BACKHAUL SOLUTIONS - Weighing up the options
Everyone agrees that backhaul is expensive, but is there an ideal one-size-fits-all 
solution, asks Lance Hiley
The headlines are clear for everyone to see: backhaul is one of the biggest issues and expenses facing mobile operators today. There isn't much consensus within the industry on what to do about it, but one thing that everyone does agree on is that the cost of backhaul represents 30 per cent of the capital and operational expenditure spend of the average operator each year. This could represent nearly $20 billion this year, and the figure has grown over the last few years with more data being consumed. Indeed, figures from Yankee Group indicate that transmission costs as part of operational expenditure (opex) in 2G networks can be as little as 10 to 20 per cent, but rises to 30 to 40 per cent in existing 3G networks. Global expenditure is predicted to reach $23billion by 2013.
Carrying data is clearly expensive, and unless this cost is brought down, it will continue to increase with the problem being exacerbated as mobile networks are built and upgraded to support new mobile data services and standards such as HSPA, WiMAX and LTE. If operators are to roll out the next generation of data services and importantly, realise significant profits, both opex and capex need to be reduced - doing ‘more of the same' is no longer an option.
Whilst doing more of the same is no longer enough, to solve the backhaul issues facing operators around the world and equip them for the future, we need to recognise that the majority of operators will have legacies of leased line and point-to-point backhaul infrastructure already in place. As such, we cannot simply recommend discarding the past and beginning with a clean slate. Particularly in Western Europe, with the predominance of point-to-point microwave links connecting cellular base stations, recommending that each link is replaced is simply not a realistic option for operators.
Achieving higher backhaul capacity is not just a matter of adding bandwidth; it also involves increasing the efficiency of traffic handling. As the industry evolves to a full packet environment, microwave must be able to support Ethernet IP protocols in addition to legacy 2/3G interfaces, such as time division multiplexing (TDM) / asynchronous Transfer Mode (ATM) and synchronous optical networking (SONET) / synchronous Digital Hierarchy (SDH).If we look briefly at the options available to operators for backhaul - leased line, point-to-point, point-to-multipoint - we begin to see that only two technologies effectively extend the benefits of IP/Ethernet principles to the network edge - which is where it needs to be to get the necessary bandwidth at reduced opex.
Deployment time | CAPEX | OPEX | Capacity | Reliability/Operator control | |
Leased lines | Leased from third party | Low | High | T1, multiple Ts Low | Unpredictable; dependent upon suppliers |
| Fiber | Slow | High; increase with distance but diminishes over time | Dependent upon regulatory market in local environment | High | Medium - subject to civil works and environmental damage |
| Microwave | Fast | Medium to Low; Flexible, not related to distance | Low | Medium to High | High, users have total control |
The table above is a useful comparison prepared by Yankee Group of the different backhaul technologies and approaches available. It is clear that there are several trade-offs to be understood when deciding on a backhaul strategy.
Leased lines and fibre tend to be seen as a panacea for the industry, but clearly there are disadvantages. Older leased-line technologies such as T1 and E1 cannot be dimensioned easily to cope with the unpredictable traffic demands of mobile data networks, and a network planner has to make quality of service decisions such as dimensioning a link for the peak or mean traffic coming from a particular cell site. The ratio between peak to mean traffic coming from a cell site can be as much as 10:1. Designing for the mean will result in customers being limited in performance (and experience) at busy periods. Designing for the peak will result in underutilised resources for most of the operating day - a waste of operating capital.
Fibre reduces some of the issues of leased lines in that the acuteness of designing for the peak and mean does not present itself (unless an operator is paying for the fibre on a Mb/s basis) but the cost is higher and in many cases the wait longer. Fibre is well suited for very high traffic cells in a dense urban environment where fibre access is likely to be good. Outside of this environment, other options, such as microwave, seem to be a better choice.
There are two other factors to be considered when choosing between leased lines, fibre and microwave - cost and reliability. As the name implies, leased lines are an ongoing cost (lease) as well as an asset that an operator may not own or control. This is an important consideration when assessing the strategic aspects of building a backhaul network. Leased lines are great - provided that an operator trusts the independence and business model of their supplier. Leasing capacity from a competitor is always a risk - regardless of the strength of the local regulator - if there is one!
Reliability of leased lines is not a topic that we hear about often but it needs to be considered. Availability of lines in Europe tends to be very good - especially in markets where, by and large, they are buried underground. However in markets like North America where much of the lines are still strung between poles, reliability can be an issue and data integrity may be compromised.
Globally, an increasing percentage of new backhaul investment is in microwave. The business case for microwave rests on ease of deployment, and greater range, performance and flexibility. With zero dependence on renting or leasing wired lines both overall expenditure and running costs are reduced plus systems can be installed quickly and are not prone to cable cuts, increasing overall reliability. Already, according to Yankee group, globally microwave represents 50 per cent of all backhaul, and outside of North America microwave penetration is more than 60 per cent.
There are two flavours of microwave: point-to-point microwave and point-to-multipoint microwave. Point-to-point (PTP) is best suited for longer range links, rural areas and short very high capacity links. PTP microwave generally require a spectrum license for each link and are designed to provide a fixed capacity bandwidth link. PTP microwave operates over a range of frequencies - some of which are affected by atmospheric conditions. To deal with this, they sometimes employ adaptive modulation to step-down the capacity for a short period of time whilst an atmospheric event - like a snow storm - passes though the region where the microwave links are operating.
Because they are point-to-point links, and operate at a fixed frequency and capacity, PTP microwave are very much like leased lines in that an operator has to design its network to provision for peak loads, and as such, an operator may find himself spending capex on spectrum for links that are only operating at 10 per cent of their capacity most of the time. This is frequently called the ‘fat-pipe' approach to backhaul but clearly, it is a poor use of valuable spectrum resources.
Point-to-multipoint microwave uses a different architecture to address the backhaul issue. Rather than point-to-point links, point-to-multipoint backhaul architectures bring a number of cell site links back to a single aggregation point or hub. Immediately, this reduces the number of radios and antennae making the network less expensive to build. However, because the spectrum for the system is licensed across a number of radios, the resource is in effect shared - making the utilisation of the spectrum more efficient. PMP microwave systems also lend themselves to a more IP-like approach to packet data management.
Beginning with an already impressive raw data rate, of over 150Mbps gross throughput in a sector, PMP solutions utilise data optimisation and statistical multiplexing, together with its advanced on-air bandwidth control and interference management, to provide an ‘efficiency gain factor' of up to 4x.
The question is how to ensure a smooth migration to new backhaul networks that reduce costs and improve customer experience. Operators need to invest in a backhaul solution that takes into account the realities of their current network infrastructure as well as the vision of their future network. With its inherently traffic-neutral, flexible, innovative architecture, PMP microwave will in most cases fit the bill.
Not only is it easier to deploy than other backhaul technologies it offers increased capacity at a much lower ‘cost per bit' with cost estimates for a typical Western European operator running at cost savings of up to 44 per cent of capex and in excess of 58 per cent of opex compared with point-to-point links.
Clearly there is no ‘one size fits all' for every operator, but when weighted up against competing options, microwave and in particularly PMP microwave offers a compelling argument based on the four main metrics which matter to operators - capacity, quality of service, capex and opex.
Lance Hiley is VP Market Strategy, Cambridge Broadband Networks, and can be contacted via tel: +44 1223 703000; e-mail: LHiley@cbnl.com
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