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  • Public defence: 2024-08-23 13:15 ACAS, A-building, Linköping
    Stenvall, David
    Linköping University, Department of Management and Engineering, Economics. Linköping University, Faculty of Arts and Sciences.
    Essays on Housing Markets and Financial Shocks: Energy Efficiency, Dependence, and Dynamics2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    There are two important lessons to be learned from the global financial crisis of 2007-2009. First, it emphasized the importance of understanding the driving forces behind housing markets and their linkages with other economic sectors. Second, it demonstrated how shocks originating in financial markets can impact the overall economy. This thesis aims to provide new empirical insights into the complex dynamics and drivers of housing markets, and to understand how financial fluctuations can affect the Swedish macroeconomy.   

    Throughout this thesis, the theme of heterogeneity has been thoroughly explored. For example, most chapters focus on how different regions and sectors are affected by macroeconomic variables or shocks. My aim has also been to examine the effects on different housing types and explore outcomes for variables that have previously received limited attention in the literature. The thesis consists of five separate chapters/articles that deal with various aspects related to the housing market or how financial shocks affect the macroeconomy.  

    In the first chapter, the relationships between prices of energy commodities (oil, coal, and natural gas) and nine regional housing markets in the USA are examined. Instead of only examining the relationship between oil prices and the housing market, the study expands the literature by including additional energy commodities. Additionally, the study uses methods aimed at measuring not only linear but also non-linear relationships.  

    In the second chapter, we investigate the effect of energy efficiency on the sale price of tenant-owned apartments in Sweden. Despite numerous studies examining how energy efficiency affects the sale prices of single-family houses, no previous study has focused solely on tenant-owned apartments. The results show mixed effects of energy efficiency. The study indicates that there is a need for more targeted measures if the goal is to fully integrate energy efficiency into prices of tenant-owned apartments.   

    In the third chapter, a Panel VAR (Vector Autoregression) with interaction variables (IPVAR) is used to analyze how institutional factors, related to rental market size and regulations, can explain the response of housing markets in different countries to macroeconomic shocks.  

    In the fourth chapter, structural VAR models (Bayesian and factor-augmented) are used to provide a comprehensive overview of how financial shocks affect the Swedish labor market. Instead of only focusing on how financial shocks affect the labor market at the national level, the study also examines the effects on regions and sectors. The results suggest a significant variation in response across different sectors and regions. 

    In the fifth chapter, just like in the fourth, VAR models are used to investigate how financial shocks affect the Swedish housing market at both national and regional levels. The analysis reveals that financial shocks tend to affect prices more than housing starts and building permits. From the regional analysis, it is found that house prices in some areas are more sensitive to financial shocks than others. Prices in areas with inelastic supply react more strongly than those in elastic areas, although this result is highly dependent on the model specification. 

    List of papers
    1. Nonlinear tail dependence between the housing and energy markets
    Open this publication in new window or tab >>Nonlinear tail dependence between the housing and energy markets
    Show others...
    2022 (English)In: Energy Economics, ISSN 0140-9883, E-ISSN 1873-6181, Vol. 106, article id 105771Article in journal (Refereed) Published
    Abstract [en]

    This paper examines the quantile dependence between energy commodities (oil, coal, and natural gas) and the real housing returns of the nine US census divisions for the period 1991-2019. In contrast to the literature on the association between oil and housing markets, we contribute by studying the effect of additional commodities on the housing market returns. We use a cross-quantilogram and quantile regression approach and find regional variation in the impact of energy commodities on housing returns. The effect within the same region varies over the quantile distributions. In general, we observe that all energy commodities are negatively associated with real housing returns. Significant correlations are found more often when the oil and housing returns are in similar quantiles. Coal and natural gas show a stronger relationship with higher quantiles of housing returns. Further, the results for coal and natural gas remains relatively stable after controlling for macroeconomic variables.

