ITUR WP8B Radar Symposium

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ITU-R WP8B Radar Symposium

• History and Status of 5 GHz RLAN and Radar
  Dynamic Frequency Selection (DFS)
• In the United States
• Frank Sanders
• U.S. Department of Commerce
• Institute of Telecommunication Sciences
• www.ntia.doc.gov
• September 2005

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Radar/DFS Background and History

• WRC-03 allocated the bands 5250-5350 and
  5470-5725 MHz to the mobile service on a
  co-primary basis with the existing services.
  WRC-03 adopted Resolution 229 that provides
  conditions for use of the bands by the mobile
  service. Resolution 229 provides limits for the
  protection of existing services including the use
  of DFS as a means to protect radiolocation
  systems.
• In the ITU-R, Recommendation M.1652 was produced
  by Joint Task Group (JTG) 8A/9B internationally
  to facilitate development of the RLAN devices.
  The recommendation contains 5 GHz radar system
  characteristics and a description of the RLAN
  channel move times along with other information.
• In the United States, the Federal Government in
  coordination with the RLAN Industry Vendors have
  been working together for two years to develop
  certification test plans and procedures for
  devices that operate in the bands 5250-5350 and
  5470-5725 MHz bands.
• Bench tests with 5 GHz devices from RLAN
  manufacturers have already taken place at the ITS
  Laboratories in Boulder, Colorado over the past
  two years

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What is Dynamic Frequency Selection?

• DFS is an interference mitigation/avoidance
  mechanism in which a Radio Local Area Network
  (RLAN) device operating in the bands 5250-5350
  and 5470-5735 GHz is supposed to automatically
  sense if a radar is operating in its vicinity
  and vacate that frequency in a timely manner when
  detection occurs. This allows the RLAN devices to
  share spectrum with radars operating in those
  bands by selecting channels not being used by the
  radars in its local area. The DFS functions in
  the RLAN device are not user controlled or
  accessible.
• The RLAN devices must totally vacate the
  channel (no emissions) with 10 seconds of radar
  detection and have 260 ms of time within that to
  shut the network down. It must not use that
  channel for 30 minutes and must check the new
  channel for 1 minute before it uses it.

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These Bench tests included

• Power-on test No RLAN emissions until after the
  power-up cycle has been completed and the
  power-on channel is monitored for 1 minute.
• Radar detection 6 seconds into initial channel
  check after power-on cycle completed.
• Radar detection 6 seconds before end of initial 1
  minute check time after power-on cycle completed.
• In-Service monitoring This is the most
  comprehensive test as the RLAN device must detect
  various synthesized radar waveforms
  representative of those operating the 5 GHz
  bands.
• For In-service tests, a MPEG file is streamed
  from computer to computer using an Access point
  (AP) and a Client device to load the RF
  channel. The AP has the DFS functions built-in.
• 30 minute non-occupancy test Once a channel has
  been identified as being used by a radar, the
  RLAN device must not use it for 30 minutes.

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Engineers at ITS developed a test bed that has
two main sub-systems

• Radar signal generator and synthesizer
• Produces bursts of un-modulated and chirped
  pulses in 5 GHz bands
• Variable and user selectable frequency, of
  pulses, pulse width, pri, and chirp bandwidth
• RF Power control on pulses
• Uses Agilent Vector Signal Generator and other
  test devices
• Timing measurement system
• Monitors RF activity on Rlan channel
• Uses Agilent Vector Signal Analyzer and E4440
  spectrum analyzer to have fine and coarse
  measurement of the RF emissions of the Rlan AP
  and client transmissions over 12 seconds
• Very accurate as shown on page 9 of this
  presentation.
• The two systems are synchronized so that a press
  of a button starts an in-service test and
  collects data for 12 or 24 seconds.

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Results of First Round of Radar/DFS Bench tests

• 5 GHz RLAN devices from four different
  manufacturers were tested at the ITS
  Laboratories, consisting of Access points (APs)
  and Client devices.
• Three used 802.11 Wi-fi architectures, and one
  was a frame based system where the frame
  talk/listen ratio was user controlled.
• For the in-service tests, the devices were tested
  with three radar waveforms
• The radar waveform parameters are contained in
  the 5 GHz Report and Order (see FCC docket 03-122
  at http//gullfoss2.fcc.gov/prod/ecfs/comsrch_v2.c
  gi)
• Two were fixed frequency and one was frequency
  agile.
• The tests were based on MPEG video and MP3 audio
  files streaming from one access point to one
  client using two computers, aggregate tests were
  not performed (AP with multiple clients).
• Access Point had DFS capabilities, not the Client
  card.
• Ad-hoc networks were not tested (client-
  to-client).

