Telecoms.com periodically invites expert third-party contributors to submit analysis on a key topic affecting the telco industry. In this piece Fastback Networks CEO Kevin Duffy discusses the impact the growth of LTE has had on wireless backhaul and how unlicensed spectrum in the 5GHz and mmWave bands is being employed to provide additional capacity.

The rapid uptake of 4G (LTE) has taken the industry by surprise. Already prevalent in the U.S. market, global adoption has exceeded forecasts with markets like the UK leading the way with subscriber figures hitting the 10 million mark.

There has been plenty of discussion about RAN expansion and network densification, and of how operators are looking to a mixture of macrocell and small cell solutions to add capacity and maintain high levels of performance. But, data usage is only going to increase, so where does this leave network backhaul? Advanced wireless backhaul solutions that operate in unlicensed bands can provide operators with the ability to match and sustain network growth now and into the future. Much needed surplus capacity can be found in the sub 6GHz and mmWave bands, reducing reliance on more expensive licensed spectrum.

Wireless provides the obvious solution for backhaul due to the scarcity of fiber, particularly in dense urban environments where the vast majority of data usage is consumed. Fiber will still play a key role in backhauling data traffic to the core network but a hybrid approach is required with wireless systems that deliver fiber-like performance. As network densification continues, wireless backhaul systems will have to contend with physical obstructions throughout indoor and outdoor public spaces.

Traditionally, wireless backhaul systems operate in direct line-of-sight paths (LOS), but because of growing capacity demands on LTE networks, this is no longer sufficient. To address this, operators are now adopting advanced solutions that can transmit radio signals in non-line-of-sight (NLOS) or near-line-of-sight (nLOS) conditions.  And systems that support higher capacity and are efficient over shorter ranges, covering geographical areas where data usage is at its most intense.

New advanced wireless backhaul solutions that operate in sub 6GHz and mmWave bands are able to perform the dual role of sustaining the Gigabit-range high throughput, and extreme low latency requirements of LTE in dense urban environments. Legacy wireless backhaul is being displaced by more advanced solutions that deliver this fiber-like performance. A concept that was unheard of five years ago, this demonstrates how rapidly wireless backhaul technology has advanced.

Fiber-based carrier Ethernet is the industry go-to backhaul solution to meet bandwidth requirements, but it is often not available, or economically viable, particular in metropolitan areas where it is expensive to install fiber. Wireless backhaul is much lower cost and quicker to deploy, and can support cell sites deployed in areas where fiber cannot reach. Advanced wireless backhaul systems are capable of circumnavigating physical obstructions but also mitigating the RF interference generated by multiple base stations, operating on various cellular frequencies, and Wi-Fi access points that are now ubiquitous in dense urban environments.

Today LTE is predominantly a channel for delivering data services and, with the exception of third party VoIP applications, it has not yet been widely used to deliver voice services, but all that is about to change with the onset of VoLTE. This represents a big disruption for the mobile industry. Unlicensed frequencies in the sub 6GHz and mmWave bands provide a robust backhaul spine to support ambitious LTE rollouts. Not only does this immediately improve LTE services by providing higher capacity Gigabit backhaul in areas that need it the most, it also allows support for future technology standards.

Operators are now adopting solutions that leverage the benefits that both sub 6GHz and mmWave have to offer. These are naturally complimentary technologies. The former is well suited to environments rife with obstructions and the latter delivers highest speeds for short distance LOS links in the most densely concentrated LTE usage areas. Legacy wireless backhaul cannot perform to these demands. A network is like a chain – only as strong as its weakest link – and the transition to more advanced systems is critical to prevent backhaul from becoming just that as the topology of the operators’ networks changes.

Advanced wireless backhaul solutions in these frequencies help operators reach the goal set by LTE standards, to achieve more bandwidth per square area in any location, supporting more users and maintaining a healthy level of customer satisfaction. By using the combined sub 6GHz and mmWave bands for wireless backhaul systems, operators can address the complexities of LTE today as well as the emerging requirements for LTE-A, and eventually 5G.

Kevin Duffy has 25 years of experience developing and monetizing advanced telecommunications and networking technologies. Formerly, Mr. Duffy was CEO, Proxim, where he led the company’s pioneering efforts in the convergence of new technologies, including wireless LAN, cellular backhaul, and multipoint access systems. Previously, Mr. Duffy held a series of positions of expanding responsibility with Siemens in Germany, including VP & General Manager, and Director of Product Development for a variety of product lines including cellular handsets and home networking. In his early career, Mr. Duffy held positions with Nortel and Tracor Aerospace. BS Computer Science, University of Texas, US Air Force.