11-frequency hopping, maio management & synchronized radio network
DESCRIPTION
FHOP and MAIOTRANSCRIPT
Frequency Hopping, MAIO Management & Synchronized Radio
NetworkThis chapter contains the features Frequency Hopping, MAIO
Management and Synchronized Radio Networks.
11/03813-LZU 108 3704 Uae Rev G
Frequency Hopping
HFS – Hopping Frequency Set
GSM Radio Network Features
Principle of frequency hopping: Instead of transmitting and receiving bursts on a fixed frequency, the bursts will be sent on different frequencies.
A frequency change can be performed for every new burst sent, that is 217 times per second.
The hopping can be performed on all the frequencies allocated to a channel group. The hopping over the frequencies can be made in several ways. This slide shows so called cyclic frequency hopping.
Note that the BCCH (TS 0 on the BCCH carrier) does not hop, but is fixed.
11/03813-LZU 108 3704 Uae Rev G
Effect on the Air Interface
GSM Radio Network Features
Frequency diversity
Frequency hopping can reduce the influence of signal strength variations caused by multipath fading.
Multipath fading is frequency dependent. This implies that the fading dips appear at different locations for different frequencies. Thus a mobile utilizing frequency hopping will not remain in a specific fading dip for a longer time than one single burst. Thereby signal strength variations are broken up into pieces of a duration short enough for the interleaving and speech coding process to correct for errors. Multipath fading dips, causing low signal strength, are thus apparently leveled out, and slowly moving mobiles (and cars stuck at a red light) will perceive a more even radio environment. Frequency hopping makes most of the fading dips appear more shallow.
Interference averaging
Frequency hopping can also break up persistent interference into periodic occasions of single burst interference. The cell planning margin against situations of bad radio conditions can thus be decreased, since the probability of encountering these conditions decreases.
11/03813-LZU 108 3704 Uae Rev G
Frequency Diversity
GSM Radio Network Features
This figure shows the received signal strength as a function of distance for two different frequencies (dashed & thin solid). The Rayleigh fading dips appear in different places for different frequencies. The thick solid line corresponds to the apparent signal strength obtained by frequency hopping, known as frequency diversity.
11/03813-LZU 108 3704 Uae Rev G
Interference Diversity
GSM Radio Network Features
This slide illustrates schematically the effect on the C/I-distribution depending on what features are switched on. FH and BTSPC are using a Robin Hood principle, whereas DTX give a net gain in C/I (at least if the other features are active).
11/03813-LZU 108 3704 Uae Rev G
Achievements
GSM Radio Network Features
The benefits of frequency hopping are noticeable already when hopping over two frequencies.
The wider band the better.
A high traffic load will decrease the number of idle time slots and will increase the number of interfering bursts. In a situation where almost all time slots on all frequencies suffer from interference, there will be no gain from interference averaging.
Usage of DTX and dynamic power control will decrease the number of interfering bursts. This will increase the gain of interference averaging.
From a subscriber point of view, frequency hopping gives an improved speech quality in many situations. From an operator point of view, the benefits are:
tighter frequency reuse and increase in capacity,
a more robust radio environment,
a possibility to give subscribers a more uniform speech quality.
11/03813-LZU 108 3704 Uae Rev G
A higher RxQual can be tolerated
GSM Radio Network Features
When frequency hopping is used, a higher RxQual value can be tolerated. This is because the “bad” bursts are distributed more evenly so that the GSM coding and interleaving is utilized efficiently.
When the combination of frequency hopping and DTX is used an even higher rxqual value can be tolerated. The reason for this is not clear.
(note: with no FH and no DTX sometimes maximum acceptable rxqual for acceptable speech quality is 4.5)
RxQual is seldom a very good way of describing quality.
11/03813-LZU 108 3704 Uae Rev G
Capabilities
Up to 128 frequencies can be assigned per cell
Note: maximum of 32 frequencies per Channel Group (CHGR)
Frequencies can be reused (except the BCCH frequency) in other CHGRs within the cell
Note: Use MAIO planning to avoid co-channel interference
GSM Radio Network Features
Hopping Sequences - Cyclic
GSM Radio Network Features
There are two types of hopping sequences - cyclic and random. In a cyclic sequence the frequencies are used consecutively. This sequence gives a slightly better frequency diversity than the random sequences.
A cyclic sequence is specified by setting parameter HSN (hopping sequence number) to 0. There is only one cyclic sequence defined in the GSM specifications. The sequence of frequencies goes from the lowest absolute frequency number in the set of frequencies specified for that channel group, to the highest, and over again.
11/03813-LZU 108 3704 Uae Rev G
Hopping Sequences - Random
GSM Radio Network Features
A random hopping sequence is implemented as a pseudo-random sequence. The sequence is stored in a look-up table in the mobile as well as in the base stations. 63 independent sequences are defined. Which of the 63 sequences to be used is specified with parameter HSN.
