5G wireless technology and next-generation public safety connectivity. Image: MobileNet Services

Technology will undoubtedly evolve over the next few years, driven by the undeniable promise of 5G and the voracious demand for data that fuels it. But there are non-trivial physics and engineering problems in 5G that are unlikely to be easy or quick to resolve.

5G continues to evolve with equipment providers and carriers around the world announcing trials and hyping this next generation of technology.

5G Performance

Rajeev Nuri, CEO of Nokia networks recently said “We also believe that 5G is likely to last longer and be deeper than we first thought. This is not just a small cell game; 5G will go big into the macro world; it will cover low, mid, and high bands to address both capacity and coverage”

With predictions of service deployment ranging anywhere from 2018-2022 it is hard to get a good grasp on what is actually happening here. The first issue is the variable definition of what constitutes 5G. Some proponents see 5G as a natural evolution of the existing 4G technology, and view most of the key attributes as primarily network based enhancements such as network slicing and edge computing. This evolutionary approach to 5G also incorporates 4G advances such as carrier aggregation in existing spectrum to support the higher bandwidths that are a key promise of 5G and deliver improved latency, higher capacity and Gigabit speeds.

Another view is that 5G is all the above but also includes use of new waveforms and new technologies (and in particular high frequencies) to improve capacity and speeds and open new markets. This is the more traditional definition of 5G and exploration of MIMO, beam forming, advanced channel coding and waveforms continues apace in standards bodies. This type of technology advancement is the next ‘big step’ worthy of its own “G”. However, these RF advances as proposed by various 5G standards development groups, are a long way from reality at this point. (However, surely the marketing groups in the various cellular carriers will latch onto an evolving definition of 5G and it will be featuring soon as a reason to buy a new phone!)

The generally accepted RF path for next generation 5G is the use of millimeter waves. So far 15GHz, 28GHz and 39GHz have been favored but there are other, even higher bands under consideration. There are several problems to overcome for a ‘5G’ RF network based on mmWaves which are worth exploring. One very subtle effect is channel coherence length. At 28GHz a user moving at only 30Km/H (~17mph) would travel ¼ wavelength in 320uS which makes it very difficult to track i.e. there is just not enough time in the beam to send any useful data. Even if this issue can be overcome other considerations include the low Power Amplifier efficiencies currently seen at these frequencies and the fact that the waveforms being considered for 5G are very challenging and make power efficiency even harder to achieve. Power Amplifier inefficiency takes its toll on battery life. So you may enjoy up to 1Gbps …but not for very long. Another more prosaic issue is where to place the many antennas that any Massive MIMO system would require.

Undoubtedly, technology will advance to overcome these limitations, particularly in the semiconductor domain where the economics’ of 5G will drive further innovation over time. However, the reality is that first generation 5G solutions are likely to be fixed wireless access systems where issues of power, space and mobility are greatly reduced. These systems would provide high speed connectivity as a competitor to fiber to the Home (FTTH).The primary advantage is the ability to provision high speed service to many simultaneous properties without having to dig up roads, a significant economic benefit.

Last year AT&T used millimeter wave spectrum in the 15 GHz and 28 GHz bands, to test enterprise 5G applications in partnership with Ericsson and Intel. Dave Wolter, AT&T Labs AVP of Radio Technology and Strategy said, “We started out with small business users and here we’re putting the device in the customer’s premise behind a window pointing out towards our base stations.” Wolter added that the company is generally putting the technology through its paces and is studying millimeter wave propagation characteristics at these frequencies.

One of the problems to overcome is reportedly the use of Low-E glass; which is highly reflective at mmW frequencies. In a recent report by RCR on fixed wireless access, Wolter said AT&T had to replace infrared reflective glass with more traditional dual pane glass. “That’s going to be a concern that people have to think about if you’re trying to do any kind of indoor deployment”.

5G Network and Distributed Antenna Systems (DAS)

The corollary of this is that 5G is unlikely to improve in building performance (which coincidentally is where all the people are) or offer high speed low latency communications inside a structure unless it is built inside. Good news for DAS companies. The downside is the sheer complexity and the fact that mmWave properties are generally line of sight, and their propagation characteristics in a highly cluttered environment such as a building, are not well understood or characterized.

Stand by for 5G, but be wary of the hype. That next “G” might not mean Generation of Technology but the next Generation of wireless users.