This guideline describes methods for calculating PMD due to
optical fibre cables and optical components in an optical link.
Example calculations are given to illustrate the methods for
calculating total optical link PMD from typical cable and optical
component data. The calculations include the statistics of
concatenating individual optical fibre cables drawn from a
specified distribution. The calculations assume that all components
have PMD equal to the maximum specified value.

NOTE The statistical specification of the distribution of the
PMD of optical fibre cables is a current work item to amend IEC
60794-3, in SC86A/WG3 [2]¹. The agreements following the
last ballot (86A/501/CD) are aligned with the methods given in this
technical report.

The calculations described cover first order PMD only. This
study of PMD continues to evolve, therefore the material in this
technical report may be modified in the future. The following
subject areas are currently beyond the scope of this technical
report, but remain under study:

– calculation of second and higher order PMD;

– accommodation of components with polarization dependent loss
(PDL) – if it is assumed that PDL is negligible in optical fibre
cables;

– system impairments (power penalty) due to PMD;

– interaction with chromatic dispersion and other nonlinear
effects.

Measurement of PMD is beyond the scope of this technical report.
Guidelines on the measurement of PMD of optical fibre and cable are
given in IEC 61941. The measurement of optical amplifier PMD will
be documented in IEC 61290-11-1². The measurement of
component PMD will be documented in IEC 61300-3-32³.

¹ Figures in brackets refer to the bibliography.

² To be published

³ To be published

Chromatic dispersion (ps/nm) is the derivative, with respect to
wavelength, of the group delay (ps) induced by the spectral content
of light propagating through an optical element or fibre. Chromatic
dispersion is normally a function of wavelength and can be either
positive (group delay increasing with wavelength) or negative
(group delay decreasing with wavelength).

The presence of chromatic dispersion can induce distortions in
signals leading to bit errors depending on

– source spectral width;

– source chirp;

– bit period;

– distance.

In addition, chromatic dispersion is interactive with the
effects of non-linear optical effects and second order polarisation
mode dispersion (PMD). The above system impairments are beyond the
scope of this technical report.

When different components or fibres are combined, the chromatic
dispersion of the combination is the total of the chromatic
dispersion values of the individuals, on a wavelength-
by-wavelength basis. A section with high chromatic dispersion will
be balanced by sections with lower values. The variation in the
total dispersion of links will therefore be dependent on the
distributions of the products that are used in the link. This
document provides methods to calculate the distribution statistics
of concatenated links based on information on the distributions of
different fibre or component populations.

NOTE In the clauses that follow, examples are given for
particular fibre and component types. These examples are not
necessarily broadly representative.

Generally, dispersion compensation and accommodation is used in
the 1 550 nm region with cables incorporating conventional
(dispersion-unshifted) single-mode category B1 fibre as shown in
IEC 60793-1 and IEC 60793-2. In this wavelength region, the fibre
has a positive dispersion coefficient that averages at about 17
ps/nm–km. There are two subcategories of such fibre. The cutoff
wavelength of B1 fibre is low enough for the fibre to be used in
either the 1 310 nm or the 1 550 nm region. Such fibre makes up the
vast majority of installed fibre optic cable world wide. The cutoff
wavelength of B1.2 fibre is high enough for the fibre to be used in
the 1 550 nm region only. Such fibre is used in some submarine
systems.

Smaller values of dispersion are attainable with
dispersion-shifted category B2 fibre and with non-zero-dispersion
category B4 fibre. Dispersion accommodation or compensation may
sometimes be used with these fibre types as well, but only category
B1 fibres will be discussed in this technical report.

Compensation refers to techniques or components that reduce the
value of the dispersion or the dispersion slope of a fibre optic
link to enable transmission at digital bit-rates and at analogue
frequencies higher than would be possible without these techniques.
Effectively, the cumulative zero-dispersion wavelength of the
optical path is moved from the 1 310 nm region to somewhere in the
1 550 nm region. A link of dispersion-unshifted B1 fibre and an
in-line dispersion compensator can be made to resemble, in some
cumulative respects, a link of dispersion-shifted B2 fibre.
Examples of passive dispersion compensating components include
dispersion-compensating fibre, fibre Bragg gratings, and
etalons.

