INTERNATIONAL MARITIME ORGANIZATION
E
IMO
SUB-COMMITTEE ON
RADIOCOMMUNICATIONS AND
SEARCH AND RESCUE
10th session
Agenda item 12
COMSAR 10/12/3
23 December 2005
Original: ENGLISH
REVISION OF THE PERFORMANCE STANDARDS FOR SART
Expected range for “AIS Search and Rescue Transmitters” (AIS-SARTs)
Theoretical calculations and initial trials
Submitted by Norway
SUMMARY
Executive summary:
This document presents the result of calculations and trials with
AIS-SART, carried out to indicate the expected range for
such equipment
Action to be taken:
Paragraph 4
Related documents:
COMSAR 10/12/2 and resolution A.802(19)
Introduction
1
In connection with the ongoing consideration of the AIS-SART alternative, theoretical
calculations of the expected range have been performed. During December 2005 the Norwegian
company Jotron Electronics also carried out initial trials with AIS-SART, on behalf of the
Norwegian Maritime Directorate.
2
The purpose of these initial trials was to verify the suitability of the AIS-system to detect
signals from an AIS Search and Rescue Transmitter (AIS-SART). The results of these trials are
presented in the annex to this document. As noted in the annex, additional trials are planned to
further verify which range AIS-SART can be expected to provide in practice.
3
The present document should be considered as a supplement to document
COMSAR 10/12/2 by Norway.
Action requested of the Sub-Committee
4
The Sub-Committee is invited to consider the information presented in the annex to this
document in connection with the task of revising resolution A.802(19) so as to include the
alternative AIS-SART.
***
For reasons of economy, this document is printed in a limited number. Delegates are
kindly asked to bring their copies to meetings and not to request additional copies.
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COMSAR 10/12/3
ANNEX
THEORETICAL RANGE (line of sight)
1
The theoretical distance that the AIS-SART may be detected is limited to the radio line of
sight. The VHF radio range is somewhat larger than the optical line of sight (* 1.15) because the
radio signals will bend a little over the earth surface (refraction).
2
The VHF Radio Line of Sight is given by the formulae:
RLOS = 2.22*SQRT(h1)+2.22*SQRT(h2), where:
RLOS = VHF Radio Line of Sight [nm]
h1 = Height of AIS-SART transmitter [m]
h2 = Height of AIS receiver [m]
AIS-SART (MASL)
RECEIVER Height Above Sea Level (m)
0
1
2
3
4
5
0
0
2.2
3.1
3.8
4.4
5
1
2.2
4.4
5.4
6.1
6.7
7.2
2
3.1
5.4
6.3
7
7.6
8.1
3
3.8
6.1
7
7.7
8.3
8.8
4
4.4
6.7
7.6
8.3
8.9
9.4
5
5
7.2
8.1
8.8
9.4
9.9
6
5.4
7.7
8.6
9.3
9.9
10
7
5.9
8.1
9
9.7
10
11
8
6.3
8.5
9.4
10
11
11
9
6.7
8.9
9.8
11
11
12
10
7
9.2
10
11
11
12
12
7.7
9.9
11
12
12
13
14
8.3
11
11
12
13
13
16
8.9
11
12
13
13
14
18
9.4
12
13
13
14
14
20 100 200 500
9.9 22 31 50
12 24 34 52
13 25 35 53
14 26 35 53
14 27 36 54
15 27 36 55
1,000
70
72
73
74
75
75
Table 1
Radio Line of Sight (RLOS) [nm], vs. antenna heights [m]
PATH LOSS AND POWER BUDGET
3
The path loss is given by the formulae:
Loss = 37.9 + 20 * log(d) + 20 * log(f), where:
d = distance [nm]
f = frequency [MHz]
LOSS[dB]
Distance [nm]
1 2 3 4 5 6 7 8
9
10 12 25 50 75 100
82 88 92 94 96 98 99 100 101 102 104 110 116 120 122
Table 2
Path Loss [dB] vs. distance (free space)
4
Assuming a practical AIS-SART, it may have an output power of 2W (=33 dBm) and a
helicoil antenna (G= -10 dB). Totally the emitted radiated power (ERP) will be of +23 dBm
(33 dBm –10 dB) or 200mW.
5
The AIS receiver system will have a sensitivity of –101 dBm, an antenna gain of +2.2
(dipole antenna), and if we assume a cable loss of –2.2 dB we end up with an effective received
power of –101 dBm.
6
Totally the system can tolerate a total loss of: 23 dBm - (-101) = 124dB. This means that
the system will have a theoretical range limit on approximately 100 nm when a search is
performed from a plane. The power budget for various distances is shown in Table 3. This table
indicates that the proposed system with 2W output power may be sufficient, but to improve the
margin further an increase in the output power may be necessary.
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COMSAR 10/12/3
ANNEX
Page 2
Distance[nm]
1
2
3
4
5
6
7
8
9 10 11 12 14 16 18 20
EAIS output power [dBm]
33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33
EAIS antenna gain [dB]
-10 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10 -10
Total emitted power [dBm] 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23
Path loss [dB]
-82 -88 -92 -94 -96 -98 -99 -100 -101 -102 -103 -104 -105 -106 -107 -108
Receiver antenna gain [dB] 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2
Receiver cable loss [dB]
-2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2 -2.2
Received power [dBm]
-59 -65 -69 -71 -73 -75 -76 -77 -78 -79 -80 -81 -82 -83 -84 -85
Sensitivity (BER=10-3)
-101 -101 -101 -101 -101 -101 -101 -101 -101 -101 -101 -101 -101 -101 -101 -101
Margin [dB]
42 36 32 30 28 26 25 24 23 22 21 20 19 18 17 16
Table 3
Transmit and receive power budget vs. distance
VERIFICATION OF RANGE AND POWER
7
Two tests have been carried out to verify the power budget and theoretical range
calculations. One of the tests was carried out over land, while the other was carried out between
two boats at sea.
8
Testing equipment:
-
AIS receiver, type Jotron TR-2500 with a dipole antenna.
AIS-SART, prototype with 2W output power and helicoil antenna – 20 cm long.
Land trials
9
The AIS receiver antenna was placed on a high building and the prototype AIS-SART
was installed in a car, moving away from the building. Due to topographical limitations, it was
not possible to verify distances greater than 7.5 nm. However, this distance was easily achieved.
Sea trial
10
The AIS receiver with antenna was placed on board the rescue vessel “Askerbaeringen” –
call sign LK3384, and the prototype AIS-SART was installed on board a small fishing vessel
“Torill II”. The receiver antenna height was about 5 m above sea level (asl), and the antenna height
of the AIS-SART was about 2 m asl. From Table 1 it is possible to achieve approximately 8 nm
with these antenna heights. However, during these initial tests reception terminated at a range of
just above 4 nm. It was not possible to establish with certainty the causes of this discrepancy
between the calculated and the practical range. However, there were indications that particular
noise problems in the vessel carrying the AIS receiver, could be responsible.
CONCLUSIONS
11
The work carried out so far, indicates that the alternative AIS-SART will work in
practice, and will provide a location range equal to or exceeding 9 GHz SARTs. However, the
results regarding achievable range for AIS-SART are not yet conclusive. Further tests are
planned to be carried out to establish this range. In future tests the output power may be
increased in order to increase the power margin, thus being able to achieve a result closer to the
calculated values.
___________
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