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With the current deployment of high-bandwidth access networks happening at an ever-increasing pace, the need for efficient, high-bandwidth backhaul infrastructure becomes more and more relevant. In fact, the construction of these new access networks depends upon the backhaul network for both technical and financial performance. Today’s cellular networks typically deploy leased T1 or E1 lines to get user traffic to/from base station sites in a given metropolitan area network.

It is not unusual for a large metro city to have many hundreds or even thousands of base station sites. As WiMAX and other high-bandwidth mobile access technologies like LTE grow, deployment bandwidths on the order of 40 to 100 Mbps per base station are envisioned. With this large increase in bandwidth demand and the connectionless nature of the traffic comes the need for a highly capable, wireless metro Ethernet backhaul solution, one that can be deployed faster and more cost effectively than its predecessors or its optical cable counterparts.

This article investigates the application of high-bandwidth radio technology to the creation of the next generation metro backhaul networks. Typical network topologies and operating attributes are highlighted with emphasis on how these impact the underlying radio technology implementations.

What is Driving the Bandwidth Demands in Mobile Networks?

Historically, bandwidth demand in mobile networks has been driven by voice services and services related to voice. This translated into steady growth for many years. However, there is now a large push for mobile data services. The industry has now seen that data-based services represent a larger portion of overall network traffic (see Figure 1).

Data traffic has a different growth attribute than voice, primarily because general voice calling is dependant upon a ‘human’ application, which has not significantly changed. Our patterns of phone conversation have not changed much over time. Data sessions are largely dependant on the latest applications or services being consumed. For example, a low data-rate e-mail retrieval session can become a very high-bandwidth file download session. Also shown in the figure is the trend toward Ethernet backhaul. This is no surprise since the selected transport technology generally performs most efficiently when it is transporting information already “packaged” in the same transport format. In this case, as packet-based data traffic dominates, it is naturally more efficiently transported in Ethernet form.