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Wireless Backhaul Addresses the Broadband Stimulus Challenge
by Greg Friesen, Director, Product Management
6/10/2009
The economic stimulus funding for RUS and NTIA will drive tremendous broadband service deployment to rural and underserved areas in the next few years. Delivering broadband services will create a huge backhaul challenge, especially in the RUS case which is targeted at rural areas, with limited backhaul infrastructure. Microwave backhaul is expected to deliver a solution for this backhaul, but there are many considerations that will be important to delivering a successful Microwave backhaul network for this application.
Backhaul Challenges
The stimulus funding is targeted at trigger deployments that would not otherwise be deployed, which by its very nature means there will be significant unique challenges to these deployments. Some of the major challenges on the backhaul side of these deployments will include:
Capacity on future scalability
Network Reach to rural areas
Limited site options for deployment
Long repair times, driving redundancy
Must be economically viable after initial capital expenditures.
Delivering high capacity services such as WiMAX will require significant backhaul scale. Each site may have requirements growing up to 50 to 100 Mbps per tower. In many cases, multiple tower sites will be aggregated together across a single link before reaching fiber. This will drive some backhaul capacities up to nearly a Gigabit in some cases. This will provide a major scaling challenge, as there today will be limited or no facilities at these sites. In addition, the capacities will be much lower to begin with as the service uptake is low, so their will be a requirement to minimize initial costs, while being able to scale rapidly with customer uptake and increased usage.
A key focus of the stimulus plan is to deliver services to unserved areas, which means very rural, and often quite remote from significant telecom infrastructure. This will often rule out fiber options, as fiber for long routes is very expensive, and can take along time to get rights of way and to actually build. This will not fit into the 2 year timeframe of the stimulus plan. So, a more rapid alternative, such as microwave must be considered. There are additional considerations, such as the distance to the nearest fiber infrastructure (often 10-30 miles), that microwave can address..
The rural nature of the RUS initiative leads to many challenges related to infrastructure and zoning. Many of the areas will not have towers or high buildings. Limited infrastructure may drive deployment on unusual sites such as water towers, small commercial buildings churches, etc. These sites are not traditional telecom sites, and will usually not have indoor rack equipment space, and in addition will likely have antenna size restrictions. Even when suitable space does exist, in many cases there may not be sufficient power available, and if there is power, it may no have a backup.
Another effect of the remote nature of these deployments means that it will often take a long time to send out repair crews to sites when there are failures. This will drive the need for the backhaul network to be self-healing in order to prevent long outages.
The last, but perhaps most important consideration, is that one of the stimulus plan criteria, is that after the initial CAPEX expenditure, the network must be economically viable for all future years. In order to achieve this, the backhaul solution must minimize ongoing operational costs. This will mean minimizing leased fiber and leased services, and reducing ongoing site leasing costs, such as antenna spaces, and indoor mounting.
Addressing the Challenges
The first backhaul challenge is to deliver the high Ethernet capacity required at each of these sites. With some of the recent licensed Ethernet microwave systems introduced on the market, capacities of 400Mbps up to over a Gigabit are not available. These solutions can provide high capacity last-mile transport as well as serve on aggregation links shared among multiple sites. In addition, some of these radios have capacity scalability via remote software keys. This can enable a lower initial cost without sacrificing future scalability.
The wide range of distances that will be required for these deployments will drive a wide range of frequencies. In rural areas, for long hops, 6 GHz, may be required. The downside to this, is that there are only 30 MHz channels in this band, limiting the throughput to about 200Mbps per license. In addition, at 6 GHz there is a minimum antenna size of 6 feet, making deployment more difficult and expensive, and driving up tower space leasing costs. A good alternative is 11 GHz, which supports an antenna size of 2.5 feet, and 40 MHz channels, allowing close to 300Mbps throughput per license, with a much simpler installation, and reduced infrastructure requirements. For the shorter hops, as you move into NTIA funding covering underserved areas, 18 GHz, 23 GHz, and even higher bands like 28 GHz can be considered. Some of these bands allow 1 foot antennas, and they all have 50 MHz channels, enabling up to 400 Mbps throughput per license. In addition to considering multiple spectrum options, reach can be significantly increased though Adaptive Modulation, which is now available on some licensed microwave systems. Adaptive modulation will shift to a lower capacity and modulation during a rain fade, maintaining the link, but at a reduced capacity. During this event, the link will prioritize the critical traffic, to ensure services such as voice calls are maintained. Adaptive modulation allows the service provider to engineer the link distance based on a lower modulation, while primarily deliver the capacity of the higher modulation, resulting in a significant increase in reach capabilities.
