SIST EN 60835-2-7:2002

SLOVENSKI STANDARD
01-oktober-2002
Methods of measurement for equipment used in digital microwave radio
transmission systems - Part 2: Measurements on terrestrial radio-relay systems -
Section 7: Diversity switching and combining equipment (IEC 60835-2-7:1994)
Methods of measurement for equipment used in digital microwave radio transmission
systems -- Part 2: Measurements on terrestrial radio-relay systems -- Section 7: Diversity
switching and combining equipment
Meßverfahren für Geräte in digitalen Mikrowellen-Funkübertragungssystemen -- Teil 2:
Messungen an terrestrischen Richtfunksystemen -- Hauptabschnitt 7:
Geräteeinrichtungen für Schalt- und Kombinationsdiversity
Méthodes de mesure applicables au matériel utilisé pour les systèmes de transmission
numérique en hyperfréquence -- Partie 2: Mesures applicables aux faisceaux hertziens
terrestres -- Section 7: Equipement de diversité par commutation et combinaison
Ta slovenski standard je istoveten z: EN 60835-2-7:1994
ICS:
33.060.30 Radiorelejni in fiksni satelitski Radio relay and fixed satellite
komunikacijski sistemi communications systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

NORME CEI
INTERNATIONALE IEC
60835-2-7
INTERNATIONAL
Première édition
STAN DARD
First edition
1994-07
Méthodes de mesure applicables au matériel
utilisé pour les systèmes de transmission
numérique en hyperfréquence
Partie 2:
Mesures applicables aux faisceaux hertziens
terrestres
Section 7: Equipement de diversité par
commutation et combinaison
Methods of measurement for equipment used in
digital microwave radio transmission systems
Part 2:
Measurements on terrestrial radio-relay systems
Section 7: Diversity switching and
combining equipment
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835-2-7 © IEC:1994 – 3 –
CONTENTS
Page
FOREWORD 7
INTRODUCTION 9
Clause
1 Scope
2 Normative references
3 Switching diversity
3.1 General considerations
3.2 Isolation between the ports of a diversity switch
3.3 Delay difference between diversity channels
3.4 Switching due to the BER alarm
3.5 Synchronization time
4 Combining diversity
4.1 General considerations
4.2 BER/receiver input level characteristic
4.3 In-band amplitude dispersion characteristic
4.4 BER/phase difference characteristic
4.5 Fading signatures
Figures
1 Base-band switching equipment used in diversity systems
2 Arrangement for measuring the tolerable delay difference by a variable
ri. delay line
3 Arrangement for measuring the tolerable delay difference by a variable
base-band delay line
4 Arrangement for measuring base-band switching equipment functions
BER 35
due to
5 Arrangement for measuring the synchronization time
6 Simplified block diagrams of diversity combining equipment
7 Arrangements for measuring trie BER/receiver input level characteristic
8 Example of a BER/receiver input level characteristic 43

835-2-7 © I EC:1994 - 5 -
Figures Pages
9 Arrangement for measuring in-band amplitude dispersion characteristic 45
10 In-band amplitude dispersion characteristic 45
11 Arrangement for measuring the
BER/phase difference characteristic 47
12 Arrangements for measuring the signature of a combining system 49
13 Example of signature curves as a function of level difference AP
(positive delay) 51
835-2-7 © I EC:1994 — 7 —
INTERNATIONAL ELECTROTECHNICAL COMMISSION
METHODS OF MEASUREMENT FOR EQUIPMENT
USED IN DIGITAL MICROWAVE
RADIO TRANSMISSION SYSTEMS
Part 2: Measurements on terrestrial radio-relay systems
Section 7: Diversity switching and
combining equipment
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international cooperation on all questions concerning standardization in the electrical and
electronic fields. To this end and in addition to other activities, the IEC publishes International Standards.
Their preparation is entrusted to technical committees; any IEC National Committee interested in
the subject dealt with may participate in this preparatory work. International, governmental and
non-governmental organizations liaising with the IEC also participate in this preparation. The IEC
collaborates closely with the International Organization for Standardization (ISO) in accordance with
conditions determined by agreement between the two organizations.
2)
The formal decisions or agreements of the IEC on technical matters, prepared by technical committees on
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
3)
They have the form of recommendations for international use published in the form of standards, technical
reports or guides and they are accepted by the National Committees in that sense.
4)
In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
International Standard IEC 385-2-7 has been prepared by sub-committee 12E: Radio-relay
and fixed satellite communications systems, of IEC technical committee 12: Radiocommuni-
cations.
The text of this standard is based on the following documents:
DIS Report on voting
12E(CO)149 12E(00)161
Full information on the voting for the approval of this standard can be found in the report
on voting indicated in the above table.

