GSM Railway, Rel. RGR40
SP1, Operating
Documentation, Issue 02
BSS03050: Frequency
Hopping
DN09242688
Issue 1-0-0
BSS03050: Frequency Hopping
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BSS03050: Frequency Hopping
Table of Contents
This document has 26 pages
Summary of changes..................................................................... 6
1
Overview of Frequency Hopping....................................................7
2
2.1
2.2
2.3
2.4
Technical description of Frequency Hopping................................. 8
Restrictions to Frequency Hopping................................................ 8
RF hopping management...............................................................9
Baseband hopping management................................................. 10
Interworking.................................................................................. 11
3
3.1
3.2
3.3
3.4
Functionality of Frequency Hopping.............................................16
Fault Management of Frequency Hopping/recovery examples....18
Implementation principles of Frequency Hopping, functional split...
20
BTS implementation of Frequency Hopping................................ 21
BSC implementation of Frequency Hopping................................ 22
4
User interface of Frequency Hopping.......................................... 25
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BSS03050: Frequency Hopping
List of Figures
4
Figure 1
A call hopping over four frequencies.................................................... 8
Figure 2
A 3-TRX BTS using RF hopping...........................................................9
Figure 3
A 4 TRX BTS using baseband hopping.............................................. 11
Figure 4
Hopping groups in BB and RF hopping segments............................. 14
Figure 5
Example of baseband hopping........................................................... 17
Figure 6
Example of RF hopping...................................................................... 18
Figure 7
Initial configuration of baseband hopping BTS................................... 18
Figure 8
MSS handled by TRXs 1, 3, and 4 can hop over all 4 frequencies.... 19
Figure 9
TRX-1 is blocked and does not carry traffic nor participate in hopping..
19
Figure 10
Initial configuration of RF hopping BTS.............................................. 19
Figure 11
TRX-2 is blocked out of use............................................................... 20
Figure 12
Relations between logical radio network objects................................23
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List of Tables
Table 1
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Maximum BTS configurations supporting Frequency Hopping.......... 20
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Summary of changes
BSS03050: Frequency Hopping
Summary of changes
Changes between document issues are cumulative. Therefore, the latest document
issue contains all changes made to previous issues.
This is the first issue of the document.
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Overview of Frequency Hopping
1 Overview of Frequency Hopping
Frequency Hopping (FH), or more accurately Slow Frequency Hopping (SFH), is a
software designed to the GSM to increase quality and capacity in an urban propagation
environment. This is achieved by means of frequency diversity and interference
diversity.
Slow Frequency Hopping in the GSM means that the frequency of a radio time slot
(RTSL) is changing burst by burst at regular intervals. The frequency remains the same
during a burst (0,577 ms). All dedicated channel types and their associated channel
types (TCH/SACCH/FACCH, SDCCH/SACCH) can hop.
This description introduces the implementation of Frequency Hopping in GSM Base
Station Subsystem (BSS). This description explains the functionality of the radio
frequency (RF) and baseband (BB) hopping applications. Neither the theory behind
Frequency Hopping nor radio network planning with associated capacity calculations are
discussed here.
Frequency Hopping is used by features such as Dynamic Frequency and Channel
Allocation (DFCA), and Antenna Hopping. For more information on these features, see
Dynamic and Channel Allocation in BSC and Activating and Testing BSS11134: Antenna
Hopping.
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Technical description of Frequency Hopping
BSS03050: Frequency Hopping
2 Technical description of Frequency Hopping
2.1 Restrictions to Frequency Hopping
There are some restrictions concerning the cell allocation frequencies on the Abis and
Radio interface messages of the EGSM/GSM 1800/GSM 1900 system. The following
allocation coding methods can be used:
•
•
•
•
Range 1024
This allows encoding 2 - 16 frequencies (17 if frequency 0 is in), the frequencies
being spread among up to 1024 consecutive ARFCNs.
Range 512
This allows encoding 2 - 18 frequencies, the frequencies being spread among up to
512 consecutive ARFCNs.
Range 256
This allows encoding 2 - 22 frequencies, the frequencies being spread among up to
256 consecutive ARFCNs.
Variable bit map
This allows any combination among 112 consecutive ARFCNs.
Note that in addition to MA list frequencies, the cell allocation frequencies include all
used frequencies of the certain band in the segment.
Only one hopping mode (BB or RF) can be active on a BTS at a time.
The values of the training sequence codes (TSCs) of all the TRXs of a BB hopping layer
must be equal. If the BCCH TRX's frequency is used in a BB hopping layer, then the
TSCs of all TRXs of that BB hopping layer must be the same as the BTS color code
(BCC).
Figure 1
A call hopping over four frequencies
frequency
time
The exact frequency on a certain moment of time is defined as a function of frequency
hopping parameters related to a cell and a “logical Radio interface channel” (CA, MA,
MAIO, (HSN), and the Radio interface absolute frame number (see 3GPP
documentation 45 series). The frame number synchronizes MS and BTS operation on a
time basis.
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Technical description of Frequency Hopping
There are two main options for the implementation of Frequency Hopping: baseband
hopping and radio frequency hopping. Both of these are supported by BSS. If the
transceivers of the BTS are of the hopping synthesiser type (MetroSite, UltraSite, Flexi
EDGE or Flexi Multiradio), you can choose the frequency hopping mode between nonhopping, RF hopping, and BB hopping.
