One of the first in-depth reviews I’ve found for T-Mobile’s fixed cellular broadband was published in the Verve. It’s not particularly flattering to T-Mobile, and this particular customer found the performance to be unreliable—fast sometimes and barely functioning at other times. But I’ve seen other T-Mobile customers raving about the speeds they are receiving.

We obviously can’t draw any conclusions based upon a single review by one customer, but his experience and the contrasting good reviews by others prompted me to talk about why performance on cellular broadband networks can vary so significantly.

I’ve always used the word wonky to describe cellular performance. It’s something I’ve tracked at my own house, and for years the reception of the cellular signal in my home office has varied hour-by-hour and day-by-day. This is a basic characteristic of cellular networks that you’ll never find the cellular carriers talking about or admitting.

The foremost issue with cellular signal strength is the distance of a customer from the local cellular tower. All wireless data transmissions weaken with distance. This is easy to understand. Wireless transmissions spread after they leave a transmitter. The traditional way we depict a wireless transmission shown in the diagram below demonstrates the spread. If two customers have the same receiver, a customer who is closer to the tower will receive more data bits sooner than somebody who is further after the signal has spread. The customer in the bad review admitted he wasn’t super close to a cell tower, and somebody in his own neighborhood who lives closer to the cell site might have a stronger signal and a better opinion of the product.

There are other factors that create variability in a cellular signal. One is basic physics and the way radio waves behave outdoors. The cellular signal emanating from your local cell tower varies with the conditions in the atmosphere—the temperature, humidity, precipitation, and even wind. Things that stir up the air will affect the cellular signal. A wireless signal in the wild is unpredictable and variable.

Another issue is interference. Cellular companies that use licensed spectrum don’t want to talk about interference, but it exists everywhere. Some interference comes from natural sources like sunspots. But the biggest source of interference is the signal from other cell towers. Interference occurs any time there are multiple sources of the same frequency being used in the same area.

The customer in the review talks about the performance differing by the time of day. That is a phenomenon that can affect all broadband networks and is specific to the local robustness of the T-Mobile network. Performance drops when networks start getting too busy. Every DSL customer or cable company broadband customer has witnessed the network slowing at some times of the day. This can be caused by too many customers sharing the local network—in this case, the number of customers using a cell tower at the same time. The problem can also because caused by high regional usage if multiple cell towers share the same underlying broadband backbone.

The final issue that is somewhat unique to cellular networks is carrier priority. It’s highly likely that T-Mobile is giving first priority to customers using cell phones. That’s the company’s primary source of revenue, so cell phones get first dibs at the bandwidth. That means that the data left over for the fixed cellular customers might be greatly pinched in busy times. As T-Mobile and other carriers sell more of the fixed product, I predict the issue of having second priority will become a familiar phenomenon.

This blog is not intended to be a slam against fixed cellular broadband. The customer who wrote the review switched to cellular broadband to get a less expensive connection than his cable company. This customer clearly bought into the T-Mobile advertising hype because a cellular broadband signal will never be as reliable as a signal delivered through wires.

We can’t forget the real promise of fixed cellular broadband—bringing broadband to folks who have no alternatives. Somebody that switched to T-Mobile from a 1 Mbps rural DSL product would have written a different and more glowing review of the same product. The bottom line is that anybody buying cellular broadband should recognize that it’s a wireless product—and that means the product comes with the quirks and limitations that are inherent with wireless broadband. I imagine that we’re going to continue to see bad reviews from customers who want to save money but still want the performance that comes with wired broadband. This is another reminder that judging a broadband product strictly by the download speed is a mistake—a 100 Mbps cellular broadband product is not the same as a 100 Mbps cable company connection.