In order to address the limited site options that will often be available in rural areas, operators will need to consider emerging microwave mount options. Some licensed microwave systems now offer complete outdoor solutions, eliminating the need for any indoor telecom space, and enabling mounting in unusual locations such as water towers. In addition, the use of adaptive modulation can help to minimize antenna sizes, which will provide more mounting options, as smaller antennas will have less sway restrictions, and provide less tower loading strain. Today, there are some stealth mount options available, which address zoning concerns on locations that do not want to sacrifice their building style or town look. For power limitations that exist at site, new, lower power systems reduce the need for additional infrastructure. In addition, some solutions now have all outdoor power solutions including rectifiers, and battery backup. For some sites, solar power can be used to eliminate any need for the power grid.
The deployment of ring/mesh architectures can provide not only equipment redundancy, but also path redundancy for a protection against rain fades. This protection will ensure the network is available even during long repair intervals. In some places the topology is not suited for a ring architecture. In these cases, a 1+1 protection is available to provide full equipment redundancy.
In order for the network to be economically viable in the future, it is important to choose a wireless backhaul architecture that can scale with minimal additional investment. Minimizing ongoing costs is the most important aspect rural carriers should consider. As shown in the figure above, the RUS funding only addresses the upfront costs, which are less than 20% of the total cost of ownership in a traditional architecture. So, it is critical to use this investment to minimize the operating costs that make up more than 80% of the total cost. A ring /mesh architecture can help with, as it extends the reach of the network, minimizing the requirement for expensive fiber leases. As well, its inherent link hardening helps to reduce antenna sizes and the resulting ongoing antenna space lease costs. The reduction in antenna size through adaptive modulation helps to further reduce leasing costs. Lastly, an all outdoor architecture can eliminate expensive indoor leasing costs.
The economic stimulus provides fantastic drivers to help deliver broadband access ubiquitously across the United States. However, to be able to achieve this, it is imperative that not only the access method and services are considered, but that the backhaul infrastructure is part of the initial planning, as this will be one of the major bottlenecks if not addressed up front.About the Author
Greg Friesen is Director, Product Management for DragonWave.
Greg Friesen holds B.Sc. in Electrical Engineering from University of Saskatchewan. Mr. Friesen has 10 years experience in network design, planning, engineering, and product management at a number of communications firms, namely Nortel Networks, Innovance Networks, and Fundy Telecom. As Senior Product Manager at Innovance Networks he was responsible for all product definition, architecture, and network design. He has been involved in the planning and engineering of over 10 nationwide network deployments. His experience ranges from operations and Capex modeling to network architecture design to site and link engineering.
Mr. Friesen has authored numerous papers and magazine articles in publications like Xchange,Telephony Online, Last Mile, AGL, Radio World, and has spoken at numerous industry conferences such as WiMax World, CTIA, Telecom Next, ISPCon and UTC. Greg holds 2 granted patents and has 3 pending applications in the networking area.
About DragonWave
DragonWave™ is a leading provider of high-capacity wireless Ethernet equipment used in emerging IP networks. DragonWave designs, develops, and markets carrier-grade microwave radio frequency networking equipment that transmits broadband voice, video and data. DragonWave's products, which are based on a native Ethernet platform, function as a wireless extension to an existing fibre-optic core telecommunications network. The principal application for DragonWave's products is the backhaul function in a wireless communications network. Additional applications for DragonWave's products include point-to-point transport in private networks, including municipal and enterprise networks. DragonWave's corporate headquarters is located in Ottawa, Ontario, with sales locations in Europe, Middle East and North America.
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