2.2 RF hopping management
The frequencies for a hopping cell are defined by attaching the cell to one of the mobile
allocation frequency lists (MA-lists) defined by the operator. The system calculates the
MAIOs, and the operator gives the HSN for the cell. The BCCH transceiver cannot hop,
but it transmits a continuous BCCH frequency. Note that the MA used must contain at
least as many frequencies as there are unlocked hopping transceivers in the BTS. The
MA or the HSN can be changed only when the hopping BTS object is locked.
You can create up to 3000 MA-lists and use them freely with different cells. One list can
contain up to 63 frequencies. If, however, GPRS is in use in the following configurations,
the number of frequencies is smaller (see restrictions concerning the cell allocation
frequencies in chapter Restrictions to Frequency Hopping):
•
•
If EGPRS is supported, there can be up to 51 frequencies in the MA-list.
If EGPRS is not supported, there can be up to 56 frequencies in the MA-list.
Changes in the transceiver configuration of an RF hopping cell affect only the transceiver
that is being handled, other transceivers are not disturbed. The hopping mode can be
changed when the BTS is locked. If an alarm is received from the BCF indicating a fault
that has an effect on Frequency Hopping, the BSC blocks the faulty object.
Figure A 3-TRX BTS using RF hopping shows an example of a 3-TRX BTS using RF
hopping. Note that only one mobile allocation frequency list can be attached to the BTS
at a time.
Figure 2
A 3-TRX BTS using RF hopping
fa
TRX-1
B
TRX-2
0
0
0
0
0
0
0
0
TRX-3
1
1
1
1
1
1
1
1
(fb)
B=BCCHtimeslot. TRXdoesnothop.
Non-BCCH TRXsarehoppingover
theMA-list(f1,f2,f3,...,fn)attachedtothecell.
(fc)
MAIOshavetobedifferentbetween
sameRTSLsinsamehoppinggroup.
Onlyonehoppinggroup.OnlyHSN-1ismeaningful.
Freeform RF hopping
Adjacent frequencies cannot be used in the mobile allocation frequency list since it would
cause adjacent channel interference within the cell and also between the cells in the
same BTS site. However, in order to fully benefit from the very tight reuse factor and
fractional loading in the hopping network offered by the use of RF hopping, the operator
needs means to share the same frequency sets between adjacent sectors of a BTS site.
At the same time channel collisions and adjacent channel interference have to be
avoided. Thus the operator needs to be able to define all the frequency hopping
parameters, including MAIOs.
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Technical description of Frequency Hopping
BSS03050: Frequency Hopping
The operator is provided with two parameters for MAIO manipulation to use RF hopping
more flexibly and more efficiently:
•
•
User-defined parameter to set the starting point for allocation of the MAIOs per cell,
that is, the lowest MAIO in a cell can be bigger than zero.
User-defined parameter to allow discontinuous MAIO numbering to be used in a cell,
for example, MAIOs 0, 2, 4, 6.
2.3 Baseband hopping management
There are two different hopping groups used with baseband hopping in each BTS. When
the Intelligent Frequency Hopping (IFH) software is used, an additional hopping group
3 is in use. See section Intelligent Frequency Hopping for more information on IFH and
hopping on layer basis. For more information, see Intelligent Underlay-Overlay.
Group 1
All radio time slots (RTSL-0), except the BCCH time slot, on the BTS belong to Group 1.
It is managed through FHS-1 in the BSC's database. Hopping Sequence Number 1
(HSN1) is related to this group.
Group 2
All radio time slots (RTSL-1 to 7) on the BTS belong to Group 2. It is managed through
FHS-2 in the BSC's database. HSN2 is related to this group.
If baseband hopping is used on the BTS, all radio time slots belonging to the BTS are
defined as hopping. The only exception to this is the BCCH time slot, which is always
defined as non-hopping. In case there are dedicated signalling channels (SDCCH,
CBCH) on the BCCH time slot, they do not hop either.
These hopping groups are maintained by adding and removing the absolute radio
frequency channel number (ARFCN) of the TRXs used in Frequency Hopping in the
BTS. Based on the available ARFCNs in the BTS, the following hopping parameters,
stored in the BSS Radio Network Configuration Database (BSDATA), are updated:
•
•
Mobile Allocation (MA)
Mobile Allocation Index Offset (MAIO)
The ARFCN of a TRX is always removed from the hopping systems when the user sets
the TRX to the administrative state LOCKED. The ARFCN is also removed from hopping
if the system takes the TRX out of operational use because of a Carrier Unit (CU) or
Transceiver Unit fault in the BTS. These operations cause clearing of calls in a BB
hopping cell.
The frequency hopping systems are configured and the parameters are implicitly defined
by radio network configuration management in the BSC, when a BTS is created. For
more information, see Radio Network Configuration Management.
Through the BSC MMI, you can define whether the BTS uses Frequency Hopping or not.
If baseband hopping is used in the BTS, you have to give a hopping sequence number
(HSN) for all the hopping groups in the BTS.
If baseband hopping is used in the BTS, the modification of the administrative state or
the ARFCN of a TRX and the creation or deletion of a TRX is possible only when a BTS
has first been set in the administrative state LOCKED.