835-2-7 © IEC:1994 — 9 —
INTRODUCTION
The availability of a radio-relay link for service may be influenced by the reliability of the
equipment itself and by propagation conditions. Fading due to multipath propagation
arises from interfering paths refracted in a stratified atmosphere. Since all the interfering
paths are delayed relative to the direct path, multipath fading results in frequency-
dependent amplitude and group-delay variations, in addition to variations in the received
signal level (flat fading).
One way to overcome the propagation effects is by transmitting or receiving the signals
over two (or more) diversity channels, as described in CCIR Report 376-6 (see clause 5 of
this section). Diversity reception is based upon the fact that radio signals arriving at the
receiving site by separate paths and/or at different frequencies have partially correlated
impairments.
Therefore the effects of flat fading and/or .multipath propagation upon the time during
which the link is available for service may be decreased by suitably switching or combining
the outputs of the diversity receivers.
The following types of diversity systems are in general use:
–
frequency and cross-band diversity systems: these diversity arrangements use dif-
ferent frequencies in the same band or different frequency bands;
– space diversity systems: these use a single transmitting antenna and two or more
receiving antennas.
835-2-7 ©IEC:1994 - 11 -
METHODS OF MEASUREMENT FOR EQUIPMENT
USED IN DIGITAL MICROWAVE
RADIO TRANSMISSION SYSTEMS
Part 2: Measurements on terrestrial radio-relay systems
Section 7:
Diversity switching and
combining equipment
1 Scope
This section of IEC 835-2 deals with measurements for diversity equipment used in digital
microwave systems. For the purpose of this section, diversity equipment is assumed to
consist of the circuits for switching and/or combining the diversity channels, excluding the
channel equipment itself, i.e. transmitters, receivers, modulators, demodulators, etc. al-
though these may also be involved in the measurements.
2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of this section of IEC 835-2. At the time of publication, the
editions indicated were valid. All normative documents are subject to revision, and parties
to agreements based on this section of IEC 835-2 are encouraged to investigate the
possibility of applying the most recent editions of the normative documents indicated
below. Members of IEC and ISO maintain registers of currently valid International
Standards.
IEC 835-1-2: 1992, Methods of measurement for equipment used in digital microwave
radio transmission systems - Part 1: Measurements common to terrestrial radio-relay and
satellite earth stations - Section 2: Basic characteristics
IEC 835-1-4: 1992,
Methods of measurement for equipment used in digital microwave
radio transmission systems - Part 1: Measurements common to terrestrial radio-relay and
satellite earth stations - Section 4: Transmission performance
IEC 835-2-5: 1993,
Methods of measurement for equipment used in digital microwave
radio transmission systems - Pa rt
2: Measurements on terrestrial radio-relay - Section 5:
Digital signal processing subsystem
IEC 835-2-8: 1993, Methods of measurement for equipment used in digital microwave
radio transmission systems - Pa rt
2: Measurements on terrestrial radio-relay - Section 8:
Adaptive equalizer
CCITT Recommendation G. 703: 1972, Physical/electrical characteristics of hierarchical
digital interfaces
CCITT Recommendation 752, 1992,
Diversity techniques for radio-relay systems

835-2-7 © IEC:1994 – 13 –
3 Switching diversity
3.1 General considerations
In all diversity switching sub-systems, equipment alarm signals are fed to a logic circuit
which generates a switch-drive signal. Switch-over from one channel to the other may be
monitored by an internal test point. In the following, all the test arrangements described
will be assumed to include hit-less switching equipment as shown in figure 1 a.
In the case of hit-less base-band switching equipment, a circuit compares the two input
signals and aligns one of them with the other.
When making measurements, a high isolation between each of the paths is necessary to
avoid degrading the BER, for example not less than 20 dB. In addition the following should
be observed:
–
all measurements should be made for several specified settings of the equipment
controls provided for adjustments of the switch-over conditions;
–
step attenuators should not be used in order to avoid momentary interruption of the
signal when the attenuation is altered;
– to avoid unnecessary switching in many two-channel switching equipments, the
switch retains its last position, even if the original conditions in the failed channel are
restored. The measurement methods which follow are also applicable to such "no
switch-back" type systems.
3.2 Isolation between the ports of a diversity switch
Diversity switching equipment has two or more input po rts and one output port, so it is
necessary to measure the isolation between the input port which is not in use and the in-
put port which is in use.
Attenuation measurements should be carried out in accordance with IEC 835-1-2.
3.3 Delay difference between diversity channels
3.3.1 General considerations
For satisfactory diversity operation, a switching circuit which does not cause excessive
transmission impairment during switch-overs is required. To achieve this the delay
difference between the two bit streams, OT, needs to be shorter than the pulse duration
time T, for example one-third of T, T/3.
In high-capacity systems
OT may become greater than the tolerable delay time difference
due to the variation of the propagation delay-time. In such cases automatic delay-time
compensation is needed.
The maximum tolerable delay-time difference,
at which switch-over is possible
ATmax,
without loss of synchronization or bit-slip, has to be greater than the largest expected
delay-time difference between diversity channels.