The actual frequency to be used at each instant is obtained by an algorithm with the available frequencies, see 3GPP Technical Specification 45.002.
11/03813-LZU 108 3704 Uae Rev G
Two Hopping Modes
GSM Radio Network Features
In baseband hopping, each transmitter is assigned with a fixed frequency.
Synthesizer hopping means that one transmitter handles all bursts that belong to a specific connection.
11/03813-LZU 108 3704 Uae Rev G
Baseband Hopping
transmitter
filter
Baseband hopping : Each transmitter transmits on a fixed frequency.
The bursts from the transceiver controller are routed to the different
transmitters by a bus.
+
A narrow-band filter combiner can be used. To this combiner it is
possible to connect up to 6 TRX:s without more than 3dB combiner
loss.
-
It is impossible to hop on more frequencies than there are TX:s.
GSM Radio Network Features
The bursts are routed to the appropriate transmitter by a bus.
The benefit of baseband hopping is that low loss narrow band filter combiners with up to six inputs and only 3 dB loss can be used. This is because each TX transmits on a fixed frequency.
The negative is that it is impossible to have more frequencies than there are TXs.
Minimum carrier separation for filter combiners is 600 kHz.
11/03813-LZU 108 3704 Uae Rev G
Synthesizer hopping
+
-
Hybrid combiners must be used. When connecting many transmitters the
loss will be big.
GSM Radio Network Features
In this case the bursts of a connection are transmitted by one and the same TX, and the TX changes frequency for each burst. Since the transmitter transmits over many frequencies wide hybrid combiners must be used. These transmitters have only two inputs and about 3 dB loss.
The advantage of synthesizer hopping is that it is possible to hop on more frequencies than there are transmitters.
Minimum carrier separation for hybrid combiners is 400 kHz.
11/03813-LZU 108 3704 Uae Rev G
Co Filling at Baseband Hopping
•
controller
controller
controller
controller
f
0
f
1
transmitter
f
2
transmitter
f
3
transmitter
TRX1
TRX2
TRX3
TRX4
combiner
transmitter
filter
TS
0
TS
1
TS
2
TS
3
TS
4
TS
5
TS
6
TS
7
f
0
f
1
f
2
f
3
c
0
filling
c
0
filling
c
0
filling
c
0
filling
c
0
filling
c
0
filling
c
0
filling
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
SDCCH
TCH
BCCH
Co i.e. the BCCH carrier is special:
1. It contains the Broadcast Control Channel which must not be hopping.
2. It must always be on air since all mobiles measure SS on that frequency, i.e. the transmitter must send dummy bursts when nothing arrives from the controller.
The slide shows a configuration of 4 TRXs with 30 TCHs and hopping on the BCCH frequency
TS0 may cause alarms since it will normally not be used a lot if you choose TCH for maximum number of frequencies to hop on.
11/03813-LZU 108 3704 Uae Rev G
Co Filling at Synthesizer Hopping With an Extra Transmitter
•
•
•
All traffic bursts that are to be sent on Co are routed to Co transmitter.
TS
0
TS
1
TS
2
TS
3
TS
4
TS
5
TS
6
7
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
SDCCH
f
n
f
0
f
1
f
2
f
3
GSM Radio Network Features
A transmitter configured for synthesizer hopping can not perform Co filling (i.e. transmitting dummy bursts when nothing else arrives from the controller). There are different ways to solve this problem, one way is to equip the BTS with an extra fixed transmitter, which only transmits on Co. A bus routes the bursts to be sent on Co to this transmitter. When nothing arrives from the controller, the transmitter will send dummy bursts.
11/03813-LZU 108 3704 Uae Rev G
•
•
One transmitter acting only as Co filler and one “BCCH controller”
•
All traffic bursts that are to be sent on Co are routed to this
transmitter.
TS
0
TS
1
TS
2
TS
3
TS
4
TS
5
TS
6
7
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
SDCCH
f
n
f
0
f
1
f
2
f
3
Co Filling at Synthesizer Hopping
With Two Channel Groups
•
If utilization of hardware is more important than it is to hop on the
BCCH frequency.
Prior configurations can be seen as waist of hardware.
If it is not so important that the TCHs on the BCCH carrier are hopping the frequencies can be split into two channel groups, one hopping and one non-hopping.
11/03813-LZU 108 3704 Uae Rev G
MAIO MANAGEMENT
11/03813-LZU 108 3704 Uae Rev G
Purpose of MAIO Management
The MAIO Management feature provides increased control over synthesized frequency hopping to minimize channel interference within a site (or between sites if synchronized network is used).
This is beneficial in a network with tight re-use of frequencies, such as 1/1 & 1/3.
