GSM Frequency Planning

Sujit KhadkaMSD, Jawalakhel

GSM Frequency BandGSM 900Uplink (MS to BTS): 890 915 MHzDownlink (BTS to MS): 935 960 MHzFrequency Band: 25 MHz

Duplex Separation (Tx-Rx difference): 45 MHzCarrier Bandwidth: 200 KHz

GSM Frequency BandGSM 1800Uplink (MS to BTS): 1710 1785 MHzDownlink (BTS to MS): 1805 1880 MHzFrequency Band: 75 MHz

Duplex Separation (Tx-Rx difference): 95 MHzCarrier Bandwidth: 200 KHz

GSM Channel NumberingGSM900 FU(n) = 890 + 0.2n MHzFD(n) = Fu(n) + 45 MHz 1 n 124

Where, n is called Absolute Radio Frequency Channel Number.

GSM1800 Fu(n) = 1710.2 + 0.2(n-512) MHz FD(n) = Fu(n) + 95 MHz512 n 885

After the completion of the 3.5M project the total number of the subscribers in GSM will be more than 5M. The total number of S444 900 MHz BTS in KTM will be 425 The total number of S666 1800 MHz BTS in KTM will be 239.The planned traffic per subscriber is 35mErl.

Allocated frequency for NT in 900MHz is 7.2MHz (permanent) +4.8 MHz (temporary)9MHz (permanent) + 6MHz (temporary) In 1800MHz Allocated frequency for SNPL in 900MHz is 6 MHz (permanent) +2 MHz (temporary)9MHz (permanent) + 2MHz (temporary) In 1800MHz And for NSTPL is 9MHz in 1800MHzFor STM 2.4MHz in 900MHz

The allocated Absolute Radio Frequency Channel Number is 1 to 36 (permanent). And the allocated Absolute Radio Frequency Channel Number 37 to 60 (temporary).

Why Cellular Networks?

To address requirement for greater capacity For efficient use of frequencyTo increase coveragereplaces a large transmitter with smaller ones in cellssmaller transmitting powereach cell serves a small geographical service area and assigned a portion of the total frequency

Frequency Assignment Plan

S duplex channelsS channels divided into N cellsEach cell allocated a group of k channelsTotal available channels S = k NReplicate a cluster M times in the networkTotal number of duplex channels, C=MkN=MS

Cell ClustersA cluster of 7 cells

the pattern of cluster is repeated throughout the network

Excitation of CellsThe location of the base station within the cell is referred to as cell excitationIn hexagonal cells, base stations transmitters are either:centre-excited, base station is at the centre of the cell oredge-excited, base station at 3 of the 6 cell vertices

Frequency Reuse DistanceThe following equation is used to estimate frequency reuse distance: D frequency reuse distanceR cell radius N frequency reuse factor. N=9 for 33; N=12 for 4 3For 3/9 frequency reuse,D=5.2RFor 4/12 frequency reuse,D=6R

Frequency PlanEach base station is allocated a group of channels within its geographical area of coverage called a cellAdjacent cells are assigned completely different channel groups to their neighborsIn same cell, the frequency distance between BCCH and TCH is at least 400KHzThe frequency distance of TCH should be more than 400KHz

43 Frequency Reuse4 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.

33 Frequency Reuse3 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.

33 Frequency Reuse

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

Frequency HoppingReduce co-channel interference by averaging interference for all active usersFrequency hopping refers to the hopping of carrier wave frequencies according to a certain sequence in a very wide frequency range. The carrier frequency changes under the control of pseudo-random codes, the sequence of which is frequency-hopping sequence.

Frequency HoppingBaseband Hopping

RF Hopping

Baseband hoppingEach TRX works at fixed frequencyEach user hops at different TRX (frequency)

RF hoppingEach TRX hops at different frequencyEach user works at fixed TRX

Co-channel interferenceFrequency reuse implies that in a given coverage area there are several cells that use the same set of frequencies.These cells are called co-channel interference.Unlike thermal noise which can be combated by simply increasing the signal noise ratio (SNR)Co-channel interference cannot be combated by simply increasing the carrier power of a transmitter.

