How real simultaneous dual band Wi-Fi enables next-generation in-vehicle connectivity -

How real simultaneous dual band Wi-Fi enables next-generation in-vehicle connectivity

Remember the days when GPS did not exist and maps were the essential tool for navigation? Back then, the only source of in-car entertainment was AM/FM radio or physical media like cassettes and CDs. This was a time when cars were primarily differentiated by their drivability. Then came the era when Bluetooth began to be integrated into vehicles to for hands-free calling and basic music streaming, and car buyers because focusing more on in-car functionality when making purchase decisions.

Today, many vehicles offer at least this level of in-car connectivity. However, the rising number of cell phones, tablets, and other smart devices has increased the average consumer’s technological awareness. As a consequence, their expectations are stretching the limits of in-car connectivity requirements.

Infotainment systems have now become a key differentiating factor in automobiles. These systems are highly complex and powerful, including both driver-assist systems as well as entertainment support for the driver and passengers. Cars are being equipped with rear seat high-definition displays for video. Apps like Apple CarPlay and Android Auto allow each user’s phone to be seamlessly connected to the vehicle’s infotainment system.

As all of these devices are connecting wirelessly in the constrained environment of a vehicle, the available RF spectrum must be used efficiently to maximum possible usage with available wireless technologies. In this article, we will explore in-car connectivity use cases, their technical requirements, and how these can be addressed effectively to provide the best in-car experience.

Infotainment system features are advantages

The following are a few of the use-cases/features of an infotainment system that are either available in today’s cars or being introduced in upcoming vehicles, as well as their advantages:

  • Hands-free calling – This feature allows user to attend or make calls using controls available on the steering wheel without touching the phone. This feature not only makes it easy to access the phone’s calling function, it also makes driving safer as a user does not need to handle the phone physically.
  • Ability to read text messages – This feature allows users to read text messages on an infotainment system’s screen using the controls available on the steering wheel without the need for touching the phone. Similar to hands-free calling, this feature also makes driving safer as users do not need to physically access the phone to read a text message. Text-to-voice is often combined with this capability to provide a distraction-free experience.
  • Audio-synchronization to play music – This feature allows a user to synchronize a phone’s audio with the infotainment system. Using this feature, music on a phone can be enjoyed over in-car speakers and can be controlled using various buttons available on the steering wheel or the dashboard controls. With wireless audio synchronization, there is no need to connect an axillary cable to the infotainment system and music can be controlled by any passenger.
  • Support for new apps like Apple CarPlay and Android Auto – A car that supports these apps allows the phone’s display to be replicated on the dashboard LCD display, providing easy access to various phone features and commonly used applications like maps, music etc. For example, with support of these apps, navigation can be displayed on the dashboard display, or a YouTube video can be played solely using dashboard touch screen. This feature not only allows access to the phone, it also provides an alternative to generally complicated infotainment system user interfaces, by allowing the user to retain their familiar smartphone interface.
  • Video streaming to rear seat displays – This feature allows video streaming to rear seat high-definition display using a car’s LTE modem or a local media device, or through the smartphone’s Wi-Fi hotspot. It can be used by children or by passengers who do not need to concentrate on the road.
  • Internet access through a car’s built-in LTE modem – This feature allows passengers to access the Internet on phones, tables or laptops using the car’s built-in LTE modem.

Wireless technology needed by infotainment features

Figure 1 shows a high-level block diagram of in-car connectivity. The actual implementation varies on the system architecture. Also, this diagram does not capture use cases that may extend to body electronics (although wireless connectivity is becoming increasingly popular for these use cases as well).

Figure 1: Connectivity with infotainment/telematics system (Source: Cypress)

Bluetooth – Bluetooth in vehicles is been around for more than a decade. Features like hands-free calling, reading text message and audio synchronization features use Bluetooth.

Wi-Fi – Features like rear seat video streaming and Internet access through a car’s built-in LTE modem use Wi-Fi. Apple CarPlay and Android Auto applications started with wired connectivity to the infotainment system but are now moving to wireless and use Wi-Fi for over-the-air connectivity.

Almost all of these features need to be available simultaneously. For instance, when the driver is on a call, maps must be displayed at the same time and rear-seat entertainment must not be interrupted. However, it is important to understand the constraints imposed by limited spectrum available for over-the-air communication. Bluetooth uses 2.4 GHz ISM band for communications as do most Wi-Fi devices. Until IEEE 802.11n, Wi-Fi used 2.4 GHz band for communication. Both Bluetooth and Wi-Fi operating in the 2.4 GHz band without coordinated coexistence measures in place can result in choppy audio and severely impacted Wi-Fi throughput.

