP) with an efficient key establishment component for the high resource-constrained devices in IoT. CHIP delegates the expensive cryptographic operations to the resource rich devices in the local networks. Finally, by providing quantitative performance evaluation and descriptive security analysis, we demonstrate the applicability of the key establishment in CHIP for the constrained IoT devices rather than the existing HIP variants.

• 359.
Univ Oulu, Finland.
Univ Oulu, Finland. Univ Oulu, Finland. Linköpings universitet, Institutionen för datavetenskap, Databas och informationsteknik. Linköpings universitet, Tekniska fakulteten. Univ Oulu, Finland.
Managing Mobile Relays for Secure E2E Connectivity of Low-Power IoT Devices2019Ingår i: 2019 16TH IEEE ANNUAL CONSUMER COMMUNICATIONS and NETWORKING CONFERENCE (CCNC), IEEE , 2019Konferensbidrag (Refereegranskat)

The widespread Internet of Things (IoT) ecosystems empower the deployment of various Bluetooth Low Energy (BLE) sensor nodes in many ambient assisted living (AAL) type applications. Regardless of their limitations, these low-power IoT sensor nodes need pervasive and secure connections to transfer the aggregated data to the central servers located in remote clouds which will perform further processing and storing functions. The common practice is to use one or multiple dedicated gateways to assist the communication between the sensor and the cloud. This paper presents a mobile-based relay assistance solution for establishing secure end-to-end (E2E) connectivity between low power IoT sensors and cloud servers without using a dedicated gateway. za The prototype implementation and the described security features verify the technical readiness of the proposed solution.

• 360.
Department of Electronics and Communication Engineering, National Institute of Technology, Silchar, India.
Department of Electrical Engineering, Indian Institute of Technology Delhi, New Delhi, India. Department of Electronics and Communication Engineering, National Institute of Technology, Silchar, India.
Coverage-constrained base station deployment and power allocation for operational cost minimization2018Ingår i: 2017 IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 1-5Konferensbidrag (Refereegranskat)

To address the ever-increasing data traffic demand, there is a need for novel cost-efficient network deployment schemes. In this work, we investigate the joint optimization of base station (BS) location, its density, and transmit power allocation to minimize the overall network operational cost required to meet an underlying coverage constraint at each user equipment (UE), which is randomly deployed following the binomial point process. As the joint optimization problem is nonconvex and combinatorial in nature, we propose a non-trivial solution methodology that effectively decouples it into three individual optimization problems. Firstly, by using the distance distribution of the farthest UE from the BS, we present novel insights on optimal BS location for a given number of BSs and sectoring type. After that we provide a tight approximation for the optimal transmit power allocation to each BS. Lastly, using the latter two results, the optimal number of BSs that minimize the operational cost is obtained. Numerical results validate the analysis and provide practical insights on optimal BS deployment. We observe that the proposed joint optimization framework, that solves the coverage probability versus operational cost tradeoff, can yield a significant reduction of about 65% in the operational cost as compared to the benchmark fixed allocation scheme.

• 361.
Department of Electronics and Communication Engineering, National Institute of Technology, Silchar, India.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten. Department of Electronics and Communication Engineering, National Institute of Technology, Silchar, India.
Joint Optimization Framework for Operational Cost Minimization in Green Coverage-Constrained Wireless Networks2018Ingår i: IEEE Transactions on Green Communications and Networking, E-ISSN 2473-2400, Vol. 2, nr 3, s. 693-706Artikel i tidskrift (Refereegranskat)

In this paper, we investigate the joint optimization of base station (BS) location, its density, and transmit power allocation to minimize the overall network operational cost required to meet an underlying coverage constraint at each user equipment (UE), which is randomly deployed following the binomial point process (BPP). As this joint optimization problem is nonconvex and combinatorial in nature, we propose a non-trivial solution methodology that effectively decouples it into three individual optimization problems. Firstly, by using the distance distribution of the farthest UE from the BS, we present novel insights on optimal BS location in an optimal sectoring type for a given number of BSs. After that we provide a tight approximation for the optimal transmit power allocation to each BS. Lastly, using the latter two results, the optimal number of BSs that minimize the operational cost is obtained. Also, we have investigated both circular and square field deployments. Numerical results validate the analysis and provide practical insights on optimal BS deployment. We observe that the proposed joint optimization framework, that solves the coverage probability versus operational cost tradeoff, can yield a significant reduction of about 65% in the operational cost as compared to the benchmark fixed allocation scheme.

• 362.
Linköpings universitet, Institutionen för systemteknik, Reglerteknik.
Radio Localization with GSM2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

Detta examensarbete undersöker möjligheten att lokalisera mobiltelefoner med GSM teknologi genom att använda en Falsk Basstation (FBS). En FBS är en radio transceiver som emulerar beteendet hos en legitim GSM basstation för att lura omodifierade mobiltelefoner att ansluta till den. Undersökningen tar reda på hur en FBS kan användas för att estimera positionerna av anslutna mobiltelefoner inom ett målområde. För att undersöka detta har ett Proof-Of-Concept-system ta- gits fram. Systemet består av en mobil FBS som som mäter propageringstid (TOA) och mottagen signalstyrka (RSS). FBS:ens positioner bestäms med GPS. Systemet använder kalibreringsfria algoritmer för lokalisering, då vi antar att miljön och mobiltelefonernas hårdvara är okänd. Tester av systemet har utförts utomhus i ett 180x100 m2 Line-Of-Sight-område. Dessa tester visar att lokaliseringsalgorit- merna ger ett genomsnittligt fel på mindre än 10 meter. Detta anses vara till- räckligt för de flesta tillämpningar av intresse. Utöver detta visar även testerna att RSS-baserad lokalisering ger bättre resultat än TOA-baserad lokalisering när medelavståndet mellan FBS och mobiltelefon är omkring 50 meter. TOA-baserad lokalisering ger däremot ett bättre resultat än RSS-baserad lokalisering när me- delavståndet ökar till omkring 75 meter.

