Electronic Design
Spectrum and Backhaul Inhibit Wireless Growth

Spectrum and Backhaul Inhibit Wireless Growth

Two major critical issues are affecting the growth of wireless: spectrum and backhaul network capacity.

With only a finite amount of spectrum available, cellular operators are constantly fretting over their holdings, wondering if there will ever be enough to completely implement their Long-Term Evolution (LTE) and 4G systems to come. With spectrum so expensive, every megahertz becomes a prize to cherish.

Will there be enough to implement the National Broadband Plan put forth by the government last year? The Federal Communications Commission (FCC) is working to find more spectrum and may even begin taking assigned spectrum from the TV stations for auctioning and repurposing. While spectrally efficient modulation and access methods are helping, the only real thing stopping wireless growth will be a lack of spectrum.

Meanwhile, three basic types of backhaul connect basestations back to the carrier’s switching centers: copper, fiber, and microwave. In the U.S., most backhaul has been achieved by TDM-based (time domain multiplexing) T1 lines. But as data traffic has grown, this backhaul has become inadequate.

Adding more T1 lines at great expense has not been the best solution. Fiber has replaced copper in some instances, but the cost of running fiber is high. Microwave is a growing option. Licensed bands in the 11-, 18-, and 23-GHz range are available at moderate cost and can provide data rates as high as 4 to 5 Gbits/s. A modern 3G cell site needs a capacity of up to 100 Mbits/s, but a 4G/LTE site needs 100- to 300-Mbit/s capacity to be useful.

The new microwave systems based on Ethernet with Carrier Ethernet or multiprotocol label switching (MPLS) are now available to carry the increasing Internet protocol (IP) load. Most are hybrid systems that also support the legacy TDM systems as well (see the figure).

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