1
General concept General concept of of
Frequency hoppingFrequency hopping
Slide : 2
BackgroundBackground
During a call, a number of physical effects influence theperceived radio environment between a mobile station and a
base station. One such effect is multipath fading, whichmeans that transmitted signals reach the receiver via multiple
paths. Depending on the difference in path length.Another effect is various types of interference. The
dominating type is normally co-channel interference, butother types, such as adjacent channel interference,
intermodulation products, military sources etc. must beconsidered as well.
Slide : 3
Multipath fadingMultipath fading
The destructive interference produced by multipath fading is called “fading-dips”. Fading dips may cause speech quality degradation.
For different frequencies, the fading dips will occur at
slightly different positions in space.
Slide : 4
Co-channel interferenceCo-channel interference
The interference situation for a mobile is strongly dependent on which frequency and time-slot that the mobile happens to use.
Normally co-channel interference is caused by frequency re-use
Slide : 5
What can be achivedWhat can be achived
Frequency diversityInterference averaging
Slide : 6
Frequency diversityFrequency 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.
Slide : 7
Interference averagingInterference averaging
Frequency hopping can also break up persistent interference into periodic occasions of single burst interference.
Changing frequency at each burst offers a way to improve the interference situation described above. The co-channel interference will change at every burst.
The more frequencies that are used in the hopping, the more rare such frequency collisions will be.
Slide : 8
Short technical descriptionShort technical description
Baseband frequency hoppingSynthesizer frequency hopping
Slide : 9
Baseband frequency hoppingBaseband frequency hopping
At baseband hopping each transmitter operates
on a fixed frequency.The advantage with this mode is that narrow-band
tuneable filter combiners can be used.The disadvantage is that it is not possible to use a
larger number of frequencies than there are
transmitters.
Slide : 10
Baseband frequency hoppingBaseband frequency hopping
ControllerTRX1
ControllerTRX4
ControllerTRX3
ControllerTRX2
Transmitterf1
Transmitterf4
Transmitterf3
Transmitterf2
Bus for routing of burst
Combiner
X
X
X
X
Slide : 11
Synthesizer frequency Synthesizer frequency hoppinghopping
The transmitter tunes to correct frequency at transmission of each burst.The advantage is that the number of frequencies that can be used for hopping is not dependent on the number of transmitters . The disadvantage is that wide-band hybrid combiners have to be used .
Slide : 12
Synthesizer frequency Synthesizer frequency hoppinghopping
ControllerTRX1
ControllerTRX4
ControllerTRX3
ControllerTRX2
Transmitterf1,f2,…,fn
Transmitterf1,f2,…,fn
Transmitterf1,f2,…,fn
Transmitterf1,f2,…,fn Hybrid
Combiner
Slide : 13
AlgorithmAlgorithm
Hopping sequenceCyclic hoppingRandom hopping
Interference avoidOrthogonal hoppingIndependence hopping
Slide : 14
Cyclic hoppingCyclic hopping
In cyclic hopping the frequencies are used in aconsecutive order. For instance,the sequence offrequencies for cyclic hopping between fourfrequencies may appear as follows:
... , f 4 , f 1 , f 2 , f 3 , f 4 , f 1 , f 2 , f 3 , f 4 , f 1 , f 2 , ...
A cyclic sequence is specified by setting theparameter HSN (hopping sequence number) to zero.
Slide : 15
Random hoppingRandom hopping
A random hopping sequence is actually implemented as apseudo-random sequence. 63 independent sequences are defined. When random hopping is used, the frequencies will beused (pseudo-) randomly, and a hopping sequence for fourfrequencies may appear as follows:
... , f 1 , f 4 , f 4 , f 3 , f 1 , f 2 , f 4 , f 1 , f 3 , f 3 , f 2 , ...
The period for a random sequence is 6 minutes.
Slide : 16
Orthogonal sequencesOrthogonal sequences
In the baseband hopping, four channels utilize thesame time slot. They will be given the different
HSN. In order not to interfere with each other, they maynot use the same frequency simultaneously. A frequency offset is automatically assignedto each channel at configuration. Each traffic channel uses the same sequence, butwith different frequencies at each instance in time.
Slide : 17
Orthogonal sequences with Orthogonal sequences with Baseband hoppingBaseband hopping
The random sequence of baseband hopping will appear as
follows for four frequencies:
ControllerTRX1
ControllerTRX4
ControllerTRX3
ControllerTRX2
Transmitterf1
Transmitterf4
Transmitterf3
Transmitterf2
Bus for routing of burst
Combiner
X
X
X
X
... , f 1 , f 4 , f 4 , f 3 , f 1 , f 2 , ...
... , f 2 , f 1 , f 1 , f 4 , f 2 , f 3, ...
... , f 3 , f 2 , f 2 , f 1 , f 3 , f 4 , ...
... , f 4 , f 3 , f 3 , f 2 , f 4 , f 1, ...
Slide : 18
Orthogonal sequences with SFHOrthogonal sequences with SFH
Control orthogonal sequence by MAIO and HSN
1. MAIO (Mobile Allocation Index Offset)
Define the first frequency of sequence for the first burst.
2. HSN (Hopping Sequence Number)
Define the sequence of frequency for the next burst.
