Transceiver Group Synchronization
FUNCTION SPECIFICATION
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Copyright
© Ericsson AB 2003, 2005, 2010, 2012-2014, 2016. All rights reserved. No part
of this document may be reproduced in any form without the written permission
of the copyright owner.
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continued progress in methodology, design and manufacturing. Ericsson shall
have no liability for any error or damage of any kind resulting from the use
of this document.
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owners.
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Contents
Contents
1
General Information
1
1.1
Revision Information
1
1.2
Introduction
1
2
Function
3
2.1
Overview
3
3
Operational Conditions
7
3.1
External Conditions
7
3.2
Application Parameters
7
3.3
Commands
7
3.4
Printouts
8
3.5
Capabilities
8
4
Concepts
9
Glossary
13
Reference List
15
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Transceiver Group Synchronization
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General Information
1
General Information
1.1
Revision Information
The changes introduced in revision H of the document are the following:
•
NGS configuration is mentioned in Section 2.1 on page 3.
•
Sector TG cluster introduced.
The changes introduced in revision G of the document are the following:
•
Unconditional slave can be configured with TF Compensation value given
from BSC. Changes are introduced in Section 2.1 on page 3 and Section
2.1.1 on page 5.
•
IDL2 cluster concept is introduced. Changes are introduced in Section 2.1
on page 3, Section 2.1.1 on page 5, Section 3.5 on page 8, and Section 4
on page 9.
The changes introduced in revision F of the document are the following:
•
Unconditional slave is introduced as a new value of administrative TF mode
in Section 2.1 on page 3,
•
New concepts Administrative TF Mode and Configured TF Mode are added
in Section 4 on page 9.
The changes introduced in revision E (G13A) of the document are the following:
1.2
•
Updates to remove BTS logical model G01 support are done in the Section
1.2 on page 1, Section 2.1 on page 3, Section 3.5 on page 8, and Section 4
on page 9.
•
Transceivers are referenced to in the Section 1.2 on page 1 instead of
transceiver units.
Introduction
The purpose of this function is to provide transmission synchronization of many
collocated Base Transceiver Stations (BTSs).
A Transceiver Group (TG) cluster is composed of a number of co-located TGs,
one master and the rest slaves, where the slaves synchronize to the master.
A TG cluster can be logical with the defined TG cluster identity or notional
when TG cluster identity is not defined.
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Transceiver Group Synchronization
A sector TG cluster is compromised of a number of TGs co-located on
Baseband Radio Node.
Global System for Mobile Communications (GSM) requires all channels within
a cell to be synchronized on the radio interface, that is, each carrier used within
a cell must be synchronized, which means that the Time Division Multiple
Access (TDMA) frames are started simultaneously. Transceivers (TRXs) in the
same TG are synchronized to the common Timing Function (TF) for that TG. A
multi-TG cell implies that the TGs must be able to exchange timing information
with each other.
TG Synchronization enables definition of number of TGs which can be
connected to channel groups belonging to one cell. This allows:
2
•
More TRXs per cell if needed for capacity reasons
•
Grouping of TGs into a logical TG cluster with defined TG cluster identity,
which allows less complicated maintenance of the TG cluster and automatic
recovery of the TG cluster in case of master failure when Automatic Master
Reselection is active.
•
Grouping of TGs into a sector TG cluster, which allows automatic
maintenance of sector TG cluster and automatic recovery of the sector TG
cluster in case of master TF failure.
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Function
2
Function
2.1
Overview
Each TG contains a TF which maintains an accurate frequency reference
and real time clock, from which the frame number, burst timing and radio
frequencies are derived.
TFs can operate in one of three modes:
•
Stand-Alone
•
Master
•
Slave
In stand-alone mode the TF in each TG operates independently. It derives
stable timing from synchronization source such as Pulse Code Modulation
(PCM) transmission network, Global Positioning System (GPS), or Common
Public Radio Interface (CPRI).
Master mode is identical to stand-alone in the way that TF derives stable timing
from synchronization source. In addition to this a master TF exports timing
signal towards one or more slave TFs.
In slave mode the TF is synchronized to the timing signal exported from the
master TF.
If synchronization with the network is lost a TF can operate as a local oscillator
for a limited period until the network synchronization source is re-established.
This mode of operation is defined as Holdover Mode. Anchoring to a stable
synchronization source gives good long-term stability while Holdover Mode
provides redundancy with acceptable short-term stability.
BTS logical model G12
It is assumed that master TF and all slave TFs referenced below are in the
same physical TG cluster.