Denna undersökning är en del av Smart Savannah projektet som innefattar flera olika övervakningssystem, utvecklade för att skydda noshörningar från tjuv- skyttar. Målet med vårt lokaliseringssystem är att det ska kunna användas för att upptäcka och lokalisera tjuvskyttar utan deras vetskap. Vi tror även att lokalise- ringssystemet kan användas vid eftersökning- och räddnings-operationer för att lokalisera försvunna personers mobiltelefoner.

• 363.
Performance of OTDOA Positioning in Narrowband IoT Systems2017Ingår i: 28th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC): Proceedings, IEEE, 2017Konferensbidrag (Refereegranskat)

Narrowband Internet of Things (NB-IoT) is an emerging cellular technology designed to target low-cost devices, high coverage, long device battery life (more than ten years), and massive capacity. We investigate opportunities for device tracking in NB-IoT systems using Observed Time Difference of Arrival (OTDOA) measurements. Reference Signal Time Difference (RSTD) reports are simulated to be sent to the mobile location center periodically or on an ondemand basis. We investigate the possibility of optimizing the number of reports per minute budget on horizontal positioning accuracy using an on-demand reporting method based on the Signal to Noise Ratio (SNR) of the measured cells received by the User Equipment (UE). Wireless channels are modeled considering multipath fading propagation conditions. Extended Pedestrian A (EPA) and Extended Typical Urban (ETU) delay profiles corresponding to low and high delay spread environments, respectively, are simulated for this purpose. To increase the robustness of the filtering method, measurement noise outliers are detected using confidence bounds estimated from filter innovations.

• 364.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
Routing on Resource Allocation in Free Space Optical Network.2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

Free space optical Networks (FSO) provide benefits such as high speed, cost efficiency and licence-free high bandwidth. However, these networks are susceptible to different atmospheric conditions.

The purpose of this thesis is to study the effects of weather on the performance of resource allocations and routing algorithms on the FSO network in order to investigate how to achieve an efficient data flow within the FSO systems.

In FSO networks, resource allocation involves allocating communication resources to the links of the network. The optimal routing of the data depends on the link capacities which are a function of the communications resources allocated to the links.

In this thesis, the resource allocation and routing problems are a multi-commodity network flow problem. In order to solve the resource allocation and routing problems in Free Space Optical network systems, what is proposed is a Lagrangian relaxation-based solution that uses both a dual decomposition method and Dijkstra's algorithm.

The algorithm performs under three weather conditions: without atmospheric turbulence; under normal weather conditions and under severe weather conditions. The results of these methods and the proposed solutions will be described.

• 365.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
Mobility analysis with mobile phone data2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

The thesis evaluates mobility based on mobile phone positions. The aim is to develop and assess different methods for travel demand estimation based on CDR data. Besides this estimation location data in cellular data is explained in more detail and a previous work based on mobile phone data and travel demand estimation is reviewed. The different methods of travel time estimation include both static and dynamic estimation. The static travel demand estimation evaluates movements in the city based on predefined time periods, whereas the dynamic estimations are based on different definitions of a trip. A trip can be defined as movements between important places, or just simply count a trip between each position, or a filtering of active states to create more accurate origin-destination matrices. The second part of the thesis includes evaluation of travel time based on CDR data before the final conclusions are drawn. The main finding of the thesis is that it is possible to assess mobility in a city based on CDR data, even if there are no validation data available.

• 366.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem.
A Study on the Impact of Antenna Downtilt on theOutdoor Users in an Urban Environment2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

Inter-site interference distribution acts as a basic limitation on how much performance a network service provider can achieve in an urban network scenario. There are many different ways of controlling this interference levels. One such method is tuning the antenna downtilt depending on the network situation. Antenna downtilt can also be seen as a powerful tool for load balancing in the network.

This thesis work involves a study of the impact of the antenna downtilt in an urban environment, involving non-uniform user distribution. A realistic dual ray propagation model is used to model the path gain from the base station to a UE. Such a propagation model is used along with a directional antenna radiation pattern model to calculate the overall path gain from the base station to a UE. Under such modeling, the results of the simulations show that the antenna downtilt plays a crucial role in optimizing the network performance. The results show that the optimal antenna downtilt angle is not very sensitive to the location of the hotspot in the network. The results also show that the antenna downtilt sensitivity is very much dependent on the network scenario. The coupling between the antenna downtilt and the elevation half power beamwidth is also evaluated.

• 367.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem.
Detection and Classification of Interference in Mobile Communication Systems2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

The usage of wireless technology has in the past decade vastly increased and it continues to do so as well. Because of this, we become more and more reliant on this considerably fragile technology. Wireless technology, which uses radio waves to transmit data from one point to another can easily be interfered by radio jammers. This thesis work is about the detection and classification of the interference that is produced by jammers over the Global System for Mobile Communications (GSM) air interface. A typical GSM jammer that can be found on the Internet is analyzed but also more advanced GSM jammers are analyzed. The GSM standard is analyzed to find vulnerabilities that a jammer can take advantage of. The result is an interference detector that can be used to detect and classify interference over the GSM networks. The detector is constructed with an Universal Software Radio Peripheral (USRP) but is also portable to other software-defined radio (SDR) platforms.

• 368.
EIT, LU.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. EIT, LU. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. Bell Laboratories, Alcatel-Lucent, Murray Hill, USA. EIT, LU. EIT, LU.
Scaling up MIMO: Opportunities and Challenges with Very Large Arrays2013Ingår i: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 30, nr 1, s. 40-60Artikel i tidskrift (Refereegranskat)

Multiple-input multiple-output (MIMO) technology is maturing and is being incorporated into emerging wireless broadband standards like long-term evolution (LTE) [1]. For example, the LTE standard allows for up to eight antenna ports at the base station. Basically, the more antennas the transmitter/receiver is equipped with, and the more degrees of freedom that the propagation channel can provide, the better the performance in terms of data rate or link reliability. More precisely, on a quasi static channel where a code word spans across only one time and frequency coherence interval, the reliability of a point-to-point MIMO link scales according to Prob(link outage) ` SNR-ntnr where nt and nr are the numbers of transmit and receive antennas, respectively, and signal-to-noise ratio is denoted by SNR. On a channel that varies rapidly as a function of time and frequency, and where circumstances permit coding across many channel coherence intervals, the achievable rate scales as min(nt, nr) log(1 + SNR). The gains in multiuser systems are even more impressive, because such systems offer the possibility to transmit simultaneously to several users and the flexibility to select what users to schedule for reception at any given point in time [2].