GSM Radio Network Features
MAIO Management provides increased control over synthesizer frequency hopping to avoid co- and adjacent channel interference within a cell as well as in co-sited or Synchronized cells. This is beneficial in a network with tight re-use of frequencies such as 1/1 & 1/3.
Note that MAIO Management only increases control over the interference between cells if the cells are synchronized, i.e. cells within a site using one TG or a site using Transceiver Group Synchronization or Synchronized Radio Networks.
11/03813-LZU 108 3704 Uae Rev G
Algorithm
At frequency hopping MAIO values are used (together with the HSN and the current FN) to point out the frequencies to be used from the HFS at an instant in time.
Cyclic hopping
Random hopping
"pointer" = (MAIO+random value) modulo (number of frequencies in HFS)
GSM Radio Network Features
FN Frame Number
11/03813-LZU 108 3704 Uae Rev G
Example
Cyclic hopping, 3 TRX:s in a cell, nine frequencies in the HFS. The current FN is 1.
The first TRX use frequency number:
(FN+MAIO) mod (# of frequencies in HFS) = (1+0) mod 9 = 1 (which will relate the pointer to the second frequency in the HFS
The next time FN=2 and the pointers will be shifted downwards one step.
0, 2, 4
Default MAIO list:
Example: Cyclic hopping, 3 TRXs, 9 frequencies and FN=1.
The default MAIO-list is 0, 2, 4. We can say that each TRX is assigned a MAIO number of its own.
11/03813-LZU 108 3704 Uae Rev G
Default MAIO list
The number of MAIO values in the default list are the same as the number of frequencies in the HFS.
The order of the MAIO values in the default list are arranged in a "first even then odd MAIO values" manner.
The actual MAIO values to be used for a CHGR depends on the number of TRXs for the CHGR.
GSM Radio Network Features
The number of MAIO values in the default list are the same as the number of frequencies in the HFS. The values themselves stretch from 0 up to one less than the number of frequencies in the HFS. E.g. If there are 15 frequencies in the HFS, the MAIO list will contain the values 0-14.
The order of the MAIO values in the default list are arranged in a "first even then odd MAIO values" manner. This means that the beginning of the list will consist of all even MAIO values in ascending order. After these even values all the odd values are arranged in ascending order. E.g. for a HG with HFS containing 7 frequencies the default list will be 0, 2, 4, 6, 1, 3, 5.
The actual MAIO values to be used for a CHGR depends on the number of TRXs for the CHGR. If e.g. three TRXs are used for a CHGR, only the first three MAIO values in the MAIO list will be used. With 7 frequencies in the HFS (as in the previous example), the used default MAIO values would be 0, 2, 4. The remaining values, i.e. 6, 1, 3, 5, will not be used unless additional TRXs are added.
11/03813-LZU 108 3704 Uae Rev G
Example of Default MAIO list
If there are seven frequencies in the HFS, the MAIO list will contain the values 0-6.
MAIO=0, 2, 4, 6, 1, 3, 5
If three TRXs are used for a CHGR, only the first three MAIO values in the MAIO list will be used, i.e. 0, 2, 4.
GSM Radio Network Features
Manual MAIO list
A manual MAIO list for a CHGR can be created by specifying up to 32 values for the parameter MAIO.
If the manual MAIO list is too short then random MAIO values will be added on to the end of the list.
If there is an invalid MAIO value in the manual MAIO list it will be skipped in favor of the next MAIO value in the list.
GSM Radio Network Features
A manual MAIO list for a CHGR can be created by specifying up to sixteen values for the parameter MAIO .
If the manual MAIO list is too short (i.e. the length of the MAIO list is less than the number of TRXs for the CHGR), then random MAIO values will be added on to the end of the list. This process will be randomized as much as is reasonable whilst minimizing the risk of having consecutive MAIOs in the list. This means that at installation of an additional TRX for a cell, additional MAIO values will be allocated.
If there is an invalid MAIO value (a value that is equal to or higher than the number of frequencies in the HFS) in the manual MAIO list it will be skipped in favor of the next MAIO value in the list. This means that any invalid MAIO values that are specified by the operator are not allocated and a randomized valid MAIO value will be allocated to the last BPC in the HG.
11/03813-LZU 108 3704 Uae Rev G
Recommendations
Manual MAIO Planning is beneficial to use when using a 1/1 re-use or when frequencies are repeated in different CHGRs in a cell
If there are adjacent frequencies within the HFSs, only even (or odd) MAIO values should be used within the site
When reusing frequencies in a cell, it is important that the frequency is not used at the same time in both the CHGRs.
