CEPT
ECC
Electronic Communications Committee
CPG-PTD(14)135
CPG-15 PTD
CPG-15 PTD #6
Luxembourg, 28 April – 2 May 2014
Date issued: 18 April 2014
Source: United Kingdom
Subject: 5GHz Radar studies and associated CEPT Brief text
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Summary:
This document provides comments and views on the RLAN-radar sharing studies submitted to the
February 2014 meeting of ITU-R JTG 4-5-6-7 looking at DFS and possible sharing with Frequency
Hopping and Bi-static radar. Annex 1 to this document provides some suggested changes to the
CEPT brief to address the instruction of CPG to review and revise the text related to these bands
with regard to the radar sharing issues.
Proposal:
To take account of this document in the eventual PTD output documents presenting studies of
sharing between RLANS and Radar.
Background:
In this paper we provide a summary of some thoughts from the UK on the studies so far analysing at
the capabilities in the RLAN DFS mechanism to recognise bi-static and frequency hopping radar. In
particular we analyse some of the assumptions and methodology used in JTG Document 4-5-67/436-E and Document 4-5-6-7/450-E. We also provide suitable wording for the current status of
studies on the 5GHz bands between radar and RLAN for the draft CEPT brief WRC-15 AI 1.1.
Comments on JTG Document 4-5-6-7/436-E
Analysis of Dynamic Frequency Selection (DFS) as mitigation measure for the co-existence of
Radio Local Area (RLAN) systems and radiolocation service systems in the 5 350 -5 470 MHz
and 5 725-5 925 MHz band
This document gives a very basic initial analysis of the DFS as it is currently described in ITU-R
Rec. M.1652. It also gives some basic background information and some general information on
the expected operational use that radars in 5350 – 5470 MHz and 5725 – 5925 MHz bands
would be expected to perform. The UK has some queries and comments on section 2 and 3 of
the document as well as some of the conclusions made.
Section 2 comments
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In paragraphs one and two of this section there is quite a comprehensive list of uses and
applications that radars are expected to perform in the 5GHz range. It is not clear in this
document whether all of the uses outlined in these paragraphs are covered by the two
radars (Radar 22 and 23) subsequently analysed in the paper.
We notice the characteristics of radar 22 and 23 are very different so if each radar was
designed to perform specific operations it would be good to have some information on
which of the uses outlined in paras 1 and 2 they would be likely to perform.
We also notice that the parameters and characteristics of both radar types have been
combined into one table, it would also be good to have some clarification on composition
of the table and whether both radar would be expected to cover all of the different radar
characteristics identified in table 2.
Some of the characteristics in the table seem to indicate conflicting assumptions that
may need to be clarified.
There is no indication if these radars currently operate across all of the 5250 – 5850
MHz range or are limited to the ranges where there is currently no RLAN use.
Is there a minimum or maximum amount of spectrum these radars need to have access
to be effective?
Section 3 comments
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It would be good to see the calculation of the main beam probability explained a little
more as the figure seems very low compared to what are considered to be the more
stringent cases in M.1652.
Channel probability seems to assume the use of the whole 5250 – 5850 MHz band
which seems strange considering we are only studying parts of this spectrum. It also
assumes the RLAN channel will be 20MHz which would increase to at least 80 MHz if
the additional mitigation techniques are assumed.
The assumptions for the listening probability seem to be based on one fully loaded
RLAN device listening whereas it would probably be a number of RLAN devices on an
RLAN network listening. This will need to be considered more for WiFi systems.
In Excess threshold probability there are a number of assumptions based on the false
alarm rate. We assume more information on how this is mitigated is something that only
the RLAN community can provide.
The section on current standards needs to be updated to include the US standard and
ESTI standard EN 302502 which has a test for frequency hopping radar.
Comments on the Conclusions of the analysis
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We can agree that the current DFS requirements in ITU M.1652 are not complete and
an important omission is the detection probability. However this is defined in both the US
and ETSI standards for DFS.
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We can also agree that, the current standards as currently specified, do not provide
specific tests for some of the functionalities and patterns that are indicated as suitable
parameters for radar 22 and 23 in this document. However we cannot say that current
DFS implementations cannot recognise these radar unless we carry out specific tests to
prove this.
We also agree that suitable studies should take place to analyse and recomend ways to
provide suitable protection for radars 22 and 23.
We cannot agree that there needs to be a process within the remit of ITU to require that
all of the different global standards for DFS are checked and validated. This is not
something under the remit of ITU, however we do agree that suitable guidance could be
developed within ITU (e.g. ITU-R Report or Recomendation).
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Comments on Document 4-5-6-7/450-E
Bistatic Radars in the 5 GHz-Band
The document indicates that there is a possibility of Bi-static radar may be used within these
bands and does a simple analysis looking at an MCL analysis and suitable interference
distances of RLANs from identified radar types 10 and 14 in the document. The document also
provides some characteristics for these radars and explains the concept of Bi-static radar that
the transmitter and receiver will not be co-located. Below are some initial thoughts the sharing
issues that need to be considered in this document.
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The DFS detection ranges for RLAN for these types of radar and the likely separation
distances will need to be considered in an initial analysis.
Based on the power levels of these radars the distance (in line of sight conditions) from
the transmitter for the DFS detection threshold of -64dBm to be exceeded may be
greater that the protection distance to protect the receivers.
No information is provided on the amount transmitters and receivers that are likely to
be deployed in operational scenarios for these radars.
A Geo-location database and/or some sort of collaborative technique may provide a
solution to recognise these radar if normal DFS does not provide suitable protection.
Proposals for the Draft CEPT brief
Annex 1 to this document gives some suggested changes to the CEPT brief to address the
instruction of CPG to review and revise the text related to these bands with regard to the radar
sharing issues.
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Annex 1 – UK comments on 5GHz radar part of-_AI_1.1_-_Revised_Draft_CEPT_Brief
UK comments on
5GHz radar part of-_AI_1.1_-_Revised_Draft_CEPT_Brief[1].docx
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