Hi Gouse,
GSM is an old version of mobile communication where TDMA is utilised while CDMA is new one where codes are allotted to each mobile user.3G is WCDMA(Wideband code division multiple access, BW=5MHZ)is a further development of CDMA(BW=1.25MHZ)having a number of applications.Capacity of CDMA is much more comparing to GSM and it is flexible.If a channel accomodates 80 users in CDMA, it can accomodate further more at the cost of quality and coverage.As number of users increase noise
increases and coverage reduces due to a phenomena called cell breathing.Unlike GSM where frequency planning is required using a number of frequencies, code planning is required in CDMA using same frequency in adjacent cells without any interference.