By having different MAIO values for each CHGR, e.g. odd values in one and even in the other, collisions are avoided
GSM Radio Network Features
SYNCHRONIZED RADIO NETWORK
Synchronized Radio Network
Frame Synchronization between cells belonging to different sites is possible
MAIO Planning is not restricted to the site
ICDM (Inter Cell Dependency Matrix) can be used to identify interfering cells
Hopping Sequence Number
- All sites synchronized
GSM Radio Network Features
Synchronized Radio Network offers the possibility to frame synchronize cells located on different sites with each other. This gives opportunities to enhance performance even more for FLP networks, since interfering cells can be handled no matter on which site they are located. In a synchronized radio network interference is not only managed by planning of MAIO but also appropriate handling of for example HSN, TSC and FN Offset is needed. As a basis for the planning it is necessary to identify which cells are interfering each other, this is described in the ICDM (Inter-Cell Dependency Matrix) which can be assembled with the help of the Frequency Allocation Support (FAS) tool in OSS.
11/03813-LZU 108 3704 Uae Rev G
Increased frequency utilization
GSM Radio Network Features
Synchronization of cells allows a more efficient spectrum utilization for frequency hopping channels when combined with MAIO Management and tight reuse of frequencies, such as 1/1 and 1/3. The benefit is that traffic capacity can be increased within a radio network without requiring additional frequencies. This is valuable for operators with a limited set of available frequencies.
11/03813-LZU 108 3704 Uae Rev G
Interference Rejection Combining (IRC)
IRC performance vs MRC
3-5 dB for 1 non-synchronized interferer
Equal coverage
TSC
TSC*
TSC*
GSM Radio Network Features
Interference Rejection Combining is a new receiver algorithm for the transceiver which drastically improves interference robustness. Simulations show that IRC can provide a C/I gain of up to 11 dB, with a value in typical urban environments of around 5-6 dB, compared to the currently used receive algorithm.
A prerequisite for IRC is that two receive antennas (receive antenna diversity) are used. This means that there are two versions of the signal available in the transceiver that are slightly different due to the antenna diversity. IRC also uses the training sequence (as defined by the Training Sequence Code, TSC), which is a known bit pattern in the middle of each burst. By comparing the received signal with the training sequence it is possible to estimate the characteristics of the interfering signal. The IRC algorithm can utilize this information to efficiently remove interference from the wanted signal.
IRC performs best when the desired signal and the interfering signal are synchronized in time, since then the interfering signal is the same during the whole burst and the interference characteristics estimated during the training sequence are more likely to be valid for the whole burst.
In order to have synchronized interference between cells on the same site, the features FAJ 122 854 RBS 2000 Synchronization or FAJ 122 855 RBS 200 and 2000 in the same Cell might be needed depending on the site configuration and the RBS type. To also have synchronized interference between cell located on different sites, the feature FAJ 122 081 Synchronized Radio Networks is needed.
The gain that IRC provides will solve interference problems that are encountered on the uplink, this also means that radio network capacity can increase in places where the uplink is the limiting link. In all networks IRC will improve speech quality and data throughput in the uplink, thereby increasing subscriber satisfaction.
In radio environments not limited by interference, IRC will perform as well as the currently available receiver diversity algorithm.
IRC is available for all dTRU, EDGE sTRU and RBS 2308. Older transceivers cannot be supported due to the increased processing capacity required by the IRC algorithm.
(Today’s MRC* diversity gives ~3-5 dB in both C/N and C/I)
11/03813-LZU 108 3704 Uae Rev G
Synchronization areas
A Synchronized Radio Network is possible to deploy on a small scale within a limited area or on a grand scale over a larger area
Synchronization of cells in a GSM radio network is realized per:
TG
Radio Network
Parameters (I)
HOP is the switch for tuning frequency hopping on or off, defined per channel group. HOP defines whether all channels except the broadcast channel hop ( HOP = ON), or no channels at all hop (HOP = OFF).
HSN is the hopping sequence number, defined per CHGR. This parameter specifies which hopping sequence to be used. All timeslots in one channel group are configured with the same HSN. HSN = 0 yields a cyclic sequence. HSN = 1 to 63 yields pseudo-random sequences.
GSM Radio Network Features
Parameters (II)
FHOP selects which hopping method to be used, baseband (FHOP = BB) or synthesizer ( FHOP = SY) hopping. It is defined per TG.
COMB specifies which combiner type that has been connected, a wide-band hybrid combiner (COMB = HYB) or a narrow-band filter combiner (COMB = FLT). It is defined per TG. If a filter combiner is connected, only baseband hopping can be used.
GSM Radio Network Features
Parameters (III)
MAIO This parameter allows operators to specify a MAIO list of, up to 16 MAIO values (with a range of 0-31), in the order of allocation, to a channel group or specify the channel group to use default MAIO list (MAIO = DEFAULT).