• 369.
Massive MIMO in LTE with MRT Precoder: Channel Ageing and Throughput Analysis in a Single-Cell Deployment2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

Mobile data traffic is growing exponentially due to the popularization of smart phones, tablets and other data traffic appliances. One way of handling the increased data traffic is to deploy large antenna arrays at the base station, also known as Massive MIMO. In Massive MIMO, the base station having excessive number of transmit antennas, can achieve increased data rate by spatial-multiplexing terminals into the same time-frequency resource.

This thesis investigates Massive MIMO in LTE in a single-cell deployment with up to 100 base station antennas. The benefits of more antennas are investigated with single-antenna terminals in a typical urban environment. The terminal transmitted sounding reference signals (SRS) are used at the base station to calculate channel state information (CSI) in order to generate an MRT precoder. With perfect CSI, the results showed that the expected terminal SINR depends on the antenna-terminal ratio. It was also showed that with spatial-multiplexed terminals and 100 base station antennas, the maximum cell throughput increased 13 times compared with no spatial-multiplexed terminals.

Channel ageing causes inaccuracy in the CSI, the thesis showed that the variation in terminal SINR increased rapidly with less frequent SRS transmissions. When having moving terminals at 3 km/h, the difference between the 10th and 90th SINR percentile is 1 dB with an SRS transmission periodicity of 20 ms, and 17 dB with an SRS transmission periodicity of 80 ms. With 100 base station antennas and moving terminals at 3 km/h with an SRS periodicity of 20 ms, the maximum cell throughput decreased with 13% compared to when the base station has perfect CSI.

The result showed that the maximum cell throughput scaled linearly with the number of base station antennas. It also showed that having the number of spatial-multiplexed terminals equal to the number of antennas is a reasonable assumption when maximizing the cell throughput.

• 370.
Development of Simulation Tool and New Tracking Algorithms for Radio Occultation Receivers2011Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

När en radiovåg passerar genom atmosfären kommer den att fördröjas, inte bara avavståndet mellan sändare och mottagare utan också av atmosfären. Givet kunskapom karaktäristiken hos den sända signalen kan atmosfärens effekt erhållas från denmottagna signalen. Detta koncept kallas för radio-ockultation. Radio-ockultationkan med hög noggrannhet ge profiler för temperatur, tryck och vattenånga genomatmosfären.Denna rapport ämnar presentera det jobb och de resultat som uppnåtts genomett examensarbete genomfört på RUAG Space i Göteborg. Examensarbetets syftevar att implementera en simulator som med hög noggrannhet kan generera ensignal så som den hade sett ut då den propagerat genom atmosfären.Vi kommer att visa att den genererade signalen uppnår de krav som ställts.

• 371.
Adversarial Attacks on Deep-Learning Based Radio Signal Classification2019Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 8, nr 1, s. 213-216Artikel i tidskrift (Refereegranskat)

Deep learning (DL), despite its enormous success in many computer vision and language processing applications, is exceedingly vulnerable to adversarial attacks. We consider the use of DL for radio signal (modulation) classification tasks, and present practical methods for the crafting of white-box and universal black-box adversarial attacks in that application. We show that these attacks can considerably reduce the classification performance, with extremely small perturbations of the input. In particular, these attacks are significantly more powerful than classical jamming attacks, which raises significant security and robustness concerns in the use of DL-based algorithms for the wireless physical layer.

• 372.
Department of Electrical Engineering, Indian Institute of Technology, New Delhi, India. Department of Electrical Engineering, Indian Institute of Technology, New Delhi, India.
Novel subcarrier pairing strategy for DF relayed secure OFDMA with untrusted users2018Ingår i: 2017 IEEE Globecom Workshops (GC Wkshps), Institute of Electrical and Electronics Engineers (IEEE), 2018, Vol. 2018-January, s. 1-6Konferensbidrag (Refereegranskat)

This paper investigates joint resource allocation problem involving subcarrier allocation, subcarrier pairing (SCP), and power allocation for maximizing sum secure rate in a decode-and-forward (DF) relay assisted OFDMA system with untrusted users. Optimal SCP is highlighted as a novel notion of channel gain tailoring rather than conventional channel gain matching. It is proven that the optimal SCP intends to pair subcarriers such that the variance between the effective channel gains is minimized. It is also shown that depending on the individual power budget constraints at source and the relay, SCP can take either a subordinate role for improving the energy efficiency or the main role of improving the spectral efficiency of the system. SCP as a channel gain tailoring strategy and its role in improving the spectral as well as energy efficiency of cooperative secure communication are highlighted through the simulation results.

• 373.
Department of Electrical Engineering and Bharti School of Telecom, Indian Institute of Technology Delhi, New Delhi, India.
Department of Electrical Engineering and Bharti School of Telecom, Indian Institute of Technology Delhi, New Delhi, India. Department of Electrical Engineering and Bharti School of Telecom, Indian Institute of Technology Delhi, New Delhi, India.
OFDMA-Based DF Secure Cooperative Communication With Untrusted Users2016Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 20, nr 4, s. 716-719Artikel i tidskrift (Refereegranskat)

In this letter, we consider resource allocation for OFDMA-based secure cooperative communication by employing a trusted decode and forward (DF) relay among the untrusted users. We formulate two optimization problems, namely, 1) sum rate maximization subject to individual power constraints on source and relay, and 2) sum power minimization subject to a fairness constraint in terms of per-user minimum support secure rate requirement. The optimization problems are solved utilizing the optimality of KKT conditions for pseudolinear functions.

• 374.
Department of Electrical Engineering and Bharti School of Telecom, IIT Delhi, New Delhi, India. Department of Electrical Engineering and Bharti School of Telecom, IIT Delhi, New Delhi, India.
Utility Regions for DF Relay in OFDMA-Based Secure Communication with Untrusted Users2017Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 21, nr 11, s. 2512-2515Artikel i tidskrift (Refereegranskat)

This letter investigates the utility of a trusted decode-And-forward relay in OFDMA-based secure communication system with untrusted users. For deciding on the use of relay, we first present optimal subcarrier allocation policies for direct communication (DC) and relayed communication (RC). Next, we identify exclusive RC mode, exclusive DC mode, and mixed (RDC) mode subcarriers which can support both the modes. In RDC mode, we present optimal mode selection policy and a suboptimal strategy independent of power allocation which is asymptotically optimal at both low and high SNRs. Via numerical results we present insights on relay utility regions.

