Marc Pallot
email: marc.pallot@ensam.eu

Sylvain Fleury
email: sylvain.fleury@ensam.eu

Benjamin Poussard
email: benjamin.poussard@ensam.eu

Simon Richir
email: simon.richir@ensam.eu

What are the Challenges and Enabling Technologies to Implement the Do-It-Together Approach Enhanced by Social Media, its Benefits and Drawbacks?

Keywords: Do-It-Yourself (DIY), Do-It-Together (DIT), User Driven Innovation (UDI), Social Media, New Product Development (NPD), Social Product Development (SPD), Social Manufacturing (SM), Circular Economy, Sharing Economy, Immersive Design, Immersive eXperience

Inspired by the Do-It-Yourself (DIY) movement, the Do-It-Together (DIT) collaborative approach was successfully trialed in 2018, hence opening the door to the application of User Driven Innovation for realizing product individualization. In the meantime, other megatrends like digitization, social media, sustainability, the circular economy, and collaborative consumption have pushed toward a renewed DIT approach for tackling social and societal issues.

Industrial organizations, especially Small and Medium-sized Enterprises (SMEs), are currently facing several challenges, namely: (i) the fourth industrial revolution known as "Industry 4.0" (I4.0); (ii) an open innovation paradigm shift; (iii) digitization; (iv) collaborative consumption; (v) the new product individualization trend. According to [START_REF] Lecossier | UX-FFE Model: An Experimentation of a New Innovation Process Dedicated to a Mature Industrial Company[END_REF], the survival strategy of mature industrial companies, through their conventional incremental innovation and traditional organizational structure for preserving their market share, is no longer adequate to fulfil the everchanging customer demand. On the one hand, consumers feel much more concern about societal issues like sustainability [START_REF] Sikhwal | Design for Mass Individualisation: Introducing Networked Innovation Approach[END_REF] and individualized products based on cultural and gender differences, as well as other societal considerations [START_REF] Kumar | Private Label Strategy: How to Meet the Store Brand Challenge[END_REF][START_REF] Koren | Product Design for Mass-Individualization, Design Confer[END_REF][START_REF] Sikhwal | Identification of Optimised Open Platform Architecture Products for Design for Mass Individualisation[END_REF]. On the other hand, businesses are moving toward a more collaborative and responsible attitude regarding both social and societal issues. Inspired by the DIY movement and DIT collaborative culture [START_REF] Hirscher | Social Manufacturing in the Fashion Sector: New Value Creation Through Alternative Design Strategies?[END_REF] promoted by the Web 2.0 (e.g., User Content Creation, crowdsourcing), we elaborate on renewing the DIT approach according to the social media impact on New Product Development (NPD). Such a new DIT approach combines several socially extended concepts including Social Ideation

II

Journal of Innovation Economics & Management 2022 -pre-published [START_REF] Schleich | Social Open Innovation in Online Brand Communities with Particular Regard to the Social Exchange Theory and Brand Management[END_REF], Co-creation [START_REF] Ramaswamy | The Power of Co-Creation: Build it with them to Boost Growth, Productivity, and Profits[END_REF], Social Product Development (SPD) [START_REF] Piller | From Social Media to Social Product Development: The Impact of Social Media on Co-Creation of Innovation[END_REF] and Social Manufacturing (SM) [START_REF] Jiang | Social Manufacturing as a Sustainable Paradigm for Mass Individualization[END_REF] in the context of User Driven Innovation [START_REF] Pallot | The Living Lab Approach: A User Centred Open Innovation Ecosystem, Webergence Blog[END_REF][START_REF] Füzi | Quadruple Helix and its Types as User-Driven Innovation Models[END_REF]. This is an opportunity for industrial organizations, especially SMEs, independent experts, such as: designers, architects, and makers, and consumers, to overcome these above-mentioned challenges in implementing this renewed DIT approach thanks to enabling technologies like Additive Manufacturing (AM), eXtended Reality (XR), Big Data (BD) and Artificial Intelligence (AI).

The DIT approach is intended to be generic enough to be applied within any business sector where consumers are engaged in the innovation process. The furnishing business sector is a perfect example, combining the furniture sector and interior design personalization. In fact, home owners are increasingly looking for opportunities to contribute to individualization in terms of furnishing their house or apartment while decorating and providing it with furniture and fittings. In fact, this is not restricted to furniture and interior design as it could also include furnishing smartification, while taking into account sustainability principles described in the report FURN360 (2018). This exploratory study is intended to identify DIT implementation challenges to be tackled, induced benefits, and eventual drawbacks, while anticipating to what extent enabling technologies would contribute to overcoming these challenges. In this study, a particular focus is given to immersive eXtended Reality (XR) in the context of social ideation and co-design, named "Immersive Design" [START_REF] Dietrich | Virtual Reality in Social Marketing: A Process Evaluation[END_REF]. Our motivation comes from the willingness to obtain more knowledge and comprehensiveness about the implementation of this renewed DIT approach into a twin digital and physical platform. This twin DIT platform will be trialed in the furnishing business sector and interior design including smartification. The furniture sector is a rather good example of a traditional market that could evolve toward an Immersive Design ecosystem; especially for home owners that increasingly wish to be engaged in the design and production of personalized furniture according to their interior design requirements and the emergence of appliances and other electronic means, driven by the Internet of Things (IoT).

The DIT approach disrupts the traditional industrial setup in which designers are highly valued employees whose bursts of inspiration must be jealously kept within the brand walls. In our vision, designers and interior architects are freelancers while customers are both producers and consumers. This dual role of customers, which was already identified in 1980 by Toffler through the name "prosumers", leverages the DIT platform in proposing their personalized concepts while getting feedback from other customers.

They could even contribute by enhancing customers' ideas and interacting with potential suppliers (e.g., manufacturing SMEs or FabLab makers) so that the new product design grows faster and much closer to the actual expectations of its future users. Makers and prosumers possess the fabrication knowledge related to the specific production machines they regularly use (e.g., 3D printers, computer numerical control -CNC). Hence, their role is more about prototyping designed parts that can, once validated, eventually be transferred to a local production site like a FabLab or an SME manufacturer for a higher quality production, depending on the amount to be produced. However, prosumers could be more interested in a one-of-a-kind manufacturing approach that perfectly fits with FabLab self-production through 3D printers. Additionally, the DIT approach establishes regional industrial innovation hubs that are meant to let customers and professionals (e.g., freelancers), involved in the finalization of a new design, get their hands on all the selected elements (materials, shapes, technical solutions) in experimenting with the virtual (XR technologies) or physical (e.g., 3D printing) prototyping and manufacturing process. It relies on a distributed network of qualified makers and small local producers making their production capabilities available to the ecosystem; thus, at the same time, creating new business opportunities for them and establishing a virtual and dynamic production system that can locally produce individualized products according to each consumer's specific context and expectations.

The overall DIT-enabled ecosystem also achieves a seamless adoption into each factory operation, thanks to standardization of the product's blueprints and of their processing into production instructions that are compatible with a broad set of working machines. The DIT approach, in terms of objectives and targeted value elements, is visually represented as a vision to attain (Figure 1). These objectives are operatively pursued in developing the following elements: (i) Co-creation digital platform, establishing a digital melting pot where a market-aware designer's creativity and talent closely interact with customers while being influenced by their ideas and needs; (ii) Compatibility layer, translating the co-created smart-object design into machine production instructions toward shortening the time-to-market of new concepts; (iii) Industrial production network, offering close-to-thecustomer local production capabilities and technical know-how for flexible, sustainable and open smart-object manufacturing, even in small lots or in one-of-a-kind; (iv) Industrial innovation hubs, acting as the front-end of the whole system where gaps between digital design and hard manufacturing techniques are filled by providing hands-on experience and a value network cross-fertilization of know-how. We draw on the work of Hämäläinen et al. (2018) to overcome barriers to sustainability toward personal fabrication and the emerging concept of social manufacturing. These provided a summary table describing 13 concepts, from distributed manufacturing to the platform economy, related to personal fabrication and distributed production. Among these concepts, between mass customization and peer production, there is the concept of personalization represented by the following trio: "design, choose & buy". Here, we suggest including the concept of individualization [START_REF] Koren | Product Design for Mass-Individualization, Design Confer[END_REF][START_REF] Sikhwal | Design for Mass Individualisation: Introducing Networked Innovation Approach[END_REF][START_REF] Chang | The Joint Effects of Customer Participation in Various New Product Development Stages[END_REF]; that is, going one step further as it represents prosumers co-creating value, through ideation, design and fabrication, while obtaining the expected resulting experience. In our vision, we interpret the individualization concept as another trio: "experience, produce & adopt". Certainly, there is no need to necessarily "choose" between different options as it is designed to fit in with the particular customer's expectations. Then, "buy" is more intended to acquire a product on a shelf rather than to pay for a cocreation experience, which includes ideation and design iterations, leading to the expected solution.

