Perhitungan Kapasitas Kanal Pada Sistem CDMA Arif Hidayat ST
Overview System CDMA • Kapasitas System CDMA tergantung dari bayaknya interferensi dari system tersebut • Untuk memaksimalkan kapasitas dari system CDMA perlu dilakukan pengaturan power dan mengurangi interferensi system. • Bloking pada sistem CDMA terjadi ketika total interferensy melebihi Noise
Persamaan Energy Per Bit • Assuming: • P denotes the received power from each subscriber at the base station antenna • R denotes the data rate (9600 bps for Rate Set 1, 14400 bps for Rate Set 2) • Power control is perfect • Subscribers are transmitting just enough power to be received • Uniform subscriber distribution
Interferensi Total
• W=Bandwidth of the channel • N = Jumlah User (Kanal N)
Energi Bit dibanding Noise • Jika dilakukan perbandingan Energi Bit dibandingkan dengan Noise di dapat :
• Pendekatan
Perhitungan Level Interferensi • Persamaan di atas adalah pada kondisi ideal • Pada aplikasinya terdapat interferensi yang didapat dari cell lain sehingga di dapat persamaan
Perhitungan level Interferensi Io = Interference power density impacted by other cells, and the number of users with an average voice or data activity rate f = 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 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
Perhitungan Level Interferensi • Sehingga Persamaan Total Energi Bit dibanding dengan nilai Interferensi menjadi
• Dengan melakukan pendekatan di dapat
Perhitungan Jumlah Kanal • Pendekatan Nilai N
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 noise adjusted fo imperfect power control W = Bandwidth of the channel
Kapasitas Kanal Reverse Lanjutan R =Data rate W /R =Processing gain f = 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 a single cell to account for the interference generated by other users in a multiple cell system. Ρ =Average voice or data Gs = Sectorization gain
Adjusted Eb/Io • The adjusted Eb/(No+Io) requirement to account for imperfect power control (power control deviation) can be determined by:
Signal / (Interference plus noise) ratio requirement under perfect power control Standard deviation in imperfect power control Constant value equal to ln(10)/10
Rasio Power Intra dan Inter Cell • Some reverse link pole equations may use the term F, where F is defined as the ratio of 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.
Referse N Capacity Final •
Persamaan Referse N Capacity Final
Assuming the following values for the various parameters, the reverse link pole capacity 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 pole capacity or the point at which no more users can be added without seriously degrading 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
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
Reverse Pole Capacity Lanjutan
