Wi-Fi in the car: how to meet the concurrent needs of multiple systems and applications
One of the challenges facing car manufacturers today is to find the best way to integrate internet connectivity into the vehicle’s user interfaces, such as the Infotainment system, and to provide a fast, robust wireless internet connection for the smart devices that the driver and passengers bring with them into the car.
Many consumers will value, and pay for, the ability to use in-vehicle communication, productivity and entertainment applications. By integrating wireless internet access into the vehicle’s user interfaces, the car maker can also enable the driver to safely use many internet applications and functions while driving.
To do so, car makers will have to master the art of providing reliable, high-speed Wi-Fi® connectivity to multiple users simultaneously, while also supporting system functions that require Wi-Fi bandwidth. This article describes the challenges of managing concurrent wireless connections and applications, and outlines the essential features of hardware architectures which may be used to overcome these problems.
The applications for in-vehicle Wi-Fi networks
Modern vehicle designs today already offer Bluetooth® wireless connectivity as a standard feature for hands-free calling and audio music streaming from brought in mobile phones, as well as data services for phone book access, messaging and vehicle information uploads.
But for functions that require wireless internet connectivity between devices and a router or access point, Wi-Fi is the universally accepted standard technology, and the primary wireless technology under consideration for this role in cars. To provide internet connectivity to multiple end user devices, vehicle manufacturers are integrating LTE (mobile phone network) modems to provide a pipe to the internet, and a Wi-Fi access point for smart devices.
On the highway, users’ internet traffic will be routed via the LTE modem. In some locations, such as shopping mall car parks (parking lots) or in city centres, the in-vehicle Wi-Fi can connect to the internet via public Wi-Fi access points rather than via the LTE modem. Just as in mobile phones, Wi-Fi offloading of the LTE network can reduce total subscription costs and help manage cellular traffic.
Connecting user devices is not, however, the only function that the in-vehicle Wi-Fi network will support. New system functions can also derive huge value from the high data transfer rates and standards-based connectivity that a Wi-Fi network provides. Two such functions in particular are exciting vehicle systems designers:
- smart over-the-air upgrades – increasingly, a vehicle’s functions will become updateable and regularly improved. Just like smartphone apps, a vehicle’s systems will be supported by the manufacturer through regular online security and functional updates. By providing these updates over-the-air, the vehicle manufacturer avoids the need to call the vehicle to a service center.
- display sharing – services such as Apple’s CarPlay, Android Auto and MirrorLink display the driver’s smartphone screen and functions to the vehicle’s infotainment display (see Figure 1). This allows the driver to use a smartphone’s applications and content while driving, accessing them via the touchscreen display or via voice commands. CarPlay, for instance, lets the driver use Apple’s Siri® voice recognition software to control smartphone applications such as text messaging while keeping both hands on the steering wheel and eyes on the road. Today, display sharing is a feature provided in high-end cars, or an expensive option in mid-range vehicles using USB. Increasingly, however, display sharing will use Wi-Fi connectivity and will be deployed at the low end of manufacturers’ ranges as well, since it allows them to implement functions such as navigation via the driver’s smartphone. This enables them to avoid integrating a dedicated navigation system into the vehicle itself, saving cost and simplifying the car’s design.
Applications for the in-vehicle Wi-Fi network exhibit important differences from typical uses in the home. At home, a Wi-Fi router only does one thing: it provides a pipe to the internet for multiple devices. In the vehicle, the Wi-Fi router will simultaneously be offering internet access, and providing a high-bandwidth link between a smartphone and the head unit for CarPlay, Android Auto or similar services, and checking the manufacturer’s cloud servers for software updates, and downloading them when necessary. Other concurrent Wi-Fi applications for in-car remote controls, cameras and speaker systems are also being explored.
Maintaining concurrency and quality of service across applications is a challenge for traditional Wi-Fi chips that were designed to support single-application use cases: a tablet user in the rear seats who is watching a live stream of an important football game will not tolerate periodic content buffering while the Wi-Fi network is busy mirroring mapping and navigation content from the driver’s smartphone to the head unit.