IV

Furthermore, co-creation also means that all stakeholders, including users and suppliers, share knowledge and contribute to creating new knowledge [START_REF] Ramaswamy | The Power of Co-Creation: Build it with them to Boost Growth, Productivity, and Profits[END_REF][START_REF] Pallot | A Holistic Model of User Experience for Living Lab Experiential Design[END_REF]. Nowadays, there are mobile apps allowing people to easily capture a 3D representation of their rooms directly from their smartphone camera. Then, there are immersive technologies, especially XR, which include Virtual Reality (VR), Augmented Reality (AR) and Mixed Reality (MR) devices, enabling people to create and concurrently experience alternative solutions. The eXperience Design (XD) iterative process is particularly appropriate for this kind of immersive design where stakeholders are immersed into a virtual 3D representation in order to live a close to real experience of their living environment [START_REF] Dietrich | Virtual Reality in Social Marketing: A Process Evaluation[END_REF]. According to iSMA (2014), social marketing originates from commercial marketing and seeks to create marketing concepts and techniques influencing behaviors that benefit both individuals and society. [START_REF] Sikhwal | Design for Mass Individualisation: Introducing Networked Innovation Approach[END_REF] consider the concept of Mass Individualization (MI) as a new product design paradigm. They present individualization as a product that is highly personalized reflecting usage requirements and ensuring a longer product life cycle. They argue that this new product design paradigm serves product adaptability, upgradability, and sustainability, while meeting usage requirements.

Besides introducing the background, motivation and purpose of this exploratory study toward the implementation of a renewed DIT approach enhanced by social media impacts on the NPD, the extensive literature

VI Journal of Innovation Economics & Management 2022 -pre-published
review is presented before unveiling the findings through several tables dedicated to DIT challenges, benefits, and drawbacks. Finally, we conclude in discussing the limitations of this study and future work while summarizing its main contribution.

Methodology

In the current body of knowledge and besides the "NPD and social media" research stream, we have identified two other research streams that would mainly match the DIT approach, namely: "Social Product Development" and "Social Manufacturing". The first one contributes to the study of the social media impact on NPD within the Open Innovation paradigm, while the second one contributes to the study of the social media impact on manufacturing within the I4.0 smart and individualized manufacturing paradigm. Therefore, it would make sense to bring common knowledge about the challenges facing DIT implementation, as well as potential benefits and eventual drawbacks. The goal is also to better understand how enabling technologies could fit with the implementation of the DIT approach. Second, sometimes it appears that concepts are awkwardly defined while the use of synonyms brings even more confusion. Furthermore, there is a lack of empirical studies on the assessment of NPD with social media, SPD, and SM in terms of implementation challenges, induced potential benefits, and eventual drawbacks. It also appears that very few studies related to the DIT research domain investigate potential negative impacts (e.g., drawbacks, disadvantages, shortcomings) while there are plenty of publications which rather present the positive impacts (e.g., benefits, advantages) as reported in Table 1. The main goal of this study is to deliver a comprehensive picture of DIT implementation in terms of challenges to be overcome by enabling technologies, induced benefits, and drawbacks. This is intended to lead to a better understanding of individualized product business both in terms of opportunities and risks for prosumers, designers, interior architects, makers, and SMEs operating in the furnishing sector. This could then be adapted to other business sectors facing a similar growing demand of individualized products.

A research process, based on a systematic literature review, was intended to identify: (i) the DIT-relevant publication streams and databases; (ii) challenges, enabling technologies, potential benefits and eventual drawbacks for implementing the DIT approach on the basis of social media applied to NPD in the context of the circular economy and the sharing economy. A multikeyword search derived from the application of social media within the different product life-cycle stages was carried out among different publication pre-published -Journal of Innovation Economics & Management 2022 VII databases (IEEE Xplore, JSTOR, Blackwell, Emerald, Springer, sciencedirect, worldscientific). In the meantime, through the use of an advanced search, "Social Product Development" and "Social Manufacturing" were emerging as relevant publication streams. A search for relevant previous work was based on the combination of specific keywords, namely: "New Product Development" and "social media" or "Social Product Development" or "Social Manufacturing". Other complementary keywords: "challenges", "benefits" and "drawbacks", which represent the most important elements of the topic under scrutiny, were included in this search for previous work and were mapped against a Search, Appraisal, Synthesis and Analysis framework [START_REF] Grant | A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies[END_REF]. This literature review was intended to bring the necessary elements for answering the following research questions: (RQ1) What are the DIT implementation challenges to be overcome in the context of the circular economy and the sharing economy? (RQ2) What are the potential benefits induced by DIT implementation? (RQ3) What are the potential drawbacks induced by DIT implementation? (RQ4) What are the enabling technologies for overcoming the DIT implementation challenges?

The search process was executed on the main keywords (NPD and social media, SPD, SM) appearing in the title that gave the following number of articles for each of the publication streams: "NPD": 32, "SPD": 32, "SM": 98, which represented overall 162 articles. Having the search done through keywords appearing in the title resulted in a limited, but extremely relevant, number of articles. All selected articles were scrutinized for collecting evidence leading to the identification of challenges, induced benefits and drawbacks, or synonyms like advantages or disadvantages or shortcomings.

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Journal of Innovation Economics & Management 2022 -pre-published The filtering is based on secondary keywords: challenges, benefits, drawbacks or synonyms like advantages or disadvantages resulted in 38 selected articles that are presented with their characteristics in Table 1. Another search was executed on the remaining selected articles in order to identify the enabling technologies and economy types also shown as characteristics in the same table. The advanced search of relevant articles was executed in the 2010-2021 time range, as these concepts are pretty recent as they are linked to the use of social media within the different Product Life-Cycle (PLC) stages as they are described in the next section (FFE, co-design, open manufacturing, co-marketing, field testing, green logistic, social reuse). The grouping of identified challenges, induced benefits, and possible drawbacks is based on their location within PLC stages.

Findings

DIT Stages

The social dimension of the DIT approach reflects the effort to engage external participants, through the use of social media, with different expertise along the product life-cycle, such as independent designers, interior architects, makers, suppliers and especially customers or prosumers. There are several stages that make up this DIT-related PLC as presented in the selected articles. On the DIT economical dimension, there are the digital economyincluding the platform economy, experience economy, and sharing economy -the knowledge economy, and the circular economy, which impact the DIT NPD process. Each of the seven identified PLC stages is briefly described in Table 2.

Co-creation or social ideation reflects the early stage of PLC, which is known as the Fuzzy Front-End (FFE) stage [START_REF] Lecossier | Towards Radical Innovations in a Mature Company: An Empirical Study on the UX-FFE Model[END_REF][START_REF] Kim | Focusing the Fuzzy Front-End in New Product Development[END_REF], in which all stakeholders, including customers, co-create ideas that bring value. The second PLC stage is named co-design; however, nowadays it partly overlaps with co-creation for the rapid conceptualization of ideas and usage scenarios including virtual prototyping through the use of an iterative XD process [START_REF] Pallot | Evaluating User eXperience as a Means to Reveal the Potential Adoption of Innovative Ideas[END_REF]; and manufacturing for issuing physical prototypes in order to validate the concepts and start the industrialization phase. The third PLC stage is open manufacturing, in which individuals (e.g., makers, prosumers) can by themselves produce a one-of-a-kind through the use of additive manufacturing (e.g., 3D printers), as is done, in fact, for physical prototyping, or in using small CNC robotized production units. The fourth PLC stage, co-marketing or social marketing, is about the marketing communication mix including Word-of-Mouth (WoM) and influencer marketing, where social media play an important role. Social commercialization, the 5th PLC stage, is more about field testing to make the new product error-free and launching it. This stage also includes the validation of the positioning and marketing mix while collecting feedback from customers about product performance, degree of usability, experience and level of satisfaction, as well as remaining issues. Then, the green collaborative logistics, 6 th PLC stage, represents crowdsourced activities such as product maintenance (e.g., regular upgrades) and repairing (e.g., makers) for a longer life cycle that could require producing parts locally on demand through 3D printing; as well as the reverse logistics for taking care of retired products. Finally, there is the 7th PLC stage, named "social reuse", for ensuring the lowest possible level of product waste, through crowdsourced activities like refurbishing, repurposing, and possibly upcycling. (*) in co-creation in order to facilitate the emergence of new ideas, their evaluation and validation through the use of diversity and appropriate creativity tools and methods. Better insight into the needs of the consumers. Knowledge Sharing.

S2

Co-design Open Design (*) in co-designing different alternatives of potential solutions, exploring and experimenting their usage scenarios through the co-evaluation of mock-up and prototype. This includes the need for rich designs in individualization and high-quality local materials for sustainability, repair, reuse, remanufacture and recycling.

S3

Open Manufacturing (*) in making sure that everyone, especially makers and prosumers, can access and feed, with digital design (e.g., CAD drawings), autonomous production machines (e.g., 3D printers, robotized production units) and assembling the instructions and necessary tools & equipment for quality control. Recycling production waste to make new production resources.

Identified DIT Challenges and Benefits

In the context of the DIT approach, each PLC stage has different challenges to be overcome leading to potential benefits and possible drawbacks as presented in the following tables. However, it should be noted that all the benefits and drawbacks mentioned are the ones identified during the literature review. A first statement about this particular literature review is that there are far more published studies presenting induced benefits rather than drawbacks. It explains the breakdown of the presentation of all identified challenges and benefits into several tables while there is only one table about drawbacks. Besides the obvious DIT platform (implementation of the DIT approach) of the overall benefit of democratizing co-creation, design and manufacturing [START_REF] Hirscher | Social Manufacturing in the Fashion Sector: New Value Creation Through Alternative Design Strategies?[END_REF], people face numerous issues/challenges to implement an effective distributed innovation and collaboration mode. Individualized products and on-demand production partly characterize social manufacturing, which encourage open innovation through social collaboration and intellectual resource sharing [START_REF] Jiang | Social Manufacturing as a Sustainable Paradigm for Mass Individualization[END_REF]. The DIT platform is based on the sharing economy principle of borrowing or renting assets (e.g., 3D printers for prototyping, head-mounted-displays for immersive design) owned by someone else [START_REF] Lanz | Social Manufacturing and Open Design[END_REF], which represents other major benefits not only from easier access to shared resources and lower usage cost but also from shared knowledge and skills.