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Technical description of Frequency Hopping
Figure A 4 TRX BTS using baseband hopping shows an example of a 4-TRX BTS using
baseband hopping:
Figure 3
RTSL
TRX-1
TRX-2
A 4 TRX BTS using baseband hopping
01234567
B
0 0
0
0
0
0 0
f1
B =BCCHtimeslot.Itdoesnothop.
Timeslots1...7ofall TRXs
hopoverMA(f1,f2,f3,f4).
ThishoppinggroupusesHSN-2.
0
1
1
1
1
1
1
1
f2
TRX-3
1
2
2
2
2
2
2
2
f3
TRX-4
2
3
3
3
3
3
3
3
f4
MAIOshavetobedifferentbetween
sameRTSLsinsamehoppinggroup.
Timeslot0of TRX-2,-3,-4hopoverMA(f2,f3,f4).
ThishoppinggroupusesHSN-1.
2.4 Interworking
Handovers
When Frequency Hopping is used in the target cell, the handover command contains the
respective MA-list, MAIO, HSN, and the Cell Allocation list of the target cell.
In intra-BTS handover cases the TCH of the best quality will be allocated primarily from
another TRX than the actual one, regardless of the MS power class or whether the
actual TRX is a hopping one or not.
Intelligent Underlay-Overlay, Intelligent Frequency Hopping (IFH)
The different interference characteristics of the regular and the super-reuse layers in
Intelligent Underlay-Overlay require that the frequency plan is constructed separately for
each layer. The super-reuse layer has frequency hopping parameters of its own, which
allow hopping separately for both layers of an IUO cell. A dedicated hopping group is
introduced for that purpose.
The following parameters are definable separately for both layers: Hopping Mode HSN
(UHSN), MA-list (UMAL), MAIO Offset (UMO), MAIO Step (UMS). It is
possible to make only one of the IUO layers hopping. Both baseband hopping and RF
hopping modes are supported.
All the super-reuse TRXs in a cell have to belong to the same IUO frequency group,
because Frequency Hopping is performed between all the TRXs.
The child cell is a special part of the IUO concept. The hopping group arrangement is
somewhat different from normal IUO cells as there are only super-reuse TRXs in a child
cell. With BB hopping there are two hopping groups in use and with RF hopping there is
only one group. HSN1 and UHSN are used with a BB hopping child cell and only UHSN
with a RF hopping one.
For more information, see Intelligent Underlay-Overlay.
DFCA Hopping
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Technical description of Frequency Hopping
BSS03050: Frequency Hopping
DFCA Hopping utilized in Dynamic Frequency and Channel Allocation is based on RF
hopping. When DFCA Hopping is employed in a BTS object, the non-DFCA TRXs of the
BTS can either be non-hopping TRXs or they can use RF hopping. Intelligent Frequency
Hopping (IFH) and baseband frequency hopping (BB) are not supported in the DFCA
BTS.
For more information, see Dynamic Frequency and Channel Allocation in BSC.
Antenna Hopping
Antenna Hopping enables the TRXs in an RF hopping BTS to transmit with all the TX
antennas in the BTS. Antenna Hopping uses the existing BB (baseband) hopping
functionality in the BTS. Antenna Hopping can be used with or without RF hopping.
Antenna Hopping cannot be used simultaneously with baseband hopping. For more
information, see Antenna Hopping.
Cell Broadcast
The Cell Broadcast Channel (CBCH) is not hopping if it is using an SDCCH/4
subchannel in the BCCH time slot. Otherwise (SDCCH/8 subchannel) the CBCH is
hopping, if located in a hopping TRX. The channel description (hopping parameters) for
the CBCH (max. 32 frequencies) is broadcasted to the mobiles in a system information
message. For more information, see Cell Broadcast.
Half Rate
If cyclic hopping (HSN = 0) is used, the Half Rate channels use only half of the
frequencies defined in the MA-list in the hopping sequence, thus reducing the benefit
reached with hopping over all frequencies in an MA-list. With random hopping the HR
channels are hopping over all frequencies defined in the MA-list, thus getting the same
profit from Frequency Hopping as FR channels. For more information, see Half Rate in
BSC.
Downlink DTX
Baseband hopping combined with downlink DTX causes problems in the mobile stations
because in the silent phase dummy frames are sent on the BCCH frequency, causing
malfunction in the mobile stations. ETSI has approved a solution to solve the problem
and it is implemented in BSS. The solution is to use a special training sequence code in
the dummy burst, yet, it does not guarantee that all mobile station models of different
manufacturers are working error free.
In addition, cyclic baseband hopping HSN1 & HSN2 = 0 should be avoided in two TRX
sectors when Downlink DTX and Power Control are used as it may lead to a degradation
in KPIs (such as Rx Level based HO) when compared to using non cyclic hopping
configuration.
Extended Range Cell
Only RF hopping is supported and only for the TRXs serving the normal coverage area.
The TRXs serving the extended coverage area cannot hop.
MS Speed Detection
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Technical description of Frequency Hopping
The speed detection algorithm in the BTS works only for non-hopping channels. In case
of Frequency Hopping the speed information in the Measurement Result message from
BTS to BSC is set to the value 'non-valid' indicating that speed information is not
available from that particular cell. For more information, see MS Speed Detection.
