What Options are Available?
External Antenna
As mentioned, some devices can be outfitted with an external antenna. This is more common with embedded, fixed devices, like routers and modems. An externally mounted antenna will provide improved reception to the individual device the antenna is connected to, but will not benefit any other devices. In an implementation where only one device requires cellular service, an external antenna is viable. But in scenarios where multiple devices require service, connecting external antennas to each of them can be costly and a practical challenge.
SIMs: Multi-Operator / Multi-SIM solutions
The cellular account’s credentials and supporting security and authentication parameters are stored on a SIM (subscriber identity module) card. SIM cards are typically supplied to the customer by the network service provider. The subscriber inserts the SIM card into the target device to enable connectivity. When in place, roaming agreements – where a SIM is allowed to connect to other networks via contract between network providers – are one way to improve coverage.
However, roaming is costly. Most network operators are not supplying roaming agreements to customers as a standard way to move between networks, but rather as a fallback solution to accommodate “what if” scenarios when a given UE (User Equipment) has temporarily left the primary network. Users that frequently roam between networks benefit from solutions that do not require roaming in the traditional sense, for example in Europe, where networks often follow country borders.
One option for working around extra roaming charges is to employ multiple SIM cards in a single device. Software on the device can be configured to use the appropriate SIM for the network coverage detected. Employing a system that takes advantage of multiple SIMs, or multiple virtual SIMs, can greatly improve coverage (and lower the overall cost of coverage) for mobile or nomadic devices. The downside of supporting multiple SIMs is an increase in both hardware costs and overall system complexity. Products that support multiple SIMs are typically in the premium categories, so it can be a challenge to find low-cost multiple SIM solutions which are targeted for broad deployment.
Also, in a situation where the device is simply physically hard to reach with cellular services, as with a device buried inside a vehicle, multiple SIM solutions will not offer much help.
eUICC mobile embedded SIM technology is a new standard for the SIM card, also called “eSIM.” Rather than having credentials stored on a user-removable SIM card, credentials are stored on a chip that is soldered to the device’s PCB (printed circuit board) at time of manufacture. Credentials can be uploaded to the eSIM after the card has been delivered to market. The advantage here is that operator provisioning can essentially be changed on the fly, without having to physically access the device. This technology is particularly useful for wireless solutions that are built-in to the device, as with automobiles. The automotive industry seems to have endorsed the eSIM technology for OEM solutions, proposed by the GSMA, and it should become standard practice over the next 5-7 years as new connected car designs hit the market. Services, like the eSIM service from Sierra Wireless, are emerging that take advantage of the eUICC technology and provide entirely new value propositions to the global mobile device marketplace.
Signal Boosters (and Repeaters)
Cellular repeaters and signal boosters have been employed in the mobile cellular context for many years throughout the world. There is a wide spectrum of regional adoption of repeaters, due to a variety of reasons, like regulatory controls, consumer and market expectations, and more.
Cradle-based Repeaters
A cradle-based repeater will typically have some sort of cradle that functions to mount and secure a mobile handset. The amplifier will typically be mounted out of the way, under a seat, or in the trunk. It will be connected to an external antenna that will be permanently or temporarily mounted to the vehicle exterior. The cradle itself contains passively coupled antennas that pick up the radiated signal transmitted from the handset, boosts it, and sends it to the network via the external antenna. (And vice versa.) These products can be used to boost a single mobile handset.
There are however a couple of downsides to the cradle-style architecture. One, it only benefits one handset at a time, so is best used in a vehicle with an individual user. Two, it only really works with a phone. Connected devices like a laptop, tablet, or hotspot are unlikely to get any benefit from a cradle repeater.
Smart Signal Boosters
Smart Signal Boosters can capture the exterior cellular signal, ‘clean’ the signal by eliminating noise, and then boost the signal into the interior of the vehicle. They have been endorsed by the FCC as “a cost-effective means of improving our nation’s wireless infrastructure.” One of the key benefits of the Smart Signal Booster architecture is that all devices within range (approximately 20 m2) will benefit. There are no requirements for each device to be connected to an antenna, or otherwise modified. A Smart Signal Booster simply brings the external signal in, and boosts it.