Regarding social ideation, [START_REF] Zhan | Leveraging Social Media in New Product Development: Organisational Learning Processes, Mechanisms and Evidence from China[END_REF]'s findings show that while social media facilitates information search and knowledge acquisition, the degree of product ideation success mainly relies on the capacity to seek inspiring and reliable knowledge. This knowledge relies on both internal and external resources and information that are crucial for the innovativeness and success of NPD. They are pretty prolific in terms of identifying the key benefits grouped within three NPD stages, as shown in their Table 1. All the discussed benefits within PLC stages S1 to S3 that contribute to the overall benefit of the democratization of co-creation, design and manufacturing were included in Table 3. Regarding the other PLC stages from S4 marketing to S7 re-use, one of the major benefits is to avoid the traditional end-of-life leading to the continuous increase of waste. According to [START_REF] Lanz | Social Manufacturing and Open Design[END_REF], "the circular economy aims at reducing solid waste, landfill, and emissions through activities such as reuse, remanufacturing, and/or recycling". Other significant benefits about S4 social marketing include stronger customer engagement through participation to co-creation activities [START_REF] Pallot | A Holistic Model of User Experience for Living Lab Experiential Design[END_REF] and emotional attachment to co-designed products [START_REF] Hirscher | Social Manufacturing in the Fashion Sector: New Value Creation Through Alternative Design Strategies?[END_REF]. As for social collaborative commercialization, [START_REF] Zhan | Leveraging Social Media in New Product Development: Organisational Learning Processes, Mechanisms and Evidence from China[END_REF]'s findings show that social media platforms bring a significant benefit as they • Enhanced sense of belonging in customers.

• Increase the degree of customer satisfaction through their empowerment in decision-making.

• Ensure lower failure rates.

• Result in a higher rate of product acceptance/adoption meaning more successful products.

S1B1

Engaging all stakeholders in co-creation DIT Social Media for NPD (SPD) • Reduce the risk of adopting the wrong product concepts

• Allow rapid speed of communication • Generate deep emotional satisfaction with consumers as they co-create meaning by making a product with their own skills

• Make consumers satisfied due to their expended effort and success in doing something by themselves

• Increase customers' emotional attachment to their product while increasing its value, making it less likely to be discarded Rautela et al., 2020;[START_REF] Abhari | Experience First': Investigating Co-creation Experience in Social Product Development Networks[END_REF][START_REF] Abhari | Modeling Social Product Development Process, Technology, and Governance[END_REF][START_REF] Lanz | Social Manufacturing and Open Design[END_REF][START_REF] Zhu | Ideator Expertise and Co-Creator Inputs in Crowdsourcing Based New Product Development[END_REF][START_REF] Roberts | Mapping the Impact of Social Media for Innovation: The Role of Social Media in Explaining Innovation Performance in the PDMA Comparative Performance Assessment Study[END_REF][START_REF] Pallot | Living Lab Research Landscape: From User Centred Design and User Experience Towards User Co-Creation, First European Summer School "Living Labs[END_REF] S1B2: all references in Table 1 and [START_REF] Zhan | Leveraging Social Media in New Product Development: Organisational Learning Processes, Mechanisms and Evidence from China[END_REF]. S1B3: Rojo et al., 2018;[START_REF] Nguyen | Brand Innovation and Social Media: Knowledge Acquisition from Social Media, Market Orientation, and the Moderating Role of Social Media Strategic Capability[END_REF][START_REF] Hemsley | Knowledge and Knowledge Management in the Social Media Age[END_REF]. S2B1: Sigala, 2012;[START_REF] Piller | From Social Media to Social Product Development: The Impact of Social Media on Co-Creation of Innovation[END_REF][START_REF] Cooper | Agile-Stage-Gate Hybrids: The Next Stage for Product Development Blending Agile and Stage-Gate Methods can Provide Flexibility, Speed, and Improved Communication in New-Product Development[END_REF][START_REF] West | Open Innovation: The Next Decade[END_REF][START_REF] Du | Sustainability, Social Media Driven Open Innovation, and New Product Development Performance[END_REF][START_REF] Manyika | Open Data: Unlocking Innovation and Performance with Liquid Information[END_REF][START_REF] Zhan | Unlocking the Power of Big Data in New Product Development[END_REF][START_REF] Hoyer | Consumer Cocreation in New Product Development[END_REF][START_REF] Roberts | Mapping the Impact of Social Media for Innovation: The Role of Social Media in Explaining Innovation Performance in the PDMA Comparative Performance Assessment Study[END_REF]. S2B2: all references in Table 1 in [START_REF] Zhan | Leveraging Social Media in New Product Development: Organisational Learning Processes, Mechanisms and Evidence from China[END_REF]. S2B3: Hirscher et al., 2018;[START_REF] Mohajeri | The Impact of Social Manufacturing on the Value Chain Model in the Apparel Industry[END_REF]. S3B1: Alcácer, Cruz-Machado, 2019;[START_REF] Li | Additive Manufacturing, Prosumption and Construction Safety[END_REF][START_REF] Tofail | Additive Manufacturing: Scientific and Technological Challenges, Market Update and Opportunities Mater[END_REF][START_REF] Jiang | Social Manufacturing as a Sustainable Paradigm for Mass Individualization[END_REF]. S3B2: Niaros et al., 2017;[START_REF] Seravalli | Building Fabriken: Design for Socially Shaped Innovation[END_REF][START_REF] Anderson | Makers: The New Industrial Revolution[END_REF][START_REF] Ahmed | Smart Virtual Product Development (SVPD) System to Support Product Inspection Planning in Industry 4.0[END_REF][START_REF] Hirscher | Social Manufacturing in the Fashion Sector: New Value Creation Through Alternative Design Strategies?[END_REF][START_REF] Jiang | Social Manufacturing as a Sustainable Paradigm for Mass Individualization[END_REF][START_REF] Govindaraju | Measuring and Benchmarking of Policy Factors Influencing I4R: A Reality Check for ASEAN[END_REF][START_REF] Bressanelli | Reshaping the Washing Machine Industry through Circular Economy and Product-Service System Business Models[END_REF]. S3B3: Hirscher et al., 2018;[START_REF] Jiang | Social Manufacturing as a Sustainable Paradigm for Mass Individualization[END_REF][START_REF] Bocken | Product Design and Business Model Strategies for a Circular Economy[END_REF]. • Replace the desire to consume more.

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• Generate participants' experience with the feeling of "joy" in co-creating an individualized product.

• Change the prosumers' role to that of a teacher, advisor, and recommender for others as they increase their skills over time

S4B4

Make the commercialization more collaborative DIT approach, market testing and market commercialization • Create DIT-related segmentation through knowing how that new product will survive with # user communities

• Provide an opportunity to develop services for young, environmentally-aware consumers offering an emotional experience

• Decrease the effect of an emotional experience created by fashion purchases

• Offer practical and innovative ways of interacting with a wide range of consumers [START_REF] Dougherty | The Maker Movement[END_REF][START_REF] Henard | Why some New Products are More Successful than Others[END_REF][START_REF] Adams | The Future of Sustainability: Re-thinking Environment and Development in the Twenty-first Century[END_REF][START_REF] Ertz | Collaborative Consumption or the Rise of the Two-sided Consumer[END_REF][START_REF] Umezawa | Growth of Ecomaterials and Eco-Efficiency in Major Metallic Structural Materials[END_REF]. S4B2: Hirscher et al., 2018;[START_REF] Pallot | A Holistic Model of User Experience for Living Lab Experiential Design[END_REF]Rautela et al., 2020. S4B3: Hirscher et al., 2018;[START_REF] Pallot | A Holistic Model of User Experience for Living Lab Experiential Design[END_REF][START_REF] Herrera | Dynamics of Service Innovation Management and Co-Creation in Firms in the Digital Economy Sector[END_REF][START_REF] Mahmoud | Service Innovation and Customer Satisfaction: The Role of Customer Value Creation[END_REF]Rautela et al., 2020. S4B4: Hirscher et al., 2018;[START_REF] Pallot | A Holistic Model of User Experience for Living Lab Experiential Design[END_REF]; Rautela et al., 2020. S5B1: Henard, Szymanski, 2001;[START_REF] Nambisan | Designing Virtual Customer Environments for New Product Development: Toward a Theory[END_REF][START_REF] Glessner | The Value of Open Innovation for B2B Companies, Kalypso Viewpoints[END_REF]Rautela et al., 2020. S5B2: Roberts, Candi, 2014;[START_REF] Henard | Why some New Products are More Successful than Others[END_REF][START_REF] Wang | Does Customer Participation Hurt New Product Development Performance? Customer Role, Product Newness, and Conflict[END_REF][START_REF] Chang | The Joint Effects of Customer Participation in Various New Product Development Stages[END_REF][START_REF] Pienaar | A Framework for Successful New Product Development[END_REF][START_REF] Yang | Customers as Co-Creators: Antecedents of Customer Participation in Online Virtual Communities[END_REF]Rautela et al., 2020. S5B3: Kaplan, Haenlein, 2012;[START_REF] Ind | The Meanings of Cocreation[END_REF][START_REF] Fuller | Clarifying the Integration of Trust and TAM in E-commerce Environments: Implications for Systems Design and Management[END_REF][START_REF] Wang | Does Customer Participation Hurt New Product Development Performance? Customer Role, Product Newness, and Conflict[END_REF][START_REF] Abdolmaleki | The Relationship between Product Characteristics, Customer and Supplier Involvement, and New Product Development[END_REF][START_REF] Seyyedamiri | Social Content Marketing, Social Media and Product Development Process Effectiveness in High-Tech Companies[END_REF][START_REF] Sheng | NPD Speed Vs. Innovativeness: The Contingent Impact of Institutional and Market Environments[END_REF]Rautela et al., 2020. S6B1: Bocken et al., 2016;[START_REF] Gaiardelli | An Empirical Approach for After Sales Service Portfolio Planning[END_REF][START_REF] Go | Multiple Generation Life-Cycles for Product Sustainability: The Way Forward[END_REF][START_REF] Bressanelli | Reshaping the Washing Machine Industry through Circular Economy and Product-Service System Business Models[END_REF][START_REF] Santoso | How Open Innovation Strategy and Effectuation within Platform Ecosystem can Foster Innovation Performance: Evidence from Digital Multi-Sided Platform Startups[END_REF]. S7B1: Bressanelli et al., 2017. S7B2: Hirscher et al., 2018. S7B3: Hirscher et al., 2018. facilitate reflective learning and knowledge transformation within all PLC stages and especially during the product testing and launch process. As for the PLC stage S6 Social Logistic, [START_REF] Bressanelli | Reshaping the Washing Machine Industry through Circular Economy and Product-Service System Business Models[END_REF] argue that reverse supply chain and second-hand markets are not sufficiently developed yet for the circular economy to have a chance to succeed (Table 4).