DL Power Control
If baseband hopping is being used in the BTS, the BSC sends the power control (PC)
commands also to the BCCH transceiver. All bursts of one hopping group, except the
burst on the BCCH frequency are transmitted with the commanded power level. All
bursts in the BCCH frequency are transmitted with the predefined BCCH power level. If
Frequency Hopping is not being used, the BSC does not send the PC commands to the
BTS via the BCCH transceiver. Frequency Hopping does not affect sending PC
commands to the MS.
Interference Level Measurement
The BTS performs continuous interference level measurement on each idle RTSL and
reports the results to the BSC at regular intervals. The BSC uses the information when
rating the channels for the channel allocation procedure. In case of a hopping RTSL the
measurement is performed according to the actual hopping sequence. Thus, the result is
an average over the RTSLs hopping together, reflecting the same perceived interference
that an active channel would do.
Radio Channel Allocation
For interference reasons, it is sometimes reasonable to favour the BCCH TRX in channel
allocation. But sometimes it is better to choose a channel from a non-BCCH TRX,
especially when RF hopping is used in a cell.
TCH allocation between TRXs in a BTS object is managed by a BTS-level parameter
TRX priority in TCH allocation, which defines whether the BCCH TRX or
the non-BCCH TRXs are preferred.
For more information, see Radio Channel Allocation.
Multi BCF Control and Common BCCH Control
With Multi BCF Control, the operator can combine several base transceiver stations into
one logical cell. This is done by introducing the segment object in the BSC. The
segment may include many BTS objects from different BTSs.
The basic idea behind the Common BCCH Control is to include resources from different
frequency bands into one cell by letting them share a common BCCH that has been
allocated from one frequency band used in the cell.
Frequency Hopping is BTS-specific even if the Multi BCF Control or the Common BCCH
Control is in use.
In the segment, the resources of different types are grouped as separate BTSs. All the
resource types have their own hopping parameters and hopping groups. Figure Hopping
groups in a segment gives an example of the different hopping groups of a segment in
Common BCCH Control.
The segment architecture enables the network to have BTSs without a BCCH TRX. This
reduces the amount of hopping groups in the regular area of a BTS because of no need
for a separate group for the BCCH TRX in RF hopping. In the case of BB hopping, TSL0
and other TSLs are separated and these are seen as two different hopping groups.
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Technical description of Frequency Hopping
Figure 4
BSS03050: Frequency Hopping
Hopping groups in BB and RF hopping segments
BBhopping
PGSM900BTS,
twohoppinggroups
EGSM900BTS,
twohoppinggroups
GSM1800BTS,
twohoppinggroups
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
RFhopping
PGSM900BTS,
onehoppinggroup
EGSM900BTS,
onehoppinggroup
GSM1800BTS,
onehoppinggroup
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
For more information, see Common BCCH Control in BSC and Multi BCF Control in
BSC.
PGSM 900 - EGSM 900 BTS
Frequency hopping cannot be used in a PGSM 900 - EGSM 900 BTS without Single MA
list for PGSM and EGSM or GPRS/EDGE Support for PGSM-EGSM BTS software,
when the BCCH is on PGSM900 frequency band.
For more information, see PGSM 900 - EGSM 900 BTS in BSC
ER-GSM
The operator can define any frequency from the ER-GSM band ( 940 <= ARFCN <=
974 ) in the RF hopping list, but the [955; 974] ARFCN range must be used if not all
terminals are ER-GSM capable.
For more information on the feature and functionality interworking with ER-GSM, see
RG302294: Support of ER-GSM, Feature Description.
BSS101610 Several Cell Allocations in One Band
This feature allows the BSC to build a separate CA list for each BTS object in a segment
instead of a common CA list for the whole band. Also BSC can use the BTS object
specific CA list for the respective BTS object. Currently, different BTS objects of a
segment can be defined to use the different parts of the frequency band allocation, but a
common frequency band specific CA list is provided for a segment (cell) and signaling in
radio interface limits the number of frequencies in the list when frequency range is larger.
This feature allows the following new setups within one segment:
A) 900/1800 Dual band
•
•
14
50 BCCH (900) - BTS1
601-624 (1800) - BTS2
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•
Technical description of Frequency Hopping
841-850 (1800) - BTS3
B) 1800
•
•
•
598 BCCH (1800) - BTS1
601-624 (1800) - BTS2
841-850 (1800) - BTS3
This feature works together with all type of frequency hopping modes used in BSC.
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Functionality of Frequency Hopping
BSS03050: Frequency Hopping
3 Functionality of Frequency Hopping
When Frequency Hopping is used, the Basic Call procedure differs from the non-hopping
case only in the channel assignment phase.
The BSC selects a free logical dedicated channel in a hopping BTS in the same way as
in the non-hopping BTS.
The channel selection procedure is influenced by the idle channel interference levels
measured by the BTS. In a hopping BTS the idle channel interference measurements
are done in all frequencies included in the Mobile Allocation list.
If hopping is not used, the radio interface channel can be defined with ARFCN, Radio
Time slot number, and subchannel number. If hopping is used, the ARFCN is replaced
with an MA, MAIO, and HSN. The MA determines which frequencies from the Cell
Allocation are used in the hopping sequence.
After the selection of a dedicated channel, the BSC determines the required MAIO, HSN,
and MA for the selected channel and sends them to the mobile station in the
IMMEDIATE_ASSIGNMENT or ASSIGNMENT message. The MS reads the Cell
Allocation from the System Information Messages which are broadcast on the BCCH.