• 375.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
A distributed, load-aware, power and frequency bargaining protocol for LTE-based networks2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

In this thesis a distributed, dynamic, load aware, joint power and frequency allocation protocol for 4G networks along with system-level simulated results are presented. In all cellular networks, a key limiting factor for throughput is inter-cell interference, especially at the cell edges. Several methods have been proposed and adopted in each mobile network generation to cancel or suppress its effects, whereas each method has its drawbacks in terms of receiver complexity or additional control nodes. However, the proposed protocol presented here does not impose any architectural changes.  In 4G networks such as LTE, the choice of OFDMA for the air interface has paved the way for selective frequency and power allocation in the available spectrum. Taking advantage of this opportunity, fractional frequency reuse (FFR) has been proposed in OFDMA based mobile networks in order to reduce the throughput loss at the cell edges due to inter-cell interference. In FFR, center users lose part of available spectrum that is dedicated to the edge users.  Our protocol aims to minimize this loss of center users incurred by FFR, at the cost of minimal degradation at the edges.

An eNodeB, only when overloaded, requests its neighbours’ edge band to be used for its center users at a reduced power level. This is done via small message exchange between the eNodeBs. The neighbors of the overloaded eNodeBs solve a small local knapsack problem to decide whether band lending is feasible or not. A distinguishing feature of this protocol is the power level adjustment for the borrowed band, which is mutually decided by the borrower and lender. The band is released when it is not needed or it is causing unacceptable loss to the lender. The implementation is done in a Matlab based LTE system level simulator. For the implementation of our protocol in the simulator, starting point was implementation of FFR-3 functionality, a prerequisite and a baseline for comparison with our protocol.

Results are compared among three different setups of re-use1, FFR-3 and our protocol by varying number of overloaded eNodeBs for various numbers of scenarios and the comparison is made based on the center users’ throughput, edge users’ throughput. An estimation of time and protocol overhead is also presented. We have observed center users’ throughput gain up to 46%, at the cost of 9% edge users’ throughput loss, when compared to the classic FFR-3 scheme. The overall system throughput goes up to 26 % in heavily loaded scenario.

The utility of the protocol for an LTE system is evident from the results, which is supported by the dynamic and decentralized nature of the protocol. This ensures better utilization of spectrum, by temporarily allocating more bandwidth where it is needed more.

• 376.
University of Pisa, Italy; CentraleSupelec, France.
National and Capodistrian University of Athens, Greece. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. CentraleSupelec, France.
Large System Analysis of the Energy Consumption Distribution in Multi-User MIMO Systems With Mobility2015Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, nr 3, s. 1730-1745Artikel i tidskrift (Refereegranskat)

In this work, we consider the downlink of a single-cell multi-user MIMO system in which the base station (BS) makes use of N antennas to communicate with K single-antenna user equipments (UEs). The UEs move around in the cell according to a random walk mobility model. We aim at determining the energy consumption distribution when different linear precoding techniques are used at the BS to guarantee target rates within a finite time interval T. The analysis is conducted in the asymptotic regime where N and K grow large with fixed ratio under the assumption of perfect channel state information (CSI). Both recent and standard results from large system analysis are used to provide concise formulae for the asymptotic transmit powers and beamforming vectors for all considered schemes. These results are eventually used to provide a deterministic approximation of the energy consumption and to study its fluctuations around this value in the form of a central limit theorem. Closed-form expressions for the asymptotic means and variances are given. Numerical results are used to validate the accuracy of the theoretical analysis and to make comparisons. We show how the results can be used to approximate the probability that a battery-powered BS runs out of energy and also to design the cell radius for minimizing the energy consumption per unit area. The imperfect CSI case is also briefly considered.

• 377.
The University of Arizona, USA.
Ben Gurion University, Israel. The University of Arizona, USA. University of Helsinki, Helsinki, Finland. University of Helsinki, Helsinki, Finland. The University of Arizona, USA. Ben Gurion University, Israel.
Optimization schemes for protective jamming2014Ingår i: Mobile Networks and Applications, ISSN 1383-469X, Vol. 19, nr 1, s. 45-60Artikel i tidskrift (Refereegranskat)

In this paper, we study strategies for allocating and managing friendly jammers, so as to create virtual barriers that would prevent hostile eavesdroppers from tapping sensitive wireless communication. Our scheme precludes the use of any encryption technique. Applications include domains such as (i) protecting the privacy of storage locations where RFID tags are used for item identication, (ii) secure reading of RFID tags embedded in credit cards, (iii) protecting data transmitted through wireless networks, sensor networks, etc. By carefully managing jammers to produce noise, we show how to reduce the SINR of eavesdroppers to below a threshold for successful reception, without jeopardizing network performance. We present algorithms targeted towards optimizing power allocation and number of jammers needed in several settings. Experimental simulations back up our results.

• 378.
Nonparametric Message Passing Methods for Cooperative Localization and Tracking2012Doktorsavhandling, monografi (Övrigt vetenskapligt)

The objective of this thesis is the development of cooperative localization and tracking algorithms using nonparametric message passing techniques. In contrast to the most well-known techniques, the goal is to estimate the posterior probability density function (PDF) of the position of each sensor. This problem can be solved using Bayesian approach, but it is intractable in general case. Nevertheless, the particle-based approximation (via nonparametric representation), and an appropriate factorization of the joint PDFs (using message passing methods), make Bayesian approach acceptable for inference in sensor networks. The well-known method for this problem, nonparametric belief propagation (NBP), can lead to inaccurate beliefs and possible non-convergence in loopy networks. Therefore, we propose four novel algorithms which alleviate these problems: nonparametric generalized belief propagation (NGBP) based on junction tree (NGBP-JT), NGBP based on pseudo-junction tree (NGBP-PJT), NBP based on spanning trees (NBP-ST), and uniformly-reweighted NBP (URW-NBP). We also extend NBP for cooperative localization in mobile networks. In contrast to the previous methods, we use an optional smoothing, provide a novel communication protocol, and increase the efficiency of the sampling techniques. Moreover, we propose novel algorithms for distributed tracking, in which the goal is to track the passive object which cannot locate itself. In particular, we develop distributed particle filtering (DPF) based on three asynchronous belief consensus (BC) algorithms: standard belief consensus (SBC), broadcast gossip (BG), and belief propagation (BP). Finally, the last part of this thesis includes the experimental analysis of some of the proposed algorithms, in which we found that the results based on real measurements are very similar with the results based on theoretical models.