Accommodation refers to techniques or components that utilize
dispersion to enable transmission at digital bit-rates and at
analogue frequencies higher than would be possible without these
techniques. Examples of active dispersion accommodation include
optical or electrical prechirping at the transmitter,
dispersion-assisted transmission, midspan spectral inversion, and
receiver signal processing. Accommodation will be treated in future
revisions of this technical report.

Management referring to techniques that vary the dispersion
coefficient along the optical path (both sign and magnitude)
remains under study.

All abbreviations are presented in the singular, but are equally
applicable to the plural.

Annex A provides a GSM / GMR-2 Terminology Translator.

Cellular telephony has been adopted by many segments of the
business community and has enjoyed strong growth over the years.
With this growth has come an increasing recognition that there is a
need for a geographically limited capability that offers
affordable, light-weight, portable/mobile communications. The
concept raised by this need is that certain specialized services
need to be offered exclusively to a set of users called a "closed
user group."

Typically, the users of such systems might be expected to be
able to access PBX/CENTREX^TM features in the same way as
they would on wired PBX/CENTREX^TM terminals. It is also
expected that as systems and features designed for closed user
groups evolve, there will be a need to support other applications,
such as those in residences, campuses, sports facilities, etc. It
is further expected that there will be a need to allow subsets of
the closed user group subscribers to use their handsets on the
macrocellular network.

This standard provides the minimum specifications for an air
interface that will support such a closed user group with limited
geographic capability within a macrocellular service area.

The purpose of this standard is to provide an air interface
specification that allows wireless 800 MHz cellular services to be
delivered to a closed user group. The closed user group may be
provided with special sets of service features, or specialized
charging arrangements, or combinations of both.

It is intended that this standard will support systems that
conform to the classification of "auxiliary system" of a cellular
system as described in the FCC Report and Order for Docket 87-390.
As such, the systems which employ this standard will be expected to
avoid interference to or disruption of the macrocellular system(s)
in the area where they are operating.

Also, in conformance with applicable regulations, it is intended
that auxiliary systems employing this standard will be operated
under the auspices of the appropriate licensed cellular
provider.

General Description

Service Option 4 provides asynchronous (abbreviated as "async"
hereafter) data transmission capability on TIA/EIA/IS-95-A wideband
spread-spectrum cellular systems using the protocols and procedures
defined herein. Service Option 5 provides Group-3 facsimile
(abbreviated as "fax" hereafter) transmission capability for these
systems.

These two Service Options are defined in a single standard
because their user interfaces and associated call control
procedures are similar. This parallels the current trend in analog
modems, which commonly provide both fax and async data services
through the same modem unit.

All sections marked with a superscript are optional. Sections
marked with a superscript "A" provide for the optional narrow
analog mode of operation. Sections marked with a superscript "B
provide for optional WRE mode of operation. Sections marked with a
superscript "C" provide for optional CAPCS mode of operation.
Sections not marked with a superscript may contain optional
functionality.

Compatibility, as used in connection with these standards and
the compatibility specification, is understood to mean: Any
subscriber unit is able to place and receive calls in any cellular
system. Conversely, all cellular systems are able to place and
receive calls with any subscriber unit.

To assure compatibility, it is essential that both radio system
parameters and call processing parameters be specified. The speech
filtering, modulation, and RF emission parameters commonly
encountered in two-way radio systems have been updated and expanded
to reflect the unique radio plan upon which cellular systems are
based. The sequence of call processing steps that the mobile and
land stations execute to establish calls has been specified in the
compatibility specification along with the digital control messages
and analog signals that are exchanged between the two stations.

A subscriber unit is intended to be used while in motion or
during halts at unspecified points. It is assumed that subscriber
units include portable units (e.g., hand-held "personal" units) as
well as units installed in vehicles.

Although the basic purpose of cellular telecommunications has
been voice communication, evolving usages (e.g., data) may allow
the omission of some of the features specified herein provided that
the system compatibility is not compromised.

These standards concentrate specifically on the Subscriber Unit;
they cover the operation of the land station, the cellular switch,
and the cell control equipment only to the extent that
compatibility with the compatibility specification is assured.