The BTS has received the used MAIO, HSN, and MA in the BTS configuration phase via
O&M signalling link.
Example:
Baseband hopping
Four consecutive calls are made in a cell with four TRXs. Baseband hopping is used in
the cell. For all calls, the BSC allocates the RTSL-2 in different TRXs. Figure Example
of baseband hopping illustrates how the bursts are organised in the air interface. In this
case only RTSL-2 is observed.
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Functionality of Frequency Hopping
Figure 5
Example of baseband hopping
Call1: TRX1,RTSL 2,MAIO=0,MA(f1,f2,f3,f4),HSN=0(CyclicHopping)
RTSL
0
1
TRX1
B
0
0
2
0
3
0
4
0
5
0
6
0
7
0
BurstsinRTSL 2
f1
TRX2
0
1
1
1
1
1
1
1
1
f2
TRX3
1
2
2
2
2
2
2
2
2
f3
TRX4
2
3
3
3
3
3
3
3
3
f4
2
2
2
Call2: TRX2,RTSL 2,MAIO=1,MA(f1,f2,f3,f4),HSN=0(CyclicHopping)
RTSL
0
1
2
3
4
5
6
7
TRX1
B
0
0
0
0
0
0
0
0
f1
TRX2
0
1
1
1
1
1
1
1
1
f2
TRX3
1
2
2
2
2
2
2
2
2
f3
TRX4
2
3
3
3
3
3
3
3
3
f4
3
4
5
6
RTSL
0
1
TRX1
B
0
0
0
0
0
0
0
0
f1
TRX2
0
1
1
1
1
1
1
1
1
f2
TRX3
1
2
2
2
2
2
2
2
2
f3
TRX4
2
3
3
3
3
3
3
3
3
f4
7
3
4
5
6
2
2
2
Time
2
2
2
2
2
Time
2
2
2
2
2
Time
BurstsinRTSL 2
2
2
2
Call4: TRX4,RTSL 2,MAIO=3,MA(f1,f2,f3,f4),HSN=0(CyclicHopping)
2
2
BurstsinRTSL 2
2
2
2
Call3: TRX3,RTSL 2,MAIO=2,MA(f1,f2,f3,f4),HSN=0(CyclicHopping)
2
2
RTSL
0
1
7
BurstsinRTSL 2
TRX1
B
0
0
0
0
0
0
0
0
f1
TRX2
0
1
1
1
1
1
1
1
1
f2
TRX3
1
2
2
2
2
2
2
2
2
f3
TRX4
2
3
3
3
3
3
3
3
3
f4
2
2
2
2
2
2
2
2
Time
Example:
RF hopping
RF hopping on TRX-2 in a two-TRX cell. The first call is made on RTSL-2 of the nonhopping BCCH TRX and the second call is made on RTSL 2 of the RF hopping TRX.
Figure Example of RF hopping illustrates how the bursts are organised in the air
interface. In this case only RTSL-2 is observed.
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Functionality of Frequency Hopping
Figure 6
BSS03050: Frequency Hopping
Example of RF hopping
Call1: TRX1,RTSL 2, ARFCN=f1
RTSL
0
TRX1
B
TRX2
0
1
2
3
4
5
6
7
BurstsinRTSL 2
f1
0
0
0
0
0
0
0
f2
f3
f4
2
2
2
Call2: TRX2,RTSL 2,MAIO=0,MA (f2,f3,f4),HSN=0(CyclicHopping)
RTSL
0
TRX1
B
TRX2
0
1
2
3
4
5
6
7
2
2
2
2
2
Time
2
2
2
2
2
Time
BurstsinRTSL 2
f1
0
0
0
0
0
0
0
f2
f3
f4
2
2
2
3.1 Fault Management of Frequency Hopping/recovery
examples
The following three examples show the recovery of a hopping BTS.
TRX LAPD link fault, baseband hopping BTS
Figure 7
Initial configuration of baseband hopping BTS
RTSL 01234567
TRX-1 B
0 0
0
0
0
0 0
f1
B =BCCHtimeslot.Itdoesnothop.
TRX-2
Timeslots1...7ofall TRXs
hopoverMA(f1,f2,f3,f4).
ThishoppinggroupusesHSN-2.
0
1
1
1
1
1
1
1
f2
TRX-3
1
2
2
2
2
2
2
2
f3
TRX-4
2
3
3
3
3
3
3
3
f4
MAIOs have tobedifferentbetween
sameRTSLsinsamehoppinggroup.
Timeslot 0of TRX-2,-3,-4hopover MA(f2,f3,f4).
ThishoppinggroupusesHSN-1.
1. The BSC detects that a LAPD link of TRX-2 has failed. The BSC sets alarm (7705,
7704).
2. The BSC clears all the calls that are allocated to those Abis circuits corresponding to
TRX-2. Calls on TRXs 1, 3, and 4 remain untouched.
3. The BSC blocks TRX-2 to restrict new traffic for Abis circuits related to it.
It must be noted that in the case of Nokia MetroSite EDGE BTS, the LAPD link failure is
handled in the same way as TRX failure. For more information, see the next topic: TRX
fault, baseband hopping BTS.
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BSS03050: Frequency Hopping
Functionality of Frequency Hopping
In this fault type, the BSC can assume that the TRX is functioning properly, so the
hopping parameters can be left untouched.
MSS handled by TRXs 1, 3, and 4 in this example can hop over all 4 frequencies.