    Place, publisher, year, edition, pages
    Elsevier, 2022
    Keywords
    Housing market; Oil; Coal; Natural gas; Tail-dependence; Cross-quantilogram
    National Category
    Economics
    Identifiers
    urn:nbn:se:liu:diva-183786 (URN)10.1016/j.eneco.2021.105771 (DOI)000762555300011 ()
    Note

    Funding Agencies|Jan Wallander and Tom Hedelius Foundations, Sweden [W2016:0364:1]; Swedish Energy AgencySwedish Energy AgencyMaterials & Energy Research Center (MERC); Ministry of Education of Japan (MEXT)

    Available from: 2022-03-25 Created: 2022-03-25 Last updated: 2024-05-21
    2. Does energy efficiency matter for prices of tenant-owned apartments?
    Open this publication in new window or tab >>Does energy efficiency matter for prices of tenant-owned apartments?
    2022 (English)In: Environmental Science and Pollution Research, ISSN 0944-1344, E-ISSN 1614-7499, Vol. 29, p. 66793-66807Article in journal (Refereed) Published
    Abstract [en]

    In this study, we use Energy Performance Certificate (EPC) information to investigate the effect of energy efficiency on the selling price of Swedish tenant-owned apartments. While there is a large body of literature on how energy efficiency affects the sales price of single-family houses, none has exclusively focused on tenant-owned apartments. For owners of tenant-owned apartments in Sweden, heating is for a large share included in the monthly fee paid to the tenant association, which usually does not change on a short-term basis. This raises the question whether homebuyers incentives for acquiring energy-efficient tenant-owned apartments are large enough to be capitalized into the prices. By hedonic models and matching methods, we found mixed results. In our most optimistic scenarios, tenant-owned apartments enclosed in energy-efficient buildings are sold with a premium of approximately 0.8 to 1.2% compared to apartments in non-efficient buildings. The results in this study are not robust to all model specifications and vary across regions. In comparison with recent studies using data for single-family houses in Sweden, our detected capitalization is smaller. Our results highlight a need for targeted measures if EPCs are to be fully capitalized in prices for all dwelling types in which buyers have different economic incentives for reducing their energy consumption.

    Place, publisher, year, edition, pages
    Springer Heidelberg, 2022
    Keywords
    Energy performance certificates; Housing markets; Tenant-owned apartments; Energy efficiency; Green premium
    National Category
    Other Environmental Engineering
    Identifiers
    urn:nbn:se:liu:diva-185277 (URN)10.1007/s11356-022-20482-w (DOI)000790632500017 ()35508850 (PubMedID)
    Note

    Funding Agencies|Linkoping University - Swedish Energy Agency [46898-1]

    Available from: 2022-05-25 Created: 2022-05-25 Last updated: 2024-05-21Bibliographically approved
    3. Rental market structure and housing dynamics: An interacted panel VAR investigation
    Open this publication in new window or tab >>Rental market structure and housing dynamics: An interacted panel VAR investigation
    2024 (English)In: International journal of finance and economics, ISSN 1076-9307, E-ISSN 1099-1158Article in journal (Refereed) Epub ahead of print
    Abstract [en]

    This article uses the interacted panel VAR method to analyse how institutional factors related to the structure of the housing market explain cross-country heterogeneity in responses to macroeconomic shocks. While the previous literature focused on the stabilizing role of the mortgage market, we argue that housing tenure structure also plays an important role. In the baseline, we use data for nine OECD members to investigate how the size and regulations of the rental market affect the response of the housing market to interest rate shocks. As a reference, we also conduct a similar analysis with the mortgage market structure as the institutional factor. We find that both the rental market size and maximum loan-to-value ratios are important in explaining heterogeneity of housing market responses to macroeconomic shocks.

    Place, publisher, year, edition, pages
    WILEY, 2024
    Keywords
    housing dynamics; impulse response function; monetary policy shock; panel data; rental market structure; vector autoregression
    National Category
    Business Administration
    Identifiers
    urn:nbn:se:liu:diva-200939 (URN)10.1002/ijfe.2937 (DOI)001156626600001 ()
    Available from: 2024-02-20 Created: 2024-02-20 Last updated: 2024-05-21
  • Public defence: 2024-09-06 13:15 K2, NorrköpingOrder onlineBuy this publication >>
    Naz, Farah
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Improving Transport Efficiency in the Construction Supply Chain2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Construction is responsible for a large part of carbon dioxide (CO2) emissions worldwide (39%) and environmental concerns in construction are growing. Construction is transport intensive since the final construction products like buildings are built directly at the site of use and all resources need to be transported to and from the construction site. The environmental impact of construction transport is significant and requires attention since 90% of the transport within construction is road transport. However, historically both regulatory bodies and the construction companies have overlooked construction transport causing transport to remain unnoticed as a separate activity. Construction transport efficiency (CTE) is low, but CTE can be improved using solutions such as logistics services, digital tools, and information sharing which in turn add value to the involved actors and reduce CO2 emissions. However, there is a need to better understand how to improve CTE.

