Function-critical design of wireless hardware
Since the beginning of the millennium, wireless devices have had a – sometimes well-founded – reputation for being unreliable. However, it is possible to design wireless systems with secure communication.
We have all experienced the connection to our mobile telephone disappearing in areas where there should be network coverage, our Bluetooth headset suddenly falling out, or that the wireless remote control ‘just stops working’.
But it is entirely possible to design wireless systems with secure communication. For example, in 1990 the Voyager 1 satellite sent images back to earth across a distance of around 150 million kilometres (source: https://www.jpl.nasa.gov/news/news.php?feature=4484). We also use radar and radio transponders to avoid plane crashes, while the police, fire and ambulance services use TETRA to communicate with each other in life or death situations. There are many examples of wireless communication functioning extremely reliably; so what is it that designers and companies do that makes it work so effectively?
Wavebands and technology
The first factor is the technology and the waveband you choose. Much of our radio communication is currently transmitted across unlicensed wavebands, which are vulnerable to disturbances from other communication systems. In addition to the waveband there are also other choices to be made, specifically about the technology. For example, the standardisation of 5G is currently focused on making three branches of the technology (source: https://tandcca.com/fm_file/4g-and-5g-for-public-safety-pdf/):
- Ultra broadband with data transfer rates over 10 gigabit/second
- Massive Machine-to-Machine with 10-100 times more devices than the mobile network we use today
- Critical communication, with latency under 1 millisecond and reliable delivery of data.
Here, it is essential to note that these three branches have very different goals to live up to, and that in the case of the latter, both speed and number of devices have often been sacrificed in favour of more reliable communication. Speed is often sacrificed because a lower data transfer rate also entails longer detection time per byte, making faster speeds easier to detect. A low number of devices is due to a lower risk of collisions with other devices, as well as more space to retransmit the content.
Hardware-specific initiativesHowever, it is not enough to work solely with the technology. There are also hardware-specific initiatives that can increase the reliability of the communication. The first is often to ensure full functionality in all environments. As radio designs in general, especially oscillators, are highly sensitive to parasitic capacitance and inductance, they are often extremely sensitive to temperature variations.
In addition, radios often use shielding that are mounted onto the circuit board. As it is crucial for these to stay securely attached to the circuit board in order to maintain the shielding effect, it is relevant to perform a vibration test on these as well. This also applies to antennae, where soldering to a top-hat antenna in particular, can often break in vibration-filled environments. Unfortunately, when it comes to the antennae, it is often the case that these are not optimally designed from the start. As this affects the range of the wireless communication directly, it is essential to ensure that it is implemented correctly.
The next level in reliability is to add the antenna diversity. This principle is based upon having multiple antennae that receive the same signal. It can be added to existing technologies with a selection combiner or a maximum ratio combiner. The components thus select the strongest signal from one of several antennae or combine the signals in order to achieve optimal conditions.