Some interesting talks from top regulators where given at the QUASAR regulator workshop hosted by BT in London. Among the most interesting developments is that the two “pioneer” countries in TV White Space usage now both abandon what has been perceived as THE key feature of Cognitive Radio – spectrum sensing. Both the FCC and OFCOM now issue regulation that requires geolocation and database lookup (see previous blog post) to get transmission permission whereas “sensing is no longer required” as Douglas Sicker, FCC Chief Scientist expresses it(left). So if its not required, why would any equipment vendor include it? Is the Cognitive Radio concept dead – when one of its corner stones is set a side?
Well, I think declaring the demise of Cognitive Radio is somewhat premature. As has been demonstrated several times, TV White Space is not the place where sensing makes sense ;-). The key problem is that sensing the TV transmitters provides very little information of the whereabouts and pathloss to the (silent) TV receivers, the victims of interference. Knowing that a certain TV channel is used in the area is about as much information we can get – and that information we can get more reliably through the geolocation database. This is a fundamental problem and has nothing to do with imperfections of sensing – we can improve the sensing schemes as much as we like – even “perfect” sensing can add anything significant to the database approach. The problem is that sensing detects signals, and not what we really want to detect – spectrum opportunities (= if we can avoid TV-receiver interference).
So, is there anywhere sensing works? Well, sensing should for example work well whenever the transmitter and receiver are closely co-located, i.e. for short range primary systems. One such example is Wireless Microphones. If we from afar detect such a transmitter, that reveals significant information regarding the interference we may cause on the primary receiver. Any two-way system like WLANs, should also work great since there is no silent receiver. Another interesting example is radar systems, where in fact the transmitter and receiver are co-located. If we know the transmitter power of the radar we can calculate the path loss to the radar and exactly estimate the interference at the receiver.
So Spectrum Sensing is not (quite) dead – but not as vigorous tool as we believed it to be! But what about Cognitive Radio – is it blindfolded without effective sensing?