    The purpose of the thesis is "to investigate how to improve construction transport efficiency by using logistics services, digital tools and information sharing to add value for the involved actors".

    Three research questions (RQs) have been developed to achieve the purpose of the thesis:

    RQ1a: What activities constitute construction transport?

    RQ1b: What are the challenges in improving construction transport efficiency?

    RQ2: How can logistics services, digital tools and information sharing improve construction transport efficiency?

    RQ3: How does improving construction transport efficiency add value for the involved actors?To answer the RQs, a case study has been used as a primary research approach to develop an in-depth and detailed understanding of construction transport. The thesis comprises five studies over the period of five years. Data has been collected mainly through observations, interviews, and company’s internal statistical data. Furthermore, construction transport flows have been studied from different actor’s perspective such as transporter, main contractor, material supplier, and waste collector.

    The thesis highlights the lack of efficiency within construction transport by identifying value adding, non-value adding, and necessary but non-value adding activities. The underlying reasons for the low CTE are lack of planning, poor communication, and lack of standard operating procedures (SOPs). Lack of planning leads to poor routing, empty travelling, and an increased number of transport. Likewise, poor communication results in outdated plans, last-minute changes, delayed deliveries whereas lack of SOPs results in non-standardized processes, lack of proper loading and unloading zones and improper material handling leading to damages. Due to poor transport planning, poor communication and lack of SOPs, construction transport uses more resources (such as time, fuel, vehicle, energy, and effort) than needed, adding less value to the involved actors (i.e. transporter, main contractor, material supplier and waste collector) as well as impacting the environment negatively.

    The thesis emphasizes the value of logistics services (such as material management, on-site vendor management inventory (VMI), waste management) for the involved actors in terms of improving CTE and how CTE can be improved using logistics services, digital tools and information sharing. Given the critical importance of delivery reliability within construction transport, the thesis provides value by detailing the time taken by each activity within construction transport flow via value stream mapping approach. Moreover, the thesis broadly adds knowledge to Logistics and Construction Management research areas whereby focusing specifically on construction transport—so far unnoticed as a distinct activity.

    List of papers
    1. The Potential of Improving Construction Transport Time Efficiency - A Freight Forwarder Perspective
    Open this publication in new window or tab >>The Potential of Improving Construction Transport Time Efficiency - A Freight Forwarder Perspective
    2022 (English)In: Sustainability, E-ISSN 2071-1050, Vol. 14, no 17, article id 10491Article in journal (Refereed) Published
    Abstract [en]

    Construction transport, in general, is not carried out efficiently, resulting in unnecessary costs and CO2 emissions. Although it has been found that there is a great potential to improve construction transport, little research has been conducted within this field. The purpose of this study is to contribute to the construction transport time efficiency by identifying non-value-adding activities and their causes from a freight forwarder perspective. A single case study was conducted and two flows, a goods delivery flow and a waste material flow, were mapped and analyzed with the help of value stream mapping (VSM). We ran two workshops to discuss the findings of the VSM. The results from this study show that there is large potential for improving construction transport time efficiency as over 40% of the time was used for non-value-adding activities. Although transport suffers from similar non-value-adding activities undertaken in other industries, this study identifies the transport activities with respect to construction transport. The findings further highlight areas of potential improvements, such as improved information sharing, planning, and coordination among all stakeholders. This knowledge can be used by the freight forwarder and the main contractor to improve construction transport time efficiency. The limitation of this study is that it is based on a single case of a freight forwarder. It does not provide a full picture of construction transport efficiency but rather a starting point for future studies.

    Place, publisher, year, edition, pages
    MDPI, 2022
    Keywords
    transport efficiency; construction transport activities; value stream mapping
    National Category
    Environmental Management
    Identifiers
    urn:nbn:se:liu:diva-188614 (URN)10.3390/su141710491 (DOI)000851867300001 ()
    Note

    Funding Agencies|Trafikverket (Swedish Transport Administration) [2019.2.2.5]

