1. Accounting interference:
impact of interference on
revenue
Vânia Gonçalves
IBBT-SMIT, VUB
NG Wireless Workshop
Cognitive Networks: Interference Sensibility
21-01-10, IBBT-Ghent

2. Overview
 Spectrum allocation
 Spectrum is underutilised
 Changes taking place
 Spectrum sensing
 Modelling revenue
 Case studies
 802.15.4 and Wi-Fi
 UMTS and UWB
 WiMAX and FWA
 Conclusions
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3. Spectrum allocation
 Spectrum allocation has always been assigned on a static
basis in order to avoid interference
EFFICIENT?
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4. Spectrum is underutilised
McHenry M.,Tenhula P. & McCloskey D.,
Chicago Spectrum Occupancy
Measurements & Analysis
and a Long-term Studies Proposal, 2005
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5. Spectrum is underutilised
Willkomm D. et al, 2009
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6. Changes are taking place
 Regulatory changes: FSM, DSA, ...
 Cognitive radios
 Sharing is becoming a necessity
 Coexistence of secondary networks with primary owners
of spectrum is possible
 Opportunities for new sources of revenue
BUT…
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7. Spectrum usage varies greatly in a matter of
minutes
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8. Spectrum sensing
 Sensing is the enabler for spectrum sharing
 But perfect sensing of primary users of spectrum is difficult
 Technical requirements and procedures might still be set
to mitigate harmful interference
 Higher likelihood of services interfering with each other
 Few incentives for primary owners to allow opportunistic/
secondary usage
 Possible losses in revenue?
 Important to model the impact of secondary users on
primary users’ performance and primary owners’ revenue
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9. Modelling revenue
 Ercan et al. (2008) propose a three player Stackelberg
game model between the PO, PUs and SUs in which:
 SUs share the channel with primary users in time
 Secondary user access through a non-perfect listen-
before-send scheme
 SUs are allowed to use the channel it when it is not
being used by any PU but keeping interference to PUs
below a maximum
 Accounts for interference probability
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10. Modelling revenue
 Shown that the spectrum owner can enhance revenue by
allowing opportunistic access with a non-zero interference
probability to the primary users:
 In exchange for the degraded QoS of the PUs due to
interference from SUs, the PO offers the PUs a lower
subscription fee
 The enhancement of the revenue comes from the
subscription fee of the SUs and better spectrum usage
 Weaknesses:
 Only one channel and a single spectrum owner is
considered
 Simple listen-before-send model
 Maximum tolerated interference not dependent of
technologies involved
 The user utility metrics are assumed to be equal to their
average throughput and not based on the time of application
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11. Case studies
 Maximum tolerated interference varies with technologies
involved: estimation of interference probability different if PU
technology ≠ SU technology
 The impact to the application/service needs to be considered
 Service metrics
 User throughput
 Delay/jitter
 Users’ outage
 Coverage
 QoS
 …
 The context the application serves
 emergency services ≠ office building
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12. 802.15.4 and Wi-Fi
 Office environment scenario
 200 802.15.4 sensor nodes spread out over 3 floors
 Main interference source: wifi networks
Nighttime measurements
Measured at IBCN, 2009
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13. ZigBee and Wi-Fi
Daytime measurements
Measured at IBCN, 2009
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14. UMTS and UWB
 Operational UMTS network
 Main interference source: UWB devices
 Distance of 1 meter between UMTS terminal and UWB devices
 UMTS in idle mode
 Degradation is
noticeable but
connection is not lost,
except for the cases
with 12 and 16 UWB
devices
Hämäläinen, M et al., 2006
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15. UMTS and UWB
 UMTS in voice and
data modes
 With a small number
of active devices, no
measurable impact is
seen
 For voice connections,
the connection is lost
with more than 12
active UWB devices
Hämäläinen, M et al., 2006 15

16. WiMAX and FWA
 FWA service
 Main interference source: WiMAX
 Urban dense areas
 Co-channel, adjacent channel, and zero guard band transmission
Shamsan and Rahman, 2008 16

17. WiMAX and FWA
 FWA service
 Main interference source: WiMAX
 Urban dense areas
 Co-channel, adjacent channel, and zero guard band transmission
Shamsan and Rahman, 2008
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18. Conclusions
 Spectrum sensing may create opportunities for efficient usage
of spectrum and increased revenue
 The impact of interference to be a combination of the
interference generated by the technologies, application and
context
 Maximum tolerated interference to be dependent on intended
output of service metrics and technologies
 Next steps:
 To be able to narrow down to costs -> definition of concrete
scenarios:
 Frequency bands
 Spectrum access
 Interference scenarios/technologies involved
 Application and context
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19. Thank you!
Questions?
vania.goncalves@vub.ac.be
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20. References
 Hamalainen, M., et al., Co-existence measurements between
UMTS and UWB systems. IEE Proceedings - Communications,
2006. 153(1): p. 153-158.
 Shamsan, Z.A. and T.A. Rahman, On the comparison of
intersystem interference scenarios between IMT-Advanced and
Fixed Services over various deployment areas at 3500MHz.
Progress In Electromagnetics Research, 2008. 5: p. 169–185.
 Ercan, A.O., et al., A Revenue Enhancing Stackelberg Game
for Owners in Opportunistic Spectrum Access., in Proceedings
of DySPAN 2008, 2008.
 Willkomm, D., et al., Primary user behavior in cellular networks
and implications for dynamic spectrum access. Comm. Mag.,
2009. 47(3): p. 88-95.
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