How to get past the limits of 4G wireless networks

Even though 4G networks are just starting to roll out, its physical radio limits are spurring research into speeding up other network aspects

Using more spectrum and advanced antennas, cellular network vendors and operators plan to increase 4G mobile speeds as that technology rolls out over the next several years. But cellular technology has hit a fundamental wall in the physics of what the radio signals themselves can carry, so researchers are looking at other ways to increase speed and capacity of 4G networks, nearly all of which will use a standard called LTE. the keys to increasing speeds as researchers look at future networks are to shorten the distance between users and base stations and allowing them to automatically be reconfigured.

Historically, a new mobile generation has included two basic components: a mobile standard and spectrum allocation, says Håkan Djuphamma , vice president of architecture and portfolio at radio equipment maker Ericsson.

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Because LTE is at the limit of what is physically possible, it now makes less sense to develop another standard from the ground up, Djuphammar says, as a new standard couldn't change laws of physics. Another issue that a new technology standard can't really address is that the allocation of spectrum has become increasingly fragmented because the airwaves are so crowded.

The development of so-called het nets, or heterogeneous networks is key to how mobile networks evolve, says Djuphammar. Het nets use a mixture of traditional large base stations and smaller cells, placed in areas where there are a lot of users. The basic idea is the same as with today's femtocells, which are most often placed in homes to offload the rest of the network, while also improving coverage and providing better capacity for subscribers connected to it. But in a het net, the smaller base stations would be more integrated with the rest of the network.

It's about building network structures that would allow devices with 2G, 3G, 4G, and in most cases Wi-Fi to jump among different forms of access depending on the load in the different parts of the network and the application currently used. These network structures would also dynamically manage device access in an intelligent way, says Djuphammar. But doing all that is a pretty challenging task, he says.

The same spectrum bands would also be used for different mobile standards. Depending on what kind of devices are connected to a base station, that station could change the amount of spectrum used to maximize performance in real time. "Today we have a static allocation of spectrum, but in the future it will be completely dynamic. For example, if there are no phones in a cell that need to use GSM, the entire spectrum can be used for 4G. But when a GSM phone comes back into the cell, the base station again reconfigures its spectrum allocation," Djuphammar says.

Sweden's KTH Royal Institute of Technology has started to examine what networks could look like by 2020. The aim is a thousand-fold capacity increase, says Jens Zander, a professor in Radio Communications at the university and head of its center for wireless systems Wireless@KTH. Zander is a big proponent of denser mobile networks where the distance between base stations is much shorter and thus there's higher effective carrying capacity per segment.

"Beyond LTE, I think the most important things are finding good and cheap solutions over short distances and having base stations that are as easy to install as Wi-Fi but have much higher capacity and have better coordination with the rest of network," Zander says.

An import part of simplifying the installation process is the concept of self-organizing networks, which allow operators or users to connect a base station to the network and it would automatically be installed. "A big part of the cost for current networks is that they have to be carefully planned," Zander says.

Short-term improvements to 4G networks will include the use of more spectrum and multiple antennas. Continuous spectrum is a limited resource, so vendors have come up with carrier aggregation, which allows operators to bunch together spectrum in different bands and use them as one data link.

Another way to increase capacity, which is already used today, is MIMO antenna technology, which uses multiple antennas in the base station and on the device to increase speeds; more antennas mean more capacity. For MIMO to work, the antennas need to see a slightly different version of the radio signal, which the distance between the antennas allow them to do.

The big challenge with MIMO is to fit all the needed antennas on the user device. It is very difficult to fit more than two antennas in a mobile phone, says Zander. The growing size of many high-end smartphones, thanks to the use of larger screens, will help. Laptops and tablets are more amenable to the use of multiple antennas due to their larger sizes.

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