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Test Signals used for first round of 5 GHz
Radar/DFS bench tests at the ITS Laboratories
Note 1 This represents the number of pulses seen
at the unit under test (UUT) per radar scan N
antenna beamwidth (deg) x pulse repetition
rate (pps) / scan rate (deg/s) Note 2
Burst period represents the time between
successive scans of the radar beamB 360/scan
rate (deg/s) Note 3 Radar bandwidth is less
than that of the unlicensed U-NII device. Note 4
The characteristics of this frequency hopping
radar do not correspond to any specific system.
It can hop across the 5250-5725 MHz band. The
frequencies will be selected by using a random
without replacement algorithm until all 475
frequencies have been used. After all have been
used, the pattern is reset and a new random set
is generated.
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Results of First Round of Radar/DFS Bench tests

• The results of the initial bench tests showed
  that the 5 GHz devices needed more development on
  their detection algorithms to achieve a good rate
  of radar signal detection. Overall, between all
  the manufacturers the radar detection
  capabilities of the devices tested was moderate
  at best and the radar detection was highly
  dependent upon the RF loading of the channel.
  That is, detection occurred at a higher rate when
  the audio file was being streamed.
• A key finding is that the devices were not
  able to detect radar pulses that were comparable
  in length to a typical 802.11 data packet. The
  devices had no way to determine if the long radar
  pulse was a true radar signal or a corrupted
  802.11 data packet. To eliminate false
  detections and unnecessarily vacate a channel,
  was the challenge to the RLAN Industry in
  developing proper algorithms.
• Radars that use longer pulse widths and their
  characteristics are contained in ITU-R M.1652 and
  these radars must be protected and detected in a
  timely manner.
• Similar Rlan/radar DFS tests performed by other
  Administrations have also drawn similar results
  and conclusions. Their tests used similar radar
  test signals that were used in the NTIA bench
  tests.

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Sample Data fromRadar/DFS Bench tests using SA
and VSA
Radar burst at start of 1 min. check time (SA)
1 minute power-on test (SA)
Radar burst at end of 1 min. check time (SA)
In-Service test with MPEG file (VSA)
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Typical data flowing/radar burst/channel move
sequence
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To move things forward, the Federal Government
and Industry did the following

• Developed a set of radar signal parameters,
  including those with long pulses, that are
  representative of radar systems operating in the
  5 GHz band for type acceptance compliance tests.
• Guarded against specific radar signal pattern
  recognition by having a wide variance in the
  characteristics, i.e., pulse width, pri, of
  pulses per burst, and chirp bandwidth.
• Performed another round of bench tests at the ITS
  laboratories in August 2005 with the new set of
  radar signal parameters and updated 5 GHz devices
  provided by the RLAN Industry. Results are still
  being analyzed.
• Develop rules to prevent any end user from
  accessing the RLAN device algorithms and
  extracting ANY information about the radar signal
  that was detected.
• Use the results of the bench and field tests to
  validate the radar signal test parameters, the
  test procedures, and true proof of concept.
  (pending)
• Publish a final set of type acceptance rules and
  test procedures for companies that want to market
  and sell these devices. (pending)

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Parameters for the radar signal characteristics
for recent Bench tests
Table 1 Fixed System Radars (no modulation)

Table 2 Long Pulse Radar signal with linear FM
Chirp
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Parameters for the radar signal characteristics
for recent Bench tests
Table 3 Frequency Hopper (no modulation)

• The test signal parameters shown in Table 1
  represent the first set of test signals to be
  used to perform the conformance test procedures.
  The percentage of detection (as shown in figure
  1) calculated by
• Formula 1
• In addition an average probability of detection
  is calculated as follows
• Formula 2

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Parameters for the radar signal characteristics
for recent Bench tests

• The minimum step values for each of the variable
  radar parameters shown in Tables 1 and 2 is an
  interval of 0.1 µsec for Pulse Width, a 1 µsec
  step interval the PRI, and a step interval of 1
  for the number of pulses.
• Exact values for acceptable pass/fail percentages
  are still being coordinated between U.S.
  Government and RLAN Vendors.
• The parameters in Table 3 are fixed and include
  that a minimum of 10 trials per set be run with a
  minimum probability of detection calculated by

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Summary of 5 GHz Radar/DFS Activities

• Bench tests with new set of radar characteristics
  were performed in August 2005 at ITS Laboratories
  in Boulder, Colorado with three Rlan vendors
  supplying devices. Each vendor had up to 1 week
  of laboratory time and was allowed some
  modifications of their equipment prior to actual
  tests with some experimentation with the radar
  test signals.
• The results of the August 2005 bench tests showed
  that the RLAN manufacturers have greatly improved
  their devices ability to detect the radars
  (simulated) that are listed in ITU-R M. 1652,
  over the results from the previous bench tests.
• The target date to allow these devices to share
  spectrum in the 5 GHz band is in early 2006,
  pending additional work and coordination between
  the U.S. Government and the RLAN Industry on some
  key issues.

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Overview of test set-up
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Fixed Frequency Radar Simulator
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Frequency Hopping Radar Simulator