For a better understanding of this issue, consider how Bluetooth and IEEE 802.11b use the spectrum. Bluetooth has 79 1-MHz channels from 2.402 GHz to 2.480 GHz. Wi-Fi has 20/22 MHz channels within same frequency range. Figure 2 shows what happens when both Bluetooth (red) and Wi-Fi (blue) try to communicate using channels with common frequencies.

Figure 2: Collision when Bluetooth and Wi-Fi operate in 2.4 GHz band (Source: Cypress)

The biggest challenge in constrained environments like a car is enabling both Bluetooth and Wi-Fi to communicate in close proximity at the same time with high throughput.  Active coexistence measures using a packet traffic arbiter can mediate whether Bluetooth or Wi-Fi gets access to the spectrum to achieve better performance for both Bluetooth and Wi-Fi. It is important to understand the quality of coexistence before selecting an approach for automotive applications as basic time-multiplexing-based coexistence is very inefficient and not suitable for Bluetooth synchronous links.

Active coexistence can help Bluetooth and Wi-Fi to coexist in 2.4 GHz band. However, this requires both the Bluetooth and Wi-Fi radios to be collocated. Throughput is limited as spectrum is not available all the time to either technology as they are still sharing the spectrum on a per-packet basis (rather than a fixed time-split manner when the radios are not collocated). Wi-Fi takes a maximum hit for in-car connectivity use cases. For example, the continuous nature of hands-free calling and music streaming significantly impact Wi-Fi throughput because the coexistence packet traffic arbiter tries to give higher priority to HFP or A2DP packets. Packet drop during a call is unacceptable because calls are live data packets. Data buffering or resending is not an option as everything happens in real time. This is almost the same case with music. Packet drop will result in degraded audio quality and, in turn, impacts the overall user experience. Moreover, 2.4 GHz has its own limitations as it is crowded by the relatively large number of devices using it.

The answer to Wi-Fi throughput issues is moving to the 5 GHz band. With 802.11n, the 5 GHz band became available for Wi-Fi communications. This has enabled Wi-Fi and Bluetooth to coexist without either compromising on performance.  Compare this to the nearly 50% reduction in throughput when 2.4 GHz coexistence measures are used.

With 5 GHz band operation in IEEE 802.11n and 802.11ac, Wi-Fi throughput is not impacted when Bluetooth is being used for hands-free calling or music streaming. Also, the 5 GHz band is less congested than the 2.4 GHz band, several other technologies use 2.4 GHz band including most Wi-Fi devices in use today. Thus, the 5 GHz band provides lower packet drop compared to 11n. Even though both .11ac and .11n support the 5 GHz band, .11ac becomes the only choice for in-car connectivity due to very high throughput requirement. .11ac uses 256-QAM modulation whereas .11n uses only 64-QAM modulation. .11ac offers 20-MHz, 40-MHz, 80-MHz and 160-MHz channels while .11n allows only 20-MHz and 40-MHz channels. That makes .11ac more appropriate than .11n for in-car connectivity.

Wi-Fi devices that support 2.4 GHz and 5 GHz for Wi-Fi connectivity are known as dual-band Wi-Fi devices. As a term, dual band is most commonly misunderstood as a device that can transmit at both 2.4 GHz and 5 GHz at the same time. In reality, these dual bands can’t be used at the same time in most devices. Rather, the system multiplexes between 2.4 GHz and 5 GHz traffic. In this way, a device can switch between 2.4 GHz and 5 GHz bands to support devices that use 2.4 GHz and 5 GHz channels respectively. However, this impacts throughput significantly. Due to time multiplexing and the delay of switching from one mode to another, effective throughput is less than 50% of what could be achieved if both bands were active all the time. This kind of implementation is also called virtual simultaneous dual band. For automotive use cases that require several devices to be connected for video streaming, hands-free calling and data access, there is a need for Real Simultaneous Dual Band (RSDB) Wi-Fi.

Real simultaneous dual band

Real simultaneous dual band means that a device can communicate using both 2.4GHz and 5GHz bands at the same time. RSDB ensures 100% bandwidth utilization based on each band compared to less than 50% in the case of virtual dual band implementations. For example, a 2.4GHz 20-MHz channel provides PHY rates of 72 Mbps, resulting in TCP throughput of 50 Mbps. A 5GHz 80-MHz channel supports PHY rates of 433 Mbps, resulting in 300 Mbps TCP throughput. With both a 2.4GHz 20-MHz channel and 5 GHz 80-MHz channel, a RSDB implementation provide 50 Mbps and 300 Mbps throughput for these bands with an effective throughout of 100% compared to what can be achieved using separate single band operations.

