So much has been written about 5G that it’s impossible for mere mortals to form their own conclusions about what it will actually achieve. Although it’s far too early to know for sure, this hasn’t stopped the continuing deluge of marketing hype throughout the industry promising something for everyone. In the hope of providing some clarity on these issues, this article addresses some of the primary areas of confusion.
The Demise of “Traditional” Microwave Components?
One of the less reported issues is whether 5G will put a significant dent in the market for “conventional” microwave products, the chip-and-wire microwave integrated circuits (MICs) and other single- or multifunction devices that have served commercial, industrial, and defense applications since the end of the Second World War. Will they simply fade into the background with SoCs and other compact devices, making them all but obsolete? And will their comparatively archaic architecture render them unsuitable for all but a few niche applications?
Neither of these outcomes seems likely in the foreseeable future, for several reasons. First, MICs and Integrated Microwave Assemblies (IMAs) are either offered as standard products such as amplifiers or as custom products designed to meet the requirements of a specific system or platform (Figure 1). Their use of both discrete components and MMICs and semi-automated production allows them to be tailored for use in systems that require very low volumes.
For example, defense electronic systems have stringent performance requirements that are often unique to a specific platform, of which only a few hundred or perhaps 1,000 will be produced over the course of their service lives, which can be several decades. Thus, the total requirement for such a device could be several thousand spread over a very long time.
This requires that the device manufacturer guarantee that the product and the devices within it will be available for up to 15 years (and sometimes longer), which is far beyond what commercial suppliers are generally able to accommodate. In addition, volumes are far too low to be of any interest to a company manufacturing primarily commercial products.
In contrast, highly integrated devices such as SoCs are designed to perform many functions, often a complete subsystem such as an RF front end. They serve systems whose specifications are fixed, which justifies the very high cost of development and fabrication, which can be amortized through large volume production. These devices can be available for many years but still are less than what an aerospace or defense contractor would require.
Nevertheless, MICs and IMAs will be used in 5G applications, obviously not in smartphones, but in wireless infrastructure, including microwave point-to-point radios that along with optical fiber are the two main solutions for backhaul. These microwave radios (Figure 2) have relied on MICs and other components for years, a trend that is likely to continue for many years. They are also employed in macro cells that although being deployed in fewer numbers today, are still a significant market, along with upgrades to existing ones for new frequency bands and other capabilities. MICs also play a significant role in test and measurement for applications ranging from amplifier modules to various types of passive components, including power combiners and dividers.
There are other diverse markets for MICs and IMAs that collectively support the more than 100 companies manufacturing them throughout the world. So, in short, the venerable microwave “hogged-out” box has many years to go before it becomes truly obsolete.
Who Needs the Speed?
One of the biggest misconceptions is that everyone needs the gigabit-per-second-plus downlink data rates promised by 5G. In fact, few people will ultimately benefit from such speed, at least for the foreseeable future. A downlink speed of 25 to 30 Mb/s can accommodate streaming of any video format including 4K (Ultra HD) and the most resource-intensive multi-player games can get by with 10 Mb/s.
These speeds are available from the major wireless carriers in urban and suburban locations throughout the U.S. and will likely be increasingly available elsewhere in the coming years, as LTE-Advanced deployments continue. (For what it’s worth, streaming a single 4K movie will consume about 7 Gbytes of mobile data, according to Netflix). So, with a reliable, steady connection and data rates of 100 Mb/s (already achievable with LTE-Advanced), most applications work just fine.
Latency: When Less Is More
What’s at least as important as speed is latency, especially for gaming and other applications requiring split-second decisions. Basically, the faster the round-trip time between when an action is taken on one end of the connection and a response is received from another, the better the experience. Reducing latency is one of the most difficult challenges facing the wireless industry because achieving a specific value (in milliseconds) is based on a combination of factors. It’s also misunderstood by most people.
In short, latency is delay; it is inescapable and there will always be some latency because signal propagation in any medium takes time, so distance traveled by two points determines, fundamentally, how short latency will (or can) be. In an ideal scenario in which the only required metric is the speed of travel (in air, slightly less than the speed of light in a vacuum), latency will be determined only by distance.
But in practice, there is no such thing as an “ideal” signal path because of the many impediments a signal encounters along the way, each one potentially reducing speed. The transmission medium itself causes latency, as do routers and the innumerable other components the signal encounters. Running of the many Internet speed tests on the smartphone, for example, shows latency as the result of a “ping” of a specific network path, and varies dramatically from tens of dozens of milliseconds. Latency is also directly related to the bandwidth of the channel and the media it travels through. So, if a network provider states downlink speed of 25 Mb/s but latency is high (and vice versa), the response time will seem slow. Figure 3 illustrates typical latency during the 2019 Super Bowl.
