## 1 Introduction
### Mobility as a Service  
Recently, Mobility as a Service (MaaS) has attracted great attention from both industry and academia in transport-related fields. Initially, [PERSON] proposed the concept of MaaS to integrate all-in transportation services based on user demand [4], which is similar with the phone plan offered by operators. Subsequently, many MaaS service models have been deployed in North America, Oceania and Europe, such as UbiGo in Sweden, SMILE in Austria, EMMA in Montpellier, Moovel in Germany, and SkedGo in Australia, etc. [5; 6; 7; 8; 9]. Those service models try to relieve urban traffic congestions [10] and residents' travel pressure [11], encourage shared transport mode [12] and low-carbon travel [13], and increase the rural mobility [14] etc., which contribute to sustainable transportation in an environmentally-friendly way. MaaS intends to offer ticketless [15] and integrated transport solutions through combining private cars, public transports, shared travels and walking [16; 17]. In order to meet users' expectations, it requires that MaaS should be user-friendly [18] and the service providers need to understand users' preferences. The detailed implementations to please the target customers include: (1) preseting the preference options within the application, e.g., desired traveling mode, time spending, cost or special needs (e.g., infant and the disabled) [19]; (2) utilizing users' cumulative behavior data from mobile terminals [16] and their associated social media accounts [20]. In this way, the decision-making and prediction will be performed more easily to further satisfy end users' demands. Moreover, the relatively flexible travel and payment solutions enable consumers to choose the desired plan from all-inclusive service packets at will [13; 21]. Depending on the digital platform, MaaS service aggregates numerous mobile applications [8; 22; 23], including the functionalities of planning [10], trip creation and management [24], ordering and payment [25; 26], and real-time trip information [27] (e.g., weather forecast [20], road condition [28]). Whim App operated by MaaS Global is the first commercialised solution to provide mixed transport and travel packages since 2016 ([[https://whimapp.com](https://whimapp.com)]([https://whimapp.com](https://whimapp.com))). By integration in a single interface, a variety of requirements can be satisfied on an one-step platform [29]. While the end users can use single account [30] to pay the selected plan integrated with multiple transport modes, e.g., car-sharing, car rental, metro, rail, bus, bike-sharing, and taxi via the subscription of on-demand instant purchase and affordable monthly package [31; 32]. There is no denying that Information and Communications Technology (ICT) plays a vital role to support the MaaS functionality and quality of service (QoS), such as mobile network [20], edge computing [33; 34] and Internet of Things (IoT) [35]. In other words, MaaS combines business model with ICT to realize technology-enabled mobile service management [36; 37]. Therefore, we can see that the MaaS solution is technique-sensitive and will evolve along with the development of more sophisticated wireless and intelligent technologies. A series of MaaS solutions or models for the transportation scenarios have been proposed, while the MaaS ecosystem is initially formed. The partners consist of transport operators [38; 39], payment providers [28], data providers [8; 17], software developers [40], ICT and platform providers [38; 41] and etc. With the evolution of MaaS, new services and models can be developed and added to the MaaS ecosystem [18], especially when new partners have the background of technical innovation. We think that the current MaaS ecosystem still has a modified potential and some existing partners need to improve the QoPE by vehicle-mounted applications. In addition to basic services of the MaaS (e.g., multi-transport mode planning, routing, and mobile payment, etc.