Busting the biggest myths around microwave transport

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Myth 1 - Microwave cannot handle 5G capacities

One of the main assumptions about microwave is that it cannot handle the capacities required for 5G backhaul. Ever since 3G and the subsequent generations, there have been fears that microwave wouldn’t be able to handle the capacities required, but ultimately, those fears have proven to be unfounded - at the same time as radio access technology has evolved, so too has microwave.

Over the years microwave has added higher frequency bands, with increasingly wider channels, and increased modulations to send more bits/hertz. These and many other techniques have given us higher and higher capacities.

In the traditional frequency bands, from 6 to 42 GHz, we have evolved from narrow channels like 7 and 14 MHz to 28 and 56 MHz, and in recent years on into 112 MHz or even 224 MHz. Such wide channels offer a capacity of 1 to 2.5 Gbps through a single radio, with high availability and over long distances. With two polarizations, you can double that to close to 5 Gbps.

We are also using higher frequency bands such as the E-band at 70/80 GHz, where we can have channels as wide as 2000 MHz, and this results in much higher capacities, in some cases up to 10 – 20 Gbps. It should be remembered that E-band involves shorter distances and slightly lower availability when compared to the more traditional bands.

The great thing though, is that today you do not even have to choose one or the other - you can combine a traditional band with the E-band in something that we call Multi-band booster. In these cases, a wide high-frequency channel is bonded with the narrow low-frequency channel.

The result is a link where you get the best of both worlds - high capacity over a long distance for most of the year, while at the same time securing the high availability for your high-priority traffic. This will give you up to 10 times higher capacity over distances that are three times longer.

It is often possible to increase capacities on existing hardware too - most modern microwave links deployed in the last 10 years support adaptive modulation, meaning that they can support greater capacities than what they were initially configured for, and in some cases this extra capacity can be activated remotely. This means that capacity can be increased without the need for new hardware or site visits – as an example, one operator in the Philippines using Ericsson’s microwave backhaul was able to increase capacity by 44% by activating adaptive modulation.

Don’t just take our word for it – today we see requirements for backhaul capacities ranging from 75 Mbps in low-capacity rural sites to 7 Gbps at the highest-capacity distributed end sites in urban areas, and by 2027 these microwave capacities are predicted to increase even further, landing in a range between 300 Mbps and 25 Gbps.

Backhaul capacity per distributed site. Source: Ericsson 2022

Modern microwave backhaul can already today comfortably handle up to 20 Gbps over a hop, and technology trials have successfully demonstrated 100 Gbps hops, so there is no longer any doubt that microwave can handle the requirements of 5G backhaul – and beyond.

Myth 2 - Microwave is not a low-latency solution

One of the great advantages of fiber networks is of course their speed; it’s hard to get any faster than the speed of light, and it’s very easy to imagine data flashing through fiber networks and arriving at its destination microseconds later.

That said, microwave works on the same principle. Both light and microwave are electro-magnetic waves and both travel at the speed of light in vacuum. In real-life networks, any material they have to pass through will provide some “resistance”, changing the speed and slowing things down somewhat, and this is where microwaves have an advantage – they travel through air where there is less resistance, and this actually makes them faster than fiber.

In a vacuum, electro-magnetic waves travel at a speed of 3.336 microseconds (μs) per kilometer (km). Through the air, that speed is a tiny fraction slower, clocking in at 3.337 μs per km, while through a fiber-optic cable it takes 4.937 μs to travel one kilometer – this means that microwave transport is actually 48% faster than fiber-optic, all other things being equal.

A good indicator of which method is fastest can be found by following the money to modern financial markets, where milliseconds matter when it comes to trading driven by algorithms.

In high-frequency trading (often referred to as HFT or ‘black box’ trading), latency is a huge factor; given the choice, traders would prefer to install their computer systems directly on the same premises as that of a securities exchange’s data center, because any delay in acting on price information can result in lost profits. This is not always possible, and as a result they need to connect to the exchange over a network with the lowest possible latency; here, the technology in use at the moment is microwave.

Another reason for the low latency is a relatively simple one - microwave hops are a line-of-sight solution that takes the shortest path between two points. Fiber optic networks can seldom follow the same principle as they are often deployed in rings or meshes, effectively increasing the distance between the two points.

On top of the propagation latency we also have processing latency.The more “hops” we have in our networks, the more processing latency is added. This applies to both microwave and fiber networks; however, a fiber network encompassing a whole city will have to traverse more points to arrive at its final destination than a microwave signal going point-to-point.

Lower latency thanks to network design and physics vs urban topography that restricts the installation of a straight cable, thus increasing latency.

