Comparison between CDMA and GSM

Comparison between CDMA and GSM

Description	GSM	CDMA
Definition	GSM – Global System for Mobile Communication.	CDMA – Code Division Multiple Access
Frequency	Commercially deployed using 900 Mhz 1800 Mhz  1900 Mhz	Commercially deployed using 450 Mhz 850 Mhz Uplink:   827Mhz-849Mhz; Downlink:   869Mhz-894Mhz.
Bandwidth	The method chosen by GSM is a combination of Time­ and Frequency Division Multiple Access (TDMA/FDMA).  The FDMA part involves the division by frequency of the total 25 MHz bandwidth into 124 carrier frequencies of 200 kHz bandwidth.  One or more carrier frequencies are then assigned to each base station.  Each of these carrier frequencies is then divided in time, using a TDMA scheme, into eight time slots.  One time slot is used for transmission by the mobile and one for reception.	CDMA, all users share the same 1,250kHz wide carrier, but unique digital codes are used to differentiate subscribers. The codes are shared by both the mobile station and the base station and are called "pseudo-random code sequences". Base stations in the system distinguish themselves from each other by transmitting different portions of the code at a given time. In other words, the base stations transmit time-offset versions of the same pseudo-random code
Air Interface channels	Physical Channels are specified by specified time slots in a specific channel / Carrier Frequency. Logical Channels are run over a Physical Channel are classified further into traffic channels and control channels. The Interface channels used in GSM are standard with no customization and scalable up to 3G.	Access Channel, Pilot channel, Paging channel, Synchronization channel, Forward traffic and Reverse traffic.
Interface	Standard Interfaces are present in GSM .The interfaces are unique worldwide for GSM	A-Interface:MSC-BSC, ATER Interface: BSC - TC, Abis Interface:BSC-BTS, A9 and A10 for PDSN,A11 for EVDO.
Protocol Stack	ITU The MAP protocol structure has some special features over the ANSI TCAP.	ANSI TCAP over ITU SCCP
Speech flow	The speech codecs used in GSM are called Half-Rate (HR), Full-Rate (FR), Enhanced Full-Rate (EFR) and Adaptive Multirate (AMR).	EVRC  - Enhanced Variable Rate Coder
Paging	Paging happens through the paging channel to catch hold of the subscriber during the terminating call. Paging power required is 32dbm.Pre Paging happens for Signalling link establishment and then ISUP call gets established. LAC based paging present. Pre Paging done in GSM has some signaling advantages over GSM	Paging happens through the paging channel to catch hold of the subscriber during the terminating call. Here both Pre Paging happens for signalling link establishment and Post paging for ISUP call establishment. System paging and Intersystem Paging present in CDMA
Location Update	IMSI based. The Location update done in GSM is on IMSI and IMSI is unique worldwide in GSM	Currently MIN Based
Security and Authentication Mechanism	The authentication algorithm used in the GSM system is known as the A3 algorithm. Most GSM network operators utilize a version of the COMP128 algorithm as the implementation of the A3 algorithm.  A3's task is to generate the 32-bit Signed Response (SRES) utilizing the 128-bit random challenge (RAND) generated by the Home Location Register (HLR) and the 128-bit Individual Subscriber Authentication Key (Ki) from the Mobile Station's Subscriber Identity Module (SIM) or the Home Location Register (HLR). A3 actually generates 128 bits of output. The first 32 bits of those 128 bits form the Signed Response.  The A3 algorithm is implemented in the Subscriber Identity Module (SIM). A3 Algorithm based on Version2 prevents cloning and authentication level is superior in GSM	CDMA network security protocols rely on a 64-bit authentication key (A-Key) and the Electronic Serial Number (ESN) of the mobile. A random binary number called RANDSSD, which is generated in the HLR/AC, also plays a role in the authentication procedures. The A-Key is programmed into the mobile and is stored in the Authentication Center (AC) of the network. In addition to authentication, the A-Key is used to generate the sub-keys for voice privacy and message encryption. CDMA uses the standardized CAVE (Cellular  Authentication and Voice Encryption) algorithm to generate a 128-bit sub-key called the “Shared Secret Data” (SSD). The A-Key, the ESN and the network-supplied RANDSSD are the inputs to the CAVE that generates SSD. The SSD has two parts: SSD_A (64 bit), for creating authentication signatures and SSD_B (64 bit), for generating keys to encrypt voice and signaling messages. The SSD can be shared with roaming service providers to allow local authentication. A fresh SSD can be generated when a mobile returns to the home network or roams to a different system.
HLR Services	Voice Services; Circuit Switched Data Services, General Package Services, Short Message Services and Supplementary, Services. Please refer to the excel sheet for additional HLR services.	Voice Services; Circuit Switched Data Services, General Package Services, Short Message Services and Supplementary Services.
Release Versions used in TTSL	GSM Release 4	CDMA 1X IS41D
SMSC	SMSC is store and forward.  GSM uses a unique message centre address that is preconfigured in the SIM Card to submit SMS. MSC acts transparent. SMS in GSM is very superior and  different applications can be managed easily .	SMSC is store and forward.  CDMA uses either the MIN or the called party to submit the SMS.  MSC is present for message submission. SMS in CDMA is customized and some customizations are required to manage applications.
Prepaid	The prepaid scenario in GSM is based on CAMEL Standards. Prepaid applications are more superior in GSM including roaming. Phase 3 for voice and data works on online charging.	The prepaid scenario in CDMA is based on the IS826 (WIN Charging) standards. Prepaid applications are not that much superior and goes for offline charging in Data services and roaming.
Roaming	GMS supports Domestic, National and International. Prepaid , Postpaid and Data Roaming is present. In case of Prepaid roaming everything goes for online charging.	GMS support both Domestic, National and International (Where ever CDMA coverage is not available, CDMA subscribers use GSM Network and the protocol conversion is done thru Syniverse). No Prepaid roaming present as it is offline charging.
Data Elements	GMS uses SGSN, GGSN and AAA. Online Charging possible.	CDMA uses PDSN and AAA. Only offline charging.
Future	3G, 4G and HSS. Around the world 80% of the operators are working on GSM technology and only 20% are working on CDMA technology. More features are being developed in GSM. More roaming flexibility for subscribers around the world.	CDMA20001X EV-Do Revision B,CDMA20001X EV-Do Revision C, 3G and HSS
Equivalent Nodes Comparison.	HLR	HLR
	MSC	MSC
	BSC	BSC
	SGSN	PDSN
	GGSN	PDSN and AAA
	EIR(For IMEI Check)	No EIR