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Spectrum Congestion

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Spectrum Congestion Radio Link & Environment The Shannon s Law assumes an isolated communication channel no fading, no inter-symbol interference, no shadowing no Co ... – PowerPoint PPT presentation

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Title: Spectrum Congestion


1
Spectrum Congestion
2
Radio Link Environment
  • The Shannons Law assumes an isolated
    communication channel
  • no fading,
  • no inter-symbol interference,
  • no shadowing
  • no Co- or Adjacent Channel interference
  • No radio link can be isolated as radio waves
    cannot be confined to any specific volume.

3
Degree of Isolation
  • Any radio link interacts with its EM environment
  • The Shannons model of communication channel is
    to be modified to include interaction with
    environment
  • The degree of this interaction can be described
    by Isolation Index

4
Isolation index
Isolated link N gtgt I, a ? 1
  • Definition
  • a N / (I N)
  • Environmental noise
  • Intrinsic noise power

Link coupled to its environment I gtgt N, a ? 0
5
Isolation Depends on
  • System characteristics
  • Modulation, Coding, Signal processing,
  • Equipment characteristics
  • Power, Frequency, Polarisation,
  • Spatial deployment
  • Distance, Direction, Polarization,
  • Environment
  • Propagation effects
  • Reflections, Terrain shadowing,

6
Capacity Degradation
R/Blog2(1aq) q S/N
With constant bandwidth, the amount of bits
transmitted per second per Hz (R) increases with
the isolation index (a) and signal-to-noise ratio
(q).
7
Amount of Information
Isolated radio link
Radio link coupled to environment
t
Log(1q)
Log(1aq)
t
B
B
8
Congestion ? Loss of Capacity
  • A cluster of mutually coupled radio links.
  • Capacity of each radio link is reduced due to
    the impact of other links.
  • The worst case
  • Co capacity of an isolated link
  • k number of other links (identical)

C/Co log21 (S/N)/ 1 k(Io/N)
9
Summary
  • The congestion increases as new radio users
    appear, the capacity of radio links deteriorates,
    and the existing users suffer
  • A reduced amount of information can be
    transmitted in a given time and bandwidth
  • A wider bandwidth is required to transmit a given
    amount of information within a given time
  • A longer time is required to transmit a given
    amount of information within a given bandwidth
  • It means increased transmission costs
  • The concepts of isolation and capacity loss due
    to congestion might serve
  • As objective measures of spectrum congestion
    and/or as a criterion in comparing various
    trade-offs that may be difficult to compare
    otherwise (in system design and in spectrum
    management)
  • As a criterion in optimisation projects seeking
    min. capacity loss of a specific radio link
    (local optimum), a specific set of radio links
    (local optimum extended), or all radio links in
    question (global optimum)
  • Was proposed recently - has not been generally
    accepted yet

10
References
  • Struzak R Spectrum Congestion and Capacity of
    Radio Links, Annals of Operations Research 107,
    339-347, 2001-2002, Cluwer Academic Publishers
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