NSMA Conference

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NSMA Conference
Interference Temperature Round Table
May 18, 2004
Les Wilding Cingular Wireless 5565 Glenridge
Connector Atlanta, GA 30342
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Topics for Discussion
1. Interference Temperature as it Applies to
Point-to- Point Microwave Links. 2.
Interference Temperature as it Applies to CMRS
Networks. 3. Summary
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Interference Temperature and Point-to-Point MW

• In the NPRM section the Commission discusses
  applying the
• interference temperature concepts to both the FSS
  and FS services.
• Band Segments selected by the Commission for
  deployment of
• unlicensed devices are
• FSS Band Segment 12.75 - 13.25 GHz
• (excluding 13.15-13.2125 GHz)
• F S Band Segment 6525 MHz to 6700 MHz
• Note In the FS category the Commission selected
  the lower half
• of the full (6525-6875 GHz) upper 6 GHz
  band.

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Interference Temperature and the Digital MW
Link Commission Assumption 1 126 dB margin
When computing interference, the interfering path
(path C to B) must be below the interference
objective for the victim microwave link (path A
to B).
Figure 1
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Interference Temperature and Point-to-Point MW
Coordination objectives for interference are
based on published T/I curves for the victim
receiver and the interfering carrier. The
Interference objective for coordinating a typical
MW link is I (Coordination) 75.5 dBm
34 dB 5 dB 114.5 dBm Where 75.5 dBm
the Static BER Threshold of 10-6 34 dBm
the Specific T/I threshold for the victim and
interfering bandwidths and frequency offsets.
5 dBm Multiple Exposure Allowance The
unfaded C/I (Coordination) for a digital link is
-40 dBm- (-114.5 dBm) 74.5 dB
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Interference Temperature and the Digital MW Link

The NPRM describes an unlicensed device that is
transmitting on 6600 MHz with an output of
-41.25 dBm/MHz and operating 100 meters from a
FS receiver with a discrimination angle of 20
degrees. The formula for calculating the
operating margin is EIRP (A) - Path loss (A to
B) - C/I (Coordination) gt EIRP (C) - Path
loss (C to B) Disc Loss (B to C) Using
the coordination data for the MW path and
correcting the EIRP of the unlicensed device for
3.75 MHz bandwidth yields 64 dBm-140 dB-74 dB
gt -35.5 dBm -93 dB - 43 dB which -150 dBm gt
-171.5 dBm 21.5 dB margin This is the margin
for ALL interferers not the 126 dB in the NPRM
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Interference Temperature and the Digital MW Link
Commission Assumption 2 Use of Transmit Power
Control TPC Use of Dynamic Freq.
Selection DFS
Figure 2
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Interference Temperature and the Digital MW Link

• For this to work, the TPC and DFS detectors in
  unlicensed device
• would have to hear the MW signal from site A
  and make decisions
• about what is happening at site B in order to
  set its transmit level.
• The propagation path (A to C) is primarily along
  the ground and not
• subject to atmospheric disturbances. Whereas
  the FS link (A to B) is
• subject to atmospheric disturbances.
• This could lead to a situation where there is a
  lot of fading activity on
• path (A to B) that is not seen by the ground
  based unlicensed receiver
• thus causing false decisions and cases of
  interference into site B.

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Interference Temperature and the CMRS Network

• CMRS networks already manage interference in real
  time
• Transmitter Power Control
• Frequency hopping modulation coding techniques
• CMRS operators have greatly reduced
  self-interference
• Improved capacity and higher data throughput
• Increased cell coverage uses total radio channel
  sensitivity
• Unlicensed Devices are incompatible with CMRS
  networks
• CMRS operator can not control external
  interference
• External interference raises noise floor,
• Lowers system capacity
• Lowers system/customer data throughput
• Increases mobile transmit power/lowers battery
  life
• Lowers quality of service

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Interference Temperature

• Summary
• Interference Temperature is a CONCEPT
• It needs to be adequately defined and quantified
  before it
• has any value in spectrum management.
• SDR and Cognative Radios are in their infancy and
  are not ready
• to take on the tasks envisioned by the
  Commission.
• Most users of licensed spectrum make use of the
  total range of
• receive levels down to and including the
  thermal noise floor of
• their communications systems.
• FS and FSS licensed services can not tolerate
  interference levels
• greater than the currently authorized Part 15
  levels.