Now consider 5G’s promise of achieving 1 ms latency, a widely touted specification that can only be achieved over short distances, which means that an end user must be very close to a base station, which will require an enormous number of small cells. Considering the cost and complexity of such an endeavor, there is considerable controversy about whether achieving anything close to 1 ms will be obtainable, except in places where it is essential for specific applications such as the autonomous vehicle environment, telesurgery, and robotics.
This brings up another issue: the use of millimeter-wave frequencies that will contribute most to reducing latency to the promised 1 ms while the much-needed bandwidth required by data-intensive applications and network traffic in general. The spectral region above the microwave region (roughly 20 GHz) is best known for its inhospitable propagation characteristics that increase in severity with frequency (except for a few slices of spectrum), which have relegated this region to a small number of applications, none of which (except in space) have anything to do with wireless communications.
Implementing the millimeter-wave portion of the 5G spectrum is another tough challenge, and although these hurdles have been widely reported, the media reports them as though they are simply just a few other hurdles among many to be surmounted. It’s actually a lot more that, so much so that some in the industry are finally “coming clean” about what the role of the millimeter-wave will ultimately be. Let’s clear the air.
Where Millimeter Wavelengths Make Sense
Millimeter wavelengths are best suited for adding capacity to a network rather than addressing mobility, for which low-and mid-band frequencies are best suited, which means that regardless of whether Samsung, Apple, and presumably other smartphone manufacturers may include these bands, they’ll be available in certain places. Those places will be numerous in cities, but much less so in suburban areas and won’t make it to rural areas for many years, at best. In addition, there is almost no millimeter-wave infrastructure in place; it will take years for there to be enough of it to be useful for people on the move, and it’s questionable if it can play any role in mobile environments.
This infrastructure will have to be an order of magnitude greater than the number of base stations currently in use, because they’ll be needed where “true 5G” can claim to be supported by wireless carriers. Estimates about how much this will cost range from $100 billion to $200 billion, excluding the $130 billion to $150 billion required for optical fiber to support their backhaul requirements, when 5G reaches its proposed 90% of the population (which means the remaining 10%—rural customers—may never have it). Where all this money will come from remains to be seen.
With all this in mind, it’s reasonable to ask why the wireless industry is hell-bent on making millimeter wavelengths a core component of 5G; this requires a multi-part answer. The reason most cited is that there are, for obvious reasons, few current users in the millimeter-wave spectrum, which for wireless carriers is like discovering a new universe of immense available spectrum.
Further, the inability to communicate more than a few hundred feet in a line-of-sight path can actually be beneficial because of the required narrow antenna beamwidth that must be rapidly steered. This requirement and short-range propagation reduce the potential for interference. Finally, millimeter-wave components of every kind are inherently smaller than their lower frequency counterparts, which allows millimeter-wave subsystems to be smaller as well, a bonus for devices like small-cell base stations.
Why Not Use Lower Frequencies?
It is indeed possible to achieve low latency and very high data rates using low-and mid-band frequencies up to about 6 GHz with current device technologies and other techniques. Doing so eliminates the need for elaborate antenna architectures such as electronically-steered phased-arrays and the digital beamforming required to compensate for the vagaries of millimeter-wavelengths. All it takes is available spectrum, and it’s here where the trouble lies, because in the U.S. almost all of this spectral region is already in use. In addition, not all U.S. carriers have acquired enough low-and mid-band spectrum over the years, but have acquired substantial millimeter-wave spectrum.
America is one of very few countries where this is the case, so most of the world is using lower frequencies first, adding millimeter-wave spectrum as needed in the future, which is logical considering all the technology (and bandwidth) is readily available. So it should be no surprise that the FCC is frantically trying to “find” new mid-band spectrum by every means possible, no matter how disruptive to existing services, while opening up frequencies above the current 3 GHz (such as 6 GHz) for use by 5G. It’s also why Verizon Wireless was first out of the gate with 5G in the form of fixed wireless access (FWA) as a replacement for fiber and cable for broadband service and operating at 28 GHz.
AT&T is also pursuing this path, but not as vigorously, while T-Mobile, which has substantial lower frequency assets but very little millimeter-wave spectrum. It’s been a terrific marketing opportunity for T-Mobile as it, as a company not known for low-profile marketing, has been proclaiming that it doesn’t need millimeter-wave spectrum to achieve 5G and is now in the process of proving its case.
Summing It Up
The issues described above are far from the only controversial aspects of 5G, but in fairness, a revolutionary leap like 5G will obviously be a work in progress for years. Nevertheless, it doesn’t help that the heavy-handed marketing is confusing everyone about what 5G will accomplish long before it’s even available, which is a sure way to alienate even the most ardent supporters. The best news for the microwave industry, however, is that the massive infusion of tiny multifunction devices won’t be very disturbing for the vast base of microwave device manufacturers that have served the world for generations. In fact, as 5G has something to offer everyone, it’s likely to boost the fortunes of these companies as well.