SIST EN 60835-2-8:2002

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 8: Adaptive equalizer (IEC 60835-2-8:1993)
Methods of measurement for equipment used in digital microwave radio transmission
systems -- Part 2: Measurements on terrestrial radio-relay systems -- Section 8: Adaptive
equalizer
Meßverfahren für Geräte in digitalen Mikrowellen-Funkübertragungssystemen -- Teil 2:
Messungen an terrestrischen Richtfunksystemen -- Hauptabschnitt 8: Adaptative
Entzerrer
Méthodes de mesure applicables au matériel utilisé pour les systèmes de transmission
numérique en hyperfréquence -- Partie 2: Mesures applicables aux faisceaux hertziens
terrestres -- Section 8: Egaliseur auto-adaptatif
Ta slovenski standard je istoveten z: EN 60835-2-8:1993
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
60835-2-8
INTERNATIONAL
Première édition
STAN DARD
First edition
1993-05
Méthodes de mesure applicables au matériel
utilisé pour les systèmes de transmission
numérique en hyperfréquence
Partie 2:
Mesures applicables aux faisceaux hertziens
terrestres
Section 8: Egaliseur auto-adaptatif
Methods of measurement for equipment used in
digital microwave radio transmission systems
Part 2:
Measurements on terrestrial radio-relay systems
Section 8: Adaptive equalizer
© IEC 1993 Droits de reproduction réservés — Copyright - all rights reserved
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835-2-8 © IEC:1993 — 3 —
CONTENTS
Page
FOREWORD 7
Clause
1 Scope 9
2 General 9
2.1 Frequency domain equalizer 11
2.2 Time domain equalizer 11
2.3 Evaluation of system parameters influenced by the equalizers 13
3 Outage signature 15
3.1 Definition and general considerations 15
3.2 Measurement method 17
3.3 Presentation of results 19
3.4 Details to be specified 19
4 Return signature 19
4.1 Definition and general considerations 19
4.2 Measurement method 21
4.3 Presentation of results 21
4.4 Details to be specified 21
5 Measurement of dynamic fading effects 23
6 Recovery time 23
6.1 Definition and general considerations 23
6.2 Measurement method 23
6.3 Presentation of results 25
6.4 Details to be specified 25
7 Additional measurements 25
7.1 Outage signature with flat fading 25
7.2 Outage signature with interfering adjacent channels 25

835-2-8 © IEC:1993 – 5 –
Page
Figures
1 Linear distortion and crosstalk in a QAM system caused by multipath fading 27
2 Block diagram of a linear baseband equalizer 27
3 Basic arrangement for the measurement of signatures 29
4 Example of an outage signature 29
5 Example of an outage signature with possible unusual signature values 31
6 Presentation of the signature, minimum phase and non-minimum phase, on the same
ordinate scale 31
7 Example of the return signature 33
8 Arrangement for the measurement of recovery time 33
9 a) Bit sequence illustrating the definition of recovery time 35
b) Designation of normal alarm
and conditions 35
Annex A – Bibliography 37
835-2-8 © IEC:1993 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
METHODS OF MEASUREMENT FOR EQUIPMENT
USED IN DIGITAL MICROWAVE RADIO
TRANSMISSIONS SYSTEMS
Part 2: Measurements on terrestrial radio-relay systems
Section 8: Adaptive equalizer
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.
This section of the International Standard IEC 835-2 has been prepared by sub-
committee 12E: Radio relay and fixed satellite communication systems, of IEC technical
committee 12: Radiocommunications.
The text of this standard is based on the following documents:
DIS
Report on Voting
12E(CO)146 12E(CO)157
Full information on the voting for the approval of this standard can be found in the repo
rt
on voting indicated in the above table.

835-2-8 © IEC:1993 - 9 -
METHODS OF MEASUREMENT FOR EQUIPMENT
USED IN DIGITAL MICROWAVE RADIO
TRANSMISSIONS SYSTEMS
Part 2: Measurements on terrestrial radio-relay systems
Section 8: Adaptive equalizer
1 Scope
This section of IEC 835-2 deals with measurements pertaining to the adaptive equalizers
used in digital microwave radio-relay systems. These measurements are intended to
characterize the system equalizer in the presence of selective fading and may also be
performed on systems without adaptive equalizers.
To take account of those properties of the system which are especially influenced by the
use of frequency and/or time domain equalizers, the results of measurements performed
on the system are presented by so-called signatures. Additional measurements provide
further means to characterize the performance of the system.
2 General
The performance of a digital radio-relay link may be influenced by multipath pro-
pagation [1]*. This is especially true in the case of high capacity multi-state QAM systems.
In addition to reducing the received signal level, i.e. "flat fading", multipath propagation
results in linear distortion, i.e. "dispersive fading", producing amplitude and phase
distortion. Multistate modulation systems are especially vulnerable to this form of fading
(see 835-2-4: Part 2: Measurements on terrestrial radio-relay systems - Section 4:
Transmitter/receiver (in preparation)).
For a system operating under multipath propagation conditions the vulnerability of the
time-variant channel to linear distortion is of utmost impo rt
ance. In the majority of
high-capacity line-of-sight digital radio-relay systems, adaptive equalizers are used to
counteract "dispersive fading" in order to decrease outages.
The following types of equalizers are generally in use:
- frequency-domain equalizers, which are mainly, but not necessarily, implemented
at i.f, and
- time-domain equalizers, which are mainly, but not necessarily, implemented at
baseband.
The figures in square brackets refer to annex A.