• 379.
University of Gävle, Sweden. University of Gävle, Sweden. University of Gävle, Sweden. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. Swedish Defense Research Agency (FOI), Linköping, Sweden. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Measurement Analysis and Channel Modeling for TOA-Based Ranging in Tunnels2015Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, nr 1, s. 456-467Artikel i tidskrift (Refereegranskat)

A robust and accurate positioning solution is required to increase the safety in GPS-denied environments. Although there is a lot of available research in this area, little has been done for confined environments such as tunnels. Therefore, we organized a measurement campaign in a basement tunnel of Linköping university, in which we obtained ultra-wideband (UWB) complex impulse responses for line-of-sight (LOS), and three non-LOS (NLOS) scenarios. This paper is focused on time-of-arrival (TOA) ranging since this technique can provide the most accurate range estimates, which are required for range-based positioning. We describe the measurement setup and procedure, select the threshold for TOA estimation, analyze the channel propagation parameters obtained from the power delay profile (PDP), and provide statistical model for ranging. According to our results, the rise-time should be used for NLOS identification, and the maximum excess delay should be used for NLOS error mitigation. However, the NLOS condition cannot be perfectly determined, so the distance likelihood has to be represented in a Gaussian mixture form. We also compared these results with measurements from a mine tunnel, and found a similar behavior.

• 380.
Experimental Study of Indoor Tracking Using UWB Measurements and Particle Filtering2016Ingår i: 2016 IEEE 17TH INTERNATIONAL WORKSHOP ON SIGNAL PROCESSING ADVANCES IN WIRELESS COMMUNICATIONS (SPAWC), IEEE , 2016Konferensbidrag (Refereegranskat)

Target tracking with ultra-wideband (UWB) signals in indoor environments is a challenging problem due to the presence of multipath and non-line-of-sight conditions (NLOS). A solution to this problem is to use particle filtering (PF), which is able to handle both nonlinear models and non-Gaussian uncertainties that typically appear in the presence of NLOS. In this paper, we compare four different PF variants, that differ in terms of how  NLOS measurements are handled. According to our experimental results, based on the measurements from a basement tunnel,    multiple features from the UWB impulse response should be used, and  the ranging likelihood function should make use of both LOS and NLOS measurements. Standard time-of-arrival (TOA) based methods, even with NLOS rejection, are not good enough. Instead we advocate TOA-based algorithms that can actively mitigate errors due to NLOS.

• 381.
Fingerprinting-Based Positioning in Distributed Massive MIMO Systems2015Ingår i: Proc. of IEEE 82nd Vehicular Technology Conference (VTC2015-Fall), Sept. 2015., Institute of Electrical and Electronics Engineers (IEEE), 2015Konferensbidrag (Refereegranskat)

Location awareness in wireless networks may enable many applications such as emergency services, autonomous driving and geographic routing. Although there are many available positioning techniques, none of them is adapted to work with massive multiple-in-multiple-out (MIMO) systems, which represent a leading 5G technology candidate. In this paper, we discuss possible solutions for positioning of mobile stations using a vector of signals at the base station, equipped with many antennas distributed over deployment area. Our main proposal is to use fingerprinting techniques based on a vector of received signal strengths. This kind of methods are able to work in highly-cluttered multipath environments, and require just one base station, in contrast to standard range-based and angle-based techniques. We also provide a solution for fingerprinting-based positioning based on Gaussian process regression, and discuss main applications and challenges.

• 382.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten. University of Gavle, Sweden. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten. Swedish Defense Research Agency (FOI), Linköping, Sweden.
Kernel Methods for Accurate UWB-Based Ranging with Reduced Complexity2016Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 15, nr 3, s. 1783-1793Artikel i tidskrift (Refereegranskat)

Accurate and robust positioning in multipath environments can enable many applications, such as search-and-rescue and asset tracking. For this problem, ultra-wideband (UWB) technology can provide the most accurate range estimates, which are required for range-based positioning. However, UWB still faces a problem with non-line-of-sight (NLOS) measurements, in which the range estimates based on time-of-arrival (TOA) will typically be positively biased. There are many techniques that address this problem, mainly based on NLOS identification and NLOS error mitigation algorithms. However, these techniques do not exploit all available information in the UWB channel impulse response. Kernel-based machine learning methods, such as Gaussian Process Regression (GPR), are able to make use of all information, but they may be too complex in their original form. In this paper, we propose novel ranging methods based on kernel principal component analysis (kPCA), in which the selected channel parameters are projected onto a nonlinear orthogonal high-dimensional space, and a subset of these projections is then used as an input for ranging. We evaluate the proposed methods using real UWB measurements obtained in a basement tunnel, and found that one of the proposed methods is able to outperform state-of-the-art, even if little training samples are available.

• 383.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. University of Gävle, Sweden. Swedish Defense Research Agency (FOI), Linköping, Sweden.
Kernel Principal Component Analysis for UWB-Based Ranging2014Ingår i: IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2014, 2014, s. 145-149Konferensbidrag (Refereegranskat)

Accurate positioning in harsh environments can enable many application, such as search-and-rescue in emergency situations. For this problem, ultra-wideband (UWB) technology can provide the most accurate range estimates, which are required for range-based positioning. However, it still faces a problem in non-line-of-sight (NLOS) environments, in which range estimates based on time-of-arrival (TOA) are positively biased. There are many techniques that try to address this problem, mainly based on NLOS identification and NLOS error mitigation. However, these techniques do not exploit all available information from the UWB channel impulse response. In this paper, we propose a novel ranging technique based on kernel principal component analysis (kPCA), in which the selected channel parameters are projected onto nonlinear orthogonal high-dimensional space, and a subset of these projections is then used for ranging. We tested this technique using UWB measurements obtained in a basement tunnel of Linkoping university, and found that it provides much better ranging performance comparing with standard techniques based on PCA and TOA.