Identified DIT Challenges and Drawbacks

In terms of drawbacks, as explained earlier, it appears that there is a certain scarcity of scholars studying the negative impacts of social media on NPD from social ideation to social manufacturing.

Nonetheless, [START_REF] Lanz | Social Manufacturing and Open Design[END_REF] seem to be the most prolific scholars to have identified social design and manufacturing drawbacks, especially in terms of product quality, mainly due to the lack of verified quality assurance. They also discussed other aspects such as respect for safety regulations, customer rights, and care about potential product defects, and conformity to IPRs in relating the fact that prosumers rarely perceive reverse engineering as a violation of patented products. They also criticize the lack of concern about environmental sustainability in production, especially in the case of additive manufacturing (3D printing), arguing that the impact in economic terms on sustainability as described in circular economy frameworks is rarely considered in the literature. Finally, they have identified another drawback considering respect for occupational safety regulations, especially in the case of locally distributed manufacturing. As shown in Table 5, there was a lack of identified drawbacks in the selected articles regarding stages S4, social marketing, and S5, social commercialization. [START_REF] Roberts | Mapping the Impact of Social Media for Innovation: The Role of Social Media in Explaining Innovation Performance in the PDMA Comparative Performance Assessment Study[END_REF] pointed out that using social media to engage customers in product ideation and design could result in imitative and unimaginative products due to mismatching technology readiness and development strategies that are unaligned to current customer requirements. There are other transverse drawbacks due to digitization, such as knowledge leakages [START_REF] Alberti | Oops I did it again! Knowledge Leaks with Start-ups in Open Innovation Networks[END_REF]. [START_REF] Franke | Value Creation by Toolkits for User Innovation and Design: The Case of the Watch Market[END_REF][START_REF] Aral | Creating Social Contagion through Viral Product Design: A Randomised Trial of Peer Influence in Networks[END_REF][START_REF] Zhu | Ideator Expertise and Co-Creator Inputs in Crowdsourcing Based New Product Development[END_REF][START_REF] Culnan | How Large US Companies can Use Twitter and Other Social Media to Gain Business Value[END_REF][START_REF] Chiu | Understanding Social Media in China[END_REF][START_REF] Roberts | Mapping the Impact of Social Media for Innovation: The Role of Social Media in Explaining Innovation Performance in the PDMA Comparative Performance Assessment Study[END_REF]. S2B1: Lanz, Järvenpää, 2019;[START_REF] Lewandowski | Designing the Business Models for Circular Economy -Towards the Conceptual Framework[END_REF][START_REF] Bressanelli | Reshaping the Washing Machine Industry through Circular Economy and Product-Service System Business Models[END_REF][START_REF] Bocken | Product Design and Business Model Strategies for a Circular Economy[END_REF][START_REF] Gaiardelli | An Empirical Approach for After Sales Service Portfolio Planning[END_REF][START_REF] Go | Multiple Generation Life-Cycles for Product Sustainability: The Way Forward[END_REF][START_REF] Sundin | Product Design for Product/Service Systems: Design Experiences from Swedish Industry[END_REF]. S3B1: Lanz, Järvenpää, 2019. S3B2: Lanz, Järvenpää, 2019. S3B3: Lanz, Järvenpää, 2019. S6B1: Bressanelli et al., 2017. S7B1: Bressanelli et al., 2017;[START_REF] Hirscher | Social Manufacturing in the Fashion Sector: New Value Creation Through Alternative Design Strategies?[END_REF].

XXIV

Identified Co-creation Challenges and XR Implementation Benefits

Regarding the enabling technologies, the analysis of selected articles focuses on immersive technologies, especially XR (Table 6), leaving analysis of the remaining identified enabling technologies like AM, BD, AI and IoT to future work.

It appears, as was the case some decades ago with CAD/CAM technologies facilitating the industrial design of products, that XR technologies greatly facilitate the immersive design of compelling experiences [START_REF] Pallot | Laval Virtual Vision 2025: Blurring the Lines between Digital and Physical Worlds[END_REF]. However, social immersion and distributed collaboration are emerging trends in the Immersive Virtual Environment (IVE) research context that have actually turned out to be hot research topics toward an Immersive Collaborative Environment (ICE) platform in which all stakeholders can be immersed. Empirical studies on the use of XR technologies have highlighted the positive impact of the use of IVE (VR/AR/MR) for stimulating imagination and creativity [START_REF] Fleury | Studying the Effects of Visual Movement on Creativity[END_REF][START_REF] Mille | Effects of Digital Tools Feature on Creativity and Communicability of Ideas for Upstream Phase of Conception[END_REF][START_REF] Gorisse | Effect of Avatar Anthropomorphism on Body Ownership, Attractiveness and Collaboration in Immersive Virtual Environments[END_REF] leading to an increase of fluency and originality of produced ideas. Other empirical studies have demonstrated the power of virtual prototyping within the ICE [START_REF] Pallot | ICE Breaking: Disentangling Factors Affecting the Performance of Immersive Co-creation Environments[END_REF][START_REF] Dupont | A Universal Framework for Systemizing the Evaluation of Immersive And Collaborative Performance[END_REF] and transverse drawbacks like cybersickness phenomena induced by immersive environments, as well as the fact that XR devices currently remain expansive.