835-2-7 © IEC:1994 — 15 —
3.3.2
Method of measurement
The arrangements for measuring the limits of the tolerable delay-time difference are
shown in figures 2 and 3. Figure 2 represents a transmit-receive section including an r.f.
variable delay. Automatic switch-over is initiated by decreasing the r.f. input level.
Attenuators RF-1 and RF-2 in figure 2 are first adjusted to obtain nominal receiver input
levels. The delay AT is adjusted to zero, and the position of the diversity switch, for exam-
ple channel 1, is noted. Then the r.f. input level in channel 1 is decreased until switch-over
to channel 2 occurs at a specified BER. During switch-over neither clock synchronization
loss nor bit-slip is allowed.
The same procedure is then repeated for channel 2. The measurement is then repeated by
increasing the delay AT up to a value when bit-slip or synchronization loss occurs.
OTmax
The tolerable delay difference can also be measured by the test arrangement shown in
figure 3, which includes a base-band variable delay. This can be checked by noting, for
example, the synchronization alarm, as in figure 5.
In this case, manual switch-over is initiated by an external trigger signal, and the delay is
similarly increased, as explained in figure 2. The base-band switching equipment includes
the bit-error detectors in this example.
3.3.3 Presentation of results
The results should be presented as in the following example:
— the delay time at which clock synchronization loss or bit-slip occurs, i.e. x ps;
ATmax,
— the number of errors during switch-over, i.e.
y.
3.3.4 Details to be specified
The following items should be included, as required, in the detailed equipment
specification:
a) the tolerable propagation delay difference above which clock synchroniz-
ATmax'
ation loss occurs;
b) permitted maximum number of bit-errors during switch-over at nominal input levels
and a given propagation delay difference. (This should be zero for "hit-less" switching.)
3.4 Switching due to the
BER alarm
3.4.1 General considerations
Bit-stream errors may be detected by bit-error detectors in the demodulators of each
receiver or in each channel of the base-band switching equipment.

- 17 -
835-2-7 © IEC:1994
Fast detection methods, such as the parity check method or pseudo-error detection by
measuring the eye-height, are necessary for error-free or "hit-less" diversity switching in
fading conditions.
The BER
should be measured in accordance with IEC 835-1-4.
3.4.2 Method of measurement
The arrangement for measuring the switching criteria in base-band switching equipment is
shown in figure 1 b.
Attenuators RF-1 and RF-2 are first adjusted to obtain nominal received input levels, and
the position of the diversity switch, for example channel 1, is noted. The r.f. input level in
channel 1 is decreased until switch-over to channel 2 occurs and the BER is measured.
The same procedure is then repeated for channel 2. Whilst carrying out these measure-
ments, the correct switch-over operation should be verified when reaching the operate and
recovery levels of the BER alarm.
If the base-band switching equipment is a self-contained unit then the switching criteria
can also be measured without a transmit-receive section by error insertion techniques at
base-band, as shown in figure 4.
According to this set-up, which includes BER detectors,
switch-over is initiated by increasing the number or errored bits in channel
1, and then in
channel 2.
The arrangement for measuring the
BER alarm and BER recovery conditions are
described in IEC 835-2-5.
3.4.3 Presentation of results
The operate and recovery BER should be tabulated and the BER
alarm and BER recovery
conditions should be given in accordance with IEC 835-2-5. The position of the base-band
switch should be noted.
3.4.4 Details to be specified
The following items should be included, as required, in the detailed equipment
specification:
a) the required operate and recovery
BER (e.g. 10-4 and 10 -6 , respectively);
b) BER alarm and BER
recovery in accordance with IEC 835-2-5.
3.5 Synchronization time
3.5.1 Definition and general considerations
Synchronization time is defined as the time interval needed to re-establish synchronization
between the two bit streams following their restoration. In order to measure the
synchronization time following a propagation interruption,
...