Figure 8
MSS handled by TRXs 1, 3, and 4 can hop over all 4 frequencies
RTSL 01234567
TRX-1
B
0 0
0
0
0
0 0
f1
0
1
1
1
1
1
1
1
f2
TRX-3
1
2
2
2
2
2
2
2
f3
TRX-4
2
3
3
3
3
3
3
3
f4
TRX fault, baseband hopping BTS
Initial configuration: as in figure Initial configuration of baseband hopping BTS.
In this example, the BCCH TRX has failed. The fault is such that the Transceiver Unit of
TRX-1 does not work any more.
1. The BTS alarms the BSC. TRX-1 is suspected to be faulty.
2. The BSC blocks all the TRXs of the BTS for a while. This causes clearing of all
ongoing calls of the BTS.
3. The BSC reconfigures the BCCH to another TRX, if possible.
4. The BSC calculates new hopping parameters.
5. The BSC deblocks TRXs 2, 3, and 4. New hopping and TRX parameters are
transferred to the BTS via Abis O&M interface. The TRX-2 is restarted with BCCH on
RTSL-0, and hopping is reconfigured.
6. The BSC allows new traffic for TRXs 2, 3, and 4.
Figure 9
TRX-1 is blocked and does not carry traffic nor participate in hopping
RTSL 01234567
TRX-1
f2
TRX-2
B
0
0
0
0
0
0
0
f1
TRX-3
0
1
1
1
1
1
1
1
f3
TRX-4
1
2
2
2
2
f4
2
2
2
Frequenciesareswapped. TRX-1is
lockedanddoesnotcarrytraffic.
TRX fault, RF hopping BTS
Figure 10
TRX-1
B
TRX-2
0
Initial configuration of RF hopping BTS
0
0
0
0
0
0
0
fa
B=BCCHtimeslot. TRXdoesnothop.
(fb)
Non-BCCH TRXishoppingover
theMA-list(f1,f2,f3)attachedtothecell.
Onlyonehoppinggroup.OnlyHSN-1ismeaningful.
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Functionality of Frequency Hopping
BSS03050: Frequency Hopping
1. The BTS alarms the BSC, or the BSC detects a non-functional LAPD. TRX-2 is
suspected to be faulty.
2. The BSC clears all the calls which are allocated to those Abis circuits corresponding
to TRX-2. Calls on TRX-1 remain untouched.
3. The BSC blocks TRX-2 in order not to allow new traffic for Abis circuits related to it.
Figure 11
TRX-2 is blocked out of use.
TRX-1
B
TRX-2
-
-
-
-
-
-
-
-
For more information, see Radio Network Recovery and State Management.
3.2 Implementation principles of Frequency Hopping,
functional split
In the GSM system the BSS is responsible for implementing Frequency Hopping. The
MSC is not involved in it. The only indirect MSC impact in hopping is that some MSCtransparent A interface messages (handover command information coming from the
target BSC) are longer than in the non-hopping case.
NetAct is involved in managing the BTS and hopping parameters. They are managed
from NetAct like other cell parameters. Fault management from NetAct's point of view
has no special functions related to Frequency Hopping. Alarms from a hopping BTS are
handled like alarms from a non-hopping BTSs.
The maximum BTS configurations supporting hopping are listed in table Maximum BTS
configurations supporting Frequency Hopping.
Table 1
Maximum BTS configurations supporting Frequency Hopping
BTS type
Baseband hopping
Note
RF hopping
Omni
12 TRXs
12 TRXs
Sectorised
4+4+4 TRXs
4+4+4 TRXs
note
MetroSite
Omni
4 TRXs
1)
4 TRXs
Sectorised
2+2 TRXs
1)
2+2 TRXs
UltraSite
Omni
Sectorised
20
12 TRXs
12 TRXs
2)
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BSS03050: Frequency Hopping
Table 1
Functionality of Frequency Hopping
Maximum BTS configurations supporting Frequency Hopping (Cont.)
BTS type
Baseband hopping
Note
RF hopping
note
Flexi EDGE
Omni
12 TRXs
Sectorised
12 TRXs
3)
3)
4)
4)
Flexi Multiradio
Omni
12 TRXs
Sectorized
1) MetroSite BB hopping is pseudo-BB hopping. The same hopping group of the cell cannot include
both normal TRXs and high-power TRXs.
2) UltraSite limitations for sector configuration are: a maximum of 12 TRXs / sector and a maximum
of 6 sectors / BCF. Thus the possible sector configurations go from 2+2+2+2+2+2 TRXs to 6+6
TRXs. The same hopping group of the cell cannot include both normal TRXs and high-power
TRXs.
3) Flexi EDGE limitations for sector configuration are: a maximum of 12 TRXs / sector, a maximum
of 6 sectors / BCF and a maximum 24 TRXs / BCF. The same hopping group of the cell cannot
include both normal TRXs and double power TRXs or IDD TRXs when antenna or BB hopping is
used.
4) Flexi Multiradio BTS, GSM/EDGE limitations for sector configuration are: a maximum of 16
TRXs / sector, a maximum of 12 sectors / BCF and a maximum 36 TRXs / BCF. The same hopping
group of the cell cannot include both normal TRXs and IDD TRXs when antenna or BB hopping is
used.
