Tom Wang -


Evolution of cellular 5G backhaul architecture faces challenges

Backhaul has become trendy again and for good reason. 5G backhaul architecture means network architects will have to reconsider how their networks can handle 1 Gbps speeds.

Thanks to 5G and the evolution of Wi-Fi standards, backhaul has become trendy again.

For the purpose of this article, we'll keep the definition simple: Backhaul is the connection from a wireless node to the main, wired network. Backhaul has become newly interesting. Historically, it wasn't always an intriguing topic. But 5G and the latest Wi-Fi standards have changed the dynamics. Today, those technological enhancements are shining a new spotlight on 5G backhaul architecture and its role in mobile communications.

A quick thought on Wi-Fi backhaul

For several generations of 802.11-based wireless LAN (WLAN), we'd hang access points (APs) and backhaul them with a single cable run back to a wired Ethernet switch. The switch provided both operational voltage and either a 100 Mbps or gigabit connection back to the network.

This provided more than enough wired-side capacity for anything the radios were generating for network traffic. But, when 802.11ac and 802.11ax came along, the math changed. Those standards theoretically can top 1 Gbps of traffic on the wireless side of an AP. So, the industry responded with Multigigabit Ethernet (mGig), or NBASE-T, switches that can deliver increments of 2.5 Gbps, 5 Gbps and even 10 Gbps to an AP on the same copper wire run.

This was a major evolution in backhaul for WLANs. 5G is sparking the need for a similar technological advance, but the options and challenges here get a lot muddier.

5G backhaul challenges

As with Wi-Fi, backhaul's role in cellular networks wasn't that exciting for many years. Drive down the highway, see the cell tower that you connect to with any cellular technology, like 3G or 4G, and picture a fiber cable running from the shack at the base of the tower back to the carrier's core network.

As the larger 5G network landscape comes to fruition, fiber will still be preferred. But it also won't be a viable option in many locations.

Alternatively, a microwave link might be used instead of fiber or as a segment of the backhaul path. Either way, the basic construct was simple: Most cell sites were equipped with backhaul links running at 1 Gbps or less.

The benefits promised by 5G change the components of 5G backhaul architecture. With new ultralow-latency connectivity, client-facing data rates that theoretically exceed 10 Gbps and support for thousands of simultaneous clients per cell, 5G shatters current mobile infrastructure design -- provided the technology lives up to the standard's allowed top-end specs.

For instance, 5G sheds 4G's reliance on towers. Instead, 5G relies on an infinite number of small cells bolted to utility poles, buildings and other structures to make its higher-frequency, shorter-range network access signaling accessible. Each one of those cells will need backhaul -- and backhaul that can deliver on 5G's performance promises.

And what about fiber?

As the larger 5G network landscape comes to fruition, fiber will still be preferred. But it also won't be a viable option in many locations. And, while microwave and free-space optical technologies can deliver 10 Gbps connectivity, they tend to be expensive and have strict line-of-sight requirements that won't work well in many places where 5G small cells have to go.

So, what's the answer?

I'm guessing it will be 5G cells that can use traditional backhaul approaches. Others will likely have to compromise their performance top ends by using 5G backhaul architecture designs that create the least amount of bottlenecks among client devices.

It also stands to reason that, like mGig, the networking industry may come up with some new technology specifically aimed at enhancing 5G backhaul in difficult locations.

Whatever occurs, the next evolution of backhaul will be an interesting space to monitor.

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