Calculation of C/IWhere, Pown_cell is the signal strength of current cell; Pi_BCCH is BCCH signal strength of interfering cell i measured by MS.

Co-channel Interference (C/I)This is because an increase in carrier transmit power increases the interference to the neighboring co-channel cells.To reduce co-channel interference, co-channel cells must be physically separated by a minimum distance to provide sufficient isolation due to propagationGSM specification regulates that C/I >9dB. In implementing, it requires C/I>12dB.

Adjacent channel interference (C/A)Interference resulting from signals which are adjacent in frequency to the desired signal is called adjacent channel interference.keeping the frequency separation between each cell as large as possible

Adjacent channel Interference (C/A)Interference from other cells using the adjacent frequency ( 200 KHz)Ratio of signal strength of serving cell to interfering cell using adjacent frequencyC/A -6 dB

Current frequency plan in GSM 900MHz Band width: 7.2MHz (permanent) + 2.4MHz (Temporarily provided)+ 2.4MHz (Temporarily provided)Frequency Number: 1~60Frequency Reuse: 5x3 (BCCH), 1x3 (TCH)ARFCN: 32~46(BCCH), 1~30 (TCH)Guard Band ARFCN: 31Guard band between TCH hopping and Micro BTS carriers:47Frequency number: 48-60 (for Micro BTS, Macro BTS in highly congested area)BTS Configuration:S444

Current frequency plan in GSM 1800MHz Band width: 9MHz (permanent) + 6MHz (temporarily provided)Frequency Number: 512~586Frequency Reuse: 8x3 (BCCH), 1x3 (Hopping)ARFCN: 512~535 (BCCH), 542~586 (TCH)Guard Band Frequency: 541Guard band between TCH hopping and Micro BTS carriers:536Frequency for Micro-BTS and Macro BTS in highly congested area: 537~540BTS Configuration:S666

Plan for 9.6MHzARFCN: 1-48Frequency Range: 1-15 (BCCH), 17-43 (TCH)Frequency Reuse: 5x3 (BCCH), 1x3 (Hopping)Guard band: 16Guard band between TCH hopping and Micro BTS carriers:44Hopping Load: 33%BTS Configuration:S4444 carriers free : 45,46,47,48

Plan for 7.2MHz

ARFCN: 1-36Frequency Reuse: 4x3 (BCCH), 1x3 (Hopping)ARFCN: 1-12 (BCCH), 14-34(TCH)Guard band between BCCH and TCH: 13Hopping Load: 42.8%Max. BTS Configuration:S444Guard band between TCH hopping and Micro BTS:35Available carriers for Micro BTS:36

Frequency plan for 12MHz in 900ARFCN: 1-60Frequency Reuse: 6x3 (BCCH), 1x3 (Hopping)ARFCN: 1-18 (BCCH), 20-58(TCH)Guard band between BCCH and TCH: 19Hopping Load: 38.46%Max. BTS Configuration:S666Guard band between TCH hopping and Micro BTS:59Available carriers for Micro BTS:60

Antennatransform wire propagated waves into space propagated waves.

Wave propagation

PolarizationDirection of oscillation of the electrical field vectorHorizontal polarizationVertical polarization

PolarizationVerticalHorizontal

Radiation Pattern

Beamwidth

Panel antenna

Antenna tilt

Non down tilt

Electrical downtilt

Mechanical downtilt

Antenna TypesBy frequency band: GSM900, GSM1800, GSM900/1800 By polarization: Vertical, Horizontal, 45 linear polarizationBy pattern:Omni-directional, directionalBy down-tilt:mechanical, electrical adjustmentBy function:Transmission, receiving, transceiving

GPS Receiver

Compass

Tilt meter

Mobile Set

Optimization Software

Thank you

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