BCCD Defines if the channel group frequencies are allowed (YES) or not (NO) for Immediate Assignment. It might not be possible to set BCCD=YES for all channel groups in the cell. This is due to restrictions on the maximum number of hopping frequencies allowed for Immediate Assignment and their maximum ranges for different frequency bands.
GSM Radio Network Features
Value Ranges and Default Values
GSM Radio Network Features
Parameter name
Default value
Recommended value
Value range
0-63
and frequency
and the bandwidth
•
9702689
C/I
consecutive fading dips.
6 minutes long.
averaging (if the network is planned using
frequency groups.)
frequencies.
9702816
11/03813-LZU 108 3704 Uae Rev G
Frequency Hopping
HFS – Hopping Frequency Set
GSM Radio Network Features
Principle of frequency hopping: Instead of transmitting and receiving bursts on a fixed frequency, the bursts will be sent on different frequencies.
A frequency change can be performed for every new burst sent, that is 217 times per second.
The hopping can be performed on all the frequencies allocated to a channel group. The hopping over the frequencies can be made in several ways. This slide shows so called cyclic frequency hopping.
Note that the BCCH (TS 0 on the BCCH carrier) does not hop, but is fixed.
11/03813-LZU 108 3704 Uae Rev G
Effect on the Air Interface
GSM Radio Network Features
Frequency diversity
Frequency hopping can reduce the influence of signal strength variations caused by multipath fading.
Multipath fading is frequency dependent. This implies that the fading dips appear at different locations for different frequencies. Thus a mobile utilizing frequency hopping will not remain in a specific fading dip for a longer time than one single burst. Thereby signal strength variations are broken up into pieces of a duration short enough for the interleaving and speech coding process to correct for errors. Multipath fading dips, causing low signal strength, are thus apparently leveled out, and slowly moving mobiles (and cars stuck at a red light) will perceive a more even radio environment. Frequency hopping makes most of the fading dips appear more shallow.
Interference averaging
Frequency hopping can also break up persistent interference into periodic occasions of single burst interference. The cell planning margin against situations of bad radio conditions can thus be decreased, since the probability of encountering these conditions decreases.
11/03813-LZU 108 3704 Uae Rev G
Frequency Diversity
GSM Radio Network Features
This figure shows the received signal strength as a function of distance for two different frequencies (dashed & thin solid). The Rayleigh fading dips appear in different places for different frequencies. The thick solid line corresponds to the apparent signal strength obtained by frequency hopping, known as frequency diversity.
11/03813-LZU 108 3704 Uae Rev G
Interference Diversity
GSM Radio Network Features
This slide illustrates schematically the effect on the C/I-distribution depending on what features are switched on. FH and BTSPC are using a Robin Hood principle, whereas DTX give a net gain in C/I (at least if the other features are active).
11/03813-LZU 108 3704 Uae Rev G
Achievements
GSM Radio Network Features
The benefits of frequency hopping are noticeable already when hopping over two frequencies.
The wider band the better.
A high traffic load will decrease the number of idle time slots and will increase the number of interfering bursts. In a situation where almost all time slots on all frequencies suffer from interference, there will be no gain from interference averaging.
Usage of DTX and dynamic power control will decrease the number of interfering bursts. This will increase the gain of interference averaging.
From a subscriber point of view, frequency hopping gives an improved speech quality in many situations. From an operator point of view, the benefits are:
tighter frequency reuse and increase in capacity,
a more robust radio environment,
a possibility to give subscribers a more uniform speech quality.
11/03813-LZU 108 3704 Uae Rev G
A higher RxQual can be tolerated
GSM Radio Network Features
When frequency hopping is used, a higher RxQual value can be tolerated. This is because the “bad” bursts are distributed more evenly so that the GSM coding and interleaving is utilized efficiently.
When the combination of frequency hopping and DTX is used an even higher rxqual value can be tolerated. The reason for this is not clear.
(note: with no FH and no DTX sometimes maximum acceptable rxqual for acceptable speech quality is 4.5)
RxQual is seldom a very good way of describing quality.
11/03813-LZU 108 3704 Uae Rev G
Capabilities
Up to 128 frequencies can be assigned per cell
Note: maximum of 32 frequencies per Channel Group (CHGR)
Frequencies can be reused (except the BCCH frequency) in other CHGRs within the cell
Note: Use MAIO planning to avoid co-channel interference
GSM Radio Network Features
Hopping Sequences - Cyclic
GSM Radio Network Features
There are two types of hopping sequences - cyclic and random. In a cyclic sequence the frequencies are used consecutively. This sequence gives a slightly better frequency diversity than the random sequences.
A cyclic sequence is specified by setting parameter HSN (hopping sequence number) to 0. There is only one cyclic sequence defined in the GSM specifications. The sequence of frequencies goes from the lowest absolute frequency number in the set of frequencies specified for that channel group, to the highest, and over again.
