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Perhitungan Kapasitas Kanal

Pada Sistem CDMA

Arif Hidayat ST

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Overview System CDMA

Kapasitas System CDMA tergantung dari

bayaknya interferensi dari system tersebut

Untuk memaksimalkan kapasitas dari

system CDMA perlu dilakukan pengaturanpower dan mengurangi interferensi

system.

Bloking pada sistem CDMA terjadi ketikatotal interferensy melebihi Noise

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Persamaan Energy Per Bit

Assuming:

P denotes the received power from each subscriber at the basestation antenna

R denotes the data rate (9600 bps for Rate Set 1, 14400 bps for RateSet 2)

Power control is perfect

Subscribers are transmitting just enough power to be received

Uniform subscriber distribution

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Interferensi Total

W=Bandwidth of the channel N = Jumlah User (Kanal N)

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Energi Bit dibanding Noise

Jika dilakukan perbandingan Energi Bit

dibandingkan dengan Noise di dapat :

Pendekatan

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Perhitungan Level Interferensi

Persamaan di atas adalah pada kondisi

ideal

Pada aplikasinya terdapat interferensi

yang didapat dari cell lain sehingga didapat persamaan

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Perhitungan level Interferensi

Io = Interference power density impacted by

other cells, and the number of users withan average voice or data activity rate

f = Ratio of out of cell (inter-cell) interference

power to in cell (intra-cell) interferencepower. This factor is used to adjust the

capacity of a single cell to account for the

Interference generated by other users in a multiple

cell system.

=Average voice or data activity factor

=Thermal noise

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Perhitungan Level Interferensi

Sehingga Persamaan Total Energi Bit

dibanding dengan nilai Interferensimenjadi

Dengan melakukan pendekatan di dapat

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Perhitungan Jumlah Kanal

Pendekatan Nilai N

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Kapasitas Kanal Reverse Persamaan Kapasitas Kanal Reverse

Io= Total received signal

No=Thermal noise power

Eb=Energy per bit

Ratio of Signal energy bit to the sum of interference and noiseadjusted fo imperfect power control

W = Bandwidth of the channel

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Kapasitas Kanal Reverse Lanjutan

R =Data rate

W /R =Processing gainf= Ratio of out of cell (inter-cell) interference

power to in cell (intra-cell) interference power.

This factor is used to adjust the capacity of asingle cell to account for the interferencegenerated by other users in a multiple cellsystem.

=Average voice or data

Gs = Sectorization gain

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Adjusted Eb/Io The adjusted Eb/(No+Io) requirement to account

for imperfect power control (power controldeviation) can be determined by:

Signal / (Interference plus noise) ratiorequirement under perfect power control

Standard deviation in imperfect powercontrol

Constant value equal to ln(10)/10

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Rasio Power Intra dan Inter Cell

Some reverse link pole equations may use

the term F, where F is defined as the ratioof in cell (intra-cell) interference power to

the sum of out of cell (inter-cell)

interference power and in cell (intra-cell)

interference power. F is related to f by the

following equation.

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Referse N Capacity Final Persamaan Referse N Capacity Final

Assuming the following values for the various parameters, the reverse link polecapacity for an IS-95 Rate Set 2 site would be 19 users or roughly 12.3

Erlangs per sector (assuming an Erlang B model with 2% grade of service)for a three sector site (57 users per site). This value represents the polecapacity or the point at which no more users can be added without seriouslydegrading the quality of the system.

= Bandwidth of the channel (only one CDMA Channel) 1228800 Hz

= Data rate 14400 bps

= Ratio of out of cell (inter-cell) interference power to in cell 0.7= Average voice or data activity factor 0.4

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Referse Pole Capacity Calculation

=Sectorization gain per sector for a three

sector site 2.4/3

= Signal / (Interference plus noise) ratio

requirement under perfect power

control 6.5 dB

= Standard deviation in imperfect power

control 2.5= Constant value ln(10)/10

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Reverse Pole Capacity Lanjutan