I am often asked by cities about the option of building a municipal fixed wireless broadband network. As a reminder, fixed wireless, in this case, is not a cellular system but is the point-to-multipoint technology used by wireless Internet service providers (WISPs). My response has been that it’s possible but that the resulting network is probably not going to satisfy the performance goals most cities have in mind.

There are several limitations of fixed wireless technology in an urban that must be considered. The first is the spectrum to be used. Cities tend to be saturated with unlicensed WiFi signals, and the amount of interference will make it a massive challenge to use unlicensed WiFi for broadband purposes. Most folks don’t realize that cellular carriers can snag a lot of the free WiFi spectrum in cities to supplement their cellular data networks—meaning that the free public spectrum is even more saturated than what might be expected.

Licensed spectrum can provide better broadband results. But in cities of any size, most of the licensed spectrum is already spoken for and belongs to cellular companies or somebody else that plans to use it. It never hurts to see if there is spectrum that can be leased, but often there will not be any.

Even if licensed spectrum is available, there are other factors that affect performance of fixed wireless in highly populated areas. The first is that most fixed wireless radios can only serve a relatively small number of customers. Cities are probably not going to be willing to make an investment that can only serve a limited number of people.

Another issue to consider is line-of-sight. In practical terms, this means that neighbor A’s home might block the signal to reach neighbor B. In the typical city, there are going to be a lot of homes that cannot be connected to a fixed wireless network unless there are a lot of towers—and most cities are averse to building more towers.

Even when there is decent line-of-sight, an urban wireless signal can be disturbed by the many routine activities in the city, such as seasonal foliage, bad weather, and even traffic. One of the more interesting phenomenons of spectrum in an urban setting is how the signal will reflect in scatter in unexpected ways as it bounces off buildings. These factors tend to cause a lot more problems in a dense neighborhood than in a rural setting.

A point-to-multipoint fixed wireless system is also not a great solution for multi-tenant buildings. These networks are designed to provide bandwidth connections to individual users, and there is not enough bandwidth to deliver broadband from one connection to serve multiple tenants. There are also challenges with where to place antennas for individual apartments.

The combination of these issues means that fixed wireless can only serve a relatively small number of customers in an urban area. The speeds are going to bounce around due to urban interference. Speeds are not likely going to be good enough to compete with cable technology.

There is a good analogy to understand the limitations of wireless technologies in cities. Cell carriers have one advantage over many WISPs by owning licensed spectrum. But even with licensed spectrum, there are usually numerous small dead spots in cities where the signals can’t reach due to line-of-sight. Cellular radios can serve a lot more customers than fixed wireless radios, but there are still limitations on the number of customers who can buy cellular FWA broadband in a given neighborhood. Any issues faced by cellular networks are worse for a point-to-multipoint network.

The bottom line is that there are a lot of limitations on urban fixed wireless networks that make it a risky investment. Tower space is usually at a premium in cities, and it’s hard to build a network that will reach many customers. There are a lot more interference and line-of-sight issues in a city that makes it hard to maintain a quality connection.

But this doesn’t mean there are no applications that make sense. For example, a fixed wireless network might be ideal for creating a private network for connecting to city locations that don’t need a lot of broadband, like sensor monitoring. That makes a lot more sense than trying to use the technology as an alternative ISP connection for residences and businesses.