|
Mobile & Wireless
4G backhaul options
Evaluating key requirements a must for operators
by Greg Freisen, Director, Product Manager, DragonWave
There is an emerging wave of 4G deployments, using WiMax and LTE access technologies, set to deliver an entirely new suite of mobile broadband services. This will result in a dramatic increase in backhaul requirements, which existing copper leased lines will struggle to deliver due to copper capacity limitations. Operators are now evaluating backhaul technologies that can meet the requirements of their new service offerings. The two primary technologies being considered are microwave and fiber. In addition, 60-80 GHz millimeter wave options are being evaluated for some limited applications.
LTE and WiMax networks have several common characteristics in their technical backhaul requirements. These deployments will require extremely high bandwidths to deliver their edge service offerings; initial capacities commonly considered are 30 Mbps per site, with future scalability beyond 100 Mbps per site. With the majority of mobile network growth being driven by IP-based services, native packet transmission technologies will offer the greatest operational and economic advantages for operators. In order to handle the various service levels associated with these new applications, it will be essential for backhaul networks to prioritize and deliver service levels from 99.9% to 99.999%. Synchronization is another important consideration and one of the common technologies enabling this in LTE networks is Synchronous Ethernet (SynchE), which necessitates a SynchE capable transport layer.
In addition to the above technical backhaul requirements, there are some key commercial requirements that must be addressed with any backhaul deployment, the first being time to market. In some cases, 4G deployments may cover over 30,000 sites – meaning the backhaul architecture must be deployable on a large scale, in as short a cycle as possible. The other critical commercial requirement is total cost of ownership. Backhaul is becoming an increasingly major portion of the total service cost for mobile operators and will be an even larger challenge as operators struggle to deliver 10-fold capacity increases at similar end user prices. The operator will therefore be very sensitive to minimizing not only the CAPEX, but also the total lifecycle costs of the backhaul network.
Examining each of the backhaul technologies in the context of the key 4G requirements will allow us to determine their fit within a 4G backhaul rollout. The three technologies in question are fiber backhaul, licensed microwave backhaul (6-38GHz range), and millimeter wave backhaul (60-80 GHz range).
Fiber
Fiber is technically very well suited for 4G backhaul. With systems that can easily scale well beyond 10 Gbps, fiber resolves any capacity issues operators may have. Fiber can be deployed in high availability redundant ring topologies but the infrastructure to do so may significantly increase costs. Lastly, emerging fiber ADMs have queuing as well as Synchronous Ethernet capabilities, allowing for the delivery of multiple service levels and providing LTE synchronization. Given these capabilities, if fiber has already been deployed and is readily available, it is a perfect option for 4G backhaul. However, in the case where a new fiber build is required, significant commercial challenges arise. Obtaining right of way permits, followed by the physical digging required to lay fiber mean that getting fiber to a single site may take 18 months or longer. Depending on the distances involved, deploying fiber can also be very costly. The expenses associated with deploying fiber consist of building access costs, right of way costs, physical fiber costs, and the construction and digging costs. All but the building access costs scale linearly with distance, making total fiber deployment costs rise dramatically for longer link spans. The cost per foot depends greatly on where the fiber is being deployed, ranging from $10/foot in rural areas to well in excess of are in $100 per foot in urban areas.
Microwave
Traditionally, microwave has had capacity limitations in the range of about 150 to 300 Mbps. However, emerging microwave technologies are now able to deliver well over 1 Gbps with some systems delivering up to 4 Gbps. There are still many versions of microwave systems available, with packet-based microwave technologies commonly be used for 4G backhaul. . Emerging microwave products offer SynchE capability in order to distribute synchronization for LTE base stations. Some microwave products come equipped with ring switching capabilities, allowing for ring and mesh architectures and delivering very high end-end service availabilities. With the wide range of frequencies available for microwave, these systems can be deployed with links ranging from less than a half-mile to greater than 30 miles. In terms of deployability, licensed microwave systems can be implemented very rapidly, with the licensing process taking less than 30 days, and the installation process taking only hours – without the need for specialized equipment. In terms of economics, the cost of a microwave deployment is not very sensitive to distance as the electronics and installation costs are fairly consistent regardless of distance. There are a few distance break points, where larger antenna sizes are required, but those do not typically occur until 3 or more miles.
Below is a comparison of the 10-year lifecycle costs of fiber vs. microwave including CAPEX, installation, tower lease costs and licensing costs. In this comparison, we see that fiber is very cost effective for short distances, and that microwave becomes more cost effective than urban and suburban fiber after about 0.2 miles, and more cost effective than rural fiber after approximately 1 mile.
Millimeter Wave Technologies
Recently, some operators have started evaluating millimeter wave technologies for 4G backhaul. These products can generally meet the 4G capacity requirements, with most systems delivering a gigabit of throughput. Many of these systems offer prioritization so that multiple service levels can be delivered. The 60-80 GHz systems do not currently provide SynchE capabilities but it is assumed they likely will as the LTE deployments require it. In terms of economics, the 60-80 GHz economics are fairly similar to that of microwave. The primary challenges with the 60-80Ghz bands lie in deployability, range and service availability. Millimeter Wave systems have very narrow beamwidths due to their high frequencies. This means, that they must be deployed on structures with very little twist or sway, eliminating the possibility of towers and even some very tall buildings. In addition, due to this very narrow beamwidth, aligning the systems can be very difficult-requiring highly trained crews for deployment. Beyond these issues, the greater challenge with millimeter wave systems is with their availability and resulting range capabilities due to rain fade. Because the millimeter wave bands are in such high frequencies, they are very susceptible to rain, which results in limited link lengths in order to achieve reasonable availabilities. A comparison plotting the reach differences for Microwave vs. mmwave systems at various capacities is shown in the graph below. This is using 2’ antenna, 99.995% availability in 45 mm/hr rain region.
As shown in this graph, the mmwave system is limited to about 1.5 miles, whereas the microwave options has range up to 15 miles at 100Mbps, and over 5 miles at 1 Gbps.
There are clearly several viable options to meet the backhaul requirements of 4G access networks and no network will use a single technology. There will certainly be a mix of two or more technologies, with the optimal network driven by site location and distribution of sites. For new build sites requiring more than 1 or so miles of reach, microwave will typically be the preferred technology from a cost and availability point of view. However, in a large network there will be some fiber in the core where very high capacities are needed, and there may be some mmwave technology in the middle mile of the network if reach permits.
About the author:
 Greg Friesen has 10 years experience in network design, planning, engineering, and product management at a number of communications firms. As Director, Product Manager at DragonWave he is 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 and he holds 2 granted patents and has 3 pending applications in the networking area.
|
|
|
