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​One gigabit 4G: The coming of LTE Advanced

Technically, we can do it. Practically, that's another matter. But, we are still on our way to much faster 4G speeds.
Written by Steven Vaughan-Nichols, Senior Contributing Editor

Today, you're doing well if you get 12 Mbps from your 4G LTE connection. For tomorrow, companies such as Ericsson and Qualcomm are working on delivering Gigabit LTE speeds to your smartphones. One carrier, Swisscom, even boasts that it's hit data transfer speeds of 1Gbps on its mobile network. Here's how it works.

LTE-A Carrier Aggregation

With carrier aggregation, your smartphone will bond data together from multiple bands of network traffic.


First, LTE Advanced (LTE-A) is not a single technology. It's a mix of three different techniques to deliver not just superior bandwidth but better connections in general at cell edges.

Carrier Aggregation: What most of you care about is getting faster speeds. To do that, the main method that LTE-A uses is carrier aggregation. This employs the ancient technique, which I first used with phone modems back in the 1980s, of bonding the bandwidth of multiple connections into a single virtual connection.

LTE "component data carrying carriers," or bands, can have a bandwidth of 1.4, 3, 5, 10, 15 or 20 MHz. With LTE-A, up to five bands can be aggregated together for up to 100 MHz on a single connection. In practice, most LTE-A implementations can only combine three bands.

The best way to implement carrier aggregation is to use contiguous bands. But, you don't have to do it that way. You can combine bands even if they're not right next to each other.

MIMO: To make carrier aggregation work well you need Multiple Input Multiple Output technology (MIMO). MIMO is a tried-and-true technology that's been used since 802.11n showed up in Wi-Fi devices to increase bandwidth.

MIMO works by taking one of radio communication's oldest problems, multipath, and turning it into a solution. Multipath is what happens when signals bounce off objects or structures and take multiple paths to the receiver. If you listen to your car radio, you run into the multipath problem every day. For example, if your favorite radio station fades out every day in a certain location, you're hearing an example of what's called multipath fading or Rayleigh fading.

What's happening is that your antenna is receiving both the transmitter's main signal and its reflections. When these signals arrive out of phase with each other, they cancel each other, and your morning traffic report fades out. But, it was discovered back in the 1990s that you could use these reflections as a separate channel.

Today, in LTE-A, the overall bandwidth is increased by bonding the data streams from two or more antennas. When we said "antenna" in this context, I'm not talking about visible antennae on your phone. These antennae can be so small that they fit on a chip.

Together, MIMO and carrier aggregation combine to send and receive data in parallel streams. This is much faster than earlier techniques.

Relay Nodes: These are low power base stations that will provide enhanced coverage and capacity at cell edges. They also make MIMO and carrier aggregation more efficient. Typically these will be upgraded microcells and picotells. Even femocells, with their radius of ten-meters, will be included.

Eventually, these will be used as part of Coordinated Multi Point operation (CoMP). The idea here is to enable your device to use multiple cell sites at once. This is very much a work in progress and I don't expect to see it in the field this decade.

When can you expect for LTE Advanced to be working on your smartphone? It will be a while.

The good news is LTE-A is both backward- and forward-compatible. Your current 4G phone will work with LTE-A network. To use it you'll need an LTE-A compatible smartphone or device. Fortunately, these have started shipping. For example, Apple's iPhone 6s and Samsung's Galaxy 7 and 7 Edge both support LTE-A.

The bad news is that while all the major carriers have said they'll support LTE-A, they're doing it slowly and piecemeal. My own carrier, Verizon, is calling LTE-A "5G", and releasing it this year in only a handful of test sites.

In addition, LTE-A can only deliver network speeds as fast as the backbone can deliver it to the cell towers. Outside of a test environment, I don't think I'll be seeing Gigabit to my smartphone this decade. What I do expect is 150 Mbps to my device.

My bet is we won't see even 150 Mbps real world LTE-A widely available until 2017 at the earliest. Still, once it's here, I expect at least 10 times the speed I currently get on my Galaxy S7. I don't know about you, but that sounds good to me.

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