Air Force Flight Test Center. Defending Our Spectrum: What Do You Mean When You Say You ve Used Spectrum

Transcription

1 Air Force Flight Test Center Defending Our Spectrum: What Do You Mean When You Say You ve Used Spectrum Charles H. Jones, PhD 812TSS/ENTI I n t e g r i t y - S e r v i c e - E x c e l l e n c e 1

2 Outline Spectrum Overviewed Example Propagation Two Definitions of Use Legal Allocation Licensed and Scheduled Dimensional Separation On-Demand Buffering Misc Comments Summary and Conclusion 2

3 Defending Our Spectrum Over the last several years the T&E community has been asked to provide spectrum usage data Part of the response has been based on data from the Interrange Frequency Deconfliction System (IFDS) This data captures when data was scheduled We ve been asked what our real usage is This presentation discusses why scheduled usage is real usage 3

4 Spectrum Radio Frequencies (RF) Electromagnetic waves from about 3 Hz to 300 GHz propagating through time and space. Commonly called wireless communication Dimensions of Spectrum Three of Space Time Frequency Power Polarization 4

5 First Definition of Use Spectrum is used if there are electromagnetic waves propagating through a particular geographic location at a particular time. 5

6 First Definition of Use Spectrum is used if there are electromagnetic waves propagating through a particular geographic location at a particular time. It is the intent of this presentation to convince people that this is a naïve definition. 6

7 Omnidirectional Propagation Consider a standard FM Radio Station with a dipole antenna Ideal radiation pattern emits energy in all horizontal directions Consider a standard airborne telemetry dual antenna transmission pattern Ideal radiation pattern is spherical about the moving platform 7

8 Antenna Patterns Antenna Pattern slice in the azimuth plane

9 Non-Ideal Propagation The porcupine composite antenna shape is due to difference in amplitude and phase of the signals being transmitted between the top and bottom antennas The edge of a radio station pattern is amorphous due to geography and multipath that interfere with the radial propagation Transmission power and receiver sensitivity affect distance The frequency is actually the center frequency in a band of contiguous frequencies 9

10 What Spectrum is Used? Do the non-lobe portions of the antenna pattern represent spectrum use? There is no, or little, electromagnetic energy propagating through those portions of space. At what distance do we say that a radio station is no longer using the spectrum in its geographic vicinity? The point here is that even when doing a simple spatial analysis, it is not clear what use is in terms of RF transmission. 10

11 Second Definition of Use Use is Denial to Others Propagating energy through portions of the spectrum is a primary method of denying use to others But there are many legitimate reasons for denying use to others even when no energy is being propagated. 11

12 Legal Allocation Spectrum is legally allocated for use to individuals or organizations through a complex, often political, process. The U.N. Treaty created Radio Bureau of the International Telecommunications Union (ITU-R) establishes international radio regulations which are then used as the basis for national level allocations Meets at the World Radiocommunication Conference (WRC) every 3 years. 12

13 United Nations The International Process International Telecommunications Union National Telecommunications Delegates etc US State Department Regional Organizations US DOC FCC DoD Federal Users FAA Non-Federal Users

14 National Level Allocation After the ITU-R process is over, then the individual nations make more detailed allocations. 14

15 The National Process Congress Federal Communications Commission FCC Commissioners (5) Participation / License Applications FCC Bureaus Licenses President appoints Non-Federal Users Commercial State & local government NGOs Private individuals Coordination President Department of Commerce Asstnt Sctry of Commerce for Comm and Information (Administrator, NTIA) National Telecommunications & Information Administration Interdepartment Radio Advisory Committee All Federal Users 15 A s s i g n m e n t s

16 U.S. Spectrum Allocation Which leads to the following chart (Ovals added to point out some of the Mobile Telemetry Bands) 16

17 L-Band S-Band 17

18 Assignments and Licenses This trickles down to assignments of use of particular frequencies at particular times by particular organizations. This assignment is what T&E Frequency Managers do. Commercial users get licenses. The spectrum auctioned off in recent years is via licenses. When spectrum is auctioned off and repurposed it changes the words on the previous chart. 18

19 No Obligation Many licenses and assignments contain no legal obligation to transmit. Legal ownership is denial to others without necessarily transmitting. 19

