Date:
Meeting:
Author:
Subject:
11 th
October 2001
RSSPWG
Peter Gibson
Document Reference: prRSSP 0401 032 0
Paper Number: RSSP (04-01)/32
DMC Stratex Networks
Link length policy for 15 and 18 GHz
Introduction
Currently the RA link length policy has been applied to the RA centrally managed spectrum bands. At a previous Industry forum the issue of applying a link length policy to bands that are currently under management by individual operators was discussed. The RA indicated that the same link length policy would apply for those bands prior to taking back management of the spectrum. The rationale is to protect the spectrum against inappropriate use and ensure that sufficient spectrum will be available in the future when the bands become RA managed.
The current link length policy has been discussed in detail at several RSWG and FLCC meetings. As a consequence the RA has developed a policy that is acceptable by Industry. The 15 and 18 GHz bands require specific minimum link length limits in line with the RA’s link length policy.
Study
DMC Stratex Networks has conducted a study on the maximum link lengths that are practical for a typical link using the following system characteristics.
Modulation type – 4FSK, 16QAM and 128QAM where appropriate
Availability – 99.99%, 99.995% and 99.999%
Typical Tx output power – various according to link type/modulation and frequency band. Values taken from between 3 – 5 different vendors data sheets
Rx threshold values – ETSI figures for BER 10
-6
Antenna size – assumed 0.3m and 0.6m on each link
Rain zones – studied three ITU-R rain zone regions, E, F and K
The results of the study are detailed in the following tables.
16E1 4FSK
E
99.99%
18GHz 23GHz 26GHz 28GHz 38GHz
22.5 17.25 13.25 11.75 7.25
99.995%
99.999%
19.25
12.75
14.25
9
10.5
6.75
9.25
5.75
5.75
3.75
F
99.99%
99.995%
99.999%
20.75
17
10.5
14.75
11.75
7.25
11
8.75
5.5
9.75
7.5
4.75
6
4.75
3
K
99.99%
99.995%
99.999%
16
12.25
7.25
10.75
8.25
5
7.75
6.25
3.75
6.75
5.25
3.25
4.5
3.5
2.25
Page 1 of 3

16E1 16QAM
99.99%
18GHz 23GHz 26GHz 28GHz 38GHz
21.5 15 12 10.5 6.5
E 99.995% 18.25 12.5 9.5 8.5 5.25
F
99.999%
99.99%
99.995%
99.999%
12
19.5
16
9.75
8
12.75
10.25
6.5
6
9.75
7.75
5
5.25
8.75
7
4.25
3.4
5.4
4.3
2.75
K
99.99%
99.995%
99.999%
14.75
11.5
6.75
9.25
7.25
4.5
7
5.5
3.5
6.25
5
3
4
3.2
2
STM-1 16QAM
99.99%
18GHz 23GHz 26GHz 28GHz 38GHz
16 11 10 9 5.5
E 99.995% 13.75 9 8.25 7.25 4.5
99.999%
99.99%
9.25
14.25
6
9.25
5.25
8.5
4.75
7.5
2.9
4.6
F 99.995%
99.999%
11.75
7.5
7.5
5
6.75
4.25
6
3.75
3.75
2.4
K
99.99%
99.995%
99.999%
10.75
8.5
5.25
7
5.5
3.5
6.25
5
3.25
5.5
4.25
2.75
3.4
2.8
1.8
STM-1 128QAM
E
99.99%
99.995%
18GHz 23GHz 26GHz 28GHz 38GHz
10.75
9
8
6.75
7
5.75
6.5
5.25
4.5
3.75
F
K
99.999%
99.99%
99.995%
99.999%
99.99%
99.995%
6.25
9.25
7.75
5.25
7
5.75
4.75
6.75
5.75
4
5.25
4.25
4
6
5
3.25
4.5
3.75
3.5
5.5
4.5
3
4
3.25
2.5
3.9
3.2
2.1
2.9
2.4
99.999% 3.75 2.75 2.5 2 1.6
These tables confirm that the RA’s link length policy is in line with what can be practically implemented. Taking an STM-1 system using a modulation scheme of 128 QAM (worst case) suggests that the min and max link lengths deployed in the UK are as follows.
Rain zone F with 99.99% availability objective
23 GHz
26 GHz
2.5 – 6.75 Km
2.5 – 6 Km
38 GHz 0.1 – 3.9 Km
Rain Zone F with 99.995% availability objective
23 GHz
26 GHz
38 GHz
2.5 – 5.75 Km
2.5 – 5 Km
0.1 – 3.2 Km
Page 2 of 3

It is observed that the difference between minimum and maximum link lengths for 23 – 38 GHz are generally the same for each availability objective. i.e. for 99.99% the spread is 3.5/4Km and for
99.995% the spread is 2.5/3 Km.
For PDH capacities assuming a 16E1 system using a modulation scheme of 4FSK suggests that the min and max link lengths deployed in the UK are as follows.
Rain zone F with 99.99% availability objective
23 GHz 5 – 14.75 Km
26 GHz
38 GHz
5 – 11 Km
1 – 6 Km
Rain Zone F with 99.995% availability objective
23 GHz
26 GHz
5 – 11.75 Km
5 – 8.75 Km
38 GHz 1 – 4.75 Km
The spread for PDH capacities is not as clear. The difference between minimum and maximum link lengths for 23 – 38 GHz are as follows, for 99.99% the spread is 5/10 Km and for 99.995% the spread is 4/7 Km. However given that the 23 GHz is preferred for PDH capacities the spread is not as important.
Proposal
Applying the same rationale to the 18 GHz band would suggest that the minimum link length should be 10 Km for PDH capacities and 4 Km for STM-1.
For the 15 GHz band the suggestion would be to apply the same minimum link length as already applied to the 13/14 GHz bands. The 15 GHz will in the future be used as a spill over band for the 13
GHz band so applying the same link length policy would be a sensible approach.
The proposal is based on both a 99.99 and 99.995% availability objective. This would cover the majority of links that are currently assigned by the RA. 99.999% availability is considered on a caseby-case basis and would therefore be subject to specific agreement with the RA.
Page 3 of 3