In discussions with clients and industry analysts about Non-Terrestrial Networks (NTN), Direct to Vehicle (D2V) connectivity is increasingly a topic of conversation. The ecosystem from satellite networks to end devices is also developing, with recent announcements such as the one from LG Innotek, unveiling a module they have developed for 5G Automotive communications. What is driving these developments and what are the services and technology behind all of this interest?
What is the use case?
There are many use cases envisioned for D2V, for both commercial vehicles such as trucks, lorries and vans, and passenger service vehicles including coaches and buses. But there are also a number of mass-market applications and services for private cars. The automotive industry and manufacturers talk about applications grouped by data requirements. There are many applications that need only a narrowband connection, such as traffic information, status monitoring and emergency alerting, but there are also those that need broadband data such as HD mapping, driver support and in- car entertainment.
While none of these use cases strictly requires NTN, as they can often be served today by terrestrial networks, a satellite-based network fills the coverage gaps and makes these applications available everywhere. Even with the advent of 5G networks there are still considerable areas of no or poor coverage within urban areas, and the issue is more pronounced in remote and rural locations. For example, a cloud-based service allowing a car to be locked and monitored from a smartphone will benefit from ubiquitous coverage.
The importance of standards
Since its beginning the mobile industry has been an exemplar of the benefits of adherence to open industry standards, and it’s very clear that for D2V to be successful it must also use solutions that are standards-based. Vehicle manufacturers will be much more willing to design in a terminal into a vehicle if it uses an industry standard form factor and can be sourced from multiple vendors. Perhaps more importantly, they will not accept a situation where key features of their products are dependent on a single network. They also want as much commonality across global markets as possible. Evidence of this drive for standards can be seen from the 5G Automotive Association (5GAA), an organisation with over 130 member companies, that joined 3GPP several years ago and submitted requirements for vehicle mounted NTN terminals to 3GPP in December 2023 [1].
Performance gains from vehicle mounted devices
The 5GAA submission centres around the performance of devices mounted on a vehicle, compared to the performance of a handheld device and it is in this performance where we see one of the aspects that makes these services so interesting. Firstly, the Association is suggesting that a roof mounted antenna with a gain of 3dBi over a handheld device should be considered for cellular bands such as S and L bands. Such an antenna is similar to that found in cars today and, whilst it only gives a modest improvement in downlink performance, it delivers approximately double the performance in terms of uplink throughput. Second, is the opportunity to increase the device power class from what the standards define as Power Class 3 (PC3) to the higher Power Class 2 (PC2). Implementing PC2 in a handheld is challenging, but relatively straightforward in a car. According to the 5GAA study behind their submission[2], if we take the combined gains of PC2 and a more aggressive target of 6dBi for the antenna, we see an 11X increase in uplink throughput and a 1.25X increase in downlink throughput.
Uplink v Downlink
Why this difference between uplink and downlink? Well, in a handheld device being served by a satellite 600km away, the challenges of the uplink are much greater than the challenges of the downlink, so any improvement in the uplink link budget has a disproportionate impact. This also shows just how critical the receiver performance on the satellite is for NTN networks. For example, the AccelerComm LDPC decoder delivers a 0.8dB gain over industry standard decoders when used for NTN applications, and that gain equates to approximately a 33% improvement in uplink throughput.
We can see that for S and L band frequencies, a car provides a significant improvement over a handheld device, but the data rates involved are always less than 10Mbps in the uplink and perhaps 4 or 5 times that in the downlink. This has to be shared between all users in the satellite beam footprint which is typically hundreds of square kilometres. These throughputs are viable for basic messaging but not enough for voice and certainly not a broadband service. Services that use A and L band will always be limited by the lack of available spectrum, and so it is when we turn to higher frequencies such as Ku and Ka band that the difference between a handheld device and a car becomes game changing.
Panel antennas enable Ku and Ka band usage
Satellite broadband services such as Starlink and Amazon’s Kuiper use frequencies in the Ku and Ka bands, much higher frequencies than used by cellular. The advantage of these bands is that there is much more spectrum available, but the disadvantage is that they require the use of a panel antenna. Kuiper’s smallest antenna is 18cm square and Starlink's is a little larger. Clearly using a panel antenna of this size on a handheld device is impractical but mounting it on a car opens up a range of new possibilities.
In their liaison statement, 5GAA suggests antennas with gains ranging from 25dBi to 31dBi. The study calculates these gains based on panel sizes between 6cm x 6cm and 21.75cm x 12.75cm. These could deliver uplink performances of 200 – 400 Mbps, 40X that available with 5G NR Frequency Band 1 (FR1). It is easy to imagine a panel antenna of this size being integrated into a car, enabling broadband levels of throughput to be available in any outdoor location, however remote. The car could even serve as a Wi-Fi hotspot for the passenger’s mobile phone and other devices.
The other advantage of panel antennas is that they are inherently directional. The receiver in a car with a panel antenna will electrically ‘steer’ the antenna beam towards the satellite serving it and ignore the rest of the sky. This selectivity enables multiple satellites to use the same spectrum in overlapping beams. This, combined with the greater availability of spectrum in bands like Ka, will allow operators to offer much higher data rates at a lower cost than will be possible directly to handheld devices.
The dawn of a new era
It’s a case of ‘back to the future’ for the mobile industry. At the dawn of the cellular age in the 1980s, car mounted phones, taking advantage of the available power and good antenna mounting opportunities, were at the centre of the industry. It may be that over 50 years later we will see the car mounted communication device once again playing a prominent role.
[1] 3GPP TSG RAN Meeting #102 - RP-232733
[2] Maximising the benefit of future satellite communications for automotive – 5GAA
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