Support for RSDB is defined by the hardware’s architecture. A true RSDB implementation requires dual MAC, PHY, and radio hardware to allow both bands to operate concurrently. Newer devices that use 5GHz for their operation can make the best use of available spectrum without worrying about Bluetooth that operates at 2.4GHz and takes priority for various activities like phone calls and music. The requirement for RSDB is primarily driven by the fact that many consumer devices still use 2.4 GHz for Wi-Fi. For optimal performance, it is required that both the 2.4 GHz and 5 GHz bands are available at the same time. With RSDB, 2.4 GHz can be used to connect to phones, tablets, and laptops that support only 2.4 GHz Wi-Fi operation. Also, Internet access for data can be time-multiplexed with Bluetooth since providing priority to Bluetooth for this use case does not impact the user experience significantly while 5 GHz band can be used for rear seat display and apps like Android Auto. Thus, a combination of efficient coexistence and RSDB is the key to providing the best user experience (i.e., always available 5 GHz communication with 2.4 GHz Wi-Fi communication and Bluetooth to coexist on 2.4 GHz band for in-car connectivity). Such solutions are becoming available on the market. For example, the CYW89359 from Cypress is single-chip RSDB Wi-Fi + Bluetooth solution that provides a parallel coexistence interface for an efficient coexistence solution.

For mid-end and high-end cars that are equipped with all this sophisticated technology to connect everything in their car, reliability, performance, and interoperability are of the utmost important. Thus, it is critical for OEMs to choose a hardware platform that can provide the required throughput with a guarantee to work with other devices like mobile phones, PCs, tablets, and laptops.

Cypress provides 11ac RSDB + Bluetooth combo devices that can support either 2.4GHz and 5GHz SISO (Single Input Single Output) simultaneous operation + Bluetooth, 2.4GHz 2×2 MIMO (Multiple Input Multiple Output) + Bluetooth, or 5GHz 2×2 MIMO + Bluetooth. The most widely deployed Wi-Fi and Bluetooth stacks are supported. 2.4 GHz and 5 GHz SISO with Bluetooth is the most desirable use case for infotainment systems where some of the devices use 5 GHz and some use 2.4 GHz. However, in use cases where only one band is needed for communication, 2×2 MIMO can be used so that the system can transmit and receive data using multiple antenna and provided 2x throughput for the given band compared to a SISO operation.

The automotive industry is going though an in-car connectivity revolution. Multiple devices need to be connected simultaneously and wirelessly. In-car connectivity has evolved from the need to support basic hands-free calling to the need to support sophisticated infotainment systems. Throughput requirements have increased as well, require enough throughput to support multiple displays, Internet access, screen sharing, and Bluetooth connectivity.

The 11ac RSDB Wi-Fi standard is the only protocol able to address the continuously growing demand of throughput. To provide a reliable and efficient connectivity to all technologies available in a car – Bluetooth and Wi-Fi in most cases – a Wi-Fi + Bluetooth radio implementation is the most efficient and economical solution. As coexistence is handled by device itself, OEMs do not need to invest a lot of time and money addressing coexistence issues that have already been solved. Selecting an industry-supported approach provides the backbone for commercially successful in-car connectivity as it already works with every Wi-Fi or Bluetooth device that could ever intended to be connected. In addition, this approach reduces design investment and time, enabling these resources to be spent on interoperability testing.

Sachin Gupta is working as Staff Product Marketing Engineer in IoT business unit with Cypress Semiconductor. He holds a Bachelor’s degree in Electronics and Communications from Guru Gobind Singh Indraprastha University. He has nine-years of experience in SoC application development and product marketing. He can be reached at .

Jeff Baer is Senior Director of Product Marketing for Wireless Major Accounts, IoT Business Unit at Cypress. Mr. Baer joined Cypress in July 2016 as a result of the acquisition of Broadcom’s IoT line of business. Mr. Baer first joined Broadcom in 2004, where he successfully pioneered the company’s entry into the rapidly growing embedded WLAN market. While at Broadcom, Mr. Baer led business development in the Asia-Pacific region for the company’s Mobility WLAN and WLAN+Bluetooth combo devices (including a 3-year stint with Broadcom Japan), as well as marketing efforts for Embedded RF Technology in the U.S.  He led the initial push of Broadcom into the “Internet of Things” market, and was a co-founder of the WICED (Wireless Internet Connectivity for Embedded Devices) product family of IoT devices and software.

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