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amir Why 4G Mobile Networks Need Microwave Backhaul
By Amir Zoufonoun, Chief Executive Officer and Founder • Exalt Communications

As carriers roll out 4G services like LTE and WiMAX, mobile backhaul will play a larger role than ever. Rather than simply viewing content from the downlink, users are increasingly creating content and transporting up into the network it via cell site backhaul. Microwave backhaul has proven itself as a reliable and scalable backhaul technology for cellular networks, and many mobile operators are now taking a closer look at the technology as an alternative to fiber and T1 as they plan their 4G deployments.

In this article, we will explore the rising need for microwave backhaul in mobile networks along with the key requirements for successful deployments.

Backhaul is Changing
Mobile backhaul infrastructure is in transition. In 2G mobile networks, many cell sites needed only a single T1 line to backhaul voice and SMS traffic. But with the advent of 3G and 4G networks, whole new classes of smart phones have emerged that are changing bandwidth requirements throughout the network.

As pioneered by the iPhone and now supported by BlackBerry and Android smart phones, consumers now exchange data with applications over the network at the rate of several gigabits per month. As a result, these users are squeezing available backhaul bandwidth and creating a huge bottleneck in the network. Network planners agree that many cell sites will need 300 megabits per second (Mbps) of backhaul capacity to support rapid growth in smart phones and devices like the iPad 3G.

Another aspect of emerging 4G services is that they will require far more cell sites than did 3G services. The only way to deliver the promised 10+ Mbps of bandwidth to each user is to split the infrastructure into much smaller cells. Each of these new cell sites will also need a backhaul connection.

Mobile operators are at a crossroads where they must decide the most efficient and cost-effective way to backhaul 4G traffic. At 1.5 Mbps per line, T1 is clearly inadequate and impractical. The only other choices are fiber and microwave.

Pros and Cons of Fiber-Based Backhaul
In today’s 3G networks, some cell sites are backhauled over fiber, and many mobile operators used to dealing with third party telecommunications companies or other divisions of their own organizations to deliver those fiber connections. Fiber is a known technology that can easily deliver adequate bandwidth, and existing fiber can be connected fairly easily to nearby cell sites.

However, fiber does not run everywhere. It can cost $200,000 per mile to trench new fiber to a cell site, and the process can take one to two years. Cell sites in remote areas can’t be cost-effectively linked with fiber given the sparser subscriber populations in those locations. Moreover, even in urban areas, it may be impossible or take years to get the requisite permits to deploy new fiber under crowded streets or historic buildings.

So while fiber is a good bandwidth solution, it is often costly, slow to deploy and economically impractical for many cell site locations.

Microwave Trumps Fiber
Microwave technology has advanced significantly in recent years to deliver the reliability and capacity needed to support carrier backhaul when fiber is impractical. New microwave backhaul systems can deliver 1 gigabit per second (Gbps) over a span 20 to 30 miles or more at a cost of $20,000 to $40,000. With microwave, unlike fiber runs, the carrier owns the links and eliminates monthly recurring lease payments.

In addition, microwave backhaul systems can be mounted and made operational within days because carriers needn’t obtain permits for excavation. Many microwave backhaul systems are small and unobtrusive and can easily be mounted on building roofs, masts or towers.
Today’s microwave systems can support the same network management and security features that fiber offers, so the network can be monitored, configured and maintained from a central console.

Finally, microwave backhaul systems work with carrier-grade reliability in all weather conditions. Fiber can crack in locations where the ground freezes in the winter, forcing costly repairs each spring. Microwave systems are impervious to this kind of damage, not to mention fiber cuts from backhoes.

Requirements for Successful Microwave Deployment
Microwave is proving itself as a reliable and practical mobile backhaul technology. Operators should be careful to meet several key requirements in selecting a system.

IP and TDM Capabilities – The backhaul system should support both native TDM and IP traffic in any combination. Despite the appearance of new services, legacy 2G services will be necessary for several years, so the microwave system should support those services today while enabling a smooth transition to all-IP networks in the future. Although some microwave systems support TDM traffic over IP emulation (pseudowires), this method introduces latency that can degrade the quality of voice services.

Scalable Capacity – Ideally, the backhaul system should offer easily scalable capacity, so carriers can backhaul 4G services on a pay-as-you-grow basis. Advanced microwave systems can be scaled from 10 Mbps up to 1 Gbps through license upgrades and capacity aggregation, allowing the network to remain operational as capacity is added.

Reliability – The microwave backhaul system must deliver the same or better reliability as any other potential solution. Modern microwave systems can deliver 99.999 percent TDM voice reliability with 99 percent link availability, which is effectively better than operators today get from fiber or T1 lines. Advanced electronics and failover systems built into the most advanced microwave systems deliver sub-50 millisecond recovery time to comply with carrier standards.

Flexibility – Mobile operators will want backhaul systems that support a full range of frequencies to address the particular challenges of each cell site location. The most advanced radios offer support for multiple bands within a particular frequency and can be tuned in 1 MHz increments to optimize performance under interference conditions.

Another issue is the network topology. Legacy networks use a hub-and-spoke model, but these are giving way to mesh and ring topologies in newer 3G and 4G networks, now made possible by the advent of IP services. The microwave backhaul system should support any of these topologies so it can serve equally well in different types of networks.

Finally, carriers will want a choice of system configurations, including all-outdoor, all-indoor and split-mount to meet the needs of a particular cell site’s architecture.

Remote Management – Mobile operators always seek to minimize truck rolls for maintenance. Advanced microwave systems support this goal with Web-based management interfaces that allow configuration, alarming and troubleshooting from a central console. In addition, the best systems have a built-in spectrum analyzer so users can accurately gauge radio conditions at the system’s location, making it easy to recognize and tune around any interference issues.

Security – The microwave backhaul system should support the same level of data security as other technologies. While some microwave systems offer 128- and 256-bit AES encryption, their ability to deliver this service depends on the level of throughput of the radio. Mobile operators should ensure that the microwave backhaul systems they select can provide AES encryption at any throughput level.
Interference Mitigation – Interference is a fact of life in radio systems, but carriers can minimize the impact of interference by selecting licensed frequencies and by selecting advanced microwave systems that offer interference mitigation technology along with tuning in 1 MHz increments.

4G networks will deliver far more bandwidth to subscribers, but they will need far more cell sites and much higher backhaul capacity. T1 lines are out of the question as a backhaul solution for 4G, and fiber can’t meet much of the demand due to issues of cost, time to deploy or simple practicality. Only microwave technology can support high-bandwidth backhaul at any cell site location, providing the flexibility, low cost, scalability and rapid deployment mobile operators need to roll out 4G services quickly and profitably.

Amir Zoufonoun founded Exalt Communications in 2004 and has served as its president, chief executive officer and chairman of the Board since inception. Amir has more than 30 years of experience in the wireless telecom and networking industry. For more information contact pvalentine@exaltcom.com.