Conclusion and Future Work

This study has several limitations inherited from the fact that previous relevant work might have been missed or wrongly discarded. This is due to the subjectivity of the selected articles considered as most relevant through the search keywords. The decision to group the challenges, benefits, and drawbacks within NPD PLC stages is also an arbitrary decision, even if extremely useful for avoiding the duplication of benefits. The identification of the NPD PLC stages is based on previous work; nonetheless, these selected PLC stages are not recognized as a standard among scholars. Despite the fact that we have used many keyword synonyms in the search process, some challenges, benefits, and drawbacks might have been missed as well. Further to this, despite the fact that we started by using an overall Google Scholar search in order to identify the most prolific databases, there might be other databases and potentially relevant articles that we have missed. [START_REF] Fleury | Studying the Effects of Visual Movement on Creativity[END_REF]S1B2: Guegan et al., 2016S1B3: Mille et al., 2020;[START_REF] Gasques | What you Sketch is What You Get: Quick and Easy Augmented Reality Prototyping with Pintar[END_REF][START_REF] Ibrahim | Comparison of CAD and Manual Sketching Tools for Teaching Architectural Design[END_REF][START_REF] Jackson | Lift-Off: Using Reference Imagery and Freehand Sketching to Create 3D Models in VR[END_REF][START_REF] Yang | Examining Creativity through a Virtual Reality Support System[END_REF][START_REF] Feeman | Exploration and Evaluation of CAD Modeling in Virtual Reality[END_REF]B1: Gorisse et al., 2020;[START_REF] Seyama | The Uncanny Valley: Effect of Realism on the Impression of Artificial Human Faces[END_REF]B2: Serras et al., 2020;[START_REF] Pallot | ICE Breaking: Disentangling Factors Affecting the Performance of Immersive Co-creation Environments[END_REF][START_REF] Dupont | A Universal Framework for Systemizing the Evaluation of Immersive And Collaborative Performance[END_REF]. B3: Mille et al., 2020;[START_REF] Eynard | Impact of Verbal Communication on User Experience in 3D Immersive Virtual Environments[END_REF][START_REF] Pallot | ICE Breaking: Disentangling Factors Affecting the Performance of Immersive Co-creation Environments[END_REF][START_REF] Dupont | A Universal Framework for Systemizing the Evaluation of Immersive And Collaborative Performance[END_REF]. B4: Jeong et al., 2020;[START_REF] Eynard | Impact of Verbal Communication on User Experience in 3D Immersive Virtual Environments[END_REF][START_REF] Pallot | ICE Breaking: Disentangling Factors Affecting the Performance of Immersive Co-creation Environments[END_REF][START_REF] Dupont | A Universal Framework for Systemizing the Evaluation of Immersive And Collaborative Performance[END_REF]. S2B1: Lee et al., 2019;[START_REF] Eynard | Impact of Verbal Communication on User Experience in 3D Immersive Virtual Environments[END_REF][START_REF] Pallot | ICE Breaking: Disentangling Factors Affecting the Performance of Immersive Co-creation Environments[END_REF][START_REF] Dupont | A Universal Framework for Systemizing the Evaluation of Immersive And Collaborative Performance[END_REF]. S2B2: Lee et al., 2019;[START_REF] Pallot | ICE Breaking: Disentangling Factors Affecting the Performance of Immersive Co-creation Environments[END_REF][START_REF] Dupont | A Universal Framework for Systemizing the Evaluation of Immersive And Collaborative Performance[END_REF]. S2B3: Calderon-Hernandez, et al., 2019;[START_REF] Eynard | Impact of Verbal Communication on User Experience in 3D Immersive Virtual Environments[END_REF][START_REF] Pallot | ICE Breaking: Disentangling Factors Affecting the Performance of Immersive Co-creation Environments[END_REF][START_REF] Dupont | A Universal Framework for Systemizing the Evaluation of Immersive And Collaborative Performance[END_REF] This study investigated the challenges, induced potential benefits, and possible drawbacks as well as enabling technologies to implement this renewed DIT approach. Regarding enabling technologies, this study was restricted to the analysis of challenges overcome by XR technologies and their induced benefits, as well as transverse drawbacks at the earlier stages of the NPD PLC. Overall, this study contributes to the required clarification of the DIT approach and implementation. It also contributes to bringing new knowledge to both scholars and practitioners interested in the democratization of innovation, design, and manufacturing as well as individualized products. The results confirm the uniqueness of this DIT approach, which stands at the crossroads of several phenomena, namely: (i) the 4 th industrial revolution (I4.0); (ii) the digitization era; (iii) the consumer trend toward individualized products; (iv) the democratization of innovation, design, and manufacturing through the digital economy and its satellites, such as the platform/sharing economy; (v) and the increased citizens' concern on sustainability driving the implementation of the circular economy. They also demonstrate the long list of challenges to be overcome to implement this DIT approach and induced benefits as well as possible drawbacks; though this study has revealed a lack of empirical studies that observe these negative impacts while there is a plethora of observations on positive impacts.

XXVIII

Last but not least, XD technologies appear to be an appropriate enabler of DIT implementation, especially at the ideation and design stages, thanks to the power of virtual prototyping, enabling stakeholders' ability to: (i) quickly reach a mutual understanding of an idea, its related concepts and usage scenario; (ii) anticipate the resulting UX; hence, the ability to deduct the degree of customer satisfaction and a willingness to adopt the represented solution; (iii) acquire the necessary knowledge by quickly learning by doing without any risk; (iv) follow a secured step-by-step process to fulfil a task. Finally, besides a SWOT study on the I4.0 implementation [START_REF] Calabrese | Evolutions' and 'Revolutions' in Manufacturers' Implementation of Industry 4.0: A Literature Review, A Multiple Case Study, and A Conceptual Framework[END_REF], we did not find any previous study on the identification of challenges, benefits, and drawbacks covering the same spectrum of implementation platform. Therefore, we had to identify and collect these within previous studies from different publication streams such as the more obvious ones within SPD and SM research communities, as well as less obvious ones within NPD and social media intersecting the digital economy, platform/sharing economy and I4.0, as well as immersive technologies.

In terms of drawbacks, besides the fact that there is a scarcity of empirical studies on negative impacts, we found some significant drawbacks such as the lack of suitable customer skills for appropriately contributing to design and manufacturing activities. This could result in imitative and unimaginative pre-published -Journal of Innovation Economics & Management 2022 XXXIII solutions, and transverse ones such as peoples' concern about ownership and respect for regulations [START_REF] Lanz | Social Manufacturing and Open Design[END_REF]. The DIT sustainability, individualization, and democratization approach looks promising for the fashion and furnishing business sectors, especially for fulfilling demand from young digital natives and sustainability-aware customers, as this is currently ongoing in the tourism sector in order to abandon the unsustainable mass tourism approach. In terms of future work, it would make sense to carry out surveys about DIT players' expectations (e.g., manufacturers, makers, designers, interior architects, marketers, consumers, prosumers) whatever the business sector. Such surveys would constitute the second step of a holistic appraisal, as the first step was the literature review that allowed us to identify the most relevant DIT implementation challenges, induced benefits, and drawbacks. Then, based on these two steps, a conceptual framework could be developed in order to obtain a comprehensive picture of DIT implementation, through enabling technologies (XR, BD, AI), including benefits and drawbacks as well as a better understanding of business opportunities and risks. Finally, an analysis of the remaining enabling technologies (AM, BD, AI) needs to be carried out in order to identify their particular induced benefits and drawbacks.

Figure 1 -

 1 Figure 1 -DIT approach objectives and targeted value elements (Extended by authors from an original diagram initiated by Marc Pallot during the INEDIT project proposal)

  pre-published -Journal of Innovation Economics & Management 2022 XIII XIV Journal of Innovation Economics & Management 2022 -pre-published Marc Pallot et al.

  Journal of Innovation Economics & Management 2022 -pre-published Marc Pallot et al.

  Journal of Innovation Economics & Management 2022 -pre-published pre-published -Journal of Innovation Economics & Management 2022 XXV What are the Challenges and Enabling Technologies

  Journal of Innovation Economics & Management 2022 -pre-published pre-published -Journal of Innovation Economics & Management 2022 XXIX What are the Challenges and Enabling Technologies

Table 1 -

 1 Characteristics of selected articles

A: App economy; C: circular economy; D: Digital economy; E: Experience economy; P: Platform economy; S: Sharing economy; Se: Service economy. pre-published -Journal of Innovation Economics & Management 2022 IX

Table 2 -

 2 Description of product life-cycle stages

	N°Stage	Description
	S1	Co-creation (Social Ideation)

Table 3 -

 3 Description of DIT stages 1 to 3 challenges and benefits

	Benefits
	Concepts
	Challenge
	St

  What are the Challenges and Enabling Technologies

		Ref			S2B1	S1B2 S2B2				S1B3
	© De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57)	St Challenge Concepts Benefits	• Enhance the organization's knowledge to be embedded in	the product R&D	• Develop innovative products S2 Social Co-Design • Generate new ideas • Ensure customer base growth • Solve problems and achieve competitive advantages Enabling innovation among designers, makers, prosumers & producers DIT Social Media for NPD (SPD) produce more data-driven products stakeholders • Utilize social media data and reporting capabilities to from external and online platforms perceptions virtual communities knowledge and Open forms of NPD, extracting creating products in isolation Sharing and • Deliver more valued products conversely to companies • Integrate its design programme with a variety of social media channels • Result in a community-powered social commerce platform • Rapid development of new products that have strong market attractiveness • Improve innovativeness and efficiency • Reduce costs • Ensure better adoption of products • Improve customer relationships • Enable consumers to become value co-creators through the entire value chain	• Generate new knowledge and apply to where it is required	for later use and integration DIT Social Media for	• Result in high levels of media-rich modalities for Increase Product NPD (Social Product	Sharing knowledge Organizational learning, DIT Social in Co-creation Media for NPD (SPD) collaboration • Offer a powerful means of knowledge acquisition and integration for organizational learning • Leverage social media to search for new knowledge Life-cycle Development), Open Design	• Provide multiple sources of knowledge through integration,	guiding to action	• Result in an in-depth understanding of relationships among	knowledge search patterns	© De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57)

pre-published -Journal of Innovation Economics & Management 2022 XV

•

  Make consumers more responsible by valuing their goods for longer, and slowing down consumption cycles S2B3 © De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57) © De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57) Marc Pallot et al.