Traditional Wi-Fi chips use a single Media Access Controller (MAC) to switch across channels and bands, and their performance becomes very limited when multiple applications and multiple bands are required. The solution is to provide two separate Wi-Fi connections simultaneously and in different frequency bands, from the same Wi-Fi access point chip. A radio system-on-chip for automotive systems from Cypress Semiconductor, the CYW89359, offers two separate MACs to enable a feature for concurrent operation called Real Simultaneous Dual Band (RSDB).
The single-chip CYW89359 includes a dual-band, dual-MAC radio, enabling simultaneous operation at both 2.4GHz and 5GHz. Each radio has a separate MAC and physical layer interface (PHY) to its own antenna (see Figure 2). This means that in a typical automotive implementation, a vehicle can run a display-sharing service on the 5GHz radio while providing an uninterrupted internet connection for user devices on the 2.4GHz radio.
This problem of concurrency extends beyond the provision of Wi-Fi connectivity to include 2.4GHz Bluetooth connections as well. In the scenario outlined above, a second passenger may be conducting a voice call over a Bluetooth audio link. In fact, the Bluetooth radio is active even when no device is paired to it. A Bluetooth host continually advertises itself, broadcasting an ‘I’m available’ message to devices in range. Different manufacturers implement Bluetooth advertising in different ways. Reducing the advertising duty cycle saves power, but risks extending the time before a Bluetooth end user device is recognised by the host and paired.
Many car manufacturers maintain a 100% Bluetooth advertising cycle for the best user experience, but this has the effect of saturating the 2.4GHz band and greatly limiting the use of 2.4GHz Wi-Fi if shared on the same antenna. In the CYW89359, the Bluetooth radio has its own dedicated RF path and antenna, enabling the host’s advertising broadcasts to be transmitted via one antenna while the 2.4GHz and 5GHz Wi-Fi radios operate via separate antennas. This provides for concurrent Bluetooth and Wi-Fi operation without interruption.
Securing the internet interface
By installing a Wi-Fi radio into cars, manufacturers provide a communications channel capable of carrying large over-the-air software updates – a valuable new feature both for the manufacturer and for the user of the vehicle. But this capability also exposes the vehicle to the risk of harm from malicious attack, in the same way that networked personal computers are vulnerable.
The security of a connected car is a systems issue which concerns every ‘pipe’ between the vehicle and the outside world, whether Wi-Fi, Bluetooth, LTE or a hard wire. But securing the Wi-Fi channel is an important part of a complete security strategy for the car. Any Wi-Fi chip embedded in the vehicle should therefore support the latest, proven standards for encryption and authentication. The CYW89359 supports technologies including:
- WPA and WPA2 for authentication
- the Chinese Wireless Authentication and Privacy Infrastructure (WAPI) standard
- Advanced Encryption Standard (AES) and Temporal Key Integrity Protocol (TKIP) for encryption
Key issues in Wi-Fi implementation in the vehicle
This article has described the most likely use cases for an in-vehicle Wi-Fi network. It is clear from this description that any implementation of Wi-Fi in a passenger car needs to provide for seamless, uninterrupted and concurrent operation of multiple applications over the 2.4GHz and 5GHz radio frequencies, including internet connectivity for end user devices, display sharing services, and Bluetooth applications.
Car manufacturers specifying wireless connectivity need to integrate solutions that offer simultaneous operation of separate communications streams over the 2.4GHz and 5GHz Wi-Fi channels and over the Bluetooth 2.4GHz channel.
This is the requirement that the CYW89359 from Cypress meets, while providing a complete on-chip implementation of the Wi-Fi and Bluetooth protocols, thus relieving a host controller of the burden of implementing these radio functions.
About the author:
Richard Barrett is Automotive Product Marketing Director, Cypress Semiconductor (www.cypress.com)