How I learned to Stop Worrying and Love Interference
UW Econ NPI Brownbag
12 December 2010
Pierre de Vries
1
Intro
Who I am
– Physicist by training; VC, consulting; managing software development; then tech policy
– Self-supporting researcher: EPRC, SFC
Goal of Talk
– Get you interested
• Survey of radios & regulation
• Give a flavor of the problem
– Get feedback and ideas
• Outline the 3Ps proposal
• Sketch a model
Three perspectives/guilds
– Law
– Engineering
– Economics
Jargon Test:
– FCC, APA
– dB, OOBE
– Coase Theorem, Cathedral Rules
2
Outline
Introduction to Radio Regulation
– Radio communications
– Interference mechanisms
– Regulatory landscape
The 800 MHz case
An approach to regulation
– Problems
– Principles
– Proposal
A Model
3
Radio Communications
Radios produce electromagnetic waves that move through space
4
Transmitter Receiver
Antenna Antenna
Transmission Line Transmission Line
Radio Waves
Source: Dale Hatfield
Radio boundaries are Fuzzy
Geography
Frequency
(Omitted: Time, Coding, Polarization, …)
5
KOMO contour
http://maps.google.com/?q=http://www.fcc.gov/fcc-bin/contourplot.kml?gmap=2%26appid=429542%26call=KOMO-TV%26freq=0.0%26contour=41%26city=SEATTLE%26state=WA
6
KOMO coverage
http://www.tvfool.com/?option=com_wrapper&Itemid=90 7
KOMO Coverage (detail)
8
Site General Propagation Model
Source: NTIA ITS (?) via Hatfield
Site Specific Propagation Model
Source: NTIA ITS (?) via Hatfield
U.S. Frequency Allocations
11
Bart’s Head
http://www.electronicsweekly.com/blogs/engineering-design-problems/2008/10/post-2.html
12
802.11 Waveform
http://www.home.agilent.com/agilent/editorial.jspx?cc=US&lc=eng&ckey=606355&nid=-34861.0.00&id=606355
13
Interference Mechanisms
Geography
Frequency
(etc.)
Interference happens in the Receiver
14
Geography: Co-channel interference
15
Desired Signal
Interfering or UndesiredSignal
Transmitter A
Transmitter B
Frequency
SignalPower
Receiver B
Frequency: Co-channel spill-over (“Splatter”)
16
Desired Signal
Interfering or UndesiredSignal
Transmitter B
Frequency
SignalPower
Receiver B
Transmitter A
FiltersIdealized Filter Actual Filter
Frequency
SignalPower
Frequency
SignalPower
Resulting energy in Receiver
Frequency
SignalPower
Resulting energy in Receiver
Frequency
SignalPower
Frequency: Adjacent channel/band (1)
Desired Signal
Interfering or UndesiredSignal
Transmitter B
Receiver B
Transmitter A
Frequency
SignalPower
18
Frequency: Adjacent channel/band (2)
19
Desired Signal
Interfering or UndesiredSignal
Transmitter A
Transmitter B
Frequency
SignalPower
Channels & Bands
20
Frequency
Lower AdjacentBand
DesiredBand
Upper AdjacentBand
Band Filter
Channel Filter
Lower AdjacentChannel
Upper AdjacentChannel
DesiredChannel
Radio Regulation
“ The rules, processes and institutions
for defining, assigning, and enforcing
radio operating rights”
21
The Situation
Challenges
– Exploding demand
– Technical & regulatory constraints
Solutions
– Denser packing
– More flexibility
Complications
– Ambiguity in rights definitions
– Regulator in the loop
22
Challenges
Exploding demand for operating rights
– data traffic from smartphone and mobile Internet use is exploding
– a 5 MB download contains as much data as a one hour phone call
– a single YouTube video is the equivalent of 5,000 text messages
– industry analysts predict data traffic rates will increase as many as 22 to 47 times by 2014
But:
– Limits on concurrent operation (technology dependent)
– Uncertain radio propagation and interference environment
– Constraints on throughput (in bits/second/Hz) imposed by Shannon’s Law
– Regulatory and technical rigidities -> administrative scarcity
23
Responses
Solutions
– Denser packing – fewer guard bands
