Nokia Siemens projects a five-fold increase in spectral efficiency beyond 4G

When wireless industry experts point to huge capacity increases in the future, they’re usually talking about adding carrier bandwidth, not increasing the overall efficiency of the network. Future technologies like LTE-Advanced achieve much of their enormous speeds by layering on more spectrum, aggregating carriers into monster 100 MHz-wide configurations that can support 1 Gb/s connections--they build more lanes in the spectral highway rather than make the cars go faster. The reason for this is because wireless engineers have started bumping against a limit—called Shannon’s Limit after Bell Labs researcher Claude Shannon—that prevents them from packing any more useful data into a hertz of spectrum before any capacity gains are lost to noise. With long-term evolution and high-speed packet access plus (HSPA+) technologies, the industry almost reached that limit. Most of the future capacity gains we read about come not from building more efficient pipes, but from building fatter pipes through carrier or from laying many more pipes. Small cells, for instance, mean that the same spectrum can be re-used in more places, while multiple input-multiple output (MIMO) smart antenna technologies send parallel but separate transmissions over the same airwaves.

In a new white paper, however, Nokia Siemens Networks explores technologies and techniques that would boost network spectral efficiency between four and five times than that achievable in the LTE networks being deployed today, not by overcoming the Shannon’s Limit, but by sidestepping it. According to NSN’s engineers, no individual wireless link can exceed Shannon’s barrier, but the spectral efficiency of the overall system can. By building a network in which multiple cells interact with one another and turn the individual cells’ weaknesses into a system-wide strength, vendors will be able to design networks with an overall spectral efficiency greater than the individual links within it.