From the administrative point of view the TF can be defined in one of four
modes:
•
Stand-Alone
•
Master
•
Slave
•
Unconditional Slave
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Transceiver Group Synchronization
A TF administratively defined as an unconditional slave can never be selected
to become a master, it may only be configured as a slave. A TF administratively
defined as a slave can be selected to become a master by the functionality
Automatic Master Reselection. It may temporarily be configured as a master.
There are two kinds of TG clusters:
•
Notional TG cluster. All TGs within a TG cluster are physically connected
via External Synchronization Bus (ESB) but do not have a defined TG
cluster identity. One of the collocated TGs in the TG cluster is defined as a
master, all others in the TG cluster must be defined as slaves.
•
Logical TG cluster. All TGs within a TG cluster are physically connected
via ESB or DU Link version 2 (IDL2) and must have defined the same TG
cluster identity. One of the collocated TGs in the TG cluster is defined
as a master, all others in the TG cluster must be defined as slaves or
unconditional slaves.
Each slave or unconditional slave must have defined the TF compensation
settings.
•
In case of a logical TG cluster, the TF compensation can either be set to a
numeral value for an unconditional slave or to internal compensation for
a slave or an unconditional slave. Internal compensation means that a
TG automatically calculates the TF compensation value. When it is used,
the TG must support Automatic Parameter Setting and the master in the
logical TG cluster must support reporting of its own Transmitter Chain
Delay known as Master Transmitter Chain Delay. When a slave TF is being
configured, it receives Master Transmitter Chain Delay from the BSC and
automatically calculates its TF compensation value.
•
In case of a notional TG cluster, the TF compensation value is set by the
operator, with OMT or BSC command.
Two or three TGs interconnected with IDL2 form an IDL2 cluster defined in the
BSC as a logical TG cluster. One of the TGs, which is configured as a master
in the logical TG cluster, distributes synchronization signal over IDL2 to slave
TGs. The logical TG cluster may be extended with more slave TGs that are
synchronized from the master over ESB.
Multistandard Mixed Mode (MSMM) TG can work in logical TG cluster only in
role of master. If BTS supports Node Group Synchronization (NGS) and MSMM
TG is connected with slaves through CPRI link, synchronization source shall be
set to default and frame start offset shall be defined.
BTS logical model G31
TG synchronization function automatically groups TFs belonging to one
Baseband Radio Node into sector TG cluster with assigned identity that is
unique within BSC. When sector TG cluster contains one TF its configured TF
mode is stand-alone. When sector TG cluster contains more than one TF,
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Function
TG synchronization function automatically selects one master TF basing on
capabilities. Remaining TFs are configured as slave TFs.
2.1.1
Fault Handling
BTS logical model G12
A TG monitors its synchronization source. A master TF detects PCM network
faults and GPS faults, a slave TF knows when ESB or ILD2 fault occurs or
when the master TF stops to provide synchronization.
If the master TF loses its synchronization source, it starts to work in Holdover
Mode which means that it uses its internal oscillator for synchronization. The
master TF maintains the ESB and/or IDL2 synchronization for the slave TFs
when it works in Holdover Mode.
If the slave TF synchronized by ESB does not get the synchronization, it starts
to work in Holdover Mode.
If the slave TF synchronized by IDL2 does not get the synchronization, it starts
to work in Holdover Mode, if it detects an IDL2 fault. If the synchronization is
lost due to expiry of the master TF holdover period, no holdover applies to the
slave TF and the slave TF reports a BTS EXTERNAL (MO AFFECTED) fault.
If the source of synchronization recovers within holdover period, then TF goes
back to normal operation. If the synchronization source is lost for longer time,
then the TF reports a BTS EXTERNAL (MO AFFECTED) fault which causes
that TF is blocked and taken out of operation.
If initial synchronization fails for the slave TF, then the BTS still reports
successful configuration and the slave TF is enabled. Then, the BTS
immediately reports a BTS EXTERNAL (MO AFFECTED) fault and
corresponding alarm may be raised. Hence the slave TF goes to the same
state as if it had a permanent ESB or IDL2 fault. Having the slave TF in the
same state in both those error cases simplifies bringing the slave TFs back
into operation.
If GPS is used as the synchronization source it is possible that faults may occur
with the GPS equipment, either because of the physical faults in the GPS
receiver itself or by the logical fault such as GPS Shadow. Further problems
can occur in these situations if the holdover period expires. Alarms will be
generated according to the GPS fault.
Holdover period duration depends on the used configuration. For details refer
to RBS documentation.
