Dealing with Interference Part 1 of 2
You’re sitting with a friend at a café chatting about the latest viral YouTube video, when the lady at the table next to yours begins to talk on her phone.
Only she isn’t talking, she’s yelling. Her voice is far too loud and it’s obnoxious. You can’t even understand your friend anymore. In technical terms, this lady’s voice is causing interference to your conversation. M2M and IoT devices using wireless connectivity deal with the same thing, only Loud Voice lady is some other device hanging around.
In a prior post, we talked about why Ingenu unabashedly loves the 2.4 GHz band. Sometimes we get asked about how busy that band can be and what we do to deal with interference. In this post, we’re going to tell you all about how we handle interference on the 2.4 GHz band when it happens (and it does sometimes).
Interference is an issue any wireless technology will have to deal with, the question is, can it deal with it effectively.
Unlike you and your friend who can just find a table further away, many devices stay right where they are. One of the simplest ways to deal with interference is channel coding, also known as forward error correction (FEC). FEC is kind of like scrambling your message in a fancy and efficient redundant way, and then sending the scrambled message. Sure, some of the packets might get shot out of the air like clay pigeons in a Texan sky, but you are much more likely to get the message through.
The issue some LPWA providers face with FEC (that RPMA doesn’t) is the fact that it requires capacity throughput, that they just don’t have, to encode the data in a redundant way. In other words, dealing with interference is partly a function of your technology’s throughput. RPMA’s throughput is >40,000 bps uplink, and >20,000 bps downlink (FCC). Cellular providers don’t have this issue of course being consumer focused. LPWA providers however, struggle to provide this kind of interference protection with only 1-5% of RPMA’s uplink capacity and 0.02% of RPMA’s downlink capacity. This means RPMA has plenty of room to provide extremely robust transmissions and many other capabilities such as enterprise grade security and firmware downloads. Take that Loud Voice lady!
A naïve approach to protecting against interference like that is simply repeating the message a set number of times, hoping the message makes it through. That’s like you sitting there, blindly repeating what you said from start to finish several times, even if your friend got it the first time, or still repeating the whole thing even if they heard the first half but not the second half. Not only would you have a bewildered buddy, but you would also have wasted everyone’s time and energy. Waste not want not, right? But there’s more to this story.
Continue learning how RPMA intelligently handles interference, by reading our followup blog post, Dealing with Interference, Part 2.
Why RPMA Unabashedly Loves the 2.4 GHz ISM Band
Ingenu’s RPMA utilizes the 2.4 GHz ISM band. There, we said it. And we love it! The 2.4 GHz band offers many reasons why it is a practical choice for M2M communication if you are savvy enough to use it right.
At first glance some think that the 2.4 GHz band is inferior to the sub GHz band due to propagation. But this is trivially overcome with antenna diversity. In plain English, we put two antennae on our modules rather than one, because we can. The 2.4 GHz band wavelength is shorter than the 900MHz so we are able to place two antennae and still have flexible and practical small form factors. And just like that, propagation issues are overcome.
As with many things, government regulations are the largest hurdle for most frequency bands, including the 900 MHz family of bands. However, the 2.4 GHz band has very favorable government regulations in both the US and Europe. For example, in the US, narrowband transmissions are restricted to 400ms (or 0.4 seconds), but this doesn’t affect RPMA as it utilizes direct-sequence spread spectrum (DSSS) modulation. +1 RPMA!
Another advantage of the 2.4 GHz band is the enormous amount of bandwidth available in the 2.4 GHz band. We have 80 MHz of bandwidth in the US. That means in the US we have 40 completely independent channels to choose from. And in Europe we have an enormous amount compared to only 500 kHz for the 900 MHz band.
What’s more is the 2.4 GHz band is truly available worldwide cost-free. It’s as if some worldwide organization back in the mid 20th century decided that the 2.4 GHz band should be available worldwide. Wait, they did! The 900 MHz family has the ‘family’ in its name because in Europe it is actually 868 MHz and in the US it is 915 MHz; so it isn’t actually available worldwide as a single continuous band.
RPMA was designed to utilize the 2.4 GHz band because it is available worldwide, has more bandwidth, is cost free, and has extremely favorable regulatory conditions. In the end, it isn’t just the frequency band that matters; it’s what you can do with it. And what RPMA does is simply genius.