835-2-8 ©IEC:1993 – 11 –
2.1
Frequency domain equalizer
It is the purpose of a frequency domain equalizer to correct the power density spectrum of
the received signal, which, for example, can be analyzed with the aid of a bank of band-
pass filters. Since there is usually no major redundant information in the transmitted
signal, it is not possible to gain any information about the phase or group delay distortion
of the channel; only the attenuation distortion can be recognized properly.
In some cases, the equalization network is of the minimum-phase type where the phase
and magnitude responses are linked to each other via the Hilbe
rt transform. If the channel
distortion is also of the minimum-phase type, then by equalizing the magnitude response
the phase response is equalized as well.
If the channel distortion is of the non-minimum phase type, for example in the case of two-
path propagation where the weaker signal arrives before the stronger signal at the
receiver site, the phase distortion may be increased and in some cases even doubled
when the attenuation is equalized. This is the basic shortcoming of such a frequency
domain equalizer.
Its main advantage, however, is that it will operate correctly, with ce
rtain limitations, with-
out any need for a recovered carrier signal (for synchronous demodulation), or for a recov-
ered timing signal (for making correct timing decisions). Therefore, in contrast to time
domain equalization systems, lock-in/lock-out properties need not be investigated.
2.2 Time domain equalizer
It is the purpose of a time domain equalizer to achieve an intersymbol-interference-free
(151-free) pulse shape at the input of the decision circuitry, although the channel itself may
cause a considerable amount of ISI due to multipath propagation.
Basically, time domain equalizers optimize the eye-opening either in the worst-case
sense, i.e. by using the zero-forcing algorithm, or in the minimum-mean-square-error
(MMSE) sense, i.e. using the MMSE algorithm [2]. For proper operation, they require at
least a correctly recovered timing signal. On the other hand, it is possible for the carrier-
and timing-recovery circuits to take advantage of the operation of the equalizer by using
the already equalized signal for the control of these loops.
By looking at the pulse response of the channel, time domain equalizers are usually
capable of counteracting both minimum and non-minimum phase channel distortion.
In general, multipath propagation causes not only distortion in the I-I path and in the Q-Q
path but also cross-talk contamination between the
quadrature signals in a QAM system,
(see figure 1). Therefore the time domain equalizer, if realized at baseband, shall have
equalizing circuits not only in the I-I and Q-Q path, but also in the I-Q and Q-I path (see
figure 2).
If this equalizer is realized at i.f., only two equalization networks may be used and it may
be possible to have only two independent controls.

835-2-8 © IEC:1993 - 13 -
2.3 Evaluation of system parameters influenced by the equalizers
To evaluate the properties of a radio-relay system with respect to selective fading the
impo rt
ant concept of the so-called signature is widely used. It is based on a two-path (two-
ray) propagation model [3]. Due to peculiarities which occur in connection with equalizers,
several variants of signature measurements are usually performed in addition to the basic
signature measurement given in IEC 835-2-4.
In IEC 835-2-4, the signature is defined as the locus in the relative echo-amplitude versus
notch offset-frequency plane or in the notch depth versus notch offset-frequency plane
along which the system shows a given state. For example this state is characterized
either by a specified bit-error ratio, BER, e.g. 10-3 or 10-6, or by "lock-in" or "lock-out"
conditions.
The relative echo-amplitude b is defined as the ratio of echo ray amplitude to direct ray
B
amplitude. The notch depth is defined as follows:

B = -20 log (1-b) for b<1
B =
-20 log (1-1/b) for b > 1
Note that the two-path delay difference has a fixed value for the signature measurement.
The calculation of the outage of a radio-relay system covers two main parts:
- channel statistics, and
- system properties.
The aim of the signature measurement is to characterize the system properties under
specific propagation conditions. The fixed 6.3 ns delay difference, used in the signature
measurement in accordance with [3], is not the average of a physical delay time, but only
rtant
a useful fitting parameter to match measured data and a numerical model. It is impo
to note that a consistent use of this fixed value of delay difference is also the basis for
using the signature for system comparison.
The outage signature defined below is an important special case of the general signature
definition.
All subsequent measurements are taken on systems equipped with or without equalizers,
not on isolated equalizers.
To quantitatively evaluate system performance under selective fading, a two-path simul-
ator is inserted into the signal path. With the aid of this simulator and additional measuring
equipment the behaviour of the system under the following situations is evaluated by the
measurements described below:
- A slow increase of two-path distortion until outage occurs:
. measurement of the "outage" signature. (The term signature without further
specification, in common use until now, is defined hereinafter as outage signature.)

835-2-8 © I EC:1993 –15 –
–
A slow decrease of two-path distortion after an outage caused by the most severe
selective fading:
• measurement of the "return" signature.
–
A fast variation of two-path channel parameters, at least notch frequency and notch
depth:
• measurements of the "dynamic" signature.
Sudden improvement of the channel after the most severe fading:
• values of the return signature;
• measurements of the recovery time.
The outage and return signatures are the bases for the calculation of the outage pro-
bability of the radio-relay system taking into account the propagation statistics of the hop
under consideration. The dynamic signature and the recovery time provide additional
information on the equalizers utilized.
Commercial two-path fading simulators are now available that can provide precise control
of notch depth, notch frequency and notch sweep-speed.
3 Outage signature
3.1 Definition and general considerations
Outage of a system is defined as having occurred either if a control loop locks out or if the
BER reaches a certain limit (this BER is named BERL, i.e. the bit error ratio limit).
It is possible during the measurement of the outage signature that wi
...