Terminal mode provides solutions to some of the problems of the iPod Out model while keeping many of its advantages. As with the iPod Out model, with terminal mode applications reside in the smartphone, connectivity between the head unit and the smartphone is provided by USB or Bluetooth, and connectivity to the cloud is provided by the smartphone.
Figure 7: Terminal mode replicates the smartphone HMI on the head unit, which has some control over how and where it is displayed.
Unlike the iPod Out model, however, the smartphone does not simply push content out through the head unit to speakers and screens. Instead, the smartphone acts as a server to the head unit's VNC (Virtual Network Computing) client. This client replicates the smartphone's HMI, which may be modified for in-vehicle use, and controls the applications on the smartphone through this replicated HMI.
Figure 6: Terminal mode uses a VNC client on the vehicle head unit, and a server on the smartphone.
The advantages of terminal mode include, like the iPod Out model, simplicity and user familiarity with the HMI. Other advantages include:
Control — the vehicle's infotainment HMI has control over scale and position of elements in the display, though not of content of these elements. For instance, the vehicle's HMI can instruct the VNC client to scale the display from the smartphone to fit a portion of the in-vehicle display, say, navigation instructions into a corner of the infotainment display.
Non-proprietary — terminal mode can be implemented with any smartphone. It is not limited to a specific vendor's products, though work is of course required to support different smartphone designs.
Applications and features — terminal mode can support whatever applications and features are available for the supported smartphones.
Terminal mode carries many — but not all— of the same disadvantages as the iPod Out model, plus some additional drawbacks:
Usability — the HMI designed for a smartphone is replicated on the vehicle infotainment system's display, and may be difficult to use.
Safety — even with modifications, the HMI is not designed for in-vehicle use; it may thus distract the driver and even be dangerous.
Dependency — terminal mode is completely dependent on the smartphone to run applications and to access the cloud.
Retrofits — although the protocol supports applications' displaying vehicle-specific HMIs, retrofitting applications is a significant undertaking. It might be easier to simply build a new HMI.
The remote skin model can be summed up as terminal mode with tailored clothes. Instead of replicating the smartphone application-specific HMI, the vehicle infotainment system uses its own lightweight HMI. This HMI uses a TCP/IP connection to communicate with the smartphone over Bluetooth or USB. From the perspective of the smartphone, where the applications run, this lightweight HMI (or skin) is remote.
Figure 8: The remote skin model hands control of the HMI over to the in-vehicle system.
The remote skin model offers some advantages over terminal mode, as well as compared to other designs that place more responsibility on the vehicle head unit. These include:
Simplicity — the remote skin doesn't need to implement all application logic. It merely needs to provide the HMI veneer, and is thus cheaper and faster to build, test and implement than a complete application.
HMI design — by taking over HMI design, the remote skin model ensures that the user interface is appropriate for in-vehicle systems, reducing the risk of driver distraction. This model also allows manufacturers to reinforce HMI look and feel across all applications used in the vehicle.
Branding — with control of the HMI, manufacturers can brand applications being used in the vehicle, even if they are running on the smartphone.
The remote skin model resolves the issues of in-vehicle HMI design and branding of the infotainment system. However, it does so at some cost, and it is not without its drawbacks:
Dependency — the remote skin model is highly dependent on the smartphone, since this is where applications reside and run.
Cost — building the remote skin is cheaper and faster than building complete applications, but it still requires design work, development and testing that that is not needed with the strict terminal mode approach, and this cost is usually born by the automaker. The cost of this development is compounded by the number and variety of smartphones which the HMI must accommodate.
Upgrades — as new smartphone models and applications come on the market, the automaker must upgrade the remote skin to accommodate them and keep the vehicle infotainment system current. Without a built-in mechanism for safe, sandboxed deployment, all new applications will require a new validation cycle.
Simple UI Protocol
Simple UI protocol was developed by QNX and RIM with Harman Becker. It will soon be publicly available and open to all OEMs and Tier 1 suppliers. With this model, the vehicle head unit controls the applications, which reside and run on the smartphone. Bluetooth provides the connectivity.
Instead of replicating the smartphone HMI on the in-vehicle system, simple UI protocol transfers icons, text, and labels for two application buttons to the vehicle head unit. The smartphone application can use this minimalist HMI any way it wants to provide users with a simple interface.
Figure 9: Simple UI protocol can used to deliver a minimalist HMI to the vehicle head unit
Simple UI protocol offers some advantages over other models:
Safety — simple UI protocol is designed specifically to reduce driver distraction.
HMI — the minimalist HMI is easy to use with limited text, labels and buttons
Adaptable — a smartphone application can use simple UI protocol on the vehicle head unit in whatever way is most appropriate for that application.
Updates and upgrades — adding new smartphone applications that use simple UI protocol is simple, and it requires no revalidation of the in-vehicle system.
Open protocol — simple UI protocol is an open protocol. It will be open to all OEMs, mobile phone manufacturers, and Tier 1 suppliers.
Like other models, the simple UI protocol has some disadvantages:
Control — application and UI controls remain exclusively with the smartphone
Connectivity — all connectivity is through the smartphone, and does not, therefore make use of the vehicle's more powerful antennae