Carrier aggregation is a popular concept to increase the capacity of wireless access technologies such as HSPA+, LTE-Advanced or even Wi-Fi. Simply put: combine several radio carriers together into a single logical pipe and you get more capacity.
This winning formula also successfully applies to microwave transport, but the benefits are beyond just adding capacity.
More capacity yes, but the sum is greater than the parts
If you combine several microwave physical channels, i.e. different spectrum bands, you mathematically get the sum of individual capacities. In reality, as the waves spread in the air, they are impacted by the varying propagation conditions due to rain and snow, for example. Each individual channel can dynamically adapt its capacity thanks to adaptive modulation. The good news is, frequencies and therefore channels, are not impacted the same way at the same time. By grouping the channels, the system can dynamically allocate the traffic to the best one, hence statistically increasing the capacity and reliability. This approach allows an optimal usage of the spectrum and is widely used today on commercial networks around the globe.
More capacity for less money
Adding capacity is good, but it’s even better if it can be done at low, or no cost. Here, the idea is to combine licensed and unlicensed bands. Then priority traffic is carried on the licensed spectrum to guarantee the quality of service, while the unlicensed band is used for best effort traffic such as most of the internet traffic. This configuration can be exploited to help the business case to connect remote areas or to provide different level of security for example.
Nokia commercially deployed longhaul links using carrier aggregation with the unlicensed 5.8GHz band, has on-going trials and has also exploited this setup in the latest Open Networking Foundation proof of concept (ONF PoC) on the software-defined network (SDN) use case.
Stretching the capabilities of a microwave link
Carrier aggregation is also a smart way to combine the characteristics of different frequency bands. For example, traditional bands (from 4 to 42GHz) provide very good reliability over long distances. On the other hand, millimeter wave frequencies, such as the so called E-band (80GHz), offer high capacity and low latency but the propagation is not as good and the reliability rapidly reduces with distance. Combining a traditional band, such as 18GHz, with an E-band allows for best-of-breed microwave link, where the traditional band supports the priority traffic (essentially voice) while the E-band provides the best effort high capacity for bursty data traffic. This kind of configuration is drawing the industry’s attention as it brings multi-gigabit capacity, low latency, and reliability in a single wireless link.
Combine it with SDN, get ready for telco cloud and 5G!
Thanks to carrier aggregation, microwave links can handle the most stringent transport requirements. Consider this capability network-wide and add Carrier SDN to the picture: Carrier SDN can dynamically create and optimize the best route for each service, hence optimizing the overall transport. You now get a fully programmable transport network, a key enabler for telco-cloud and 5G.
For more information, check our webinar on Carrier Aggregation.
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