By now you have undoubtedly heard of LTE, which most carriers refer to as 4G cellular. The term stands for "long-term evolution," which seemed like a good name when work on this technology began in 2004. But here we are in 2013, and the successor to LTE, known as LTE-Advanced technology, is beginning to see the light of day.
LTE itself is amazing technology, specifying peak throughput of up to 300 Mbps and an all-IP core network. The term "4G" has an official definition from the International Telecommunications Union, but most people are more familiar with its use as an umbrella marketing term that covers HSPA, HSPA+ and a few other networking technologies in addition to LTE, the clear leader.
LTE-Advanced is the real 4G. Its speed won't necessarily blow individual users away, but it will allow carriers to keep up with increasing bandwidth demands. Once it overcomes some hurdles, which will take several years, it will be the cellular technology that carries all of our traffic for the foreseeable future.
Demand on cellular networks limits speeds
LTE-Advanced technology promises throughput of up to 1 Gbps. Yes, that's a billion bits per second, downlink, from the base station to a subscriber device. We don't expect to see that kind of performance anytime soon; current LTE implementations don't even live up to their 300 Mbps throughput potential. LTE-Advanced will, however, serve a key role in keeping up with rapidly growing demand for mobile broadband service globally. It's possible, but unlikely, that individual users could see, say, tens of megabits per second.
Here's the problem: The greater the amount of available spectrum, the greater the potential throughput. This universal truth is the most important element of Shannon's Law, the key equation in determining any throughput over any communications channel. To achieve a billion bits per second, one must have at least 100 MHz of radio spectrum, which is pretty hard to come by. Essentially, all RF spectrum less than 3 GHz is spoken for, and radio-wave propagation of more than 3 GHz becomes challenging for mobile applications. No matter how much technology we throw at the problem, we still have to deal with congestion caused by multiple users accessing multiple applications, signal degradation and other problems. So it's important to set expectations accordingly.
At present we're assuming LTE-Advanced technology will offer only about 20 Mbps of throughput to most users, because demand for wireless services will continue to increase, resulting in oversubscription of available bandwidth. Although LTE-Advanced provides more aggregate capacity, that capacity is spoken for most of the time. Thus, it might be best to look at LTE-Advanced as a technique available to carriers to keep up with demand and not as an enabler for higher per-user throughput.
Other trends in networking and mobile computing may provide some hope for higher throughput, however: the move toward using smaller cells, which enable more efficient reuse of radio spectrum over shorter ranges, as well as the ubiquity of Wi-Fi networks, which may lessen the demand on cellular networks. The broad availability of LTE-Advanced will likely provide the catalyst to move to these more advanced cellular architectures and deployment strategies.
LTE-Advanced technology adoption barriers
Many existing LTE base stations can be upgraded through software alone, so LTE-Advanced will be arriving over the next few years, at least on amounts of radio spectrum less than 100 MHz. Some of these services are already operating in various parts of the world today.
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But even as the sophistication of today's standards, technologies and carrier equipment all ease the way for LTE-Advanced technology, we're not looking at a slam dunk. There are a number of additional factors that will influence its adoption:
Business case. Building out a cellular network is an enormously expensive proposition. The major cost is radio spectrum, which is made available in most parts of the world via an auction process. Finding a free 100 MHz chunk of spectrum is unlikely without governments taking complex actions, and even if such spectrum became available, that chunk would undoubtedly sell for a very high price at auction. In response, consider how much a carrier might have to charge for access to recover that investment. The business models here are not well-established.
Backhaul. Even though LTE is capable of very high throughput, many current implementations are limited by the restricted and inadequate amount of bandwidth applied to interconnect cells within the remainder of a carrier's infrastructure and, ultimately, to external networks. This capacity, commonly called backhaul, can be upgraded, but as above, the economics of these upgrades need to be considered in making the business case for LTE-Advanced.
Devices. There are no phones, tablets, wireless routers, or the like on the market today that support LTE-Advanced. Qualcomm and other major vendors are very far along in the designs of LTE-Advanced-enabled components, and we will shortly see products with the technology built in. LTE-Advanced is backward-compatible with LTE, so we might refer to these devices as LTE-Advanced Ready while we wait for the infrastructure to be built out.
Major leaps forward, such as LTE-Advanced, always have significant associated lead time, and estimates as to availability are almost always optimistic. Based on the above considerations, we will be well into the next decade before LTE-Advanced technology becomes the default for cellular networking. But it's nice to know that the next great leap forward in capacity, if not individual throughput, is on the way.