Freq reuse intro

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Frequency reuseFrequency reuseintroductionintroduction


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GSM Frequency Band

GSM900Upward 890 915 MHz

Downward 935 960 MHzTx-Rx difference is 45MHz carrier space is

200KHz GSM1800

Upward 1710 1785 MHzDownward 1805 1880 MHz

Tx-Rx difference is 95MHz carrier space is

200KHz


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GSM Channel Numbering

GSM900 FU(n) = 890 + 0.2 n MHz

FD(n) = Fu(n) + 45 MHz 1 n 124E-GSM900: F U(n) = 890 + 0.2 (n-1024) 974 n 1023

FD(n) = Fu(n) + 45 MHzn is called Absolutely Radio Frequency Channel Number.

GSM1800:

Fu(n) = 1710.2 + 0.2 (n-512) MHzFD(n) = Fl(n) + 95 MHz 512 n 885374 channels


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Cellular Architecture


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Definition of C/I and C/A

Co-channel Interference C/IC/I refers to the interference of another cell using

the same frequency to the current cell. The ratio of carrierto interference is called C/I.

=

6

1_

_

BCCH i

cellown

PP

I C

Where, P own_cell is the signal strength of current cell;P i_BCCH is BCCH signal strength of interfering cell i

measured by MS.


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C/I and C/A

Co-channel Interference C/IGSM specification regulates that C/I >9dB. In

implementing, it requires C/I>12dB.

Adjacent channel interference C/AC/A refers to interference of adjacent cell to thecurrent cell. The ratio is called C/A. The GSM

specification regulates that C/A>-9dB. In implementing, itrequires C/I>-6 dB.


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z Group Frequency Reuse Pattern (4 3,3 3)z

Multiple Reuse Pattern (MRP)z Concentric Circle (normal concentric circle,

intelligent concentric circle)

Frequency Reuse Patterns

Frequency Planning andInterference Analysis


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43 Frequency Reuse

4 3 frequency reuse pattern is that each site is divided into 3sector. 12 frequencies form a group which are distributed to 4different sites. Each site owns 3 cells.

A3

D 2B1

C3

B2D 1

D 3

A2C1

B3

C2A1

B3

C2A1

A3

A1B1

D 1

D 3D 2

C3

B2A1

C3D 2

C3

C1

D 2B1C2A1

A2C1

D 3


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43 Frequency Reuse

GroupAFN

TRXA1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3

1 1 2 3 4 5 6 7 8 9 10 11 12

2 13 14 15 16 17 18 19 20 21 22 23 24

3 25 26 27

C/I=18 dB


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33 Frequency Reuse

3 3 frequency reuse pattern is that each site is divided into 3sector. 9 frequencies form a group which are distributed to 3different sites. Each site owns 3 frequencies.

A3

C2B1

B3

A2C1

C3

B2A1

A3

C2B1

B3

A2C1

B3

A1C1

A1

A3A2

C3

B2A1

A3A3

C3

C1

B2A1B2A1

A2C1

B3


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A3

A1

A2

A3

A1

A2

A3

A1

A2

A3

A1

A2A3

A1

A2

A3

A1

A2

A3

A1

A2

1*3 FH DPC DTX

Most densely reuse pattern

BCCH (4*3)

Combined with anti-interference technology

Generally only use 50% of the whole available frequency

C/I= 9.43 dB

13 Frequency Reuse


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Set-forth of MRP(1)

The adoption of frequency reuse pattern dependsmainly on the condition of sites. In reality, there aregreat differences in antenna height, earth shape andcoverage. Moreover, different cells have differenttraffic requirement, the number of TRXs needed is alsodifferent. So, its unreasonable to adopts idealized andregular frequency reuse pattern indiscriminately, whichwill cause low frequency utilization rate .


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Set-forth of MRP(2)

So, in regard to real wireless network situation,dynamic assigning frequency to cells according to theirtraffic is the developing trend of frequency reuseplaning. Multiple frequency Reuse Pattern (MRP) is anirregular and dynamic frequency reuse mode designedaccording to GSM features.


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Principle of MRP

MRP is an irregular frequency reuse mode utilizingirregularity and frequency hopping technology of GSMsystem. That is, dividing frequency band into differentcombinations, each combination adopting different

frequency reuse pattern. Each carrier of a cell mayadopts different frequency reuse pattern.


