05) frequency and capacity planning-25

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FREQUENCY AND CAPACITFREQUENCY AND CAPACITY PLANNINGY PLANNING


GSM FREQUENCY BANDGSM FREQUENCY BAND

SYSTEM P-GSM 900 E-GSM 900 GSM 1800 GSM 1900Frequencies- Uplink- Downlink

890 - 915 MHz935 - 960 MHz

880 - 915 MHz925 - 960 MHz

1710 - 1785 MHz1805 - 1880 MHz

1850 - 1910 MHz1930 - 1990 MHz

Wavelength ~33 cm ~33 cm ~17 cm ~16 cmBandwidth 25 MHz 35 MHz 75 MHz 60 MHzDuplex Distance 45 MHz 45 MHz 95 MHz 80 MHzCarrier Separation 200 kHz 200 kHz 200 kHz 200 kHzRadio Channels 124 174 374 299


GSM CHANNEL NUMBERINGGSM CHANNEL NUMBERING

GSM900 • GSM900: FU(n) = 890 + 0.2n MHz

FD(n) = Fu(n) + 45 MHz， 1 n 124

124 Channels

• E-GSM900 FU(n) = 890 + 0.2(n-1024)

FD(n) = Fu(n) + 45 MHz ， 974 n 1023

49 Channels

n = Absolute Radio Frequency Channel Number (ARFCN)

GSM1800 Fu(n) = 1710.2 + 0.2(n-512) MHz

FD(n) = Fl(n) + 95 MHz， 512 n 885

374 channels


FREQUENCY RE-USEFREQUENCY RE-USE

Frequency reuse is referred to as the same frequency is reused after a certain distance in cellular wireless system. Generally, a limited frequency band is divided into many groups, each containing a few carriers, which are in turn assigned to adjacent cells.


FREQUENCY RE-USEFREQUENCY RE-USE

Basic Concept:

–Frequency Reuse Cluster–Frequency Reuse Factor–Frequency Reuse Distance–C/I and C/A


FREQUENCY RE-USE DISTANCEFREQUENCY RE-USE DISTANCE

•The following equation is used to estimate frequency reuse distance:

D = 3 N * R

D —— frequency reuse distance

R —— cell radius

N - frequency reuse factor. N=9 for “3 3” N=12 for “4 3”• For “3/9” frequency reuse, D=5.2R• For “4/12” frequency reuse, D=6R


DEFINITION OF C/I AND C/ADEFINITION OF C/I AND C/A

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

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

GSM specification regulates that C/I >9dB. In implementing, it requires C/I>12dB. Adjacent channel interference C/A

C/A refers to interference of adjacent cell to the current cell. The ratio is called C/A. The GSM specification regulates that C/A>-9dB.


CALCULATION OF C/ICALCULATION OF C/I

Where, Pown_cell is the signal strength of current cell; Pi_BCCH is BCCH signal strength of interfering cell i measured by MS.


Frequency Reuse

Ordinary frequency reuse: “43”, “33” and more close “26” and “13”.

MRP: different layers adopt different frequency reuse patterns.

Concentric: the Underlay and Overlay adopt different frequency reuse patterns respectively.


4 X 3 FREQUENCY RE-USE PATTERN4 X 3 FREQUENCY RE-USE PATTERN

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

A3

D2B1

C3

B2D1

D3

A2C1

B3

C2A1

B3

C2A1

A3

A1B1

D1

D3D2

C3

B2A1

C3D2

C3

C1

D2B1C2A1

A2C1

D3



A3

C2B1

B3

A2C1

C3

B2A1

A3

C2B1

B3

A2C1

B3

A1C1

A1

A3A2

C3

B2A1

A3A3

C3

C1

B2A1B2A1

A2C1

B3

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



TRX A1 B1 C1 A2 B2 C2 A3 B3 C3

1 1 2 3 4 5 6 7 8 9

2 10 11 12 13 14 15 16 17 18

3 19 20 21 22 23 24 25 26 27


MRP

• It’s unreasonable to adopts idealized and regular frequency reuse pattern indiscriminately, which will cause low frequency utilization rate and difficult to ensure the C/I requirement.

• Multiple frequency Reuse Pattern (MRP) is an irregular and dynamic frequency reuse mode designed according to GSM features.

• That is, dividing frequency band into different combinations, each combination adopting different frequency reuse pattern. Each carrier of a cell may adopts different frequency reuse pattern.


TCH2 FRF=6

BCCH FRF=12

TCH1 FRF=9

For Microcell

MRP

FRF:Frequency Reuse Factor

Bandwidth=6 MHz


MRP Characters

Increase network capacity greatly and decrease average frequency reuse factor to 8, thus increasing frequency reuse efficiency greatly.

Flexible channel allocation. Different frequency reuse pattern may be adopted step by step according to capacity requirement.

Some carriers can be released for micro-cells. Should combine with FH, DPC and DTX to lower

interference. Especially for sites distributed unevenly.


22

2

2

2

2

2 2 22

22

2

2

2

Concentric


Concentric

• The principle of ordinary concentric is that a cell is divided into underlay and overlay,

• The coverage of Underlay is the same as that of ordinary cell, while the Overlay use small transmitting power and thus has smaller coverage.

• The frequency reuse factor of overlay differs from that of underlay.

• The BCCH and SDCCH are used by Underlay, in which the call will be set up.

• A brand new switching algorithm should be added.


Concentric

• The absorbing of traffic by overlay is limited by traffic lay-out and coverage. It will increase the capacity by 10-30% and is related to traffic distribution.

• The overlay is more suitable for outdoor traffic concentrated in the vicinity of BTSs because of its smaller transmitting power.

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


C/I-based Concentric IUO

222

222

222

222

2

2

2

2

2

22

2

2

2

2

2


IUO (intelligent underlay overlay)

• IUO has the same network structure as ordinary concentric, consisting of Overlay and Underlay.

• In general, the two layers share the same site and antenna. Similar to ordinary cell, the Underlay adopts 4*3

frequency reuse pattern, while the Overlay adopts closer pattern.

• Same like ordinary concentric, the control channel functions within Underlay where calls are established.


IUO

• Different from ordinary concentric, the Underlay and Overlay of IUO both use the same transmitting power.

• Because the Overlay adopts closer frequency reuse pattern, the chances of co-channel and adjacent channel interference increase.

• IUO adopts a handover algorithm based on C/I to solve this problem.

• It functions as follows: the call is established within Underlay, the BSC continuously monitor the downward C/I in Overlay. 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 inapplicable threshold.


IUO

• The implementation of IUO is easy. Little modification is needed and no special requirement to MSs.

• Because of adopting special algorithm on handing over, measurement and estimation on C/I, the speech quality can be guaranteed while increasing the system capacity.

• Because both Underlay and Overlay have the same transmitting power, it’s very suitable for absorbing traffic inside building which has a strong isolation capability to radio signal.


Capacity of C/I Based Concentric Technology

Capacity comparison with “4x3”pattern：Grade 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

Standard 4X3

Underlay 3x3

Underlay 2x3

Underlay 1x3

Subsc./bts2TRXs Overlay 1TRXs Overlay All overlay

05) frequency and capacity planning-25

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