As discussed in recent blogs, 5G’s momentum is unstoppable, with trials by commercial operators due to be in place in several cities globally this year. But despite the technology’s rapid advances and the success of early deployments, there are still some major challenges that need to be overcome. One of the most significant of these is in delivering high-frequency 5G signals to users’ mobile devices reliably, in typical urban environments.
As you may have heard, 5G adds new spectrum both sub-6 GHz and at mmWave frequencies above 24 GHz. More spectrum is key to delivering the multi-gigabit speeds promised by 5G. The new sub-6GHz frequencies behave similarly to existing LTE spectrum, but the new mmWave frequencies are notorious for high propagation loss, directivity, and sensitivity to blockage.
mmWave frequencies don’t travel well through solid objects, such as buildings, car bodywork, or even our own bodies. In practice, this means that a user could potentially lose a 5G mmWave signal simply by holding or using their device in the ‘wrong’ way.
You may recall the ‘Antennagate’ issue that Apple faced back in 2010, in which its iPhone 4 would lose signal when it was held by the lower-left corner. This forced Apple to give away free bumper cases so that users’ hands wouldn't touch the edge of the phone, where the antenna was positioned. It’s a problem that can affect any handheld device because skin and bone is a very effective absorber of radio waves. However, the mobile industry can’t afford to have similar issues affect an entire generation of 5G phones and tablets.
To compound this issue, it’s also hard to predict what will happen to 5G mmWave signals when the receiver, the transmitter, or obstacles between them are moving relative to each other, such as in a busy city street. Earlier this year, Keysight and NTT DOCOMO cooperated on a channel sounding study at mmWave frequencies, investigating signal propagation at 67 GHz in urban areas with crowds of people.
The research found that the radar cross section of human bodies varies randomly over a range of roughly 20 dB – a significant variance. It also concluded that ‘the effects of shadowing and scattering of radio waves by human bodies on propagation channels cannot be ignored.’
Given this, it’s essential to conduct channel sounding tests in real-world environments rather than just in the lab, simply because the complexities and constant changes of real-world usage cannot easily be replicated. For example, indoor channels will behave differently to outdoor channels. Even factors such as the number of people in the room, or whether a window in a room is single-paned or double-paned will influence signal behavior.
Outdoor environments add a vast number of unpredictable complications. People, vehicles, foliage and even rain or snow will affect 5G mmWave signals, introducing free-space path losses, reflection and diffraction, Doppler shifts, and more.
Further variables include the base station’s antenna gain, pattern, and direction; the behavior of the channel itself; and the mobile device’s antenna gain, pattern, and direction. When the base station and user device’s antenna beams are connected, they need to maintain that connection as the device moves in space or changes orientation. The user device may also need to switch to another base station, repeating the beam-directing and forming cycle.
The result of all this is clear: exhaustive real-world testing of mmWave 5G base stations and user devices is critical to 5G’s commercial success. And at Keysight, we’re accelerating our testing capabilities to help the wider mobile ecosystem gain insights and advance their innovations. Find out more about our 5G testing methodologies and system solutions.