Frequency Hopping in

GSM Networks

Outline

Frequency Hopping in GSM Networks

Implementation Aspects

Frequency Assignment in FH Networks

Summary

Implementation Aspects

Frequency Hopping in GSM Networks

Frame N° 0Frame N° 1Frame N° 2Frame N° 3

Baseband FH

RF1

RF2

RF3

RF4

BB1

BB2

BB3

BB4

Logical Channel

1

2

3

4

Synthesizer FH

• Mobiles use Synthesizer Hopping only• BS implementation: power down, synthesizer re-

tuning and power up again within guard period 2 Synthesizers are implemented

RF1..n

RF1..n

RF1..n

BB1

BB2

BB3

BB4

RF1..n

Logical Channel

1

2

3

4

Implementation AspectsKey Differences Between

Baseband and Synthesizer FH

Baseband FH Synthesizer FH

Implementation Aspects Combining Equipment in

Baseband and Synthesizer FH

RF1

RF2

RF3

RF4

BB1

BB2

BB3

BB4

1

2

3

4

Filt

er

Com

bin

ing

TX Antenna

RF1..n

RF1..n

RF1..n

BB1

BB2

BB3

BB4

RF1..n

1

2

3

4H

ybrid

Co

mb

ing

TX Antenna

• Narrow Band• Low insertion loss (3-4 dB)

• Wide band• Higher insertion losses (~3 dB/stage)• On-air combining possible (DUCOM)

• Software Release: BR 3.7 or higher

• Cell Synchronization: up to 2/2/2 BS 6x/2x

up to 8/8/8 BS 24x

• No. of Hopping Frequencies:max. 16 per cell (BFH incl.

BCCH)max. 15 per cell (SFH w/o

BCCH)max. 64 per cell with BR 6.0

• BS11: SFH only (BR 4.0)

Implementation Aspects Hardware and Software for

Synthesized Frequency Hopping

• Baseband hopping Narrowband RFcombining sufficient

BCCH TRX except for TS0 may hop

• Synthesizer hopping Wideband RF combining required

One TRX per hopping frequency required!

• No. of RF = No. of TRX

• No. of RF > No. of TRX BCCH TRX must not hop

More hopping frequencies than TRXs feasible

Implementation Aspects Key Differences Between Baseband and

Synthesizer FH

Implementation AspectsHardware Requirements:

Repeater Wideband Repeaters:

• Usable for SFH and BFH

• Careful implementation (amplification of

signals

in the whole frequency band)

Channel selective Repeaters:

• Usable for BFH

• Number of frequencies is limited

• Usually not usable in tight reuse scenarios

Frequency Assignment in Hopping Networks

Frequency Hopping in GSM Networks

Frequency PlanningProcess Frequency

Assignment

Split of BandBCCH - TCH

DedicatedCommon

Multiple Reuse

Planning of BoundariesHopping – Non Hopping

Available Spectrumfor Hopping

Frequencyassignment with

fixed reuse schemes

Reuse 1x3 Reuse 1x1 other

Tools Interference Table Separation Settings

Tool optimizedfrequencyassignment

MAIO and HSNPlanning

Cyclic HoppingRandom Hopping

DatabaseGeneration

Planning of AnchorFrequencies in SFH

• Guideline for RF-planners

• Focus on SFH planning and hopping TCH - carriers

• BCCH - carrier assignment: planning with tool is always recommended

• Planning must be adjusted to each individual network

Frequency Planning Common Band - Dedicated Band -

Multiple Re-Use Patterns

5 hopping frequenciesPC on, DTX on

[%]

90%@FER2%

Dedicated Band 71.8%

Dedicated Band

15 BCCH carriers 28 TCH carriersCommon Band

59.7%

Common Bandtotal operator bandwidth 8.6 MHz = 43

carriers

43 carriers for both BCCH and TCH

MRP 54.3%

15 BCCH carriers12 TCH + 9 TCH + 7 TCH carriers

Multiple Re-use Patterns (MRP)

Achievable System Load

Fixed reuse scheme to all hopping cells

possible reuses:3/9, 2/6, 1/3, 1/1

Tool supported frequency assignment based on interference matrix considering FH gains

Frequency PlanningFrequency groups - Tool

supported planning

TCH 1 TCH 3

TCH 2

TCH 1 TCH 3

TCH 2

TCH 1 TCH 3

TCH 2

TCH 1 TCH 3

TCH 2

Frequency Planning Planning of BCCH

BCCH 3 BCCH 2

BCCH 1

BCCH 9 BCCH 8

BCCH 7

BCCH 6 BCCH 5

BCCH 4

BCCH 13 BCCH 11

BCCH 10

BCCHe.g. 4 x 12 Reuse

• Reliability

• Neighbor Measurements

• BSIC Decoding

• BCCH Frequency active at all timeslots in the downlink-> no interference averaging

Cluster 1/3

Channel

1, 4, 7, 10, ...

