Why Sub-GHz Continues to be a Critical Piece of the Smart Home Puzzle

As the diversity of smart home devices and solutions continues to grow—making our lives even more convenient and connected—understanding the communications framework underpinning them is more important than ever. We sat down with Mariusz Malkowski, director of customer success and integration, Building36 Technologies, to discuss his thoughts on why sub-GHz frequencies continue to be a critical aspect of smart home technology, as well as the future outlook for devices and solutions making use of sub-GHz.

The Genesis of the Smart Home

Ask Malkowski how long smart home technology has relied on the sub-GHz layer to communicate, and he will tell you that we first need to establish when the "smart home" really started.

"I think the breaking point for smart home was the iPhone in 2007 when consumers started wanting to do more with their handheld devices," he said. "You will find devices 20-30 years ago that were in a smart home space, but they were probably not called smart home back then. Instead, 'home automation' was the big word. Back then, you could get a smart home system installed for a couple hundred thousand dollars, but it has since become much more reliable and more affordable."

Since those early days of home automation, a proliferation of proprietary and standards-based solutions has offered consumers various options on both the 2.4GHz and sub-GHz layers. Only sub-GHz, however, provides the fundamental advantages of a more extended range, longer battery life, better reliability, and reduced crowding.

Maximizing Range and Battery Life

"Given the same power budget—the same amount of energy used—you're going to get about double the range from Z-Wave when compared to 2.4GHz, and that's just down to the physics of it," Malkowski explained. "Now, that gets thrown out the window with Z-Wave long-range, where your typical range is going to be about a mile, and on 2.4GHz, you're lucky to get 300 feet. The lower the frequency, the better the range, the better the penetration."

A white paper published by Austin, Texas-based Silicon Laboratories expanded on this particular advantage of sub-GHz. It cited three main reasons for better range performance over 2.4GHz applications: "As radio waves pass through walls and other obstacles, the signal weakens. Attenuation rates increase at higher frequencies. Therefore the 2.4GHz signal weakens faster than a sub-GHz signal." Secondly, it said, "2.4GHz radio waves also fade more quickly than sub-GHz waves as they reflect off dense surfaces. In highly congested environments, the 2.4GHz transmission can weaken rapidly, which adversely affects signal quality." And finally, it said, "Though radio waves travel in a straight line, they do bend when they hit a solid edge. As frequencies decrease, the angle of diffraction increases, allowing sub-GHz signals to bend farther around an obstacle, reducing the blocking effect."

Regarding battery longevity, Malkowski explained that sub-GHz frequencies can support up to double that of comparable 2.4GHz devices without replacement. "The same door lock from a given manufacturer with a radio frequency at 900MHz—you're probably going get about 18 to 24 months before needing to replace that. For 2.4GHz, on the other hand, because of the nature of the communication, it's going to be about 12 to 16 months," he said.

To this point, the Silicon Laboratories white paper explained, "The sensitivity is inversely proportional to channel bandwidth, so a narrower bandwidth creates higher receiver sensitivity and allows efficient operation at lower transmission rates." It continued, "In general, all radio circuits running at higher frequencies … need more current to achieve the same performance as lower frequencies."

An Open, Reliable Highway

Take a moment to count the number of Wi-Fi- or Bluetooth-enabled devices in your home. When you consider that your computer, smartphone, smart speaker, smart TV, gaming consoles, remote controls—even, occasionally, your microwave—are all competing to operate over 2.4 GHz, it's easy to understand how things can get a bit congested.

The sub-GHz layer, on the other hand, does not suffer from the same amount of traffic, explained Malkowski: "The more devices you have within the same space in 2.4GHz, the less reliability, potentially. That's why being in sub-GHz is so important."

This sentiment was echoed by the Silicon Laboratories white paper, which stated, "Sub-GHz ISM [industrial, scientific, and medical] bands are mostly used for proprietary, low-duty-cycle links and are not as likely to interfere with each other. The quieter spectrum means easier transmissions and fewer retries, which is more efficient and saves battery power."

Another facet of greater sub-GHz reliability is reduced latency. Malkowski explained, "With respect to latency—or how fast you can talk to devices—you can open a Z-Wave door lock within two seconds, and that's the worst case. In ZigBee or OpenThread, on the other hand, it would be eight to 10 seconds. Does that difference really matter? Sometimes it does, sometimes it doesn't."

Malkowski summarized the advantages of sub-GHz frequencies using an analogy: "On the sub-GHz layer, I'm getting the experience of being on a six-lane highway packed with cars, and I'm just cruising by myself in the left lane." He emphasized that reliability and a lack of interference with other devices will ultimately be critical to the future advancement of smart home solutions.

Different Countries, Different Frequencies

Sub-GHz's most commonly cited disadvantage is that frequencies need to be re-adjusted based on your country. "Companies that are using technologies other than Z-Wave—they very often point out that it's not a global solution," Malkowski said. "With ZigBee or OpenThread we can make one device and sell it all over the world, but with Z-Wave that's not possible."

But despite the hurdle that device manufacturers face when it comes to making their products available to a global market, it is essential to note that for the average smart home consumer in the United States—for whom automated lighting control and garage door openers being operable abroad is not an altogether essential feature—this constraint on sub-GHz is of little concern.

A Future-Proof Solution

With the rapidly evolving smart home technology market, one could be forgiven for worrying that the sub-GHz layer itself will eventually become too crowded—or simply become a non-viable option for device manufacturers, whether due to some new FCC regulation or replacement by its higher-frequency counterparts.

But Malkowski is not overly concerned: "We're seeing new additions to the sub-GHz layer like Amazon Sidewalk, but we're still far away from where they are frequency-wise. They use spread spectrum, which allows them to jump on different frequencies. So, the probability of it becoming overcrowded is much less than 2.4, which has fixed channels. That's the major difference." He added, "Furthermore, it's usually the emergency services that dictate what frequencies are available or not. I anticipate that the same bands we have access to today will still be available 20-plus years from now."

Far from being overshadowed—sub-GHz frequencies are a faster, more reliable, and more cost-effective device communication solution that will continue to benefit smart home technology consumers for decades to come.