frequency hopping

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%