Transcript No Slide Title

NSMA Conference
Interference Temperature Round Table
May 18, 2004
Les Wilding
Cingular Wireless
5565 Glenridge Connector
Atlanta, GA 30342
Topics for Discussion
1. Interference Temperature as it Applies to Point-toPoint 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).
Victim Microwave Link
Tx A
Rx B
Discrimination
angle for Ant B
Interfering path
Tx C
Unlicensed Device
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) =>
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 => -35.5 dBm -93 dB - 43 dB
which = -150 dBm > -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
Victim Microwave Link
Tx 6525-6700 MHz
Rx 6700-6875 MHz
Rx 6525-6700 MHz
Tx 6700-6875 MHz
Tx/Rx A
Interfering path
for Ant C
Rx/Tx B
Interfering path
Discrimination
angle for Ant B
Tx/Rx C
Unlicensed
Device
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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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 link’s 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, EIRP’s 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
Maximum Interferer Power
(Microwatts)
Maximum Interferer Power vs MW Ant Height
above Ground
8000.00
7000.00
6000.00
5000.00
4000.00
3000.00
2000.00
1000.00
0.00
MW ant @ 30 Meters
MW ant @ 50 Meters
MW ant @ 70 Meters
Averaged levels
0.1
0.5
0.9
3
5
7
Distance from Tower (km)
Figure 3
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The FCC’s 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 FCC’s Definition of Interference Temperature
The FCC’s 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 (I+N)
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 FCC’s 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 FCC’s 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.
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