As the internet of things (IoT) continues to evolve, a wealth of connectivity options—utilizing a variety of different spectrum options—are emerging. The 2.4 GHz band—also called unlicensed spectrum—has thrown its hat into the ring as a legitimate option. There are three key reasons 2.4 GHz has a rightful place as an IoT connectivity contender:
Reason 1: Cost-free IoT coverage
Many are under the impression that the 2.4 GHz band provides inferior range and coverage to the sub-GHz bands (915 MHz band in United States and 868 MHz in Europe). It is true that, all things being equal, sub-GHz signals propagate further than 2.4 GHz signals according to the textbook Friis equation. However, in the real world, all things are not equal. Propagation loss is only one input of many that feed into the range/coverage of a wireless technology. The coverage figure of merit for how well a wireless technology works is called link budget and consists of other factors including antenna diversity, receiver sensitivity, and amount of interference.
As a matter of fact, the use of antenna diversity in the 2.4 GHz band can largely compensate for the Friis equation disadvantage. Devices with two antennas are uniquely feasible in the 2.4 GHz band because the quarter-wavelength separation is supportable in most IoT form factors, which is often not the case for the sub-GHz bands with larger wavelengths. And thus, the relative coverage of 2.4 GHz vs. sub-GHz bands is often dominated by the receive sensitivity of the modules and the amount of interference in the bands.
Additionally, if the technology uses direct sequence spread spectrum (DSSS) modulation, it has an extremely favorable global regulatory environment. This is summarized in the table below. Two main points to take away are that the 2.4 GHz band has from 7x to 67x the bandwidth of the sub-GHz band, depending on the regulatory environment, which provides an enormous capacity advantage. And, the 868 MHz band is constrained to one percent duty cycle limitations as well as extremely fractured availability around the world.
Reason 2: Simplest global deployments
The 2.4 GHz band is freely available worldwide, in every country on earth, at one single frequency. A device maker can build a single device, assign a single SKU, and it will work anywhere in the world. Essentially, that means a wireless module can be installed in a washing machine in a factory anywhere in the world, without concern for which country it is getting shipped to. This offers device makers access to the global market with just a single device using the 2.4 GHz band.
Reason 3: Instant global reach
Perhaps one of the greatest benefits of the 2.4 GHz band is the fact that it offers instant access to the global market. Wireless technologies using licensed bands or the unlicensed sub-GHz band suffer from a very fractured market. Device makers in those markets have to be careful about their market strategy and must choose the customers they want to serve or bear the expense of supporting numerous bands or versions of hardware.
The best of all worlds
The 2.4 GHz band can easily have comparable range with the sub-GHz bands when all inputs to link budget are accounted for. When combined with the more favorable regulatory environment for DSSS in the 2.4 GHz band, suddenly wireless technologies in that band can produce much better range than sub-GHz peers. The 2.4 GHz band also has worldwide availability at a single frequency. This means that device makers only have to make one device to reach any market in the world, removing the need for complex device management, and gives them access to more customers than any other band. With 7x to 67x the bandwidth of other bands, the 2.4GHz band offers the capacity to support IoT applications today and plenty of room to grow for the IoT applications of tomorrow.
Ted Meyers, co-Founder and chief technology officer, Ingenu
Myers is a recognized expert in wireless communication systems and digital signal processing theory. Prior to co-founding Ingenu, Myers was a founder of CommASIC, where he developed the WBSP processor and its first application to the 802.11 a/b/g physical layer. Based on this architecture, the resulting chipset was a first-pass success and industry best in cost and power consumption, which led to the acquisition of CommASIC by Freescale Semiconductor in 2005. While at Freescale Semiconductor, he applied the WBSP processor architecture to various other wireless applications. Earlier in his career he led and/or contributed to numerous other physical layer designs for cellular applications and government satellite systems. Myers has a Ph.D. and B.S. in Electrical Engineering from Virginia Tech and an M.S. in Electrical Engineering from the University of Maryland at College Park.
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