3.3 BTS implementation of Frequency Hopping
Nokia Flexi EDGE implementation
Flexi EDGE BTSs support baseband (BB) and Synthesised (RF) Frequency Hopping.
The frequency hopping mode is configured separately for each BTS object. Only one
type of hopping mode is allowed in a BTS object. However, different BTS objects can
have different hopping modes active at the same time.
BTS O&M in the system module generates the sector specific hopping configuration and
distributes it to the appropriate TRX O&M instances of the sector. TRX_OM forwards the
hopping parameters to the appropriate DSP located in the Dual TRX modules. The DSP
calculates the frequency by using the hopping sequence generation algorithm in
accordance to other DSPs belonging to the same hopping BTS object. The DSP does
the routing and RF control on timeslot basis depending on the hopping type. The
synthesised Frequency Hopping (RF hopping) functionality is available in configurations
that have at least two TRXs per sector, since one of the TRXs in each sector is a BCCH
TRX (if Multi BCF Control in BSC is not used). The BCCH TRX cannot hop because the
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Functionality of Frequency Hopping
BSS03050: Frequency Hopping
BCCH frequency must be continuously transmitted in a cell to enable the MS to measure
BCCH signal strength. This means that only non-BCCH TRXs can employ synthesised
Frequency Hopping.
The maximum number of frequencies available for hopping is 63 per hopping group. All
RF hopping DSPs are initialised with hopping groups generated by the BTS O&M
according to hopping information received in the BTS_CONF_DATA message sent from
the BSC. Synthesizers in a particular TRX are tuned to different channels according to
hopping sequence. RF hopping is not supported with cavity combiner (RTC)
configurations. A TRX connected to the cavity must remain in the tuned channel all the
time. The Flexi EDGE baseband hopping functions so that Rx samples are distributed
between DSPs in the Dual TRX modules over 1 Gb Ethernet bus via system module.
Each DSP calculates the hopping algorithm separately. Baseband hopping is supported
also with cavity combiner configurations.
Flexi Multiradio implementation
Flexi Multiradio BTSs support Baseband Hopping (BB) or Radio frequency (RF) hopping.
With Intelligent Frequency Hopping, it is possible to reuse frequencies more intensively,
and therefore achieve a higher radio network capacity. It is also possible to avoid
frequency dependent fading on the radio path. When Intelligent Frequency Hopping is in
use, the operator can use Intelligent Underlay- Overlay simultaneously with frequency
hopping in the same cell. Either baseband (BB) or radio frequency (RF) hopping can be
used. Intelligent Frequency Hopping enables the use of separate Mobile Allocation
Frequency lists of radio frequency hopping for the layers of an Intelligent UnderlayOverlay cell.
3.4 BSC implementation of Frequency Hopping
BSC functionality related to Frequency Hopping is implemented by a software. There are
no hardware dependencies.
Telecom software
In the telecom BSC software Frequency Hopping is not very visible. The main principle is
that the BSC handles the logical channels of cells (the number of channels varies) and in
case of Frequency Hopping there are just some additional parameters (MA, MAIO, HSN)
attached to those channels when needed. The parameters are offered for the use of
telecom software by a database maintained by O&M software.
In Abis and Radio interface (RR-level) signalling, Frequency Hopping is seen in
CHANNEL_ACTIVATION (Abis), IMMEDIATE_ASSIGNMENT (Radio),
ASSIGNMENT_COMMAND (Radio) and HANDOVER_COMMAND (Radio) messages.
In system info messages there are also some hopping related parameters : Cell
Allocation bitmap (CA), PWRC indicator and channel description of
the CBCH (cell broadcast channel).
O&M; Configuration Management
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BSS03050: Frequency Hopping
Functionality of Frequency Hopping
It is possible to manage the BSS radio network data locally in the BSC site by means of
local MMI or/and in NetAct. The NetAct and BSC radio network management
communicate with each other via the Q3 interface. The modifications that are made in
the radio network parameters stored in the BSS Radio Network Configuration Database
with the BSC's local MMI are updated in NetAct.
Relations between logical radio network objects
The overview of the partial containment hierarchy for the logical radio network objects
stored in the BSS Radio Network Configuration Database (BSDATA) is presented in
figure Relations between logical radio network objects.
Figure 12
Relations between logical radio network objects
BSC
TRK_TBL
BCF
MA
BA
BTS
FHS
HOC
TRX
POC
ADJC
RTSL
In general, a higher-level object instance has to be created in the BSDATA before the
related lower-level object can be created.
Frequency Hopping System (FHS) object instances are created implicitly in the BSDATA
when a BTS object instance is created by means of MMI. Time slot (RTSL) object
instances are also implicitly created when the related TRX object instance is created in
the BSDATA.
HOC, POC, FHS, and RTSL object instances cannot be independently removed from the
BSDATA, but they are removed from the database when the related higher-level object
instance (the BTS or TRX) is removed from the database by means of MMI.
The administrative state of the BCFs, BTSs, TRXs, and RTSLs can be defined
independently of the administrative state of the related objects.
O&M; Fault Management
The BTS may send alarms which indicate that there is a fault affecting the hopping
capabilities. The BSC then takes actions to minimise the influences of the fault.
