CDMA channel number in 25 MHz band

[sajib333]

HELLO
for CDMA (800 or 850 whatever you call), the total frequency range is:
824–849 MHz/869–894 MHz (uplink/downlink)

Consider either up-link or down-link, the total band is 25 MHz. We know CDMA use 1.25 MHz band, hence the number of total channel/band for either link should be (25/1.25) MHz= 20; This is logical, just like GSM 25 MHz band has 124 channel, each with 200 KHz width + guard bands.
However I hardly could find any information in the Internet regarding the total number of channel in CDMA. Thus, I understand that there might be some other facts that need to be considered in such a band.
SO, please clarify me if the channel number 20 is right?. Please be precise while answering and do answer only if you are well aware of this matter.

Thanks in advance.

 

[vfone]

In CDMA the channel spacing is 1250 kHz, but channel raster (step) is 30 kHz for 850 MHz band, and 50 kHz for 1900 MHz (PCS) band.
The 30 kHz raster in 850 band came from the correlation with the old analog AMPS network.

In WCDMA the channel spacing is 5 MHz, but raster is 200 kHz.

To find the available number of channels divide the frequency range to channel raster.

The network planning allocate to the carrier provider the available channels.

 

[E Kafeman]

Vfone is correct but if you want to make it a bit more complicated does it also depend on for what use you want the number of channels.
There are at least two common ways to assign channel number and substandards for how these channels should be numbered in communication between handset and base station.

CDMA channel numbering standarad: C.S0057-C-v1.0_3GPP2_Band_Class.pdf This is the channel numbers you need to know if you write software for controlling a CDMA phone.
Digg for more: ftp://ftp.3gpp2.org

UTRA Absolute RF Channel Number (UARFCN): wc_uplink_channel_uarfcn.htm Not complete but you get the idea. This is a common way to number cannels in communication test equipment.

 

[goal]

unlike GSM, CDMA has a reuse factor of 1, since the users are discriminated with respect to codes. all the frequencies with in band(824-849MHz) separated by channel raster 200KHz(in case of WCDMA) can be used as channels. you can read ETSI/UMTS standard for channel numbering. there is a formula to derive the channels.