				What are the Challenges and Enabling Technologies
		Ref	S3B1	S3B2			S3B3
	© De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57)	St Challenge Concepts Benefits pre-published -Journal of Innovation Economics & Management 2022 S3 Open Manufacturing Make the production systems more flexible, autonomous and collaborative (I4.0) DIT Additive Manufacturing, Open Manufacturing • Decrease data processing due to parts directly manufactured from CAD data files • Greater customization without extra tooling or manufacturing cost • Increase the capacity to manufacture complex geometries • Manufacturing of hollow parts (achieving less weight) or lattice structures • Maximization of material utilization for the "zero waste" approach • Smaller operational footprint toward manufacturing a large variety of parts • On-demand manufacturing and excellent scalability. Recycle used material (e.g., plastic, wood) Disrupt current mass production and mass customization Individualized Production, Democratized Manufacturing • Provide opportunities to re-organize manufacturing locally in a democratized and individualized production • Reduce manufacturing costs through the sharing of manufacturing resources among individuals within a makerspace or a FabLab • Easier input mode, self-production and assessment • Promote a decentralized and non-hierarchical structure of production within the sharing economy • Shift the economy toward the sharing economy through the diffusion of open hardware in manufacturing S1B1:	• Open access to makerspaces and production machines (e.g.,	FabLabs)	Democratize access DIT approach, • Validating production quality through successive product prototypes (e.g., 3D printing) to machines and FabLabs, Resource • Reducing resource flow through the design of longer-life environment respect Efficiency products or an extension of the product life	• Closing the resource loop, through the design of products XVII that are easy to reuse and recycle	© De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57)

XVI Journal of Innovation Economics & Management 2022 -pre-published

Table 4 -

 4 Description of DIT stages 4 to 7 challenges and benefits

		Ref						S4B1											S4B2
		Benefits	• Capture first-hand customers' feedback on	anticipated experience impacting positioning and	marketing mix	• Replace the traditional marketing motto from "Make	people want things" to "Make things people want"	• Changed product consumption habits in reflecting	people's willingness to undertake more sustainable	practices	• Increased ethical awareness in challenging product	consumption practices	• Reduce the fast disposal of product waste in	changing consumption practices	• Value emotionally when consumers engage	passionately with objects during co-creation	• Changed behavior of consumers and aspirations as	they feel more than just consumers through shared	experiences	• Contribute to building a story captured within the	made product	• Increased product value when participants achieve	deeper individualized person-product attachment	(personal memories)	• Create new business opportunities where a network	of people creates a new business logic	• Increased sustainability awareness
	© De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57)	St Challenge Concepts				S4 Social Marketing S5 Social Commerce facet and ethical awareness with environmental sustainable practices marketing mix aligned eXperience Design, positioning and DIT approach, Co-create product DIT and PD approaches, Product Co-create the Individualization, product's emotional Sustainable and economical facets development and	Collaborative Making		© De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57)

XX Journal of Innovation Economics & Management 2022 -pre-published Marc Pallot et al.

Table 5 -

 5 Description of DIT PLC stages challenges and drawbacks

	Drawbacks
	Concepts
	Challenge
	Stage

XXVI Journal of Innovation Economics & Management 2022 -pre-published Marc Pallot et al.

Table 6 -

 6 Description of DIT social ideation & co-design stages challenges and XR implementation benefits

	Benefits
	Concepts
	Challenge
	Stage

XXX Journal of Innovation Economics & Management 2022 -pre-published Marc Pallot et al. XXXII Journal of Innovation Economics & Management 2022 -pre-published Marc Pallot et al.

© De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57) © De Boeck Supérieur | Téléchargé le 21/10/2022 sur www.cairn.info (IP: 89.207.171.57)

(*) Engage external participants -through the use of social media -such as: independent designers, interior architects, makers and especially prosumers S1:Rautela et al., 2020;[START_REF] Abhari | Modeling Social Product Development Process, Technology, and Governance[END_REF][START_REF] Cascini | Exploring the Use of AR Technology for Co-Creative Product and Packaging Design[END_REF][START_REF] Zhan | Leveraging Social Media in New Product Development: Organisational Learning Processes, Mechanisms and Evidence from China[END_REF][START_REF] Lanz | Social Manufacturing and Open Design[END_REF][START_REF] Zhu | Ideator Expertise and Co-Creator Inputs in Crowdsourcing Based New Product Development[END_REF][START_REF] Roberts | Mapping the Impact of Social Media for Innovation: The Role of Social Media in Explaining Innovation Performance in the PDMA Comparative Performance Assessment Study[END_REF][START_REF] Mukhat | A Hierarchical Classification of Co-Creation Models and Techniques to Aid in Product or Service Design[END_REF]. S2: Rautela et al., 2020;[START_REF] Lanz | Social Manufacturing and Open Design[END_REF][START_REF] Aral | Creating Social Contagion through Viral Product Design: A Randomised Trial of Peer Influence in Networks[END_REF][START_REF] Zhu | Ideator Expertise and Co-Creator Inputs in Crowdsourcing Based New Product Development[END_REF][START_REF] Roberts | Mapping the Impact of Social Media for Innovation: The Role of Social Media in Explaining Innovation Performance in the PDMA Comparative Performance Assessment Study[END_REF][START_REF] Govindaraju | Measuring and Benchmarking of Policy Factors Influencing I4R: A Reality Check for ASEAN[END_REF][START_REF] Bressanelli | Reshaping the Washing Machine Industry through Circular Economy and Product-Service System Business Models[END_REF] S3: Lanz, Järvenpää, 2019;[START_REF] Ahmed | Smart Virtual Product Development (SVPD) System to Support Product Inspection Planning in Industry 4.0[END_REF][START_REF] Hirscher | Social Manufacturing in the Fashion Sector: New Value Creation Through Alternative Design Strategies?[END_REF][START_REF] Jiang | Social Manufacturing as a Sustainable Paradigm for Mass Individualization[END_REF][START_REF] Gogineni | User Stories of Collaborative Engineering needs[END_REF][START_REF] Govindaraju | Measuring and Benchmarking of Policy Factors Influencing I4R: A Reality Check for ASEAN[END_REF][START_REF] Bressanelli | Reshaping the Washing Machine Industry through Circular Economy and Product-Service System Business Models[END_REF][START_REF] Yin | Understanding Data-Driven Cyber-Physical-Social System (D-CPSS) Using a 7C Framework in Social Manufacturing Context[END_REF][START_REF] Naghshineh | Social Impacts of Additive Manufacturing: A Stakeholder-Driven Framework[END_REF]. S4: Dougherty, 2012;[START_REF] Ertz | Collaborative Consumption or the Rise of the Two-sided Consumer[END_REF][START_REF] Umezawa | Growth of Ecomaterials and Eco-Efficiency in Major Metallic Structural Materials[END_REF][START_REF] Dietrich | Virtual Reality in Social Marketing: A Process Evaluation[END_REF][START_REF] Cheung | The Effects of Customer Involvement on Perceived Service Performance and Word-Of-Mouth: The Mediating Role of Service Co-Creation[END_REF][START_REF] Rautela | Deconstructing the Seven Cs of Social Media: A Summative Perspective[END_REF]. S5: Glessner, 2012;[START_REF] Roberts | Leveraging Social Network Sites in New Product Development: Opportunity or Hype?[END_REF][START_REF] Wang | Does Customer Participation Hurt New Product Development Performance? Customer Role, Product Newness, and Conflict[END_REF][START_REF] Chang | The Joint Effects of Customer Participation in Various New Product Development Stages[END_REF][START_REF] Pienaar | A Framework for Successful New Product Development[END_REF][START_REF] Yang | Customers as Co-Creators: Antecedents of Customer Participation in Online Virtual Communities[END_REF] Rautela et al., 2020;[START_REF] Liu | The Usage of Social Media in New Product Development Process: The Benefits and the Challenges[END_REF][START_REF] Cheung | The Effects of Customer Involvement on Perceived Service Performance and Word-Of-Mouth: The Mediating Role of Service Co-Creation[END_REF]. S6: Santoso et al., 2020;[START_REF] Gogineni | User Stories of Collaborative Engineering needs[END_REF][START_REF] Cheng | Enhancing the Performance of Supplier Involvement in New Product Development: The Enabling Roles of Social Media and Firm Capabilities[END_REF][START_REF] Wang | Leveraging Sustainable Design Practices through Supplier Involvement in New Product Development: The Role of the Suppliers' Environmental Management Capability[END_REF]. S7: Bressanelli et al., 2017;[START_REF] Hirscher | Social Manufacturing in the Fashion Sector: New Value Creation Through Alternative Design Strategies?[END_REF][START_REF] Govindaraju | Measuring and Benchmarking of Policy Factors Influencing I4R: A Reality Check for ASEAN[END_REF][START_REF] Corona | Towards Sustainable Development through the Circular Economy: A Review and Critical Assessment on Current Circularity Metrics[END_REF][START_REF] Wang | Leveraging Sustainable Design Practices through Supplier Involvement in New Product Development: The Role of the Suppliers' Environmental Management Capability[END_REF][START_REF] Ford | Additive Manufacturing and Sustainability: An Exploratory Study of the Advantages and Challenges[END_REF] Gordo Lopez et al., 2021.


Muralikrishnan Srinivasan

Sotiris Skaperas

Arsenia Chorti

On the Use of CSI for the Generation of RF Fingerprints and Secret Keys

This paper presents a systematic approach to use channel state information for authentication and secret key distillation for physical layer security (PLS). We use popular machine learning (ML) methods and signal processing-based approaches to disentangle the large scale fading and be used as a source of uniqueness, from the small scale fading, to be treated as a source of shared entropy secret key generation (SKG). The ML-based approaches are completely unsupervised and hence avoid exhaustive measurement campaigns. We also propose using the Hilbert Schmidt independence criterion (HSIC); our simulation results demonstrate that the extracted stochastic part of the channel state information (CSI) vectors are statistically independent.

I. INTRODUCTION

The renewed interest in physical layer security (PLS) technologies for sixth-generation (6G) systems stems from the emergence of massive-scale Internet of things (IoT) networks, which have an extensive range of non-functional (security) constraints as well as computational, power and energy limitations, delay and latency constraints, etc. [START_REF] Zou | A survey on wireless security: Technical challenges, recent advances, and future trends[END_REF], [START_REF] Al-Fuqaha | Internet of things: A survey on enabling technologies, protocols, and applications[END_REF]. One of the most popular physical layer security (PLS) techniques is for the transmitter (Alice) and the receiver (Bob) to extract a key from the wireless channel realisations exploiting the common randomness of the wireless channels during the channel coherence time [START_REF] Chorti | Physical layer security: a paradigm shift in data confidentiality[END_REF], [START_REF] Shakiba-Herfeh | Physical Layer Security: Authentication, Integrity, and Confidentiality[END_REF].