    Available from: 2022-09-20 Created: 2022-09-20 Last updated: 2024-05-30
    2. Clarifying the Interface Between Construction Supply Chain and Site: A Key to Improved Delivery Efficiency
    Open this publication in new window or tab >>Clarifying the Interface Between Construction Supply Chain and Site: A Key to Improved Delivery Efficiency
    2023 (English)In: Advances in Production Management Systems: Production Management Systems for Responsible Manufacturing, Service, and Logistics Futures / [ed] Erlend Alfnes, Anita Romsdal, Jan Ola Strandhagen, Gregor von Cieminski, David Romero, Cham: Springer, 2023, p. 140-153Conference paper, Published paper (Refereed)
    Abstract [en]

    The purpose of the paper is to capture non-value adding activities of the order-to-delivery process at the interface between construction site and the supply chain to identify efficiency improvement potentials. The paper is based on a case study of a Swedish construction site. The unit of observation has been the activities taking place at the interface between construction supply chain and construction site. i.e. deliveries and on-site material handling. Data is collected through observations in the unloading zone of the construction site, unstructured interviews, and a workshop with site management. The findings of the paper show that there exists fuzziness in the interface of construction supply chain and construction site causing the observed non-value adding activities such as waiting, excessive material handling, unnecessary vehicle movements etc. The root causes of the fuzziness are poor planning, lack of communication between site management and transporter/material supplier, and lack of standard operating procedures for unloading. The paper provides knowledge of the importance of managing interface between construction supply chain and site to remove non-value adding activities. Additionally, the paper provides a clear view of the different actors’ roles in the non-value adding activities and give suggestions of how to improve efficiency of construction deliveries. The paper is based on a single case study and further studies are needed to provide deeper insights into the phenomenon.

    Place, publisher, year, edition, pages
    Cham: Springer, 2023
    Series
    IFIP Advances in Information and Communication Technology, ISSN 1868-4238, E-ISSN 1868-422X ; 691
    Keywords
    Construction Supply Chain, Logistics Planning and Control, Non-Value Adding Activities
    National Category
    Construction Management
    Identifiers
    urn:nbn:se:liu:diva-203929 (URN)10.1007/978-3-031-43670-3_10 (DOI)9783031436697 (ISBN)9783031436703 (ISBN)
    Conference
    IFIP WG 5.7 International Conference, APMS 2023 Trondheim, Norway, September 17–21, 2023
    Available from: 2024-05-30 Created: 2024-05-30 Last updated: 2024-06-10Bibliographically approved
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  • Public defence: 2024-09-24 09:15 Ada Lovelace, B-building, LinköpingOrder onlineBuy this publication >>
    Kunnath Ganesan, Unnikrishnan
    Linköping University, Department of Electrical Engineering, Communication Systems. Linköping University, Faculty of Science & Engineering.
    Beyond Boundaries: Evolving Connectivity with Massive MIMO2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The forthcoming sixth generation (6G) wireless networks signify an evolutionary leap in connectivity, surpassing conventional limitations through the integration of massive multiple-input multiple-output (MIMO) technology. Three primary application scenarios that are expected to drive the development of 6G networks are as follows: (i) enhanced mobile broadband (eMBB) promises lightning-fast data rates and expanded capacity for bandwidth-intensive applications such as virtual reality (VR) and high-definition (HD) video streaming, marking a significant evolution in connectivity; (ii)ultra-reliable low latency communication (URLLC) ensures ultra-reliable, low-latency connectivity critical for applications like autonomous vehicles and remote surgery, further emphasizing the evolution towards more reliable and responsive connections; (iii) massive machine type communications (mMTC) cater to the connectivity needs of millions of Internet-of-Things (IoT) devices across various sectors like smart cities and healthcare, expanding the boundaries of connectivity to encompass a vast array of interconnected devices. Moreover, 6G networks prioritize rural connectivity, aiming to bridge the digital divide by extending high-speed internet access to underserved areas. Through the integration of cutting-edge wireless technologies, 6G networks stand ready to redefine connectivity, offering ultra-fast, reliable, and ubiquitous communication services across a wide range of application scenarios, thereby paving the way for a more connected and equitable future. 

    In this thesis, various aspects of the evolution of distributed massive MIMO connectivity are explored, including: (i) synchronization of distributed access points (APs); (ii) partially coherent (PC) operation of APs; (iii) Grant-free random access of mMTC devices; (iv) extreme multiplexing capabilities; and (v) SuperCell massive MIMO communication. 

