真乄科技業的頂尖投資團隊

 The fifth generation of mobile communications technology will see the end of the “cell” as the fundamental building block of communication networks.

It may seem as if the fourth generation of mobile communications technology has only just hit the airwaves. But so-called 4G technology has been around in various guises since 2006 and is now widely available in metropolitan areas of the US, Europe and Asia.

It’s no surprise then that communications specialists are beginning to think about the next revolution. So what will 5G bring us?

Today we get some interesting speculation from Federico Boccardi at Alcatel-Lucent’s Bell Labs and a number of pals. These guys have focused on the technologies that are most likely to have a disruptive impact on the next generation of communications tech. And they’ve pinpointed emerging technologies that will force us to rethink the nature of networks and the way devices use them.

The first disruptive technology these guys have fingered will change the idea that radio networks must be made up of “cells” centered on a base station. In current networks, a phone connects to the network by establishing an uplink and a downlink with the local base station.

That looks likely to change. For example, an increasingly likely possibility is that 5G networks will rely on a number of different frequency bands that carry information at different rates and have wildly different propagation characteristics.

So a device might use one band as an uplink at a high rate and another band to downlink at a low rate or vice versa. In other words, the network will change according to a device’s data demands at that instant.

At the same time, new classes of devices are emerging that communicate only with other devices: sensors sending data to a server, for example. These devices will have the ability to decide when and how to send the data most efficiently. That changes the network from a cell-centric one to a device-centric one.

“Our vision is that the cell-centric architecture should evolve into a device-centric one: a given device (human or machine) should be able to communicate by exchanging multiple information flows through several possible sets of heterogeneous nodes,” say Boccardi and co.

Another new technology will involve using millimetre wave transmissions, in addition to the microwave transmission currently in use. Boccardi and co say that the microwave real estate comes at a huge premium. There is only about 600MHz of it. And even though the switch from analogue to digital TV is freeing up some more of the spectrum, it is relatively little, about 80MHz, and comes at a huge price.

So it’s natural to look at the longer wavelengths and higher frequencies of millimetre wave transmissions ranging from 3 to 300 GHz. This should provide orders of magnitude increases in bandwidth.

But it won’t be entirely smooth going. The main problem with these frequencies is their propagation characteristics—the signals are easily blocked by buildings, heavy weather and even by people themselves as they move between the device and the transmitter.

But it should be possible to mitigate most problems using advanced transmission technologies, such as directional antennas that switch in real time as signals become blocked. “Propagation is not an insurmountable challenge,” they say.

Next is the rapidly developing multiple input-multiple output or MIMO technology. Base stations will be equipped with multiple antennas that transmit many signals at the same time. What’s more, a device may have multiple antennas to pick up and transmit several signals at once. This dramatically improves the efficiency with which a network can exploit its frequencies.

However, it will mean larger antennas, perhaps spread out across the surface of skyscrapers. That’s fine in modern cities with plenty of surface area that is relatively easily accessible. It’d be harder to manage in older cities where large panels will be harder to conceal.

Smarter devices should also help shape the networks of the future. So instead of signals being routed by the base station, smart devices will do this job instead, choosing between a variety of different options. For modern smartphones, that should be a relatively straightforward task.

And the final disruptive technology these guys identify is the ability for devices to communicate with each other without using the network at all. Boccardi and co say this will be essential for the ways in which future networks will be used. For example, a sensor network may have ten thousand devices transmitting temperature data. That will be easier if they can send it from one device to the next rather than through a single base station.

Of course, many of these developments pose significant technology challenges but none of these should be showstoppers. “New research directions will lead to fundamental changes in the design of future 5G cellular networks,” say Boccardi and co confidently.

5G is not a question of if but when.

Ref: arxiv.org/abs/1312.0229: Five Disruptive Technology Directions for 5G

Source:MIT