If the master of a logical TG cluster becomes not operational and the Automatic
Master Reselection is active, then a new master will be selected from the TFs
defined as an administrative slave, based on their capabilities.
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Transceiver Group Synchronization
If the master of a notional TG cluster becomes not operational, then the
operator must reconfigure the TG cluster by defining a new master. The
same applies to the master of a logical TG cluster when Automatic Master
Reselection is not active or unable to find a new master.
If the physical PCM fault (O&M fault) on the link towards the master occurs
and due to Automatic Master Reselection a new master TF is found, then
the new master TF will force the existing master TF to stop the timing signal
distribution on ESB before it can start its own timing signal distribution. If the
existing master TF rejects this request, then the new master TF will report a
BTS EXTERNAL (MO AFFECTED) fault and it will be blocked. No master
reselection will take place anymore in this case.
If the operator neglects to define a master TF for a TG cluster the following
applies:
•
In a notional TG cluster all the slave TFs will report a BTS EXTERNAL
(MO AFFECTED) fault and all slave TFs will be blocked, as none will be
able to reach initial synchronization.
•
In a logical TG cluster with Automatic Master Reselection not active all
slave TFs will report a BTS EXTERNAL (MO AFFECTED) fault and all slave
TFs will be blocked, as none will be able to reach initial synchronization.
•
In a logical TG cluster with Automatic Master Reselection active a
master TF will be selected based on the capabilities within other TFs
administratively defined as a slave in the logical TG cluster. If the feature
Synchronized Radio Networks is available then observation alarm will be
raised indicating missing administrative master TF in the logical TG cluster.
If none of the TFs is selected as a new master, then all slave TFs will report
a BTS EXTERNAL (MO AFFECTED) fault and all slave TFs will be blocked,
as none will be able to reach initial synchronization.
If the operator defines more than one master TF in a notional TG cluster or
using an ESB cable connects other TG acting as a master to the TG cluster
with already working master, then the master TF will report a BTS EXTERNAL
(MO AFFECTED) fault and it will be blocked.
It is not possible to define more than one master TF in a logical TG cluster.
BTS logical model G31
TF supervises its synchronization source and reports its condition to BSC by
means of TF MO operational condition. If TF MO becomes not operational it is
blocked. When master TF is blocked, TG synchronization function selects new
master TF from remaining TFs in sector TG cluster basing on capabilities.
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Operational Conditions
3
Operational Conditions
3.1
External Conditions
The availability of the 'RBS TG Synchronization' depends on commercial
agreements.
The availability of the 'Synchronized Radio Networks' depends on commercial
agreements.
3.2
Application Parameters
The following BSC Exchange Property can be changed during operation by
function Administration of BCS Exchange Properties (see Reference [1]):
EXMASTERRES
Automatic Master Reselection
In BTS logical model G12 the property determines
if function Automatic Master Reselection shall be
triggered when master TF becomes not operational.
The property can have a value 0 or 1. The default
value is 0 which means that function Automatic Master
Reselection will not be triggered when master TF
becomes not operational.
3.3
Commands
RXBSP
This command is used to print MO status data reported
by BTS.
RXMOI
This command is used to define a Managed Object
(MO). The TG cluster identity can be defined by means
of this command.
RXMOC
This command is used to change the administration
data of an MO which is out of service. The TG cluster
identity can be changed by means of this command.
RXMSC
This command is used to change a restricted set of
the administration data of an MO which is in or out of
service.
RXMOP
This command is used to print the administration data
of an MO.
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Transceiver Group Synchronization
3.4
Printouts
•
RADIO X-CEIVER ADMINISTRATION BTS STATUS DATA
This printout gives status data reported by BTS for specified MO.
•
RADIO X-CEIVER ADMINISTRATION MANAGED OBJECT DATA
This printout gives the current administrative values for the specified MOs.
•
RADIO X-CEIVER ADMINISTRATION MASTER TF NOT DEFINED
This printout is the observation alarm indicating that administrative master
TF is not defined in a logical TG cluster.
•
RADIO X-CEIVER ADMINISTRATION MANAGED OBJECT FAULT
This printout is the observation alarm indicating a fault on an MO.
3.5
Capabilities
Up to 16 collocated TGs may be in TG cluster.
Up to 3 TGs may be clustered together using IDL2.
Up to 2048 collocated TGs may be in sector TG cluster.