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Functionality of Frequency Hopping
BSS03050: Frequency Hopping
O&M; Radio Network Recovery
The radio network configuration management determines the recovery actions of the
BSC in abnormal situations of the BSS radio network, such as faults, fault cancels, and
initialisations that concern the BSS. For more information on radio network configuration
management, see Radio Network Recovery and State Management. The function class
receives radio network recovery requests from the Radio Network Maintenance function
class.
The recovery actions are executed if the errors occur in the functional blocks of the BTS,
such as the Transceiver (TRX), functional blocks common to whole BTS (cell), or the
functional blocks common to the whole BTS site, for example the Frequency Hopping
Unit (FHU). In addition to this, the recovery actions are executed if the D-channel of the
Abis interface fails or if there are failures detected by the call control of the BSC in
connection with the radio channel allocation procedure.
The recovery actions are determined based on the faulty functional block type and they
are based on the radio facilities configured to the faulty block.
The following actions are performed in fault cases with a hopping BTS:
TRX fault: Block the TRX. In case of baseband hopping, remove the frequency from the
MA(s) and recalculate the MA(s) and MAIOs for the remaining TRX(s).
BCF fault: Block the BCF. If only hopping capability was lost, the cells can be manually
changed into non-hopping mode.
BCCH recovery is executed normally but in case of a baseband hopping BTS all the
TRXs of the BTS, or all the TRXs of the layer if IUO is used, are blocked during the
operation.
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BSS03050: Frequency Hopping
User interface of Frequency Hopping
4 User interface of Frequency Hopping
Parameters of Frequency Hopping
The following parameters are related to Frequency Hopping.
BCF type (TYPE)
hopping mode of the cell (HOP/UHOP)
Mobile Allocation Frequency Lists (MA)
identification number of the MA list attached to the cell (MAL/UMAL)
initial frequencies of the transceivers (FREQ)
Hopping Sequence Numbers (HSN1, HSN2, and UHSN)
MAIO Offset (MO/UMO)
MAIO Step (MS/UMS)
•
•
•
•
•
•
•
•
On the Abis O&M interface, the hopping mode and the MA, MAIOs, and HSNs are sent
to the BCF when it is configured. If the BCF does not accept the configuration and sends
a negative acknowledgement, an alarm is set. Yet, the data is stored in the BSC
database until the user modifies it again.
With the MAIO Offset parameter you can set the lowest MAIO value per sector to
other than 0. This makes it possible to use the same MA list for two or more sectors in
the site without collisions. However, because the sectors controlled by one BCF operate
in frame synchronisation, the HSN values must be equal between the sectors in order to
each frequency to be used only once during one frame period. If the HSN values differ
between the sectors, collisions will occur regularly. Using the MAIO Offset parameter
requires that the sectors operate in frame synchronisation.
With the MAIO Step parameter you can use successive channel numbers within a
single cell. For example, with step value '2' 400kHz channel separation is achieved.
When both MAIO Offset and MAIO Step parameters are used, even re-use 1/1 is
possible in a 3-sector BTS site, without any co-channel collisions or detrimental
interference from adjacent frequency channels.
t
Tip: Make sure that the MA-list is long enough. For example, if you have a 3-sector
site, 4 TRXs in each, and you want to share a single MA-list between all of those with
400 kHz minimum channel separation, you have to reserve at least 18 frequencies for
the MA-list plus 3 BCCH frequencies, that is 21 frequencies altogether.
Creation of BB hopping BTS
A baseband frequency hopping BTS is created in a similar way to any BTS.
1. First the BCF is created. In this phase the BTS generation is given to the system,
checkings that are made later on are based on this information.
2. When the BTS is created, hopping related parameters of the BTS can be set.
3. The rest of the parameters and procedures are similar to the parameterisation of a
non-hopping BTS.
4. The hopping configuration parameters are transferred from the BSC to the BTS site
when the user unlocks the BTS. The BSC sends a configuration message via the
Abis O&M link to the BTS including CA, MA, MAIO, HSN, ARFCN, and hopping
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User interface of Frequency Hopping
BSS03050: Frequency Hopping
mode. The BCF (BTS-OMU) of the site then re-formats the hopping related
parameters and forwards them to the hopping control units of the BTS (CHDSP in
Nokia MetroSite and Nokia UltraSite, and DSP in Nokia Flexi EDGE BTS).
5. When the BTS is up and running, the hopping system is in place and working even
though no signal (except BCCH) is transferred. The call related hopping parameters
(MA, MAIO etc.) over the Abis telecom interface are not configuring the BTS any
more, they go to the MSS.
Creation of RF hopping BTS
The creation of an RF hopping BTS has MA-handling as an extra step.
1. First the BCF is created. In this phase the BTS generation is given to the system.
Checkings that are made later on are based on this information.
2. Before RF hopping of the BTS can be fully defined, the MA-lists must be defined at
the BSC-level.
3. When the BTS is created, the hopping related parameters of the BTS can be set.
The BTS must also be attached to an MA-list.
4. See steps 3 , 4 and 5 in Creation of BB hopping BTS.
Mobile Allocation Frequency List
With the commands of the BCCH and Mobile Allocation Frequency List and RA Handling
command group (EB) you can create, modify, remove, and display mobile allocation
frequency list objects in the BSS Radio Network Configuration Database. For more
information, see BCCH and Mobile Allocation Frequency List and RA Handling.
With the commands of the Base Transceiver Station Handling command group (EQ) you
attach any of these lists to a BTS. For more information, see Base Transceiver Station
Handling in BSC.
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