HSN = 0 : Cyclic hopping
HSN = 1-63 : Pseudo-random hopping
Slide : 19
Orthogonal sequences with SFHOrthogonal sequences with SFH
The random sequence of synthesizer hopping will appear
as follows for eight frequencies: (HSN = 0)
ControllerTRX1
ControllerTRX4
ControllerTRX3
ControllerTRX2
Transmitterf1, f2, .., f8
Transmitterf1, f2, .., f8
Transmitterf1, f2, .., f8
Transmitterf1, f2, .., f8
Combiner
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 2)
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 0)
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 4)
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 6)
Index : 0, 1, 2, 3, 4, 5, 6, 7
fn : frequency of the first burstfn : frequency of the second burst
Slide : 20
Independence sequencesIndependence sequences
For the interference averaging mechanism to work well,
the sequence of frequencies in co-channel cells must be
different. Connections in these cells will then use the same
frequencies, but not always at the same time. The number of collisions per second will depend on the
number of frequencies in the channel group.
Slide : 21
Independence sequencesIndependence sequences
The frequency collisions, i.e. the instances of co-channel
disturbance, are indicated with bold type:
Cell 1: ... , f 1 , f 4 , f 4 , f 3 , f 1 , f 2 , f 3 , f 1 , f 3 , f 4 , f 2 , ...
Cell 2: ... , f 3 , f 1 , f 1 , f 1 , f 4 , f 3 , f 2 , f 1 , f 2 , f 1 , f 4 , ...
Cell 3: ... , f 3 , f 4 , f 3 , f 3 , f 2 , f 1 , f 4 , f 1 , f 3 , f 2 , f 1 , ...
Since there is only one cyclic sequence, cyclic sequences
can be orthogonal (if they have different MAIO), but never
independent.
Slide : 22
Implementation with SFHImplementation with SFH
Constrain Separate frequency band for BCCHRe-use patternMAIOHSNFraction load
Slide : 23
ConstrainConstrain
HW & SW constrainCoverage overlapping constrainFrequency constrain
Slide : 24
HW & SW ConstrainHW & SW Constrain
HW required for SFH
TPU2, HPA, MPA, HYCOM, DUCOM, DUAMCO
SW required for SFHBS-20/21 and BS 60/61 BR3.7 and higher
BS 11 Release Version S2 and higher
BS240 BR5.0 and higher
Slide : 25
Coverage overlapping Coverage overlapping constrainconstrain
Due to SFH with 1x1 or 1x3 are tight re-use patterns then coverage control is major constrain.
Homogeneous network is recommended.
Slide : 26
Frequency constrainFrequency constrain
Performance of SFH depends on one factor which called “Fractional load”
Maximum fractional load is 50% means number of frequency required is at least 2 time number of TCH Trxs used.
Slide : 27
Separate frequency band for Separate frequency band for BCCHBCCH
BCCH cannot cope with high interference as
TCH due to : BCCH is not hop with SFH. Power control and DTX are not support on BCCH.
Siemens recommends number of frequencies for
BCCH band is 20 frequencies.
Slide : 28
Re-use pattern for SFHRe-use pattern for SFH
Standard re-use pattern
1. Re-use 1x1
2. Re-use 1x3
Other re-use pattern
1. Re-use 2x2 (or re-use 2x1)
2. Multi re-use pattern for SFH
Slide : 29
Re-use 1x1Re-use 1x1
Define every frequencies to every BTS. Avoid co-channel by MAIO and HSN Consider all frequencies assigned as frequency group A re-
use pattern will be as follow:
GroupA
GroupAGroupA
GroupA
GroupAGroupA
GroupA
GroupAGroupA
Slide : 30
Re-use 1x3Re-use 1x3
Separate all frequencies into 3 groups. Define 3 frequency groups to every sites. Avoid co-channel by MAIO and HSN Consider all frequencies assigned as frequency group A,B and C re-
use pattern will be as follow:
GroupA
GroupCGroupB
GroupA
GroupCGroupB
GroupA
GroupCGroupB
Slide : 31
Mobile allocation index offsetMobile allocation index offset
Define the first frequency of group for the first burst.
Index 0 1 2 3 4 … N-1
Frequency group f1 f2 f3 f4 f5 .. fn
Slide : 32
Example of MAIO settingExample of MAIO setting
The random sequence of synthesizer hopping will appear
as follows for eight frequencies: (HSN = 0)
ControllerTRX1
ControllerTRX4
ControllerTRX3
ControllerTRX2
Transmitterf1, f2, .., f8
Transmitterf1, f2, .., f8
Transmitterf1, f2, .., f8
Transmitterf1, f2, .., f8
Combiner
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 2)
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 0)
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 4)
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 6)
Index : 0, 1, 2, 3, 4, 5, 6, 7
fn : frequency of the first burstfn : frequency of the second burst
Slide : 33
Fraction loadFraction load
Ratio to determine how tight of frequency re-use for SFH.
Define by :Number of frequencies used at a time (per re-use cluster) * 100
Number of frequencies per group
Siemens recommends fraction load = 35-40% GSM defines maximum fraction load = 50%
Slide : 34
Example of fraction load Example of fraction load calculationcalculation
1x3
Number of frequencies : 46
Number of frequencies for BCCH and GB : 16
Number of TCH frequencies per group : 10
Site configuration : 6+6+6 (Tch : 5+5+5)
Fractional load = 5/10 = 50%
Slide : 35
Example of fraction load Example of fraction load calculationcalculation
1x1
Number of frequencies : 46
Number of frequencies for BCCH and GB : 16
Number of TCH frequencies per group : 30
Site configuration : 6+6+6 (Tch : 5+5+5)
Fractional load = 15/30 = 50%