Hi
1. The GSM stands for global system for mobile communication and CDMA for code division multiple accesses.
2. GSM is a form of multiplexing, which divides the available bandwidth among the different channels. Most of the times the multiplexing used is either TDM (Time division multiplexing) or FDM (Frquency division multiplexing). On the other hand CDMA is a type of multiple access sceheme( which means allotting the given bandwidth to multiple users) and makes use of spread spectrum technique which is essentially increasing the size of spectrum.
3. In CDMA each user is provided a unique code and all the conversation between 2 users are coded. This provides a greater level of security to CDMA users than the GSM ones.
Thanks