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Benefits of LTE-A carrier aggregation

Posted: 27 May 2015 ?? ?Print Version ?Bookmark and Share

Keywords:data traffic? network capacity? LTE? Wi-Fi? carrier aggregation?

It is apparent that the growing thirst for more wireless data is driven mostly by the increasing transfer of pictures and video on smartphones. Think Instagram, YouTube and Skype for starters.

What's more, the appetite for bigger screens and ever-higher resolutions is gobbling up even more data with each new Smartphone generation. Subscribers don't usually associate their new, bigger smartphones with their larger screens and their higher resolution as consuming more data, but it is also a big factor in monthly data budgets.

And smartphone cameras have ever-growing pixel counts, with rear ones of 20 MP and front ones of 5 MP becoming more common. You can imagine that even higher pixel counts are coming, with their attendant greater data consumption. The chart below illustrates the exponentially higher bandwidth required for each new generation of displays, from quarter VGA (QVGA) through Ultra High Definition (UHD).

Figure 1: The factors that drive increased uplink traffic.

Network giant Cisco Corp. estimates that mobile data traffic will grow at a compound annual rate of 65% from 2013 through 2018. Consequently, both network capacity and device throughput must outpace this growth to improve user experience of both consuming and (increasingly) generating all of this traffic.

To accommodate the growing data appetite of its subscribers, mobile operators like AT&T, Verizon, and China Mobile must provide greater spectral bandwidth. Because of the patchwork of global spectrum allocations, an operator may not have the luxury of simply assigning its carrier to a higher bandwidth.

How do we increase upload speeds?
There are stop-gap measures for increasing download (but not upload) speeds, like combining LTE and Wi-Fi carriers, but with higher upload speeds for Instagram and videoconferencing, a better way for increasing effective bandwidth (and its higher-speed capability) is through LTE carrier aggregation (LTE-CA).

Figure 2: Carrier aggregation.

The basic concept of carrier aggregation (CA) is not new; it was employed in land-line ISDN more than two decades ago. Digital Signal Processing (DSP) technology enables the bonding of two or more fixed-bandwidth carriers to make them act as one with twice (or greater) the bandwidth. And tying three carriers together provides 3x bandwidth and so forth. Up to five 20 MHz LTE carriers are allowed in the 3GPP specifications, as illustrated below. However, 2x and 3x implementations are more feasable in the near term.

In the mobile world, we have gone from 2G to 3G for greater bandwidth and now 4G, through its flagship, LTE-Advanced. But, until there is an approved 5G technology in the next decade, LTE-CA has become the technology of choice. Carrier aggregation allows combining lower and higher frequency bandsleveraging better coverage of the former with higher availability of the latter.

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