– More flexibility – more inter-service boundaries
– Talk of “sharing”
Complication: regulatory approach hasn’t changed
– New allocations envisaged, but incumbents cling to option value
– More cross-channel, more problematic than co-channel
– Ambiguity in rights definitions
– Regulator always in the loop
Result
– Prolonged disputes - > loss to Treasury (800 MHz); delayed investment (AWS-3)
24
Cross-channel issues are more problematic than co-channel
Scope
– Interference can occur at any location within the geographic service area, not just at the edges
– The number of players or stakeholders involved may be much larger and involve the general public directly
Asymmetry
– The actual or perceived risk or consequences of interference may be asymmetrical
– The architectures and technologies may be vastly different
– Providers in adjacent band are more likely to have very different perspectives, incentives and even cultures – e.g., public safety entities versus commercial entities
Receiver performance
– Especially important and complex role in adjacent channel/adjacent band interference issues
– Not regulated
– Sometimes outside the control of the service provider
As spectrum use intensifies, adjacent channel/adjacent band interference issues are apt to become even more challenging
25
The 800 MHz Case
a.k.a. “Public Safety vs. Nextel”
26
800 MHz Case
Interleaving
– Fine while both high-power/high-tower
– Problems when Nextel cellularized
Both operated within rights
Transaction costs
– large number of public safety operators
Nextel deal – moved to new frequencies
– FCC bore first $2.8 bn of cost, Nextel any over-runs
– Four years to negotiate
27
FCC Spectrum Allocation of 800 MHz Band Prior to Rebanding
28
TV
Broadcast
Ch. 60-69
General
Category
Includes Nextel,
B/ILT & a few
Public Safety
Upper 200 SMR
(Nextel)
806 825816
851 870861 866
809.75
854.75
NPSPAC
821 824
869
- SMR (80 channels) INCLUDES NEXTEL- Business/SMR (50 channels) INCLUDES NEXTEL- Industrial/SMR (50 channels) INCLUDES NEXTEL
- Public Safety (70 channels))*
[7.5 MHz] [12.5 MHz] [10 MHz] [6 MHz]
CELLULAR
Source: APCO/Gurss via Hatfield
The 800 MHz Case
29
Public Safety
Nextel
Frequency
Nextel
Nextel
Nextel
Nextel
An Alternative Approach
Problems
Postulates
Proposals
30
Moral of the Story
Increased density leads to problems
Unclear who’s at fault
Expensive to negotiate resolution
31
Postulates
Radio conflict is unavoidable and necessary
– Aim regulation at maximizing concurrent operation, not minimizing harmful interference
Conflict resolution is primarily a bilateral activity between those involved
Any initial entitlement point is unlikely to be, or remain, optimal
– So: Define, assign and enforce entitlements in a way that facilitates transactions
32
Enable bargaining by effective delegation
Limit the number of parties
– Optimize assignment
– Minimize the number of recipients/borders
– Minimize role of regulator
Create unambiguous rights
– Technical: 3Ps
– Legal: Stipulate the remedy (injunctions or damages) that attaches to an operating right when it is issued
– Institutional: a complete and current public registry of every entitlement
Don’t change the rules during the game
– Leave parameter values unchanged after an entitlement has been defined, (values may be adjusted by negotiation between operators)
– Add new parameters only at license renewal
– Refrain from rulemaking during adjudication (2 roles)
33
Better Rights
Technical
– Probabilistic Permissions and Protections
Legal
– Stipulate remedies ex ante
Institutional
– Public registry
34
The Three Ps
Transmission Permissions: resulting field strength over space and frequency, rather than radiated power at a transmitter.
