Relation between 3.84 Mcps & 5 Mhz BW in WCDMA

[chompak]

Hi experts,

I want to know exactly what is the correlation between 3.84 Mcps & 5 Mhz BW in WCDMA. How spreading @3.84Mbcs fits into 5Mhz. How many voice calls at 7.5Kbps (SF=256) can be accomodated in 5Mhz?

Can anybody pl.

Chompak

[_lisi4king]

Hi experts,

I want to know exactly what is the correlation between 3.84 Mcps & 5 Mhz BW in WCDMA. How spreading @3.84Mbcs fits into 5Mhz. How many voice calls at 7.5Kbps (SF=256) can be accomodated in 5Mhz?

Can anybody pl.

Chompak

Let me start.

From book Radio Access Networks for UMTS we can find a phrase: The chip rate of 3.84 Mcps difines the approximate bandwidth of the WCDMA signal if the frequancy domain, i.e. the approximate bandwidth after baseband filtering is 3.84 MHz

I can only guess, the rest 5-3.84 it is for redundancy between bands (or 99% of useful data inside of 3.84 MHz)

Are you sure that 7.5Kbps (SF=256)? 3.84/7.5 = 512.

In any case you can count it like: 512 - number of codes (SF=512) occupied by service information. And i guess it will be near 300.

[Mctest]

Hi experts,

I want to know exactly what is the correlation between 3.84 Mcps & 5 Mhz BW in WCDMA. How spreading @3.84Mbcs fits into 5Mhz. How many voice calls at 7.5Kbps (SF=256) can be accomodated in 5Mhz?

Can anybody pl.

Chompak

In WCDMA the RRC filter is used in digital domain for signal filtering.And then occupied bandwidth you can calculate with formula B=chiprate(1+alpha) where alpha is coefficient of the characteristic of RRC filter.According to the standard alpha=0.22. And the result is approximately 5Mhz.

[plannerguy]

Hi

Same is due to UMTS in frequncy domain reponse.

there will be side lobes in both ends.same is guard band



Regards
Plannerguy

[Philippe]

In WCDMA the RRC filter is used in digital domain for signal filtering.And then occupied bandwidth you can calculate with formula B=chiprate(1+alpha) where alpha is coefficient of the characteristic of RRC filter.According to the standard alpha=0.22. And the result is approximately 5Mhz.

Here is the real story of the 3.84Mcps:
- The initial solution for WCDMA UMTS was defined for 4.096Mcps by European ETSI. As a matter of fact 4.096Mcps x 1.22 (alpha coefficient of RRC filter) = 5 MHz
- At the time of submission to ITU for IMT-2000 solution, there was trial of harmonization between European and American solutions for 3G IMT-2000.
- The CDMA based solution proposed by US standardization body was CDMA 3x: 3 times CDMA one using 1.228Mcps = 3.68Mcps, favourizing a smooth upgrade from CDMA One to 3G
- During the harmonization process, the WCDMA UMTS (and GSM) pros proposed as a trade-off to use 3.84Mcps for the merged solution
- Finally, there was never harmonization between the 2 solutions but the UMTS W-CDMA remained with 3.84Mcps (instead of the optimal 4.096Mcps).

[dekili]

Just to add...
Next to the pulse shaping (alpha or rho, depending on the book that you read), 3.84Mcps allows operators to move carrier frequency in steps of 600kHz from original one. This is used in some situations when pulse shaping does not provide good enough results regarding the cochannel interference.