    Distributed APs operate with independent local oscillators (LOs), resulting in frequency and timing mismatches between them. In narrow-band systems, any discrepancies in frequency or timing among distributed transmit nodes translate into relative phase offsets within a symbol interval. These offsets must be compensated for coherent signal combining during transmission to a user. Paper A delves into the synchronization of distributed APs in massive MIMO systems. This synchronization is pivotal for reaping the benefits of distributed massive MIMO. The paper analyzes the synchronization requirements from a reciprocity perspective, considering multiplicative impairments due to mismatches in radio frequency (RF) hardware. It introduces BeamSync, a novel over-the-air synchronization protocol, which calibrates geographically separated APs without relying on fronthaul for sending measurement data to the central processing unit (CPU). The key concept involves beamforming the synchronization signal in the dominant direction of the channel between APs. Results demonstrate that the proposed BeamSync method outperforms traditional beamforming techniques significantly. 

    While advancements like those detailed in Paper A enable synchronization within localized areas, achieving network-wide AP synchronization remains daunting. Consequently, synchronized clusters exist, yet phase alignment across clusters poses a challenge. Addressing this, Paper B introduces a novel PC framework crucial for realizing the full potential of cell-free massive MIMO technology. Initially, an AP clustering algorithm groups APs into phase-aligned clusters. Subsequently, combining and precoding optimization algorithm maximizes the downlink sum data rates. Additionally, a novel data stream allocation algorithm enhances the sum data rate of PC operation. Results demonstrate that PC operation approaches the sum rate of ideal fully coherent (FC) operation. This underscores the practical deployment potential of PC in cell-free massive MIMO networks. 

    As cellular technology advances, machine type communication (MTC) becomes increasingly significant. The Paper C delves into activity detection within grant-free random access for mMTC in cell-free massive MIMO net-works. It introduces a maximum-likelihood (ML) activity detection algorithm and demonstrates through results that the macro-diversity gain inherent in the cell-free architecture significantly enhances activity detection performance, particularly in scenarios with large coverage areas, outperforming co-located architectures. 

    RadioWeaves technology is a novel wireless infrastructure designed for indoor applications, leveraging the advantages of both massive MIMO and cell-free massive MIMO systems. Paper D explores the extreme multiplexing capabilities of RadioWeaves, demonstrating its ability to deliver high data rates while operating at low power levels. The findings reveal that RadioWeaves deployments excel in spatially separating users compared to conventional co-located setups, thus mitigating losses attributed to grating lobes and substantially reducing transmit power requirements.

    Rural connectivity is an important aspect to consider in the development of 6G networks, as it addresses the challenge of providing high-quality, reliable internet access to under-served or remote areas. Amidst the surge in data traffic within urban areas and the consequent neglect of rural regions due to lower profitability, Paper E explores the performance of SuperCell massive MIMO systems in rural settings. Addressing the unique challenges and opportunities of rural communication environments, the paper proposes an innovative solution. This solution involves the utilization of elevated base stations (BSs) equipped with sectorized antennas boasting large apertures, coupled with a user scheduling algorithm to ensure comprehensive digital coverage. Through rigorous analysis, the study evaluates the coverage range and high-rate service provision capabilities of this SuperCell system in rural contexts. 

    List of papers
    1. BeamSync: Over-The-Air Synchronization for Distributed Massive MIMO Systems
    Open this publication in new window or tab >>BeamSync: Over-The-Air Synchronization for Distributed Massive MIMO Systems
    2024 (English)In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, p. 1-1Article in journal (Refereed) Published
    Abstract [en]

    In distributed massive multiple-input multiple-output (MIMO) systems, multiple geographically separated access points (APs) communicate simultaneously with a user, leveraging the benefits of multi-antenna coherent MIMO processing and macro-diversity gains from the distributed setups. However, time and frequency synchronization of the multiple APs is crucial to achieve good performance and enable joint precoding. In this paper, we analyze the synchronization requirement among multiple APs from a reciprocity perspective, taking into account the multiplicative impairments caused by mismatches in radio frequency (RF) hardware. We demonstrate that a phase calibration of reciprocity-calibrated APs is sufficient for the joint coherent transmission of data to the user. To achieve synchronization, we propose a novel over-the-air synchronization protocol, named BeamSync, to calibrate the geographically separated APs without sending any measurements to the central processing unit (CPU) through fronthaul. We show that sending the synchronization signal in the dominant direction of the channel between APs is optimal. Additionally, we derive the optimal phase and frequency offset estimators. Simulation results indicate that the proposed BeamSync method enhances performance by 3 dB when the number of antennas at the APs is doubled. Moreover, the method performs well compared to traditional beamforming techniques.