Wireless channels consist of two parts, namely the largescale fading, which includes the path loss and shadowing, and a small-scale multipath fading [START_REF] Goldsmith | Wireless communications[END_REF]. The path loss is deterministic and therefore is not secure for key generation [START_REF] Zhang | Key generation based on large scale fading[END_REF]. Shadowing limits the key generation performance due to its slow temporal variation [START_REF] Zhang | A new frontier for iot security emerging from three decades of key generation relying on wireless channels[END_REF]. However, the small-scale fading is usually unpredictable and is a valuable source of key generation. In the 6G era of massive and critical IoT, lightweight PLS schemes are now considered. In this contribution, we demonstrate that the wireless communication medium offers the platform for providing building blocks for two cornerstone security operations:

1) Authentication through RF fingerprinting. In particular, large scale fading that is largely predictable can be treated as a source of uniqueness (fingerprint). Importantly, large scale fading effects (path loss and shadowing) are directly related to positioning, allowing for localisation to be used as a second factor of (soft) authentication in multi-factor authentication protocols;

2) Symmetric secret key generation (SKG), i.e., unpredictable variations in the channel state information (CSI) due to small scale fading in the wireless channel, that can be treated as a source of entropy to distil keys from shared area. We note in passing that in standard cryptography, the concept of "unpredictability" is central to evaluating the quality of pseudo-random number generators.

In essence, the quality of a pseudo-random source is evaluated against the ability to build next bit predictors by a powerful adversary having access to all effective algorithms (i.e., algorithms that can run in polynomial time). A secure key generation depends on three principles: channel reciprocity between Alice and Bob, spatial decorrelation and temporal variations [START_REF] Zhang | A new frontier for iot security emerging from three decades of key generation relying on wireless channels[END_REF]. Spatial decorrelation is particularly important because a passive eavesdropper (Eve) present close to the legitimate users can generate the duplicate keys by exploiting the shared spatial correlation. Based on Jakes' model, the channel will be uncorrelated when a third party is located half-wavelength away [START_REF] Goldsmith | Wireless communications[END_REF].

Under this assumption, to facilitate reconciliation, the authors of [START_REF] Li | High-agreement uncorrelated secret key generation based on principal component analysis preprocessing[END_REF] carry out a theoretical study on pre-processing algorithms such as principal component analysis (PCA) to establish a high-agreement uncorrelated secret key by retaining only the first few dominant components of the channel vectors. The core hypothesis in this work is that the PCA can improve the cross-correlation between the channel measurements of Alice and Bob because the noisy observation is removed by only keeping principal components.

However, experimental results show that a half-wavelength distance spatial decorrelation is valid only in rich scattering environments [START_REF] Edman | On the security of key extraction from measuring physical quantities[END_REF]- [START_REF] Ji | Vulnerabilities of physical layer secret key generation against environment reconstruction based attacks[END_REF]. As a counter-example, in line-of-sight conditions, retaining the first few dominant principal components is equivalent to retaining the eigenvectors related to the predictable large-scale features; therefore, such an approach would be counterproductive in these conditions.

The second important point is that in literature, statistical tests evolve around correlation measures. There is no guarantee that spatial or temporal decorrelation implies independence. Note that in most works of the existing literature, SKG is performed without systematically removing the predictable spatially or temporally correlated component of the wireless channel coefficients [START_REF] Li | High-agreement uncorrelated secret key generation based on principal component analysis preprocessing[END_REF], [START_REF] Peng | Secret key generation based on estimated channel state information for tdd-ofdm systems over fading channels[END_REF], [START_REF] Mitev | Authenticated secret key generation in delay-constrained wireless systems[END_REF].

A secure key generation process is instrumental for confidentiality and integrity, e.g. when used with symmetric key encryption algorithms. However, secret key generation cannot as such be used for the authentication [START_REF] Zhang | A new frontier for iot security emerging from three decades of key generation relying on wireless channels[END_REF]; authentication requires a predictable and verifiable source of uniqueness, such as the node location and RF fingerprinting. In [START_REF] Wang | Physical-layer authentication for wireless security enhancement: current challenges and future developments[END_REF]- [START_REF] Fang | Learning-aided physical layer authentication as an intelligent process[END_REF] physical layer authentication approaches are proposed by exploiting different channel parameters. To the best of our knowledge, only a few papers such as [START_REF] Shi | Ask-ban: Authenticated secret key extraction utilizing channel characteristics for body area networks[END_REF], [START_REF] Shi | Mask-ban: Movement-aided authenticated secret key extraction utilizing channel characteristics in body area networks[END_REF] aim to achieve both device authentication and SKG simultaneously in the context of body area networks.

Despite the immense bibliography in both RF fingerprinting and SKG, a systematic treatment of the CSI as both a source of uniqueness and a source of entropy is missing. Therefore, in this contribution, we aim at filling this gap and presenting machine learning (ML) and signal processing based approaches to disentangle the large scale fading (source of uniqueness) from the small scale fading (source of shared entropy), inspired by the popular channel charting methods introduced in [20]- [START_REF] Lei | Siamese neural networks for wireless positioning and channel charting[END_REF]. Note that these methods are entirely online and do not require any training samples. To ensure secrecy, we not only enforce spatial decorrelation between locations but also guarantee a much stronger spatial independence using the dvariable Hilbert-Schmidt independence criterion (dHSIC) [START_REF] Pfister | Kernel-based tests for joint independence[END_REF].

II. PRE-PROCESSING USING PCA

Consider single-antenna legitimate nodes, referred to as Alices and a base station referred to as Bob, over a multicarrier fading channel. Alices' spatial locations are denoted by {x n } N n=1 n = 1, . . . , N , where {x n } N n=1 ∈ R L and L denotes the spatial dimensions considered (typically L = 2). Let the channel function mapping the spatial locations to the M × 1 CSI vectors {h n } N n=1 denoted by H : R L → C M , where M is the number of orthogonal frequency division multiplexing (OFDM) subcarriers. Alice and Bob exchange pilot signals so that their respective observations can be modelled as

y nu = h n x + n nu , n = 1, . . . , N , u ∈ {a, b}, (1)
where the index a denotes Alice, b denotes Bob; n na and n nb are complex circularly symmetric Gaussian noise variables and the pilot symbols x are chosen from binary phase-shift keying (BPSK) constellation. The channel estimates at Alice and Bob, respectively, are denoted by ĥna = y na and ĥnb = y nb for n = 1, . . . , N . Inspired from the popular channel charting methods introduced in [START_REF] Studer | Channel charting: Locating users within the radio environment using channel state information[END_REF], we learn the functional mapping that captures the dominant predictable spatially correlated components of the CSI vectors. Among the various approaches like principal component analysis (PCA), autoencoders, etc., for performing channel-charting, in this paper, we focus primarily on PCA to determine the first D dominant components from each of the M dimensional channel vector [START_REF] Studer | Channel charting: Locating users within the radio environment using channel state information[END_REF]. Let Ĥu = ĥ1u , • • • , ĥNu denote the observed channel. PCA transforms the observed M × N matrix Ĥu into the lower dimension, D-dimensional channel matrix Ŵu , where D is the new number of variables and D < M . The PCA transformation is given by the M × D matrix U , such that,

Ŵu = Ĥu U D (2)
where U D is the matrix whose columns are the eigenvectors of the matrix Cov H u , corresponding to the dominant D eigenvalues.

The inverse PCA gives us the reconstructed form of the observed channel, based on the first D principal components (PCs) as follows,

Hu = Ŵu U D , (3)
where Hu = h1u , • • • , hNu for u ∈ {a, b} is a N × M matrix. Finally, the residuals of the inverse PCA are given by,

ẑnu ( D) N n=1 = { ĥnu -hnu } N n=1 , for u ∈ {a, b}. (4)
where { hnu } N n=1 , considering the structure of ( 4), can also be called as the predictable part of the observed channel.

To efficiently decompose (4) in terms of the predictable and the unpredictable part, the number of PCs D have to be chosen such that the residuals are uncorrelated and independent. In the following subsections we evaluate the spatial correlation and independence of the residuals ẑnu ( D) N n=1 by means of Pearson correlation coefficient and dHSIC. If the residuals are uncorrelated, or more strongly, if they are independent, implying that their behaviour is also unpredictable, they can be used for SKG and withstand passive eavesdropping attacks.

A. Correlation Coefficient

The straightforward metric to measure the degree of spatial decorrelation of the residuals between locations is the Pearson correlation coefficient. Given a pair of residuals ẑn1u and ẑn2u at two locations n 1 and n 2 respectively, the Pearson correlation coefficient is given by

ρ u (n 1 , n 2 ) = E ẑn1u -E ( ẑn1u ) E ẑn2u -E ( ẑn2u ) σ n1u σ n2u , (5)
where σ n1u and σ n2u are the respective standard deviations.