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BCCH

4 3

TCH1

3 3

TCH2

2 3

TCH3

1 3

MRP+FH+DTX+DPC


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60

64

68

62

66

7063

67

7161

65

69

72

75

78

73

76

7972

75

7874

77

80

89

91

93

90

92

94 9092

94

89

91

93

81

83

85

8284

8682

84

8183

85

86

1) BCCH 4 3 2) TCH1 3 3

4) TCH3 2 3 3) TCH2 2 3

Application of MRP


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MRP Characters

Increase network capacity greatly and decrease averagefrequency reuse factor to 7.5, thus increasing frequency

reuse efficiency greatly.Flexible channel allocation. Different frequency reusepattern may be adopted step by step according tocapacity requirement.Some carriers can be released for micro-cells.Should combine with FH, DPC and DTX to lowerinterference.Especially for sites distributed unevenly.

Comparison of the system capacities with group


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Multiplex mode BS configuration Average stationcapacity

subscriber

Capacityratio

6MH Z 4 3 3/2/2 or 3/3/2 1440 1

3 3 3/3/3 1788 1 24

1 3 4/4/4 2640 1 83

MRP 12, 9, 6 ** 3/3/3 1788 1 24

2 6 2/2/2/2/2/2 2160 1 5

9.6MH

Z

4 3 4/4/4 2628 1

3 3 5/5/5 3384 1 29

1 3 6/6/6 4272 1 63

MRP 12, 9, 6 ** 6/6/6 4272 1 63

2 6 3/3/3/4/4/4 4416 1 68

Comparison of the system capacities with groupmultiplexing and MRP technologies


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22

2

2

2

2

2 2 22

22

2

2

2

Concentric

C i 2


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Concentric 2

The principle of ordinary concentric is that a cell is dividedinto underlay and overlay, both having the same site andsharing the same TRXs, antenna and BCCH. The coverage of

underlay is the same as that of ordinary cell, while the overlayuse small transmitting power and thus has smaller coverage.The frequency reuse factor of underlay differs from that of overlay. The former adopts frequency reuse pattern of 4 3,while the latter adopts closer pattern of 3 3, or 2 3. TheBCCH and SDCCH are used by underlay, in which the callwill be set up. As a cell is subdivided into two layers, a brandnew switching algorithm should be added. Inter-cell hand-overis conducted in overlay,while overlay-underlay and intra-

underlay is added to intra-cell hand-over.


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Concentric 3

The absorbing of traffic by overlay is limited by trafficlay-out and coverage. It will increase the capacity by10-30% and is related to traffic distribution. Theoverlay is more suitable for outdoor traffic concentratedin the vicinity of BTSs because of its smaller

transmitting power. More attention should be paid when network planning

is carried out using concentric technology. On the

condition that the network quality will not be affected,a closer frequency reuse pattern should be adopted. Atthe same time, DPC and DTX technology should beadopted to ensure network quality.


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C/I-based Concentric IUO

22

2

22

22

2

2

2 22

2

2

2

2

2

22

2

2

2

2

2

IUO:Intelligent Underlay Overlay


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IUO 3

Different from ordinary concentric, the Underlay andOverlay of IUO both use the same transmitting power.Because the Overlay adopts closer frequency reusepattern, the chances of co-channel and adjacent channelinterference increase. So, IUO adopts a handing overalgorithm based on C/I to solve this problem. Itfunctions as follows: the call is established withinUnderlay, the BSC continuously monitor the downwardC/I in Underlay. When C/I reaches applicable threshold,the call will be handed over to Overlay. At the same time,the C/I is monitored continuously and the call will be

handed over to Underlay if it deteriorates to inapplicablethreshold.


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IUO 4 The implementation of IUO is easy. Little modification

is needed and no special requirement to MSs. Becauseof adopting special algorithm on handing over,measurement and estimation on C/I, the speech qualitycan be guaranteed while increasing the system capacity.Because both Underlay and Overlay have the sametransmitting power, its very suitable for absorbingtraffic inside building which has a strong isolationcapability to radio signal. When implementing thenetwork, the C/I based handing over parameter shouldconfigured correctly. The DPC and DTX should also be

considered.


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Concentric Overlay smaller transmitting

power Handover based on power or

TA Overlay coverage is fixed

but not reasonable Absorb limited traffic Handover algorithm is easy

IUO U/O same transmitting

power Handover algorithm based

on C/I Overlay coverage is fixed

and reasonable Absorb more traffic Handover algorithm is

complicated

Comparison

Capacity of C/I Based


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p yConcentric Technology

Capacity comparison with 4x3patternGrade of Service (GOS) 2 %Per subscriber traffic at busy hour 0.03 ErlBandwidth: 6MOverlay adopts 4x3 pattern

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Subsc./bts

Standard 4X3

overlay 3x3

Overlay 2x3

Overlay 1x3

2TRXs Undererlay 1TRXs Underlay All underlay


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Planning of adjacent cells

A

B

C


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Subscriber forecast

Growth trend forecast method Population penetration method Growth curve method Conic method

Growth trend forecast


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Population penetration method


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Population penetration method


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Freq reuse intro

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