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Concepts
4
Concepts
For a list of general concepts, see the BTS Logical Model Function Specification
(Reference [2] and Reference [3]).
administrative TF mode
This mode defines the wanted mode of the TF in the
TG in the BTS logical model G12. This data is used to
configure the TF. The following modes are applicable:
•
Master - The TF should be configured as master but
may be configured as slave temporarily.
•
Slave - The TF should be configured as slave but
may be configured as master temporarily.
•
Stand-Alone - The TF is not included in the TG
cluster.
•
Unconditional Slave - The TF may be configured
as slave only.
configured TF mode
This mode indicates the configured mode of the TF in
the TG and describes time synchronization relations
with other TGs. The following modes are applicable:
•
Master - The TF is synchronized to the
synchronization source and is distributing
synchronization to other TFs.
•
Slave - The TF is synchronized to the master TF.
•
Stand-Alone - The TF is synchronized to the
synchronization source.
The configured TF mode can change dynamically. In
case of the BTS logical model G12 the configured TF
mode may differ from the administrative TF mode.
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Transceiver Group Synchronization
distribution delay - on external timing bus
The delay on the external timing bus between the
master and the slave in a TG cluster. There can be
different delays for each TG slave. Elements that affect
this delay are:
•
Cable length
•
Cable type
•
Cabinet types
•
TG-cluster topology
frame start offset
It indicates the offset of the frame start position of a
frame with zero FN offset relative the nominal position.
GPS shadow
The radio signals from the GPS satellites do not reach
the GPS RX due to obstacles (for example, buildings).
holdover mode
This is when a TF temporarily operates as a local
oscillator, for a period of typically one hour, due to loss
of its synchronization source.
IDL2 cluster
A logical TG cluster or part of it. It consists of
two or three TGs that are connected with IDL2 for
synchronization purposes.
logical TG cluster
A TG cluster with assigned TG cluster identity.
notional TG cluster
A TG cluster without assigned TG cluster identity.
Relations between TGs are determined by physical
connections.
operational condition
Operational condition indicates whether each of the
functions supported by an MO in the BTS logical model
G31 is running properly, according to supervision in the
BTS. An MO can be in the following conditions:
10
•
Operational, supervision did not find any problems
with the MO.
•
Degraded, some condition may influence the
BSC use of the MO, but the MO is still capable of
supporting traffic.
•
Not operational, traffic functionality or O&M
functionality of the MO may be affected.
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Concepts
sector TG cluster
A number of co-located TGs in the BTS logical model
G31. A sector TG cluster comprises of either one
stand-alone TG, or one master TG and one or more
slave TGs. The TG configured as master acts as a
timing source for TGs configured as slaves.
synchronization delay
The combined value of the distribution delay on external
timing bus and the TX chain delay, so as to provide
synchronized transmission of all TGs in the TG cluster.
TF Comp
The TF compensation value in a TG cluster. This must
be defined for each slave TF relative to the master TF.
It can be calculated by:
TF Comp = distribution delay between master TG and
slave TG + own TG TX chain delay - master TG TX
chain delay
TG cluster
Consists of 2 up to 16 co-located TGs in the BTS logical
model G12. The TF of each TG is physically linked.
One of the TGs, configured as master in the cluster acts
as a timing source for other TGs which are configured
as slaves. A TG cluster may be either notional or logical.
TG cluster identity
An instance used to identify all TGs within one logical
TG cluster.
transmitter chain delay
The delay within the cabinet. There can be different
delays for each TG. Elements that affect this delay are:
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•
TX
•
Combiner
•
Feeder
•
Antenna
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Transceiver Group Synchronization
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Glossary
Glossary
BSC
Base Station Controller
TDMA
Time Division Multiple Access
BTS
Base Transceiver Station
TF
Timing Function
CPRI
Common Public Radio Interface
TG
Transceiver Group
DU
Digital Unit
TRX
Transceiver
ESB
External Synchronization Bus
FN
Frame Number
GPS
Global Positioning System
GSM
Global System for Mobile Communications
IDL2
Inter DU Link version 2
MCTR
Multi Carrier Transceiver
MO
Managed Object
MSMM
Multistandard Mixed Mode
NGS
Node Group Synchronization
OMT
Operation and Maintenance Terminal
PCM
Pulse Code Modulation
RBS
Radio Base Station
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Transceiver Group Synchronization
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Reference List
Reference List
Ericsson Documents
[1]
ADMINISTRATION OF BSC EXCHANGE PROPERTIES
FUNCTION SPECIFICATION
[2]
BTS Logical Model G12
FUNCTION SPECIFICATION
[3]
BTS Logical Model G31
FUNCTION SPECIFICATION
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