11/03813-LZU 108 3704 Uae Rev G
Hopping Sequences - Random
GSM Radio Network Features
A random hopping sequence is implemented as a pseudo-random sequence. The sequence is stored in a look-up table in the mobile as well as in the base stations. 63 independent sequences are defined. Which of the 63 sequences to be used is specified with parameter HSN.
The actual frequency to be used at each instant is obtained by an algorithm with the available frequencies, see 3GPP Technical Specification 45.002.
11/03813-LZU 108 3704 Uae Rev G
Two Hopping Modes
GSM Radio Network Features
In baseband hopping, each transmitter is assigned with a fixed frequency.
Synthesizer hopping means that one transmitter handles all bursts that belong to a specific connection.
11/03813-LZU 108 3704 Uae Rev G
Baseband Hopping
transmitter
filter
Baseband hopping : Each transmitter transmits on a fixed frequency.
The bursts from the transceiver controller are routed to the different
transmitters by a bus.
+
A narrow-band filter combiner can be used. To this combiner it is
possible to connect up to 6 TRX:s without more than 3dB combiner
loss.
-
It is impossible to hop on more frequencies than there are TX:s.
GSM Radio Network Features
The bursts are routed to the appropriate transmitter by a bus.
The benefit of baseband hopping is that low loss narrow band filter combiners with up to six inputs and only 3 dB loss can be used. This is because each TX transmits on a fixed frequency.
The negative is that it is impossible to have more frequencies than there are TXs.
Minimum carrier separation for filter combiners is 600 kHz.
11/03813-LZU 108 3704 Uae Rev G
Synthesizer hopping
+
-
Hybrid combiners must be used. When connecting many transmitters the
loss will be big.
GSM Radio Network Features
In this case the bursts of a connection are transmitted by one and the same TX, and the TX changes frequency for each burst. Since the transmitter transmits over many frequencies wide hybrid combiners must be used. These transmitters have only two inputs and about 3 dB loss.
The advantage of synthesizer hopping is that it is possible to hop on more frequencies than there are transmitters.
Minimum carrier separation for hybrid combiners is 400 kHz.
11/03813-LZU 108 3704 Uae Rev G
Co Filling at Baseband Hopping
•
controller
controller
controller
controller
f
0
f
1
transmitter
f
2
transmitter
f
3
transmitter
TRX1
TRX2
TRX3
TRX4
combiner
transmitter
filter
TS
0
TS
1
TS
2
TS
3
TS
4
TS
5
TS
6
TS
7
f
0
f
1
f
2
f
3
c
0
filling
c
0
filling
c
0
filling
c
0
filling
c
0
filling
c
0
filling
c
0
filling
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
SDCCH
TCH
BCCH
Co i.e. the BCCH carrier is special:
1. It contains the Broadcast Control Channel which must not be hopping.
2. It must always be on air since all mobiles measure SS on that frequency, i.e. the transmitter must send dummy bursts when nothing arrives from the controller.
The slide shows a configuration of 4 TRXs with 30 TCHs and hopping on the BCCH frequency
TS0 may cause alarms since it will normally not be used a lot if you choose TCH for maximum number of frequencies to hop on.
11/03813-LZU 108 3704 Uae Rev G
Co Filling at Synthesizer Hopping With an Extra Transmitter
•
•
•
All traffic bursts that are to be sent on Co are routed to Co transmitter.
TS
0
TS
1
TS
2
TS
3
TS
4
TS
5
TS
6
7
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
TCH
SDCCH
f
n
f
0
f
1
f
2
f
3
GSM Radio Network Features
A transmitter configured for synthesizer hopping can not perform Co filling (i.e. transmitting dummy bursts when nothing else arrives from the controller). There are different ways to solve this problem, one way is to equip the BTS with an extra fixed transmitter, which only transmits on Co. A bus routes the bursts to be sent on Co to this transmitter. When nothing arrives from the controller, the transmitter will send dummy bursts.
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One transmitter acting only as Co filler and one “BCCH controller”
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All traffic bursts that are to be sent on Co are routed to this
transmitter.
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Co Filling at Synthesizer Hopping
With Two Channel Groups
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If utilization of hardware is more important than it is to hop on the
BCCH frequency.
Prior configurations can be seen as waist of hardware.
If it is not so important that the TCHs on the BCCH carrier are hopping the frequencies can be split into two channel groups, one hopping and one non-hopping.
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MAIO MANAGEMENT
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Purpose of MAIO Management
The MAIO Management feature provides increased control over synthesized frequency hopping to minimize channel interference within a site (or between sites if synchronized network is used).
This is beneficial in a network with tight re-use of frequencies, such as 1/1 & 1/3.