2, 5, 8, 11, ...

3, 6, 9, 12, ...

With a deliberately MAIO - assignment and identical HSN assignment to sectors you can avoid adjacent-channel interference between the sectors within one site

Frequency Planning Examples for frequency

groups (I)

Co-channel interference is avoided by the frequency groups MAIO TRX1 TRX2 TRX3 ...

Sector 1 0 2 4 ...

Sector 2 1 3 5 ...

Sector 3 0 2 4 ...

Min # RF 6 12 18

TCH C TCH B

TCH A

TCH C TCH B

TCH A

TCH C TCH B

TCH A

TCH C TCH B

TCH A

TCH C TCH B

TCH A

TCH C TCH B

TCH ATCH A

TCH B

TCH C

Frequency Planning Examples for frequency

groups (II)• Each sector within a site

uses a different Frequency Group

• No co-channel collisions between sectors of a site

• Synchronisation between the sectors and MAIO management avoid adjacent channel collisions

• Homogeneous network:no co-channel collisions between serving cell and all nearest neighbour cells

TCH uses each frequency onlypart of the time (e.g. 50%)

50% fractional load

TCH 1 TCH 3

TCH 2

TCH 1 TCH 3

TCH 2

TCH 3

TCH 2

TCH 1 TCH 3

TCH 2

TCH 1

Cluster 1/1

• All sectors same frequency group

• Identical HSN to sectors of one site

• MAIO assignment to avoid co- and adjacent channel interference

Frequency PlanningExamples for frequency

groups (III)

MAIO TRX1 TRX2 TRX3 TRX4 ...

Sector 1 0 6 12 18 ...

Sector 2 2 8 14 20 ...

Sector 3 4 10 16 22 ...

Min # RF 6 12 18 24

Frequency PlanningExamples for frequency

groups (IV)

• Each sector within a site uses the same frequency group

• Synchronisation between the sectors and MAIO management required to avoid co-channel collisions

• Homogeneous network:Co-channel collisions between serving cell and nearest neighbor

TCH TCH

TCH

TCH TCH

TCH

TCH TCH

TCH

TCH TCH

TCH

Frequency PlanningHopping Sequence Generation

(I)MAI = (FN + MAIO) modulo N if HSN = 0 (cyclic hopping)

GSM 05.02.

MAI ... Mobile Allocation Index (integer 1...N-1)

FN ... TDMA Frame Number (0... 26*51*2048-1 = 2 715 647)

MAIO ... Mobile Allocation Index Offset (0 ... N -1)

N ... Number of allocated frequencies For example: (MAIO=0)

MA = 1,4,7,10,13,16,19,21,24,27,30,33,36,39,41

set of ARFCN numbers to be used in the hopping

sequence N=15

1. burst FN = 0: MAI = (0 + 0) mod 15 = 0 ARFCN = 12. burst FN = 1: MAI = (1 + 0) mod 15 = 1 ARFCN = 4

14. burst FN = 14: MAI = (14 + 0) mod 15 = 14 ARFCN = 4115. burst FN = 15: MAI = (15 + 0) mod 15 = 0 ARFCN = 1 16. burst FN = 16: MAI = (16 + 0) mod 15 = 1 ARFCN = 4etc...

Frequency PlanningHopping Sequence Generation

(II)MAI = (S + MAIO) modulo N if HSN 0 (random hopping)

with:

S = M’ if M’ < N

S = (M’ + T’) modulo N else

M’ = M modulo [2^Integer(log2(N)+1)]

T’ = T3 modulo [2^Integer(log2(N)+1)]

M = T2 + RNTABLE((HSN xor T1R)+T3)

T1R, T2, T3 ... Different Time ParameterRNTABLE ... Table of 114 Integer numbers

Frequency PlanningExample for MAIO -

Management (I) Frequency group 1x1 reuse / Random Hopping (1, 2, 10, 7, . . . )

10

7

Time (TDMA - frame)

Time (TDMA - frame)

1

35

911

13

1517

2

46

8

TRX0

TRX1

TRX2

TRX3

BCCH

MAIO = 2

MAIO = 8

MAIO = 14

TRX0

TRX1

TRX2

BCCH

MAIO = 4

MAIO = 10

MAIO = 16 TRX3

TRX0

TRX1

TRX2

TRX3

BCCH

MAIO = 0

MAIO = 6

MAIO = 12

1012

14

1618

1 2 3 4 5 6 1817161514131211987 10

1214

16

182

4

68

7

9

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

. . .