Get a more detailed comparison of the 2.4 GHz band and 900 MHz band by reading our forthcoming white paper, Unlicensed Spectrum: 2.4 GHz and 900 MHz Compared.
2.4 GHz – The Ideal Unlicensed Spectrum for Long-Range IoT Networking (Part III)
Supporting the Broadest Global Deployments
The IoT market is global – companies developing applications want to be able to deliver their solution to the widest available market. Similarly, serving the largest available market drives down costs by utilizing common components, infrastructure and so on.
The 2.4 GHz band has a substantial advantage over 900 MHz on this dimension. As shown in the figure below, 2.4 GHz provides a single spectrum choice with virtually global availability, under very similar rules. The 900 MHz band is a more fractured story, with different frequency bands in different geographies, variation in critical rules and some countries, without availability.
Global ISM Bands
More Spectrum Means Greater Capability and Flexibility
In addition to its global availability, the 2.4 GHz ISM band provides a large absolute amount of spectrum – covering 80 MHz of bandwidth. Move available bandwidth provides more capability and flexibility in delivering real-world solutions.
On-Ramp’s RPMA system is architected around a one MHz channel bandwidth. An entire RPMA network can be deployed as a single channel network using only one MHz of the entire 80 MHz of available spectrum. This small channel footprint in the broad frequency band provides flexibility in deployment models to improve the capabilities and performance of RPMA networks. RPMA networks are designed so that additional frequencies can be used to increase capacity, extend coverage, and provide robustness to interference. Up to four independent RPMA networks can exist in the same area providing maximum benefit of channel flexibility for each.
RPMA – Specifically Designed for the Unlicensed Spectrum
The 2.4 GHz spectrum is ideal for delivering the benefits of the On-Ramp Wireless RPMA long-range IoT network with:
- Unparalleled coverage: RPMA breaks through the barrier in wireless communications by delivering wide-area coverage with a simple network architecture. The system’s performance parity and antenna diversity enabled by 2.4 GHz offset the propagation advantages of 900 MHz.
- Global Availability: RPMA technology has the operational advantage of virtually global availability in single frequency band
- More Deployment Options: The 2.4 GHz band results in substantially more available spectrum to provide enhanced deployment flexibility.
If you’re interested in deploying an M2M application, please get in touch with the experts at On-Ramp Wireless.
2.4 GHz – The Ideal Unlicensed Spectrum for Long-Range IoT Networking (Part II)
2.4 GHz vs. 900 MHz – range, flexibility and the global marketplace
Range – Propagation and Other Key Factors
For building long-range IoT (Internet of Things) networks, the cost of connectivity is heavily driven by the coverage that can be achieved by each base station deployed in the network. Conventional wisdom says that long-range applications should use 900 MHz due to better propagation. Simply put, a technology with identical technical characteristics (receiver sensitivity, power output, etc.) will cover a wider area implemented in 900 MHz than in 2.4 GHz. Expressed in link budget, this advantage translates into a roughly 9 dB advantage for a 900 MHz system.
What is Link Budget? Link budget, along with assumptions on path loss, is sufficient to give the area covered for a given probability of coverage and a given indoor/underground penetration value. However, for real-world performance, the trade-off is not that simple. The 900 MHz and 2.4 GHz systems have other differences besides propagation loss that are important to performance of the overall system in providing coverage (See Table). Antenna diversity is a well-known technique for improving the effective link budget performance of wireless systems – two antennas with sufficient separation can be governed by independent fade margins. The separation required is directly related to the wavelength in question – providing a distinct advantage to 2.4 GHz systems. The much smaller separation required makes antenna diversity in IoT scale endpoints possible at 2.4 GHz – an option not even available to a technology implemented in 900 MHz spectrum. The improvement in effective link budget from antenna diversity in On-Ramp Wireless’ RPMA system is roughly 8 dB – almost completely offsetting the propagation advantage of a 900 MHz alternative.
What does this mean for the actual coverage of RPMA? Simply put, given the offsetting effects of these two differences, one can simply use link budget to compare the coverage performance of an RPMA system vs. any system implemented in 900 MHz.
2.4 GHZ vs. 900 MHz Comparison
(Stay tuned for the next week’s conclusion of this article)