New Radio Tuner Architecture – Moving the Radio and Antenna Closer Together
The close proximity of radio tuner and antenna offers a number of important advantages for automotive manufacturers. To achieve this, a modified E/E architecture is essential and so has to be taken into account at an early stage. All the reception electronics for terrestrial radio are contained in a remote tuner module (RTM), which is positioned as close as possible to the antenna. This brings advantages in terms of cost, weight and, above all, quality – advantages that the industry is increasingly coming to recognize. The trend toward RTMs is continuing unabated and is set to change the architecture of in-car radios forever.
Despite the increasing popularity of streaming services, audiobooks and podcasts, the radio remains the number one in-car medium, thanks above all to the immediacy of the information broadcast, its ease of use, constant availability and wide selection of broadcasting stations. Even if some experts are already predicting the end of the radio both in cars and in general, cars without radios remain inconceivable for the foreseeable future.
Since they were invented 100 years ago, radios have undergone continuous development encompassing everything from subtle tweaks to whole new radio standards. Digitalization in radio technology again brought new standards offering enhanced functionality. The DAB (Digital Audio Broadcast) system was introduced in Europe, while the US had HD radio and Japan ISDB-T for radio and TV. And China is currently developing its own digital radio standard. In parallel with these developments, however, many of the old, traditional services such as AM/FM radio are being switched off. But whatever the trend, automotive manufacturers and suppliers are constantly faced with new challenges. The market is in flux.
Satellite Radio: A Special Case
Satellite radio is especially useful in very large countries, which is why the US and Canada have something that no other country in the world has: Sirius XM satellite radio. The two companies Sirius Satellite Radio and XM Satellite Radio merged in 2008. The transmission technology, frequency range, tuner elements and antennas used for satellite radio are completely different to those used for standard, terrestrial radio. The fundamental difference here is obvious: The broadcasting station is in orbit rather than grounded here on Earth. The RTM from TE Connectivity was specially developed for terrestrial radio and demonstrates its strengths here. TE has also designed a solution for satellite radio within an RTM architecture, although this is not discussed in detail below.
What’s Next for Radio?
Three major trends are currently dominating the automobile industry: electromobility, connectivity and automated driving (ADAS). The latter two trends are well established in new vehicles, which already offer a variety of advanced driver-assistance features (e.g. lane departure warning system, distance control, parking assist system) and communication systems (e.g. Bluetooth, WLAN, LTE, eCall). This inevitably results in a higher number of electronic control units (ECUs), all of which need to be accommodated within the limited installation space available. The increase in electronics also raises the question of the most suitable E/E architecture. As much integration as possible in a single unit? Or is modular distribution the better option? The innovation and update cycles of all these different systems must also not be forgotten. A telephone modem, for example, has a much faster innovation cycle than, say, an audio amplifier.
The terrestrial radio reception system – i.e. only the reception electronics with tuner – is usually located within the head unit (central infotainment control unit). In terms of the aforementioned challenges associated with accommodating an ever greater number of electronic components, each with different service lives, we now have to ask ourselves whether installing the radio in the head unit is still a viable solution in modern cars.
Advantages of RTM Architecture
A new approach to in-car E/E architecture involves moving the radio reception system from the head unit to a remote location (RTM = remote tuner module). “Remote” is a relative term here when you consider the antenna, amplifier and radio electronics as a whole. This is because the reception electronics are positioned close to the antennas and antenna amplifiers and so even closer to other important system components. Ideally, the remote tuner can be installed precisely where, in the latest systems, the antenna amplifier is located. The advantage here is that instead of finding a new installation space, developers simply have to slightly expand the installation space already used for antenna amplifiers (Fig 1).
The shorter distance between the antenna and radio yields the first key advantage of the RTM architecture: the lack of antenna amplifiers. One or even multiple antenna amplifiers are needed if the antennas are located in the rear of the vehicle (rear window or rod antennas) and the radio in the front. The received signal is amplified and fed into an around five-meter-long coaxial cable. Without amplifiers, the received signal would be too weak to generate useful audio data. But if the tuner is in close proximity to the antenna, amplification is no longer necessary.