• 384.
An Experimental Study of RSS-Based Indoor Localization Using Nonparametric Belief Propagation Based on Spanning Trees2010Ingår i: Proc. of Intl. Conf. on Sensor Technologies and Applications, 2010, s. 238-243Konferensbidrag (Refereegranskat)

Nonparametric belief propagation (NBP) is the well-known method for cooperative localization in wireless sensor networks. It is capable to provide information about location estimation with appropriate uncertainty and to accommodate non-Gaussian distance measurement errors. However, the accuracy of NBP is questionable in loopy networks. Therefore, in this paper, we propose a novel approach, NBP based on spanning trees (NBP-ST) created by breadth first search (BFS) method. In addition, we propose a reliable indoor model based on obtained received-signal-strength (RSS) measurements in our lab. According to our experimental results, NBP-ST performs better than NBP in terms of accuracy and communication cost in the networks with high connectivity (i.e., highly loopy networks).

• 385.
Indoor Positioning Using Nonparametric Belief Propagation Based on Spanning Trees2010Ingår i: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, s. 1-12Artikel i tidskrift (Refereegranskat)

Nonparametric belief propagation (NBP) is one of the best-known methods for cooperative localization in sensor networks. It is capable of providing information about location estimation with appropriate uncertainty and to accommodate non-Gaussian distance measurement errors. However, the accuracy of NBP is questionable in loopy networks. Therefore, in this paper, we propose a novel approach, NBP based on spanning trees (NBP-ST) created by breadth first search (BFS) method. In addition, we propose a reliable indoor model based on obtained measurements in our lab. According to our simulation results, NBP-ST performs better than NBP in terms of accuracy and communication cost in the networks with high connectivity (i.e., highly loopy networks). Furthermore, the computational and communication costs are nearly constant with respect to the transmission radius. However, the drawbacks of proposed method are a little bit higher computational cost and poor performance in low-connected networks.

• 386.
Chalmers University of Technology, Sweden.
Simultaneous Localization and Tracking via Real-time Nonparametric Belief Propagation2013Ingår i: EIII  International Conference on Acoustics, Speech, and Signal Processing (ICASSP), 2013, IEEE , 2013Konferensbidrag (Refereegranskat)

Target tracking in wireless sensor networks is traditionally achieved by localization and tracking (LAT), where the sensors are first localized, and in a later stage the target is tracked. This approach is sub-optimal since the sensor-target observations are not used to refine the position estimates of the sensors. In contrast, simultaneous localization and tracking (SLAT) uses these observations to track the target while simultaneously localizing the sensors. In this paper, we propose a novel centralized SLAT method based on real-time nonparametric belief propagation, which has nearly the same complexity and the same communication cost as LAT, and can provide both sensors' and target's estimated distributions in non-Gaussian form.

• 387.
Chalmers University of Technology, Sweden. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Simultaneous Sensor Localization and Target Tracking in Mine Tunnels2013Ingår i: IEEE Proc. of International Conference on Information Fusion, 2013, s. 1427-1433Konferensbidrag (Refereegranskat)

Mine tunnels are extensive labyrinths with irregularly-shaped walls, in which a hundreds of employees are working on extraction of valuable ores and minerals. Since the working conditions are extremely hazardous, a (wireless) sensor network (WSN) is deployed to increase the safety in tunnels. One of the most important applications of WSN is to track the personnel, mobile equipment and vehicles. However, the state-of-the-art algorithms assume that the positions of the sensors are perfectly known, which is not necessarily true due to the imprecise placement and/or possible sensor drops. Therefore, we propose an automatic approach for simultaneous refinement ofsensors’ positions (localization) and target tracking. We use a measurement model from a real mine, and apply a discrete variant of real-time belief propagation, which can efficiently solve this high-dimensional problem, and handle all non-Gaussian uncertainties typical for mining environments. Comparing with standard Bayesian target tracking and localization algorithms, both the sensors’ and the target’s estimates are improved.

• 388.
Chalmers University of Technology, Gothenburg, Sweden. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Target Tracking in Confined Environments with Uncertain Sensor Positions2016Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 65, nr 2, s. 870-882Artikel i tidskrift (Refereegranskat)

To ensure safety in confined environments such as mines or subway tunnels, a (wireless) sensor network can be deployed to monitor various environmental conditions. One of its most important applications is to track personnel, mobile equipment and vehicles. However, the state-of-the-art algorithms assume that the positions of the sensors are perfectly known, which is not necessarily true due to  imprecise placement and/or dropping of sensors. Therefore, we propose an automatic approach for simultaneous refinement of sensors' positions and target tracking. We divide the considered area in a finite number of cells, define dynamic and measurement models, and apply a discrete variant of belief propagation which can efficiently solve this high-dimensional problem, and handle all non-Gaussian uncertainties expected in this kind of environments. Finally, we use ray-tracing simulation to generate an artificial mine-like environment and generate synthetic measurement data. According to our extensive simulation study, the proposed approach performs significantly better than standard Bayesian target tracking and localization algorithms, and provides robustness against outliers.

• 389.
Chalmers University of Technology, Sweden. Politecnico di Torino, Italy. Technical University of Madrid, Spain.
Optimized edge appearance probability for cooperative localization based on tree-reweighted nonparametric belief propagation2011Ingår i: Proc. of IEEE Intl. Conf. on Acoustics, Speech and Signal Processing (ICASSP), 2011, s. 3028-3031Konferensbidrag (Refereegranskat)

Nonparametric belief propagation (NBP) is a well-known particle-based method for distributed inference in wireless networks. NBP has a large number of applications, including cooperative localization. However, in loopy networks NBP suffers from similar problems as standard BP, such as over-confident beliefs and possible non-convergence. Tree-reweighted NBP (TRW-NBP) can mitigate these problems, but does not easily lead to a distributed implementation due to the non-local nature of the required so-called edge appearance probabilities. In this paper, we propose a variation of TRW-NBP, suitable for cooperative localization in wireless networks. Our algorithm uses a fixed edge appearance probability for every edge, and can outperform standard NBP in dense wireless networks.