Reception Protections: maximum electromagnetic energy an operator can expect from other operations
– Undertaking by the regulator to implement these ceilings when determining the respective transmission permissions of other allocations
– Does not form an entitlement against other, existing operators.
Probabilistic: ≤ X at Y% of locations, Z% of time
Does not require a definition of harmful interference
– Delegated to operators and, should negotiation fail, adjudicators
– Hence, it also does not require receiver standards.
35
Probabilistic Permissions and Protections
36
Reception protection for Rae’s license
Frequency
ResultingEnergy
Transmission permission for Tom’s license
Allowed energy ≤ limit at Y% of locations, Z% of time
Liability or Injunction?
37
Tom’s license allows operation up to E = E0
Entitlement assigned to
Tom Transmitter Rae Receiver
Entitlement type
Injunctive(“property”)
Tom has discretion tooperate at E < E0 if hechooses, e.g. afterpayment from Rae
("Cathedral" Rule 3)
Rae can prevent Tom fromoperating at E > E0 unlesse.g. Tom makes a paymentto Rae
("Cathedral" Rule 1)
Damages(“liability”)
Rae may persuade court toreduce Tom’s power to E <E0, but then has to paydamages to Tom
("Cathedral" Rule 4)
Rae cannot prevent Tomfrom operating at E > E0,but is entitled to damages
("Cathedral" Rule 2)
E0E < E0 E > E0
Rules of the Game
Regulator can’t change values
Use license renewal to add parameters
Separate rulemaking and adjudication
38
A Model of Radio Externalities
39
A model
40
W Net social welfare
EMaximum resulting energy as a result of transmission
N Number of receivers
BT(E)Benefit derived from operating transmissions with maximum resulting energy E
BR(N) Benefit derived from operating N receivers
H(E, t, r) Monetary harm per receiver
fT(t)Total spending on precaution by Tom as a function of his out-of-band attenuation t dB
fR(r)Spending per receiver on precaution by Rae as a function of her out-of-band attenuation r dB
Rae’s operating
frequencies
Tom’s operating
frequencies
E
t
Suppression of E achieved by Rae in her receivers through OOB
filtering
Suppression of E in Rae’s receivers achieved by Tom
through transmitter filtering
Resulting energy
r
First Order Conditions
41
Rae’s operating
frequencies
Tom’s operating
frequencies
E
t r
N: number of receiversH: harmfT: Tom’s precaution costfR: Rae’s precaution cost
Liability regime
Strict liability
– Rae is entitled to compensation for all her damages but cannot stop the harmful interference from occurring
– Leads to efficient precaution by Tom
– However, since Rae is fully compensated, she has no incentive to invest in precaution, i.e. out-of-band filtering for her receivers, or limit the number of her receivers
– Hence, Tom will suppress E and t below optimum
Marginal liability
– Tom is only liable for damages if he takes less than the optimum amount of precaution (t)
– But will then push E up, since he’s not liable to Rae, suppressing N below optimum
42
Property (aka injunction) regime
Rae can block Tom from operating
Tom will thus purchase rights to cause harmful interference up to the point where marginal gain from operating, very high at the beginning, eventually decreases to equal the marginal cost of precaution (his and Rae’s) plus harm
Tom will compensate Alice to operate with optimal receiver filters
But, if there are many Rae’s that Tom cannot identify and compensate ex ante, there will be an incentive to deploy too many receivers
43
Some Open Questions
Can functional forms be found?
Given functional forms:
– Can model predict existing rules?
– Can one recommend best remedy regime?
What happens when assumptions fail?
– High transaction costs (e.g. public safety, unlicensed)
– No adjudication venue (e.g. FCC vs. NTIA)
– Player doesn’t have monetary incentive (e.g. DoD)
– Functional forms don’t lead to first order solutions (e.g. non-convex harm curve, non-monotonic precaution cost)
Making trade-offs to reduce number of boundaries
Time adjacency44