The RTM is a full-fledged radio that provides all the core functions such as tuning, demodulation and decoding. Operation of the radio – for example, the presentation and selection of radio channels – is defined by the automotive manufacturer and is independent of the RTM. The end result is a PCM audio stream and data channel, which has to be transported to the head unit. Digital bus systems such as Ethernet or A2B, which enable loss-free transmission, are now used for this purpose. This means that the expensive coaxial cable can be replaced by a simple two-wire line, which not only saves on additional costs but also reduces the overall weight of the vehicle.
The RTM also offers all the necessary software algorithms that a state-of-the-art car radio needs. So if a broadcasting station is available in both FM and DAB, for example, automatic and seamless blending between the two must be possible. Since there is often a time delay between the two transmission paths, the radio adjusts the playback speed of the audio stream. And to calculate the time delay in the first place, CPU-intensive audio correlation is required. The RTM performs all these tasks independently. The RTM also presents current channel lists, keeps a look out for alternative frequencies and provides data such as RDS and DAB slide shows.
In summary, all the complexities and country-specific features are encapsulated within the RTM and, therefore, outside the head unit. Via a logically structured API, the head unit can cover the entire radio functionality and always receives a PCM audio stream, regardless of position or region.
Additional advantages of the RTM architecture relate to the head unit. The regional differences in the sales markets usually demand different head unit variants. In the most straightforward scenario, different software is all that’s required; sometimes, however, different hardware is needed as well. The radio itself is the “driver” of this hardware diversity because the global radio standards are received with different tuner ICs. When the radio is fully integrated, the number of head unit variants multiplies with each radio variant. For example, regional differences mean that there are seven head unit variants. On top of this are three radio variants (EU, US, RoW). This is the bare minimum required for serving the global market. So in all, a total of 21 head unit variants are needed. But with RTM architecture, the number of variants can be reduced to seven because all specific radio components are contained in the RTM.
Relocating the radio means that the head unit consumes less power and so less heat is generated – after all, the thermal design of a highly integrated head unit presents a challenge that often demands active ventilation. The EMC design is also simpler because fewer electronic components are needed. In particular, the highly sensitive tuner chips, which were specially developed for receiving signals, must be protected against interference from the adjacent electronics. The head unit in an RTM architecture is supplied not with analog signals but with digital signals, which are much less sensitive to faults in the wiring harness or inside the head unit.
Typical installation locations for an RTM include the C-pillar, tailgate or under the roof – in other words, anywhere that’s in close proximity to the radio antennas. The temperature requirements in these locations, however, are more stringent than in a head unit. TE Connectivity has spent years working on a solution to this problem and developed a number of measures that combine to form a solution that does not involve active cooling. The development of thermosimulation expertise has proven very useful. The simulation results are highly realistic and enable shorter development times for the RTM because it’s no longer necessary to design tests in advance.
Lower Costs, Lower Weight, Simpler Architecture and Full Functionality
The radio remains a central component of the in-car infotainment system. But at the same time, cars are becoming home to an ever-increasing number of electronic systems with services lives of varying lengths. The limited installation space requires a solution that reduces reliance on the head unit, which is why relocating the radio unit to the rear of the vehicle offers exciting potential. This does away with the need for antenna amplifiers, and expensive coaxial cables can be replaced with digital bus systems such as Ethernet or A2B. In addition, manufacturers can significantly reduce the number of head unit variants required due to the different radio standards in the sales markets. The RTM architecture generates less heat in the head unit, while the use of digital rather than analog signals means less sensitivity to faults. These are all highly compelling reasons for relocating the radio in the vehicle. An RTM, which can be easily positioned in the C-pillar, tailgate or under the roof, frees up significant space for additional electronic components, cuts costs, reduces weight and ensures perfect radio reception.
About the author:
Steffen Lang is Manager Product Management, TE Connectivity.
Since 2014, Steffen Lang heads the product management team for Automotive Wireless at TE Connectivity (Neckartenzlingen/Germany). Steffen and his team focus on identifying new market trends in the antennas and connectivity space and developing TE Connectivity’s product portfolio accordingly.
Steffen holds an electrical engineering degree from University of Applied Sciences Esslingen/Germany and an MBA from Babson College/Massachusetts. He has 15+ years experience in the development of electronic and software systems. Before TE, he worked for Bose Corporation in both Germany and the USA, focusing on automotive sound systems.