20 Business In 2006, SpectrumCo LLC, (Comcast, Time Warner, Cox, Advance/Newhouse and Sprint Nextel), won 137 wireless spectrum licenses for $2.37 billion in the FCC s auction Verizon is trying to buy these for $3.6 billion. For 6 years there s been no transmission. TV broadcasters white space is another example of spectrum with no transmission over a long period of time. Business decisions can lead to denial to others without necessarily transmitting. 20

21 Scheduling At the bottom of this legal process, T&E Frequency Managers schedule spectrum by assigning contiguous blocks of spectrum to particular test programs. These assignments can be thought of as rectangles in the time/frequency grid. Due to logistical reasons it is not always possible to transmit during the entire time scheduled. Scheduling is denial to others. 21

22 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 Frequency (MHz) Time/Frequency Grid Y Scheduled Mission X Time (Hours) 22

23 Dimensional Separation To avoid interference, transmission signals are separated in one or more dimensions. This evolves from the physics of transmission techniques This separation includes purposely not transmitting in portions of the spectrum between the separated signals. In some cases there may be RF leakage or spurious transmissions into the separation zones, which is why the zones are created 23

24 PCM/FM Separation dbc Frequency (MHz) 24

25 TDMA Separation Time Division Multiple Access (TDMA) provides time slots dedicated to particular users. Because of timing inaccuracies, guard bands (small time slices) are created between the assigned time slots inet will be using TDMA User 1 G B User 2 G B User 1 G B User 2 25

26 Dimensions Spatial separation is near universal Frequency separation is common There are no even decimals on the FM dial Scheduled telemetry separates in space, frequency, and time Separation via polarization is rare, but is used Spread spectrum techniques, such as CDMA used by cell phone companies, separate in the dimension of power Use of separation zones is denial to others. 26

27 Spread Spectrum and CDMA In a CDMA system the same frequency can be used in every cell, because channelization is done using pseudo-random codes The power is spread out over more frequencies than necessary This allows multiple people to use the same frequency at the same time and location This could be considered Power Division Multiple Access since each user is allowed a certain amount of power on a common frequency 27

28 CDMA and Pseudorandom Codes XOR Data Signal and Pseudorandom Code to Transmission Signal. XOR Transmitted Signal and Pseudorandom Code to get the Data Signal. 28

29 On-Demand Buffering Cell phones use spectrum on an on-demand basis, coming and going on individual whim. CDMA lends itself to this type of access WiFi and garage door openers are also examples There must be a constant surplus of spectrum in order to accommodate on-demand service Cell phone frequencies are used almost continuously but rarely, if ever, at full capacity There is transmission over frequencies but not to a maximal power limit 29

30 T&E and Cell Phones A Comparison Scheduled spectrum for T&E is a form of ondemand buffering. A best effort is made to schedule exactly when spectrum will be used The logistical difficulties of coordinating all assets for a test make it virtually impossible to be transmitting exactly when scheduled T&E buffers in the dimension of time Cell Phones buffer in the dimension of power On-demand buffering is denial to others. 30

31 Efficiency Every method and application of RF transmission can be questioned as to their efficiency. 4G is more efficient than 3G SOQPSK is more efficient than PCM/FM Probably even SpectrumCo would not claim they made efficient use of their spectrum Inefficient transmission is denial to others. 31

32 Other Examples The National Radio Quiet Zone around Green Bank National Observatory (NTIA Manual 8.3.9). Any transmission in any frequency in this area interferes with Radio Astronomy Some national borders have frequency buffer zones for cross border non-interference There is one along the U.S. Mexican border Radar is not a continuous transmission Spectrum can be fragmented due to difficulties of scheduling 32

33 Standardization Effort The Range Commander s Council (RCC) Frequency Manager s Group (FMG) has established a formal Task to develop a standard on frequency management metrics. Part of this will include formally defining spectrum use within the context of T&E. 33

34 Summary Just because there is no electromagnetic energy flowing through time and space, does not mean that that spectrum is not being used Legal authority to use Impacts of business decisions Dimensional separation On-demand buffering Other reasons 34

35 Conclusion In order to define and quantify spectrum use it is necessary to look at many factors Functional requirements Physics and technology used Business incentives Legal realities A one-size-fits-all definition is not practical It seems reasonable to start with Use is Denial to Others then develop application specific refinements 35