Myth 3 - Microwave networks do not work in bad weather

Straight off the bat - everyone knows that microwave networks can be adversely affected by rain and other inclement weather, with the high-frequency, high-capacity E-band particularly susceptible. This is one reason for this issue being more of a discussion point around microwave compared to radio access, as radio access is using lower frequencies.

However, we can mitigate this by proper planning, and a well-designed microwave system will offer multiple Gigabits per second and still maintain an availability of 99.999 percent (often referred to as “five nines” availability), which equates to as little as five minutes of less capacity spread over the whole year.

There are a number of tools and technologies available to combat what are known as fading conditions, such as heavy rain. Automatic Transmit Power Control (ATPC) increases transmission power during bad weather and decreases it again when the bad weather has passed, securing the capacity and availability.

Another useful technology is adaptive modulation, which allows a radio to automatically adapt its modulation, increasing or decreasing it depending on the weather conditions. During bad weather the modulation and capacity will be lower, but the prioritized traffic is secured. Under normal conditions the modulation will be high, enabling high capacity.

Adaptive modulation – Securing priority traffic during rainy weather

An additional tool for E-band hops is what we previously mentioned in myth 1, combining E-band with the traditional frequencies over the same hop, achieving both high availability and high capacity, in a multi-band booster hop.

Microwave has been used successfully for many decades around the world, in all kinds of climate zones, and there are many tools available to ensure that they continue to work, even in poor conditions.

Myth 4 - Same-spectrum resources cannot be used for both microwave backhaul and 5G New Radio (NR)

Microwave links are very narrow, concentrated and controlled, and are used to send high-capacity point-to-point, while 5G NR uses a wide beam for coverage. Additionally, 5G NR is a TDD (Time Division Duplexing) band while microwave bands use FDD (Frequency Division Duplexing), posing the question – can the two be used together, using the same spectrum?

The answer is yes, and the key to getting it to work is licensing, so that the usage is controlled by a national regulatory institute. For example, coordination can be implemented by deployments in different geographical areas - or even in the same area - by means of antenna coordination and certain physical separation. For instance, if the spectrum in 5G NR is used in densely-populated areas, with the microwave backhaul employed in lower-density or rural areas, they can use the same spectrum without interfering with each other.

There is also unlicensed use, such as Wi-Fi, NR-U (NR in unlicensed spectrum) that is not controlled. Deployment of unlicensed services in microwave backhaul bands, which are designed for interference-free environment and are sensitive to short traffic burst, should be avoided.

Sharing with another licensed service, such as 5G NR, is more feasible, and it requires coordination where needed at a national level. There are also interference detection solutions based on artificial intelligence (AI) available, but ultimately it comes down to having licensed use so that interference can be minimized or eliminated entirely.

Global and regional view on used microwave spectrum including 5G impact on backhaul spectrum. Source: Ericsson 2022

Myth 5 - Fiber is more reliable than microwave

Though fiber is often considered to be the “perfect” medium for transport networks, the fact that they need a physical unbroken connection to work makes them vulnerable to everything from breaks in cables caused by over-enthusiastic construction workers to animals and natural disasters. Depending on their location, outages caused by physical breaks can take days – or even weeks – to fix.

The reason for that is a simple one – many elements of modern networks are self-healing, sometimes discovering potential issues that might affect performance and remedying them before they even occur. However, a physical break in a fiber link cannot fix itself, which means sending out technicians, sometimes digging holes and searching until the physical fault or break is located before repairing it.

This is bad enough in cities, but imagine such an outage in a remote rural area that is hard to reach , for example an island or a mountain in the winter.

That was the case when the connection to the remote Manu’a Islands in American Samoa went down during the Independence Day weekend of 2021 - Ericsson and American Samoa Telecommunications Authority (ASTCA) restored their vital connection to the world with an extremely long microwave backhaul link. Here microwave came to the rescue.

As described above when busting the bad-weather myth, microwaves also have their limitations as they need to maintain as clear a line of sight as possible between their two points, which means they can be affected by rain, snow and temporary obstructions, but they are not dependent on physical links between sites.

Microwave backhaul systems can of course suffer from hardware failures, but they are extremely reliable, and as a result, they are often installed to provide backup and redundancy for fiber-optic networks, helping to manage the risk of communication loss and minimize any downtime.

There are a lot of perceived truths about microwave technology that don’t quite hold true when you analyze them. Some are myths that have no basis in fact, while others are limitations that can be worked around with a little thoughtful planning.

So the next time you’re sitting down to sketch out your transport solution of the future, don’t let the myths around microwave backhaul cloud your thinking!

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