GSM Radio Network Features
MAIO Management provides increased control over synthesizer frequency hopping to avoid co- and adjacent channel interference within a cell as well as in co-sited or Synchronized cells. This is beneficial in a network with tight re-use of frequencies such as 1/1 & 1/3.
Note that MAIO Management only increases control over the interference between cells if the cells are synchronized, i.e. cells within a site using one TG or a site using Transceiver Group Synchronization or Synchronized Radio Networks.
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Algorithm
At frequency hopping MAIO values are used (together with the HSN and the current FN) to point out the frequencies to be used from the HFS at an instant in time.
Cyclic hopping
Random hopping
"pointer" = (MAIO+random value) modulo (number of frequencies in HFS)
GSM Radio Network Features
FN Frame Number
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Example
Cyclic hopping, 3 TRX:s in a cell, nine frequencies in the HFS. The current FN is 1.
The first TRX use frequency number:
(FN+MAIO) mod (# of frequencies in HFS) = (1+0) mod 9 = 1 (which will relate the pointer to the second frequency in the HFS
The next time FN=2 and the pointers will be shifted downwards one step.
0, 2, 4
Default MAIO list:
Example: Cyclic hopping, 3 TRXs, 9 frequencies and FN=1.
The default MAIO-list is 0, 2, 4. We can say that each TRX is assigned a MAIO number of its own.
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Default MAIO list
The number of MAIO values in the default list are the same as the number of frequencies in the HFS.
The order of the MAIO values in the default list are arranged in a "first even then odd MAIO values" manner.
The actual MAIO values to be used for a CHGR depends on the number of TRXs for the CHGR.
GSM Radio Network Features
The number of MAIO values in the default list are the same as the number of frequencies in the HFS. The values themselves stretch from 0 up to one less than the number of frequencies in the HFS. E.g. If there are 15 frequencies in the HFS, the MAIO list will contain the values 0-14.
The order of the MAIO values in the default list are arranged in a "first even then odd MAIO values" manner. This means that the beginning of the list will consist of all even MAIO values in ascending order. After these even values all the odd values are arranged in ascending order. E.g. for a HG with HFS containing 7 frequencies the default list will be 0, 2, 4, 6, 1, 3, 5.
The actual MAIO values to be used for a CHGR depends on the number of TRXs for the CHGR. If e.g. three TRXs are used for a CHGR, only the first three MAIO values in the MAIO list will be used. With 7 frequencies in the HFS (as in the previous example), the used default MAIO values would be 0, 2, 4. The remaining values, i.e. 6, 1, 3, 5, will not be used unless additional TRXs are added.
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Example of Default MAIO list
If there are seven frequencies in the HFS, the MAIO list will contain the values 0-6.
MAIO=0, 2, 4, 6, 1, 3, 5
If three TRXs are used for a CHGR, only the first three MAIO values in the MAIO list will be used, i.e. 0, 2, 4.
GSM Radio Network Features
Manual MAIO list
A manual MAIO list for a CHGR can be created by specifying up to 32 values for the parameter MAIO.
If the manual MAIO list is too short then random MAIO values will be added on to the end of the list.
If there is an invalid MAIO value in the manual MAIO list it will be skipped in favor of the next MAIO value in the list.
GSM Radio Network Features
A manual MAIO list for a CHGR can be created by specifying up to sixteen values for the parameter MAIO .
If the manual MAIO list is too short (i.e. the length of the MAIO list is less than the number of TRXs for the CHGR), then random MAIO values will be added on to the end of the list. This process will be randomized as much as is reasonable whilst minimizing the risk of having consecutive MAIOs in the list. This means that at installation of an additional TRX for a cell, additional MAIO values will be allocated.
If there is an invalid MAIO value (a value that is equal to or higher than the number of frequencies in the HFS) in the manual MAIO list it will be skipped in favor of the next MAIO value in the list. This means that any invalid MAIO values that are specified by the operator are not allocated and a randomized valid MAIO value will be allocated to the last BPC in the HG.
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Recommendations
Manual MAIO Planning is beneficial to use when using a 1/1 re-use or when frequencies are repeated in different CHGRs in a cell
If there are adjacent frequencies within the HFSs, only even (or odd) MAIO values should be used within the site
When reusing frequencies in a cell, it is important that the frequency is not used at the same time in both the CHGRs.
By having different MAIO values for each CHGR, e.g. odd values in one and even in the other, collisions are avoided
GSM Radio Network Features
SYNCHRONIZED RADIO NETWORK
Synchronized Radio Network
Frame Synchronization between cells belonging to different sites is possible
MAIO Planning is not restricted to the site
ICDM (Inter Cell Dependency Matrix) can be used to identify interfering cells
Hopping Sequence Number
- All sites synchronized
GSM Radio Network Features
Synchronized Radio Network offers the possibility to frame synchronize cells located on different sites with each other. This gives opportunities to enhance performance even more for FLP networks, since interfering cells can be handled no matter on which site they are located. In a synchronized radio network interference is not only managed by planning of MAIO but also appropriate handling of for example HSN, TSC and FN Offset is needed. As a basis for the planning it is necessary to identify which cells are interfering each other, this is described in the ICDM (Inter-Cell Dependency Matrix) which can be assembled with the help of the Frequency Allocation Support (FAS) tool in OSS.
