Forward and Reverse

Now i'll try to explain more about message transfer in CDMA network. The method of communicating between system & user in cellular system is basically similar. There is Forward / Transmit part and Reverse/ receive.

Forward is refer to transport of message from network to Cellphone (mobile).




Reverse is refer to transport of message from Cellphone (mobile) to network.



In CDMA 2000 1x , there are additional channel to improve it's capacity and speed in data communication.

The following graphic shows the differences between IS95 and 2000 1x. Suplementary channel (sch) in CDMA 2000 1x system is use to handle packet data communication with speed aprox. 156.3 kbps .

SPREADING .....

There are various ways used by CDMA to "spread" the original message. The term spread refers to method of scrambling with certain pattern and both party (sender & receiver) able to de-scrambler the coded message.



click picture for better view

walsh code is generated by chipset which produced by Qualcom. You don't need to be confused by huge matrix and one-zero waving numbers . It's all qualcom secret, and every cdma handset and BTS channel card involve qualcom chipset. One user use one walsh code, and since the matrix is huge, the probability of same walsh code use at one place is one to million



Short PN is use at BTS part, to differentiate every subcell ( sector) of the BTS. This code is re-useable.


Long code is equal with ESN ( electronics serial numbers) plus A-key (authentication key). CDMA handset has different ESN and some operator apply A-key to avoid handset fraud or cloning.

The Forgotten Fundamental

Sometime we always forget the basic thing while we always get busy by daily routine, then why don't we get back and see once again CDMA system in the simplest way.

click the picture for better view