What is microwave backhaul?

01 January 2010 |


Microwave backhaul refers to the transportation of traffic (voice, video and data) between distributed sites and a more centralised point of presence via a radio link.

Operators can lease microwave spectrum and build networks that deliver several E1/T1s, STM1/OC3s and Ethernet services over the air, providing an instant, reliable and relatively low-cost solution to the growing global demand for backhaul capacity.

Microwave is already the backhaul technology used by most mobile operators worldwide, and outside the US nearly 70% of backhaul traffic travels over microwave links. This trend is likely to continue since microwave is a scalable and economical backhaul option compared to leased line copper and new fibre.

Why do we need additional backhaul?

Over the next few years, mobile carriers will transition their networks from 2G/3G radio access to 4G access technologies. These networks will need to deliver far more bandwidth to support richer applications and demand for backhaul capacity will rise geometrically. Microwave radio systems are emerging as a good way to deliver capacity without undue strain on budgets. The mobile backhaul infrastructure carries voice and data communications traffic from the access network (cell sites) to the core network. Most cell sites have been connected to the core network via E1 lines. Sometimes these lines are owned by the same company, but for many mobile operators they must be leased from a company with a competitive wireless service.

With 2Mbps of service per line, E1 lines have traditionally been used in groups to provide up to 10Mbps of backhaul capacity per cell site. This strategy has been adequate for 2G voice and GPRS or EDGE data services, but it is inadequate for 3G services such as HSPA and UMTS, and it won’t even begin to support 4G services such as LTE and Wimax.

On today’s 3G networks, devices such as the Apple iPhone are demanding far more bandwidth than earlier devices due to their heavy use of data-intensive applications. 4G services, combined with the widespread use of smartphones, will demand even more bandwidth from the mobile infrastructure. These 4G services will require 10 to 100 times as much backhaul capacity as the current E1-based infrastructure provides.

What backhaul options are available?

Mobile carriers currently have three choices available to them when looking to meet the growing backhaul demands of their consumers.

They can deploy or lease additional E1 lines. This will work as a stopgap measure, but it is ultimately impractical because of the sheer number of lines required to support the huge increase in capacity. Even if it is possible to use additional E1 lines temporarily, they require a linear increase in backhaul costs of as much as £1,000 per E1 per month.

Fibre represents another alternative and offers plenty of bandwidth, but at a cost of more than £100,000 per km to deploy a 1Gbps service, this is a very expensive option, and trenching for new fibre may be impossible in historic districts or other areas with strict building codes. Even if it is possible to lay new fibre, the process takes several months.

The third alternative is wireless. Microwave radio links can be deployed within days at a one-time cost of roughly £20,000 for an LTE-ready backhaul connection. Clearly, microwave radio systems provide more backhaul bandwidth at a far lower cost.

What is the business case?

Microwave backhaul presents a compelling business case from day one, providing a flexible solution that delivers measurable advantages to the mobile carrier looking to meet strict budgets and deadlines.

Carriers are able to achieve a rapid time-to-service and are able to react quickly to developments within the market, with systems capable of being deployed within hours or days. Software-upgradable capacity offers further flexibility, allowing carriers to adopt a “pay as you grow” strategy, for example starting with a relatively low-speed link (20Mbps, for example), and scale it via software licence keys to hundreds of Mbps. These upgrades are also inexpensive, driving down the overall cost per Mbps as capacity increases to further reduce payback times.

Additional expansion can be achieved through capacity aggregation, allowing carriers to further increase capacity – up to 1Gbps or more – by using multiple radios to drive traffic over one link. Further economy of scale is achieved through the ability to carry both native TDM traffic as well as Ethernet, enabling operators to accommodate any mix of traffic and migrate easily to IP-centric traffic over time.

Microwave radio systems are also available in licensed and licence-exempt frequencies, giving carriers flexibility to support interference-free service for any application and data rate over distances of up to 80km. Combined with the ability to offer 99.999% throughput availability – less than five minutes of outage per year – advanced interference mitigation techniques provide the ability to deliver a carrier-grade service.

Next steps

Mobile carriers won’t upgrade their backhaul networks overnight, but only microwave radio systems offer the low initial costs, high scalability, service flexibility and rapid deployment that allow carriers to migrate at their own pace. In many cases, microwave radio systems will enable faster and more profitable 4G roll-outs as carriers continue to provide legacy 2G and 3G services.