Time (TDMA - frame)

Frequency PlanningExample for MAIO -

Management (II) Frequency group 1x1 reuse / Random Hopping (1, 2, 10, 7, . . . )

1 2 3 4 5 6 1817161514131211987 10

Avoid Co - channel collision:

min # RF = number of hopping TRX (example 9 frequencies)

Avoid Adjacent - channel collision:

only odd or even RF numbers on air at same time

Minimum total number of frequencies for hopping system with MAIO - Management = 2* number of hopping TRX of site

(18 frequencies in example)

TRX0

TRX1

TRX2

TRX3

BCCH

MAIO = 2

MAIO = 8

MAIO = 14

TRX0

TRX1

TRX2

BCCH

MAIO = 4

MAIO = 10

MAIO = 16 TRX3

TRX0

TRX1

TRX2

TRX3

BCCH

MAIO = 0

MAIO = 6

MAIO = 12

Frequency PlanningExamples for frequency groups

and MAIO - Assignment

TRX0

TRX1

TRX2

TRX0

TRX1

TRX2

TRX0

TRX1

TRX2

TRX0

TRX1

TRX2

TRX0

TRX1

TRX2

TRX0

TRX1

TRX2

TRX0

TRX1

TRX2

HSN = 1

HSN = 2

HSN = 3

TRX0

TRX1

TRX2

TRX3

f B

f B

f B

f B

f B

f B

f B

f C

f C

f C

f C

f C

f C

f C TRX3

TRX0

TRX1

TRX2

TRX3

BCCH

BCCHBCCH

BCCH

BCCHBCCH

BCCH BCCH

BCCH

MAIO = 0

MAIO = 1MAIO = 0

MAIO = 0

MAIO = 1MAIO = 0

MAIO = 0 MAIO = 1

MAIO = 0

MAIO = 2

MAIO = 3MAIO = 2

MAIO = 2

MAIO = 3MAIO = 2

MAIO = 2 MAIO = 3

MAIO = 2

f A

f A

f A

f A

f A

f A

f A

MAIO = 5MAIO = 4

MAIO = 4

Frequency group: A: 1 4 7 10 13 16B: 2 5 8 11 14 17C: 3 6 9 12 15 18

Frequency Planning ToolsThe Automatic Frequency

Planning Process

Input datafrom radio networkplanning tool

•Automatized Planning Routines•Variety of Planning Algorithms

•Setting of planning constraints•Common / Dedicated Band Planning

•Global / Local Parameter Settings

Frequency Assignment

Live Network

Data

Minimisation of

interference

•Consideration of FH, PC, DTX

Evaluation of the assignments•C/I and FER plots•C/I and FER analysis on per carrier basis

Evaluation of the assignments•C/I and FER plots•C/I and FER analysis on per carrier basis

Frequency Planning ToolsThe SIEMENS Advanced

Automatic Frequency Planning Tool

Efficient algorithms for different optimization targets: Minimizing global interference

Minimizing worst interfering cell relations

...

Features for advanced network planning strategies Frequency hopping

Power Control

Discontinuous transmission

Graphical evaluation of frequency assignments based on C/I

FER

Very good results in European research program COST 259 benchmarks in quality of result at short execution times (typically seconds to minutes)

High performance proved in live networks with different customers

Frequency Planning Tools Consideration of Radio Link

Control Options Automatic consideration of hopping gains and

interference reduction due to PC and DTX on cell basis

during

• interference matrix calculation

• optimum assignment of frequencies by using highly

efficient optimisation algorithms

Graphical evaluation of the assignment results based

on FER

Frequency Planning Tools

Required C/I in FH-GSM (TU3),

Cyclic Hopping

FH Gains as determined via Real Network Simulations

Shift: 6.5 dB 13.5 dBGain: up to 7 dB

NH2 Ch3 Ch4 Ch5 Ch8 Ch

50%

Frequency AssignmentFrequency Reuse & C/I values

(Non Hopping) Required no. of frequencies Cluster size / Reuse distance: q = SQRT(3*N) C/I rule of thump: C/I abs 1,5 * N2

