CEPT
ECC
Electronic Communications Committee
Doc. PTD(17)23
CPG PT D
2nd meeting of CPG Project team D
Helsinki, Finland, 10th – 12nd January 2017
Date issued:
4 January 2017
Source:
France
Subject:
Test signals for Frequency Hopping radars
Group membership required to read? (Y/N)
N
Summary:
During the 1st CPG19 PTD meeting, the group agreed on that CEPT will support studies to be performed
under agenda item 1.16 in accordance with Resolution 239 (WRC-15). This includes sharing and
compatibility studies between RLANs and existing primary services, in particular to look at suitable RLAN
mitigation techniques to enable RLAN use in the following frequency bands: 5150 – 5350 MHz, 5350 -5470
MHz, 5725 – 5850 MHz and 5850 – 5925 MHz.
In this context, we propose a set of test signals which are representative of FH radars waveforms and
characteristics. The proposed test signals are to be used for the validation of the efficiency of the new
proposed DFS techniques.
Proposal:
France invites CPG/PTD to take into account the proposed test signals as a basis input for the conduction of
studies dedicated to propose an improvement of the DFS required to protect frequency hopping radars.
It should also be noted that, if an enhanced DFS is designed, its final validation should require a prior
verification in laboratory, followed by field tests of its efficiency.
Background:
AI 1.16 and necessity to drive sharing studies.
Page 2
1
INTRODUCTION
The bands 5350 – 5470 MHz and 5725 – 5850 MHz are studied as possible RLAN extension bands to the
existing RLAN bands at 5150 – 5350 MHz and 5470 – 5725 MHz.
The studies conducted up-to-now, have shown that the protection of frequency hopping radars in the bands
5350 – 5470 MHz and 5725 – 5850 MHz could not be ensured by the current DFS. Thus, enhanced DFS
techniques needs to be designed. In this context, to allow assessment of possible enhanced new DFS, we
propose in this paper, test signals that provide a representative set of frequency hopping radar waveforms.
They could be included in an evolution of the RLAN standard after validation of the efficiency of the proposed
DFS when dealing with these test signals. For example, the ETSI standard FWA (EN302502) for RLAN
include tests for a specific type of Frequency Hopping Radar which are not representative of the other types
of frequency hopping radars. Thus, the inclusion of valid test signals has to be considered.
2
WEAKNESS OF DFS VERSUS FREQUENCY HOPPING RADARS
We remind that radars that operate in the 5GHz band can hop across the whole 5250-5850 MHz band. The
frequencies will be selected by using a random without replacement algorithm until all frequencies have been
used. After the use of all frequencies, the pattern is reset and a new random sequence is generated.
The fact that the radars are hopping from one frequency to another makes the work of DFS very challenging.
Indeed, an FH radar hopes very quickly from one frequency to another, and the probability that it come back
to one frequency during the observation time of the RLAN is very weak. Thus the DFS catches no radar
signal or part of it (in the best cases), which makes the detection of the radars most of the time impossible.
Faster is the hopping, weaker the detection probability will be. Other considerations related to parameters
like antenna rotation speed would in practice limit the ability of a DFS to detect the radar signal.
An example of a frequency hopping radar signal and the corresponding hopping sequence in the time
domain is shown on figure below. Blue pulses represent caught pulses by the DFS and grey pulses
represent the missed one.
Figure 1 Example of a Frequency hopping radar signal sequence in the time-frequency domain.
We can observe, that not all the pulses are observed by the DFS reducing the amount of observed energy
(the DFS is seeing a limited samples of the radar emission), and thus affecting negatively the detection
probability.
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Another similar phenomenon to point out, is that during the observation period, the DFS is focusing on a
single frequency. Observing one single frequency makes the DFS miss what is happening in other adjacent
frequencies, it will as well catch a limited number of samples of the radar emission.
Other considerations related to parameters like antenna rotation speed, antenna aperture, … would in
practice limit the ability of a DFS to detect the radar signal. Studies conducted for different radars
configurations showed that the mean time between 2 frequencies hops (in the visibility of DFS) is upper than
1.7s and lower than 7,5s.
