Fibre backhaul – easing the transition with multipoint microwave
When discussing backhaul technologies for mobile networks, fibre is often touted as one of the best solutions due to its efficiency and perceived infinite speed and capacity, which make light work of dealing with the data-centric traffic generated on today’s networks. There is a particular focus on the technology with operators looking to transition from 3G networks to IP-based 4G networks.
Why then do operators appear hesitant to deploy fibre networks? Part of the issue is that fibre is still expensive to deploy — a typical 1 km length could cost upwards of $85,000 1, including the costs of purchase and installation. It’s also a complex and time-consuming process. Typical mobile network cell sites are not always in the most accessible of areas and excavation work can often take days, if not weeks, to complete.
Yet built fibre isn’t the only option. Leased fibre is becoming commonplace, particularly in the mature markets. Leasing fibre from a third party provider will reduce the upfront capital investment, but without having a privileged relationship with a fibre provider the on-going lease costs, about $12,000 per cell site per year in the mature markets, will soon add up. The cost rises for operators in emerging markets where a typical leased fibre link per cell site could exceed $22,000 per year. Operators are also confined to the footprint of the fibre networks, leaving little flexibility for network planning. If you also take into consideration that the majority of fibre installations are for the delivery of business and consumer broadband services, these networks do not extend to the typical mounting points for cell sites. An operator either needs to renegotiate new mounting points at a fibre point of presence (PoP), or extend that fibre to its existing nodeB cell sites.
With reluctance towards fibre, due to this high cost and low availability, what are the alternatives for operators?
Wireless backhaul is a much lower cost solution for mobile operators than either leased fibre — because of the high opex — or built fibre — due to the large initial investment. The cost advantages increase in the emerging markets, where the costs of leasing and building fibre connectivity are typically higher than in developed markets. In a developed market wireless backhaul can save mobile operators 26% over leased fibre and 42% over built fibre over ten years. In an emerging market, these figures are 59% and 68%, respectively.
With wireless backhaul, you have two options: point-to-point (PtP) or multipoint microwave. PtP networks typically use a tree and branch architecture, where each individual link is made up of two dedicated radios, with each of these links requiring its own spectrum. When traffic over the networks was primarily voice and SMS, which is synchronous by nature, operators were able to provision each of these links to deal with the low capacity required. However, today with the unpredictable and bursty nature of data traffic, an operator would need to provision for the peak traffic across each of these links. This is not without its own issues, primarily inefficiencies in the network, with an average 75% 2 of spectrum wasted when cells are idle. This means that with the transition to LTE and 4G networks which require an even higher capacity, each individual PtP link will need to be provisioned for a much higher peak — this could be many times more than the current provisioning per link. In this scenario, operators are in danger of running out of spectrum very quickly.
Multipoint microwave, on the other hand, has some inherent advantages over PtP. Multipoint networks use a hub and spoke architecture, where a number of remote access terminals within a 90 degree sector communicate with a single point at the base station or fibre PoP. This means that instead of provisioning spectrum for peak traffic across individual links as with PtP, multipoint networks are able to ‘share’ the available capacity across sites connected to the hub — a much more efficient approach. The technology can also take advantage of techniques such as statistical multiplexing to provide much higher spectral efficiency and capacity gains than PtP. Multipoint microwave therefore allows operators to be more flexible with network design, choosing the most appropriate mounting sites for their networks based on optimal performance rather than fibre availability.
Is microwave just delaying the inevitable move to fibre?
Not at all, the high costs and uncertain availability of fibre mean that microwave solutions are actually essential in the foreseeable future but operators are fast approaching the limitations of traditional PtP microwave.
According to a recent SenzaFili white paper, ‘Wireless backhaul can ease transition to fibre’, operators that initially deploy multipoint microwave as an interim solution, whilst slowly transitioning to fibre over a 10 year period, can significantly reduce the Net Present Value (NPV) of that transition. The study shows that NPV can be reduced by up to 7% in developed markets and 31% in emerging markets compared with leased fibre, and 14% in developed markets and 27% in emerging markets compared with built fibre.
As previously mentioned, multipoint microwave has a significant initial cost reduction over built fibre. Equipment and deployment costs make it slightly more expensive initially than leased fibre, but subsequent OPEX is lower.
Operators that choose to take the hybrid approach can take advantage of the high capacity offered by multipoint microwave to cost-effectively support the requirement for the growing 3G traffic today, and the build of new LTE networks in the future. The ease and speed of deployment of the technology also enables operators to quickly and cost-effectively deploy, expand and scale the network for the purpose of increasing both coverage and capacity.
This also gives operators the flexibility needed for building networks in the first instance. An operator can deploy a nodeB cell site in the optimal location, even if there is no fibre present. Operators can then slowly transition to leased fibre when it becomes available at the required cell sites, or becomes affordable, or the operator decides to build its own fibre network; the deployment of which is no longer time constrained.
There is a long overdue need to transition to a higher capacity backhaul solution to meet the data demand. Where fibre is available and affordable, operators should adopt it as soon as they need a new backhaul link. For a leased link this is around $7,000 per year, while built fibre needs to be below $50,000 per km. However, in many markets this is not the case. Therefore, operators need to look to a longer-term strategy where both fibre and wireless are complimentary. Failure to do so could see an operator paying over the odds for their backhaul network and, ultimately, falling behind competitors who are exploiting all the available technologies to the full.
References
- Whitepaper: Wireless backhaul can ease transition to fibre, SenzaFili, May 2012.
- Press release: 40% backhaul efficiency gains: https://cbnl.com/news/cbnl-demonstrate-40-microwave-backhaul-efficiency-gain.
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