B. Independence Criterion

Note that the Pearson correlation coefficient assumes the presence of a linear relationship between the residuals. Furthermore, low values of the correlation coefficient do not necessarily mean low non-linear relationship between the residuals. Therefore, a second approach that considers the non-linear forms of dependence between the residuals is crucial. In this sub-section we explore dHSIC, an M -dimensional criterion to distinguish if the multivariate random variables (RV) are mutually independent [START_REF] Pfister | Kernel-based tests for joint independence[END_REF]. The test applies a positive-definite kernel on the M -dimensional RV and maps its distribution into the reproducing kernel Hilbert space. The RVs are mutually independent if and only if the square distance of the transformed RVs is (close to) zero. More precisely, Z = z 1 , • • • , z N be an M × N matrix based on the observations of the Mdimensional whereas the alternative

z i = [z i 1 , • • • , z i M ] T for i ∈ [1, • • • , N ]. The null hypothesis indicates that the z i for i ∈ [1, • • • , N ] are mutually independent, H 0 : F z 1 ,••• ,z N = F z 1 • • •F z N (6)
H A : F z 1 ,••• ,z N = F z 1 • • •F z N (7)
denotes that Z consists of at least two dependent vectors. An estimator dHSIC M of the statistical functional is as follows [25, Def 2.6]:

dHSIC M (Z) = 1 M 2 M i,j=1   N l=1 1 * K l ij   + 1 M 2N N l=1   M i,j=1 K l ij   - 1 M N +1 M i,j=1   N l=1 1 * 1 M K l ij   , (8)
where the operator * denotes the Hadamard product and 1 M is an M × 1 vector of ones. Also, , where med(.) is the median heuristic. Under the null hypothesis the asymptotic behaviour of dHSIC M is given by [25, Theorem 3.1],

K l = K l ij = k l (x i , x j ) ∈ R M ×M is the Gram matrix of the positive semi-definite Gaussian kernel k l , defined ∀x i , x j ∈ R by, k l = exp   - x i -x j 2 σ 2   ,
N dHSICM d -→ 2N 2 ∞ j=1 αiW 2 i , N -→ ∞, (9)
where d -→ denotes convergence in distribution, (a i : i ∈ N) are constants and (W i : i ∈ N) is an independent and identically distributed sequence of standard normal random variables. Hence, to obtain the critical values of H 0 we need to approximate equation [START_REF] Edman | On the security of key extraction from measuring physical quantities[END_REF]. Based on [START_REF] Pfister | Kernel-based tests for joint independence[END_REF], we implement the permutation test by constructing the re-sampling distribution function dHSIC Z , where Z = r 1 (z 1 ), • • • , r N (z N ) , where r 1 , • • • , r N are random resamplings without replacement. Finally, the critical value CV for a specific significance level α is given by the qth element of the vector D HSIC that contains the B Monte-carlo realisations of dHSIC( Z) in the increasing order. In other words, CV α = D HSIC q , and

q = (B + 1)(1 -α) + B i=1 1 { dHSIC(Z)= dHSIC( Zi )} (10)
if q B and ∞ otherwise. The operator . denotes the ceiling function.

III. EXPERIMENTAL RESULTS

To perform simulations, we obtain the CSI from N = 400 equi-distant (say 10 m) spatial locations within a square area on the ground, between x = 100 and x = 290 and y = -100 and y = 90 and the receiver at the location (x, y, z) = (0, 0, 10) for M = 32 sub-carriers, starting from a frequency of 2 GHz, a sub-carrier spacing (SCS) of SCS = {15, 30, 60, 100, 1000} KHz, using the popular Quadriga channel models [START_REF] Jaeckel | Quadriga: A 3-d multi-cell channel model with time evolution for enabling virtual field trials[END_REF].

First, we illustrate the effect of pre-processing, for a channel with SCS = 100 KHz and SN R = 50 dB. Fig. 1 (a) represents the magnitude of the observed channel, and Fig. 1 (b) represents the magnitude of the predictable part across the 400 locations for all the 32 subcarriers. Note that the removal of the predictable part of the channel, which is shown to model the observed channel faithfully, results in the apparent independence of the residuals in Fig. ?? (c).

In Table I, we determine the average correlation coefficient of the residuals across the locations in a neighbourhood for SN R = {10, 30, 50} dB and D = {1, 2, 3, 4, 8}. Note that, across all values of SCS and SNR, the correlation coefficient decreases with the removal of more dominant components D. However, the decrease is less pronounced in SCS ≥ 100KHz because of the frequency selective nature of the channel response across the subcarriers. Therefore, more dimensions are required to characterize and remove the predictable part of the CSI. On the other hand, with an increase in the noise power, the correlation coefficient decreases. However, this may lead to an increase in the mismatch probability between legitimate users. In order to ensure that the residual sequence is completely unpredictable, we also check if ẑnu ( D) 400 n=1 are independent across the subcarriers. In Table II, we tabulate the rejection rate of the null hypothesis of independence applying the HSIC across the locations in a neighbourhood. Like the mean correlation coefficient, the rejection rate decreases with a decrease in the SCS and SNR.

To verify the independence between the 32subcarriers at each of the locations, we depict the average critical value and the average test statistic value of the dHSIC in Fig. 2. Similar to the case of spatial decorrelation and independence of locations in Tables I andII, the features also get disentangled from each other with an increase in D. The decrease is more pronounced as the number of D increases. More precisely, even for D = 1 the dependency between the subcarriers is strong only for SCS = 60 dB and specific values of SN R, while for D 3 strong dependence exists only for SCS = 1000 and SN R = 50 dB. Furthermore, as shown in Fig. 1, there is a strong dependence among the subcarriers for the observed channel for SN R 30 and all chosen CSI values. Therefore, the implementation of the PCA-based preprocessing step seems to decrease the dependency between the subcarriers efficiently.

IV. CONCLUSIONS AND FUTURE WORK

In this paper, we have shown that it is possible to employ unsupervised learning to separate the predictable and unpredictable components of the CSI to perform RF fingerprinting and SKG. In practice, the first two or three principal PCA components suffice to capture most of the predictable part of the CSI. In future work, we propose to estimate the amplitudes using ARMA modelling [START_REF] Yuan | Machine learning-based channel prediction in massive mimo with channel aging[END_REF], [START_REF] Wu | Channel prediction in high-mobility massive mimo: From spatio-temporal autoregression to deep learning[END_REF] that could separate the deterministic and the non-deterministic part of a zero-mean covariance stationary process as an approximation of the Wold representation theorem. Also, we propose to use other ML techniques like autoencoders with input layers of convolutional neural networks and long short-term memory networks to capture the spatio-temporal dynamics.

Fig. 1 :

 1 Fig. 1: The a) observed, b) predictable and c) residuals part of the CSI, for SCS = 100 KHz, SN R = 50 dB and D = 3.

  Residual for D = 3 statistic critical (e) Residual for D = 4 statistic critical (f) Residual for D = 8

Fig. 2 :

 2 Fig. 2: log(dHSIC) of the test statistic and the critical values across the 32 subcarriers, for SCS = {15, 30, 60, 100, 1000} KHz and SN R = {10, 30, 50} dB.

TABLE I :

 I PCA: Mean Correlation coefficient across across the 9-nearest neighbours of every location.

	SNR			10 dB		30 dB		50 dB
	SCS ( KHz)	15	30	60 100 1000 15	30	60 100 1000 15	30	60 100 1000
	Observed channel 0.25 0.25 0.25 0.31 0.59 0.34 0.61 0.65 0.88 0.74 0.9 0.97 0.98 0.98 0.74
	D = 1	0.23 0.24 0.24 0.24 0.27 0.23 0.32 0.25 0.51 0.51 0.52 0.85 0.85 0.95 0.54
	D = 2	0.24 0.23 0.23 0.24 0.25 0.24 0.24 0.24 0.24 0.51 0.24 0.26 0.24 0.46 0.57
	D = 3	0.24 0.23 0.23 0.24 0.24 0.24 0.24 0.24 0.24 0.42 0.24 0.24 0.23 0.24 0.59
	D = 4	0.24 0.24 0.23 0.23 0.24 0.24 0.23 0.24 0.24 0.31 0.24 0.24 0.24 0.24 0.58
	D = 8	0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.23 0.24 0.26

TABLE II :

 II Rejection rate of the null hypothesis of independence applying the dHSIC across the 9-nearest neighbours of every location.

						SNR			10 dB	30 dB	50 dB
						SCS ( KHz)	15	30	60 100 1000 15	30	60 100 1000 15	30	60 100 1000
					Observed channel 0.05 0.04 0.08 0.03 0.41 0.05 0.41 0.13 0.88	1	0.72 1	1	1	1
					D = 1				0.05 0.04 0.05 0.05 0.18 0.05 0.3 0.06 0.86	1	0.92 0.98 0.98 1	1
					D = 2				0.02 0.06 0.04 0.05 0.05 0.04 0.04 0.03 0.07 0.98 0.05 0.06 0.04 0.56	1
					D = 3				0.04 0.05 0.04 0.05 0.05 0.04 0.04 0.04 0.07 0.59 0.04 0.04 0.05 0.04	1
					D = 4				0.06 0.04 0.05 0.04 0.06 0.06 0.05 0.05 0.04 0.16 0.02 0.04 0.04 0.06	1
					D = 8				0.05 0.06 0.05 0.04 0.04 0.04 0.03 0.04 0.06 0.09 0.03 0.04 0.05 0.04 0.1
	0	50	100	150	200	250	300	350	400