N Anzahl f q C/I [dB]2 6 2,45 7,783 9 3,00 11,304 12 3,46 13,805 15 3,87 15,746 18 4,24 17,327 21 4,58 18,668 24 4,90 19,829 27 5,20 20,8510 30 5,48 21,7612 36 6,00 23,3415 45 6,71 25,2818 54 7,35 26,8720 60 7,75 27,78

Frequency Planning Tools Analyses of FER

Graphical FER analysis of an SFH network

1x3 reuse, 0,3 fractional load 1x3 reuse, 0,6 fractional load

< 1%

< 2 %

< 3 %

3 %

FER in %

< 1%

< 2 %

< 3 %

3 %

FER in %

Frequency AssignmentExample for Tool-supported

Planned Reuse (I)

3

33

4

443

22

3

43

3

33

4

22

4

44

4

443

33

2

44

2

44Network Example:

• 11 Sites

• 33 Cells• 6 cells 2 TRX• 12 cells 3 TRX• 15 cells 4 TRX• 33 TRX BCCH• 75 TRX TCH

No. of TRX

Frequency AssignmentExample for Tool-supported

Planned Reuse (II)Given Spectrum: 42 channels

12 frequencies for BCCH - TRX

30 frequencies for TCH - TRX (hopping)

Reuse of: 4 30/4 = 7.5 frequencies per cell in average

5 30/5 = 6 frequencies per cell in average

6 30/6 = 5 frequencies per cell in average

7 30/7 = 4.2 frequencies per cell in average

Network Example:• 11 Sites• 33 Cells• 6 cells 2 TRX• 12 cells 3 TRX• 15 cells 4 TRX

Frequency AssignmentExample for Tool-supported

Planned Reuse (III)

Planning Rule: (example)

1 Hopping TRX 3 frequencies2 Hopping TRX 4 frequencies3 Hopping TRX 6 frequencies

No. of assigned

frequencies for FH

Frequency Reuse Factor:

156 / 33 = 4.7 frequ. / cell in average

30 frequ. / 4.7 frequ. per cell = 6.3

4 / 6

4 / 66 / 4

3 / 4

3 / 44 / 3

2 / 3

4 / 66 / 4

No. of TRX

Network Example:• 11 Sites• 33 Cells• 6 cells 2 TRX• 12 cells 3 TRX• 15 cells 4 TRX

Frequency AssignmentExample for Tool-supported

Planned Reuse (IV)Separations for hopping TCH:• Intra cell separation: 3

• Intra site separation: 1

• Neighbour separation: 1

Interference Matrix for hopping TCH:• co-channel: C/I curve 7 dB (50% probability)• adjacent channel: C/I curve -6 dB (50% probability)

MAIO and HSN:• HSN = 0 for all cells (cyclic hopping)• MAIO = 0 for TRX1 (TRX0 = BCCH)

• MAIO = 1 for TRX2• MAIO = 2 for TRX3 etc.

Frequency AssignmentExample for Tool-supported

Planned Reuse (IV)

etc....

Example for a site list:Site Id Sector TRX BCCH f1 f2 f3 f4 f5 f6 MAIO HSN

0001 1 0 2 - -1 1 19 36 41 0 02 0 4 - -2 1 13 18 21 25 30 42 0 02 2 13 18 21 25 30 42 1 02 3 13 18 21 25 30 42 2 03 0 9 - -3 1 15 23 27 32 0 03 2 15 23 27 32 1 0

0002 1 0 12 - -1 1 22 26 34 40 0 01 2 22 26 34 40 1 02 0 8 - -2 1 16 19 28 0 0

Frequency PlanningStrategies Cyclic Hopping -

Random HoppingCyclic hopping sequence {... f4, f0, f1, f2, f3, f4, f0, f1, f2, f3 ...}, MAIO 0Cyclic hopping sequence {... f1, f2, f3, f4, f0, f1, f2, f3, f4, f5 ...}, MAIO 2

F

r e

q

u

e n

c

y

TDMA frame

f0

f1

f2

f3

f4

Principle of Cyclic Hopping

• Optimum frequency Diversity• Sufficient Interference diversity by avoiding frequency groups• No Interference diversity using frequency groups

Random hopping sequence {... f1, f4, f2, f0, f0, f3, f0, f1, f2, f4, ...}, MAIO 0Random hopping sequence {... f3, f1, f4, f2, f2, f1, f2, f3, f4, f1, ...}, MAIO 2

F

r e

q

u

e n

c

y

TDMA frame

f0

f1

f2

f3

f4

Principle of Random Hopping

• Optimum interference diversity

• Less frequency diversity