# Design Principles of a Mixed-Reality Shopping Assistant System in Omnichannel Retail
## 1 Introduction  
The retail sector has been undergoing constant changes, including the transition towards omnichannel retailing, where retail firms are challenged to offer customers a holistic and seamless customer experience [1]. Omnichannel retailing aims to seamlessly integrate various retail channels, such as physical stores and online and mobile commerce platforms, into a single, seamless, and personalized shopping experience [2]. Traditional retailers have shown limited competence in providing these shopping experiences to contemporary customers, which poses the problem of deploying the omnichannel retail model [3; 4; 5]. One of the various solutions to push the omnichannel transition is implementing digital technologies such as immersive displays, wearables, and smartphones at different stages along the customer journey, i.e., the search, decision-making, purchase, and post-purchase phases, to provide a better shopping experience [6]. In the pre-purchase phase, customers seek information about the product, its functionalities, and the brand through online shopping assistant systems such as Google or Amazon [7]. Shopping assistant systems that leverage the functionalities of a digital technology to combine the functionalities of both physical and digital retail can deliver a holistic shopping experience along the pre-purchase phase and help them to facilitate the purchase. Even though smartphones are currently the most popular customer-owned device, they require an unnatural posture when interacting with digital or physical objects in the environment and require the engagement of hands at all times. This leads to poor focus and attention towards the surrounding environment, raises safety issues, and creates a poor experience [8; 9]. Immersive display technologies such as mixed-reality (MR)-based head-mounted displays (HMDs) have the potential to overcome these interaction limitations through hands-free, heads-up interactions, and free movement while interacting with digital and physical objects [10]. These devices have been suggested as a technology megatrend that can create seamless consumer experiences across channels; several researchers have addressed this application of MR devices at the physical point-of-sale (PoS) or in the form of smart mirrors, for example [2; 11; 12; 13]. In addition to the motivation in academia, the retail industry has started to embrace immersive technologies, with applications such as in IKEA stores [14]. Furthermore, immersive HMDs are expected to diffuse into the market for commercial use; the market revenue for immersive technology hardware and software will accelerate to USD 5 billion in 2023 [15]. Consequently, the increasing maturity and development of MR-based HMDs such as the Microsoft (MS) HoloLens have great potential to be affordable and adopted by consumers in the near future [16]. Hence, the first aim of this study was to demonstrate how MR technology can be leveraged in retail by proposing a novel MR-enabled shopping assistant system, using MS HoloLens as the archetype. The system is designed as a potential global shopping platform (such as Amazon) offering all types of products. Customers can benefit from the MR shopping assistant in a typical shopping situation (e.g., at the physical point-of-sale), on the go, or at home. The present literature lacks a clear understanding of customer perceptions towards MR-enabled shopping applications and specific design principles based on these perceptions. Hence, we posed the following research question: Which principles need to be considered in the design of an MR shopping assistant for omnichannel retail? To answer this research question, we investigated users' perceptions through 35 interviews after technology interactions in a laboratory experiment. Based on the user's feedback and the collected literature to develop the MR shopping assistant, we provide a set of preliminary design principles for MR shopping applications that aim to offer designers a set of reusable solutions for future developments of such systems.