Sharing: UMTS - How to calculate maximum number of users on a cell?

[khurrambilal01]

To calculate the maximum number of users (M) on a cell, we need to know:
W: chip rate (for UMTS 3,840,000 chips per second)
EbNo: Eb/No requirement (assuming 3dB for CS-12.2k)
i: other-cell to in-cell interference ratio (assuming 60%)
R: user data rate (assuming 12,200 kbps for CS-12.2k)
η: loading factor (assuming 50%)
Take 12.2kbps as example:
M = W / (EnNo * (1 + i) * R) * η = 3,840,000 (3 * (1 + 0.6) * 12,200) * 0.5 = 32.8
The number of users could also be hard-limited by OVSF code space. Take CS12.2k for example:
· A CS-12.2k bearer needs 1 SF128 code.
· Total available codes for CS-12.2k = 128 – 2 (1 SF64) – 2 (4 SF256) = 124.
· Consider soft-handover factor of 1.8 and loading factor of 50%: 124 / 1.8 *.05 = 34 uers/cell.

[hieuma's]

Thanks "khurrambilal01". You have result is 34 user/cell, but 34 user will be access on one seconds or other unit ???

[khurrambilal01]

Hi Hieuma's
34 users will access at any instant of time when the load is 50% If you change the load the users that can access the network vary.

Thanks "khurrambilal01". You have result is 34 user/cell, but 34 user will be access on one seconds or other unit ???

[haunhan]

Dear khurrambilal01
You don't consider that power of cell is enough or not ?

[haq_enam]

To calculate the maximum number of users (M) on a cell, we need to know:
W: chip rate (for UMTS 3,840,000 chips per second)
EbNo: Eb/No requirement (assuming 3dB for CS-12.2k)
i: other-cell to in-cell interference ratio (assuming 60%)
R: user data rate (assuming 12,200 kbps for CS-12.2k)
η: loading factor (assuming 50%)
Take 12.2kbps as example:
M = W / (EnNo * (1 + i) * R) * η = 3,840,000 (3 * (1 + 0.6) * 12,200) * 0.5 = 32.8
The number of users could also be hard-limited by OVSF code space. Take CS12.2k for example:
· A CS-12.2k bearer needs 1 SF128 code.
· Total available codes for CS-12.2k = 128 – 2 (1 SF64) – 2 (4 SF256) = 124.
· Consider soft-handover factor of 1.8 and loading factor of 50%: 124 / 1.8 *.05 = 34 uers/cell.

How did u find – 2 (1 SF64) – 2 (4 SF256) in your code calculation. I dont understand where to get those..


A CS-12.2k bearer needs 1 SF128 code.
· Total available codes for CS-12.2k = 128 – 2 (1 SF64) – 2 (4 SF256) = 124.

[bino]

How did u find – 2 (1 SF64) – 2 (4 SF256) in your code calculation. I dont understand where to get those..


A CS-12.2k bearer needs 1 SF128 code.
· Total available codes for CS-12.2k = 128 – 2 (1 SF64) – 2 (4 SF256) = 124.

They're used for control channels.

BR.

[dekili]

This calculation should consider lower number of 2 provided so it should be 32 (from 32.8) instead of 34?
Also, this is related to the situation when all users are using the same service (bearer) and in this case CS 12.2K. What is the calculation when you have users with different bearers and thus with different required Eb/No and data rates?
Thanks

[sandrommm]

Hi, what happen if use 2 carriers per cell?