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Interference Temperature
In short, I commend the Commission for thinking
outside the box BUT the Commission has
put the licensees feet into the water before the
ARK has been built to protect the licensed users
from drowning in a sea of interference.
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(No Transcript)
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Interference Temperature and Point-to-Point
MW The Digital Microwave Link

• Digital microwave paths are designed to meet a
  desired performance
• measured in
• Error free seconds.
• Unavailability in seconds per year.
• The components that make up this performance are
• Its composite fade margin (CFM).
• Its threshold to interference (T/I) margin.
• The links CFM is primarily the sum of the flat
  (thermal) and
• dispersive fade margins.

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Interference Temperature and Point-to-Point
MW The Digital Microwave Link
Figure 1
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Interference Temperature and the Digital MW Link
Commission Assumption 1. 126 dB of margin and
S/I Requirement of 30 to 50 dB
Equipment used in a typical MW link The NEC 2600
series MW is typical of the radios used in this
band Transmitter output power 28.5 dBm
max Modulation 128 QAM Modulation bandwidth
3.75 MHz Receiver threshold BER of 10-6 -75.5
dBm T/I Co-channel 34 dB T/I adjacent channel
-5 dB Receiver outage threshold BER of 10-3
-78.5 dBm (assumed to be 3 dB worse than the
static threshold) The Andrew PAR6-65 antenna is
a typical Category A antenna
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Interference Temperature and the Digital MW Link
Commission Assumption 1. 126 dB of margin and
S/I Requirement of 30 to 50 dB
Coordination of a typical MW link Microwave
transmitter output power 28.5 dBm Typical
losses on the transmit side - 3.0
dB Typical gain for a 6 foot MW dish 38.8
dBi Typical EIRP 64.3 dBm The unfaded
receive signal level for a typical 40 km path
is 64.3 dBm -140 dB (path loss) 38.8 dBi - 3
dB (feeder) -39.9 dBm In the digital world,
EIRPs range from 60 dBm to 75 dBm based on a
typical 0.5 watt to 2 watt transmitter and a 6 to
8 foot diameter standard performance dish.
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Interference Temperature and the Digital MW Link
Figure 3
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The FCCs Definition of Interference Temperature

• Originally proposed by the Spectrum Policy Task
  Force (SPTF)
• as an Interference Management Concept to
• Establish a maximum level of interference that
  can be
• tolerated by a receiver but ONLY after a
  systematic and
• thorough study of the existing RF
  environment.
• Establish a clear definition of the spectrum
  users Rights
• and Responsibilities
• Establish a clear quantifiable definition of
  Harmful Interference

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The FCCs Definition of Interference Temperature
The FCCs Interference Temperature Metric as
defined in ET Document 03-237 is A measure
of the RF power generated by undesired emitters
plus noise sources that are present in a
receiver system (IN) per unit of bandwidth.
More specifically, it is the temperature
equivalent of this power measured in units of
Kelvin.
There is no basis for the term or a definition of
Interference Temperature in any of the
Standards documents. The Commission used the
cookbook approach by taking parts of the
definitions of Antenna Temperature and System
Noise Temperature to cook up their Interference
Temperature dish.
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The FCCs Concept of Interference Control

• The Commission would have you believe that a
  licensee would
• be agreeable to accepting some guaranteed maximum
  level of
• interference (Interference Temperature Limit)
• To accomplish this the FCC is proposing to employ
  one or more
• of the following techniques
• Use of Software Defined Radios to select
  frequencies and/or
• modulation modes that would avoid interference.
  
• Use of Cognitive Radio technologies (smart
  radios).
• Deployment of remote monitoring receivers to
  sense the
• RF environment.
• Incorporation of RF interference monitoring
  technology into
• the licensed receiver to detect the presence of
  interfering
• signal levels.

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The FCCs Concept of Interference Control

• Deployment of a grid of monitoring stations that
  would sense
• the interference temperature and
  broadcast this data to all
• unlicensed devices.
• Problems with the monitoring scenarios
• These approaches, with the exception of equipping
  the licensed
• receiver with a monitor, all fail to accurately
  identify the
• interference conditions as seen by the victim
  licensed receiver.
• They all require spectrum for communications
  with/between the
• monitoring device(s) and the unlicensed
  devices.