    National Category
    Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-201117 (URN)10.1109/twc.2023.3335089 (DOI)
    Funder
    EU, Horizon 2020, 101013425
    Available from: 2024-02-22 Created: 2024-02-22 Last updated: 2024-06-12
    2. Cell-Free Massive MIMO With Multi-Antenna Users and Phase Misalignments: A Novel Partially Coherent Transmission Framework
    Open this publication in new window or tab >>Cell-Free Massive MIMO With Multi-Antenna Users and Phase Misalignments: A Novel Partially Coherent Transmission Framework
    2024 (English)In: IEEE Open Journal of the Communications Society, E-ISSN 2644-125X, E-ISSN 2644-125X, Vol. 5, p. 1639-1655Article in journal (Refereed) Published
    Abstract [en]

    Cell-free massive multiple-input multiple-output (MIMO) is a promising technology for next-generation communication systems. This work proposes a novel partially coherent (PC) transmission framework to cope with the challenge of phase misalignment among the access points (APs), which is important for unlocking the full potential of cell-free massive MIMO technology. With the PC operation, the APs are only required to be phase-aligned within clusters. Each cluster transmits the same data stream towards each user equipment (UE), while different clusters send different data streams. We first propose a novel algorithm to group APs into clusters such that the distance between two APs is always smaller than a reference distance ensuring the phase alignment of these APs. Then, we propose new algorithms that optimize the combining at UEs and precoding at APs to maximize the downlink sum data rates. We also propose a novel algorithm for data stream allocation to further improve the sum data rate of the PC operation. Numerical results show that the PC operation using the proposed framework with a sufficiently small reference distance can offer a sum rate close to the sum rate of the ideal fully coherent (FC) operation that requires network-wide phase alignment. This demonstrates the potential of PC operation in practical deployments of cell-free massive MIMO networks.

    Place, publisher, year, edition, pages
    IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2024
    Keywords
    Cell-free massive MIMO; downlink; coherent transmission; non-coherent transmission; partially coherent transmission; precoding; combining; data stream allocation
    National Category
    Telecommunications
    Identifiers
    urn:nbn:se:liu:diva-201386 (URN)10.1109/OJCOMS.2024.3373170 (DOI)001192352200002 ()
    Funder
    EU, Horizon 2020, 101013425
    Note

    Funding Agencies|ELLIIT

    Available from: 2024-03-06 Created: 2024-03-06 Last updated: 2024-06-12
    3. Clustering-Based Activity Detection Algorithms for Grant-Free Random Access in Cell-Free Massive MIMO
    Open this publication in new window or tab >>Clustering-Based Activity Detection Algorithms for Grant-Free Random Access in Cell-Free Massive MIMO
    2021 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 69, no 11, p. 7520-7530Article in journal (Refereed) Published
    Abstract [en]

    Future wireless networks need to support massive machine type communication (mMTC) where a massive number of devices accesses the network and massive MIMO is a promising enabling technology. Massive access schemes have been studied for co-located massive MIMO arrays. In this paper, we investigate the activity detection in grant-free random access for mMTC in cell-free massive MIMO networks using distributed arrays. Each active device transmits a non-orthogonal pilot sequence to the access points (APs) and the APs send the received signals to a central processing unit (CPU) for joint activity detection. The maximum likelihood device activity detection problem is formulated and algorithms for activity detection in cell-free massive MIMO are provided to solve it. The simulation results show that the macro diversity gain provided by the cell-free architecture improves the activity detection performance compared to co-located architecture when the coverage area is large.

    Place, publisher, year, edition, pages
    Institute of Electrical and Electronics Engineers (IEEE), 2021
    Keywords
    Activity Detection, Grant-Free Random Access, Cell-Free massive MIMO, massive machine-type communications (mMTC), Internet-of-Things (IoT)
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-179552 (URN)10.1109/TCOMM.2021.3102635 (DOI)000719563500032 ()2-s2.0-85112198086 (Scopus ID)
    Funder
    Swedish Research Council
    Note

    Funding agencies: Unnikrishnan Kunnath Ganesan and Erik G. Larsson were supported in part by ELLIIT and in part by Swedish Research Council (VR). Emil Bjornson was supported by the Grant 2019-05068 from the Swedish Research Council. This article was presented at 21st IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC 2020) [1].

