Microwave Transmissions: Are They Reliable?

Friday, April 19, 2013 • Marty Snyder • Microwave

One of the biggest questions I get about microwave has to do with how reliable it is.

Most people are generally unaware that Microwave has been a "staple" technology in the quiver of telecom companies for decades. In fact, most people are unaware that the onetime Telecom giant, MCI's name stood for "Microwave Communications Inc." If you make a long distance telephone call anywhere on earth, there is a decent chance part of your call will be carried over microwave. Those chances increase if the area you are calling from or to is more rural. Microwave transmission plays a major role in cellular phone companies where the connecting of thousands and tens of thousands of cell sites would not be possible without it. In the United States about 20% of all cell sites are served by microwave transmission. Outside of the US, those percentages increase in many areas of the world with less cable infrastructure. The reliability of microwave has been well understood by industry professionals. Most telecom operators in the world use microwave transmission in some form or another, so how reliable is it?

First of all we have to recognize that microwave transmission uses various frequencies in the available spectrum. Every country has established spectrum policies and many follow comparable standards. Many different frequency bands are reserved for microwave use and not all frequencies have the same characteristics. For frequencies in the lower bands such as 6, 7 & 8 GHz, climactic conditions have little effect on transmission. As you get into the higher bands, signals can be impacted by rain and weather much easier. But just because transmission can be effected by rain does not mean it won't be reliable. The trained Microwave Transmission Engineer has many tools in his/her quiver to address and overcome those issues, and allow for reliable use of any band as long as it is designed properly. Just as it is difficult to build a bridge over the San Francisco Bay, does not mean it cannot be done reliably. It just means that the engineer must follow design guidelines to achieve the desired reliability.

Designing microwave links for Ultra Low Latency requires a different thought process and therefore a different set of steps than designing microwave for other telecommunications purposes. When reducing latency is the goal, reliability can be sacrificed. While the equipment is different, so is the engineering approach. Network reliability, throughput and latency become the levers that must be understood in order to design a proper Ultra Low Latency Link. Moving one lever often negatively impacts the other. Ultra Low Latency is a function of understanding those levers, how they interact with each other, and striking the right balance that matches your low latency strategy. Selection of equipment is just as critical as the techniques employed, and goes hand in hand with the design strategy employed.

There are also outside factors that come into play in the design process such as available sites, frequency congestion, and project timeline. These outside factors also play into the design strategy to employ. Not understanding how these factors affect each other can cause the designer to develop a sub-optimal system that does not perform as desired or may take much longer than anticipated causing the stakeholders to wonder why they got into the microwave game. The outside factors often drive the overall network latency more than the engineering itself. For example, one might assume that using the fewest number of sites is the best way to design an ultra low latency network. However, site selection can be limited by multiple outside factors, making it next to impossible to select the optimal number of sites or the desired sites requiring a compromise if the network is to be completed. All of the technical factors must be balanced with real world circumstances and the real world circumstances more often than not work against the objectives of designing the best possible network.

Knowing when to compromise and when not to requires experience to understand the nuances of each of these factors and how they will directly impact your success of developing the ultimate Ultra-Low Latency microwave network.

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About Marty Snyder
Marty Snyder is President of CIC, a future thinking wireless firm founded in 2002, currently focused on microwave, satellite and small cell development.

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