Soft spectrum ahead…Sunday, June 17th, 2012 by Roberto Saracco
The use of radio spectrum continues to rise, according to CISCO the amount of data transmitted over mobile wireless is expected to increase 18 fold from now to 2016 (that is faster than the Moore’s law: 18 versus 6 times) and the available spectrum is not going to increase. Hence we need to be more efficient in using it.
This is something that has kept busy researchers in the last decade and as a matter of fact we have multiplied the capacity of squeezing bits per Hz. But we are reaching now the Shannon limit, so we need to find some ways to circumvent this barrier.
There are two ways for doing this: dynamically change the frequency used for transmitting data as a frequency becomes available (recency hopping), or and decrease the noise impact (solve the interference problem). Work is going on on both ways.
For the later we already have the theoretical foundation and we are waiting for much lower energy consumption chips, so that cell phones can talk one another to solve interference. It may take till the end of this decade to have a practical solution (although the MIMO systems already in use are a step in this direction).
For the former, frequency hopping, we are seeing good progress being made. At the core is the idea of “cognitive radio” a radio that knows what is being used at any specific instant and can hop to that frequency that in that particular instant is not used. Since most of the for is being done in software this is also referred to as “Software Defined Radio”. Statistically speaking this is always the case, there is always some part of the spectrum that is not being used, but this changes over time, and quite rapidly. So the trick is to find ways to hop instantaneously from one frequency to another as “holes” appears.
In the photo you can see their product. It is still quite expensive, around 6,000$, but has the capacity of transmitting up to 400 Mbps, enough to carry 20 HD movies at the same time.
Most importantly, it does that by looking at what frequency is available (not being used) between 100 MHz and 7.5 GHz and can switch (hop) from one frequency to another in a microsecond (although they are claiming a maximum time of 50 microseconds to sense available frequency and switch).
These approaches are at the core of the National Science Foundation initiative to create a mobile radio centric Internet with some experiments going on in several universities in the USA.
Clearly, this evolution is creating ripples in the Mobile Operators world since it will lead to a decreased value of spectrum (and licenses). At the same time, this is bound to increase the demand for wireless capacity and the offer of services. Hence, Operators will need to be in synch with this evolution to be ready to exploit the growing usage of wireless in terms of services.