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Increased frequency utilization
GSM Radio Network Features
Synchronization of cells allows a more efficient spectrum utilization for frequency hopping channels when combined with MAIO Management and tight reuse of frequencies, such as 1/1 and 1/3. The benefit is that traffic capacity can be increased within a radio network without requiring additional frequencies. This is valuable for operators with a limited set of available frequencies.
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Interference Rejection Combining (IRC)
IRC performance vs MRC
3-5 dB for 1 non-synchronized interferer
Equal coverage
TSC
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TSC*
GSM Radio Network Features
Interference Rejection Combining is a new receiver algorithm for the transceiver which drastically improves interference robustness. Simulations show that IRC can provide a C/I gain of up to 11 dB, with a value in typical urban environments of around 5-6 dB, compared to the currently used receive algorithm.
A prerequisite for IRC is that two receive antennas (receive antenna diversity) are used. This means that there are two versions of the signal available in the transceiver that are slightly different due to the antenna diversity. IRC also uses the training sequence (as defined by the Training Sequence Code, TSC), which is a known bit pattern in the middle of each burst. By comparing the received signal with the training sequence it is possible to estimate the characteristics of the interfering signal. The IRC algorithm can utilize this information to efficiently remove interference from the wanted signal.
IRC performs best when the desired signal and the interfering signal are synchronized in time, since then the interfering signal is the same during the whole burst and the interference characteristics estimated during the training sequence are more likely to be valid for the whole burst.
In order to have synchronized interference between cells on the same site, the features FAJ 122 854 RBS 2000 Synchronization or FAJ 122 855 RBS 200 and 2000 in the same Cell might be needed depending on the site configuration and the RBS type. To also have synchronized interference between cell located on different sites, the feature FAJ 122 081 Synchronized Radio Networks is needed.
The gain that IRC provides will solve interference problems that are encountered on the uplink, this also means that radio network capacity can increase in places where the uplink is the limiting link. In all networks IRC will improve speech quality and data throughput in the uplink, thereby increasing subscriber satisfaction.
In radio environments not limited by interference, IRC will perform as well as the currently available receiver diversity algorithm.
IRC is available for all dTRU, EDGE sTRU and RBS 2308. Older transceivers cannot be supported due to the increased processing capacity required by the IRC algorithm.
(Today’s MRC* diversity gives ~3-5 dB in both C/N and C/I)
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Synchronization areas
A Synchronized Radio Network is possible to deploy on a small scale within a limited area or on a grand scale over a larger area
Synchronization of cells in a GSM radio network is realized per:
TG
Radio Network
Parameters (I)
HOP is the switch for tuning frequency hopping on or off, defined per channel group. HOP defines whether all channels except the broadcast channel hop ( HOP = ON), or no channels at all hop (HOP = OFF).
HSN is the hopping sequence number, defined per CHGR. This parameter specifies which hopping sequence to be used. All timeslots in one channel group are configured with the same HSN. HSN = 0 yields a cyclic sequence. HSN = 1 to 63 yields pseudo-random sequences.
GSM Radio Network Features
Parameters (II)
FHOP selects which hopping method to be used, baseband (FHOP = BB) or synthesizer ( FHOP = SY) hopping. It is defined per TG.
COMB specifies which combiner type that has been connected, a wide-band hybrid combiner (COMB = HYB) or a narrow-band filter combiner (COMB = FLT). It is defined per TG. If a filter combiner is connected, only baseband hopping can be used.
GSM Radio Network Features
Parameters (III)
MAIO This parameter allows operators to specify a MAIO list of, up to 16 MAIO values (with a range of 0-31), in the order of allocation, to a channel group or specify the channel group to use default MAIO list (MAIO = DEFAULT).
BCCD Defines if the channel group frequencies are allowed (YES) or not (NO) for Immediate Assignment. It might not be possible to set BCCD=YES for all channel groups in the cell. This is due to restrictions on the maximum number of hopping frequencies allowed for Immediate Assignment and their maximum ranges for different frequency bands.
GSM Radio Network Features
Value Ranges and Default Values
GSM Radio Network Features
Parameter name
Default value
Recommended value
Value range
0-63
and frequency
and the bandwidth
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C/I
consecutive fading dips.
6 minutes long.
averaging (if the network is planned using
frequency groups.)
frequencies.
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