    Available from: 2021-09-24 Created: 2021-09-24 Last updated: 2024-06-12Bibliographically approved
    4. RadioWeaves for Extreme Spatial Multiplexing in Indoor Environments
    Open this publication in new window or tab >>RadioWeaves for Extreme Spatial Multiplexing in Indoor Environments
    2020 (English)In: 2020 54th Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, USA, 2020, p. ¨1007-1011Conference paper, Published paper (Refereed)
    Abstract [en]

    With the advances in virtual and augmented reality, gaming applications, and entertainment, certain indoor scenarios will require vastly higher capacity than what can be delivered by 5G. In this paper, we focus on massive MIMO for indoor environments. We provide a case study of the distributed deployment of the antenna elements over the walls of a room and not restricting the antenna separation to be half the wavelength. This is a new paradigm of massive MIMO antenna deployment, introduced in [1] under the name RadioWeaves. We investigate different antenna deployment scenarios in line of sight communication. We observe that the RadioWeaves deployment can spatially separate users much better than a conventional co-located deployment, which outweighs the losses caused by grating lobes and thus saves a lot on transmit power. Through simulations, we show that the RadioWeaves technology can provide high rates to multiple users by spending very little power at the transmitter compared to a co-located deployment.

    Place, publisher, year, edition, pages
    Pacific Grove, CA, USA: , 2020
    Series
    IEEE, ISSN 1058-6393, E-ISSN 2576-2303
    National Category
    Communication Systems
    Identifiers
    urn:nbn:se:liu:diva-178180 (URN)10.1109/IEEECONF51394.2020.9443342 (DOI)000681731800194 ()978-0-7381-3126-9 (ISBN)978-1-6654-4707-2 (ISBN)
    Conference
    2020 54th Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, USA, 1-4 Nov. 2020
    Funder
    ELLIIT - The Linköping‐Lund Initiative on IT and Mobile Communications
    Note

    Funding: ELLIIT; Swedish Research Council (VR)Swedish Research Council

    Available from: 2021-08-11 Created: 2021-08-11 Last updated: 2024-06-12Bibliographically approved
    5. Bridging the Digital Divide Using SuperCell Massive MIMO
    Open this publication in new window or tab >>Bridging the Digital Divide Using SuperCell Massive MIMO
    2022 (English)In: 2022 IEEE 96th Vehicular Technology Conference (VTC2022-Fall), London, United Kingdom: IEEE, 2022, , p. 6Conference paper, Published paper (Refereed)
    Abstract [en]

    Massive multiple input multiple output (MIMO)emerged as the leading technology for supporting fifth generation(5G) and beyond 5G cellular communication systems. Due to thetremendous increase in data traffic in urban areas and to meetsuch a significant demand, most studies consider macro/micro celldeployments in urban environments. Internet service providers(ISPs) are less interested in providing communication services inrural areas considering the relatively low profits compared to thedeployment and maintenance costs. In this paper, we investigatethe massive MIMO performance in rural scenarios. In particular,we investigate different aspects to consider while designing along-range communication system. We propose to use elevatedbase station (BS) with sectorized antennas with unusually largeaperture and implement a user scheduling algorithm at theBS to provide full digital coverage. We analyze the coveragerange of a massive MIMO system to provide high-rate services.Furthermore, we also analyze the link budget requirements andthe rates users can achieve in such a SuperCell massive MIMOnetwork.

    Place, publisher, year, edition, pages
    London, United Kingdom: IEEE, 2022. p. 6
    Series
    IEEE Conference on Vehicular Technology (VTC), ISSN 2577-2465, E-ISSN 1090-3038
    Keywords
    Massive MIMO; SuperCell; digital divide; scalability; coverage
    National Category
    Electrical Engineering, Electronic Engineering, Information Engineering
    Identifiers
    urn:nbn:se:liu:diva-191098 (URN)10.1109/VTC2022-Fall57202.2022.10012724 (DOI)000927580600032 ()9781665454681 (ISBN)9781665454698 (ISBN)
    Conference
    2022 IEEE 96th Vehicular Technology Conference (VTC2022-Fall), London, United Kingdom, 26-29 September, 2022
    Note

    Funding: ELLIIT; Swedish Research Council (VR); KAW foundation

    Available from: 2023-01-18 Created: 2023-01-18 Last updated: 2024-06-12Bibliographically approved
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