In light of the above elements, to validate any new DFS, tests need to be carried out versus signals that are
representative of frequency hopping radar waveforms.
3
PROPOSED TEST SIGNALS
The proposed frequency hopping radars test signals are based on the template of FCC 06-96 and ETSI
EN302502 standards, they include some others radars characteristics and are the result of deep studies,
tests and simulations.
The characteristics retained for these frequency hopping radar signal types do not correspond to specific
radars characteristics but have been derived in order to be representative of most of the radar used in
France and by several other European nations. Thus, some other types of radar test signals could be
needed. As a consequence, there is no full certainty that a DFS designed to deal with those test signals will
be always effective, but if the proposed test signals are not implemented, one should note that no radar
protection will be ensured.
The following table, depicts the test signals that should be implemented to assess the design of any new
enhanced DFS dedicated to protect FH radars within the bands 5350 – 5470 MHz and 5725 – 5850 MHz.
Table 1: Frequency Hopping DFS test signals
Frequency
hopping
radar type
Pulse
Width
(µsec)
(Note1)
Pulse
Repetition
Interval (pri)
(µsec)
# Number of
pulses per
frequency
hop
Burst
length
(ms)
Trial
length
(ms)
(Note 2)
Pulse
Minimum detection
modulation probability with 30%
channel load
(Note 3)
(Note 4)
1
1
200 (=5kHz)
4
0.8
480
none
Pd>80%
1
20
333 (=3kHz)
3
1
600
none
Pd>80%
1
30
500 (=2kHz)
2
1
600
none
Pd>80%
2
3
333 (=3kHz)
1 to 9
#
120
chirp
Pd>80%
2
10
500 (=2kHz)
1 to 9
#
120
chirp
Pd>80%
2
15
1000 (=1kHz)
1 to 9
#
120
chirp
Pd>80%
Note 1: Radar type 1: 475 possible frequencies (step 1 MHz) within the range 5250 – 5850 MHz, Radar
type 2: 120 possible frequencies (step 5 MHz) within the range 5250 – 5850 MHz (Note 5).A frequency is
selected randomly from a group of 600 (or 120 for radar type 2) integer frequencies ranging from 5250 –
5850 MHz, using a ‘use without re-use’ scheme. Frequency test signal changes after each burst.
Note 2:
length) =
For radars type 2, a burst is randomly composed of 1 to 9 pulses (n), then burst length (or hop
n x pri.
Note 3 :
The modulation to be used for radar type 2 is a chirp modulation with a ± 2,5 MHz frequency
deviation which is described below.
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Note 4:
The proposal includes that a minimum of 30 trials per set be run with a minimum probability of
TotalSetDetections
 100
TotalSetTrials
detection calculated by
. For RLAN ChS=10MHz, Pd>70%; for ChS = 20MHz,
Pd>80%.
Note 5 :
Although these frequency hopping radar test signals hop over the entire range from 5250 –
5850 MHz, detection of these signals is only required when operating within the 5350 – 5470 MHz and the
5725 to 5850 MHz
4
CONCLUSIONS
In its 1st meeting CPG19 PTD agreed on that CEPT will support studies to be performed under agenda item
1.16 in accordance with Resolution 239 (WRC-15), which includes to look at suitable RLAN mitigation
techniques (e.g.; DFS) to enable RLAN use in the following frequency bands: 5150 – 5350 MHz, 5350 -5470
MHz, 5725 – 5850 MHz and 5850 – 5925 MHz. Any designed new DFS should demonstrate its efficiency to
protect the frequency hopping radars, this efficiency should be tested versus signals that best reflect the
behaviour of deployed FH radars. To the best of our knowledge, up-to-date the proposed test signals in this
paper are the ones that do it at best. The CPG/PTD is kindly invited to take into account the proposed test
signals as a basis input for the conduction of studies dedicated to propose an improvement of the current
DFS techniques.