Some signal boosters are limited in the technologies they support. For example, some may only support 3G cellular service. The key is to ensure the right booster is matched to the intended application and network.
Gain
Gain is one of the most important differentiators when considering Smart Signal Boosters and Repeaters. The gain of an amplifier is the ratio of the power of the outputted signal to the input signal. Amplifiers take a signal, add energy to it, and the output is always greater than the input. When talking about boosters (or amplifiers), gain will be listed in the specification, and it will be reported in decibels (dB). All else being equal, an amplifier with a higher gain will be more powerful than an amplifier with a lower gain. A good way to assess various boosters is “cost per decibel of gain.” Take the purchase price for the unit and divide it by the amount of gain indicated. Lower numbers are better.
MIMO
As mentioned above, there are a variety of use cases for mobile wireless technology in vehicles. In applications where high-speed data is beneficial, for example mobile video, using system products that support MIMO is key. MIMO stands for “multiple in multiple out” and is a wireless technology that uses multiple transmitters and receivers to transfer more data at the same time. 4G LTE supports MIMO and can provide data rates at 100 Mb per second, and beyond.
A signal booster can reduce data rates for devices if it does not support MIMO and intelligent boosting. In general, this degrades performance. This could result in, for example, slow video downloads, buffering, service inconsistency, etc.
For a vehicle on the move, the devices inside will go in and out of MIMO-capable service availability. A standard single-input-single-output (“SISO”) booster positioned in the vehicle with these mobile devices overpowers the external MIMO signal (based on the proximity to the devices) and essentially defeats it. The result is that devices will remain at SISO data rates that could have benefitted from higher-speed MIMO connections.
In contrast, a smart signal booster has the intelligence to sense the external network and ratchet its power up and down accordingly. In areas where the MIMO signal is good, a smart signal booster will shut down or reduce its power to allow the devices to connect to the external MIMO signal source and benefit from high data rates. As the MIMO signal fades and signal quality deteriorates in general, the booster ratchets power back up and continues to provide optimal signal in sub-optimal conditions.
A Note about Regulatory Compliance
There can be wide variation in the sorts of technologies and specific power values allowed across different regions. In the USA, there are effectively three classes of boosters regulated by the FCC:
- Part 90 (Industrial): These boosters are more complicated to install, require individual approval from network operators, and are installed in a stationary context. They are not relevant to the mobile use case.
- Part 20 (Consumer Wideband): Part 20 Wideband repeaters have lower gain values, typically in the 50-60 dB (max) range, and are very common for low-end consumer applications.
- Part 20 (Consumer Provider-specific): Part 20 provider-specific smart signal boosters are professional-grade systems that support up to 100 dB of gain and offer the best performance.
Network Operators across the European Union also use signal boosters and repeaters. In the EU, RED (Radio Equipment Directive) compliance is required, and compliance can be identified with the CE mark on the product. Beyond the CE mark (or as a replacement to it) required by all EU countries, some regions have their own compliance models, and corresponding test suites and certification marks. For example, the ACMA (Australian Communications and Media Authority) in Australia requires the RCM (Regulatory Compliance Mark). The best thing to do is check with either the regulatory bodies themselves in the region, or with trusted local suppliers.
Note: Illegal, low-quality repeaters and signal boosters can be found in every region. To ensure a good experience, and to stay within compliance, it is strongly recommended to check products for proper certification marks. If a product is marked as certified, there should be a corresponding Declaration of Conformance available for public view, usually via the web site. It is recommended to check these documents, or risk potential fines for supplier or end user.
In summary, connected cars, services delivered in the mobile context in and around vehicles, are going to become an everyday part of the mobile experience. The key is to consider the variety of technologies that can be used to ensure these services remain connected, and that the wheels keep on turning.
