With Mobile World Congress in Barcelona fast approaching, the industry is abuzz with 5G, busily preparing product announcements and vision statements. Clearly, the new radio standard is on the verge of release and will enable some system improvements but will not solve the ongoing capacity crunch from operating in the frequency bands below 6 GHz, i.e., "sub6," as laid out in this article by Joe Madden of Mobile Experts.
Instead, much hope is being pinned on millimeter waves, or frequency bands around 28 and 39 GHz, to meet the increasing demands of video-hungry, cord-cutting users. However, the recent lackluster FCC auction of 28 GHz bands netted less than $1 billion, far below the valuation of sub6 auctions, indicating just how far away we are from operators betting the farm on this technology.
So what gives? The technical issues at these higher frequencies are daunting for both the operator infrastructure and the user equipment. While they have been used for decades in point-to-point communication and military applications, these applications were enabled by entities like Bell Labs and DARPA, along with very well-controlled operating environments with unconstrained budgets. Your smartphone is far from satisfying any of these conditions.
The fundamental issue with these higher frequencies is they do not travel as far as lower frequencies—in fact only a fraction of the distance achieved in mainstream frequency bands under 2 GHz. To overcome it, engineers apply truly space-age technology known as phased-arrays of multiple antennas to create a focused beam back to the base station. What could go wrong?!
First, it’s very difficult to maintain the beam focus in a changing environment. System models show that movement even at just a few km/hr will be difficult to correct for, resulting in a dropped connection. LTE can be used for control signaling to maintain a continuous connection, so the mmWave link could be limited to a role as a “carrier aggregation” band until wide beam scanning and narrow data-plane beams can be optimized fully. This has led people to refer to the "nomadic" operating condition where you can use the mmWave frequencies only while stationary, e.g. sitting in your home, a coffee shop. Not on the highway!
Then there’s a matter of what must be done inside the smartphone. As the connection is inherently unreliable, all the existing sub6-enabling components must stay in your phone. This means the mmWave phased-array must be shoe-horned into a phone with no free space, and the size is significant with between four and eight antennas and electronics spaced roughly 10 mm apart. Along with this comes major cost increases to the phone as each antenna requires its own electronic subsystem. Creating the mmWave signals is also very inefficient, resulting in high self-heating and rapid battery drain. The resulting power consumption can be as high as 4 W, or 4x higher than the current sub6 system.
Finally, the industry players creating the RF front-end solution for mmWave will be different. This is significant as the incumbents have adapted to meeting grueling build schedules of leading smartphone makers. In mmWave, the modem makers hope to take over the RF front-end content but are inexperienced with supporting the rapid prototyping required in the RF front-end. There will be stumbles ahead.
Despite the problems, mmWave offers too much tantalizing bandwidth to be ignored. The operators need the capacity of these wide bands, so huge volumes of money are being invested, and engineers will solve the problems. But like CDMA at its launch, it’s going to take a lot longer than we are being hyped to believe for mmWave technology to be widely deployed and highly usable in our smartphones. Be ready to carry around your mmWave hotspot for a couple of years if you want to be an early adopter. Because it won’t be in your smartphone until 2022.
Dylan Kelly is a 20-year veteran in the RF and analog semiconductor industries. He has been a driving force in the market in a variety of leadership positions, including product development, product management, and operations. He joined pSemi in 2000 and last served as President and Chief Operating Officer through 2018. He enjoys putting disruptive technologies into play, and market competitors know him for spearheading the industry’s transition from GaAs to RF SOI. Kelly holds a BSEE from UT Austin and an MSEE from UCSD. When he’s out of the office, the San Diego-based analyst can be found in, on, or somewhere near the beautiful California ocean.
Industry Voices are opinion columns written by outside contributors—often industry experts or analysts—who are invited to the conversation by FierceWireless staff. They do not represent the opinions of the editorial board.