Spectrum Alternatives for Aircraft Onboard Wireless Systems

1. Date: 2007-11-13 Spectrum Alternatives for Aircraft Onboard Wireless Systems Frank Whetten, Boeing

2. Lower frequencies propagate better Less shadowing and better material penetration, signals will propagate throughout aircraft with low power Require larger antennas Higher frequencies are more attenuated More line of sight (LOS) propagation, shadowing and absorption become major factors Very small antennas can be used, but more power required Desirable to have aviation spectrum near unlicensed bands Can adapt COTS equipment to avionics use via firmware load Leverage significant wireless industry investment into technology upgrades and improvements What Kind of Spectrum Do We Want? Frank Whetten, Boeing Filename.ppt| 2

3. Essentially all usable spectrum is already allocated to primary and secondary users around the world So how might we find spectrum? Two basic options: Obtain new spectrum by taking it away from an incumbent user Resistance to getting more spectrum allocations will be high Maximum opportunity for new spectrum is above 30GHz Reuse existing spectrum already allocated to aviation Aviation has a large number of dedicated frequency bands allocated in around the world Opportunities exist for more efficient use of existing aviation spectrum MLS is not deployed, DSB-AM still in use Where Will the Spectrum Come From? Frank Whetten, Boeing

4. Best opportunity for new spectrum is above 30GHz: Line of Sight (LOS) propagation High absorption due to rain, snow, etc. in atmosphere Resulting intra-airplane usage might be appropriate for: Very short distance, high-bandwidth applications Very small devices, but with sufficient power availability Examples of suitable applications might include LRU-LRU communications within an equipment rack, within the flight deck, or multiple sensors with a nearby data concentrator Examples of ill-suited applications could include Extremely low-power devices attempting to communicate long distances or in a highly shadowed environment, such as along the length of the fuselage Obtaining New Spectrum Frank Whetten, Boeing

5. Existing aviation spectrum is largely below 10GHz Consequently, the advantages of low frequencies apply Is it be possible to reuse existing spectrum? Many factors apply: Particular classification of existing spectrum (in ITU terms) Incumbent system characteristics Bandwidth potentially available for reuse How can we reuse existing spectrum? Two basic possibilities: Cognitive – the new systems can detect which parts of the frequency band the incumbent is using, and move elsewhere Underlayment – the new systems operate at power levels below what the incumbent systems can detect (the UWB model) Reusing Existing Spectrum Frank Whetten, Boeing

6. Existing Aeronautical Allocations Frank Whetten, Boeing

7. Existing Aeronautical Allocations Frank Whetten, Boeing

8. What is Cognitive Radio, and what does it have to do with reality? Cognitive radio is the concept of a coexisting system detecting another system, and moving out of the way Regulatory authorities world-wide are looking at cognitive as an answer to the shortage of good spectrum IEEE 802.11a/n operation in 5GHz band using DFS is an early implementation of cognitive capability Thus, to reuse existing avionics spectrum the new systems would: Need to know where the incumbent system is operating, and Operate around it or under it How? Announcements (via a systems bus, beacon, etc.) Detection of emissions (proven, but difficult) Cognitive Approaches Frank Whetten, Boeing

9. What is underlayment, and what does it have to do with reality? Underlaying an existing spectrum allocation relies upon operating a new system in such a way that the existing system is not interfered with in a harmful way (FAA/FCC nomenclature) Again, a major push by regulators looking for ways to gain more utility from over-desired spectrum Thus, to reuse existing avionics spectrum, the new systems would: Operate at power levels which would not interfere with the input receivers of incumbent systems How? Two factors: Output power, directionality, and gain of new system Interference path loss (IPL) between new system and the incumbent receiving antenna Underlayment Approaches Frank Whetten, Boeing

10. Shannon’s Law The theoretical maximum bit-rate through any noise-limited channel is where C=channel capacity in bits, B=channel bandwidth in Hz, and  is numeric signal-to-noise ratio Shannon’s law can be modified by MIMO technology to Where (H) is a bunch of channel and path correlation factors, and N is the number of MIMO channels How Much Bandwidth is Available? Frank Whetten, Boeing

11. How Close to Shannon Are We? Frank Whetten, Boeing

12. Underlaying Existing Systems Frank Whetten, Boeing

13. Conclusions • Two approaches to obtain dedicated and protected spectrum for intra-airplane use • Pursue a new aviation allocation through international treaties organizations • Develop methodology to re-use existing spectrum in a safe and efficient manner • A new allocation • Would likely be challenging to obtain spectrum below 10GHz, due to strong competition for spectrum resources • Would likely take several cycles of the World Radio Conference to approve • Reusing existing allocations • Significant engineering challenges in ensuring that multiple communications systems can use the same spectrum without harmful interference • Regulatory challenges pertaining to avoiding being limited by the current regulatory language and footnotes on existing bands Frank Whetten, Boeing