Did you know?…Multi-Band makes the most sense only when you combine E-Band with Licensed Microwave

Did you know?...Multi-Band makes the most sense only when you combine E-Band with Licensed Microwave

As we have talked about in previous posts, Multi-Band is a great way to improve the reliability and reach of E-Band, or to increase the capacity of licensed microwave bands, by combining both into a single, easy-to-deploy solution. More recently, we have seen Multi-Band solutions that utilize unlicensed 5 GHz band radios in place of licensed bands like 15, 18, or 23 GHz, but does this actually make sense?

Unlicensed radios are TDD—as opposed to FDD in licensed bands. FDD technology ensures high performance and uninterrupted transmission. Read more here.
Did you know?...Multi-Band makes the most sense only when you combine E-Band with Licensed Microwave

The use of a microwave link in parallel to an E-Band link is so that when the latter fades due to rain attenuation, the licensed band links will continue to support up to 99.999% availability for critical, high-priority traffic. However, if this link is supported by the unlicensed 5 GHz band instead, then that reliability and high availability will be compromised. Unlicensed band radios all work on a ‘best-efforts’ basis, meaning that their throughput at any point in time is not guaranteed and can be affected by interference from other adjacent uncoordinated links. Further, most unlicensed radios are TDD, meaning a single radio channel is shared by the traffic in each direction (as opposed to FDD in licensed bands), reducing the available throughput capacity to just a few hundred megabits (full-duplex), or less. Unlicensed radios also lack many of the carrier-grade features found as standard in licensed microwave solutions, such as high modulation up to 4096QAM, wider channel bandwidths, dual-channel operation, and advanced Carrier Ethernet features. Licensed microwave can also support much more capacity for critical traffic – up to 1 Gbit/s in a single channel, or more than 2 Gbit/s using dual-channel with Aviat’s unique A2C feature.

Also, compared to Aviat’s single-box Multi-Band WTM 4800, a solution based on 5+80 GHz would rely on separate radios, and likely not support hitless combining and selection between the 5 and 80 GHz link. In fact instead of full-duplex and sharing capacity, some solutions operate in more of a ‘hot-standby’ configuration, where the E-Band link is the primary path, and then when it fades traffic is switched (with the resultant traffic interruption) to the 5 GHz path.

In a Multi-Band system, the whole objective is to extend the distance of the E-Band link by up to 4x, while also protecting high-priority traffic on a parallel microwave path. In which case, it is essential that during the rare periods when the E-Band link fades or goes out of service that the second path is available and provides maximum capacity. This availability and capacity cannot be guaranteed when using the ‘best-efforts’ 5 GHz unlicensed band.

For these reasons, Multi-Band really only makes sense when you combine E-Band with Licensed Microwave.

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