• 390.
Chalmers University of Technology, Gothenburg, Sweden. Technical University of Madrid, Spain.
Belief consensus algorithms for fast distributed target tracking in wireless sensor networks2014Ingår i: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 95, s. 149-160Artikel i tidskrift (Refereegranskat)

In distributed target tracking for wireless sensor networks, agreement on the target state can be achieved by the construction and maintenance of a communication path, in order to exchange information regarding local likelihood functions. Such an approach lacks robustness to failures and is not easily applicable to ad-hoc networks. To address this, several methods have been proposed that allow agreement on the global likelihood through fully distributed belief consensus (BC) algorithms, operating on local likelihoods in distributed particle filtering (DPF). However, a unified comparison of the convergence speed and communication cost has not been performed. In this paper, we provide such a comparison and propose a novel BC algorithm based on belief propagation (BP). According to our study, DPF based on metropolis belief consensus (MBC) is the fastest in loopy graphs, while DPF based on BP consensus is the fastest in tree graphs. Moreover, we found that BC-based DPF methods have lower communication overhead than data flooding when the network is sufficiently sparse.

• 391.
Chalmers University of Technology, Sweden. Technical University of Madrid, Spain.
Distributed Target Tracking based on Belief Propagation Consensus2012Ingår i: Proc. of the 20th European Signal Processing Conference (EUSIPCO), 2012, s. 544-548Konferensbidrag (Refereegranskat)

Distributed target tracking in wireless sensor networks (WSN) is an important problem, in which agreement on the target state can be achieved using particle filters with standard consensus methods, which may take long to converge. We propose distributed particle filtering based on belief propagation (DPF-BP) consensus, a fast method for target tracking. According to our simulations, DPF-BP provides better performance than DPF based on standard belief consensus (DPF-SBC) in terms of disagreement in the network. However, in terms of root-mean square error, it can outperform DPF-SBC only for a specific number of consensus iterations.

• 392.
Belief Propagation Techniques for Cooperative Localization in Wireless Sensor Networks2011Ingår i: Handbook of Position Location: Theory, Practice, and Advances / [ed] Seyed A. (Reza) Zekavat, R. Michael Buehrer, Hoboken, NJ, USA: John Wiley & Sons, 2011, s. 837-869Kapitel i bok, del av antologi (Övrigt vetenskapligt)

A number of applications in wireless sensor networks (WSN) require sensor nodes to obtain their absolute or relative positions. Equipping every sensor with a GPS receiver may be expensive, energy prohibitive and limited to outdoor applications. Therefore, we consider cooperative localization where each sensor node with unknown location obtains its location by cooperating with neighboring sensor nodes. In this chapter, we apply probabilistic inference to the problem of cooperative localization. These techniques are capable to obtain, not only location estimates, but also a measure of the uncertainty of those estimates. Since these methods are computationally very expensive, we need to use message-passing methods, which are also known as belief propagation (BP) methods. BP is a way of organizing the global computation of marginal beliefs in terms of smaller local computations within the graph. It is one of the best-known probabilistic methods for distributed inference in statistical physics, articial intelligence, computer vision, error-correcting codes, localization, etc. The whole computation takes a time proportional to the number of links in the graph, which is significantly less than the exponentially large time that would be required to compute marginal probabilities naively. However, due to the presence of nonlinear relationships and highly non-Gaussian uncertainties the standard BP algorithm is undesirable. Nevertheless, a particle-based approximation via nonparametric belief propagation (NBP) makes BP acceptable for localization in sensor networks. In this chapter, after an introduction to cooperative localization, we describe BP/NBP techniques and its generalizations (GBP) for the loopy networks. Due to the poor performance of BP/NBP methods in loopy networks, we describe three improved methods: GBP based on Kikuchi approximation (GBP-K), nonparametric GBP based on junction tree (NGBP-JT), and NBP based on spanning trees (NBP-ST). The last one (NBP-ST) is currently a unique method which is computationally feasible in a large-scale WSN.

• 393.
Cooperative localization in mobile networks using nonparametric variants of belief propagation2013Ingår i: Ad hoc networks, ISSN 1570-8705, E-ISSN 1570-8713, Vol. 11, nr 1, s. 138-150Artikel i tidskrift (Refereegranskat)

Of the many state-of-the-art methods for cooperative localization in wireless sensor networks (WSNs), only very few adapt well to mobile networks. The main problems of the well-known algorithms, based on nonparametric belief propagation (NBP), are the high communication cost and inefficient sampling techniques. Moreover, they either do not use smoothing or just apply it offline. Therefore, in this article, we propose more flexible and efficient variants of NBP for cooperative localization in mobile networks. In particular, we provide: (i) an optional 1-lag smoothing done almost in real-time, (ii) a novel low-cost communication protocol based on package approximation and censoring, (iii) higher robustness of the standard mixture importance sampling (MIS) technique, and (iv) a higher amount of information in the importance densities by using the population Monte Carlo (PMC) approach, or an auxiliary variable. Through extensive simulations, we confirmed that all the proposed techniques outperform the standard NBP method.

• 394.
Nonparametric Belief Propagation Based on Spanning Trees for Cooperative Localization in Wireless Sensor Networks2010Ingår i: Proc. of IEEE 72nd Vehicular Technology Conference Fall (VTC 2010-Fall), 2010, s. 1-5Konferensbidrag (Refereegranskat)

Nonparametric belief propagation (NBP) is one of the best-known methods for cooperative localization in sensor networks. It is capable to provide information about location estimation with appropriate uncertainty and to accommodate non-Gaussian distance measurement errors. However, the accuracy of NBP is questionable in loopy networks. In this paper, we propose a novel approach, NBP based on spanning trees (NBP-ST) created by breadth first search (BFS) method. According to our simulation results, NBP-ST performs better than NBP in terms of accuracy, computational and communication cost in the networks with high connectivity (i.e., highly loopy networks).

• 395.
Nonparametric Boxed Belief Propagation for Localization in Wireless Sensor Networks2009Ingår i: IEEE Proc. of Intl. Conf. on Sensor Technologies and Applications, 2009, s. 520-525Konferensbidrag (Refereegranskat)

Obtaining estimates of each sensorpsilas position as well as accurately representing the uncertainty of that estimate is a critical step for effective application of wireless sensor networks (WSN). Nonparametric belief propagation (NBP) is a popular localization method which uses particle based approximation of belief propagation. In this paper, we present a new variant of NBP method which we call nonparametric boxed belief propagation (NBBP). The main idea is to constraint the area from which the samples are drawn by building a box that covers the region where anchorspsila radio ranges overlap. These boxes, which are created almost without any additional communication between nodes, are also used to filter erroneous samples of the beliefs. In order to decrease the computational and the communication cost, we also added incremental approach using Kullback-Leibler (KL) divergence as a convergence parameter. Simulation results show that accuracy, computational and communication cost are significantly improved.

• 396.
Nonparametric generalized belief propagation based on pseudo-junction tree for cooperative localization in wireless networks2013Ingår i: EURASIP Journal on Advances in Signal Processing, ISSN 1687-6172, E-ISSN 1687-6180, Vol. 16Artikel i tidskrift (Refereegranskat)

Non-parametric belief propagation (NBP) is a well-known message passing method for cooperative localization in wireless networks. However, due to the over-counting problem in the networks with loops, NBP’s convergence is not guaranteed, and its estimates are typically less accurate. One solution for this problem is non-parametric generalized belief propagation based on junction tree. However, this method is intractable in large-scale networks due to the high-complexity of the junction tree formation, and the high-dimensionality of the particles. Therefore, in this article, we propose the non-parametric generalized belief propagation based on pseudo-junction tree (NGBP-PJT). The main difference comparing with the standard method is the formation of pseudo-junction tree, which represents the approximated junction tree based on thin graph. In addition, in order to decrease the number of high-dimensional particles, we use more informative importance density function, and reduce the dimensionality of the messages. As by-product, we also propose NBP based on thin graph (NBP-TG), a cheaper variant of NBP, which runs on the same graph as NGBP-PJT. According to our simulation and experimental results, NGBP-PJT method outperforms NBP and NBP-TG in terms of accuracy, computational, and communication cost in reasonably sized networks.

• 397.
Pseudo-junction tree method for cooperative localization in wireless sensor networks2010Ingår i: IEEE Proc. of Intl. Conf. on Information Fusion (FUSION), 2010, s. 1-8Konferensbidrag (Refereegranskat)

Nonparametric belief propagation (NBP) is well-known probabilistic method for cooperative localization in sensor networks. However, due to the double counting problem, NBP convergence is not guaranteed in the networks with loops or even if NBP converges, it could provide us less accurate estimates. The well-known solution for this problem is nonparametric generalized belief propagation based on junction tree (NGBP-JT). However, there are two problems: how to efficiently form the junction tree in an arbitrary network, and how to decrease the number of particles while keeping the good performance. Therefore, in this paper, we propose the formation of pseudo-junction tree (PJT), which represents the approximated junction tree based on thin graph. In addition, in order to decrease the number of particles, we use a set of very strong constraints. The resulting localization method, NGBP based on PJT (NGBP-PJT), overperforms NBP in terms of accuracy and communication cost in any arbitrary network.

• 398.
Reducing Communication Overhead for Cooperative Localization Using Nonparametric Belief Propagation2012Ingår i: IEEE Wireless Communication Letters, ISSN 2162-2337, Vol. 1, nr 4, s. 308-311Artikel i tidskrift (Refereegranskat)

A number of methods for cooperative localization has been proposed, but most of them provide only location estimate, without associated uncertainty. On the other hand, nonparametric belief propagation (NBP), which provides approximated posterior distributions of the location estimates, is expensive mostly because of the transmission of the particles. In this paper, we propose a novel approach to reduce communication overhead for cooperative positioning using NBP. It is based on: i) communication of the beliefs (instead of the messages), ii) approximation of the belief with Gaussian mixture of very few components, and iii) censoring. According to our simulations results, these modifications reduce significantly communication overhead while providing the estimates almost as accurate as the transmission of the particles.

• 399.
Sensor Localization using Generalized Belief Propagation in Networks with Loops2009Ingår i: Proc. of the 17th European Signal Processing Conference (EUSIPCO), 2009, s. 75-79Konferensbidrag (Refereegranskat)

Belief propagation (BP), also called “sum-product algorithm”, is one of the best-known graphical model for inference in statistical physics, artificial intelligence, computer vision, etc. Furthermore, a recent research in distributed sensor network localization showed us that BP is an efficient way to obtain sensor location as well as appropriate uncertainty. However, BP convergence is not guaranteed in a network with loops. In this paper, we propose localization using generalized belief propagation based on junction tree (GBP-JT) method. We illustrate it in a network with loop where BP shows poor performance. In fact, we compared estimated locations with Nonparametric Belief Propagation (NBP) algorithm. According to our simulation results, GBP-JT resolved the problems with loops, but the price for this is unacceptable large computational cost. The main conclusion is that this algorithm could be used with some approximation which keeps improved accuracy and significantly decreases the computational cost.

• 400.
Sensor localization using nonparametric generalized belief propagation in network with loop2009Ingår i: IEEE Proc. of Intl. Conf. on Information Fusion (FUSION), 2009Konferensbidrag (Refereegranskat)

Belief propagation (BP) is one of the best-known graphical model for inference in statistical physics, artificial intelligence, computer vision, etc. Furthermore, a recent research in distributed sensor network localization showed us that BP is an efficient way to obtain sensor location as well as appropriate uncertainty. However, BP convergence is not guaranteed in a network with loops. In this paper, we propose localization using generalized belief propagation based on junction tree method (GBP-JT) and nonparametric (particle-based) approximation of this algorithm (NGBP-JT). We illustrate it in a network with loop where BP shows poor performance. In fact, we compared estimated locations with nonparametric belief propagation (NBP) algorithm. According to our simulation results, GBP-JT resolved the problems with loops, but the price for this is unacceptable large computational cost. Therefore, our approximated version of this algorithm, NGBP-JT, reduced significantly this cost, with little effect on accuracy.

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